Category Archives: Space Travel

People began traveling in space in 1961 in tiny spacecraft called capsules, which were launched from Earth by powerful rockets. Russian crews still travel in this kind of craft, in Soyuz capsules, but Americans now travel into space in shuttles, which are rocket-powered space planes.

There is no oxygen in space, so all crewed spacecraft carry a life-support system. This supplies air for people to breathe. The system also includes equipment to keep the air at a comfortable temperature and pressure and to remove carbon dioxide and odors.

Gravity in space is much weaker than it is on Earth. When people travel in space, they seem to become weightless. This often makes them feel sick. Their bodies do not have to work as hard, because they are not fighting gravity to sit or stand up. If they stay in space for a long time, the lack of gravity makes their muscles start to waste away. Exercise and a special diet help to combat these effects.

Astronauts on the APOLLO PROJECT traveled to the Moon, about 239,000 miles (385,000 km) away. Russian cosmonaut Valeri Poliakov traveled a distance of about 174 million miles (280 million km) around Earth while in the Mir space station.

In the space race of the 1960s, the US Apollo Project beat the Soviet Union by landing the first astronauts on the Moon. The first Moon landing, by Apollo 11, took place on July 20, 1969, when Neil Armstrong and Buzz Aldrin became the first humans to set foot on another world.

The Apollo spacecraft was launched from Earth by the Saturn V rocket. On the launch pad, the whole assembly stood 365 ft (111 m) tall. The spacecraft itself weighed 50 tons (45 metric tons). It was made from three main modules (sections). The command module for flight control housed the three-person crew. The service module carried equipment, fuel, and a rocket motor. The lunar module detached from the craft and landed two astronauts on the Moons surface.

There were six Moon landings, beginning with Apollo 11 in July 1969 and ending with Apollo 17 in December 1972. During the missions, 12 astronauts explored the lunar surface for a total of over 80 hours and brought back nearly 880 lb (400 kg) of Moon rock and dust for examination on Earth.

Continue reading here:

SPACE TRAVEL - Fact Monster

by Edoardo Albert

Lars Caron had only taken over as mission commander because Pete Boardman had died. We were the most scanned, checked, and examined group of human beings in history--after all, on the first mission to Mars, you don't want someone falling ill or freaking out on the way--and Pete had checked out clearer than any of us. Then, seven days before departure, he went and died. The autopsy said his heart gave out, but I knew, from speaking to the doctors, that they could not find anything wrong with him. Dead, he presented as perfect a physical specimen as he had when alive. Me, I think he collapsed under the burden of hope that was placed upon him; mission commander, new world, new beginning. So, I grant Lars Caron had some big shoes to fill. But three months into the voyage, we were all getting thoroughly sick of the chip on his shoulder, the unspoken assumption that we had caused every problem laid in front of him. Space is like that: stuff happens. So, the slight sigh and the lowering of his head when he saw me approaching came as no surprise. "Now what's wrong?" he asked.

Published on Aug 7, 2014

by J.W. Alden

They tell you not to wear the uniform in public these days. Folks don't like to be reminded of the war. Not long ago, things were looking grim. Defense exercises lit up the night sky every other week. The skirmishes drew nearer to home with every engagement. Doomsayers were out in force everywhere you looked, screaming about imminent invasion. Things are different now. The enemy is on the run. We're winning. But the war has shaken the public's sense of security, maybe for good. I feel the eyes on me as the hostess leads me to my table. I'm used to it. Half of them are regulars, but they still gawk like they're surprised to see me. The war had just begun when I first started coming here. People used to stare back then too, but the expressions were different. They didn't turn their heads when I looked. They smiled. Some of them would even shake my hand and thank me for my service. That doesn't happen anymore.

Published on Dec 26, 2013

by Leslie Jane Anderson

It was only an affair because he was the captain and Maria was a cadet. If they had been the same rank it might just be a mistake. The other cadets will probably call her a slut now. She hides in her room and the computer pours her a cup of tea. She looks out her window at the earth, spinning. Spinning. She dreams. The concrete basement of her parent's home has flooded, and the racks of their old clothes have fallen under the water. Wires fall from the ceiling and the electricity skitters across the surface like angry white spiders. There was no way to fix this. No way. Everything was ruined. She dreams she is bleeding into the secret caverns of herself.

Published on Dec 20, 2012

by Helena Leigh Bell

Year Zero Pilot Martha Stevenson could not bring her mother's piano, its keys yellowed and stained. Her husband chided her as she brushed away the dust, telling it goodbye.

Published on Jun 20, 2014

by Annie Bellet

The boys lay on their backs side by side staring up through the open roof of the abandoned building. Dylan clutched Meek's hand in anticipation as the ground shook and a roar filled the air. Tiny pebbles danced up from the ground around them and dust ran like water off the crumbling walls. "Ten nine eight seven six five," Dylan whispered, "four three two one."

Published on Dec 17, 2010

by Nicky Drayden

***Editor's Note: Be forewarned: the imagery may be unsettling, some language would not fit at an elegant tea.*** With a fine bone knife I make my incision, cutting back the sticky membrane of Our Tjeng's hull. I slip my hand inside and carefully widen the tear until it's big enough for me to step through. Our Tjeng has blessed Kae and me with gills to breathe within his walls. The viscous liquid is clear and burns my eyes, tart and slick on my tongue.

Published on Aug 16, 2011

by M. E. Garber

Jandara's famed purple-red plains swelled in the antiquated pleasure cruiser's windscreen as the ship lurched downward. The explosion that killed Seema's husband, Arun, had damaged the steering mechanisms of his beloved antique, and Seema fought the craft as shudders wracked it. Vibrations from the steering gears tingled, throbbed, and finally shook her arms. In the passenger compartment, Natesha, her seven-year-old daughter, wailed, echoing Seema's fear: Without Arun, I cannot survive. The ship's belly bumped the ground, rose up, and dove hard. Tearing metal shrieked louder than Natesha. Seema buffeted in her restraints as a series of booms shook what remained of the ship. Then it settled, hissing, to the ground.

Published on Aug 25, 2014

by JT Gill

They hug for what will be the last time.

Published on Sep 15, 2015

by Richard E. Gropp

I stood on the deck of the ship and watched as my planet fell dark, receding into the distance. "This is certainly the long way 'round," the ship whispered in my ear. "We have stations on both sides--you could have stepped right through. We could have folded you all the way."

Published on Oct 3, 2012

by James E Guin

You stand there watching me try on this blouse. "It looks nice," you say, and this time you're actually paying attention.

Published on Dec 4, 2013

by Amber Hayward

I... am. I suppose I am. I have words waiting to awaken. I see something in front of me. I say, "hand," and so it is.

Published on May 11, 2015

by Benjamin Heldt

The flickering light of the television cast Henry's shadow across the darkened room, and across me. Through the speakers a steady voice called time to t minus zero. The rockets fired. Henry gasped, though he didn't move. He was too close, as always, sitting cross-legged on the floor not two feet from the screen. Huge sheets of ice cracked, and fell from the scaffolding and fuel tanks, vaporizing in the blanket of smoke and fire blooming out from the launch site. "Buddy," I said, trying to keep my voice from breaking, "come sit with dad on the couch."

Published on Mar 4, 2013

by Miriah Hetherington

In the shadow of SciCorp's Public Relations building, Kai leaned on his cane and waited for the press conference to end. A sea of reporters separated him from his daughter Suukyi, standing proudly on a podium with the other twelve colonists. Twelve brilliant, highly trained, and fertile Eves; earth's Adams would be represented on the colony ship by a sperm bank.

Published on Jul 10, 2015

by Rebecca Hodgkins

The Rocketeer leans against the chrome bar, nursing a drink. She has a few choices of scenery--bad choices, in her opinion. Like always, the Rocketeer picks the best of the worst; the view out the window of the space station orbiting Mars. She looks down at the red surface polka-dotted with rockets, shiny silver spears pointing back at her, at the station, at the stars beyond. Just a quick jump down, then into a rocket, and back out into the Black again. And none of these bucks taking up the rest of the bar know what they're in for, she thinks.

Published on Sep 9, 2014

by Brian Lawrence Hurrel

Jump flash, blinding but brief. Alpha Centauri A swims into view. It takes only a few minutes after our emergence into realspace for the receiver to align itself with Earth. A long burst of static roars, fades. A voice mutters indistinctly, distorted as if bubbling up from deep under water, then suddenly rings out in shrill clarity. " and this so-called Daedalus drive is not only a scientific impossibility, but a perfect example of misappropriated resources."

Published on May 3, 2011

by K.G. Jewell

"Fifty-Nine, baby! Fifty-Nine!" Ted chortled, chipping a chunk of rock off Fenrir's surface and dumping it into the sample bag clipped to the hip of his spacesuit. He looked up at Saturn hanging overhead and flashed two fingers. Two moons to go. He was that close. He deactivated his ground anchor and stepped his aging, creaky bones towards the boxy tangle that was his ship.

Published on Jan 13, 2012

by Rachael K. Jones

My best friend LaToya was utterly fearless. In middle school she could jump farther than any kid. We'd compete for hours after school on the playground, waiting for our dads to pick us up, she in her green-soled Nikes and me in my Reeboks, digging our heels into gravel as we counted down together: "Three--two--one--go!" Then a cloud of dust. We raced three steps and launched heels-first into the sand, ploughing long ditches, stretching our gangly adolescent legs to hit the farthest mark. LaToya usually won. "Best of three," I'd say, and then amend it: "Best of five?"

Published on Jun 23, 2015

by K T

It took tens of thousands of engineers ten million man-hours and over a trillion dollars spread over the course of ten years. There had been political sacrifice, financial sacrifice, even marital sacrifice. Five people died, including a mother, a teacher, and a grandfather of twenty-five. Perhaps, by diverting the same resources, we could have finished the war in Afghanistan twenty years ago. But at last, and not without luck, a man stood atop Olympus Mons. To be that man required years of study in physics, math, chemistry, biology, geology, and languages; including English, Russian, Chinese, and C++. At minimum. It required the eyes of an eagle, the muscles of a Navy SEAL, and the brain of Deep Blue. No TV, no hobbies, no girlfriend, no family. Just blood, sweat, tears, and neurons to live the dream of every bright young male since 1957. Only the brightest, most athletic, most determined polyglot autodidactic polymathic genii could even enter the competition against one thousand equally infallible candidates from every continent.

Published on May 12, 2011

by Will Kaufman

***Editor's Note: Adult language in the story that follows*** Chapter One

Published on Apr 25, 2014

by Sara Thustra

"Now you stop it," snapped the sister. "You sit there and you smile and you tell him you miss him, damn you. Space exploration is a hard job, and one we should be proud of. It's not his fault this seems so often to us." The camera came on. The warble of great distance and stranger forces, too, played with the image. The man it showed was quite old, and dressed in a uniform from decades ago. "...Sally?" he said hesitantly.

Published on Jan 2, 2012

by Brynn MacNab

We deployed on February 14, Saint Valentine's Day, named for the saint who performed forbidden marriages. I stood in line next to a guy named Wallace Ault. Around us was much wailing and gnashing of teeth, a lot of people sobbing on each other's necks. Wallace and I weren't falling apart. He had a girl, a nice lean thing with good legs in a swirling brown knee-length skirt. She kissed him goodbye real quick and ran. I figured maybe they were secretly married themselves.

Published on Aug 5, 2014

by Caw Miller

Fleet Commander Yazle picked her way through the debris of a destroyed city on the planet Unlivil. Beside her walked the High Grasper, the leader of the largest hive on the planet. Commander Yazle wondered why she had been invited to go on this perambulation with the pale, octopus-like being. She had expected hatred, possibly a murder attempt; not grateful politeness. The High Grasper flashed three tentacles at a small winged scavenger, which took flight. The High Grasper picked up the mostly eaten carcass of a hexipod and placed it in a pouch.

Published on Aug 12, 2016

by Devin Miller

"My job as a father, Jalel," he told me one morning, "is to leave you better off than I was." It was a cold morning. On this planet, called Apella, the winters lasted years. Frost clung to some of the heartiest vegetation ever studied, and in their shadows, small animals sent up puffs of white dust in their quest for buried food.

Published on Mar 18, 2013

by KC Myers

The year EarthFed discovered hyperspace sickness was the year Jace McCallister's father never came home from outer space. They brought him back Earthside wrapped up in cotton and gauze so he wouldn't hurt himself, but his mind was still out there, caught in that strange between-place that nobody really understood, but into which spacegoers were expected to fling themselves so they could traverse the otherwise non-traversable distances between solar systems. No one knew how to treat him; no one knew why the jump had affected him that way in the first place. Jace was six. She was too little to understand why Daddy had gone out into the black, or why she couldn't visit him in the hospital now that he'd returned. She didn't understand that he hadn't returned at all. Not really.

Published on Apr 29, 2016

by Bridget A. Natale

***Editorial Advisory: Yes, there's adult language in the story that follows*** "I can't go to Bellingham with you. Not right now."

Published on May 1, 2013

by Ruth Nestvold

Published on Feb 2, 2012

by Jonathan Fredrick Parks

This is Tomorrow speaking. The voice came from the Eleven O' Thirty radio. The left bar flashed painting the storage room a green color. Are you listening? I turned the dial two clicks to the right. You are me from the future, right?

Published on Sep 2, 2011

by Ernesto Pavan

To those who were called and replied "I'll go" To those who filled the void between the stars with dreams of hope

Published on Nov 27, 2014

by Craig Pay

Something blue. Celeste: 25, Joseph: 26, Susie: 5

Published on Nov 15, 2011

by L.L. Phelps

We're falling fast through the atmosphere, what's left of the station shaking violently as it breaks apart. "We have to get to the escape pods," Natayla screams at me. I can barely hear her over the roar around us, but I can read the words on her lips as fear dances wild in her eyes. "Now!" she screams, shaking me.

Published on Mar 24, 2014

by Cat Rambo

Day One After the men in dark sunglasses ushered Djuna outside, spring's chill chased her up the steps into the bus's welcome heat. She wavered on the last step, suitcase in front of her like a wall, thinking, "My fiftieth spring on Earth, can I really leave that?" Someone pushed at her and she went in.

Published on Feb 24, 2012

by Stephen V. Ramey

Stardate 2025:325. We touch down on Mars. Flesh-colored dust settles around the capsule as the creaking, cooling fuselage ticks down to silence. Your face is pale inside the helmet; your hand grips the armrest between us. I think of your fingernails digging into my back, a shock of pain-pleasure distantly penetrating a mind preoccupied with release. The window onto this world is so small, yet the vista is endless. I breathe into my helmet until the visor fogs.

Published on May 6, 2015

by Stephen V. Ramey

Our paranoia is infinite today. And not without reason. We have just endured a journey to and from Mars orbit in full view of the world. Areas of the ship that were supposed to be off-limits were not. Every bowel movement, every wet dream and dry heave, a veritable sampler of trysts--it has all been broadcast, sprinkled across the globe like so much Hollywood glitter. The ultimate Reality Show, with our crew of six as unaware actors. Jimmy found the first pinhole camera. He brought it to me, pinched between his fingers like an insect with overlong legs. A frown fixed on his blocky face. His blue eyes blinked and blinked again.

Published on Apr 17, 2012

by Shane D. Rhinewald

Jerry sits in his favorite chair--the one with the red, plastic back. He says the others just don't feel right. His eyes dart around the room with boyish wonder, but they're a man's eyes, milky with cataracts, edged with wrinkles. He looks at the black and white pictures on the wall depicting historic events and gives me the date (down to the time of day in some cases) for everything from the Kennedy assassination to the shooting at Columbine. "Jerry, how do you feel today?" I ask, tapping my pen. Every session starts with a similar line of questioning; Jerry likes the routine. "Do you know how you feel?"

Read the original here:

Daily Science Fiction :: Space Travel

Original Dune This article or section refers to elements from Original Dune.

Space travel played a major role in the evolution and expansion of humanity throughout the known universe. Two forms of space travel existed: faster than light space travel, and conventional space travel.

For several thousand years, faster than light travel (or space-folding) was conducted exclusively by the Spacing Guild, using Spacefolder vessels piloted by Guild navigators that folded space-time and moved almost immeasurable distances in the blink of the eye.

This form of travel, while extremely expensive, was also not safe as one in ten ships that used space folding engine disappeared, at least during the early years of the technology's use before the advent of Navigators. It was utilized for both commercial and military purposes. Space-folding made use of two key factors:

Eventually, at some point between the fall of the Atreides Empire and the discovery of the Dar-es-Balat hoard, Ixian navigation machines broke the guild monopoly on foldspace by providing a means of safely navigating foldspace without a navigator.[1][2]

The old FTL conventional space travel was used mainly for travel within the confines of a star system (not for interstellar travel). However, before the discovery of the new faster-than-light travel method, it was also used for long-distance space travel. The old method was described as "outraceing photons". Even after space-folding became the primary means of interstellar travel, many Imperial warships still kept their old FTL drives as an alternative to the much faster but less reliable Holtzmann engines.

The connection between faster than light travel and the Holtzman Effect is not explicitly mentioned by Frank Herbert. It is a connection made in the prequel novels by Brian Herbert and Kevin J. Anderson.

In the 'Legends of Dune' trilogy, the pair describe the time shortly before and during the discovery of space-folding. In these works the discovery of space-folding is attributed to Norma Cenva, who goes on to become the first prescient folded space navigator. Prior to this, although described in 'The Machine Crusade' as "outracing the old faster than light method", vessels still took weeks or months to cross between even the closest stars.

Excerpt from:

Space travel - Dune - Wikia

Spaceflight (also written space flight) is ballistic flight into or through outer space. Spaceflight can occur with spacecraft with or without humans on board. Examples of human spaceflight include the U.S. Apollo Moon landing and Space Shuttle programs and the Russian Soyuz program, as well as the ongoing International Space Station. Examples of unmanned spaceflight include space probes that leave Earth orbit, as well as satellites in orbit around Earth, such as communications satellites. These operate either by telerobotic control or are fully autonomous.

Spaceflight is used in space exploration, and also in commercial activities like space tourism and satellite telecommunications. Additional non-commercial uses of spaceflight include space observatories, reconnaissance satellites and other Earth observation satellites.

A spaceflight typically begins with a rocket launch, which provides the initial thrust to overcome the force of gravity and propels the spacecraft from the surface of the Earth. Once in space, the motion of a spacecraftboth when unpropelled and when under propulsionis covered by the area of study called astrodynamics. Some spacecraft remain in space indefinitely, some disintegrate during atmospheric reentry, and others reach a planetary or lunar surface for landing or impact.

The first theoretical proposal of space travel using rockets was published by Scottish astronomer and mathematician William Leitch, in an 1861 essay "A Journey Through Space".[1] More well-known (though not widely outside Russia) is Konstantin Tsiolkovsky's work, " " (The Exploration of Cosmic Space by Means of Reaction Devices), published in 1903.

Spaceflight became an engineering possibility with the work of Robert H. Goddard's publication in 1919 of his paper "A Method of Reaching Extreme Altitudes". His application of the de Laval nozzle to liquid fuel rockets improved efficiency enough for interplanetary travel to become possible. He also proved in the laboratory that rockets would work in the vacuum of space[specify]; nonetheless, his work was not taken seriously by the public. His attempt to secure an Army contract for a rocket-propelled weapon in the first World War was defeated by the November 11, 1918 armistice with Germany.

Nonetheless, Goddard's paper was highly influential on Hermann Oberth, who in turn influenced Wernher von Braun. Von Braun became the first to produce modern rockets as guided weapons, employed by Adolf Hitler . Von Braun's V-2 was the first rocket to reach space, at an altitude of 189 kilometers (102 nautical miles) on a June 1944 test flight.[2]

Tsiolkovsky's rocketry work was not fully appreciated in his lifetime, but he influenced Sergey Korolev, who became the Soviet Union's chief rocket designer under Joseph Stalin, to develop intercontinental ballistic missiles to carry nuclear weapons as a counter measure to United States bomber planes. Derivatives of Korolev's R-7 Semyorka missiles were used to launch the world's first artificial Earth satellite, Sputnik 1, on October 4, 1957, and later the first human to orbit the Earth, Yuri Gagarin in Vostok 1, on April 12, 1961.[3]

At the end of World War II, von Braun and most of his rocket team surrendered to the United States, and were expatriated to work on American missiles at what became the Army Ballistic Missile Agency. This work on missiles such as Juno I and Atlas enabled launch of the first US satellite Explorer 1 on February 1, 1958, and the first American in orbit, John Glenn in Friendship 7 on February 20, 1962. As director of the Marshall Space Flight Center, Von Braun oversaw development of a larger class of rocket called Saturn, which allowed the US to send the first two humans, Neil Armstrong and Buzz Aldrin, to the Moon and back on Apollo 11 in July 1969. Over the same period, the Soviet Union secretly tried but failed to develop the N1 rocket to give them the capability to land one person on the Moon.

Rockets are the only means currently capable of reaching orbit or beyond. Other non-rocket spacelaunch technologies have yet to be built, or remain short of orbital speeds. A rocket launch for a spaceflight usually starts from a spaceport (cosmodrome), which may be equipped with launch complexes and launch pads for vertical rocket launches, and runways for takeoff and landing of carrier airplanes and winged spacecraft. Spaceports are situated well away from human habitation for noise and safety reasons. ICBMs have various special launching facilities.

A launch is often restricted to certain launch windows. These windows depend upon the position of celestial bodies and orbits relative to the launch site. The biggest influence is often the rotation of the Earth itself. Once launched, orbits are normally located within relatively constant flat planes at a fixed angle to the axis of the Earth, and the Earth rotates within this orbit.

A launch pad is a fixed structure designed to dispatch airborne vehicles. It generally consists of a launch tower and flame trench. It is surrounded by equipment used to erect, fuel, and maintain launch vehicles.

The most commonly used definition of outer space is everything beyond the Krmn line, which is 100 kilometers (62mi) above the Earth's surface. The United States sometimes defines outer space as everything beyond 50 miles (80km) in altitude.

Rockets are the only currently practical means of reaching space. Conventional airplane engines cannot reach space due to the lack of oxygen. Rocket engines expel propellant to provide forward thrust that generates enough delta-v (change in velocity) to reach orbit.

For manned launch systems launch escape systems are frequently fitted to allow astronauts to escape in the case of catastrophic failures.

Achieving a closed orbit is not essential to lunar and interplanetary voyages. Early Russian space vehicles successfully achieved very high altitudes without going into orbit. NASA considered launching Apollo missions directly into lunar trajectories but adopted the strategy of first entering a temporary parking orbit and then performing a separate burn several orbits later onto a lunar trajectory. This costs additional propellant because the parking orbit perigee must be high enough to prevent reentry while direct injection can have an arbitrarily low perigee because it will never be reached.

However, the parking orbit approach greatly simplified Apollo mission planning in several important ways. It substantially widened the allowable launch windows, increasing the chance of a successful launch despite minor technical problems during the countdown. The parking orbit was a stable "mission plateau" that gave the crew and controllers several hours to thoroughly check out the spacecraft after the stresses of launch before committing it to a long lunar flight; the crew could quickly return to Earth, if necessary, or an alternate Earth-orbital mission could be conducted. The parking orbit also enabled translunar trajectories that avoided the densest parts of the Van Allen radiation belts.

Apollo missions minimized the performance penalty of the parking orbit by keeping its altitude as low as possible. For example, Apollo 15 used an unusually low parking orbit (even for Apollo) of 92.5 nmi by 91.5 nmi (171km by 169km) where there was significant atmospheric drag. But it was partially overcome by continuous venting of hydrogen from the third stage of the Saturn V, and was in any event tolerable for the short stay.

Robotic missions do not require an abort capability or radiation minimization, and because modern launchers routinely meet "instantaneous" launch windows, space probes to the Moon and other planets generally use direct injection to maximize performance. Although some might coast briefly during the launch sequence, they do not complete one or more full parking orbits before the burn that injects them onto an Earth escape trajectory.

Note that the escape velocity from a celestial body decreases with altitude above that body. However, it is more fuel-efficient for a craft to burn its fuel as close to the ground as possible; see Oberth effect and reference.[5] This is another way to explain the performance penalty associated with establishing the safe perigee of a parking orbit.

Plans for future crewed interplanetary spaceflight missions often include final vehicle assembly in Earth orbit, such as NASA's Project Orion and Russia's Kliper/Parom tandem.

Astrodynamics is the study of spacecraft trajectories, particularly as they relate to gravitational and propulsion effects. Astrodynamics allows for a spacecraft to arrive at its destination at the correct time without excessive propellant use. An orbital maneuvering system may be needed to maintain or change orbits.

Non-rocket orbital propulsion methods include solar sails, magnetic sails, plasma-bubble magnetic systems, and using gravitational slingshot effects.

The term "transfer energy" means the total amount of energy imparted by a rocket stage to its payload. This can be the energy imparted by a first stage of a launch vehicle to an upper stage plus payload, or by an upper stage or spacecraft kick motor to a spacecraft.[6][7]

Vehicles in orbit have large amounts of kinetic energy. This energy must be discarded if the vehicle is to land safely without vaporizing in the atmosphere. Typically this process requires special methods to protect against aerodynamic heating. The theory behind reentry was developed by Harry Julian Allen. Based on this theory, reentry vehicles present blunt shapes to the atmosphere for reentry. Blunt shapes mean that less than 1% of the kinetic energy ends up as heat that reaches the vehicle and the heat energy instead ends up in the atmosphere.

The Mercury, Gemini, and Apollo capsules all splashed down in the sea. These capsules were designed to land at relatively slow speeds. Russian capsules for Soyuz make use of braking rockets as were designed to touch down on land. The Space Shuttle and Buran glide to a touchdown at high speed.

After a successful landing the spacecraft, its occupants and cargo can be recovered. In some cases, recovery has occurred before landing: while a spacecraft is still descending on its parachute, it can be snagged by a specially designed aircraft. This mid-air retrieval technique was used to recover the film canisters from the Corona spy satellites.

Unmanned spaceflight is all spaceflight activity without a necessary human presence in space. This includes all space probes, satellites and robotic spacecraft and missions. Unmanned spaceflight is the opposite of manned spaceflight, which is usually called human spaceflight. Subcategories of unmanned spaceflight are robotic spacecraft (objects) and robotic space missions (activities). A robotic spacecraft is a unmanned spacecraft with no humans on board, that is usually under telerobotic control. A robotic spacecraft designed to make scientific research measurements is often called a space probe.

Unmanned space missions use remote-controlled spacecraft. The first unmanned space mission was Sputnik I, launched October 4, 1957 to orbit the Earth. Space missions where animals but no humans are on-board are considered unmanned missions.

Many space missions are more suited to telerobotic rather than crewed operation, due to lower cost and lower risk factors. In addition, some planetary destinations such as Venus or the vicinity of Jupiter are too hostile for human survival, given current technology. Outer planets such as Saturn, Uranus, and Neptune are too distant to reach with current crewed spaceflight technology, so telerobotic probes are the only way to explore them. Telerobotics also allows exploration of regions that are vulnerable to contamination by Earth micro-organisms since spacecraft can be sterilized. Humans can not be sterilized in the same way as a spaceship, as they coexist with numerous micro-organisms, and these micro-organisms are also hard to contain within a spaceship or spacesuit.

Telerobotics becomes telepresence when the time delay is short enough to permit control of the spacecraft in close to real time by humans. Even the two seconds light speed delay for the Moon is too far away for telepresence exploration from Earth. The L1 and L2 positions permit 400 ms round trip delays which is just close enough for telepresence operation. Telepresence has also been suggested as a way to repair satellites in Earth orbit from Earth. The Exploration Telerobotics Symposium in 2012 explored this and other topics.[8]

The first human spaceflight was Vostok 1 on April 12, 1961, on which cosmonaut Yuri Gagarin of the USSR made one orbit around the Earth. In official Soviet documents, there is no mention of the fact that Gagarin parachuted the final seven miles.[9] The international rules for aviation records stated that "The pilot remains in his craft from launch to landing".[citation needed] This rule, if applied, would have "disqualified" Gagarin's spaceflight. Currently, the only spacecraft regularly used for human spaceflight are the Russian Soyuz spacecraft and the Chinese Shenzhou spacecraft. The U.S. Space Shuttle fleet operated from April 1981 until July 2011. SpaceShipOne has conducted two human suborbital spaceflights.

On a sub-orbital spaceflight the spacecraft reaches space and then returns to the atmosphere after following a (primarily) ballistic trajectory. This is usually because of insufficient specific orbital energy, in which case a suborbital flight will last only a few minutes, but it is also possible for an object with enough energy for an orbit to have a trajectory that intersects the Earth's atmosphere, sometimes after many hours. Pioneer 1 was NASA's first space probe intended to reach the Moon. A partial failure caused it to instead follow a suborbital trajectory to an altitude of 113,854 kilometers (70,746mi) before reentering the Earth's atmosphere 43 hours after launch.

The most generally recognized boundary of space is the Krmn line 100km above sea level. (NASA alternatively defines an astronaut as someone who has flown more than 50 miles (80km) above sea level.) It is not generally recognized by the public that the increase in potential energy required to pass the Krmn line is only about 3% of the orbital energy (potential plus kinetic energy) required by the lowest possible Earth orbit (a circular orbit just above the Krmn line.) In other words, it is far easier to reach space than to stay there. On May 17, 2004, Civilian Space eXploration Team launched the GoFast Rocket on a suborbital flight, the first amateur spaceflight. On June 21, 2004, SpaceShipOne was used for the first privately funded human spaceflight.

Point-to-point sub-orbital spaceflight is a category of spaceflight in which a spacecraft uses a sub-orbital flight for transportation. This can provide a two-hour trip from London to Sydney, which would be much faster than what is currently over a twenty-hour flight. Today, no company offers this type of spaceflight for transportation. However, Virgin Galactic has plans for a spaceplane called SpaceShipThree, which could offer this service in the future.[10] Suborbital spaceflight over an intercontinental distance requires a vehicle velocity that is only a little lower than the velocity required to reach low Earth orbit.[11] If rockets are used, the size of the rocket relative to the payload is similar to an Intercontinental Ballistic Missile (ICBM). Any intercontinental spaceflight has to surmount problems of heating during atmosphere re-entry that are nearly as large as those faced by orbital spaceflight.

A minimal orbital spaceflight requires much higher velocities than a minimal sub-orbital flight, and so it is technologically much more challenging to achieve. To achieve orbital spaceflight, the tangential velocity around the Earth is as important as altitude. In order to perform a stable and lasting flight in space, the spacecraft must reach the minimal orbital speed required for a closed orbit.

Interplanetary travel is travel between planets within a single planetary system. In practice, the use of the term is confined to travel between the planets of our Solar System.

Five spacecraft are currently leaving the Solar System on escape trajectories. The one farthest from the Sun is Voyager 1, which is more than 100 AU distant and is moving at 3.6 AU per year.[12] In comparison, Proxima Centauri, the closest star other than the Sun, is 267,000 AU distant. It will take Voyager 1 over 74,000 years to reach this distance. Vehicle designs using other techniques, such as nuclear pulse propulsion are likely to be able to reach the nearest star significantly faster. Another possibility that could allow for human interstellar spaceflight is to make use of time dilation, as this would make it possible for passengers in a fast-moving vehicle to travel further into the future while aging very little, in that their great speed slows down the rate of passage of on-board time. However, attaining such high speeds would still require the use of some new, advanced method of propulsion.

Intergalactic travel involves spaceflight between galaxies, and is considered much more technologically demanding than even interstellar travel and, by current engineering terms, is considered science fiction.

Spacecraft are vehicles capable of controlling their trajectory through space.

The first 'true spacecraft' is sometimes said to be Apollo Lunar Module,[13] since this was the only manned vehicle to have been designed for, and operated only in space; and is notable for its non aerodynamic shape.

Spacecraft today predominantly use rockets for propulsion, but other propulsion techniques such as ion drives are becoming more common, particularly for unmanned vehicles, and this can significantly reduce the vehicle's mass and increase its delta-v.

Launch systems are used to carry a payload from Earth's surface into outer space.

All launch vehicles contain a huge amount of energy that is needed for some part of it to reach orbit. There is therefore some risk that this energy can be released prematurely and suddenly, with significant effects. When a Delta II rocket exploded 13 seconds after launch on January 17, 1997, there were reports of store windows 10 miles (16km) away being broken by the blast.[15]

Space is a fairly predictable environment, but there are still risks of accidental depressurization and the potential failure of equipment, some of which may be very newly developed.

In 2004 the International Association for the Advancement of Space Safety was established in the Netherlands to further international cooperation and scientific advancement in space systems safety.[16]

In a microgravity environment such as that provided by a spacecraft in orbit around the Earth, humans experience a sense of "weightlessness." Short-term exposure to microgravity causes space adaptation syndrome, a self-limiting nausea caused by derangement of the vestibular system. Long-term exposure causes multiple health issues. The most significant is bone loss, some of which is permanent, but microgravity also leads to significant deconditioning of muscular and cardiovascular tissues.

Once above the atmosphere, radiation due to the Van Allen belts, solar radiation and cosmic radiation issues occur and increase. Further away from the Earth, solar flares can give a fatal radiation dose in minutes, and the health threat from cosmic radiation significantly increases the chances of cancer over a decade exposure or more.[17]

In human spaceflight, the life support system is a group of devices that allow a human being to survive in outer space. NASA often uses the phrase Environmental Control and Life Support System or the acronym ECLSS when describing these systems for its human spaceflight missions.[18] The life support system may supply: air, water and food. It must also maintain the correct body temperature, an acceptable pressure on the body and deal with the body's waste products. Shielding against harmful external influences such as radiation and micro-meteorites may also be necessary. Components of the life support system are life-critical, and are designed and constructed using safety engineering techniques.

Space weather is the concept of changing environmental conditions in outer space. It is distinct from the concept of weather within a planetary atmosphere, and deals with phenomena involving ambient plasma, magnetic fields, radiation and other matter in space (generally close to Earth but also in interplanetary, and occasionally interstellar medium). "Space weather describes the conditions in space that affect Earth and its technological systems. Our space weather is a consequence of the behavior of the Sun, the nature of Earth's magnetic field, and our location in the Solar System."[19]

Space weather exerts a profound influence in several areas related to space exploration and development. Changing geomagnetic conditions can induce changes in atmospheric density causing the rapid degradation of spacecraft altitude in Low Earth orbit. Geomagnetic storms due to increased solar activity can potentially blind sensors aboard spacecraft, or interfere with on-board electronics. An understanding of space environmental conditions is also important in designing shielding and life support systems for manned spacecraft.

Rockets as a class are not inherently grossly polluting. However, some rockets use toxic propellants, and most vehicles use propellants that are not carbon neutral. Many solid rockets have chlorine in the form of perchlorate or other chemicals, and this can cause temporary local holes in the ozone layer. Re-entering spacecraft generate nitrates which also can temporarily impact the ozone layer. Most rockets are made of metals that can have an environmental impact during their construction.

In addition to the atmospheric effects there are effects on the near-Earth space environment. There is the possibility that orbit could become inaccessible for generations due to exponentially increasing space debris caused by spalling of satellites and vehicles (Kessler syndrome). Many launched vehicles today are therefore designed to be re-entered after use.

Current and proposed applications for spaceflight include:

Most early spaceflight development was paid for by governments. However, today major launch markets such as Communication satellites and Satellite television are purely commercial, though many of the launchers were originally funded by governments.

Private spaceflight is a rapidly developing area: space flight that is not only paid for by corporations or even private individuals, but often provided by private spaceflight companies. These companies often assert that much of the previous high cost of access to space was caused by governmental inefficiencies they can avoid. This assertion can be supported by much lower published launch costs for private space launch vehicles such as Falcon 9 developed with private financing. Lower launch costs and excellent safety will be required for the applications such as Space tourism and especially Space colonization to become successful.

Media related to Spaceflight at Wikimedia Commons

Here is the original post:

Spaceflight - Wikipedia, the free encyclopedia

A few hundred years ago, traveling over the Earths surface was a risky adventure. Early explorers who set out to explore the New World went by boat, enduring fierce storms, disease and hunger, to reach their destinations. Today, astronauts exploring space face similar challenges.

All About Space Travel: One space shuttle launch costs $450 million

Space travel has become much safer as scientists have overcome potential problems, but its still dangerous. Its also very expensive. In order for a space shuttle to break free of Earths gravity, it has to travel at a speed of 15,000 miles per hour. Space shuttles need 1.9 million liters of fuel just to launch into space. Thats enough fuel to fill up 42,000 cars! Combine the high speed, heat and fuel needed for launching and youve got a very potentially dangerous situation.

In 1949, Albert II, a Rhesus monkey went to space. Keep reading to find out more all about space travel.

Re-entering the atmosphere is dangerous too. When a space craft re-enters the atmosphere, it is moving very fast. As it moves through the air, friction causes it to heat up to a temperature of 2,691 degrees. The first spacecrafts were destroyed during re-entry. Todays space shuttles have special ceramic tiles that help absorb some of the heat, keeping the astronauts safe during re-entry.

In 1957, the Russian space dog, Laika, orbited the Earth.

In 1959, the Russian space craft, Luna 2, landed on the moon. It crashed at high speed.

Russian astronaut, Yuri Gagarin, was the first human in space. He orbited the Earth in 1961.

On July 20, 1969, Neil Armstrong and Buzz Aldrin became the first men to walk on the moon and return home safely a journey of 250,000 miles.

Check out this cool video all about space travel:

A video about the N.E.X.T. mission for space travel by NASA.

Enjoyed the Easy Science for Kids Website all about Space Travel info? Take the FREE & fun all about Space Travel quiz and download FREE Space Travel worksheet for kids. For lengthy info click here.

Continued here:

Space Travel Facts for Kids

Human spaceflight (also referred to as manned spaceflight) is space travel with a crew or passengers aboard the spacecraft. Spacecraft carrying people may be operated directly, by human crew, or it may be either remotely operated from ground stations on Earth or be autonomous, able to carry out a specific mission with no human involvement.

The first human spaceflight was launched by the Soviet Union on 12 April 1961 as a part of the Vostok program, with cosmonaut Yuri Gagarin aboard. Humans have been continually present in space for 700849902926700000015years and 297days on the International Space Station. All early human spaceflight was crewed, where at least some of the passengers acted to carry out tasks of piloting or operating the spacecraft. After 2015, several human-capable spacecraft are being explicitly designed with the ability to operate autonomously.

Since the retirement of the US Space Shuttle in 2011, only Russia and China have maintained human spaceflight capability with the Soyuz program and Shenzhou program. Currently, all expeditions to the International Space Station use Soyuz vehicles, which remain attached to the station to allow quick return if needed. The United States is developing commercial crew transportation to facilitate domestic access to ISS and low Earth orbit, as well as the Orion vehicle for beyond-low Earth orbit applications.

While spaceflight has typically been a government-directed activity, commercial spaceflight has gradually been taking on a greater role. The first private human spaceflight took place on 21 June 2004, when SpaceShipOne conducted a suborbital flight, and a number of non-governmental companies have been working to develop a space tourism industry. NASA has also played a role to stimulate private spaceflight through programs such as Commercial Orbital Transportation Services (COTS) and Commercial Crew Development (CCDev). With its 2011 budget proposals released in 2010,[1] the Obama administration moved towards a model where commercial companies would supply NASA with transportation services of both people and cargo transport to low Earth orbit. The vehicles used for these services could then serve both NASA and potential commercial customers. Commercial resupply of ISS began two years after the retirement of the Shuttle, and commercial crew launches could begin by 2017.[2]

Human spaceflight capability was first developed during the Cold War between the United States and the Soviet Union (USSR), which developed the first intercontinental ballistic missile rockets to deliver nuclear weapons. These rockets were large enough to be adapted to carry the first artificial satellites into low Earth orbit. After the first satellites were launched in 1957 and 1958, the US worked on Project Mercury to launch men singly into orbit, while the USSR secretly pursued the Vostok program to accomplish the same thing. The USSR launched the first human in space, Yuri Gagarin into a single orbit in Vostok 1 on a Vostok 3KA rocket, on April 12, 1961. The US launched its first astronaut, Alan Shepard on a suborbital flight aboard Freedom 7 on a Mercury-Redstone rocket, on May 5, 1961. Unlike Gagarin, Shepard manually controlled his spacecraft's attitude, and landed inside it. The first American in orbit was John Glenn aboard Friendship 7, launched February 20, 1962 on a Mercury-Atlas rocket. The USSR launched five more cosmonauts in Vostok capsules, including the first woman in space, Valentina Tereshkova aboard Vostok 6 on June 16, 1963. The US launched a total of two astronauts in suborbital flight and four in orbit through 1963.

US President John F. Kennedy raised the stakes of the Space Race by setting the goal of landing a man on the Moon and returning him safely by the end of the 1960s.[3] The US started the three-man Apollo program in 1961 to accomplish this, launched by the Saturn family of launch vehicles, and the interim two-man Project Gemini in 1962, which flew 10 missions launched by Titan II rockets in 1965 and 1966. Gemini's objective was to support Apollo by developing American orbital spaceflight experience and techniques to be used in the Moon mission.[4]

Meanwhile, the USSR remained silent about their intentions to send humans to the Moon, and proceeded to stretch the limits of their single-pilot Vostok capsule into a two- or three-person Voskhod capsule to compete with Gemini. They were able to launch two orbital flights in 1964 and 1965 and achieved the first spacewalk, made by Alexei Leonov on Voskhod 2 on March 8, 1965. But Voskhod did not have Gemini's capability to maneuver in orbit, and the program was terminated. The US Gemini flights did not accomplish the first spacewalk, but overcame the early Soviet lead by performing several spacewalks and solving the problem of astronaut fatigue caused by overcoming the lack of gravity, demonstrating up to two weeks endurance in a human spaceflight, and the first space rendezvous and dockings of spacecraft.

The US succeeded in developing the Saturn V rocket necessary to send the Apollo spacecraft to the Moon, and sent Frank Borman, James Lovell, and William Anders into 10 orbits around the Moon in Apollo 8 in December 1968. In July 1969, Apollo 11 accomplished Kennedy's goal by landing Neil Armstrong and Buzz Aldrin on the Moon July 21 and returning them safely on July 24 along with Command Module pilot Michael Collins. A total of six Apollo missions landed 12 men to walk on the Moon through 1972, half of which drove electric powered vehicles on the surface. The crew of Apollo 13, Lovell, Jack Swigert, and Fred Haise, survived a catastrophic in-flight spacecraft failure and returned to Earth safely without landing on the Moon.

Meanwhile, the USSR secretly pursued human lunar lunar orbiting and landing programs. They successfully developed the three-person Soyuz spacecraft for use in the lunar programs, but failed to develop the N1 rocket necessary for a human landing, and discontinued the lunar programs in 1974.[5] On losing the Moon race, they concentrated on the development of space stations, using the Soyuz as a ferry to take cosmonauts to and from the stations. They started with a series of Salyut sortie stations from 1971 to 1986.

After the Apollo program, the US launched the Skylab sortie space station in 1973, manning it for 171 days with three crews aboard Apollo spacecraft. President Richard Nixon and Soviet Premier Leonid Brezhnev negotiated an easing of relations known as dtente, an easing of Cold War tensions. As part of this, they negotiated the Apollo-Soyuz Test Project, in which an Apollo spacecraft carrying a special docking adapter module rendezvoused and docked with Soyuz 19 in 1975. The American and Russian crews shook hands in space, but the purpose of the flight was purely diplomatic and symbolic.

Nixon appointed his Vice President Spiro Agnew to head a Space Task Group in 1969 to recommend follow-on human spaceflight programs after Apollo. The group proposed an ambitious Space Transportation System based on a reusable Space Shuttle which consisted of a winged, internally fueled orbiter stage burning liquid hydrogen, launched by a similar, but larger kerosene-fueled booster stage, each equipped with airbreathing jet engines for powered return to a runway at the Kennedy Space Center launch site. Other components of the system included a permanent modular space station, reusable space tug and nuclear interplanetary ferry, leading to a human expedition to Mars as early as 1986, or as late as 2000, depending on the level of funding allocated. However, Nixon knew the American political climate would not support Congressional funding for such an ambition, and killed proposals for all but the Shuttle, possibly to be followed by the space station. Plans for the Shuttle were scaled back to reduce development risk, cost, and time, replacing the piloted flyback booster with two reusable solid rocket boosters, and the smaller orbiter would use an expendable external propellant tank to feed its hydrogen-fueled main engines. The orbiter would have to make unpowered landings.

The two nations continued to compete rather than cooperate in space, as the US turned to developing the Space Shuttle and planning the space station, dubbed Freedom. The USSR launched three Almaz military sortie stations from 1973 to 1977, disguised as Salyuts. They followed Salyut with the development of Mir, the first modular, semi-permanent space station, the construction of which took place from 1986 to 1996. Mir orbited at an altitude of 354 kilometers (191 nautical miles), at a 51.6 inclination. It was occupied for 4,592 days, and made a controlled reentry in 2001.

The Space Shuttle started flying in 1981, but the US Congress failed to approve sufficient funds to make Freedom a reality. A fleet of four shuttles was built: Columbia, Challenger, Discovery, and Atlantis. A fifth shuttle, Endeavour, was built to replace Challenger which was destroyed in an accident during launch which killed 7 astronauts on January 28, 1986. Twenty-two Shuttle flights carried a European Space Agency sortie space station called Spacelab in the payload bay from 1983 to 1998.[6]

The USSR copied the reusable Space Shuttle orbiter, which it called Buran. It was designed to be launched into orbit by the expendable Energia rocket, and capable of robotic orbital flight and landing. Unlike the US Shuttle, Buran had no main rocket engines, but used its orbital maneuvering engines to insert itself into orbit; but it had airbreathing jet engines for powered landings. A single unmanned orbital test flight was successfully made in November 1988. A second test flight was planned by 1993, but the program was cancelled due to lack of funding and the dissolution of the Soviet Union in 1991. Two more orbiters were never completed, and the first one was destroyed in a hangar roof collapse in May 2002.

The dissolution of the Soviet Union in 1991 brought an end to the Cold War and opened the door to true cooperation between the US and Russia. The Soviet Soyuz and Mir programs were taken over by the Russian Federal Space Agency, now known as the Roscosmos State Corporation. The Shuttle-Mir Program included American Space Shuttles visiting the Mir space station, Russian cosmonauts flying on the Shuttle, and an American astronaut flying aboard a Soyuz spacecraft for long-duration expeditions aboard Mir.

In 1993, President Bill Clinton secured Russia's cooperation in converting the planned Space Station Freedom into the International Space Station (ISS). Construction of the station began in 1998. The station orbits at an altitude of 409 kilometers (221nmi) and an inclination of 51.65.

The Space Shuttle was retired in 2011 after 135 orbital flights, several of which helped assemble, supply, and crew the ISS. Columbia was destroyed in another accident during reentry, which killed 7 astronauts on February 1, 2003.

After Russia's launch of Sputnik 1 in 1957, Chairman Mao Zedong intended to place a Chinese satellite in orbit by 1959 to celebrate the 10th anniversary of the founding of the People's Republic of China (PRC),[7] However, China did not successfully launch its first satellite until April 24, 1970. Mao and Premier Zhou Enlai decided on July 14, 1967, that the PRC should not be left behind, and started China's own human spaceflight program.[8] The first attempt, the Shuguang spacecraft copied from the US Gemini, was cancelled on May 13, 1972.

China later designed the Shenzhou spacecraft resembling the Russian Soyuz, and became the third nation to achieve independent human spaceflight capability by launching Yang Liwei on a 21-hour flight aboard Shenzhou 5 on October 15, 2003. China launched the Tiangong-1 space station on September 29, 2011, and two sortie missions to it: Shenzhou 9 June 1629, 2012, with China's first female astronaut Liu Yang; and Shenzhou 10, June 1326, 2013.

The European Space Agency began development in 1987 of the Hermes spaceplane, to be launched on the Ariane 5 expendable launch vehicle. The project was cancelled in 1992, when it became clear that neither cost nor performance goals could be achieved. No Hermes shuttles were ever built.

Japan began development in the 1980s of the HOPE-X experimental spaceplane, to be launched on its H-IIA expendable launch vehicle. A string of failures in 1998 led to funding reduction, and the project's cancellation in 2003.

Under the Bush administration, the Constellation Program included plans for retiring the Shuttle program and replacing it with the capability for spaceflight beyond low Earth orbit. In the 2011 United States federal budget, the Obama administration cancelled Constellation for being over budget and behind schedule while not innovating and investing in critical new technologies.[9] For beyond low earth orbit human spaceflight NASA is developing the Orion spacecraft to be launched by the Space Launch System. Under the Commercial Crew Development plan, NASA will rely on transportation services provided by the private sector to reach low earth orbit, such as Space X's Falcon 9/Dragon V2, Sierra Nevada Corporation's Dream Chaser, or Boeing's CST-100. The period between the retirement of the shuttle in 2011 and the initial operational capability of new systems in 2017, similar to the gap between the end of Apollo in 1975 and the first space shuttle flight in 1981, is referred to by a presidential Blue Ribbon Committee as the U.S. human spaceflight gap.[10]

After the early 2000s, a variety of private spaceflight ventures were undertaken. Several of the companies formed by 2005, including Blue Origin, SpaceX, Virgin Galactic, and XCOR Aerospace have explicit plans to advance human spaceflight. As of 2015[update], all four of those companies have development programs underway to fly commercial passengers before 2018.

Commercial suborbital spacecraft aimed at the space tourism market include Virgin Galactic SpaceshipTwo, and XCOR's Lynx spaceplane which are both under development and could reach space before 2017.[11] More recently, Blue Origin has begun a multi-year test program of their New Shepardvehicle with plans to test in 20152016 while carrying no passengers, then adding "test passengers" in 2017, and initiate commercial flights in 2018.[12][13]

SpaceX and Boeing are both developing passenger-capable orbital space capsules as of 2015, planning to fly NASA astronauts to the International Space Station as soon as 2018. SpaceX will be carrying passengers on Dragon 2 launched on a Falcon 9 launch vehicle. Boeing will be doing it with their CST-100 launched on a United Launch Alliance Atlas V launch vehicle.[14] Development funding for these orbital-capable technologies has been provided by a mix of government and private funds, with SpaceX providing a greater portion of total development funding for this human-carrying capability from private investment.[15][16] There have been no public announcements of commercial offerings for orbital flights from either company, although both companies are planning some flights with their own private, not NASA, astronauts on board.

Svetlana Savitskaya became the first woman to walk in space on 25 July 1984.

Sally Ride became the first American woman in space in 1983. Eileen Collins was the first female shuttle pilot, and with shuttle mission STS-93 in 1999 she became the first woman to command a U.S. spacecraft.

The longest single human spaceflight is that of Valeri Polyakov, who left Earth on 8 January 1994, and did not return until 22 March 1995 (a total of 437 days 17 h 58 min 16 s). Sergei Krikalyov has spent the most time of anyone in space, 803 days, 9 hours, and 39 minutes altogether. The longest period of continuous human presence in space is 700849902926700000015years and 297days on the International Space Station, exceeding the previous record of almost 10 years (or 3,634 days) held by Mir, spanning the launch of Soyuz TM-8 on 5 September 1989 to the landing of Soyuz TM-29 on 28 August 1999.

For many years, only the USSR (later Russia) and the United States had their own astronauts. Citizens of other nations flew in space, beginning with the flight of Vladimir Remek, a Czech, on a Soviet spacecraft on 2 March 1978, in the Interkosmos programme. As of 2010[update], citizens from 38 nations (including space tourists) have flown in space aboard Soviet, American, Russian, and Chinese spacecraft.

Human spaceflight programs have been conducted by the former Soviet Union and current Russian Federation, the United States, the People's Republic of China and by private spaceflight company Scaled Composites.

Space vehicles are spacecraft used for transportation between the Earth's surface and outer space, or between locations in outer space. The following space vehicles and spaceports are currently used for launching human spaceflights:

The following space stations are currently maintained in Earth orbit for human occupation:

Numerous private companies attempted human spaceflight programs in an effort to win the $10 million Ansari X Prize. The first private human spaceflight took place on 21 June 2004, when SpaceShipOne conducted a suborbital flight. SpaceShipOne captured the prize on 4 October 2004, when it accomplished two consecutive flights within one week. SpaceShipTwo, launching from the carrier aircraft White Knight Two, is planned to conduct regular suborbital space tourism.[17]

Most of the time, the only humans in space are those aboard the ISS, whose crew of six spends up to six months at a time in low Earth orbit.

NASA and ESA use the term "human spaceflight" to refer to their programs of launching people into space. These endeavors have also been referred to as "manned space missions," though because of gender specificity this is no longer official parlance according to NASA style guides.[18]

The Indian Space Research Organisation (ISRO) has begun work on pre-project activities of a human space flight mission program.[19] The objective is to carry a crew of two to Low Earth Orbit (LEO) and return them safely to a predefined destination on Earth. The program is proposed to be implemented in defined phases. Currently, the pre-project activities are progressing with a focus on the development of critical technologies for subsystems such as the Crew Module (CM), Environmental Control and Life Support System (ECLSS), Crew Escape System, etc. The department has initiated pre-project activities to study technical and managerial issues related to crewed missions. The program envisages the development of a fully autonomous orbital vehicle carrying 2 or 3 crew members to about 300km low earth orbit and their safe return.

The United States National Aeronautics and Space Administration (NASA) is developing a plan to land humans on Mars by the 2030s. The first step in this mission begins sometime during 2020, when NASA plans to send an unmanned craft into deep space to retrieve an asteroid.[20] The asteroid will be pushed into the moons orbit, and studied by astronauts aboard Orion, NASAs first human spacecraft in a generation.[21] Orions crew will return to Earth with samples of the asteroid and their collected data. In addition to broadening Americas space capabilities, this mission will test newly developed technology, such as solar electric propulsion, which uses solar arrays for energy and requires ten times less propellant than the conventional chemical counterpart used for powering space shuttles to orbit.[22]

Several other countries and space agencies have announced and begun human spaceflight programs by their own technology, Japan (JAXA), Iran (ISA) and Malaysia (MNSA).

There are two main sources of hazard in space flight: those due to the environment of space which make it hostile to the human body, and the potential for mechanical malfunctions of the equipment required to accomplish space flight.

Planners of human spaceflight missions face a number of safety concerns.

The immediate needs for breathable air and drinkable water are addressed by the life support system of the spacecraft.

Medical consequences such as possible blindness and bone loss have been associated with human space flight.[32][33]

On 31 December 2012, a NASA-supported study reported that spaceflight may harm the brain of astronauts and accelerate the onset of Alzheimer's disease.[34][35][36]

In October 2015, the NASA Office of Inspector General issued a health hazards report related to space exploration, including a human mission to Mars.[37][38]

Medical data from astronauts in low earth orbits for long periods, dating back to the 1970s, show several adverse effects of a microgravity environment: loss of bone density, decreased muscle strength and endurance, postural instability, and reductions in aerobic capacity. Over time these deconditioning effects can impair astronauts performance or increase their risk of injury.[39]

In a weightless environment, astronauts put almost no weight on the back muscles or leg muscles used for standing up, which causes them to weaken and get smaller. Astronauts can lose up to twenty per cent of their muscle mass on spaceflights lasting five to eleven days. The consequent loss of strength could be a serious problem in case of a landing emergency.[40] Upon return to Earth from long-duration flights, astronauts are considerably weakened, and are not allowed to drive a car for twenty-one days.[41]

Astronauts experiencing weightlessness will often lose their orientation, get motion sickness, and lose their sense of direction as their bodies try to get used to a weightless environment. When they get back to Earth, or any other mass with gravity, they have to readjust to the gravity and may have problems standing up, focusing their gaze, walking and turning. Importantly, those body motor disturbances after changing from different gravities only get worse the longer the exposure to little gravity.[citation needed] These changes will affect operational activities including approach and landing, docking, remote manipulation, and emergencies that may happen while landing. This can be a major roadblock to mission success.[citation needed]

In addition, after long space flight missions, male astronauts may experience severe eyesight problems.[42][43][44][45][46] Such eyesight problems may be a major concern for future deep space flight missions, including a crewed mission to the planet Mars.[42][43][44][45][47]

Without proper shielding, the crews of missions beyond low Earth orbit (LEO) might be at risk from high-energy protons emitted by solar flares. Lawrence Townsend of the University of Tennessee and others have studied the most powerful solar flare ever recorded. That flare was seen by the British astronomer Richard Carrington in September 1859. Radiation doses astronauts would receive from a Carrington-type flare could cause acute radiation sickness and possibly even death.[49]

Another type of radiation, galactic cosmic rays, presents further challenges to human spaceflight beyond low Earth orbit.[50]

There is also some scientific concern that extended spaceflight might slow down the bodys ability to protect itself against diseases.[51] Some of the problems are a weakened immune system and the activation of dormant viruses in the body. Radiation can cause both short and long term consequences to the bone marrow stem cells which create the blood and immune systems. Because the interior of a spacecraft is so small, a weakened immune system and more active viruses in the body can lead to a fast spread of infection.[citation needed]

During long missions, astronauts are isolated and confined into small spaces. Depression, cabin fever and other psychological problems may impact the crew's safety and mission success.[citation needed]

Astronauts may not be able to quickly return to Earth or receive medical supplies, equipment or personnel if a medical emergency occurs. The astronauts may have to rely for long periods on their limited existing resources and medical advice from the ground.

Space flight requires much higher velocities than ground or air transportation, which in turn requires the use of high energy density propellants for launch, and the dissipation of large amounts of energy, usually as heat, for safe reentry through the Earth's atmosphere.

Since rockets carry the potential for fire or explosive destruction, space capsules generally employ some sort of launch escape system, consisting either of a tower-mounted solid fuel rocket to quickly carry the capsule away from the launch vehicle (employed on Mercury, Apollo, and Soyuz), or else ejection seats (employed on Vostok and Gemini) to carry astronauts out of the capsule and away for individual parachute landing. The escape tower is discarded at some point before the launch is complete, at a point where an abort can be performed using the spacecraft's engines.

Such a system is not always practical for multiple crew member vehicles (particularly spaceplanes), depending on location of egress hatch(es). When the single-hatch Vostok capsule was modified to become the 2 or 3-person Voskhod, the single-cosmonaut ejection seat could not be used, and no escape tower system was added. The two Voskhod flights in 1964 and 1965 avoided launch mishaps. The Space Shuttle carried ejection seats and escape hatches for its pilot and copilot in early flights, but these could not be used for passengers who sat below the flight deck on later flights, and so were discontinued.

The only in-flight launch abort of a crewed flight occurred on Soyuz 18a on April 5, 1975. The abort occurred after the launch escape system had been jettisoned, when the launch vehicle's spent second stage failed to separate before the third stage ignited. The vehicle strayed off course, and the crew separated the spacecraft and fired its engines to pull it away from the errant rocket. Both cosmonauts landed safely.

In the only use of a launch escape system on a crewed flight, the planned Soyuz T-10a launch on September 26, 1983 was aborted by a launch vehicle fire 90 seconds before liftoff. Both cosmonauts aboard landed safely.

The only crew fatality during launch occurred on January 28, 1986, when the Space Shuttle Challenger broke apart 73 seconds after liftoff, due to failure of a solid rocket booster seal which caused separation of the booster and failure of the external fuel tank, resulting in explosion of the fuel. All seven crew members were killed.

The single pilot of Soyuz 1, Vladimir Komarov was killed when his capsule's parachutes failed during an emergency landing on April 24, 1967, causing the capsule to crash.

The crew of seven aboard the Space Shuttle Columbia were killed on reentry after completing a successful mission in space on February 1, 2003. A wing leading edge reinforced carbon-carbon heat shield had been damaged by a piece of frozen external tank foam insulation which broke off and struck the wing during launch. Hot reentry gasses entered and destroyed the wing structure, leading to breakup of the orbiter vehicle.

There are two basic choices for an artificial atmosphere: either an Earth-like mixture of oxygen in an inert gas such as nitrogen or helium, or pure oxygen, which can be used at lower than standard atmospheric pressure. A nitrogen-oxygen mixture is used in the International Space Station and Soyuz spacecraft, while low-pressure pure oxygen is commonly used in space suits for extravehicular activity.

Use of a gas mixture carries risk of decompression sickness (commonly known as "the bends") when transitioning to or from the pure oxygen space suit environment. There have also been instances of injury and fatalities caused by suffocation in the presence of too much nitrogen and not enough oxygen.

A pure oxygen atmosphere carries risk of fire. The original design of the Apollo spacecraft used pure oxygen at greater than atmospheric pressure prior to launch. An electrical fire started in the cabin of Apollo 1 during a ground test at Cape Kennedy Air Force Station Launch Complex 34 on January 27, 1967, and spread rapidly. The high pressure (increased even higher by the fire) prevented removal of the plug door hatch cover in time to rescue the crew. All three, Gus Grissom, Edward H. White, and Roger Chaffee, were killed.[55] This led NASA to use a nitrogen/oxygen atmosphere before launch, and low pressure pure oxygen only in space.

The March 1966 Gemini 8 mission was aborted in orbit when an attitude control system thruster stuck in the on position, sending the craft into a dangerous spin which threatened the lives of Neil Armstrong and David Scott. Armstrong had to shut the control system off and use the reentry control system to stop the spin. The craft made an emergency reentry and the astronauts landed safely. The most probable cause was determined to be an electrical short due to a static electricity discharge, which caused the thruster to remain powered even when switched off. The control system was modified to put each thruster on its own isolated circuit.

The third lunar landing expedition Apollo 13 in April 1970, was aborted and the lives of the crew, James Lovell, Jack Swigert and Fred Haise, were threatened by failure of a cryogenic liquid oxygen tank en route to the Moon. The tank burst when electrical power was applied to internal stirring fans in the tank, causing the immediate loss of all of its contents, and also damaging the second tank, causing the loss of its remaining oxygen in a span of 130 minutes. This in turn caused loss of electrical power provided by fuel cells to the command spacecraft. The crew managed to return to Earth safely by using the lunar landing craft as a "life boat". The tank failure was determined to be caused by two mistakes. The tank's drain fitting had been damaged when it was dropped during factory testing. This necessitated use of its internal heaters to boil out the oxygen after a pre-launch test, which in turn damaged the fan wiring's electrical insulation, because the thermostats on the heaters did not meet the required voltage rating due to a vendor miscommunication.

As of December 2015[update], 22 crew members have died in accidents aboard spacecraft. Over 100 others have died in accidents during activity directly related to spaceflight or testing.

Read more here:

Human spaceflight - Wikipedia, the free encyclopedia

Space-A travel is a means by which members of United States Uniformed Services (United States Military, reservists and retirees, United States Department of Defense civilian personnel (under certain circumstances), and these groups' family members, are permitted to travel on aircraft under the jurisdiction of the United States Department of Defense when excess capability allows.

Space available travel is a privilege that derives, in part, from United States Code, title 10, section 4744, which states, "officers and members of the Military Departments, and their families, when space is available, may be transported on vessels operated by any military transport agency of the Department of Defense". Space available travel is defined as "travel aboard DoD owned or controlled aircraft and occurs when aircraft are not fully booked with passengers traveling under orders".

It is a privilege offered to United States Uniformed Services members. Retired members are given the privilege in recognition of their career and because they are eligible for recall to active duty. The criteria for extending the privilege to other categories of passengers is their support to the mission being performed by Uniformed Services members and to the enhancement of active duty Service members' quality of life.

There are rules and guidelines which apply to such travel. Uniformed personnel may only travel Space-A while on leave or pass for the full duration of their Space-A trip, and Space-A travel can not be used in conjunction with travel required by the service. Space A travel may not be used for personal financial gain or in connection with business enterprises or employment. Other nations' laws and policies, as well as U.S. foreign policy, may limit the ability to travel using Space-A.

Aside from members of the United States Marine Corps, travelers do not have to be in uniform for their flights.

Eligible passengers wanting to travel using DoD Space-A travel are required to sign up at the departing location and are then placed on a locally managed Space-A register. The registration process varies depending on the location, but most locations allow signups via electronic mail, fax, or postal mail.

Each location's passenger service center maintains their own Space-A register. Each person signing up is placed on this register using category of travel, signup date and signup time.

Based on status (active duty military, retired military, emergency traveler, etc.), Space-A travel applicants are assigned a category of travel from 1 to 6, which categorizes their priority of movement, 1 being the highest priority. Thus, an applicant with priority 1 will gain a place on an available aircraft over an applicant with priority 4, for example.

The number of space-available seats may not be known until the flight's "Roll Call" just prior to the flight departs. After sorting the signup register by category of travel and signup date, the passenger terminal personnel follow a selection procedure. If there is sufficient seating for everyone desiring a seat, then everyone boards; otherwise, a cutoff point is determined.

The branches of service eligible for Space-A travel are:

Space-A travel is not without its pitfalls. Unlike traditional commercial air traffic, military flights are not always assigned predictable takeoff times. Many factors go into planning a military flight, with space-required cargo and passengers forming the basis of planning. There is no consideration given to potential Space-A travelers during the planning process.

The majority of flights that passengers take occur on: C-5, C-17, C-40, C-130, KC-10, and KC-135 aircraft.

Space-A travelers might meet abrupt, sometimes even in-flight, changes in travel. This need for pre-planning has given rise to a small industry surrounding such travel. Non-governmental enterprises (for the most part, publishers) produce products, initially through books and maps, with more recent incarnations as websites which provide travelers with information regarding Space-A travel.

The following information Space-A links are hosted by volunteer retired military:

Originally posted here:

Space-A travel - Wikipedia, the free encyclopedia

NASA Establishes Institute to Explore New Ways to Protect Astronauts 20 New Countries to Invest in Space Programs by 2025 NASA, USAID Open Environmental Monitoring Hub in West Africa Russia, US Discuss Lunar Station for Mars Mission Dark Matter Particle Remains Elusive NASA Seeks Picometer Accuracy For Webb Telescope Return to the underwater Space Station .. A decade of plant biology in space On this day 10 years ago, Space Shuttle Discovery was launched to the International Space Station carrying ESA's European Modular Cultivation System - a miniature greenhouse to probe how plants grow ... more .. Mathematical framework prioritizes key patterns to accelerate scientific discovery Networks are mathematical representations to explore and understand diverse, complex systems-everything from military logistics and global finance to air traffic, social media, and the biological pr ... more .. Exploring inner space for outer space An international team of six astronauts from China, Japan, USA, Spain and Russia have descended into the caves of Sardinia, Italy, to explore the depths and train for life in outer space. One of the ... more .. Quantum technologies to revolutionize 21st century Is quantum technology the future of the 21st century? On the occasion of the 66th Lindau Nobel Laureate Meeting, this is the key question to be explored today in a panel discussion with the Nobel La ... more .. Blue Origin has fourth successful rocket booster landing US space firm Blue Origin conducted a successful fourth test Sunday of its reusable New Shepard rocket, which dropped back to Earth for a flawless upright landing seen on a live webcast. ... more .. TED Talks aim for wider global reach TED Talks, known for "ideas worth spreading," are aiming for a wider global audience with a new mobile application that can be used in two dozen languages. ... more .. Disney brings its brand to Shanghai with new theme park Entertainment giant Disney brings the ultimate American cultural concept to Communist-ruled China on Thursday, opening a massive theme park in Shanghai catering to a rising middle class. ... more .. Tech, beauty intersect in Silicon Valley The beauty industry has long relied on creating a sense of mystery, magic even, around its creams, powders and potions. But now it has something else up its sleeve: high technology. ... more

Read the original:

Space Travel and Exploration

This article is about paying space travellers. For other commercial spacefarers, see Commercial astronaut.

Space tourism is space travel for recreational, leisure or business purposes. A number of startup companies have sprung up in recent years, such as Virgin Galactic and XCOR Aerospace, hoping to create a sub-orbital space tourism industry. Orbital space tourism opportunities have been limited and expensive, with only the Russian Space Agency providing transport to date.

The publicized price for flights brokered by Space Adventures to the International Space Station aboard a Russian Soyuz spacecraft have been US $2040 million, during the period 20012009 when 7 space tourists made 8 space flights. Some space tourists have signed contracts with third parties to conduct certain research activities while in orbit.

Russia halted orbital space tourism in 2010 due to the increase in the International Space Station crew size, using the seats for expedition crews that would have been sold to paying spaceflight participants.[1][2] Orbital tourist flights are planned to resume in 2015.[3]

As an alternative term to "tourism", some organizations such as the Commercial Spaceflight Federation use the term "personal spaceflight". The Citizens in Space project uses the term "citizen space exploration".[4]

As of September 2012[update], multiple companies are offering sales of orbital and suborbital flights, with varying durations and creature comforts.[5]

The Soviet space program was aggressive in broadening the pool of cosmonauts. The Soviet Intercosmos program included cosmonauts selected from Warsaw Pact members (from Czechoslovakia, Poland, East Germany, Bulgaria, Hungary, Romania) and later from allies of the USSR (Cuba, Mongolia, Vietnam) and non-aligned countries (India, Syria, Afghanistan). Most of these cosmonauts received full training for their missions and were treated as equals, but especially after the Mir program began, were generally given shorter flights than Soviet cosmonauts. The European Space Agency (ESA) took advantage of the program as well.

The U.S. space shuttle program included payload specialist positions which were usually filled by representatives of companies or institutions managing a specific payload on that mission. These payload specialists did not receive the same training as professional NASA astronauts and were not employed by NASA. In 1983, Ulf Merbold from ESA and Byron Lichtenberg from MIT (engineer and Air Force fighter pilot) were the first payload specialists to fly on the Space Shuttle, on mission STS-9.[6][7]

In 1984, Charles D. Walker became the first non-government astronaut to fly, with his employer McDonnell Douglas paying $40,000 for his flight.[8]:7475 NASA was also eager to prove its capability to Congressional sponsors. Senator Jake Garn was flown on the Shuttle in 1985,[9] followed by Representative Bill Nelson in 1986.[10]

During the 1970s, Shuttle prime contractor Rockwell International studied a $200300 million removable cabin that could fit into the Shuttle's cargo bay. The cabin could carry up to 74 passengers into orbit for up to three days. Space Habitation Design Associates proposed, in 1983, a cabin for 72 passengers in the bay. Passengers were located in six sections, each with windows and its own loading ramp, and with seats in different configurations for launch and landing. Another proposal was based on the Spacelab habitation modules, which provided 32 seats in the payload bay in addition to those in the cockpit area. A 1985 presentation to the National Space Society stated that although flying tourists in the cabin would cost $1 to 1.5 million per passenger without government subsidy, within 15 years 30,000 people a year would pay $25,000 each to fly in space on new spacecraft. The presentation also forecast flights to lunar orbit within 30 years and visits to the lunar surface within 50 years.[11]

As the shuttle program expanded in the early 1980s, NASA began a Space Flight Participant program to allow citizens without scientific or governmental roles to fly. Christa McAuliffe was chosen as the first Teacher in Space in July 1985 from 11,400 applicants. 1,700 applied for the Journalist in Space program, including Walter Cronkite, Tom Brokaw, Tom Wolfe, and Sam Donaldson. An Artist in Space program was considered, and NASA expected that after McAuliffe's flight two to three civilians a year would fly on the shuttle.[8] After McAuliffe was killed in the Challenger disaster in January 1986 the programs were canceled. McAuliffe's backup, Barbara Morgan, eventually got hired in 1998 as a professional astronaut and flew on STS-118 as a mission specialist.[8]:8485 A second journalist-in-space program, in which NASA green-lighted Miles O'Brien to fly on the space shuttle, was scheduled to be announced in 2003. That program was canceled in the wake of the Columbia disaster on STS-107 and subsequent emphasis on finishing the International Space Station before retiring the space shuttle.

With the realities of the post-Perestroika economy in Russia, its space industry was especially starved for cash. The Tokyo Broadcasting System (TBS) offered to pay for one of its reporters to fly on a mission. For $28 million, Toyohiro Akiyama was flown in 1990 to Mir with the eighth crew and returned a week later with the seventh crew. Akiyama gave a daily TV broadcast from orbit and also performed scientific experiments for Russian and Japanese companies. However, since the cost of the flight was paid by his employer, Akiyama could be considered a business traveler rather than a tourist.

In 1991, British chemist Helen Sharman was selected from a pool of 13,000 applicants to be the first Briton in space.[12] The program was known as Project Juno and was a cooperative arrangement between the Soviet Union and a group of British companies. The Project Juno consortium failed to raise the funds required, and the program was almost cancelled. Reportedly Mikhail Gorbachev ordered it to proceed under Soviet expense in the interests of international relations, but in the absence of Western underwriting, less expensive experiments were substituted for those in the original plans. Sharman flew aboard Soyuz TM-12 to Mir and returned aboard Soyuz TM-11.

At the end of the 1990s, MirCorp, a private venture that was by then in charge of the space station, began seeking potential space tourists to visit Mir in order to offset some of its maintenance costs. Dennis Tito, an American businessman and former JPL scientist, became their first candidate. When the decision to de-orbit Mir was made, Tito managed to switch his trip to the International Space Station (ISS) through a deal between MirCorp and U.S.-based Space Adventures, Ltd., despite strong opposition from senior figures at NASA; from the beginning of the ISS expeditions, NASA stated it wasn't interested in space guests.[13] Nonetheless, Dennis Tito visited the ISS on April 28, 2001, and stayed for seven days, becoming the first "fee-paying" space tourist. He was followed in 2002 by South African computer millionaire Mark Shuttleworth. The third was Gregory Olsen in 2005, who was trained as a scientist and whose company produced specialist high-sensitivity cameras. Olsen planned to use his time on the ISS to conduct a number of experiments, in part to test his company's products. Olsen had planned an earlier flight, but had to cancel for health reasons. The Subcommittee on Space and Aeronautics Committee On Science of the House of Representatives held on June 26, 2001 reveals the shifting attitude of NASA towards paying space tourists wanting to travel to the ISS. The hearing's purpose was to, "Review the issues and opportunities for flying nonprofessional astronauts in space, the appropriate government role for supporting the nascent space tourism industry, use of the Shuttle and Space Station for Tourism, safety and training criteria for space tourists, and the potential commercial market for space tourism".[14] The subcommittee report was interested in evaluating Dennis Tito's extensive training and his experience in space as a nonprofessional astronaut.

By 2007, space tourism was thought to be one of the earliest markets that would emerge for commercial spaceflight.[15]:11 However, as of 2014[update] this private exchange market has not emerged to any significant extent.

Space Adventures remains the only company to have sent paying passengers to space.[16][17] In conjunction with the Federal Space Agency of the Russian Federation and Rocket and Space Corporation Energia, Space Adventures facilitated the flights for all of the world's first private space explorers. The first three participants paid in excess of $20 million (USD) each for their 10-day visit to the ISS.

After the Columbia disaster, space tourism on the Russian Soyuz program was temporarily put on hold, because Soyuz vehicles became the only available transport to the ISS. On July 26, 2005, Space Shuttle Discovery (mission STS-114) marked the shuttle's return to space. Consequently, in 2006, space tourism was resumed. On September 18, 2006, an Iranian American named Anousheh Ansari became the fourth space tourist (Soyuz TMA-9).[18]) On April 7, 2007, Charles Simonyi, an American businessman of Hungarian descent, joined their ranks (Soyuz TMA-10). Simonyi became the first repeat space tourist, paying again to fly on Soyuz TMA-14 in MarchApril 2009. Canadian Guy Lalibert became the next space tourist in September, 2009 aboard Soyuz TMA-16.

As reported by Reuters on March 3, 2010, Russia announced that the country would double the number of launches of three-man Soyuz ships to four that year, because "permanent crews of professional astronauts aboard the expanded [ISS] station are set to rise to six"; regarding space tourism, the head of the Russian Cosmonauts' Training Center said "for some time there will be a break in these journeys".[1]

On January 12, 2011, Space Adventures and the Russian Federal Space Agency announced that orbital space tourism would resume in 2013 with the increase of manned Soyuz launches to the ISS from four to five per year.[19] However, this has not materialized, and the current preferred option, instead of producing an additional Soyuz, would be to extend the duration of an ISS Expedition to one year, paving the way for the flight of new spaceflight participants. The British singer Sarah Brightman initiated plans (costing a reported $52 million) and participated in preliminary training in early 2015, expecting to then fly (and to perform while in orbit) in September 2015, but in May 2015 she postponed the plans indefinitely.[3][20][21]

Several plans have been proposed for using a space station as a hotel:

No suborbital space tourism has occurred yet, but since it is projected to be more affordable, many companies view it as a money-making proposition. Most are proposing vehicles that make suborbital flights peaking at an altitude of 100160km (6299mi).[38] Passengers would experience three to six minutes of weightlessness, a view of a twinkle-free starfield, and a vista of the curved Earth below. Projected costs are expected to be about $200,000 per passenger.[39]

Under the Outer Space Treaty signed in 1967, the launch operator's nationality and the launch site's location determine which country is responsible for any damages occurred from a launch.[53]

After valuable resources were detected on the Moon, private companies began to formulate methods to extract the resources. Article II of the Outer Space Treaty dictates that "outer space, including the Moon and other celestial bodies, is not subject to national appropriation by claim of sovereignty, by means of use or occupation, or by any other means".[54] However, countries have the right to freely explore the Moon and any resources collected are property of that country when they return.

In December 2005, the U.S. Government released a set of proposed rules for space tourism.[55] These included screening procedures and training for emergency situations, but not health requirements.

Under current US law, any company proposing to launch paying passengers from American soil on a suborbital rocket must receive a license from the Federal Aviation Administration's Office of Commercial Space Transportation (FAA/AST). The licensing process focuses on public safety and safety of property, and the details can be found in the Code of Federal Regulations, Title 14, Chapter III.[56] This is in accordance with the Commercial Space Launch Amendments Act passed by Congress in 2004.[57]

In March 2010, the New Mexico legislature passed the Spaceflight Informed Consent Act. The SICA gives legal protection to companies who provide private space flights in the case of accidental harm or death to individuals. Participants sign an Informed Consent waiver, dictating that spaceflight operators can not be held liable in the "death of a participant resulting from the inherent risks of space flight activities". Operators are however not covered in the case of gross negligence or willful misconduct.[58]

A 2010 study published in Geophysical Research Letters raised concerns that the growing commercial spaceflight industry could accelerate global warming. The study, funded by NASA and The Aerospace Corporation, simulated the impact of 1,000 suborbital launches of hybrid rockets from a single location, calculating that this would release a total of 600 tonnes of black carbon into the stratosphere. They found that the resultant layer of soot particles remained relatively localised, with only 20% of the carbon straying into the southern hemisphere, thus creating a strong hemispherical asymmetry.[59] This unbalance would cause the temperature to decrease by about 0.4C (0.72F) in the tropics and subtropics, whereas the temperature at the poles would increase by between 0.2 and 1C (0.36 and 1.80F). The ozone layer would also be affected, with the tropics losing up to 1.7% of ozone cover, and the polar regions gaining 56%.[60] The researchers stressed that these results should not be taken as "a precise forecast of the climate response to a specific launch rate of a specific rocket type", but as a demonstration of the sensitivity of the atmosphere to the large-scale disruption that commercial space tourism could bring.[59]

Several organizations have been formed to promote the space tourism industry, including the Space Tourism Society, Space Future, and HobbySpace. UniGalactic Space Travel Magazine is a bi-monthly educational publication covering space tourism and space exploration developments in companies like SpaceX, Orbital Sciences, Virgin Galactic and organizations like NASA.

Classes in space tourism are currently taught at the Rochester Institute of Technology in New York,[61] and Keio University in Japan.[62]

A web-based survey suggested that over 70% of those surveyed wanted less than or equal to 2 weeks in space; in addition, 88% wanted to spacewalk (only 14% of these would do it for a 50% premium), and 21% wanted a hotel or space station.[63]

The concept has met with some criticism from some, including politicians, notably Gnter Verheugen, vice-president of the European Commission, who said of the EADS Astrium Space Tourism Project: "It's only for the super rich, which is against my social convictions".[64]

As of October 2013, NBC News and Virgin Galactic have come together to create a new reality television show titled Space Race. The show "will follow contestants as they compete to win a flight into space aboard Virgin Galactic's SpaceShipTwo rocket plane. It is not to be confused with the Children's Space TV show called "Space Racers""[65]

Many private space travelers have objected to the term "space tourist", often pointing out that their role went beyond that of an observer, since they also carried out scientific experiments in the course of their journey. Richard Garriott additionally emphasized that his training was identical to the requirements of non-Russian Soyuz crew members, and that teachers and other non-professional astronauts chosen to fly with NASA are called astronauts. He has said that if the distinction has to be made, he would rather be called "private astronaut" than "tourist".[66] Dennis Tito has asked to be known as an "independent researcher",[citation needed] and Mark Shuttleworth described himself as a "pioneer of commercial space travel".[67] Gregory Olsen prefers "private researcher",[68] and Anousheh Ansari prefers the term "private space explorer".[18] Other space enthusiasts object to the term on similar grounds. Rick Tumlinson of the Space Frontier Foundation, for example, has said: "I hate the word tourist, and I always will ... 'Tourist' is somebody in a flowered shirt with three cameras around his neck."[69] Russian cosmonaut Maksim Surayev told the press in 2009 not to describe Guy Lalibert as a tourist: "It's become fashionable to speak of space tourists. He is not a tourist but a participant in the mission."[70]

"Spaceflight participant" is the official term used by NASA and the Russian Federal Space Agency to distinguish between private space travelers and career astronauts. Tito, Shuttleworth, Olsen, Ansari, and Simonyi were designated as such during their respective space flights. NASA also lists Christa McAuliffe as a spaceflight participant (although she did not pay a fee), apparently due to her non-technical duties aboard the STS-51-L flight.

The U.S. Federal Aviation Administration awards the title of "Commercial Astronaut" to trained crew members of privately funded spacecraft. The only people currently holding this title are Mike Melvill and Brian Binnie, the pilots of SpaceShipOne.

A 2010 report from the Federal Aviation Administration, titled "The Economic Impact of Commercial Space Transportation on the U. S Economy in 2009", cites studies done by Futron, an aerospace and technology-consulting firm, which predict that space tourism could become a billion-dollar market within 20 years.[71] In addition, in the decade since Dennis Tito journeyed to the International Space Station, eight private citizens have paid the $20 million fee to travel to space. Space Adventures suggests that this number could increase fifteen-fold by 2020.[72] These figures do not include other private space agencies such as Virgin Galactic, which as of 2014 has sold approximately 700 tickets priced at $200,000 or $250,000 dollars each and has accepted more than $80 million in deposits.[73]

Read more:

Space tourism - Wikipedia, the free encyclopedia

Time travel is the concept of movement (such as by a human) between certain points in time, analogous to movement between different points in space, typically using a hypothetical device known as a time machine, in the form of a vehicle or of a portal connecting distant points in time. Time travel is a recognized concept in philosophy and fiction, but traveling to an arbitrary point in time has a very limited support in theoretical physics, and usually only in conjunction with quantum mechanics or EinsteinRosen bridges. In a more narrow sense, one-way time travel into the future via time dilation is a proven phenomenon in relativistic physics, but traveling any significant "distance" requires motion at speeds close to the speed of light, which is not feasible for human travel with current technology.[1] The concept was touched upon in various earlier works of fiction, but was popularized by H. G. Wells' 1895 novel The Time Machine, which moved the concept of time travel into the public imagination, and it remains a popular subject in science fiction.

Some ancient myths depict moving forward in time. In Hindu mythology, the Mahabharata mentions the story of King Raivata Kakudmi, who travels to heaven to meet the creator Brahma and is shocked to learn when he returns to Earth that many ages have passed.[2][3]

The Buddhist Pli Canon mentions the relativity of time. In the Payasi Sutta, one of the Buddha's chief disciples, Kumara Kassapa, explains to the skeptic Payasi that, "In the Heaven of the Thirty Three Devas, time passes at a different pace, and people live much longer. "In the period of our century; one hundred years, only a single day; twenty four hours would have passed for them."[4]

In the Japanese tale of "Urashima Tar",[5] first described in the Nihongi (720).,[6] a young fisherman named Urashima Taro visits an undersea palace. After three days, he returns home to his village and finds himself 300 years in the future, where he has been forgotten, his house is ruins, and his family has died.

In the Talmud, Honi ha-M'agel sleeps for 70 years and awakes to find his grandchildren have become grandparents, and his family and friends have died.[7]

In the utopian novel Louis-Sbastien Mercier's L'An 2440, rve s'il en ft jamais ("The Year 2440: A Dream If Ever There Were One"), the protagonist is transported to the year 2440. A popular work, having gone through twenty-five editions since its appearance in 1771, it describes the adventures of an unnamed man who discusses with a philosopher friend the injustices of Paris, then falls asleep and finds himself in a future Paris.

Washington Irving's "Rip Van Winkle" (1819) depicts a man who takes a twenty-year nap on a mountain, waking up in a future where he has been forgotten, his wife has died, and his daughter has grown.[5] Sleep is also used as a means of time travel in H.G. Wells's The Sleeper Awakes, in which a man wakes up after a two-hundred year hibernation.

Like forward time travel, backward time travel has an uncertain origin. Samuel Madden's Memoirs of the Twentieth Century (1733) is a series of letters from British ambassadors in 1997 and 1998 to diplomats in the past, conveying the political and religious conditions of the future.[8] Because the narrator receives these letters from his guardian angel, Paul Alkon suggests in his book Origins of Futuristic Fiction that "the first time-traveler in English literature is a guardian angel.".[9] Madden does not explain how the angel obtains these documents, but Alkon asserts that Madden "deserves recognition as the first to toy with the rich idea of time-travel in the form of an artifact sent backward from the future to be discovered in the present."[8]

In 1836 Alexander Veltman published Predki Kalimerosa: Aleksandr Filippovich Makedonskii (The Forebears of Kalimeros: Alexander, son of Philip of Macedon), which has been called the first original Russian science fiction novel and the first novel to use time travel.[10] The narrator rides to ancient Greece on a hippogriff, meets Aristotle, and goes on a voyage with Alexander the Great before returning to the 19th century.

In the science fiction anthology Far Boundaries (1951), editor August Derleth claims that an early short story about time travel is "Missing One's Coach: An Anachronism", written for the Dublin Literary Magazine[11] by an anonymous author in 1838.[12] While the narrator waits under a tree for a coach to take him out of Newcastle, he is transported back in time over a thousand years. He encounters the Venerable Bede in a monastery and explains to him the developments of the coming centuries. However, the story never makes it clear whether these events are real or a dream.[13]

Some consider Charles Dickens's A Christmas Carol (1843)[14] to be one of the first depictions of time travel in both directions, as the protagonist, Ebenezer Scrooge, is transported to Christmases past and future. However, these might be interpreted as visions rather than as time travel because Scrooge experiences the time periods as an observer rather than as a participant.

A clearer example of backward time travel is found in the popular 1861 book Paris avant les hommes (Paris before Men) by the French botanist and geologist Pierre Boitard, published posthumously. In this story, the protagonist is transported to the prehistoric past by the magic of a "lame demon" (a French pun on Boitard's name), where he encounters a Plesiosaur and an apelike ancestor and is able to interact with ancient creatures.[15]

Edward Everett Hale's "Hands Off" (1881) tells the story of an unnamed being, possibly the soul of a person who has recently died, who interferes with ancient Egyptian history by preventing Joseph's enslavement. This may have been the first story to feature an alternate history created as a result of time travel.[16]

One of the first stories to feature time travel by means of a machine is "The Clock that Went Backward" by Edward Page Mitchell,[17] which appeared in the New York Sun in 1881. However, the mechanism borders on fantasy. An unusual clock, when wound, runs backwards and transports people nearby back in time. But the author fails to explain the origin of either the clock or its abilities.[18]

Enrique Gaspar y Rimbau's El Anacronpete (1887)[19] may have been the first story to feature a vessel engineered to travel through time.[20]Andrew Sawyer has commented that the story "does seem to be the first literary description of a time machine noted so far", adding that "Edward Page Mitchell's story 'The Clock That Went Backward' (1881) is usually described as the first time-machine story, but I'm not sure that a clock quite counts."[21]H. G. Wells's The Time Machine (1895) popularized the concept of time travel by mechanical means.[22]

Some theories, most notably special and general relativity, suggest that suitable geometries of spacetime or specific types of motion in space might allow time travel into the past and future if these geometries or motions were possible.[23] In technical papers, physicists generally avoid the commonplace language of "moving" or "traveling" through time. "Movement" normally refers only to a change in spatial position as the time coordinate is varied. Instead they discuss the possibility of closed timelike curves, which are world lines that form closed loops in spacetime, allowing objects to return to their own past. There are known to be solutions to the equations of general relativity that describe spacetimes which contain closed timelike curves, such as Gdel spacetime, but the physical plausibility of these solutions is uncertain.

Relativity predicts that if one were to move away from the Earth at relativistic velocities and return, more time would have passed on Earth than for the traveler, so in this sense it is accepted that relativity allows "travel into the future." According to relativity there is no single objective answer to how much time has really passed between the departure and the return, but there is an objective answer to how much proper time has been experienced by both the Earth and the traveler, i.e., how much each has aged (see twin paradox). On the other hand, many in the scientific community believe that backward time travel is highly unlikely. Any theory that would allow time travel would introduce potential problems of causality. The classic example of a problem involving causality is the "grandfather paradox": what if one were to go back in time and kill one's own grandfather before one's father was conceived? But some scientists believe that paradoxes can be avoided, by appealing either to the Novikov self-consistency principle or to the notion of branching parallel universes.

Stephen Hawking has suggested that the absence of tourists from the future is an argument against the existence of time travel. This is a variant of the Fermi paradox. Of course, this would not prove that time travel is physically impossible, since it might be that time travel is physically possible but that it is never developed or is cautiously never used; and even if it were developed, Hawking notes elsewhere that time travel might only be possible in a region of spacetime that is warped in the correct way, and that if we cannot create such a region until the future, then time travelers would not be able to travel back before that date, so "[t]his picture would explain why" the world hasn't already been overrun by "tourists from the future."[24] This simply means that, until a time machine were actually to be invented, we would not be able to see time travelers. Carl Sagan also once suggested the possibility that time travelers could be here but are disguising their existence, or are not recognized as time travelers.[25]

The theory of general relativity does suggest a scientific basis for the possibility of backward time travel in certain unusual scenarios, although arguments from semiclassical gravity suggest that when quantum effects are incorporated into general relativity, these loopholes may be closed.[26] These semiclassical arguments led Hawking to formulate the chronology protection conjecture, suggesting that the fundamental laws of nature prevent time travel,[27] but physicists cannot come to a definite judgment on the issue without a theory of quantum gravity to join quantum mechanics and general relativity into a completely unified theory.[25][28]:150

Time travel to the past is theoretically allowed using the following methods:[29]

According to the theory of relativity, a signal or matter moving faster than light from one point to another would appear in some inertial frame of reference as moving backwards in time. This is a consequence of the relativity of simultaneity in special relativity, which says that in some cases different reference frames will disagree on whether two events at different locations happened "at the same time" or not, and they can also disagree on the order of the two events. Technically, these disagreements occur when the spacetime interval between the events is 'space-like', meaning that neither event lies in the future light cone of the other.[30] If one of the two events represents the sending of a signal from one location and the second event represents the reception of the same signal at another location, then as long as the signal is moving at the speed of light or slower, the mathematics of simultaneity ensures that all reference frames agree that the transmission-event happened before the reception-event.[30]

However, in the case of a hypothetical signal moving faster than light, there would always be some frames in which the signal was received before it was sent, so that the signal could be said to have moved backward in time. And since one of the two fundamental postulates of special relativity says that the laws of physics should work the same way in every inertial frame, then if it is possible for signals to move backward in time in any one frame, it must be possible in all frames. This means that if observer A sends a signal to observer B which moves FTL (faster than light) in A's frame but backward in time in B's frame, and then B sends a reply which moves FTL in B's frame but backward in time in A's frame, it could work out that A receives the reply before sending the original signal, a clear violation of causality in every frame. An illustration of such a scenario using spacetime diagrams can be found here.[31] The scenario is sometimes referred to as a tachyonic antitelephone.

According to special relativity, it would take an infinite amount of energy to accelerate a slower-than-light object to the speed of light. Although relativity does not forbid the theoretical possibility of tachyons which move faster than light at all times, when analyzed using quantum field theory, it seems that it would not actually be possible to use them to transmit information faster than light.[32] There is also no widely agreed-upon evidence for the existence of tachyons; the faster-than-light neutrino anomaly had opened the possibility that neutrinos might be tachyons, but the results of the experiment were found to be invalid upon further analysis.

The general theory of relativity extends the special theory to cover gravity, illustrating it in terms of curvature in spacetime caused by mass-energy and the flow of momentum. General relativity describes the universe under a system of field equations, and there exist solutions to these equations that permit what are called "closed time-like curves", and hence time travel into the past.[23] The first of these was proposed by Kurt Gdel, a solution known as the Gdel metric, but his (and many others') example requires the universe to have physical characteristics that it does not appear to have.[23] Whether general relativity forbids closed time-like curves for all realistic conditions is unknown.

Wormholes are a hypothetical warped spacetime which are also permitted by the Einstein field equations of general relativity,[33] although it would not be possible to travel through a wormhole unless it were what is known as a traversable wormhole.

A proposed time-travel machine using a traversable wormhole would (hypothetically) work in the following way: One end of the wormhole is accelerated to some significant fraction of the speed of light, perhaps with some advanced propulsion system, and then brought back to the point of origin. Alternatively, another way is to take one entrance of the wormhole and move it to within the gravitational field of an object that has higher gravity than the other entrance, and then return it to a position near the other entrance. For both of these methods, time dilation causes the end of the wormhole that has been moved to have aged less than the stationary end, as seen by an external observer; however, time connects differently through the wormhole than outside it, so that synchronized clocks at either end of the wormhole will always remain synchronized as seen by an observer passing through the wormhole, no matter how the two ends move around.[34] This means that an observer entering the accelerated end would exit the stationary end when the stationary end was the same age that the accelerated end had been at the moment before entry; for example, if prior to entering the wormhole the observer noted that a clock at the accelerated end read a date of 2007 while a clock at the stationary end read 2012, then the observer would exit the stationary end when its clock also read 2007, a trip backward in time as seen by other observers outside. One significant limitation of such a time machine is that it is only possible to go as far back in time as the initial creation of the machine;[35] in essence, it is more of a path through time than it is a device that itself moves through time, and it would not allow the technology itself to be moved backward in time.

According to current theories on the nature of wormholes, construction of a traversable wormhole would require the existence of a substance with negative energy (often referred to as "exotic matter"). More technically, the wormhole spacetime requires a distribution of energy that violates various energy conditions, such as the null energy condition along with the weak, strong, and dominant energy conditions.[36] However, it is known that quantum effects can lead to small measurable violations of the null energy condition,[36] and many physicists believe that the required negative energy may actually be possible due to the Casimir effect in quantum physics.[37] Although early calculations suggested a very large amount of negative energy would be required, later calculations showed that the amount of negative energy can be made arbitrarily small.[38]

In 1993, Matt Visser argued that the two mouths of a wormhole with such an induced clock difference could not be brought together without inducing quantum field and gravitational effects that would either make the wormhole collapse or the two mouths repel each other.[39] Because of this, the two mouths could not be brought close enough for causality violation to take place. However, in a 1997 paper, Visser hypothesized that a complex "Roman ring" (named after Tom Roman) configuration of an N number of wormholes arranged in a symmetric polygon could still act as a time machine, although he concludes that this is more likely a flaw in classical quantum gravity theory rather than proof that causality violation is possible.[40]

Another approach involves a dense spinning cylinder usually referred to as a Tipler cylinder, a GR solution discovered by Willem Jacob van Stockum[41] in 1936 and Kornel Lanczos[42] in 1924, but not recognized as allowing closed timelike curves[43] until an analysis by Frank Tipler[44] in 1974. If a cylinder is infinitely long and spins fast enough about its long axis, then a spaceship flying around the cylinder on a spiral path could travel back in time (or forward, depending on the direction of its spiral). However, the density and speed required is so great that ordinary matter is not strong enough to construct it. A similar device might be built from a cosmic string, but none are known to exist, and it does not seem to be possible to create a new cosmic string.

Physicist Robert Forward noted that a nave application of general relativity to quantum mechanics suggests another way to build a time machine. A heavy atomic nucleus in a strong magnetic field would elongate into a cylinder, whose density and "spin" are enough to build a time machine. Gamma rays projected at it might allow information (not matter) to be sent back in time; however, he pointed out that until we have a single theory combining relativity and quantum mechanics, we will have no idea whether such speculations are nonsense.[citation needed]

A more fundamental objection to time travel schemes based on rotating cylinders or cosmic strings has been put forward by Stephen Hawking, who proved a theorem showing that according to general relativity it is impossible to build a time machine of a special type (a "time machine with the compactly generated Cauchy horizon") in a region where the weak energy condition is satisfied, meaning that the region contains no matter with negative energy density (exotic matter). Solutions such as Tipler's assume cylinders of infinite length, which are easier to analyze mathematically, and although Tipler suggested that a finite cylinder might produce closed timelike curves if the rotation rate were fast enough,[45] he did not prove this. But Hawking points out that because of his theorem, "it can't be done with positive energy density everywhere! I can prove that to build a finite time machine, you need negative energy."[28]:96 This result comes from Hawking's 1992 paper on the chronology protection conjecture, where he examines "the case that the causality violations appear in a finite region of spacetime without curvature singularities" and proves that "[t]here will be a Cauchy horizon that is compactly generated and that in general contains one or more closed null geodesics which will be incomplete. One can define geometrical quantities that measure the Lorentz boost and area increase on going round these closed null geodesics. If the causality violation developed from a noncompact initial surface, the averaged weak energy condition must be violated on the Cauchy horizon."[46] However, this theorem does not rule out the possibility of time travel (1) by means of time machines with the non-compactly generated Cauchy horizons (such as the Deutsch-Politzer time machine) and (2) in regions which contain exotic matter (which would be necessary for traversable wormholes or the Alcubierre drive). Because the theorem is based on general relativity, it is also conceivable a future theory of quantum gravity which replaced general relativity would allow time travel even without exotic matter (though it is also possible such a theory would place even more restrictions on time travel, or rule it out completely as postulated by Hawking's chronology protection conjecture).[citation needed]

Certain experiments carried out give the impression of reversed causality but are subject to interpretation. For example, in the delayed choice quantum eraser experiment performed by Marlan Scully, pairs of entangled photons are divided into "signal photons" and "idler photons", with the signal photons emerging from one of two locations and their position later measured as in the double-slit experiment, and depending on how the idler photon is measured, the experimenter can either learn which of the two locations the signal photon emerged from or "erase" that information. Even though the signal photons can be measured before the choice has been made about the idler photons, the choice seems to retroactively determine whether or not an interference pattern is observed when one correlates measurements of idler photons to the corresponding signal photons. However, since interference can only be observed after the idler photons are measured and they are correlated with the signal photons, there is no way for experimenters to tell what choice will be made in advance just by looking at the signal photons, and under most interpretations of quantum mechanics the results can be explained in a way that does not violate causality.[citation needed]

The experiment of Lijun Wang might also show causality violation since it made it possible to send packages of waves through a bulb of caesium gas in such a way that the package appeared to exit the bulb 62 nanoseconds before its entry. But a wave package is not a single well-defined object but rather a sum of multiple waves of different frequencies (see Fourier analysis), and the package can appear to move faster than light or even backward in time even if none of the pure waves in the sum do so. This effect cannot be used to send any matter, energy, or information faster than light,[47] so this experiment is understood not to violate causality either.

The physicists Gnter Nimtz and Alfons Stahlhofen, of the University of Koblenz, claim to have violated Einstein's theory of relativity by transmitting photons faster than the speed of light. They say they have conducted an experiment in which microwave photons traveled "instantaneously" between a pair of prisms that had been moved up to 3ft (0.91m) apart, using a phenomenon known as quantum tunneling. Nimtz told New Scientist magazine: "For the time being, this is the only violation of special relativity that I know of." However, other physicists say that this phenomenon does not allow information to be transmitted faster than light. Aephraim Steinberg, a quantum optics expert at the University of Toronto, Canada, uses the analogy of a train traveling from Chicago to New York, but dropping off train cars at each station along the way, so that the center of the train moves forward at each stop; in this way, the speed of the center of the train exceeds the speed of any of the individual cars.[48]

Some physicists have performed experiments that attempted to show causality violations, but so far without success. The "Space-time Twisting by Light" (STL) experiment run by physicist Ronald Mallett attempts to observe a violation of causality when a neutron is passed through a circle made up of a laser whose path has been twisted by passing it through a photonic crystal. Mallett has some physical arguments that suggest that closed timelike curves would become possible through the center of a laser that has been twisted into a loop. However, other physicists dispute his arguments (see objections).

Shengwang Du claims in a peer-reviewed journal to have observed single photons' precursors, saying that they travel no faster than c in a vacuum. His experiment involved slow light as well as passing light through a vacuum. He generated two single photons, passing one through rubidium atoms that had been cooled with a laser (thus slowing the light) and passing one through a vacuum. Both times, apparently, the precursors preceded the photons' main bodies, and the precursor traveled at c in a vacuum. According to Du, this implies that there is no possibility of light traveling faster than c (and, thus, violating causality).[49] Some members of the media took this as an indication of proof that time travel to the past using superluminal speeds was impossible.[50][51]

Several experiments have been carried out to try to entice future humans, who might invent time travel technology, to come back and demonstrate it to people of the present time. Events such as Perth's Destination Day (2005) or MIT's Time Traveler Convention heavily publicized permanent "advertisements" of a meeting time and place for future time travelers to meet. Back in 1982, a group in Baltimore, Maryland, identifying itself as the Krononauts, hosted an event of this type welcoming visitors from the future.[52][53][54] These experiments only stood the possibility of generating a positive result demonstrating the existence of time travel, but have failed so farno time travelers are known to have attended either event. It is hypothetically possible that future humans have traveled back in time, but have traveled back to the meeting time and place in a parallel universe.[55]

Another factor is that for all the time travel devices considered under current physics (such as those that operate using wormholes), it is impossible to travel back to before the time machine was actually made.[56][57]

There are various ways in which a person could "travel into the future" in a limited sense: the person could set things up so that in a small amount of their own subjective time, a large amount of subjective time has passed for other people on Earth. For example, an observer might take a trip away from the Earth and back at relativistic velocities, with the trip only lasting a few years according to the observer's own clocks, and return to find that thousands of years had passed on Earth. According to relativity, there would be no objective answer to the question of how much time "really" passed during the trip; it would be equally valid to say that the trip had lasted only a few years or that the trip had lasted thousands of years, depending on the choice of reference frame.

This form of "travel into the future" is theoretically allowed (and has been demonstrated at very small time scales) using the following methods:[29]

Time dilation is permitted by Albert Einstein's special and general theories of relativity. These theories state that, relative to a given observer, time passes more slowly for bodies moving quickly relative to that observer, or bodies that are deeper within a gravity well.[59] For example, a clock which is moving relative to the observer will be measured to run slow in that observer's rest frame; as a clock approaches the speed of light it will almost slow to a stop, although it can never quite reach light speed so it will never completely stop. For two clocks moving inertially (not accelerating) relative to one another, this effect is reciprocal, with each clock measuring the other to be ticking slower. However, the symmetry is broken if one clock accelerates, as in the twin paradox where one twin stays on Earth while the other travels into space, turns around (which involves acceleration), and returnsin this case both agree the traveling twin has aged less. General relativity states that time dilation effects also occur if one clock is deeper in a gravity well than the other, with the clock deeper in the well ticking more slowly; this effect must be taken into account when calibrating the clocks on the satellites of the Global Positioning System, and it could lead to significant differences in rates of aging for observers at different distances from a black hole.

It has been calculated that, under general relativity, a person could travel forward in time at a rate four times that of distant observers by residing inside a spherical shell with a diameter of 5 meters and the mass of Jupiter.[60] For such a person, every one second of their "personal" time would correspond to four seconds for distant observers. Of course, squeezing the mass of a large planet into such a structure is not expected to be within our technological capabilities in the near future.

There is a great deal of experimental evidence supporting the validity of equations for velocity-based time dilation in special relativity[61] and gravitational time dilation in general relativity.[62][63][64] A famous and easy-to-replicate example is the observation of atmospheric muon decay.[65][66] With current technologies it is only possible to cause a human traveler to age less than companions on Earth by a very small fraction of a second, the current record being about 20 milliseconds for the cosmonaut Sergei Avdeyev. A researcher from the University of Connecticut is attempting to use lasers to warp or loop spacetime.[67]

Time perception can be apparently sped up for living organisms through hibernation, where the body temperature and metabolic rate of the creature is reduced. A more extreme version of this is suspended animation, where the rates of chemical processes in the subject would be severely reduced.

Time dilation and suspended animation only allow "travel" to the future, never the past, so they do not violate causality, and it is debatable whether they should be called time travel. However time dilation can be viewed as a better fit for our understanding of the term "time travel" than suspended animation, since with time dilation less time actually does pass for the traveler than for those who remain behind, so the traveler can be said to have reached the future faster than others, whereas with suspended animation this is not the case.

Parallel universes might provide a way out of paradoxes. Everett's many-worlds interpretation (MWI) of quantum mechanics suggests that all possible quantum events can occur in mutually exclusive histories.[68] These alternate, or parallel, histories would form a branching tree symbolizing all possible outcomes of any interaction. If all possibilities exist, any paradoxes could be explained by having the paradoxical events happening in a different universe. This concept is most often used in science-fiction, but some physicists such as David Deutsch have suggested that if time travel is possible and the MWI is correct, then a time traveler should indeed end up in a different history than the one he started from.[69][70][71] On the other hand, Stephen Hawking has argued that even if the MWI is correct, we should expect each time traveler to experience a single self-consistent history, so that time travelers remain within their own world rather than traveling to a different one.[24] The physicist Allen Everett argued that Deutsch's approach "involves modifying fundamental principles of quantum mechanics; it certainly goes beyond simply adopting the MWI". Everett also argues that even if Deutsch's approach is correct, it would imply that any macroscopic object composed of multiple particles would be split apart when traveling back in time through a wormhole, with different particles emerging in different worlds.[72]

Daniel Greenberger and Karl Svozil proposed that quantum theory gives a model for time travel without paradoxes.[73][74] The quantum theory observation causes possible states to 'collapse' into one measured state; hence, the past observed from the present is deterministic (it has only one possible state), but the present observed from the past has many possible states until our actions cause it to collapse into one state. Our actions will then be seen to have been inevitable.

Quantum-mechanical phenomena such as quantum teleportation, the EPR paradox, or quantum entanglement might appear to create a mechanism that allows for faster-than-light (FTL) communication or time travel, and in fact some interpretations of quantum mechanics such as the Bohm interpretation presume that some information is being exchanged between particles instantaneously in order to maintain correlations between particles.[75] This effect was referred to as "spooky action at a distance" by Einstein.

Nevertheless, the fact that causality is preserved in quantum mechanics is a rigorous result in modern quantum field theories, and therefore modern theories do not allow for time travel or FTL communication. In any specific instance where FTL has been claimed, more detailed analysis has proven that to get a signal, some form of classical communication must also be used.[76] The no-communication theorem also gives a general proof that quantum entanglement cannot be used to transmit information faster than classical signals. The fact that these quantum phenomena apparently do not allow FTL time travel is often overlooked in popular press coverage of quantum teleportation experiments.[citation needed] How the rules of quantum mechanics work to preserve causality is an active area of research.[citation needed]

Theories of time travel are riddled with questions about causality and paradoxes. Compared to other fundamental concepts in modern physics, time is still not understood very well. Philosophers have been theorizing about the nature of time since before the era of the ancient Greek philosophers. Some philosophers and physicists who study the nature of time also study the possibility of time travel and its logical implications. The probability of paradoxes and their possible solutions are often considered.

For more information on the philosophical considerations of time travel, consult the work of David Lewis. For more information on physics-related theories of time travel, consider the work of Kurt Gdel (especially his theorized universe) and Lawrence Sklar.

The relativity of simultaneity in modern physics favors the philosophical view known as eternalism or four-dimensionalism (Sider, 2001), in which physical objects are either temporally extended spacetime worms, or spacetime worm stages, and this view would be favored further by the possibility of time travel (Sider, 2001). Eternalism, also sometimes known as "block universe theory", builds on a standard method of modeling time as a dimension in physics, to give time a similar ontology to that of space (Sider, 2001). This would mean that time is just another dimension, that future events are "already there", and that there is no objective flow of time. This view is disputed by Tim Maudlin in his The Metaphysics Within Physics.

Presentism is a school of philosophy that holds that neither the future nor the past exist, and there are no non-present objects. In this view, time travel is impossible because there is no future or past to travel to. However, some 21st-century presentists have argued that although past and future objects do not exist, there can still be definite truths about past and future events, and thus it is possible that a future truth about a time traveler deciding to travel back to the present date could explain the time traveler's actual appearance in the present.[77][78]

One subject often brought up in philosophical discussion of time is the idea that, if one were able to go back in time, paradoxes could ensue if the time traveler were to change things. The best examples of this are the grandfather paradox and the idea of autoinfanticide. The grandfather paradox is a hypothetical situation in which a time traveler goes back in time and attempts to kill his paternal grandfather at a time before his grandfather met his grandmother. If he did so, then his father never would have been born, and neither would the time traveler himself, in which case the time traveler never would have gone back in time to kill his grandfather. The paradox is sometimes posed with autoinfanticide, where a traveler goes back and attempts to kill himself as an infant. If he were to do so, he never would have grown up to go back in time to kill himself as an infant.

This discussion is important to the philosophy of time travel because philosophers question whether these paradoxes make time travel impossible. Some philosophers answer the paradoxes by arguing that it might be the case that backward time travel could be possible but that it would be impossible to actually change the past in any way,[79] an idea similar to the proposed Novikov self-consistency principle in physics.

The Novikov self-consistency principle, named after Igor Dmitrievich Novikov, states that any actions, taken by a time traveler or by an object that travels back in time, were part of history all along, and therefore it is impossible for the time traveler to "change" history in any way. The time traveler's actions may be the cause of events in their own past though, which leads to the potential for circular causation, sometimes called a predestination paradox,[80] ontological paradox,[81] or bootstap paradox.[81][82] The term bootstap paradox was popularized by Robert A. Heinlein's story "By His Bootstraps".[83] The Novikov self-consistency principle proposes that the local laws of physics in a region of spacetime containing time travelers cannot be any different from the local laws of physics in any other region of spacetime.[84]

The philosopher Kelley L. Ross argues in "Time Travel Paradoxes"[85] that in an ontological paradox scenario involving a physical object, there can be a violation of the second law of thermodynamics. Ross uses Somewhere in Time as an example where Jane Seymour's character gives Christopher Reeve's character a watch she has owned for many years, and when he travels back in time he gives the same watch to Jane Seymour's character 60 years in the past. As Ross states:

The watch is an impossible object. It violates the Second Law of Thermodynamics, the Law of Entropy. If time travel makes that watch possible, then time travel itself is impossible. The watch, indeed, must be absolutely identical to itself in the 19th and 20th centuries, since Reeve carries it with him from the future instantaneously into the past and bestows it on Seymour. The watch, however, cannot be identical to itself, since all the years in which it is in the possession of Seymour and then Reeve it will wear in the normal manner. Its entropy will increase. The watch carried back by Reeve will be more worn than the watch that would have been acquired by Seymour.

On the other hand, the second law of thermodynamics is understood by modern physicists to be a statistical law rather than an absolute one, so spontaneous reversals of entropy or failure to increase in entropy are not impossible, just improbable (see for example the fluctuation theorem). In addition, the second law of thermodynamics only states that entropy should increase in systems which are isolated from interactions with the external world, so Igor Novikov (creator of the Novikov self-consistency principle) has argued that in the case of macroscopic objects like the watch whose worldlines form closed loops, the outside world can expend energy to repair wear/entropy that the object acquires over the course of its history, so that it will be back in its original condition when it closes the loop.[86]

David Lewis's analysis of compossibility and the implications of changing the past is meant to account for the possibilities of time travel in a one-dimensional conception of time without creating logical paradoxes. Consider Lewis example of Tim. Tim hates his grandfather and would like nothing more than to kill him. The only problem for Tim is that his grandfather died years ago. Tim wants so badly to kill his grandfather himself that he constructs a time machine to travel back to 1955 when his grandfather was young and kill him then. Assuming that Tim can travel to a time when his grandfather is still alive, the question must then be raised: can Tim kill his grandfather?

For Lewis, the answer lies within the context of the usage of the word "can". Lewis explains that the word "can" must be viewed against the context of pertinent facts relating to the situation. Suppose that Tim has a rifle, years of rifle training, a straight shot on a clear day and no outside force to restrain Tim's trigger finger. Can Tim shoot his grandfather? Considering these facts, it would appear that Tim can in fact kill his grandfather. In other words, all of the contextual facts are compossible with Tim killing his grandfather. However, when reflecting on the compossibility of a given situation, we must gather the most inclusive set of facts that we are able to.

Consider now the fact that in Tim's universe his grandfather actually died in 1993 and not in 1955. This new fact about Tim's situation reveals that him killing his grandfather is not compossible with the current set of facts. Tim cannot kill his grandfather because his grandfather died in 1993 and not when he was young. Thus, Lewis concludes, the statements "Tim doesnt but can, because he has what it takes", and, "Tim doesnt, and cant, because it is logically impossible to change the past", are not contradictions; they are both true given the relevant set of facts. The usage of the word "can" is equivocal: he "can" and "can not" under different relevant facts.

So what must happen to Tim as he takes aim? Lewis believes that his gun will jam, a bird will fly in the way, or Tim simply slips on a banana peel. Either way, there will be some logical force of the universe that will prevent Tim every time from killing his grandfather.[87]

Time travel themes in science fiction and the media can generally be grouped into three general categories: immutable timeline; mutable timeline; and alternate histories (as in the many-worlds interpretation).[88][89][90][91] Frequently in fiction, timeline is used to refer to all physical events in history, so that in time travel stories where events can be changed, the time traveler is described as creating a new or altered timeline.[92] This usage is distinct from the use of the term timeline to refer to a type of chart that illustrates a particular series of events, and the concept is also distinct from a world line, a term from Einstein's theory of relativity which refers to the entire history of a single object.

An objection that is sometimes raised[by whom?] against the concept of time machines in science fiction is that they ignore the motion of the Earth between the date the time machine departs and the date it returns. The idea that a traveler can go into a machine that sends him or her to 1865 and step out into exactly the same spot on Earth might be said to ignore the issue that Earth is moving through space around the Sun, which is moving in the galaxy, and so on, so that advocates of this argument imagine that "realistically" the time machine should actually reappear in space far away from the Earth's position at that date.[citation needed] However, the theory of relativity rejects the idea of absolute time and space; in relativity there can be no universal truth about the spatial distance between events which occur at different times[93] (such as an event on Earth today and an event on Earth in 1865), and thus no objective truth about which point in space at one time is at the "same position" that the Earth was at another time. In the theory of special relativity, which deals with situations where gravity is negligible, the laws of physics work the same way in every inertial frame of reference and therefore no frame's perspective is physically better than any other frame's, and different frames disagree about whether two events at different times happened at the "same position" or "different positions". In the theory of general relativity, which incorporates the effects of gravity, all coordinate systems are on equal footing because of a feature known as "diffeomorphism invariance".[94]

Read the original post:

Time travel - Wikipedia, the free encyclopedia