Artists concept of the Dawn spacecraft with one of its ion engines firing. Credit: NASA/JPL-Caltech
The future of NASAs Dawn spacecraft, running low on hydrazine fuel and now flying around the dwarf planet Ceres without the help of internal pointing wheels, will be decided in the coming weeks by top space agency managers.
Scientists have not ruled out sending Dawn on a journey across the solar system to another destination, a voyage that counterintuitively might burn less of the crafts remaining hydrazine propellant than if Dawn stayed in orbit around Ceres, where it has resided since March 2015.
Dawns primary mission ended in June 2016, and NASA officials approved a one-year extension that expires June 30. The fate of Dawn after June 30 remains uncertain, but senior managers at NASA Headquarters are expected to soon decide whether the spacecraft should be turned off, continue exploring Ceres, or depart the dwarf planet and perhaps fly by an asteroid.
Officials are expected to consider the financial cost of Dawns operations and the scientific payoff of continuing the mission, either at Ceres or another destination.
We are in the process of assessing with NASA options for a second extended mission, said Carol Raymond, Dawns deputy principal investigator at NASAs Jet Propulsion Laboratory.
Raymond said Tuesday at a meeting of NASAs Small Bodies Assessment Group, a community of asteroid and comet scientists, that one option for Dawns future could be to send the probe away from Ceres to encounter an asteroid.
Otherwise, Dawn could remain at Ceres for further exploration of the previously-unvisited world, a dwarf planet with a diameter matching Texass, and the largest object in the asteroid belt.
The gray landscape of Ceres is scattered with impact craters, some of which contain salt deposits in the form of bright spots that greeted scientists with mystery as Dawn arrived in early 2015.
Dawn also found evidence of an ice-rich later in Ceress crust just below the worlds charcoal-colored surface, and scientists believe Ceres harbored an underground ocean in the past.
The mission also discovered a tenuous, temporary atmosphere containing water vapor around Ceres, and scientists have linked its fluctuations to the intensity of the solar wind.
Ceres was Dawns second destination after the craft orbited the giant asteroid Vesta in 2011 and 2012.
The solar-powered spacecraft, fitted with solar array wings spanning 65 feet (19.7 meters) tip-to-tip, was built by Orbital ATK and launched from Cape Canaveral aboard a United Launch Alliance Delta 2 rocket in September 2007.
The mission has exceeded all of its scientific objectives, and the last year of bonus operations at Ceres included extra imaging of the dwarf planet, and a unique opposition observation in late April that positioned the Dawn spacecraft directly between the sun and Occator Crater.
Scientists hoped the favorable sun angle would yield new insights about the bright salt material inside Occator.
Dawn lost the third of its four reaction wheels spinning devices similar to gyroscopes which use momentum to control the crafts pointing April 23, less than a week before the opposition observation opportunity.
The science campaign went ahead as planned after ground controllers restored Dawn to its regular flight mode, but using hydrazine-fueled rocket thrusters instead of reaction wheels.
Dawns first reaction wheel failed in 2010, before it reached Vesta. A second wheel stopped working in 2012 as the crafts ion propulsion system drove Dawn away from Vesta for the trip to Ceres.
Engineers designed Dawn to control its attitude, or orientation, in space with three reaction wheels, one for each pointing axis. A spare fourth reaction wheel was added for redundancy.
Experts from JPL and Orbital ATK devised a hybrid method of controlling Dawns attitude with the two remaining reaction wheels and hydrazine thrusters, the spacecraft now must fully rely on its rocket jets, wrote Marc Rayman, Dawns chief engineer at JPL, in a mission update posted on a NASA website.
With the third wheel failure, we can be grateful that each wheel provided as much benefit as it did, Rayman wrote. The wheels allowed Dawn to conduct extremely valuable work while using the hydrazine very sparingly.
Raymond said Tuesday that the third reaction wheel failure was certainly not a mission-ending event, but it does reduce our lifetime because we have to use the hydrazine at a faster rate.
Dawn will use more hydrazine to maintain its attitude when it is closer to Ceres, but spiraling the probe away from the dwarf planet with its three xenon-fueled ion engines would require even less of the hydrazine maneuvering propellant.
The amount of hydrazine Dawn uses depends on its activities, Rayman wrote last month. Whenever it fires an ion engine, the engine controls two of the three axes, significantly reducing the consumption of hydrazine.
In orbit around Vesta and Ceres, the probe often trains its sensors on the alien landscapes beneath it. The lower the orbital altitude, the faster the orbital velocity, so Dawn needs to turn faster to keep the ground in its sights, Rayman wrote. Also, the gravitational attraction of these massive worlds tends to tug on the unusually large solar arrays in a way that would turn the ship in an unwanted direction. That force is stronger at lower altitude, so Dawn needs to work harder to counter it.
The consequence is that Dawn uses more hydrazine in orbit around Vesta and Ceres than when it is journeying between worlds, orbiting the sun and maneuvering with its ion engine. And it uses more hydrazine in lower orbits than in higher ones, Rayman wrote.
There is plenty of xenon gas left aboard Dawn, officials said.
Raymond said Dawn is currently in an egg-shaped orbit around Ceres that ranges in distance between 12,000 miles (20,000 kilometers) and 30,000 miles (50,000 kilometers). The probe traveled as close as 240 miles (385 kilometers) to Ceres last year.
We have enough resources, hydrazine and xenon, to support operations through at least the end of 2018, Raymond said. That will be depending the decision at (NASA) Headquarters what we will do with those resources.
That lifetime prediction depends on Dawn remaining far away from Ceres.
One day at our low-altitude mapping orbit, which was at 385 kilometers, would be equivalent to about 18 days (of hydrazine fuel) at higher altitude, which is what were in now, Raymond said.
Lifetime at a lower altitude would likely be limited to weeks at this point, she said.
A decision on Dawns future in the coming weeks whether it will stay at Ceres or head elsewhere echoes a similar stay or go choice that faced NASA managers last June.
Dawns science team last year proposed dispatching Dawn toward asteroid Adeona, a primitive, carbon-rich remnant from a collision that destroyed a much larger body, for a relatively slow-speed flyby in May 2019, but NASA officials decided keeping the probe in orbit around Ceres would yield a greater scientific return.
One possible fate has been ruled out.
Scientists dont want Dawn to collide with Ceres and potentially spoil future exploration of the airless world.
When our planetary protection requirements were negotiated, (scientists) already made the prediction that Ceres was an ocean world in the past, and could possibly be an ocean world today, Raymond said. Weve been vindicated, so our planetary protection requirement was dont land, dont crash.
Before shutting off Dawn for good, navigators will ensure the spacecraft is on a quarantine trajectory that avoids impacting Ceres, she said.
Email the author.
Follow Stephen Clark on Twitter: @StephenClark1.
Original post:
Dawn mission managers await NASA decision on spacecraft's future - Spaceflight Now
- 2D Laser Profiling Scanner for Detecting Targets - November 8th, 2009 [November 8th, 2009]
- NASA Energy Concept Could Harness the Power of Ocean Waves - November 8th, 2009 [November 8th, 2009]
- Data Acquisition Modules - November 8th, 2009 [November 8th, 2009]
- Dr. Scott Barthelmy, Research Scientist, Laboratory for High Energy Astrophysics, Goddard Space Flight Center, Greenbelt, MD - November 8th, 2009 [November 8th, 2009]
- Laser Tracker Ensures Accurate Alignment of Ares I Components - November 8th, 2009 [November 8th, 2009]
- Dual Cryogenic Capacitive Density Sensor - November 8th, 2009 [November 8th, 2009]
- Advanced Technologies Will Help Hubble Yield More Remarkable Discoveries - November 8th, 2009 [November 8th, 2009]
- Dr. Gerard Holzmann, Senior Research Scientist at the Laboratory for Reliable Software, NASA’s Jet Propulsion Laboratory - November 8th, 2009 [November 8th, 2009]
- NASA Research Will Help Aircraft Avoid Ocean Storms and Turbulence - November 8th, 2009 [November 8th, 2009]
- NASA Awards 2008 Software of the Year - November 8th, 2009 [November 8th, 2009]
- Here Come The Tricorders - Update - November 8th, 2009 [November 8th, 2009]
- China's View on Space - November 8th, 2009 [November 8th, 2009]
- Milsat Coordination and Tracking Issues - November 8th, 2009 [November 8th, 2009]
- Trash Talking and End Runs at NASA HQ - November 8th, 2009 [November 8th, 2009]
- Ares 1-Y is Toast - November 8th, 2009 [November 8th, 2009]
- Beyond Augustine - November 8th, 2009 [November 8th, 2009]
- Analyzing LCROSS' Plume - November 8th, 2009 [November 8th, 2009]
- Live Event: NASA-Sponsored Power Beaming Challenge - November 8th, 2009 [November 8th, 2009]
- JSC Wants To Build a Replicator - November 8th, 2009 [November 8th, 2009]
- USA: Looking For Ways To Hang On - November 8th, 2009 [November 8th, 2009]
- Lunar Lander Challenge Prizes Awarded - November 8th, 2009 [November 8th, 2009]
- Senate Votes To Restore NASA Budget Cuts - November 8th, 2009 [November 8th, 2009]
- New FAA Regs for Commercial Reentry - November 8th, 2009 [November 8th, 2009]
- TEDxNASA: An Invitation-Only NASA Meeting - Unless You Are Lucky - November 8th, 2009 [November 8th, 2009]
- Close Call For Courtney Stadd - November 8th, 2009 [November 8th, 2009]
- Space: A Waste? - November 8th, 2009 [November 8th, 2009]
- Making NASA Cool - November 8th, 2009 [November 8th, 2009]
- Engaging JSC’s Next Gen: A Leadership Analysis - November 8th, 2009 [November 8th, 2009]
- Dumpster Diving for Rockets - November 8th, 2009 [November 8th, 2009]
- TEDx NASA - November 8th, 2009 [November 8th, 2009]
- Reflections On a Business Trip in Huntsville - November 8th, 2009 [November 8th, 2009]
- Staying the Course - November 8th, 2009 [November 8th, 2009]
- The Economics of Space - November 8th, 2009 [November 8th, 2009]
- Ideas at Work - November 8th, 2009 [November 8th, 2009]
- Blah Blah Blah - Why We Should Care About Social Media - November 8th, 2009 [November 8th, 2009]
- Will White House Speak Soon About NASA? - December 12th, 2009 [December 12th, 2009]
- Software Aids Design of Ares V Composite Shroud Structure - December 13th, 2009 [December 13th, 2009]
- ASDX Series of silicon pressure sensors - December 13th, 2009 [December 13th, 2009]
- Industry Update: Analysis & Simulation Software - December 13th, 2009 [December 13th, 2009]
- Battery Will Provide Backup Power for Space Shuttles - December 13th, 2009 [December 13th, 2009]
- NASA Employee Claims To Have Witnessed Hijacking Planning - December 13th, 2009 [December 13th, 2009]
- Big Party in The Mojave Tonight - December 13th, 2009 [December 13th, 2009]
- Looking at Boulders on the Moon - December 13th, 2009 [December 13th, 2009]
- SpaceBook Featured by White House - December 13th, 2009 [December 13th, 2009]
- New Ways to Use Constellation Stuff - December 13th, 2009 [December 13th, 2009]
- LaRC internal Poll Update - December 13th, 2009 [December 13th, 2009]
- Coalition for Space Exploration Does a (Much Needed) Reboot - December 13th, 2009 [December 13th, 2009]
- Lunar Orbiter: Comparing Old and New Images - December 13th, 2009 [December 13th, 2009]
- Boulder Trails On The Moon - December 13th, 2009 [December 13th, 2009]
- Vote for John Grunsfeld - National Geographic Adventurer of the YeAR - December 13th, 2009 [December 13th, 2009]
- Charlie Bolden at WIA/AIAA - December 13th, 2009 [December 13th, 2009]
- Live Webcast From The Lunar Orbiter Image Recovery Project - December 13th, 2009 [December 13th, 2009]
- Big Aerospace Warns of Job Cut Impact - December 13th, 2009 [December 13th, 2009]
- The Boulders of Copernicus - December 13th, 2009 [December 13th, 2009]
- shame on us - December 13th, 2009 [December 13th, 2009]
- 2009 Space Elevator Games - December 13th, 2009 [December 13th, 2009]
- Random Hacks of Kindness - December 13th, 2009 [December 13th, 2009]
- TEDx NASA Tickets Available to the Public - December 13th, 2009 [December 13th, 2009]
- It’s better in person - December 13th, 2009 [December 13th, 2009]
- Leading Amidst the Disruptive Innovation Storm - December 13th, 2009 [December 13th, 2009]
- Space: What’s NOT to Hope for? - December 13th, 2009 [December 13th, 2009]
- Government in the Digital Age - December 13th, 2009 [December 13th, 2009]
- SpaceUp – A Space Unconference - December 13th, 2009 [December 13th, 2009]
- Starfleet Academy? - December 13th, 2009 [December 13th, 2009]
- Crowdsourcing NASA - December 13th, 2009 [December 13th, 2009]
- Bringing Home The Bacon - December 14th, 2009 [December 14th, 2009]
- Anti-Space Mom with Pro-Space Kids - December 14th, 2009 [December 14th, 2009]
- How Quickly We Forget - December 14th, 2009 [December 14th, 2009]
- WISE Launch A Success - December 14th, 2009 [December 14th, 2009]
- Dynetics Buys Orion Propulsion - December 15th, 2009 [December 15th, 2009]
- New NASA Governance Structure Under Development - December 16th, 2009 [December 16th, 2009]
- Bolden Meets With Obama on Wednesday - December 16th, 2009 [December 16th, 2009]
- MSFC Procurement Doesn't Understand what "Open Source" Means - December 16th, 2009 [December 16th, 2009]
- Bolden Meets With Obama - December 17th, 2009 [December 17th, 2009]
- Parker Griffith AT MSFC Today - December 18th, 2009 [December 18th, 2009]
- Why Your NASA Computer May Not Work Properly - December 18th, 2009 [December 18th, 2009]
- Lakes and Fog on Titan - December 18th, 2009 [December 18th, 2009]
- Waterworld Found - December 18th, 2009 [December 18th, 2009]
- Pandora Could Exist - December 18th, 2009 [December 18th, 2009]
- Laurie Leshin Is The New ESMD Deputy AA - December 18th, 2009 [December 18th, 2009]