On 15 September 2017 at about 10pm AEST, Nasas Cassini spacecraft will plunge deep into the hostile atmosphere of Saturn on an historic but suicidal course. Its the grand finale of a 20-year mission which has revolutionised our understanding of the solar system and sent home more than a quarter of a million stunning images of Saturn and its moons.
Cassinis instruments will be running to the last, capturing every possible byte of data from its closest encounter with the ringed planet before it ultimately evaporates.
Some 1.2bn km away, in a valley just outside Canberra, Glen Nagle and his colleagues will be listening intently to what he calls the whispers from deep space. Im going to be here for 24 hours and I wont be sleeping, he says enthusiastically.
Nagle (pictured above) works at the the Canberra Deep Space Communication Complex, aka Tidbinbilla Tracking Station, home to four antennas which help track and command the many spacecraft in our solar system. Run by CSIRO, Australias national science agency, but funded by Nasa, Tidbinbilla is one of just three stations in Nasas Deep Space Network (the others are in California and Madrid) and it is here that Cassinis final radio signals will be received and relayed to a global audience.
Were going to be responsible for capturing Cassinis last breath of data, Nagle says. Itll be a bittersweet moment.
Nasa cant do it without us because the other stations are completely facing in the wrong direction. Saturn will be in our skies, our field of view. Its literally the way the planets have aligned.
Opened in 1965, Tidbinbilla is a serene station enveloped by national parks. Its a place where the low hum of the moving antennas and the occasional paging announcements are the only sounds that punctuate the silence.
The dishes look surprisingly small from a distance, dwarfed by nature itself, but up close their scale is imposing. The largest is 70m in diameter and 109m across its curvature you could throw a football field into it, Nagle says and weighs about 4,000 tonnes. They are almost millimetre-perfect parabolic surfaces.
Each dish acts as both a gigantic ear and a gigantic loudspeaker, telling the spacecrafts how to behave, ensuring their health and collecting their data. The dishes operate night and day, whether or not the skies are clear to the naked eye.
At the present time we, Earth, have about 30 missions in the solar system, so about 40 individual spacecraft, Nagle says. We communicate with them using radio waves the invisible part of the electromagnetic spectrum.
Spacecraft receive and transmit data as digital ones and zeros. Its the same way that your phone receives a radio signal before your phones software turns it back into a picture, its just those ones and zeros. We dont know whether the stream were receiving is a beautiful picture or some instrument data or some engineering data or whatever it is.
The DSN doesnt handle satellites in Earths orbit the kind that are used for mobile communications, observation, weather prediction, GPS and so on. Theyre literally too close for us, Nagle explains. We just talk to the missions that have headed out across the solar system.
The furthest of them, Voyager 1, is so far from Earth that it seems a minor miracle its signal can be heard at all. For Nagle, a self-confessed space buff since childhood who is now the outreach and administration lead at Tidbinbilla, its a thrilling thought.
Right now Voyager 1 is roughly 20.7bn km away and moving further away by about 1.4million km every day, he says. Thats about four and a quarter times further away than Pluto. So its way out there. It takes over 30 hours to get a signal there and back.
To give you some idea of what that signal is like now: Voyager transmits at around 19 watts, about half the power its taking to run the lightbulb in your fridge. So imagine already trying to see half your fridge light from four and quarter times as far away as Pluto youre not going to see it.
And it gets even smaller because as that signal travels across that 20bn km of space it spreads out, it becomes thinner and more diffuse.
In fact, he adds excitedly, the signal we get is equivalent to only about one twenty billionth billionth with a b! of the amount of power thats generated by a typical watch battery. But youre still getting the information, the ones and zeros, and even though its very weak all of the information is still there.
Up high on dish number DSS35, theres a minor problem which needs to be fixed. The ball gears are not meeting correctly and the dishs ability to slowly pivot as it must do to track the craft while the Earth rotates is being compromised.
Currently were inserting a bit of solder to measure the backlash in the gear, says antenna technician Michael Murray. We measure the crush on the solder and thatll give us an idea of what the backlash is.
As with everything in space exploration, precision counts. And yet, oddly, just a few metres away theres a kink in the safety rail where a section has been cut away and awkwardly repositioned.
John Howell, the survey electronics technician, laughs. When they built this antenna they realised the rail was in the way and they had to cut this out [for the dish to be able to fully rotate]. We do months and months of testing when things are first built, we move everything very slowly, and when they got to this bit they realised, Oh no, its not going to work. We blame the engineers.
Howell has been employed at Tidbinbilla by CSIRO for the past 15 years the same duration as Nagle but, unlike his colleague, his knowledge of the science is more cursory.
People ask me what are they tracking today and I say, Ive got no idea. As long as my things point to where theyve got to point ... I mean, when weve got a major level one support happening like the Mars rovers landing or Cassini then its quite interesting, but apart from that some of the scientific stuff is way above my head.
He adds: But I am interested in the Voyager probes. It takes forever to get a signal to them and back at the speed of sound light, Nagle interrupts apologetically Oh sorry, the speed of light! Howell continues.
They left when I was still in primary school. I find it hard to believe we can talk to something that far away. It blows my mind.
In the recently built control centre a place Matthew Purdie, senior link controller, describes as the heart of the station activity is decidedly slow. You might imagine a hive of scientists huddled around monitors awaiting fresh data but in fact theres only one CSIRO scientist based at Tidbinbilla and his research role is detached from the day-to-day communications performed on behalf of Nasa and the other space superpowers. Nasas scientists are located at the Jet Propulsion Laboratory in the US.
Purdie and his team of controllers are patiently monitoring banks of screens, waiting for the rare occasion when a command fails or for the more alarming news that a craft has become inoperable or gone missing. Occasionally they have to call the JPL to tell them their craft are sick.
We refer to ourselves as coiled springs, Purdie says. Were sort of employed to handle things when they go wrong. Most of the time were looking for green on our screens. If everythings green were good; if it goes orange or red were in trouble.
Behind him, a box of on one of his screens turns orange. Oh, thats nothing to worry about, he says assuredly. Thats a carrier out of lock. Its spacecraft 74. We lost the signal but it was an expected loss of signal because the craft occultated it went behind Mars.
Right now Im on antenna DSS34, so Im tracking three spacecraft: MRO [Mars Reconnaissance Orbiter], Maven and Mars Odyssey. Id have to get out the book to tell you exactly what each spacecraft is doing. We know the technical side of our spacecraft, what bit rates they use, command frequencies and all that stuff, but quite often we forget why theyre there.
Purdie knows plenty about Cassini, however, and has been on duty for some of its recent dives the series of 22 daring orbits between Saturn and its rings which have given the craft a unique perspective on the planet and the surrounding bands of dust, rock and ice.
Disappointingly, Purdie already knows his shift patterns will cause him to miss the finale next month. Hes tempted to come to work anyway.
I like being part of history and science, he says. I like the fact that Ive been here for landings and launchings and things like that. Years ago they used to go around to each of the stations and ask for a Go? No go?, so youd have to say, DSS45 is a go! That was so cool, I loved doing that. They dont do that any more.
Australias involvement in space exploration is six decades old and even though Nagle thinks Australia doesnt see itself as a space-faring nation it has played a critical role in some of the most inspiring moments in the history of humankind.
The dish out the front is the one from Honeysuckle Creek that received and relayed to the whole world the first pictures of Neil Armstrong walking on the moon in 1969, Nagle explains. He must have regaled people with the full story a thousand times or more, yet he makes it sound anything but tiresome.
Nasas original intention was to use their dish in California to transmit the pictures to the world and show America winning the space race, he says. When Neil came out of the spacecraft the first thing he needed to do was switch on a camera which was mounted upside down so that he could later pick it up with his big, gloved hand. Nasa were going to flip the picture but the video technician called in sick that day and his backup forgot.
Eventually they flipped it but it was highly contrasted because the signal was going to ground somewhere. Mission control couldnt show that to the world and Neil wasnt going to wait.
At the critical moment, Honeysuckle Creek had a perfect image. When Nasa saw that, Nagle continues, they flipped the switch to Australia and 600 million people around the world watched Neil come down the ladder, put his left foot on the surface of the moon and say, One small step for man, one giant leap for mankind.
I was an eight-year-old kid sitting in front of the television, glued to the screen, watching humans walk on the moon in glorious black and white. I had no idea that 40 years later Id be working at the place where I can look out of my window at the dish that brought me those pictures.
That enduring sense of wonder is shared by Greg Boyd, the senior network administrator at Tidbinbilla.
I love the science, he says. When I first started I was into everything. We used to have these things called twixes, well before we had emails. They were advisories about what was happening and Id be reading all this groovy stuff thats going on.
As time goes on you become blase. Not jaded; blase. But Im doing my dream job and Ive been doing it for the last 25 years. Where else can a boy from Australia work for Nasa and really be critically involved in their missions? This is it.
As night falls over Tidbinbilla, low-lying clouds initially block the views overhead. A group of kangaroos gathers by the perimeter fence, intrigued by the faint, eerie noises emanating from the site.
By 3am the clouds have finally dissipated and the vast, star-spangled sky is simply breathtaking. Somewhere out there, Cassini is looping the loop between Saturn and its rings.
In its lifetime Cassini and its accompanying probe, Huygens, have revealed many of the secrets of the Saturnian system: how the particles that make up Saturns rings range in size from smaller than a grain of sand to as large as mountains; how Titan, one of the moons, has prebiotic chemistry as well as rain, rivers, lakes and seas; how icy plumes of water are spraying upwards from tiger stripe fractures on Enceladus, an otherwise frozen moon.
It has also witnessed giant hurricanes at both of Saturns poles and captured the first complete view of the north polar hexagon not bad for a one megapixel camera. The finale should reveal yet more about the interior of the planet as the craft measures its gravity and magnetic field.
The decision to hurl Cassini into Saturns deadly, gaseous atmosphere next month has been made through necessity and responsibility. The craft has run out of fuel and contains a nuclear battery; Nasas scientists fear it might contaminate one of the surrounding moons should it crash into them.
We have to dispose of the spacecraft safely, says deputy project scientist Scott Edginton, whos based in California, because Titan and Enceladus have been shown to be places where there are conditions for habitability, conditions that we think are appropriate for life.
So our navigators came up with this series of grand finale orbits, flying through the gap between the planet and the rings, and eventually ending in Saturns atmosphere. When the scientists saw that plan they were like, Wow, this is unexplored territory, were going to learn so many new things. So starting April this year we entered into the grand finale orbits. Its hard to believe were almost done.
Of the final descent, he says: Think of it as were sniffing the atmosphere. It will set the ground truth for past measurements and even future measurements. Thats something Im really looking forward to.
At Tidbinbilla the following morning, the anticipation in the visitors centre is just as palpable. Its this generations Voyager, says Jonathan Kent, a self-proclaimed hack astronomer. I think its capturing peoples minds and hearts and reinvigorating our interest in space.
Ten-year-old Scout Miller is proof. Shes at the centre with her family, and talk of the discoveries made by Cassini and Juno Nasas mission to Jupiter which delivered a tranche of close-up images of the planets red spot has made her wonder what else might be out there.
There must be alien life, she says. We cant be the only people. It cant just be a coincidence that we just appeared and no one else has, and that this is the only planet with the right things for life.
Many of CSIROs staff at Tidbinbilla share her optimism and, even though Nagle forewarns that life may never be found due to the sheer scale and age of the universe, he says: It would be a fantastic thing to find because it would answer the most fundamental questions we have: Is it just us? Are we alone? Is the universe full of life? Are we the first life? Are we the last?
Future missions to Saturn and its moons may yet reveal some answers, but for Cassini the deadly denouement is imminent.
Cassinis going to end its life as a shooting star in the atmosphere of a giant ringed world, says Nagle. Theres no more poetic way for a spacecraft to finish what has been a magnificent mission.
See the article here:
Space whisperers: the Aussies guiding Cassini's suicide mission to Saturn - The Guardian
