8 Lessons From Rosetta Comet Mission
What does the European Space Agency's amazing Philae probe landing tell us about where we are as a spacefaring civilization, where we're going, and how to get there?
Picking into the details of the European Space Agency's amazing Philae probe landing on a comet reveals how far we've come, how far we have to go, and how to boldly go where no one has gone before you. While we're all still in the glow, let's take a moment to review those lessons.
The landing of the ESA probe Philae on the surface of Comet 67P/Churyumov-Gerasimenko was a triumph. After a journey of 6.4 billion kilometers and 10 years in space, the mothership Rosetta worked its way into orbit around the comet (another first), at the astonishing distance from Earth of 300 million kilometers -- further away from Earth than Mars ever gets. Rosetta then released Philae, which fell to the surface, a distance of about seven miles. In the 1/10,000th gravity of 67P/Churyumov-Gerasimenko, Philae's speed was at about one meter per second (the equivalent of falling less than four feet on Earth), so that long drop took seven hours.
Apparently the thruster intended to hold it to the surface and the screws and harpoons intended to lock it down did not work properly. The best interpretation of the data says Philae bounced back up for almost two hours, hit and bounced again for another seven minutes, and finally came to rest sitting more or less upright on the surface of 67P/Churyumov-Gerasimenko -- a good thing, because if it had landed on its back, it had no way to right itself. And with that, humanity's most popular little robot had touched down on a chunk of ice and dirt moving at 41,000 miles per hour (more than twice the speed of a low-altitude satellite).
Even if Philae had ended up ignominiously upon its back like a hapless turtle, we'd have gained vast knowledge just from its flight down to the surface. As it is, we will know much more as the data slowly trickles to Earth through Rosetta's narrow bandwidth (the mothership is a crucial relay in this system) and the light-speed limits of transmission.
Of course some of the more naive commentary, jaded by media images of spaceships the size of aircraft carriers effortlessly spanning galaxies, missed how remarkable this accomplishment was. But for the most part, the public seemed to follow that this was extraordinarily difficult and challenging, and that this stretched the human race's current space exploration capacity close to its limit.
While we're still celebrating "The Little Probe That Did" (Fox News's nickname seems to have gone viral in the English-language media), let's take a look back and forth, see how ESA did it, and think about what the implications are for the next few years in deep-space exploration.
It's the right time for it: In the long history of the technology of exploration, from the first burned-log canoe to Philae, when explorations reached farther by challenging the technological limit they revealed not just the new territories they were exploring, but also what we would need to become better at if we were to fully explore the new realm. By the time the Polynesians reached Hawaii, New Zealand, and Easter Island, their canoes and navigation systems were far beyond what they had started with back on the Asian coast. Hwang Ho and Magellan demonstrated that sailing ships would need to be bigger, faster, and more precisely navigated. Nansen and Byrd showed that airplanes would need to be bigger, longer-ranged, and higher-flying to reach into polar regions.
So before passion cools, while we're still proudly thinking "what's next," let's see what lessons we can take from the inspiring career of a metal box, physically the size of a washing machine, and historically as big as it gets.
How did ESA succeed? Where and how did they almost fail? What did they do that was good, and what did they have to do that wasn't? And how does that apply to anyone else entering the unknown with new technology?
The 20 member states of ESA all contributed parts, analysis, concepts, and experiments to the project. NASA supplied three additional instruments and the resources of its Deep Space Network to stay in touch with the distant probe; that cooperative effort was managed by the Jet Propulsion Lab in Pasadena, Calif. During the actual rendezvous and landing, control rooms worked from Darmstadt, Germany, and Toulouse, France. Universities and research centers in Gottingen and Cologne, Germany; Rome; and Paris undertook the main design for Philae. Canadians built some key components; Australian antennae were critical to staying in touch with the mission; and it was launched in March 2004 from French Guiana. Given the cost and complexity of deep-space exploration, such cooperation is going to become only more important.
In some styles of kung fu there's an expression that says: Be as graceful as an old man walking on ice.
What that means is, preserve perfect balance at all times; don't put a foot any further forward than you are sure you can take it back; depend on a good stance and groundedness -- and not on momentum -- to carry you through a tricky move; never overextend; make sure you've always got a firm grip on the ground.
I don't know how many martial artists there are in ESA, but the basic process is much the same. When an Ariane rocket blew up just weeks before Rosetta/Philae was supposed to launch, the team members scrubbed the mission on a different Ariane and waited until they were sure of the rocket again. When the thruster for bringing the lander down to the surface of Comet 67P/Churyumov-Gerasimenko appeared to malfunction, they held up the landing until they had a solution they trusted. When batteries didn't charge as fast as they hoped after the Mars fly-by, they put the whole ship into hibernation rather than risk not having enough juice at the landing end.
When they needed to pick a landing site, they spent the time it took to find the optimal one. (Not easy: Where's the best place to land on an icy dirt clod shaped like a rubber duck?)
Rosetta/Philae was originally planned for a mission to Comet 46P/Wirtanen in 2011, but delays culminating in the uncertainty about an Ariane launch delayed it by too many months. So they decided to go to 67P/Churyumov-Gerasimenko instead, via a series of gravity assists.
Along the way, planners found a course that allowed them to do flybys of the asteroids 2867 Steins and 21 Lutetia, with considerable scientific data gathered (particularly important for Lutetia, which is one very strange asteroid).
In 2010, while en route, Rosetta was also able to use its instruments and cameras at long distance to investigate whether the newly discovered body P/2010 A2 was a comet in the main asteroid belt, or an asteroid with an unusual ejection of material (it turned out to be the latter); P/2010 A2 had not even been discovered when Rosetta departed.
(ESA image of 21 Lutetia)
Old-time sailing vessels managed to explore the seas in the days before steamships, but if you look at the routes they took, you quickly see that they traveled a lot more miles a lot more slowly, because a large part of getting anywhere was figuring out where to catch the wind.
Right now planetary probes still rely on gravitational slingshots. Rosetta/Philae had to work three slingshots past Earth and one past Mars, which is why it took 10 years to get there. Within our lifetime there will probably be big boosters available to launch from orbit, and the solar system will get a great deal smaller, with travel times in months rather than years and all the advantages of being able to respond to a quickly developing situation. And if we should ever need to reach a comet or asteroid quickly, perhaps because we need to send Bruce Willis to it, those big boosters would be our one hope of doing it in a timely way.
(See larger image of Rosetta's journey on ESA's Flickr)
Using the best landing window meant that Philae was pretty close to the end of an active period when it landed, and then the two big bounces (and ESA's analysis time to figure out what they were) took additional time. Rather than drain batteries, take up bandwidth, or risk equipment to get the first surface photos out of Philae and into Rosetta for the news cycle on Earth, ESA kept the more vital instruments running and recorded the data that would have the most positive effect on mission survival. Quite a few of the Internet folks were cranky about this, as they were politely ignored. The first step of sharing with the public always has to be making sure there's something to share.
(Philae lander manager Stephan Ulamec briefs the press Thursday morning.)
Rosetta is very far away, can't carry a big antenna, and doesn't have much power to spare. Yet because everything is sent on a handshake basis, with nothing erased at the spacecraft end until its receipt is confirmed at the Earth end, the frequent interruptions, the necessarily low bandwidth, and all the other hassles have not yet cost us any data. For a deep-space probe, given how much we are paying for pure information, it is much more important that it gets here for sure than that it gets here quickly -- even if media are begging for nifty pictures.
Time lag, one way, to Rosetta can be up to 50 minutes, and until someone repeals relativity, we're stuck with that. So ESA does extensive reprogramming on the fly as circumstances change, but ultimately, at those speeds and distances, carrying out the action correctly and on time has to be up to the space probe itself.
Right now ultra-distant probes are in their infancy; for example, Philae didn't have any way to record or measure what was happening onboard, so it was some hours before analysis of the data from the ROMAP instrument (which wasn't originally planned to be used for this) revealed that double bounce. We may or may not ever know if the harpoons even fired, or whether the landing foot screws made successful contact. There just wasn't room, time, or space to instrument everything, or to put in programmable controls for adjustments or self-repair.
But in future probes, there will be; the descendants of Philae will be able to feel the surface, find a grip, confirm that they have it, and so forth. And when they're several light hours from Earth, landing on Kuiper Belt objects for example, that will be the only way they can do such things at all. The day is coming when our directions to our space probes will be a bit like Captain Kirk's at the end of the first Star Trek movie (which, a few of you nerds will recall, involved a very evolved and independent robot probe): "Out there ... thataway."
Deep space probes have to be built to last to the end of their missions -- and to make it certain that they will, they are usually very overbuilt, which means that when the mission's complete, they tend to keep chugging right along. The Mars rovers -- Spirit, Opportunity, and Curiosity -- all went far beyond their expected lifetimes, Voyagers 1 and 2 continue ever further into interstellar space decades after their missions were completed, and all of those craft continue to return valuable data. The harsh conditions -- gas clouds and flying rubble -- around a comet making a close pass at the Sun may mean that Rosetta and Philae will die on schedule, shortly after perihelion (closest pass to the sun).
Or, perhaps, not. The meetings are already scheduled and the plans already laid for a longer mission, and if the two probes survive perihelion, they may yet ride with the comet back out into the cold depths of the asteroid belt. If they do, ESA is ready to keep them at work.
Deep space probes have to be built to last to the end of their missions -- and to make it certain that they will, they are usually very overbuilt, which means that when the mission's complete, they tend to keep chugging right along. The Mars rovers -- Spirit, Opportunity, and Curiosity -- all went far beyond their expected lifetimes, Voyagers 1 and 2 continue ever further into interstellar space decades after their missions were completed, and all of those craft continue to return valuable data. The harsh conditions -- gas clouds and flying rubble -- around a comet making a close pass at the Sun may mean that Rosetta and Philae will die on schedule, shortly after perihelion (closest pass to the sun).
Or, perhaps, not. The meetings are already scheduled and the plans already laid for a longer mission, and if the two probes survive perihelion, they may yet ride with the comet back out into the cold depths of the asteroid belt. If they do, ESA is ready to keep them at work.
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