As we follow our space probes this spring, we are reminded how much we are all spoiled by Hollywood spaceships that not only make cool “whoosh” sounds, but magically pop between interesting places in minutes without spending any boring time getting there.
Unfortunately, real space travel is much slower and trickier, and robot spacecraft aren’t as magical as seen on TV. In the past few months, we have seen NASA’s Dawn probe arrive at Ceres and ESA’s Rosetta at comet 67P/CG, both of which took a decade to get there. And even now that they have “arrived”, things are still “exotic” by Earthbound standards.
Dawn’s slow looping progress…
Dawn arrived at Ceres last month, achieving gravitational capture on 6 March. But this is a long, slow mission, and the spacecraft has been slowly looping around in a long spiral in, to a target 15KM circular orbit in a few weeks. Furthermore, it has been on the dark side of Ceres which, out there, is really, really dark! So no imagery until the mapping orbit is achieved.
Marc Rayman gives us a ton of cool information about real life out there in Ceres orbit: reconfiguring the spacecraft from travel to observation mode, dealing with the loss of 2 of 4 maneuvering flywheels, calibrating the camera and so on.
Now that Dawn is there, it will begin a long campaign of observations, spiraling in to successively closer orbits as the months go by. And this will be the end of the mission: she will fade out and someday fall onto Ceres.
Rosetta’s navigation woes…
The Rosetta spacecraft has been swooping in for close passes to comet 67P/CG, which is heating up and developing an atmosphere as the ice steams off. This means that these passes are actually quite dangerous for the deep space adapted Rosetta: she’s not intended to operate in an atmosphere.
The mission has reported on problems they have had, which are kind of interesting. The big problem has been that the automated star finder system has been confused by all the ‘bright spots’ from the escaping gasses. The star finders continuous watch the sky for familiar groups of stars, which are used to keep the spacecraft on course and oriented correctly. The latter involves, critically, pointing the antenna at Earth.
Apparently the last pass encounters so many false “sightings” that the star finders got lost and the antenna skewed away from target Earth. The signal was lost for a while and data could not be transmitted.
The spacecraft recovered, though not before entering a “safe mode” partial shutdown.
(“Safe mode” sounds warm and cuddly to me, but I know that space scientists hate safe modes—they are what happens when all else has failed.)
I don’t know about you, but I’ve always be awed by guide star astrogation—it is so elegant and so universal. The spacecraft knows exactly where everything is….
And for that matter, orienting spacecraft with flywheels just blows my mind–again, so elegant, so flat out Newtonian.