If you follow spaceflight much-and probably even if you don’t-you’ll recall the Mars probe that burned up during orbital insertion a few years ago. Actually, it was the Mars Climate Orbiter and that was 16 years ago, believe it or not. The problem was that instead of the newton-seconds specified in the contract, software writers used pound-seconds in calculating the insertion parameters. Ooops. (And by the way, that was the same year Google was launched.)
I bring it up because as difficult as getting the orbital mechanics right on the way to Mars is, with its Rosetta project and recent planting of a probe on the surface of a comet, the European Space Agency pulled off something infinitely more complex. Just getting the orbital insertion calculated and executed is nothing short of mind boggling. To get it into the neighborhood of Comet 67P/Churyumov-Gerasimenko on its 10-year voyage, Rosetta did one gravity sling past Mars and three past Earth before getting close to the comets enormous elliptical orbit. Here’s a nice video showing the orbital path.
Then it took a series of complex maneuvers with the probe’s thrusters to refine the orbit, catch the comet and then slow it down for orbital insertion. It took more maneuvers to put Rosetta in what sounds like an elliptical orbit around the comet similar to those used by Apollo missions carrying lunar rovers. They had to have very low perilunes in order to minimize descent fuel burn, allowing the weight of the rover. It sounds like ESA did something similar with Rosetta to get the surface probe, Philae, on the surface. I’m inspired by the science that achieved this, not to mention the boldness of the idea itself. But the math gives me a headache. (Here’s another video showing the orbital refinement.)
For three years of its 10-year journey, Rosetta was powered down and dark except for radios. It was revived this summer for the final approach to the comet. What a piece of work is man to build a flying machine that can do this and to get it right the first time. Kudos to the ESA team. What a performance.
It will be interesting to see if Rosetta, once its official mission ends in December 2015, does what the Voyager probes have: outlived many of their creators. Voyager 1 and 2 are still alive, having entered interstellar space two years ago. They are now 37 years old and still functioning. They’re in the heliosheath, where the solar wind abates against the pressure of interstellar forces. If Rosetta chases them out that way, I wonder what secrets its more sophisticated instrument package might reveal.
A piece of work indeed.
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