Sunday, April 09, 2006
20 Trips to Mars
The good news is that thanks to the miracle of time acceleration, I took twenty trips to Mars this weekend. The bad news is that thanks to the anti-miracle of "slow learning curve," I had to take those twenty trips to Mars. For example, I spent about 4 hours discovering that 100 meters does not equal 100 kilometers. It took me this long (and an email to Andy) to figure out that the reason I kept colliding with Mars was that I had defined my orbital insertion periapsis to be 100 meters, omitting a crucial "k" in my input. The "bug" seemed familiar -- because I had done the same thing last fall when I was first learning IMFD. Mars is so unforgiving - and computers are too.
These are virtual trips in Orbiter, of course, working with Andy McSorley on the final chapter of Go Play In Space (Second Edition), for which he has been handling the Mars beat. I chimed in to try to find a better arrival date and time in October 2033 that will give us some daylight and a small orbital inclination that the Land MFD autopilot can land from (it doesn't like polar orbit approaches). I didn't do much better than what Andy started with, but at least I tested his procedures (a lot). I can see now why JPL has more than one or two people doing this stuff.
Interplanetary MFD (IMFD) is a wonderful "FMC" (flight management computer in aviation parlance) that handles general flight planning and can perform programmed engine burns automatically. The Land MFD (zip file) is an auto-lander intended mainly for bodies with no atmosphere (such as the Moon), but it works OK on Mars too, as long as you give it a decent orbit to start from.