Dear Ejay Hir and all, I've a somewhat better view of Bate, Mueller, and White, than Henryâ probably because I'm so used to it and haven't seen the other texts Henry mentions, though I should look at Chobotov. I was acquainted with Vladimir Chobotov back when he worked for Aerospace Corp., I was in the DSCS program office, and we were both losing our hair trying to explain to Colonels why it didn't make sense to do an orbital maneuver every time NORAD projected another satellite coming within a dozen miles or so of our satellite (There's a non-zero risk of a collision when error ellipsoids overlap, yesâbut there's also a non-zero risk of something like a thruster sticking open or a fuel tank exploding whenever you do a maneuver. Guess which risk is larger?) Anyway, Dr. Chobotov is a brilliant man and I'm sure his $100 book is full of good stuff.
Back to BMW. It is badly in need of an update. It was geared toward teaching USAF Lieutenants to do orbit determinations with the computers available 30 years ago, and the order of presentation of topics leads to a lot of paging back and forth. The more fun stuff about interplanetary missions is secondary and pretty basic. That said, I do think it provides a good introduction to Keplerian elements and treats the orbital plane change problem in an accessible manner. It's basically a practical how-to book for someone with a reasonable math background but relatively new to the astronautics field. You can download my Keplerian orbital mechanics review sheet for free. Though it doesn't deal with plane changes, if you have a basic idea of the geometry and terminology, and just need some formulae for calculations, it's at: http://www.nfbcal.org/~gnordley/downloads.html The plane change calculation is easy, however; if you assume a short "impulsive" maneuver done at the "node" where your orbital plane crosses the orbital plane you want to reach, it's a simple vector addition problem. The delta v you need to change your orbital plane by angle A is: delta v = 2v sin(A/2), where v is the orbital velocity. For instance, to put the Hubble (v â 7.575 km/s) in the ISS orbital plane (inclination change of 23.17 deg), where it would presumably be okay to service it by shuttle, you'd need about 3.04 km/s--about enough to send it to Mars! It's not an impossible number, howeverâbasically, you'd need to send up about 1.72 times the HST's weight of 3.04 km/s-exhaust-velocity fuel and a small rocket engine which you fire at every node for a few months or so (the HST won't take much acceleration). When it comes down to it, this brute force approach might be a lot simpler than the robotic repair mission and even cheaper now that they're talking billions for the robot! --Best, Gerald _______________________________________________ ERPS-list mailing list [email protected] http://lists.erps.org/mailman/listinfo/erps-list
