Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!linus!genrad!decvax!harpo!floyd!vax135!ariel!houti!hogpc!houxm!mhuxa!mhuxi!mhuxt!eagle!karn From: karn@eagle.UUCP Newsgroups: net.space Subject: Re: many body calculations Message-ID: <998@eagle.UUCP> Date: Tue, 14-Jun-83 02:51:12 EDT Article-I.D.: eagle.998 Posted: Tue Jun 14 02:51:12 1983 Date-Received: Wed, 15-Jun-83 03:48:42 EDT Lines: 28 This is a topic that has lately come near and dear to my heart (I'm doing the kick motor calculations for the amateur satellite Phase 3-B, due to be launched this Thursday morning). The method which Lew Mammel describes is known in the literature as the "Cowell Method", which is just the numerical integration of the second-order differential equations that describe an orbit. The beauty of this method is its simplicity and the ease with which it can include perturbing factors (other planets, air drag, earth oblateness, etc.) On the other hand, if the problem you're solving is a good approximation to two-body motion (i.e., one large body dominates the motion of your satellite) then you can integrate just the perturbing forces with respect to a reference two-body orbit, updating the reference orbit when you get too far away. This is Encke's method, and it allows larger step sizes (increasing program speed and reducing accumulated roundoff error) than Cowell's method. There are lots of methods for doing the numerical integration that these models require. Having no formal training in the subject, I'm only now becoming familiar with the Runge-Kutta method, which is apparently the simplest (but not the fastest or most accurate) algorithm available. It is, however, a refinement of the method which Lew describes, and is probably much more accurate. I'm learning to distrust anything a computer prints out with a decimal point wedged between digits... Phil Karn