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Posting-Version: version B 2.10.2 9/18/84; site petrus.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!allegra!bellcore!petrus!karn
From: karn@petrus.UUCP
Newsgroups: net.space
Subject: Re: Plane Change in Transfer Orbit
Message-ID: <313@petrus.UUCP>
Date: Fri, 22-Mar-85 02:07:43 EST
Article-I.D.: petrus.313
Posted: Fri Mar 22 02:07:43 1985
Date-Received: Sat, 23-Mar-85 01:09:34 EST
References: <1091@mordor.UUCP>, <310@petrus.UUCP>, <5300@utzoo.UUCP> <5302@utzoo.UUCP>
Organization: Bell Communications Research, Inc
Lines: 29

This is very interesting. I'd like to see the details of how this is so.

Back when I was helping to plan the orbital maneuvers for AMSAT-OSCAR-10
we wanted to change a GTO as given by an Ariane (inclination 8.6 deg)
to a Molniya approximation (63 deg). I found through some reading that
for VERY large plane changes (like the one we wanted to do), the economy
of plane changes at apogee is so strong that it actually saves fuel to
boost apogee, do your change at the new apogee, then drop back down to the
desired apogee. We didn't opt for that because of the risk involved;
we easily had enough delta-vee that an overburn at perigee would have given
us earth escape velocity. We didn't want to compete with Voyager.
In addition, communication links at 100,000km+ might have become marginal,
and with a starting perigee of 200 km, additional perturbations from the
sun and moon could be serious.

Even a "normal" plane change carried its risks. I realized that if the
engine were to shut down midway through a large maneuver, the resulting
perigee would be negative. We therefore planned a two-burn "dogleg"
compromise in which the intermediate orbit would still be useful. This
turnd out lucky -- the motor overburned on the first shot due to a wiring
error in the control circuit, and failed to burn on the second shot
due to a loss of helium pressure likely caused by the unplanned temperature
excursions resulting from a collision with the launcher shortly after
separation.

We've got a usable, functional satellite, although it's been through a
few "hard knocks".

Phil