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From: karn@petrus.UUCP
Newsgroups: net.space
Subject: re: launch windows
Message-ID: <310@petrus.UUCP>
Date: Mon, 18-Mar-85 00:38:02 EST
Article-I.D.: petrus.310
Posted: Mon Mar 18 00:38:02 1985
Date-Received: Tue, 19-Mar-85 04:24:00 EST
References: <1091@mordor.UUCP>
Organization: Bell Communications Research, Inc
Lines: 25

> 	I would like to clear up something that has me confused. Up to
> now I have assumed that the PAM upper stage starts its burn when the
> shuttle's orbit crosses the equatorial plane, and that the longitude of
> this intersection is chosen so that the transfer orbit's perigee is near
> the satellite's final station.
> 	Is this correct? Does the shuttle maneuver so as to establish
> the proper nodes? Or does PAM have a plane change capability? ( I am
> sure the IUS does).

This is essentially correct. The deployment takes place on an equator
crossing, and the PAM ignites on the next crossing, half an orbit later.
This allows the orbiter to do a separation maneuver at the time of
deployment so that it will be some distance away by ignition time.
Selecting the orbit on which deployment occurs allows the resulting transfer
orbit apogee to occur near the desired parking spot to minimize the amount
of near-stationary drifting required.

Any engine can do a plane change if it is pointed out of plane.
I've seen the transfer orbit elements for a few PAM missions and they
do reduce the inclination by about 3 degrees. I'm not sure why because
it is more efficient to let the apogee motor take it out instead; perhaps
it allows finer balance between the two stages without having to shave
out propellant.

Phil