Path: utzoo!attcan!uunet!lll-winken!lll-tis!ames!ncar!boulder!sunybcs!rutgers!bellcore!ka9q.bellcore.com!karn
From: karn@ka9q.bellcore.com (Phil Karn)
Newsgroups: sci.space.shuttle
Subject: Re: Info wanted on Atlantis "secret" mi
Message-ID: <12646@bellcore.bellcore.com>
Date: 14 Dec 88 22:46:29 GMT
References: <684@pyuxd.UUCP> <22000011@m.cs.uiuc.edu>
Sender: news@bellcore.bellcore.com
Reply-To: karn@ka9q.bellcore.com (Phil Karn)
Organization: Home for Burned-out Hackers
Lines: 25

>>...  The 57 degree inclination orbit of Atlantis's
>>payload has some nasty characteristics as far as earth illumination
>>goes; as the orbit plane precesses, there will be long intervals
>>during which most of the ground underneath the satellite is in
>>darkness, which would make a visible light satellite rather useless.

>Say again?  Any satellite orbit, over the long run, spends half its
>time with its ground track in the night hemisphere....

I misspoke myself. I meant to say that with a 57 degree inclination orbit,
there will be long intervals in which the *desired target area* will be in
darkness during every pass of the day.  There will, on the other hand, also
be long intervals in which every pass over the desired target area will be
in sunlight. In a sun-synchronous orbit, you get a happy medium, with two
sets of passes per day over any given target area; one set will be in
darkness and the other in sunlight. If bounding the maximum interval between
optical "peeks" at a given spot (the central USSR, say) is important, then
the 57 degree orbit is far worse than the sun synchronous one.

Regarding plane change maneuvers: these are extraordinarily expensive in
terms of fuel, especially in low earth orbit where velocities are high.  You
have to subtract out a substantial component of the velocity in one
direction with rockets and add it back in another; there is no "highway" up
there against which you can steer...

Phil