Path: utzoo!utgpu!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!bellcore!ka9q.bellcore.com!karn
From: karn@ka9q.bellcore.com (Phil Karn)
Newsgroups: sci.space.shuttle
Subject: Re: Info wanted on Atlantis "secret" military satellite payload
Message-ID: <12418@bellcore.bellcore.com>
Date: 7 Dec 88 05:06:37 GMT
References: <684@pyuxd.UUCP> <1988Dec4.225033.18207@utzoo.uucp> <6464@polyslo.CalPoly.EDU>
Sender: news@bellcore.bellcore.com
Reply-To: karn@ka9q.bellcore.com (Phil Karn)
Organization: Home for Burned-out Hackers
Lines: 23

>The media has said they believe the satellite uses an very powerful imaging
>radar, with a 1 meter resolution. While that does not preclude an optical
>system, it seems unlikely that a satellite with such a powerful radar system
>would also have an optical system as powerful as the Hubble telescope.

A little thought reveals that even without the benefit of the published
reports saying it's a radar satellite, it's highly unlikely that Atlantis's
payload is an optical observation satellite.  Earth observation satellites
(weather, earth resources or spy) that operate with visible light work best
in "sun synchronous" orbits, where the orbit plane keeps a constant angle to
the sun direction over a relatively long period of time.

This is a major advantage since many pictures can be taken of the same spot
over time with a relatively constant illumination angle.  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. A
radar satellite, on the other hand, doesn't care if it's night or day on the
ground. (But I'm sure the solar power availability and thermal control
problems this orbit presents gave Lacrosse's designers some real headaches.)

Phil