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