Path: utzoo!utgpu!watmath!clyde!att!rutgers!gatech!cwjcc!hal!nic.MR.NET!shamash!nis!viper!dave From: dave@viper.Lynx.MN.Org (David Messer) Newsgroups: sci.space.shuttle Subject: Re: Info wanted on Atlantis "secret" mi Message-ID: <1716@viper.Lynx.MN.Org> Date: 19 Dec 88 05:25:33 GMT References: <684@pyuxd.UUCP> <22000011@m.cs.uiuc.edu> <2721@aplcomm.jhuapl.edu> <12694@bellcore.bellcore.com> Reply-To: dave@viper.Lynx.MN.Org (David Messer) Organization: Lynx Data Systems, Eagan, MN Lines: 31 In article <12694@bellcore.bellcore.com> karn@ka9q.bellcore.com (Phil Karn) writes: >>>Say again? Any satellite orbit, over the long run, spends half its >>>time with its ground track in the night hemisphere. >> >>False. >> >>Visualize an orbit over the terminator... > >You're forgetting that such a situation can't last forever. The terminator >rotates in inertial space once per year, and it also "wobbles" north >and south through a total angle of 47 degrees. The spacecraft's orbit >plane also precesses, with the "sun synchronous" orbit being a special >case where the precession matches the mean rotation rate of the >terminator. But the wobble due to the tilt of the earth's axis >still means that in the long run, the satellite ground track will be >half lit and half dark. The terminator wobbles? I thought it always was 90 degrees from the direction to the sun... Assuming one can choose the precession rate and angle of the satellite orbit, it should be possible to maintain an orbit in the plane of the terminator. -- _____________________________________________________________________________ __ _ _ _ David Messer - Lynx Data Systems / ) / ' ) ) ) dave@Lynx.MN.Org -or- / / __. , __o __/ / / / _ _ _ _ __ ...{amdahl,hpda}!bungia! /__/_(_/|_\\/ <__(_/_ / ' (_