Path: utzoo!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!bfmny0!tneff
From: tneff@bfmny0.UU.NET (Tom Neff)
Newsgroups: sci.space.shuttle
Subject: Re: LDEF capture time change (Forwarded)
Message-ID: <15098@bfmny0.UU.NET>
Date: 14 Jan 90 18:34:24 GMT
References: <40214@ames.arc.nasa.gov> <9090002@hp-lsd.COS.HP.COM>
Reply-To: tneff@bfmny0.UU.NET (Tom Neff)
Lines: 22

In article <9090002@hp-lsd.COS.HP.COM> paulc@hp-lsd.COS.HP.COM (Paul Carroll) writes:
>	Is there any reason why LDEF is not rotating or tumbling
>	in orbit?  

The reason it's not tumbling IN GENERAL is that long satellites tend
over time (if they didn't start that way) to assume what is called
'gravity gradient' attitude, with the major axis pointing to the center
of the earth.  This is essentially a stable solution to the orbital
dynamics problem of how to fly the two ENDS of a long satellite in
'forced tandem'.  The satellite IS tumbling -- at 1/90th rpm!  Now you
know why the LDEF retrieval was such a fun job :-)

Nevertheless as satellites re-enter the atmosphere they do start
tumbling.  The reason LDEF isn't tumbling YET is that Our Friend Mr. Sun
was a good enough sport to quiet down the last couple of months, so the
exoatmosphere (which gets fluffed up by an active sun) subsided and gave
LDEF a time bonus.  If the sun hadn't quieted, this delayed Columbia
launch would probably have been too late.  As it is, LDEF tumbling and
re-entry was predicted for March.
-- 
'We have luck only with women -- not spacecraft!'     \\  Tom Neff
 -- R. Kremnev, builder of failed Soviet FOBOS probes //  tneff@bfmny0.UU.NET