Space

From: thomsona@netcom.com (Allen Thomson)
Subject: Re: Lacrosse: What's up with the antenna...?
Newsgroups: sci.space.policy
Message-ID: 
Organization: Netcom Online Communications Services (408-241-9760 login: guest)
References: <5ckjd7$j7i@news.asu.edu>
Date: Tue, 28 Jan 1997 12:31:25 GMT
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Sender: thomsona@netcom6.netcom.com
In article <5ckjd7$j7i@news.asu.edu> aufsj@imap2.asu.edu writes:
>
>	The two antennas on the FAS Lacrosse representation (assuming it 
>is accurate) may, as posted previously, be signs of a spinner.  For more 
>"normal" spacecraft using GPS for attitude determination 4 antennas is 
>much more common ( "Gadfly" comes to mind ), and if simple input into 
>post ephemeris generation is wanted, one will usually do.  As I said, on a 
>top-dollar top-flight spacecraft one would expect everything to be done 
>for a reason, and why would one include two antennas? (two receivers in 
>case of breakdown is more understandable, but fixed antennas rarely break 
>and it is relatively simple to connect two redundant receivers to a 
>common antenna).  In addition, the attitude data that such a GPS set-up 
>could provide could be crucial if the bird is indeed SIGINT (perhaps more 
>later on that).
[snip]
   Remember that the LACROSSE-1 and probably -2 design has to date from the
late-70's to, at best, the early 80's.  I could be wrong, but I'd doubt very
much that the spacecraft engineers of that era would have used GPS for 
mission-critical functions.  The first, experimental GPS satellite was
launched, IIRC, in 1978 and there was considerable lack of enthusiasm
on the part of the USAF for continuing the system for several years.