Space

Subject: Re: Lacrosse: What's up with the antenna...?
From: aufsj@imap2.asu.edu
Newsgroups: sci.space.policy
Date: 29 Jan 1997 00:57:55 GMT
Organization: Arizona State University
Lines: 61
Message-ID: <5cm7aj$jmi@news.asu.edu>
References: <5ckjd7$j7i@news.asu.edu> 
: >	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).
:    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.  
	It wouldn't be mission-critical, but certainly mission 
enhancing.  There are any number of geolocational methods that could be 
used without GPS, but having precise attitude data could only help.  It 
is pretty easy to figure on a system that utilizes GPS but degrades to 
lesser accuracy if it doesn't work.  After all, it only takes version 0 
to keep from plunging to a fiery death, but near real-time version 9 
would have the guys in the backroom doing the Macarena.
: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.
	Planning?  Designers certainly knew what was coming down the 
pike, I would expect them to try and use the stuff. In addition, Timation 
and other systems were providing space/clock functions before GPS, 
apparently, so the idea wouldn't have been out of the blue. 
	As for AF reticence, I think it came in some part from a belief 
in the programs earlier days that it wouldn't turn out to be that useful 
for locating flying objects. In addition, the cost implosion in cheap 
receivers and computing power for GPS units, I think, caught everyone by 
surprise (it sort of paralells the PC explosion). And for another thing, 
it wasn't an AF program, back in the days when the services were 
zealously gurading their respective turfs.  Of course, now the AF seems 
embarked on a mission dedicated to keeping anyone from finding out just 
how the whole thing has evolved, some of the histories I've seen border 
on professionally unethical in their complete lack of mention of the Navy 
effort/role in all this. Same as it ever was...
	The Navy has always kept the time, and was hell bent on getting 
GPS (or something similar) up whether or not anyone else was going along 
for the ride.  Every PSA for the last 30 years has been pushing time 
standards and distribution (from which navigation is a natural outgrowth) 
and the Navy has enthusiastically complied.  It is turning out fairly well, 
too, IMHO.
regards,
------------------------------------------------------------------------
Steven J Forsberg  at  aufsj@imap2.asu.edu                Wizard 87-01