Pre-solstice spysat launches: why?

Allen Thomson (thomsona@netcom.com)
Sun, 29 Dec 1996 08:34:25 -0800

    The recent (20 Dec 1996) Titan IV launch of a reconnaissance 
satellite into polar orbit (*) from Vandenberg brings up a question 
I've had for some time now:

   Why,  for the past decade, has the US launched its 
sunsynchronous spysats in the month before the winter solstice? 

   In discussions concerning this, some general explanations have 
been offered, to wit,

1) There is some technical reason, probably related to solar 
   illumination of the targets on the ground or the solar panels on 
   the spacecraft that makes pre-solstice launch desirable.
 
   The problem with this explanation is that it lacks specifics. 
   No one I've talked to has been able to demonstrate an actual 
   technical advantage.  While the "technical reason" candidate 
   sounds good and may well turn out to be true, it's still somewhat 
   in the hand-waving category.

2) Pre-solstice launch prevents northern-hemisphere optical 
   observation(**) of the payload during deployment and for two or
   three months thereafter.  There is a paucity of known optical 
   observers in the southern hemisphere, and anyway the 
   distribution of land and population down there mitigates 
   against spotting satellites launched in November and 
   December.  So, even though they might have been visible in theory. 
   I certainly don't know of any case in which a polar Vandenberg 
   launch near the northern winter solstice has been spotted by other 
   than a northern hemisphere observer the following Spring.

   But what's the point?  One would presume the USSR (now Russia) and 
   possibly other countries have been following the payloads with radar, 
   and maybe with daylight visual/IR methods from launch onward.  In any 
   event,  the launch timing, azimuth and booster configuration, along 
   with  observation of the payloads of previous similar launches let 
   the orbits be inferred quite nicely, as evinced by amateur observers' 
   success in finding and identifying the satellites when they become 
   visible in March and April.

   One slightly paranoid suggestion that's been made to resolve 
   this puzzle is that there are actually two payloads on the 
   boosters (Titan-IVs with oversize payload shrouds), and that 
   one stays in low orbit to be observed subsequently, while the 
   other does a disappearing trick in the manner of AFP-731 and the 
   NOSS-2 A objects.  This, unfortunately, doesn't account for the
   possibility of radar or daylight visual/IR observation of the 
   payload(s) during deployment.

of course, there's always

3) There's nothing to explain. The pattern didn't exist before about ten 
   years ago, not that many satellites have flown subsequently,  
   and the pre-solstice "pattern" is most likely a fluke of small-
   sample statistics.


   So I'm perplexed (actually, I'm metaperplexed: I'm perplexed 
as to whether I should be perplexed) and would welcome some 
discussion of this apparent puzzle. 


*  As announced by the NRO and VAFB folks, to general surprise and acclaim. 

** During the classical pre-dusk and -dawn periods when the satellite is 
   illuminated by the sun and the ground is in shadow.  However, work first 
   reported by MIT Lincoln Laboratory, subsequently confirmed by the Soviets 
   and the USAF Phillips lab, and now implemented by Ron Dantowitz at the 
   Boston Museum of Science and Technology shows that daylight detection and 
   imaging of satellites down through v.m. 8 in the visible and IR is quite 
   possible.