RE: NOSS 3-4A and C have been refired

From: Ted Molczan (ssl3molcz@rogers.com)
Date: Mon Jun 23 2008 - 19:50:16 UTC

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    David Brierley wrote:
    
    > Although Mike McCants has new orbits for 07-27A and C, noone 
    > seems to have commented on the major refiring that took place 
    > on 2008 June 10, raising the mean motion from 13.4122 to 
    > 13.4087. I observed the pair early on June 10 (UT).  The 
    > following evening Mike Waterman saw them running 2.4 seconds 
    > late.  The change means that they were about 4 minutes late 
    > last night (June 22/23) when I oberved them on two transits.
    > Any comments?
    
    The first three of the third generation NOSS took about 4 weeks after launch to
    manoeuvre to nearly their intended orbit, followed by several months of drift,
    after which they manoeuvred to match the mean motion of the other operational
    first, second and third generation spacecraft.
    
    Due to the problem with their Centaur, the NOSS 3-4 pair entered too low an
    orbit, which was remedied by making numerous small manoeuvres over a period of
    about six months. From mid-February of this year until late May or early June,
    they drifted with a mean motion of 13.4126 rev/d; since then, they appear to
    have been easing their mean motion downward to match the constellation's
    operational value, currently near 13.4051 rev/d.
    
    My guess is that the several months of drift of new spacecraft, is to adjust
    their spacing within the constellation, to optimize coverage.
    
    Ted Molczan
    
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