RE: NROL-28 launch

From: Bob Christy (
Date: Mon Feb 25 2008 - 18:20:33 UTC

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    You are almost certainly correct. The SDS communications constellation is
    currently up to strength with USA-137, USA-179 and USA-198. The outgoing
    USA-125 (replaced by USA-198) may also still be providing some services.
    These three SDS-3 satellites reach apogee above the Arctic Circle in turns,
    at four hour intervals. Two are available operationally at any one time.
    USA-137 is also synchronised with USA-184, the previous SIGINT launch. This
    is because they both carry an Interim Polar EHF Communications package. It
    is designed for two satellite operation and they reach polar apogee close
    together in time but sufficiently separated to ensure 24 hour coverage. The
    third package is scheduled to launch on the replacement for USA-137. After
    that, the fully-designed Polar EHF system will come on line.
    The differences between Argument of Perigee values between satellites is
    partly what allows these two constellations to work both independently and
    collaboratively at the same time.
    Presumably the new launch is the second in the constellation, following
    USA-184. Ted's estimated element sets suggest that the two RAANs will be
    separated by 90 degrees with the potential to give continuous coverage of
    higher latitudes with two satellies working a six hour shift pattern.
    Bob Christy
    > -----Original Message-----
    > From: Ted Molczan [] 
    > Sent: Sunday, February 24, 2008 4:26 PM
    > To:
    > Subject: NROL-28 launch
    ............I believe that the NRO primary payload is more likely SIGINT 
    > than communications.................
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