USA-125/90028 and NROL-24 - for information

From: Bob Christy (
Date: Sat Dec 08 2007 - 18:04:34 UTC

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    USA-125/90028 is a second-generation SDS satellite. It is a spin-stabilised
    design with a de-spun aerial array.
    Another piece of evidence that the upcoming NROL-24 is a replacement for
    this satellite comes from the fact that the de-spin mechanism of 90028 seems
    to have been turned off quite recently. The array is currently (2007 Dec 7,
    16:00 UTC) rotating once every 19.8s. If it follows the lead of 90004 and
    90020, friction will cause it to spin up and match the body with a rotation
    period near 5s.
    90004 and 90020 each reportedly show visual variability with a 5s component
    in their light curves. 90028 may join them in this.
    The evidence for the spin-up comes from radio observation. It was originally
    reported by Greg Roberts of South Africa 2007 Dec 7 and I confirmed it from
    the UK thanks to Greg's timely 'heads-up'.
    Bob Christy
    Lincoln, UK
    53.2233 deg North
    0.6004 deg West
    Height 59m
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