RE: 95-66A problem solved

From: Ted Molczan (
Date: Sun Sep 19 2004 - 16:17:59 EDT

  • Next message: Steve Newcomb: "8539 obs sept 20"

    David Brierley wrote:
    > Last night I observed 95-66A on two transits, and have now 
    > been able to find my positions of September 15 which I'd 
    > begun to think were of an aircraft.
    > Here are the observations, and an orbit with unchanged i and 
    > ndot which fits them.  I'll leave it to others to work out 
    > what the change means!
    > P.S. Just received Peter Wakelin's observation (not used yet).
    I have added Peter's obs of last night, and his corrections of Sep 16 UTC.
    I find that the spacecraft has manoeuvred to decrease its inclination by nearly
    0.2 deg:
    USA 116         15.0  3.0  0.0  5.1 v
    1 23728U 95066A   04263.06275380  .00002026  00000-0  10662-3 0    05
    2 23728  97.8108  30.1205 0286752 145.2940 216.7362 14.86568287    05
    Arc 2004 Sep 15.04 - 19.08, WRMS residuals = 0.019 deg
    David, I find that your first obs of Sep 19 UTC is about 1.18 s early. Could you
    have made a whole second error in reducing the time?
    The RAAN of the new orbit precesses at the rate of +0.98428 deg/d, very nearly
    the "exact" sun-synchronous rate of +0.985647 deg/d.
    At the epoch of the latest pre-manoeuvre elset, 04253.97534125 (Sep 09 UTC), its
    rate of precession was +1.00894 deg/d, and its RAAN was 21.1867 deg. The
    manoeuvre probably occurred soon after that epoch, at about which time the
    argument of perigee was near the equator, consistent with the circumstances of
    similar manoeuvres by spacecraft of this type.
    95066A's orbital plane had been drifting eastward relative that of 01044A /
    26934, which had replaced it as the primary eastern spacecraft in 2001 October.
    The manoeuvre to place 95066A in a more nearly precise sun-synch orbit, more or
    less halted this eastward drift, such that it will now remain approximately 17.8
    deg east of 01044A. 
    Presumably, this optimizes the overall coverage of the constellation. It also
    suggests that significant life remains in 95066A's extended mission. Now 8.80
    years old, it is the second longest lived spacecraft in the series; the record
    of 9.94 years is held by 84122A / 15423, which was de-orbited in 1994 Nov.
    Ted Molczan
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