RE: X-37B updated orbit

From: Ted Molczan (
Date: Sat Aug 21 2010 - 15:06:04 UTC

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    Adding Brad Young's observations of this morning, to Greg Roberts' of Aug 19 UTC, results in a more
    accurate mean motion. The object was nearly 3 min late this morning, relative the preliminary
    elements I posted yesterday. The updated elements should be accurate to within about 10 s, per day
    since epoch.
    The following elements are based on the assumption that inclination and eccentricity were unaffected
    by the manoeuvre:
    OTV-1                                                    430 X 447 km
    1 36514U 10015A   10233.44511480  .00000000  00000-0  00000-0 0    05
    2 36514  39.9851 336.7418 0012533 356.1476   3.9234 15.43353074    00
    Arc 20100819.75-0821.46 WRMS resid 0.049 totl 0.024 xtrk 
    I am fairly confident in the inclination, but in some doubt about the eccentricity. If the intent of
    the change in orbit was to raise the altitude, and to retain the original eccentricity, then there
    would have been two manoeuvres: one at perigee to raise the apogee, and one at apogee to raise the
    perigee; however, the data may be hinting at a single manoeuvre, at apogee, raising the perigee such
    that it became the new apogee:
    OTV-1                                                    413 X 465 km
    1 36514U 10015A   10233.44517289  .00000000  00000-0  00000-0 0    08
    2 36514  39.9851 336.7626 0037995   3.5768 356.5305 15.43259984    08
    Arc 20100819.75-0821.46 WRMS resid 0.026 totl 0.005 xtrk
    Brad's pass was nearly overhead, so he was within the plane of the orbit, which helped nail down the
    inclination and plane (RAAN), but was not ideal for resolving the eccentricity and argument of
    perigee. Barring any further manoeuvres, additional observations over the next few days will resolve
    the eccentricity question.
    The above solutions move my estimate of the date of the manoeuvre(s) to Aug 9, between 17 h and 21 h
    Observers may wish to use both of the above, to get an idea of the range of possible paths the
    object may follow.
    Ted Molczan
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