SZ 4 recovery - competition time !

From: Phillip Clark (
Date: Sat Jan 04 2003 - 13:45:29 EST

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    Sven Grahn posted an estimate of the SZ 4 recovery time tomorrow, 11.04 GMT
    I think (I have deleted your e-mail Sven !).
    Well, this could be interesting.   I am using the SZ 4 element set with an
    epoch of Jan 4.458, and that gives a final equator crossing time of around
    10.39 GMT.   Landings for SZ 2 and 3 came 35-36 minutes after the final
    equator crossing, so I am estimating a landing time tomorrow of 11.15 GMT.
    Sven, have you dropped 10 minutes in your figures ?
    Regarding the SZ 4 high orbit, way back in 2000 as an exercise I ran some
    software to calculate the repeating orbit patterns for SZ orbits, and for a
    31 circuit repeater at 42.4 minutes the repeating orbit period is 91.212
    minutes.   Using USSPACECOM data, SZ 4 manoeuvred straight into this orbit,
    and the decay rate (or lack of, compared with SZ 2 and 3) makes me wonder
    whether the Chinese are using regular low thrusts to maintain altitude.
    There was a manoeuvre announced for January 2nd, but the change in altitude
    was only of the order of 1-2 km - not 5-10 km as seen on the earlier
    Also be interesting to see what happens to the SZ 4 orbital module.   On SZ
    2 the manoeuvre was the day after landing and was to a 388-404 km orbit: on
    SZ 3 the manoeuvre was within a few hours of the landing and was to a much
    lower 353-358 km orbit: only about 3.5 weeks later did the module go up to
    382-388 km.
    Phillip Clark
    Phillip S Clark     Molniya Space
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    Publisher - Worldwide Satellite Launches
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