Shenzhou 1 made a small manoeuvre

From: Ted Molczan (molczan@rogers.com)
Date: Fri Oct 17 2003 - 19:02:44 EDT

  • Next message: Björn Gimle: "Re: PSLV-6"

    I do not claim to have read all of the available research on the flight of
    Shenzhou 1, but all of the reports I have seen state that Shenzhou 1 did not
    manoeuvre. I am now convinced that it did make a small perigee-raising manoeuvre
    very near the time of its 5th passage through apogee, about 6 h 54 m after
    launch.
    
    This finding builds on my post earlier today, in which I identified the orbital
    elements of the spacecraft and rocket body:
    
    http://satobs.org/seesat/Oct-2003/0194.html
    
    The clue was the spacecraft's perigee height, which was about 8 km higher than
    that of the rocket. Indeed, it was higher than the perigee of any of the initial
    orbits of the five Shenzhou launches to-date. And it was not a fluke in the
    elements - the elements of its orbital module had the same perigee height.
    
    Here are USSTRATCOM's earliest accurate elsets for both objects. Note that the
    spacecraft was miss-tagged as the rocket (there was a lot of miss-tagging of
    pieces from that mission):
    
    Shenzhou 1                                               214 X 341 km
    1 25957U 99061B   99324.60834382  .00606827  83585-5  56001-3 0    61
    2 25957  42.5956  23.0886 0095292 134.3737 226.4995 16.02245812    78
    
    Shenzhou 1 2nd stage                                     206 X 335 km
    1 25957U 99061B   99324.48312468  .01120080  83940-5  83715-3 0    29
    2 25957  42.5973  23.8808 0096522 132.0774 228.8342 16.04716322    53
    
    To accurately determine the time of the manoeuvre, I needed to know the
    spacecraft's pre-manoeuvre orbit, but USSTRATCOM did not issue any elements
    until well after the manoeuvre, so I estimated it with the help of Shenzhou 2's
    initial elements.
    
    First, I selected the earliest reliable elements of Shenzhou 2 and its rocket:
    
    Shenzhou 2                                               207 X 344 km
    1 26664U 01001A   01010.08344381  .00542499  83779-5  42525-3 0    38
    2 26664  42.5817 353.3256 0103319 131.5795 321.3617 16.02988096    66
    
    Shenzhou 2 2nd stage                                     207 X 338 km
    1 26665U 01001B   01010.19185864  .00749237  83820-5  57084-3 0    21
    2 26665  42.5746 352.6196 0098604 132.2840 228.6444 16.04137340    70
    
    Next, I propagated both orbits back to their first ascending node after launch:
    
    Shenzhou 2 propagated to 1st asc node                    207 X 346 km
    1 76664U          01009.75598016  .00542499  83779-5  42525-3 0    06
    2 76664  42.5817 355.4101 0104781 129.1600 231.8639 16.02632799    04
    
    Shenzhou 2 2nd stage propagated to 1st asc node          207 X 341 km
    1 76665U          01009.75596643  .00749237  83820-5  57084-3 0    03
    2 76665  42.5746 355.3987 0101290 129.0568 231.9371 16.03484167    00
    
    The difference between these elements is due almost exclusively to the firing of
    the 2nd stage rocket's separation at orbit insertion. It is reasonable to assume
    that nearly the same differences occurred on all of the Shenzhou launches;
    therefore, I used the information to construct an estimate of Shenzhou 1's orbit
    at first ascending node.
    
    First, I propagated the 2nd stage to its 1st ascending node:
    
    Shenzhou 1 2nd stage propagated to 1st asc node          206 X 341 km
    1 75957U          99323.98507110  .01120080  83940-5  83715-3 0    01
    2 75957  42.5973  27.0566 0101110 128.3912 232.6095 16.03600602    02
    
    Then, I modified its epoch, rate of decay, eccentricity and mean motion to
    account for the major differences between the orbits:
    
    Estimated Shenzhou 1 at 1st asc                          206 X 346 km
    1 75956U          99323.98508483  .00910000  83940-5  70000-3 0    05
    2 75956  42.5973  27.0566 0104781 128.3912 232.6095 16.02749110    05
    
    This estimated pre-manoeuvre elset is directly comparable to USSTRATCOM's one
    post-manoeuvre elset (miss-tagged as the rocket body):
    
    Shenzhou 1                                               214 X 341 km
    1 25957U 99061B   99324.60834382  .00606827  83585-5  56001-3 0    61
    2 25957  42.5956  23.0886 0095292 134.3737 226.4995 16.02245812    78
    
    Comparing their relative motion, I found that the pre and post-manoeuvre orbits
    nearly intersected within a few minutes of the 5th apogee, about 6 h 54 m after
    launch, which was the time of the manoeuvre. The effect of the manoeuvre was to
    raise perigee by 8 km.
    
    The timing of Shenzhou 1's small manoeuvre seems significant, because at this
    same point in their missions, Shenzhou's 3, 4 and 5 made larger manoeuvres to
    circularize their orbits.
    
    Why was Shenzhou 1's manoeuvre so much smaller? Was it intended only as a brief
    test of the propulsion module, or was it an aborted circularization manoeuvre?
    If the latter, then the problem would not appear to have been very great, given
    that the propulsion system successfully de-orbited the spacecraft later the same
    day.
    
    Ted Molczan
    
    
    -----------------------------------------------------------------
    To unsubscribe from SeeSat-L, send a message with 'unsubscribe'
    in the SUBJECT to SeeSat-L-request@satobs.org
    List archived at http://www.satobs.org/seesat/seesatindex.html
    



    This archive was generated by hypermail 2b29 : Fri Oct 17 2003 - 19:06:00 EDT