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