In a message dated 00-06-30 18:08:23 EDT, ronlee@pcisys.net writes: << TDRS-H, 12:56 UT Launch, 30 Jun 2000 30073 x 222 km 1 99999P 00 0XX A 00182.55704398 .00000000 00000-0 00000-0 0 11 2 99999 27.0100 296.9983 6934000 177.3000 0.7370 2.74900000 13 TDRS-H 27668 x 230 km 1 26388U 00034A 00182.67293384 .00036898 00000-0 43796-2 0 27 2 26388 27.0553 295.8641 6748842 178.3667 125.6576 2.99589418 00 CENTAUR R/B 27739 x 231 km 1 26389U 00034B 00182.39695846 -.00147415 00000-0 -17527-1 0 28 2 26389 26.9816 297.0399 6754362 177.2000 188.4752 2.98805543 00 The first elset was the predicted orbit. From first glance it seems like an underburn. As a general question, is it normal for the Centaur to end up with a higher apogee than the payload? Ron Lee >> The under burn I don't know about, but It looks likely. However, it could easily happen that the apogee of the upper stage could be higher than that of the payload. This would depend on the attitude of the upper stage relative to its velocity vector when the collision and contamination avoidance maneuver (CCAM) is made. A CCAM is performed by the upper stage after spacecraft separation for two reasons: 1) to move the upper stage away from the spacecraft to avoid the possibility of inadvertently recontacting it later and, 2) to deplete any remaining propellant in the upper stage tanks to avoid the possibility of an explosion llater and subsequent creation of a debris cloud that could pose a hazard to other spacecraft. The actual inertial atttiude the upper stage assumes to perform the CCAM is dependent on two things: 1) the atttiude of the spacecraft & upper stage at separation and, 2) the upper stage attitude relative to that separation attitude required to minimize spacecraft contamination by the upper stage exhaust products while also providing sufficient delta-v to assure no recontact occurs. Once the upper stage has moved a sufficient distance away from the spacecraft the tanks will be "blown down" to expel any remaining propellant. While in this case it is not known what the appropriate attitudes for these CCAM "burns" were, it doesn't seem unreasonable that the combination of these two maneuvers, with the appropriate attitudes, could result in an upper stage apogee altitude greater than that of the spacecraft. While I don't know if it is "normal", in this case, at least according to my quick "back of the envelope" calculation, the difference in perigee velocity between the two objects amounts to only about 1.4 m/s. It seems entirely possible to me that this small difference could be due to the CCAM. Daryl Bahls "Orbitologist in Residence" 47.44N 122.17W ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Fri Jun 30 2000 - 22:20:29 PDT