Tiangong Orbit Change Signals Likely Date for Shenzhou 10
by Robert Christy FBIS
Scarborough, UK (SPX) Sep 04, 2012
August 30, Tiangong 1's controllers raised its orbit by 11 kilometres, indicating that a target date for the Shenzhou 10 mission has probably been set. As August 30 dawned, Tiangong 1 was following a 344 x 356 kilometre orbit at 42.8 degrees inclination. Soon after noon UTC, a firing of its thrusters raised perigee to create a new apogee. The orbit became 355 x 366 kilometres at the same inclination as before.
It was back to the same height that had been produced by a similar manoeuvre after Shenzhou 9 departed. A history of Tiangong's orbital manoeuvres can be seen here.
Before this latest adustment, Tiangong's orbit decay would have brought it back to the 330 kilometer Shenzhou operating altitude before the end of 2012. Controllers had been experimenting for a few weeks with thruster firings to control Tiangong's rate of decay very precisely.
It seemed to be heading for a rendezvous with Shenzhou 10 around November 26 during one of two launch windows covering the last few days of November and the first couple of weeks in December.
It was probably a 'holding pattern' based on an estimate of how long it would take to review Shenzhou 9 and prepare a new vehicle for launch with a crew.
Plans may now have firmed up a little with an aim to fly the mission early in the new year. Tiangong 1's new orbit will decay to Shenzhou altitude early February, during the next pair of launch windows that extend through January to mid-February. A current estimate of the likely Shenzhou launch date can be found here.
Shenzhou 10's mission is unlikely exceed Shenzhou 9's by anything significant in duration.
Where Shenzhou 9 was used to test and develop the logistics and mechanics of getting a crew aboard a space station, the next flight has the aim of introducing operational routines and simulating space station life.
It is set to be the final mission to Tiangong 1 which will reach the end of its two year rated lifetime next October.
Its docking unit is rated for use on six occasions, and four of them have already passed with two dockings each by Shenzhou 8 and Shenzhou 9.
Tiangong 1 will then steer itself to a safe re-entry and China will turn its attention to Tiangong 2. The new laboratory will be used to build more experience of space station operation so China is ready for the challenge of operating the 20-tonne core module of a more-permanent outpost towards the end of the decade.
Robert Christy has been analysing and documenting space events since the early 1960s and currently provides information via his web site.