Alan Boyle, of MSNBC reports that the possibility of using a lunar gravity assist to manoeuvre Arabsat 4A to a useful GEO orbit is under consideration: http://www.msnbc.msn.com/id/11594666/#060301d As the article reminds us, this type of rescue was performed with Asiasat 3 in 1998. Arabsat 4A's present orbit is about 51.5 deg, 500 X 14700 km. Raising its apogee to the radius of the moon's orbit requires a delta-V of about 1300 m/s. Arabsat 4A has plenty of delta-V available in the propellant that normally would have been expended to manoeuvre from its intended GTO (geostationary transfer orbit): 14.2 deg, 3150 x 35785 km, to a zero deg, 35785 km circular orbit. A circularization burn, followed by an inclination change to zero deg inc, would have totalled 1968 m/s. That may be oversimplifying the actual manoeuvres, but it would appear that it has more than enough delta-V available to get to the moon. Additional delta-V could be obtained by using some of its station-keeping propellant. I imagine it may be months before the rescue will attempted; in the meantime, it may be worth the occasional optical observation to see whether or not, and how, the spacecraft is maintaining attitude control. Ted Molczan ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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