DIETZ@slb-test.CSNET ("Paul F. Dietz") (10/18/86)
The NY Times reported today (10/16) that engineers at Comsat Corp. have developed a technique for reducing the fuel consumption of comsats by up to 90%. The technique can be applied remotely to satellite already in orbit. Currently, on-board thrusters on comsats in GSO are used to counter perturbations induced by the moon. These perturbations cause the orbit to become nonequatorial, moving the satellite's footprint north or south. The new technique uses the thrusters to tilt the satellite so the footprint remains fixed. The new technique will require changing the pointing hardware on some ground dishes, since a satellite in a geosynchronous but nonequatorial orbit will bob up and down once a day. This technique has not been used before because electronic failure had been thought to limit satellite lifetime. Experience has shown, however, that the electronics is more reliable than was first thought. It is estimated that this change will double satellite lifetime.
karn@ka9q.bellcore.com (Phil Karn) (10/20/86)
> The NY Times reported today (10/16) that engineers at Comsat Corp. > have developed a technique for reducing the fuel consumption > of comsats by up to 90%. The technique can be applied remotely to > satellite already in orbit. I'm puzzled by this move on the part of Comsat. It has been well known for many, many years that North/South stationkeeping is much more expensive in terms of fuel consumption than East/West stationkeeping, and that a satellite that foregoes N/S thrusting will describe a "figure 8" orbit whose inclination varies cyclically with time due to lunar and solar perturbations. However, they're claiming that this is a new, novel and PATENTABLE idea. I hope there's something more to it than I've heard so far, since AMSAT has been saying (in print) for several years now that we would only do E/W stationkeeping on our Phase 4 amateur birds in order to minimize hydrazine requirements. The only problem I can see with this technique is how they are going to keep the antenna footprint in a fixed position given a spinning spacecraft. I guess they could reorient the spin axis so that it's always normal to the orbit plane. This would cause a 24-hour cycle in which the footprint would "rotate" at the equator crossings. With a three-axis stabilized (i.e., non-rotating) spacecraft, however, this could be avoided. Phil
dbb@aicchi.UUCP (Burch) (10/21/86)
This is also good for HBO et. al., since home dishes are too simple to modify for the figure 8 tracking that would be required... All that could be hoped for is that the focus might be made sloppy enough to keep the satellite in view, at the expense of gain. -- -David B. (Ben) Burch Analysts International Corp. Chicago Branch (ihnp4!aicchi!dbb) "Argue for your limitations, and they are yours"