Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site allegra.UUCP Path: utzoo!watmath!clyde!burl!ulysses!mhuxl!eagle!allegra!karn From: karn@allegra.UUCP (Phil Karn) Newsgroups: net.space Subject: Thoughts on Westar/Palapa Message-ID: <2260@allegra.UUCP> Date: Tue, 7-Feb-84 02:32:49 EST Article-I.D.: allegra.2260 Posted: Tue Feb 7 02:32:49 1984 Date-Received: Thu, 9-Feb-84 03:46:22 EST Organization: AT&T Bell Laboratories, Murray Hill Lines: 58 A few comments and bits of information regarding the Westar/Palapa fiasco. I talked with some of my friends in the satellite business today who have heard some of the details which don't make it through the "noisy channel" known as the media. The "working theory" regarding the PAM failure has to do with an overpressure in the engine caused by a temporarily blocked nozzle. The nozzle could have been blocked by a plug of initiator material which could have become rigid if the temperature was too low. After the engine had burnt for a while, the pressure eventually blew the nozzle apart. Once this happened, the chamber pressure dropped too low to sustain combustion, and the engine "flamed out". It seems there was a minor design change made to both PAMs before this mission, and... Contrary to what you may have heard, it is indeed possible to stop a solid fuel motor once it has started in a vacuum by doing just this - blowing the nozzle off and reducing the chamber pressure. For example, the solid fuel kick motor flown on AMSAT Phase 3-A (the one that was lost in 1980) was originally designed as a terminal vernier for a Titan ICBM. It had a deliberate "thrust termination feature" which involves blowing off the nozzle - needless to say, we didn't need this feature. Western Union (and the Indonesian government, assuming their satellite is in the same condition as Westar) has several options. Westar has a full load of hydrazine and, presumably, a good apogee kick motor. With these they could: 1. Circularize the orbit at its apogee altitude of 750 miles. It would be stable here indefinitely, but not very useful for communications. 2. Fire the apogee kick motor to place the satellite in a highly elliptical orbit resembling, interestingly enough, that of AMSAT Oscar-10. Here someone could theoretically get a few hours per day use out of the satellite while at apogee, where it would move slowly enough to be tracked. 3. Upon request of NORAD to "keep the skies clean", they could fire the kick motor to cause the satellite to re-enter the atmosphere and burn up. Obviously, all of these suggestions remove any possibility of shuttle retrieval. However, if I look at my STS user's manual, I note that the shuttle is in fact capable of reaching fairly high apogees in ELLIPTICAL orbits. With integral tanking, it could carry a full load to a 28 deg 185 x 900 km orbit assuming that the deorbit burn is done from apogee. With several OMS kits (extra fuel tanks) in place of payload, it could reach 1500 km (1 tank) 2250 km (2 tanks), etc. On the other hand, it would be much easier if the satellites could be dropped back to their circular 185 km orbits just before retrieval. I don't know if there is enough hydrazine on board to do that. In any event there would be a LOT of practical problems (how do you grab the satellite, reattach a new PAM, refuel the hydrazine tanks, and re-deploy the satellite when it wasn't designed for this kind of operation?) Still makes an interesting problem for speculation, and at a total stake of $200 M, who knows? They might just try it. Phil