karn@allegra.UUCP (Phil Karn) (02/07/84)
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
9212osd@houxa.UUCP (Orlando Sotomayor-Diaz) (02/07/84)
<>
One thing mentioned in a newspaper about the STS
being able to retrieve one of these satellites:
Even if it could intercept the Westar/Palapa, it could not 'grab' it
because the satellites were not designed to have some
sort of 'handle' to facilitate the operation. Of course,
this could have been a misquote of somebody, as usual.
--
Orlando Sotomayor-Diaz /AT&T Bell Laboratories, Crawfords Corner Road
Room HO-3M-325 201-949-1532 Holmdel, New Jersey, 07733
Path: {{{ucbvax,decvax}!}{ihnp4,harpo}!}houxa!9212osdultra@cmcl2.UUCP (02/07/84)
#R:allegra:-226000:cmcl2:2300002:000:453 cmcl2!ultra Feb 7 11:20:00 1984 There must be a few real NASA people reading this news group. Whoever you are, could you ask management what the realistic possibilities are for recovering these satellites and re-deploying them (as per this note I am responding to?). (I haven't heard the outcome of the MMU spacewalk.) I'm sure we're all curious, and it would also be an interesting experiment in Usenet-to-"real-world" communication. Thanks, Lars Ericson (...cmcl2!csd1!ericson)
jeff@heurikon.UUCP (02/08/84)
Ideas were to:
Change to more "useful" orbit
Send into atmosphere to burn up.
Use Shuttle to fetch, fix and redeploy.
I realize they may have trouble grabbing hold, but
why not use the Shuttle to pick up the satellite(s) and
bring them back to Earth for refitting?
--
/"""\ Jeffrey Mattox, Heurikon Corp, Madison, WI
|O.O| {harpo, hao, philabs}!seismo!uwvax!heurikon!jeff (news & mail)
\_=_/ ihnp4!heurikon!jeff (mail - fast)karn@allegra.UUCP (Phil Karn) (02/08/84)
Actually, I think the biggest obstacle to any kind of shuttle rescue is economic. The satellite owners will get their money out of the insurance companies, so they don't have a lot of incentive. Even if the satellites could be rescued, this would take much time and most of the loss to the owners would already be done in the form of lost revenue - which greatly exceeds the value of the hardware. It could not be done on this mission because of fuel limitations, but it could theoretically be done on future missions with extra OMS tanks. This would mean essentially dedicating an entire flight to the rescue. Also, if the satellites have to be rescued in their current elliptical orbits with a single flight to save costs, the shuttle would have to do two rendezvous operations. Even though the inclinations, apogee and perigee heights are the same, their arguments of perigee (where in the orbit apogee occurs) are most likely different, and maneuvers between these can be expensive of fuel. However, I don't have the orbital elements for the two spacecraft and haven't done the calculations. I wouldn't be suprised if a rescue launch time and orbit could be picked that would allow both satellites to be rescued within the shuttle limits, assuming somebody was willing to pay for the mission. Phil
eder@ssc-vax.UUCP (Dani Eder) (02/09/84)
9 February 1984
One reason the Shuttle can't retrieve the commnications satellites
is there is no place to put them in the cargo bay. Originally, the
satellites were attached to the Star-48 Solid Rocket Motor (a Morton-
Thiokol product). The motor in turn was attached to the PAM-D spin
table. The spin table is what gave the satellites their spin in the
cargo bay before deployment. It consists of a large bearing and a motor.
Now that the solid motor has separated from the satellite, there
aren't the right bolts to tie down the spacecraft.
Think about it, do you want a 1200 pound satellite rattling around
the cargo bay while performing 1.5 gee reentry, 75 degree banks, etc.?
You want it bolted down good.
DaniEder
ssc-vax!eder
Boeing Aerospace Companysew@minn-ua.UUCP (02/09/84)
#R:allegra:-226000:minn-ua:15100002:000:442 minn-ua!sew Feb 9 11:20:00 1984 Grabbing Westar/Palapa seems like the greatest problem. Once it has been grabbed, it can be brought down and refurbished (and wait forever for another shuttle slot). Fixing it on the ground should be rather easy, merely expensive and time consuming ($10M for another launch). Fixing in orbit would be an experiment. There is another alternative: put something in orbit which can push them into position (oops, have to develop it first).