fisher@dvinci.DEC (Burns Fisher, MRO3-1/E13, DTN 231-4108) (11/01/84)
>> if the apogee kick motor (of Palapa and Westar) have been fired, this >> would get rid of about...increasing the delta V capability... The AKM were fired several months ago. I believe they were used to circularize the orbits, although they were still high. Perhaps they also fixed the plane. The hydrazine thrusters then lowered the orbit and will be/have been used to slow the spin of the satellites. Burns
karn@mouton.UUCP (11/05/84)
Now that you mention it, I do remember hearing that the apogee kick motors of the two satellites were fired a few months ago. Anybody know the orbital mechanics involved? They must have put most of the delta-V into a "useless" plane change, because only a tiny fraction of the AKM's delta-V would be needed to circularize the orbit. Phil
rjnoe@ihlts.UUCP (Roger Noe) (11/05/84)
I don't really know, but I thought the satellites were left in a 28.5-degree inclination orbit. I thought the apogee kick motor is what put it into an equatorial orbit (as well as circularizing at geosynchronous altitude). I have been under the impression that the PAM-Ds only extended the apogee of the elliptical orbit. Am I off-base? Does the PAM change planes *and* increase apogee and all the AKM does is circularize? I'm fairly certain the AKMs were not fired last February because of the PAM failures. -- Roger Noe ihnp4!ihlts!rjnoe
fisher@dvinci.DEC (Burns Fisher, MRO3-1/E13, DTN 231-4108) (11/07/84)
<sacrificial comment>
Fact:
The AKMs were NOT fired on either Westar or Palapa at their scheduled time
due to the misfire of the PAM first stage. They were fired later to bring
the satellites into a more reasonable orbit, and to safe them for the
retrieval operation. (Part of the retrieval operation involves jamming a
pole up the AKM nozzle to make an attach point...not too safe when it is
full of unburned fuel).
Speculation and Inferance:
Plane changes are notoriously expensive in terms of fuel. Thus it makes
sense to me that the plane change should be accomplished mainly by the
PAM first stage, since that would mean that the first stage would not have to
push all the plane-change fuel up to a 22Kmile apogee. Whatever the case,
of course, the errant satellites could not have been (except by enormous
coincidence) in an equatorial orbit because the first stage failed and the
second stage was not fired as planned.
By the way, isn't the AKM, in this case, a second stage to the PAM, rather
than a built-in part of the comsats?
Burns
UUCP: ... {decvax|allegra|ucbvax}!decwrl!rhea!dvinci!fisher
ARPA: decwrl!rhea!dvinci!fisher@{Berkeley | SU-Shasta}henry@utzoo.UUCP (Henry Spencer) (11/11/84)
> Plane changes are notoriously expensive in terms of fuel. Thus it makes > sense to me that the plane change should be accomplished mainly by the > PAM first stage, since that would mean that the first stage would not have to > push all the plane-change fuel up to a 22Kmile apogee. ... The other side of the coin is that plane changes are much less expensive at apogee, because velocities are lower and hence delta-V for a plane change is lower. My recollection is that orthodox wisdom was "do your plane changes at apogee", but more sophisticated analysis may alter this rule nowadays. > By the way, isn't the AKM, in this case, a second stage to the PAM, rather > than a built-in part of the comsats? As far as I know, the PAM is entirely a single-stage unit. The AKM is a built-in part of the satellite in a sense, although I believe it is often jettisoned after doing its thing. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry