rjnoe@riccb.UUCP (Roger J. Noe) (09/17/85)
> . . . Westar-6 and Palapa-B had PAM failures, and > PAMs are unnecessary with Ariane because the latter puts you directly in a > 35800 x 200 km geostationary transfer orbit. Only one additional burn > is needed to reach a circular geostationary orbit. Right, but the vast majority of failures to get satellites on station are due to a problem while the payload is still within the launcher. > What's important when it comes to insurance rates is the overall probability > of the spacecraft reaching its proper orbit and actually doing its job. It > doesn't matter whether the satellite goes down in the Atlantic, gets stuck > in a useless LEO, or arrives at GEO only to die (like the recently launched > Syncom). Quite correct. But as I pointed out, both historical evidence and recent experience demonstrates that most things go wrong before the launcher has released its payload. > When it works, Ariane is a much "friendlier" launcher for communications > satellites than the Shuttle. The advantages you note for ELVs in general and Ariane in particular are granted. But the operative phrase here is "when it works." > . . . you can use a smaller apogee kick > motor, allowing increased payload weight. Only to a limit. There are a lot of satellites that simply cannot be lifted (to GEO transfer orbit) by Ariane, Delta, Atlas, or even Titan because of their maximum capacity. But since you were probably intending this to apply strictly to communications satellites (of which the HS-376 type is typical) this point is moot. > . . . Ariane deploys you immediately > after reaching orbit; the Shuttle holds onto you for a day or two during > which time you have no solar power, attitude control or control over the > thermal environment. You don't need it when you're safely tucked away in the womb of the shuttle cargo bay. Ariane can do no such thing because it does not provide as "friendly" an environment as the shuttle does. > It has been sheer luck that there have been three opportunities for in-space > salvage or repair of satellites launched on the shuttle whose upper stage > engines failed. You're right - it was sheer BAD luck for the shuttle that these "oppor- tunities" occurred. People tend to blame NASA and the shuttle even when one of its contractors, customers, or the military screws up one of the motors for which NASA has no responsibility or control. Many saw the initial failure of Westar VI and Palapa B-2 as a shuttle problem. Of course, SMM (Solar Maximum Mission) was a complete success since it was not deployed by the shuttle. There are going to be a LOT of similar events in coming years involving retrieval, repair and/or refueling of satellites in LEO. > . . . Once the satellite leaves the rather narrow set of orbits > that are accessible to the Shuttle, it's on its own. If it had been the > apogee kick motors that failed on Westar, Palapa or Syncom, there would have > been no chance for in-orbit repair, just as there is no chance of an > in-orbit repair on the one that was just launched. > > Phil All of which is true of expendable launchers as well as the shuttle. No difference at all. So what's your opinion, Phil (and anyone else), do you think the latest Ariane failure will affect insurance rates and how? Will this apply just to Ariane or to all expendable launchers? How will it affect the insurance rates of satellites launched by the shuttle? What really gets me is that ESA gets to keep all its fee for blowing up its payload. That's something NASA would never do with the shuttle. -- Roger Noe ihnp4!riccb!rjnoe
karn@petrus.UUCP (Phil R. Karn) (09/18/85)
> Right, but the vast majority of failures to get satellites on station are > due to a problem while the payload is still within the launcher. True. What do you consider to be the "launcher"? Does this include problems with the AKMs? My point was just that you should compare apples with apples by considering the PAMs to be part of the "shuttle launcher" when comparing it to Ariane. > Only to a limit. There are a lot of satellites that simply cannot be lifted > (to GEO transfer orbit) by Ariane, Delta, Atlas, or even Titan because of > their maximum capacity. But since you were probably intending this to apply > strictly to communications satellites (of which the HS-376 type is typical) > this point is moot. F'rinstance? Both Shuttle and Ariane (with its "SYLDA" - SYsteme Lancement Duel Ariane) are usually flown these days with multiple payloads. Very few communications satellites require (or can afford!) the full capacity of either a Shuttle or Ariane. > You don't need it when you're safely tucked away in the womb of the shuttle > cargo bay. Ariane can do no such thing because it does not provide as > "friendly" an environment as the shuttle does. Not quite. Read some of the back issues of AW&ST regarding the hassles SBS went through as the pioneer Shuttle customer. A major problem was the nasty thermal environment in the cargo bay. A payload like a communications satellite can withstand only brief periods (minutes to hours) in continuous shadow or sunlight. Beyond that, you start melting solar arrays or freezing batteries. The "baby buggy" shade now used with all HS-376-class payloads was the result. It has to be opened for the bay doors to close (i.e., during launch), but then it has to be closed quickly after achieving orbit in order to protect the payload. As you know, this was a problem on the last flight with the Australian satellite and it had to be deployed early. My question is, why can't they just plan to deploy satellites early in the first place and get it over with? Once a satellite like the HS-376 is spun up and deployed (with the proper attitude) it is quite able to take care of itself. Ariane gets you spun up and deployed at the proper attitude (e.g., normal to the sun line) within 15 minutes of leaving the pad, and by then the satellite temperature has hardly had a chance to change much from the nice 20C given it by the ground purge system. (more to follow) Phil
karn@petrus.UUCP (Phil R. Karn) (09/18/85)
> You're right - it was sheer BAD luck for the shuttle that these "oppor- > tunities" occurred. People tend to blame NASA and the shuttle even when one > of its contractors, customers, or the military screws up one of the motors > for which NASA has no responsibility or control. Very true! Except for the fact that you wouldn't have needed a PAM had you not been riding on the Shuttle, you're right. > So what's your opinion, Phil (and anyone else), do you > think the latest Ariane failure will affect insurance rates and how? Will > this apply just to Ariane or to all expendable launchers? How will it > affect the insurance rates of satellites launched by the shuttle? Obviously they won't go down as a result of the failure. But 10 straight successes is nothing to sneeze at; even Delta had a failure now and then. You can't get a real idea of the reliability of a launcher until its had plenty of flights. The real problem is that because of the economy of scale in launchers (big launchers are in general cheaper per kg than small launchers) people are putting lots of eggs into single baskets, and the pool of insurance money is becoming VERY strained. I don't see any easy way out of this for the near term. > What really gets me is that ESA gets to keep all its fee for blowing up its > payload. That's something NASA would never do with the shuttle. This is only partially true. According to the STS user's manual, NASA gives non-government users a "reflight guarantee". This is not insurance on the payload against a launch failure, but provides for another launch opportunity assuming that the previous payload is returned in launch condition or a replacement payload is provided by the user. This is a nice advantage of flying with the shuttle, although of course PAM failures aren't covered. The fact that the Shuttle is a lot more likely than the Ariane to come back in flyable shape even after a malfunction is what makes this guarantee possible. I admit I'm a bit down on the Shuttle because of my own experiences on the PACSAT project. We hams got spoiled by our previous experiences on expendable launchers like Delta and Ariane (except for Phase-3A, which got dumped in the drink!) On the pad we got battery charging and a telemetry/command umbilical; once in orbit we got spun up and deployed within a fraction of an orbit. There was no problem in flying a hypergolic kick motor on Oscar-10 once we convinced ESA that "we hams" knew what we were doing. This is out of the question on the shuttle, where it is said that the mass of the safety qualification paperwork is always equal to or greater than the mass of the spacecraft. Almost all of our efforts so far in PACSAT have concentrated on finding ways to do things that are made necessary only because of the shuttle (keeping batteries up without external charging during a 4-month wait on the pad, surviving -100 to +130C temperature swings for a few days in orbit in a GAS can, maneuvering into a stable orbit with a "provably safe" propulsion system, and so on.) The Shuttle is a magnificent vehicle for manned space activities. I believe the jury is still out on whether the Polish (Belgian, Chelmian, whatever) Bomber is the best way to launch unmanned spacecraft, though. Phil
wmartin@brl-tgr.ARPA (Will Martin ) (09/19/85)
Re your question about "why can't they just plan to deploy satellites early in the first place and get it over with?" -- I, too, want to know the answer to that! I include below an extract of a posting I made right after seeing the news about the sunshade problem on the last mission. There was never any answer to this query posted that I ever saw. Old posting extract: From postnews Wed Aug 28 16:41:01 1985 Subject: Satellite deployal and bad-weather launch Newsgroups: net.columbia Distribution: net The TV news stories on the Australian satellite said that, due to the jammed sunshield and the consequent overexposure to sunlight, that satellite was deployed a day ahead of time. My question is: if it could be launched when it was -- that is, there was an earlier launch window for the required orbit -- why was it planned to delay the extra day in the first place? I would think that it would be in everyone's best interests to get those satellites out of the cargo bay and into orbit ASAP. What, if anything, was changed by deploying this satellite "a day early" -- were some checkouts rushed, or other experiment start-ups delayed, or other undesireable effects incurred by this action? [... "marginal weather" portion deleted here ...] Regards, Will Martin UUCP/USENET: seismo!brl-bmd!wmartin or ARPA/MILNET: wmartin@almsa-1.ARPA *** End of old posting ***
eder@ssc-vax.UUCP (Dani Eder) (09/25/85)
In response to Phil Karns question about why the Shuttle can't deploy
comsats immediately like an expendable:
Communications satellites live in Geosynchronous Orbit, where they
orbit the earth every 24 hours. Since the earth also rotates every 24
hours, the satellite appears to hang over a single spot on earth. To
get to that specific location as quickly as possible, so as to start
producing revenue for the satellite owner as soon as possible, you want
a transfer orbit that intersects your destination.
You start a satellite on it's way to Geosynchronous one-half orbit
earlier in low earth orbit. The shuttle orbit , and hence the initial
satellite orbit, remains fairly stationary in inertial space, inclined
28.5 degrees to the equator. The transfer orbit is attached to the destination
in GEO, which is moving around once per 24 hours. Thus once every 24
hours there is an opportunity to deploy and inject a comsat.
This is why comsats are generally launched one per day starting
with the first mission day. If the satellites are spaced fairly far
apart in GEO, it would be possible to launch two or more in one day.
The alternative, which takes longer, is to launch the satellite as
soon as possible. The satellite then arrives at the wrong place in
GEO> YOU MAKE your orbit slightly un_synchronous< and drift to the
correct location> this takes weeks>
DANI EDER ??? boeing >> ssc_VAX!eder