keithl@loop.UUCP (Keith Lofstrom) (09/20/89)
Why three 2 MegaNewton SSME's rather than one 6MN engine? Back when NASA was choosing contractors for the SSME, Pratt & Whitney had a 2MN LH/LOX engine on the shelf; NASA went with Rocketdyne for political reasons. As long as Rocketdyne was developing a new engine from scratch, why did they choose three engines rather than one? While there might be some cost savings early in the development of a smaller engine, there seem to be significant operational advantages to one large one: 1) Chamber pressure - There's room back there for a 6 meter nozzle, rather than three 2.4 meter nozzles. For the same thrust, you could run at half the chamber pressure and pump pressure. The turbopumps are running at engineering limits as it is, they have to be changed out after each mission, and there has been blade cracking (a failure here could destroy the shuttle). I'm told that these pumps are running at 3 times the pressure of any previous effort. This sounds like a catastrophe waiting to happen. 2) Less things to fail - with one engine rather than three, even with the same chamber pressure, there is a 3x improvement in reliability. 3) It is probably cheaper to change out one large engine than three smaller ones. Heavier lifting equipment is required, but it's easier to use what you've got if you can come in from all sides. Well, I could run on, but perhaps someone with more knowledge of rocket engines, or the history of SSME development, can pick up from here. It's probably silly to reinvent the wheel, but it's good to know the right way to do things when the time comes to do it again. -- Keith Lofstrom keithl@loop tektronix!psueea!qiclab!loop!keithl Launch Loop, P.O. Box 1538, Portland, Oregon 97207 (503)-628-3645
rubinoff@linc.cis.upenn.edu (Robert Rubinoff) (09/22/89)
Well, for one thing, it means that if one engine fails, the other two may still be able to get the shuttle to orbit. This has in fact happened at least once. With one engine, if it cuts out, you've got yourself a sub-orbital glider. In general redundant systems are a good idea. The flip side is that you may have three times as many possibilities of catastrophic failure, but that's not a trade-off I can make judgements on. Robert
ccsupos@prism.gatech.EDU (SCHREIBER, O. A.) (09/22/89)
In article <24@loop.UUCP> keithl@loop.UUCP (Keith Lofstrom) writes: > >Why three 2 MegaNewton SSME's rather than one 6MN engine? > Would an F-1 have been possible? Less specific impulse but denser fuel. >Back when NASA was choosing contractors for the SSME, Pratt & Whitney >had a 2MN LH/LOX engine on the shelf; NASA went with Rocketdyne for >political reasons. I read about that too. For what market did P&W intend its product or why was it ready so much earlier than Rocketdyne's? Also, about the shuttle, I have an issue of "Discover" (end of '85) that deals with the design history of the shuttle. In addition to the early horizontal takeoff and landing configurations which make sense to me (less thrust necessary on the vehicle) my attention was caught by the mention that in '74 two features were dropped from the design: Air breathing engines for rentry flight and Abort rockets. If the orbiter weighs 80 tons and one has two 50 tons abort rockets to lift away the orbiter from the rest of the stack in case of SRB ("major") malfunction during ascent I think it would have been worthwhile to keep that feature in the design of what was supposed to become a routine access to space vehicle. I must add that on the drawing of 'Discover', the two rockets were positioned at the trailing edge of the wing of the Orbiter. After all, all the early manned space vehicle had abort rockets albeit in the form of escape towers. It seems to me that you don't just design a manned space vehicle by being satisfied with a percentage of catastrophic failure low enough, you ought to supply a backup escape system at least in the most traumatic sequence of flight (vertical ascent). About the Challenger accident, the public was struck by the fact that once the problem occured, the astronauts could not do anything and the press, long after Challenger exploded kept on speculating on how long some of the crew members stayed conscious. Sure, there was nothing that could be done about the shuttle to prevent the loss of the crew or may be there was...back in 1974 when they drop the escape rockets from the design. By the way, the Europeans quickly put an escape system in the planning of their Hermes project soon after the accident whereas they had not planned for any prior to that. -- Olivier Schreiber (404)894 6147, Office of Computing Services Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{allegra,amd,hplabs,seismo,ut-ngp}!gatech!prism!ccsupos ARPA: ccsupos@prism.gatech.edu
kcarroll@utzoo.uucp (Kieran A. Carroll) (09/22/89)
>keithl@loop.UUCP (Keith Lofstrom) writes: > >Why three 2 MegaNewton SSME's rather than one 6MN engine? >Back when NASA was choosing contractors for the SSME, Pratt & Whitney >had a 2MN LH/LOX engine on the shelf; NASA went with Rocketdyne for >political reasons. As long as Rocketdyne was developing a new engine >from scratch, why did they choose three engines rather than one? > One good reason for multiple engines is in order to have a "one engine out" capability --- that is, retaining the ability to attain orbit even if an engine fails sometime during launch. This capability was demonstrated on one of the early shuttle flights, when an apparent fault in one engine forced it to be shut down early; the remaining two engines were sufficient for an abort-to-orbit, as I recall. -- Kieran A. Carroll @ U of Toronto Aerospace Institute uunet!attcan!utzoo!kcarroll kcarroll@zoo.toronto.edu
henry@utzoo.uucp (Henry Spencer) (09/22/89)
In article <14647@netnews.upenn.edu> rubinoff@linc.cis.upenn.edu (Robert Rubinoff) writes: >Well, for one thing, it means that if one engine fails, the other two may >still be able to get the shuttle to orbit. This has in fact happened at >least once. With one engine, if it cuts out, you've got yourself a sub-orbital >glider. Or worse. There are points during the shuttle's ascent where a multi-engine failure is guaranteed fatal -- there is no possibility of making orbit and the altitude/speed combination is wrong for a safe reentry. -- "Where is D.D. Harriman now, | Henry Spencer at U of Toronto Zoology when we really *need* him?" | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
tmurphy@wpi.wpi.edu (Tom [Chris] Murphy) (09/29/89)
In article <1979@hydra.gatech.EDU> ccsupos@prism.gatech.EDU (SCHREIBER, O. A.) writes: >In article <24@loop.UUCP> keithl@loop.UUCP (Keith Lofstrom) writes: > --- >albeit in the form of escape towers. It seems to me that you don't >just design a manned space vehicle by being satisfied with a >percentage of catastrophic failure low enough, you ought to >supply a backup escape system at least in the most traumatic >sequence of flight (vertical ascent). It seems to me that manned aircraft are designed exactly like this, by keeping a failure rate low. Perhaps this is a bad approach, but if it's good enough for commercial aircraft, it should be valid for spacecraft as well. Thomas C. Murphy Worcester Polytechnic Institute CAD Lab Internet: tmurphy@wpi.wpi.edu tmurphy@zaphod.wpi.edu BITNET: TMURPHY@WPI BIX: tmurphy CompuServe: 73766,130 If the Universe is constantly expanding, why can't I ever find a parking space?
ccsupos@prism.gatech.EDU (SCHREIBER, O. A.) (09/29/89)
In article <4337@wpi.wpi.edu> tmurphy@wpi.wpi.edu (Tom [Chris] Murphy) writes: >>albeit in the form of escape towers. It seems to me that you don't >>just design a manned space vehicle by being satisfied with a >>percentage of catastrophic failure low enough, you ought to >>supply a backup escape system at least in the most traumatic >>sequence of flight (vertical ascent). > >It seems to me that manned aircraft are designed exactly like this, by >keeping a failure rate low. >Perhaps this is a bad approach, but if it's >good enough for commercial aircraft, >it should be valid for spacecraft as well I would like to know how low the percentage of catastrophic failure was for the shuttle when they sized its reliability. I think that they cannot make it as low as that of an airliner because of the vertical take off phase which involves by definition enormous thrust levels. This is why I say that they should have kept the concept of the escape system... or gone to a horizontal take off configuration. >Back when NASA was choosing contractors for the SSME, Pratt & Whitney >had a 2MN LH/LOX engine on the shelf; NASA went with Rocketdyne for >political reasons. For what market did P&W intend its product or why was it ready so much earlier than Rocketdyne's? Olivier Schreiber (404)894 6147, Office of Computing Services Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{allegra,amd,hplabs,seismo,ut-ngp}!gatech!prism!ccsupos ARPA: ccsupos@prism.gatech.edu -- Olivier Schreiber (404)894 6147, Office of Computing Services Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{allegra,amd,hplabs,seismo,ut-ngp}!gatech!prism!ccsupos ARPA: ccsupos@prism.gatech.edu
henry@utzoo.uucp (Henry Spencer) (09/29/89)
In article <2152@hydra.gatech.EDU> ccsupos@prism.gatech.EDU (SCHREIBER, O. A.) writes: >I think that they cannot make [risk] as low as that of an airliner >because of the vertical take off phase which involves >by definition enormous thrust levels... The thrust:weight ratio of the shuttle at launch is not much higher than modern jet fighters. (Conventional ones, not Harriers [which *can* take off vertically].) And the shuttle's engines only have to run for a few minutes between overhauls, while jet engines are expected to run for days. There is no intrinsic reason why rockets should be less reliable than jets, and NASP notwithstanding, they have enormous performance advantages. (Max Hunter has commented, roughly: "If the Wright Brothers had had engines with the thrust:weight ratio of modern rockets, there probably wouldn't be a runway on Earth.") -- "Where is D.D. Harriman now, | Henry Spencer at U of Toronto Zoology when we really *need* him?" | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
Mike.Pompura@f49.n363.z1.FIDONET.ORG (Mike Pompura) (10/04/89)
I submitted a proposal to NASA and Rockwell that involved the escape sequence for a shuttle PES system. Basically what it was is a method of escape for the astronauts in the event of a Challenger-type mishap. It was dismissed as not being cost effective. I suggested that the pressurized inner crew cabin be severed from any remaining orbiter pieces by explosive bolts <the shuttle carries a multitude of explosives already>, and provided with a series of drogue and main parachutes stowed near the front landing gear, attached to the inner crew cabin. In the event of a catastrophe that renders the orbiter non-suitable for flight <no fancy abort maneuvers>, the only other alternative for escape is either the crew abandons ship and bails out with parachutes <a clever task - ask any WWII bomber pilot>, or they remain in the crew cabin, firmly seated in their chairs - whiffing the O2 emergency supply, and having the PES system save their butts. The explosive bolts clean off any remaining debris from the crew cabin, it free-falls or "tumbles" to clear the explosion zone, and implemenets the series of parachutes near the foreward attaching area. They settle back to the earth in this aluminum tin can to either land or sea ala Apollo splashdown. The sea impact represents an additional challenge in the form of buoyancy, but nothing to impractical. The Challenger episode represented the extreme of an accident scenario...and the inner crew cabin remained INTACT untill it hit the ocean surface at 200 mph <give or take>. If they had parachutes at this point, they could have had a better chance for survival. This is one chance that apparently the powers-to-be deam non-cost-effective. I would be interested in hearing your commentsa on my PES design proposal. BTW: PES= Parachute Emergency System. -- Fidonet: Mike Pompura via 1:363/9 Internet: Mike.Pompura@f49.n363.z1.FIDONET.ORG UUCP: uunet!sceard!tarpit!libcmp!mamab!49!Mike.Pompura
shafer@elxsi.dfrf.nasa.gov (Mary Shafer) (10/11/89)
In article <538.252A3A3B@mamab.FIDONET.ORG> Mike.Pompura@f49.n363.z1.FIDONET.ORG (Mike Pompura) writes: >I submitted a proposal to NASA and Rockwell that involved the escape >sequence for a shuttle PES system. >Basically what it was is a method of escape for the astronauts in the >event of a Challenger-type mishap. It was dismissed as not being cost >effective. [Describes a cockpit jettison system with parachutes] > I would be interested in hearing your commentsa on my PES design >proposal. BTW: PES= Parachute Emergency System. As Gene Miya says, if you have a great idea to make the Shuttle better, someone probably already thought of it. The cockpit jettison, with parachutes, was proposed _long_ before the ALT (Approach and Landing Tests) in 1978. I remember Fred Haise and Gordon Fullerton sitting down in the pilots' office here, talking about it. They were picking on Fitz Fulton, because he had an escape hatch in the 747 Shuttle Carrier Aircraft (SCA). Of course, the SCA crew had run back behind the cockpit, fire the shaped charges, climb through a little tunnel, and drop out the bottom of the SCA, but it was an escape hatch. As I recall, much of the difficulty in putting an escape capsule system in the Shuttle is that the Shuttle doesn't have a cockpit "capsule" that is separable from the rest of the vehicle. The F-111, which is the best example of this type of escape system, was designed and built with just such a capsule, making it feasible. (Even it isn't perfect, BTW, but it's probably better than using a regular ejection seat supersonically.) Since the entire Shuttle would have to be rebuilt to do this, it's not practical. Or cost-effective. It's very interesting to me that the public is _so_ much more concerned about things like crew escape systems than are the astronauts. The astronauts know how dangerous the Shuttle is. They know that they'll probably die if there is an accident. Yet they still fight and politick and maneuver for crew assignments and flights, and don't want to wait around for the Shuttle to be perfectly safe. The same is true for test pilots, BTW, and military pilots. And others, as well. On the rare occasions that I've been allowed to fly in a fighter, I do think about what can go wrong, whether I'll be able to eject or not, how reliable ejection seats really are, etc, but I still go fly, because I'm willing to accept the risk. It's worth it to me. But there's risk in everything that we do. How do you deal with risk? What do you think about being an astronaut, knowing the safety record? I'd be at the Cape tomorrow, if they'd let me. Am I the only one? -- Mary Shafer shafer@elxsi.dfrf.nasa.gov ames!elxsi.dfrf.nasa.gov!shafer NASA Ames-Dryden Flight Research Facility, Edwards, CA Of course I don't speak for NASA
robina@tekig5.PEN.TEK.COM (Robin Adams) (10/12/89)
In article <538.252A3A3B@mamab.FIDONET.ORG>, Mike.Pompura@f49.n363.z1.FIDONET.ORG (Mike Pompura) writes: > I submitted a proposal to NASA and Rockwell that involved the escape > sequence for a shuttle PES system. > > Basically what it was is a method of escape for the astronauts in the > event of a Challenger-type mishap. It was dismissed as not being cost > effective. > > I suggested that the pressurized inner crew cabin be severed from any > remaining orbiter pieces by explosive bolts <the shuttle carries a > multitude of explosives already>, and provided with a series of drogue > and main parachutes stowed near the front landing gear, attached to the > inner crew cabin. In the event of ............. -- I agree. I've always felt NASA's first obligation is to ensure that all aspects of Challenger should not be able to repeat. I would however go a couple of steps further on your proposal and suggest: 1. The addition of a small escape rocket to get them out of the immediate area. 2. Quick electrical (and other) disconnects between the inner cabin and orbiter to facilitate seperation. * |_____ * | |/ Robin * | Adams |_____|\ * |
ccsupos@prism.gatech.EDU (SCHREIBER, O. A.) (10/12/89)
In article <SHAFER.89Oct11081832@drynix.dfrf.nasa.gov> shafer@elxsi.dfrf.nasa.gov (Mary Shafer) writes: >As Gene Miya says, if you have a great idea to make the Shuttle >better, someone probably already thought of it. ...and didn't do anything about it you could add. >Since the entire Shuttle would have to be rebuilt to do this, it's not >practical. Or cost-effective. That is the whole point of engineering: to design something from the start to meet some functionalities and an escape system for the propelled phase of the ascent should have been one of them way back in 1972 when the design was chosen. >flights, and don't want to wait around for the Shuttle to be perfectly >safe. I think this type of vehicle, without an escape system can never be safe enough. >still go fly, because I'm willing to accept the risk. It's worth it >to me. [...] >But there's risk in everything that we do. How do you deal with risk? How much risk is the question -- Olivier Schreiber (404)894 6147, Office of Computing Services Georgia Institute of Technology, Atlanta Georgia, 30332 uucp: ...!{allegra,amd,hplabs,seismo,ut-ngp}!gatech!prism!ccsupos ARPA: ccsupos@prism.gatech.edu
hogg@db.toronto.edu (John Hogg) (10/12/89)
In article <4900@tekig5.PEN.TEK.COM> robina@tekig5.PEN.TEK.COM (Robin Adams) writes: >>[Proposal of ``PES'' system to explosively separate shuttle cabin from >>rest of craft in Challenger-type emergency, and land it under parachute.] > > -- I agree. I've always felt NASA's first obligation is to ensure that all >aspects of Challenger should not be able to repeat. > >[Description of additional ``safety'' devices.] I myself have always felt that NASA's first obligation is to carry out research into aeronautics and space. This can't be done without risk; the key is risk management. Each ``safety feature'' that is added to a shuttle carries at least three costs: 1) Its dollar cost. Would you rather spend $10 000 000 (random figure) on Shuttle safety, where it *may* save seven lives, or on highway safety? Or AIDS research? Or supplying a proper diet to expectant mothers? Or flood control? Add your own life-saving program... 2) Its safety cost. As Henry Spencer points out every so often, military ejection seats regularly kill careless maintenance workers. Adding any sort of escape system to a shuttle incurs a non-zero risk of the system being deployed at the wrong time, with potentially disastrous consequences. Many KSC engineers were *very* worried that the recent dousing of Columbia by a (safety!) sprinkler system might have created some hidden danger. 3) Its opportunity cost. Every kilo of ``safety'' equipment is a kilo less of payload. That's a kilo more that has to be taken up by another flight. Is it safer to fly n times without the escape system, or n+1 with? I'd start ranting at this point about how Mary Shafer is dead on, and I'd jump at a shuttle berth, but we went through that post-51L. Let's let it lie this time. --- John Hogg hogg@csri.utoronto.ca Department of Computer Science, University of Toronto
henry@utzoo.uucp (Henry Spencer) (10/12/89)
In article <SHAFER.89Oct11081832@drynix.dfrf.nasa.gov> shafer@elxsi.dfrf.nasa.gov (Mary Shafer) writes: >But there's risk in everything that we do. How do you deal with risk? >What do you think about being an astronaut, knowing the safety record? >I'd be at the Cape tomorrow, if they'd let me. Am I the only one? Never mind tomorrow; my credit cards and I would be at the airport in an hour, ready to grab the first flight south. (Of course, that might well end up being tomorrow anyway...) -- A bit of tolerance is worth a | Henry Spencer at U of Toronto Zoology megabyte of flaming. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
henry@utzoo.uucp (Henry Spencer) (10/12/89)
In article <4900@tekig5.PEN.TEK.COM> robina@tekig5.PEN.TEK.COM (Robin Adams) writes: > 1. The addition of a small escape rocket to get them out of the > immediate area. When one is talking about a multi-ton crew cabin, there is no such thing as a "small" escape rocket that will get them out of the immediate area. The Apollo escape tower, with a rather smaller cabin to lift, weighed four tons. -- A bit of tolerance is worth a | Henry Spencer at U of Toronto Zoology megabyte of flaming. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
colwell@mfci.UUCP (Robert Colwell) (10/12/89)
In article <SHAFER.89Oct11081832@drynix.dfrf.nasa.gov> shafer@elxsi.dfrf.nasa.gov (Mary Shafer) writes: >It's very interesting to me that the public is _so_ much more >concerned about things like crew escape systems than are the >astronauts. The astronauts know how dangerous the Shuttle is. They >know that they'll probably die if there is an accident. Yet they >still fight and politick and maneuver for crew assignments and >flights, and don't want to wait around for the Shuttle to be perfectly >safe. And I'm sure they understand, as do the engineers, that it never will be perfectly safe, nor will airplane travel, elevators, eating, and walking down the sidewalk. I wonder if the apparent public attitude that you mentioned is somehow related to the idea that if something bad happens to me, then it necessarily follows that somebody, somewhere, needs to be sued for it? >The same is true for test pilots, BTW, and military pilots. And >others, as well. On the rare occasions that I've been allowed to fly >in a fighter, I do think about what can go wrong, whether I'll be able >to eject or not, how reliable ejection seats really are, etc, but I >still go fly, because I'm willing to accept the risk. It's worth it >to me. No, it's not, Mary. You're taking foolish risks here. Next time, call me, and I'll go up for you. I know, I know, why would a stranger do such a nice thing for you, but hey, that's just me. >But there's risk in everything that we do. How do you deal with risk? >What do you think about being an astronaut, knowing the safety record? >I'd be at the Cape tomorrow, if they'd let me. Am I the only one? Heck no. You and I are the only two. :-) I've had my application on file for about 6 years now, and they even check my references every so often. (But I guess that either my reviews aren't raving enough or they don't need computer designers in the shuttle, because that's as far as it has ever gone so far.) I think a lot of us see it the same way. There are rational risks, like flying airplanes and driving cars, and there are stupid unnecessary ones, like smoking and having the bureaucratic chain screw up on you (a la Challenger). The goal is to take the rational ones where appropriate, and minimize or eliminate the rest. Bob Colwell ..!uunet!mfci!colwell Multiflow Computer or colwell@multiflow.com 31 Business Park Dr. Branford, CT 06405 203-488-6090
phil@delta.eecs.nwu.edu (William LeFebvre) (10/12/89)
In article <2430@hydra.gatech.EDU> ccsupos@prism.gatech.EDU (SCHREIBER, O. A.) writes: >In article <SHAFER.89Oct11081832@drynix.dfrf.nasa.gov> shafer@elxsi.dfrf.nasa.gov (Mary Shafer) writes: > >>As Gene Miya says, if you have a great idea to make the Shuttle >>better, someone probably already thought of it. >...and didn't do anything about it you could add. No, I wouldn't add that. >>flights, and don't want to wait around for the Shuttle to be perfectly >>safe. > >I think this type of vehicle, without an escape system can never >be safe enough. I'd venture to say that more people die in a typical commercial airline disaster than died in the Shuttle accident. What exactly do you mean by "safe enough"? Safe enough for paying tourists? No. Safe enough for scientific experimentation (which is all it was intended for)? I think it is. And I think that over 100 employees who are in the astronaut program at NASA/JSC think so too. That's why they're still in it. If prior to 1986 they didn't understand or realize just how dangerous it was, then Challenger demonstrated it to them. But they're still there. I think that it is "safe enough" for *the intended purpose*. William LeFebvre Department of Electrical Engineering and Computer Science Northwestern University <phil@eecs.nwu.edu>
leech@alanine.cs.unc.edu (Jonathan Leech) (10/13/89)
In article <538.252A3A3B@mamab.FIDONET.ORG> Mike.Pompura@f49.n363.z1.FIDONET.ORG (Mike Pompura) writes: >I submitted a proposal to NASA and Rockwell that involved the escape >sequence for a shuttle PES system. >... >This is one chance that apparently the powers-to-be deam >non-cost-effective. It isn't cost-effective because of the enormous payload penalty. -- Jon Leech (leech@cs.unc.edu) __@/ "Opossums ran amok in Chapel Hill this weekend..." _The Daily Tar Heel_, 11/1/88
tneale@aeras.UUCP (Tom Neale) (10/14/89)
In article <SHAFER.89Oct11081832@drynix.dfrf.nasa.gov> shafer@elxsi.dfrf.nasa.gov (Mary Shafer) writes: >But there's risk in everything that we do. How do you deal with risk? >What do you think about being an astronaut, knowing the safety record? >I'd be at the Cape tomorrow, if they'd let me. Am I the only one? No Mary, your're not the only one. My application for Mission Specialist has been in to Houston for several months (no I'm not holding my breath, but I can always hope). It is unfortunate that so many people want all of their technologly totally risk free. So few advances are made without sacrifice. But, this has all been hashed over before... -- Blue skies, | ...sun!aeras!tneale | | in flight: N2103Q | The hurrieder I go Tom Neale | in freefall: D8049 | the behinder I get. | via the ether: WA1YUB |
navas@cory.Berkeley.EDU (David C. Navas) (10/14/89)
In article <9941@thorin.cs.unc.edu> leech@alanine.cs.unc.edu (Jonathan Leech) writes: >In article <538.252A3A3B@mamab.FIDONET.ORG> Mike.Pompura@f49.n363.z1.FIDONET.ORG (Mike Pompura) writes: >>I submitted a proposal to NASA and Rockwell that involved the escape >>sequence for a shuttle PES system. >>... >>This is one chance that apparently the powers-to-be deam >>non-cost-effective. > > It isn't cost-effective because of the enormous payload penalty. >-- > Jon Leech (leech@cs.unc.edu) __@/ > "Opossums ran amok in Chapel Hill this weekend..." > _The Daily Tar Heel_, 11/1/88 Hang on a minute. Do cars have ejection seats? Do passengers carry parachutes into airplanes? It seems to me that one of the original design considerations was *safe* entry into space. IE, to pilfer a semi-quote from Gary Hart, the idea is not to make the system safe to use whether it fails or not, but to make the thing free from failure to begin with. What we need is a completely new design, not merely a re-hashed version of a proven /unreliable/ spacecraft. That's not to put the SS down -- I happen to like the idea. I liked the original shuttle much better, of course. The time for the immature/veteran-pilot approach to space flight has to end someday -- why not now. Of course, that makes it easier for weenies like myself to go there.... :-) David Navas navas@cory.berkeley.edu I'm not even responsible for the things I say.... :-)