wab@rutabaga.Rational.COM (Bill Baker) (05/03/91)
In article <1991May1.162201.16502@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >In article <1991Apr30.171707.27685@isc.rit.edu> isg7243@ritvax.isc.rit.edu writes: > >The reason why the landing gear are lowered only by human command, by the >way, is that they cannot be raised again once lowered. So they'd better >not get lowered prematurely. I'm sure there is a perfectly reasonable, logical, and utterly necessary reason for this, but... Why in the *hell* can they only *lower* the landing gear? Theoretically, I suppose, you only need to lower it in flight, but it still seems like bonebrain engineering to me. * Turbopumps that fail at a hostile glance * Solid boosters as safe as a $2 skyrocket * Landing gear that only goes in one direction The Shuttle: "It's got modern, stone-age technologeeee!" ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ (Sung to the Flintstones Theme)
henry@zoo.toronto.edu (Henry Spencer) (05/03/91)
In article <1076@igor.Rational.COM> wab@rutabaga.Rational.COM (Bill Baker) writes: >Why in the *hell* can they only *lower* the landing gear? >Theoretically, I suppose, you only need to lower it in flight, but it >still seems like bonebrain engineering to me. No, it's minimum-weight engineering. Being able to raise the gear again needs extra machinery. It's common in spacecraft for actions that go only one way to be implemented with machinery that is only capable of going one way, but is simpler and lighter than two-way machinery. Pyrotechnic valves are an example: the valve opens when you fire a small explosive charge, which makes for a very lightweight and reliable valve actuator that only goes one way. -- And the bean-counter replied, | Henry Spencer @ U of Toronto Zoology "beans are more important". | henry@zoo.toronto.edu utzoo!henry
kent@vf.jsc.nasa.gov (05/04/91)
> * Turbopumps that fail at a hostile glance > ever tried buring crygenic Ox and Hydrogen at very high pressure? The Shuttle program has never had a turbo pump fail durring powered flight, some test units failed, but thats why they test them. > * Solid boosters as safe as a $2 skyrocket SRB's are not as safe as liquid fueled rockets. They cost less to deveolop and the Shuttle program was on a tight development budget. > > * Landing gear that only goes in one direction Why do you need to raise the landing gear. Is the shuttle going to wave off and go around again on a landing.? The Landing gear doors have to close very tightly to keep the heat from re-entry from getting in and burning up the tires/landing gear. In fact the doors open with a piro-technic assist. > > > The Shuttle: "It's got modern, stone-age technologeeee!" > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > (Sung to the Flintstones Theme) I don't think you have enough information to make the kind of statements you are making. -- Mike Kent - Lockheed Engineering and Sciences Company at NASA JSC 2400 NASA Rd One, Houston, TX 77058 (713) 483-3791 KENT@vf.jsc.nasa.gov
oliver@vf.jsc.nasa.gov (05/04/91)
In article <1076@igor.Rational.COM>, wab@rutabaga.Rational.COM (Bill Baker) writes: > I'm sure there is a perfectly reasonable, logical, and utterly > necessary reason for this, but... > > Why in the *hell* can they only *lower* the landing gear? > Theoretically, I suppose, you only need to lower it in flight, but it > still seems like bonebrain engineering to me. There are two major reasons that I can think of. First of all is why would you want to raise the gear? The Orbiter is a glider, it doesn't have the power to go around on a missed approach, so there is not a flight requirement to raise the landing gear. Second, all the plumbing that it takes to raise the landing gear has weight. NASA tries to eliminate all weight which serves no useful purpose, and on a space vehicle, equipment to raise the landing gear serves no useful purpose. Additionally, by not having the hydraulics system to raise the landing gear on board the overall complexity of the hydraulics system is reduced. This means fewer things which have to be checked out during the vehicle turnaround. Less cost, less risk of something breaking, and just plain good engineering. -- Pat Oliver - Lockheed Engineering and Sciences Company at NASA JSC 2400 NASA Rd One, Houston, TX 77058 (713) 483-3323 OLIVER@vf.jsc.nasa.gov
wab@rutabaga.Rational.COM (Bill Baker) (05/07/91)
In article <1991May3.111445.1@vf.jsc.nasa.gov> kent@vf.jsc.nasa.gov writes: >> * Turbopumps that fail at a hostile glance >> > > ever tried buring crygenic Ox and Hydrogen at very high pressure? > The Shuttle program has never had a turbo pump fail durring powered >flight, some test units failed, but thats why they test them. Those same tests have shown a high rate of failure for the turbo pumps. I believe their readjusted mean time to failure is now rated at some ludicrously small fraction of the initial estimates. Many other design features of the shuttle haven't failed catastrophically yet (e.g., heating tiles) but that's because NASA has spent multiples over original estimates for maintenance and replacement. My main problem with the pump is as they can be regarded as symbols of the design philosophy of the shuttle: Make the the system dependent on unproven designs that require the utmost of the technology. Designing for the last .1% of the capabilities of the technology does not portend a robust system. >> * Solid boosters as safe as a $2 skyrocket > > SRB's are not as safe as liquid fueled rockets. They cost less to > deveolop and the Shuttle program was on a tight development budget. At least you don't claim they've never failed.... >> * Landing gear that only goes in one direction > > Why do you need to raise the landing gear. Is the shuttle going to > wave off and go around again on a landing.? I had no scenario in mind when I asked the question, but an obvious one occurrs to me now: What do you do when the gear deploys partially? Hasn't this already happened or is my memory playing tricks? I seem to remember a Shuttle touching down without the nose gear down and scrubbing its nose pretty good. Regardless, NASA undoubtedly has contingency plans in place to deal with this without being able to raise the gear, but it is still a question of robustness vs. weight/complexity/cost to determine need. My problem with the robustness of the Shuttle system is that it seems to be designed to deal with just one major failure at a time. NASA's answer to those highly unlikely scenarios combining two major failures is to say that the crew is SOL. Say there is a tile failure that results in major structural damage to a wing during reentry, yet the Shuttle makes it through the remainder of the descent pattern through to final approach in one piece. Then the crew drops the gear, but only the nose and one wing gear deploy (presumably the failed gear is in the burned wing). Crippled thusly, would you rather set the bird down on two points and take the chance of tumbling if the wing snaps or would you rather raise the gear and pancake cleanly? I know, I know, wing loadings/structural stress is much higher during reentry and descent than touchdown, etc.; if you've gotten it that far, it'll probably stay in one piece. Still, that or another scenario could occur in which it would be desirous to raise the gear. >The Landing gear doors have >to close very tightly to keep the heat from re-entry from getting in and >burning up the tires/landing gear. In fact the doors open with a piro-technic >assist. I don't see why this would make it more difficult to raise the gear. Presumably it would make it more difficult to close the gear bay doors. > >> >> >> The Shuttle: "It's got modern, stone-age technologeeee!" >> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >> (Sung to the Flintstones Theme) > > I don't think you have enough information to make the kind of >statements you are making. I'm sure you NASA guys (contractors are close enough) are tired of getting ribbed about the Shuttle, but the fact is that anyone who has followed the program these many years knows the problems. Everyone from NASA to USA Today has discussed the SRBs and turbo pumps. In other words, you don't have to be a rocket scientist to know what's wrong with the Shuttle, at least with regard to the major problem components. Basically, though, my problems aren't with any one aspect of the Shuttle as much as NASA's disregard for robustness. NASA keeps claiming it wants to fly the Shuttle like a 747; year after year they have grandiose plans requiring more and more Shuttle flights, but they never meet their current launch schedule because system problems keep launches grounded. A more robust system might make it off the ground on time. Further, NASA wants to make all those flights without planning for the increased likelihood of a major failure. It boggles the mind that NASA wants to increase flights without increasing robustness. More flights equals a higher chance of failure over time. Wouldn't you want to decrease that possibility as you increase its likelihood? That is, wouldn't you want to make it less likely to fail as you give it more chances to do so? The really glaring mistakes came during the post-Challenger redesign. Given the chance to rethink the philosophy of Shuttle design, NASA essentially kept the same dogma. They upped the ratio to one major failure per 78 Shuttle flights without making any but the most minimal attempts to increase the survivability of the system, and almost no attempts to increase crew survivability in the case of such a failure (descent pole indeed). >-- > >Mike Kent - Lockheed Engineering and Sciences Company at NASA JSC > 2400 NASA Rd One, Houston, TX 77058 (713) 483-3791 > KENT@vf.jsc.nasa.gov
v071pzp4@ubvmsd.cc.buffalo.edu (Craig L Cole) (05/07/91)
In article <1082@igor.Rational.COM>, wab@rutabaga.Rational.COM (Bill Baker) writes... >In article <1991May3.111445.1@vf.jsc.nasa.gov> kent@vf.jsc.nasa.gov writes: >>> * Landing gear that only goes in one direction >> >> Why do you need to raise the landing gear. Is the shuttle going to >> wave off and go around again on a landing.? > >I had no scenario in mind when I asked the question, but an obvious >one occurrs to me now: What do you do when the gear deploys >partially? Hasn't this already happened or is my memory playing >tricks? I seem to remember a Shuttle touching down without the nose >gear down and scrubbing its nose pretty good. Pardon me, but when did _this_ happen? The only landing related failure was the last KSC landing pre-Challenger. One of the shuttle's brakes locked, blowing one of the tires. This led to the ending of KSC landings until the nosewheel steering system was installed (done) and new carbon-carbon brakes were isntalled (done, but still being tested) > > [Scenario for raising gear deleted] > >I don't see why this would make it more difficult to raise the gear. >Presumably it would make it more difficult to close the gear bay >doors. I've always been told that the landing gear mechanism is designed to be simple -- it'll only open once (per trip), but it'll always open _right_. An interesting sidenote - I've always understood that the shuttle can land completely autonomously, but someone has to be there to at least lower the landing gear, since the shuttle computers are in no way in control of it. The reason that the computers aren't able to lower them, is _because_ they only open once. NASA didn't want a computer glitch to lower the landing during launch (really ugly thought) or in orbit (still ugly). The shuttle couldn't survive reentry with its landing gear down. I can't quite agree with NASA on this one. Having landing gear you can raise would have made the system a little more complex and maybe a bit heavier, but the one-shot gear opens up a couple of new problems: 1) Inability to test gear in orbit before landing. 2) Inability to land (safely) should the astronauts become incapacitated. That, of course, is only true if the shuttle can land completely autonomously. Correct me if I'm wrong... Craig Cole University at Buffalo V071PZP4@UBVMS.CC.BUFFALO.EDU V071PZP4@UBVMS.BITNET
dbm@icarus.jsc.nasa.gov (Brad Mears) (05/07/91)
In article <1082@igor.Rational.COM>, wab@rutabaga.Rational.COM (Bill Baker) writes: |> > Why do you need to raise the landing gear. Is the shuttle going to |> > wave off and go around again on a landing.? |> |> I had no scenario in mind when I asked the question, but an obvious |> one occurrs to me now: What do you do when the gear deploys |> partially? Hasn't this already happened or is my memory playing |> tricks? I seem to remember a Shuttle touching down without the nose |> gear down and scrubbing its nose pretty good. Wrong. If that had happened, it would have done more than scrub the nose. |> My problem with the robustness of the Shuttle system is that it seems |> to be designed to deal with just one major failure at a time. NASA's |> answer to those highly unlikely scenarios combining two major failures |> is to say that the crew is SOL. Wrong. The basic design goal for shuttle has *always* been that it should be able to withstand two failures and still assure crew safety. This level of fault-tolerance exists for *most* failures. It is a harsh reality that you can't protect against some failures. For example, what do you do if a wing falls off? Deploy the backup wing? |> Still, that or another scenario could |> occur in which it would be desirous to raise the gear. Why don't you make a list of the scenarios in which it is desirous to raise the gear? Compute the probability for each of these happening. Now compute the risk you've *added* by introducing all this new equipment (motors, hydraulics, etc). Do you still want that capability? |> I'm sure you NASA guys (contractors are close enough) are tired of |> getting ribbed about the Shuttle, I'm tired of irresponsible flamage. If you ever want to have a *serious* discussion about shuttle, give me a call. |> but the fact is that anyone who has |> followed the program these many years knows the problems. Everyone |> from NASA to USA Today has discussed the SRBs and turbo pumps. In |> other words, you don't have to be a rocket scientist to know what's |> wrong with the Shuttle, at least with regard to the major problem |> components. You may not have to be a rocket scientist, but you need a better source of information than USA Today. |> Wouldn't you |> want to decrease that possibility as you increase its likelihood? Do YOU have an infinite supply of money? -- Brad Mears dbm@icarus.jsc.nasa.gov ---------------------------------------------------------------------------- Opinions are expressly forbidden. | "It is better to die on your feet I speak for myself and no other. | than live on your knees" | - Dolores Ibarruri ----------------------------------------------------------------------------
kent@vf.jsc.nasa.gov (05/08/91)
In article <1082@igor.Rational.COM>, wab@rutabaga.Rational.COM (Bill Baker) writes: >> ever tried buring crygenic Ox and Hydrogen at very high pressure? >> The Shuttle program has never had a turbo pump fail durring powered >>flight, some test units failed, but thats why they test them. > > Those same tests have shown a high rate of failure for the turbo > pumps. I believe their readjusted mean time to failure is now rated > at some ludicrously small fraction of the initial estimates. I believe the initial rating for the Space Shuttle Main Engine was 30 flights. they are now rated at 10 flights. Is that a ludicrously small fraction? > > My main problem with the pump is as they can be regarded as symbols of > the design philosophy of the shuttle: Make the the system dependent on > unproven designs that require the utmost of the technology. Designing > for the last .1% of the capabilities of the technology does not > portend a robust system. > I think you are probably right. Many of the problems of the shuttle can be trace back to the fact that NASA had to develop the technology to build the Shuttle in the first place. It just did not exist in the 70's. >>> * Solid boosters as safe as a $2 skyrocket >> >> SRB's are not as safe as liquid fueled rockets. They cost less to >> deveolop and the Shuttle program was on a tight development budget. > > At least you don't claim they've never failed.... > If NASA had the funding they would have developed liqued fuel boosters. >>> * Landing gear that only goes in one direction >> >> Why do you need to raise the landing gear. Is the shuttle going to >> wave off and go around again on a landing.? > > I had no scenario in mind when I asked the question, but an obvious > one occurrs to me now: What do you do when the gear deploys > partially? Hasn't this already happened or is my memory playing > tricks? I seem to remember a Shuttle touching down without the nose > gear down and scrubbing its nose pretty good. Has not happened. > Regardless, NASA > undoubtedly has contingency plans in place to deal with this without > being able to raise the gear, but it is still a question of robustness > vs. weight/complexity/cost to determine need. ====== Weight thats the key. By the way the shuttle has a contengeny system to deploy the gear. It has pyro assist if need be. > > My problem with the robustness of the Shuttle system is that it seems > to be designed to deal with just one major failure at a time. NASA's > answer to those highly unlikely scenarios combining two major failures > is to say that the crew is SOL. Say there is a tile failure that Its a matter of weight. If you design full robustness, they it weighs so much that you have no payload at all. You could easily add 60,000 pounds of redundant equiptment and still have a vehicle that is no where as safe as a jet plane. Lets face it, with the energies and speed and margins of error, space flight is a dangerous business. It will be a long time until we can develop systems the deliver the performance and safety of a commercial airliner without major weight penalties. You can't carry 3 extra main engines... you can't carry air breathing engines and the fuel the run them. Launch systems just can't carry that much extra weight. > > I'm sure you NASA guys (contractors are close enough) are tired of > getting ribbed about the Shuttle, but the fact is that anyone who has > followed the program these many years knows the problems. Everyone > from NASA to USA Today has discussed the SRBs and turbo pumps. In > other words, you don't have to be a rocket scientist to know what's > wrong with the Shuttle, at least with regard to the major problem > components. There are no questions that the shuttle has problems. Its is still the most advanced launch system we have. > > Basically, though, my problems aren't with any one aspect of the > Shuttle as much as NASA's disregard for robustness. NASA keeps > claiming it wants to fly the Shuttle like a 747; year after year they > have grandiose plans requiring more and more Shuttle flights, but they > never meet their current launch schedule because system problems keep > launches grounded. > A more robust system might make it off the ground on time. We are flying a when its safe not to a minute schedule. NASA has made every major launch window for plantary probes it has launched from the Shuttle. The "launch on time" thing is more of an artifact of the press than NASA. > Further, NASA wants to make all those flights without planning for the > increased likelihood of a major failure. It boggles the mind that > NASA wants to increase flights without increasing robustness. More > flights equals a higher chance of failure over time. Wouldn't you > want to decrease that possibility as you increase its likelihood? > That is, wouldn't you want to make it less likely to fail as you give > it more chances to do so? Thats true if we never flew we would never loose and orbiter. NASA's launch manifest has 7 flights this year, 9 in 1992, 10 in 1993 I hardly call that "grandiose plans requiring more and more" NASA is committed to finding the maximum SAFE flight rate. > > The really glaring mistakes came during the post-Challenger redesign. > Given the chance to rethink the philosophy of Shuttle design, NASA > essentially kept the same dogma. They upped the ratio to one major > failure per 78 Shuttle flights without making any but the most minimal > attempts to increase the survivability of the system, and almost no > attempts to increase crew survivability in the case of such a failure > (descent pole indeed). I have never seen what NASA claimed the failure rate to be before challenger but I would guess it was billed as higher than 1 per 78. The changes to many systems were major. SRB's Main engines, APU's, Brakes. All most nothing could save any crew in any vehicle from a challenger type break up. -- Mike Kent - Lockheed Engineering and Sciences Company at NASA JSC 2400 NASA Rd One, Houston, TX 77058 (713) 483-3791 KENT@vf.jsc.nasa.gov
rteasdal@polyslo.CalPoly.EDU (Falconer) (05/11/91)
In article <1991May7.120505.1@vf.jsc.nasa.gov> kent@vf.jsc.nasa.gov writes: >> (descent pole indeed). >I have never seen what NASA claimed the failure rate to be before challenger >but I would guess it was billed as higher than 1 per 78. The changes to many >systems were major. SRB's Main engines, APU's, Brakes. Almost nothing could >save any crew in any vehicle from a challenger type break up. > >-- I have met and talked to a SR-71 Blackbird pilot who punched out of his craft while travelling at just under Mach 3. He came through it all right; was more badly hurt from landing in a saguaro cactus on the ground. _If_ the shuttle had provision for crew ejection (and no, I would not claim that to be a feasible post-Challenger refit) there would have been a significant chance for STS-51L's crew (some of them) to have survived. The forensic evidence suggests that several of the people on the flight deck were alive and breathing (emergency air packs do not spontaneously switch themselves on), said persons being killed by the freely falling cabin's 350+kph impact with the Atlantic. The original shuttle should have incorporated (encapsulated?) ejection capability. That it did not was one of the most egregious design flaws yet promulgated by NASA. Let's do it right next time, eh? -- |||||| Russ Teasdale -- rteasdal@polyslo.CalPoly.EDU -- (Falconer) ||||||| ------------------------------------------------------------------------------- "Gentlemen, if we do not succeed, then we run the risk of failure." - D. Quayle
harbour@vf.jsc.nasa.gov (05/14/91)
In article <282b9084.2da2@petunia.CalPoly.EDU>, rteasdal@polyslo.CalPoly.EDU (Falconer) writes: > > > In article <1991May7.120505.1@vf.jsc.nasa.gov> kent@vf.jsc.nasa.gov writes: >>> (descent pole indeed). > >>I have never seen what NASA claimed the failure rate to be before challenger > >>but I would guess it was billed as higher than 1 per 78. The changes to many >>systems were major. SRB's Main engines, APU's, Brakes. Almost nothing could >>save any crew in any vehicle from a challenger type break up. >> >>-- > > I have met and talked to a SR-71 Blackbird pilot who punched > out of his craft while travelling at just under Mach 3. He came through > it all right; was more badly hurt from landing in a saguaro cactus on > the ground. _If_ the shuttle had provision for crew ejection (and no, > I would not claim that to be a feasible post-Challenger refit) there > would have been a significant chance for STS-51L's crew (some of them) > to have survived. The forensic evidence suggests that several of the > people on the flight deck were alive and breathing (emergency air packs > do not spontaneously switch themselves on), said persons being killed > by the freely falling cabin's 350+kph impact with the Atlantic. > > The original shuttle should have incorporated (encapsulated?) > ejection capability. That it did not was one of the most egregious > design flaws yet promulgated by NASA. Let's do it right next time, eh? > > > -- > |||||| Russ Teasdale -- rteasdal@polyslo.CalPoly.EDU -- (Falconer) ||||||| > ------------------------------------------------------------------------------- > "Gentlemen, if we do not succeed, then we run the risk of failure." - D. Quayle Actually, the shuttle had ejection seats installed for the first several (can't remember the exact number of) flights. The top of the crew compartment was rigged to blow off first, of course. This approach works fine with crews of 4 or less. But there are only 4 seats on the flight deck - the remaining crew members are in (on?) the mid-deck from which there is no easy way out. The ejection seats (and roof panel) were removed after the early flights. It just didn't seem fair to give only half the crew an ejection seat. (This is your captain speaking: we're having a bit of trouble so I'm hittin' the silk. Enjoy the rest of the flight :-). I believe that there was talk of trying to put parachutes on the crew compartment itself. But I don't remember any details. It probably ran afoul on cost, weight penalty, or both (my guess - I really don't know). -- Jeff : harbour@vf.jsc.nasa.gov : .sig void where prohibited by law
fcrary@lightning.Berkeley.EDU (Frank Crary) (05/16/91)
In article <282b9084.2da2@petunia.CalPoly.EDU> rteasdal@polyslo.CalPoly.EDU (Falconer) writes: > The original shuttle should have incorporated (encapsulated?) >ejection capability. That it did not was one of the most egregious >design flaws yet promulgated by NASA. Let's do it right next time, eh? > The incorporation of encapsulated ejection capability to the shuttle would have been quite expensive and massed several tonnes (which would have cone out of payload capacity). NASA deciede that the extra safty was not worth it. I would not call this a design flaw, unless the objective of the design was to make an spaceceaft which was as close to perfectly safe as possible. The shuttle was intended to do other things (be a "space truck"I think was the phrase.) Frank Crary UC Berkeley