Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!samsung!uunet!stanford.edu!eos!aio!vf.jsc.nasa.gov!kent From: kent@vf.jsc.nasa.gov Newsgroups: sci.space.shuttle Subject: Re: Shuttle computers (Really, "Drop the landin' gear, Jed!") Message-ID: <1991May7.120505.1@vf.jsc.nasa.gov> Date: 7 May 91 18:05:05 GMT References: <1991May1.162201.16502@zoo.toronto.edu> <1076@igor.Rational.COM> <1991May3.111445.1@vf.jsc.nasa.gov> <1082@igor.Rational.COM> Sender: news@aio.jsc.nasa.gov (USENET News System) Organization: NASA Johnson Space Flight Center Lines: 130 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