Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!uunet!igor!rutabaga!wab From: wab@rutabaga.Rational.COM (Bill Baker) Newsgroups: sci.space.shuttle Subject: Re: Shuttle computers (Really, "Drop the landin' gear, Jed!") Message-ID: <1082@igor.Rational.COM> Date: 7 May 91 02:26:06 GMT References: <1991May1.162201.16502@zoo.toronto.edu> <1076@igor.Rational.COM> <1991May3.111445.1@vf.jsc.nasa.gov> Sender: news@Rational.COM Organization: Joan Vollmer Womens Academy Lines: 113 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