henry@utzoo.uucp (Henry Spencer) (10/02/88)
In article <1543@hp-sdd.HP.COM> hinojosa@hp-sdd.hp.com.UUCP (Daniel Hinojosa) writes: >Someone here at work mentioned that the shuttle has less memory than >many home computers, in the neighborhood of 640K. Let's assume for >now that this is the case. Not only does that seem like an amazingly >low amount of memory... Remember that the shuttle computers were designed in the mid-1970s and, like a lot of space hardware, deliberately used old, well-proven technology. Space also imposes some special constraints like radiation resistance, which affects the issue; the dynamic RAMs used in PCs and the like are not usually considered fit for use in space. There is a project underway now to improve the shuttle's computers, I believe. >... now I wonder why NASA decided to stay with O rings >at all. I seem to recall in the days right after Challenger, seeing >news stories about boosters. The Air Force had made boosters for use >at Vandenberg that were all one piece. I think they were a type of >fibre glass, and spun into a cylindrical shape. These were lighter, >therefor allowing a heavier payload. What's the story? The filament-wound boosters developed with USAF funding were segmented, just like the existing ones. Their only real advantage was that the filament-wound cases were lighter. Their big disadvantage, which is why you don't hear about them now, was that the actual joints still had to be metal, meaning that each filament-wound segment had a composite center bonded to two metal joint rings, i.e. still more joints to fail. There was also some (unofficial) skepticism about how reusable they would be. NASA is now concentrating on improved metal casings for a higher- performance SRB, and the filament-wound casings seem to have been forgotten completely. Large one-piece solids were built and fired a number of years ago -- by NASA in fact! The reason for not taking that approach immediately was the desire to get the shuttle flying again without waiting several years to develop a new SRB. The reasons for not taking that approach in the long run are a combination of NASA inertia and legitimate worry about the problems of casting that big a lump of propellant in one piece. (Cracks in propellant are very bad news in any solid rocket.) -- The meek can have the Earth; | Henry Spencer at U of Toronto Zoology the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu
jetzer@studsys.mu.edu (jetzer) (10/04/88)
In article <1988Oct1.230542.11512@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > In article <1543@hp-sdd.HP.COM> hinojosa@hp-sdd.hp.com.UUCP (Daniel Hinojosa) writes: > >Someone here at work mentioned that the shuttle has less memory than > >many home computers, in the neighborhood of 640K. > Space also imposes some special constraints like radiation resistance, which > affects the issue; the dynamic RAMs used in PCs and the like are not usually > considered fit for use in space. What does 'fit for use in space' mean? As I recall, someone sent up an Apple ][+ along with an experiment (and there have, no doubt, been many other computers that have gone up). I can see that the main computers have more constraints on safety and such, but why would someone spend many thousands of dollars to send up a scientific experiment, only to have the results spoiled because of a zapped RAM. -- Mike Jetzer "Hack first, ask questions later."
henry@utzoo.uucp (Henry Spencer) (10/06/88)
In article <252@studsys.mu.edu> jetzer@studsys.mu.edu (jetzer) writes: >> Space also imposes some special constraints like radiation resistance, which >> affects the issue; the dynamic RAMs used in PCs and the like are not usually >> considered fit for use in space. > >What does 'fit for use in space' mean? It depends on what you're doing. For running some small experiment where you don't care much if there's a 1-in-100 chance of the computer failing, you can use most anything. Model 100s have flown in space. For long stays in space, e.g. controlling satellites, it is necessary to have something that can take a substantial accumulated dose of radiation without trouble. Dynamic RAMs do not qualify, unless perhaps only a short lifetime is needed. (Amsat had some dynamic RAMs on board one of their birds, although in a non-critical role, and has since regretted it.) Remember that the shuttle computers spend quite a bit of time in space over their lifetime, and continued correct functioning of those machines is *very* important. -- The meek can have the Earth; | Henry Spencer at U of Toronto Zoology the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu
wes@obie.UUCP (Barnacle Wes) (10/07/88)
In article <1988Oct1.230542.11512@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > The filament-wound boosters developed with USAF funding were segmented, > just like the existing ones. Their only real advantage was that the > filament-wound cases were lighter. Their big disadvantage, which is why > you don't hear about them now, was that the actual joints still had > to be metal, meaning that each filament-wound segment had a composite > center bonded to two metal joint rings, i.e. still more joints to fail. USAF has a large, segmented solid-fuel booster being fielded as we type :-). It has had 17 successful launches, and not one of the 17 flights has blown up, intentionally or not. But then again, they were never left out in the cold, either :-). As a matter of fact, the Shuttle SRBs are basically derivatives of this motor; they are approximately the same size, and according to a book Thiokol published as a promo item a few years ago, the fuel compounds are very similar. This booster is, of course, the 1st stage of the Peacekeeper missile. Remember good ol' MX? > There was also some (unofficial) skepticism about how reusable they would > be. NASA is now concentrating on improved metal casings for a higher- > performance SRB, and the filament-wound casings seem to have been forgotten > completely. A reusable ICBM? That's funny! > Large one-piece solids were built and fired a number of years ago -- by NASA > in fact! Well, actually, it was Aerojet Corp., during the design & analysis phase of the MX contract award. They demonstrated the capability to create a solid-fuel booster that fit the MX specs, with one single pour of the fuel, and one solid wound-fiber exterior. God and Jake Garn only know why Aerojet didn't win the contract, and the contract for the SRBs as well. > The reason for not taking that approach immediately was the desire > to get the shuttle flying again without waiting several years to develop a > new SRB. The reasons for not taking that approach in the long run are a > combination of NASA inertia and legitimate worry about the problems of > casting that big a lump of propellant in one piece. (Cracks in propellant > are very bad news in any solid rocket.) If you read the accounts around here, the reason is that the Director of NASA at the time was a Mormon, and Jake Garn was one of the bigwigs on the Senate committe allocating funds for the Shuttle. They apparently decided Utah could use the jobs, the tax revenues, and the "glamour" of developing one of the more visible portions of America's Space Station Wagon. Too bad they did such a crummy job, both on the boosters and on the advertising! -- {hpda, uwmcsd1}!sp7040!obie!wes "How do you make the boat go when there's no wind?" -- Me --
henry@utzoo.uucp (Henry Spencer) (10/10/88)
In article <212@obie.UUCP> wes@obie.UUCP (Barnacle Wes) writes: > [MX first stage] ... As a matter of fact, the Shuttle >SRBs are basically derivatives of this motor; they are approximately the >same size, and according to a book Thiokol published as a promo item a >few years ago, the fuel compounds are very similar... You're sure about this? Remember that shuttle SRB development goes back to the mid-70s. Remember also that big solid motors are pretty similar; the shuttle SRBs are not derivatives of the Titan SRBs even though they are both segmented designs using similar propellants. And I expect that the MX first stage doesn't have field joints, which is a major practical difference. (The shuttle SRB segments shipped to the Cape actually are each two casing segments joined at a factory joint before propellant casting. The factory joints have never given the slightest problem, and in fact they are still using the pre-Challenger seal design.) >> Large one-piece solids were built and fired a number of years ago -- by NASA >> in fact! > >Well, actually, it was Aerojet Corp., during the design & analysis phase >of the MX contract award... We're thinking about different events, although it may have been the same contractor -- Aerojet sounds familiar. NASA-plus-contractor built and fired several non-segmented 260-inch solids (much bigger than either the shuttle SRB or the MX) circa 20 years ago. No relation to MX. -- The meek can have the Earth; | Henry Spencer at U of Toronto Zoology the rest of us have other plans.|uunet!attcan!utzoo!henry henry@zoo.toronto.edu