Newsgroups: sci.space.shuttle
Path: utzoo!henry
From: henry@utzoo.uucp (Henry Spencer)
Subject: shuttle computers; big solids
Message-ID: <1988Oct1.230542.11512@utzoo.uucp>
Organization: U of Toronto Zoology
References: <6689@nsc.nsc.com> <1543@hp-sdd.HP.COM>
Date: Sat, 1 Oct 88 23:05:42 GMT

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