Space shuttle computers

From: Richard Erlacher <>
Date: Wed Mar 3 18:59:43 1999

I don't know what all this stuff means, but NASA paid Martin Marietta,
where I worked back in those days, a LOT of dough, and provided
documentation labeled Honeywell and showing pictures, though they were not
relevant, of a model 516 computer. I spent six months or more poring over
schematics, struggling to keep my eyes open, and making note of any
potential race conditions, running logic simulations, etc, just to document
all the potential single-point failure modes and their potential effect.
We found several conditions which seemed to be "bugs" in the system,
capable of creating catastrophic failures resulting in loss of lives and
billions of dollars' worth of equipment, but those were "ground-ruled-out,"
meaning that, for example, a power supply failure in the mode wherein it
drifts completely out of regulation, is a "normal" operating circumstance
and need not be considered . . . but, I digress . . .

The fact is, dladies and gentlemen, that the proposition of the time was
that the engine controllers were Honeywell 516's, whatever that means.
There was talk of installing a 68000-based computer in their place because
semiconductor memories were faster, and a system of that type was superior
for many reasons, not the least of which was modern read-only memories
would allow much better testing. The plated-wire memories in use on the
Challenger engine controllers allowed fault conditions which were not
detected to be inherited from a previous mission, which risks went
completely away with the newer design. It's not hard to imagine that such
an upgrade would save on power and weight, as well as providing much more
testability. It should also be enough faster to improve the system


> From: Hans Franke <>
> To: Discussion re-collecting of classic computers
> Subject: Space shuttle computers
> Date: Wednesday, March 03, 1999 12:17 PM
> (Just reaching the Internet/Shuttle thread :)
> > The best information I have suggests that the Space Shuttle does not
> > use the Honeywell DDP-516 in any capacity, and that engine control is
> > by the some of the IOP processors that are part of the IBM AP-101S
> > computers. The entire AP-101S, including both the GPC and IOP,
> > about 0.025 cubic meters, masses about 30 Kg, and consumes about 550 W.
> > A DDP-516 occupies about 2.5 cubic meters, masses about 250 Kg, and
> > over 1000 W.
> AFAIK the first generation of rocket control computers
> (thrust, angle, etc.) had HDC-601 processors (with plate
> wire core mem), And if I'm not completly wrong, the HDC-601
> is a DDP-516 compatible system. I don't know if the shuttle
> engines have been equipped with them, since the actual
> controlers are (since the mid 80s) are based on 68.000
> processors.
> And for the AF-101, I always belived the last core mem unit
> was named AF-101F not B, as mentioned in another message. In
> fact, I love the idea of using a /370s design CPU - It's just
> the best OPcode design ever :)
> BTW, does anybody know if a new design is planed ?
> Gruss
> H.
> --
> Ich denke, also bin ich, also gut
Received on Wed Mar 03 1999 - 18:59:43 GMT

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