[OT] Space shuttle explosions and computers

From: Richard Erlacher <edick_at_idcomm.com>
Date: Thu Feb 18 08:49:12 1999

I'm not at all certain about any of the mission details regarding the
January 1986 (final) Challenger mission. I will yield to your obviously
more accurate and current information. Having known that I'm gradually
going soft in the head for some time, I'm not surprised or concerned that
don't remember precise details about the final Challenger mission.

I am quite certain, however, that the documents and schematics which were
given to me as part of a FMEA/CIL team, which was a part of the NASA
"shuttle-return-to-flight" mission the following fall, were relating to the
Honeywell 516. These were not the main computers, of which there are
several, but only the engine controllers, which are configured as redundant
pairs, one for each engine. There was talk of a plan on the table at the
time to replace these with something smaller and lighter, using
semiconductor memory and having other features, but the one which we spent
half a year studying, at great expense to the taxpayer, and which was
purported to be used as that controller was definitely the Honeywell 516.
Perhaps there were other more popular models of that number, but the one on
the shuttles at that time were all of this type.

These were NOT the main computers on the shuttle, but rather the dedicated
main engine controllers. The IBM numbers to which you refer do sound to me
like the main computers. Analysis of the engine controllers, however, is
what our assigned task was, and that's what I remember. I don't suppose
they would have had 50 or so of us working for six months on something that
wasn't involved. It's conceivable, however, that there are several
versions of this processor. It doesn't seem reasonable that they would
have used two of a processor weighing what you attribute to the 516. 2.5
cu meters, however, is a small room, and sounds like approximately a 6'
rack cabinet, or maybe even a pair. Are you perhaps including a bit of
packaging hardware? What's used to control the engine is the processor.
The technology is of the same vintage as the DEC PDP-8's I've seen, with
hand-wired backplanes and built from ttl-msi. This one used plated wire
memory, since that was a mite faster (1 us) than the core of the time(1.2
us).

Let's see . . . the IBM AP-101S uses 1/40 cu Meter . . . that's a bit less
than a cu. ftm 30 kg and 550 watts. . . . seems reasonable. That they
later used one of its IOP's to replace the old model in use on the
Challenger and other shuttles at the time seems reasonable as well.

Unlike the defense industry and certainly unlike the commercial computer
industry, the domain of flight hardware is controlled by "proven-reliable"
hardware, so the "current" technology of the time, and the shuttle was
designed in the late '60's and built in the '70's, was not the technology
of choice. What's more, the engines in use in the early-mid '80's were
hand-tweaked hangar queens, not some sort of production hardware. The
controllers used "proven" software, which reflected all the caveats of the
NASA policy of the time. It's not always the latest technology that you
want on your 2-billion-dollar aircraft, but rather the most reliable that
does the job.

Dick

----------
> From: Eric Smith <eric_at_brouhaha.com>
> To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
> Subject: [OT] Space shuttle explosions and computers (was Re: Who
invented the internet?)
> Date: Wednesday, February 17, 1999 9:49 PM
>
> Allison wrote:
> > FYI the speed attained at
> > that point is some 3600mph far from orbital velocity.
>
> I'm not sure how to parse that. Are you saying that it was traveling at
> 3600 MPH, which is far from orbital velocity (i.e., a missing comma), or
> that it was travelling at 3600 MPH less than orbital velocity?
>
> (In any case, the use of the word velocity is incorrect. Velocity is
> a vector, as I had drilled into me in Physics class.)
>
> The NASA reference I posted earlier claims:
> At this point in its trajectory, while traveling at a Mach number
> of 1.92 at an altitude of 46,000 feet, the Challenger was totally
> enveloped in the explosive burn.
>
> 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
performed
> 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, occupies
> 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
consumes
> over 1000 W.
>
> The AP-101S replaced an earlier AP-101B computer that was twice the size.
> Anybody know where I can find one for my collection? :-)
Received on Thu Feb 18 1999 - 08:49:12 GMT