beowulf in space
James.P.Lux at jpl.nasa.gov
Wed Apr 16 17:53:50 EDT 2003
>So I wouldn't be incredibly surprised to see a spacecraft containing a
>bunch of "intel" or "amd" nodes, interconnected with e.g. SCI (because
>it is switchless and hence arguably more robust). Those nodes, however,
>will be built on motherboards and CPUs custom engineered for low power,
>radiation hardness, fault tolerance, redundancy, and tested ad nauseam
>before ever leaving the earth. It is cheaper to spend $100K or even
>more on each on those nodes ("identical" in function to a $2000
>board+network interface here on earth) and be almost certain that they
>won't fail than it is to deal with the roughly 10% failure rate per year
>observed for at least one component in a lot of COTS systems.
Interestingly, they needn't cost $100K... There are several firms that sell
(flight qualified) processor cards with interfaces for less. This would
generally be in a 6U form factor, conduction cooled, with some degree of
radiation tolerance, and with "flight quality" parts.
You can, for about $30-40K, buy a nifty hybrid package about 2.5x3.5 inches
with a 21020DSP, a bunch of RAM, various and sundry peripheral glue logic
(timers, serial ports, etc.) and 3 high speed IEEE-1355 serial ports.
There's also a SPARC version in the same package.
Sandia is developing a rad hard Pentium, for those preferring a x86
processor. There's also a rad hard/tolerant PowerPC (133 MHz, I think)
available from BAE. I'm pretty sure there's a '386 or '486 available as well.
One of the appeals of a Beowulf kind of concept is the idea of using a
bunch of commodity processors ganged together to get more processing
resources. For space, the difference is that commodity means something a
bit different. However, anytime you can spread the NRE cost across a
system composed of a bunch of identical parts, it's a good thing. This is
because you're always buying spares, redundant strings, engineering models,
etc., and those can help to spread the development cost, so the "flight
article" cost is less.
There's also a non-negligble cost of having more items on the "bill of
materials": each different kind of part needs drawings, documentation, test
procedures, etc., a lot of which is what makes space stuff so expensive
compared to the commercial parts (for which the primary cost driver is that
of sand (raw materials) and marketing) so again, systems comprised of many
identical parts have advantages.
>James Lux, P.E.
Spacecraft Telecommunications Section
Jet Propulsion Laboratory, Mail Stop 161-213
4800 Oak Grove Drive
Pasadena CA 91109
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