beowulf in space
edwardsa at plk.af.mil
Thu Apr 17 21:33:19 EDT 2003
There are two basic strategies for hardening: Design and process.
Processing involves special anneals, implants and oxide recipes that
are outside standard processing and so cannot be fabbed in standard
foundaries. Designs are rather old and infolve specially shaped
transistors. This is an active and promising area of pursuit. If you
are really interested, you can look at past December issues of IEEE
Transactions on Nuclear Science. You can also attend the Nuclear and
Space Radiation Effects Conference this July in Monterrey Ca.
You can, in fact, shield against alot of threats. The question is
whether you want to launch shielding or active electronics.
On Thu, Apr 17, 2003 at 04:54:17PM -0400, Robert G. Brown wrote:
> On Fri, 18 Apr 2003, Mof wrote:
> > Ok excuse my ignorance, but what is involved in rad harding hardware ?
> > Is the cost really necessary, in that couldn't you put the unprotected
> > hardware into some sort of shielded container ?
> > Or am I just being silly ? :-)
> Not really silly, but IIRC shielding is both difficult and expensive and
> sometimes actively counterproductive in space. I'm sure the NASA guys
> will have even more detail, but:
> a) Difficult, because there is a very wide range of KINDS and ENERGIES
> of radiation out there. Some are easy to stop, but some (like massive,
> very high energy nucleii or very high energy gamma rays) are not.
> b) Expensive, because to stop radiation you basically have to
> interpolate matter in sufficient density to absorb and disperse the
> energy via single and multiple scattering events. Some radiation has a
> relatively high cross section with matter and low energy and is easily
> stopped, but the most destructive sort requires quite a lot of
> shielding, which is dense and thick. This means heavy and occupying
> lots of volume, which means expensive in terms of lifting it out of the
> gravity well. I don't know what it costs to lift a kilogram of mass to
> geosynchronous orbit, but I'll bet it is a LOT.
> c) Counterproductive, because SOME of the kinds of radiation present
> are by themselves not horribly dangerous -- they have a lot of energy
> but are relatively unlikely to hit anything. So when they hit they kill
> a cell or a chromosome or a bit or something, but in a fairly localized
> way. However, when they hit the right densities of matter in shielding
> they can produce a literal shower or shotgun blast of secondary
> particles that ARE the right particles at the right energies to do a lot
> of damage (to humans or hardware). So either you need enough shielding
> to stop these particles and all their secondary byproducts, or you can
> be better off just letting those particles (probably) pass right on
> through, hopefully without hitting anything.
> Basically, we are pretty fortunate to live way down here at the bottom
> of several miles of atmosphere, where most of the dangerous crap hits
> and showers its secondary stuff miles overhead and is absorbed before it
> becomes a hazard. Our computer hardware is similarly fortunate. Even a
> mile up the radiation levels are significantly higher -- even growing up
> in subtropical India I was NEVER sunburned as badly as I was in a mere
> two hours of late afternoon exposure in Taxco, Mexico, just one mile up.
> A single six hour cross-country plane ride exposes you to 1/8 of the
> rems you'd receive, on average, in an entire year spent at ground
> level. God only knows what astronauts get. Maybe they bank gametes
> before leaving, dunno...
> So definitely not silly, but things are more complex than they might
> seem. I'm sure that if a cost-effective solution were as easy as just
> "more shielding" the rocket scientists (literally:-) at NASA would have
> already thunk it.
> Robert G. Brown http://www.phy.duke.edu/~rgb/
> Duke University Dept. of Physics, Box 90305
> Durham, N.C. 27708-0305
> Phone: 1-919-660-2567 Fax: 919-660-2525 email:rgb at phy.duke.edu
> Beowulf mailing list, Beowulf at beowulf.org
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Electronics Foundations Branch
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