vacuum-safe laptops ?

[Thomas Shaddack]

On Fri, 16 Jul 2004, Major Variola (ret) wrote:

> >Does anyone *know* (first or second hand, I can speculate myself) which
> laptops, if any, can safely go to zero air pressure (dropping from 1 atm
> to 0 in, say, 1 minute.)
> 
> Sorry so late ---but your can-shaped capacitors might not handle the
> rapid depressurization so well.

Perhaps it's time to challenge the introductory assumption. Why a laptop? 
There are many various embedded computers available on the market, eg. the 
one from <http://www.gumstix.com/>. (Question for the crowd: anybody knows 
other comparable or better Linux-ready affordable embedded computer 
solutions?) You may like to take such module and seal it in resin in order 
to shield it from the pressure changes (question for the crowd: would it 
really work?). Use memory card instead of hard drive; you don't want 
moving parts that depend on air density. The smaller size and lower power 
consumption than a laptop has makes many issues, from cooling to powering, 
much easier; vacuum-proofing and testing of the assembly is potentially 
simplified as well.

I'd also be cautious about the fluorescent tubes for the displays, the 
glass won't necessarily have to withstand the rapid change in air 
pressure. The LCDs themselves consist from two layers of glass with a 
electricalyl-sensitive light-polarizing liquid between them, make sure it 
won't have tendency to boil or vaporize in vacuum.

Optionally, for unmanned operation, do without the display completely. For 
manned operation, use something like the head-worn see-through 
<http://www.microopticalcorp.com/> display, located in the operator's 
pressure suit, and connect it to the computer by a suitable wired or 
wireless connection.

If the system has to go beyond the reach of the atmosphere, you would like 
to use some sort of radiation shielding, or use a redundant assembly with 
several computers working in parallel, compensating lower reliability 
(silicon-on-insulator chips are difficult to find in off-the-shelf 
setting) with redundancy. You may also prefer to keep critical systems 
working on lower frequencies, with older-design parts, using bipolar 
transistors instead of CMOS (which tends to trap charged particles in the 
insulator layers of the gates, which shifts the gate threshold voltage), 
and chips with larger structures (so the ionization traces of particles 
won't affect the chips that much). Protect the content of the memories - 
large arrays of rad-sensitive elements - with ECC codes. GaAs is also more 
radiation resistant material than silicon. Again, combine rad-hard design 
with redundancy for best results.

Cooling is a royal bitch. You can't use anything but radiation cooling. I 
think satellites use a neat trick with pipes containing a wick soaked in a 
suitable liquid, eg. some freon. The liquid is vaporizing on the hot end 
of the pipe, condensing on the cold end, and soaking back to the hot end 
by capillary forces; this is used to bring the heat from the power parts 
and the sun-facing side of the satellite to the dark side of the 
satellite, from where it radiates to space. (Question for the crowd: Can 
thermal imaging be used for scanning the sky for low-orbit satellites? 
Other question for the crowd: How suitable would be this wick-in-a-tube 
approach for "ground-level" computers, could it increase the efficiency of 
heat transfer from the CPU chips to the wings of the heatsinks? Eg. for 
the purpose of having the computer sealed in an RF-shielded enclosure, 
with the heatsinks being part of the case, which could eliminate the 
cooling air inlets?)