>Hard drives meant for high altitude applications are completely
>sealed with air inside, as opposed to those we use on the ground
>which have filtered air vents.  I'm certian everything with glass
>or any brittle material must have some layer of protection
>(plastic).  I would speculate that even tempered glass wouldn't
>be accepted as-is.

I do not know how much experience you have with space hardware, but what you
wrote in this email suggests you have very little, if any.

Having worked on space instrumentation for over 5 years now, I do know a
little. In terms of what plastics are allowable, there are very few, as most
of them outgas fumes that will get everywhere you do not want them, and if
there is any optics around, you definitely do not want them.

I have no experience with using hard drives per se, but there is no reason
why glass itself would need to be covered that I am aware of. Hard drives
would probably need to be ruggedised to withstand the G forces experienced
during launch, but this is probably not a problem for many laptop type
drives.

>The stuff that goes up 'on a shuttle mission' has less strict
>specs than the stuff that is part of flight control.  An off
>the shelf embedded computer, if well made, would still have
>problems though.  Not only are they concerned about whether the
device will make the trip without damaging itself or anything else,

I would be surprised if an "off the shelf" computer would be used straight
out of the box, but a suitably repackaged industrial computer should be OK,
as it would need repackaging to get it past the necessary vibration testing,
to ensure all screws stayed done up and wiring did not come adrift.

>but 'little' things like outgassing are of critical importance.
>Not only could the chip packages give off a terrible odor
>(which we wouldn't notice here, but in confined spaces with
>recycled air could lead to nausea) but the chemicals released can
>damaged air handlers and other safety critical equipment.

Well the "plastic" packages used on COTS chips are apparently OK. I am not
aware of any that outgas, as they are not really plastic, but an epoxy. As a
package they are apparently OK for radiation hardening of chips as well.

>From what little I've read there are specifications down to
>the exact solders approved.

Well we use "ordinary" 60/30 solder. There is talk of not having the lead
free imposition affect production for space instruments as well. However it
may be that specific contracts require special solder to be used in certain
instances. This may be more to do with other environmental requirements,
such as needing to match thermal expansion characteristics of packages, and
these can be using the full military temperature range of the chips, so
thermal cycling can be a real problem.

>Cosmic rays penetrate everything up there at one point of
>another, so the size of the features of the die in a chip and its
>packaging are as important as many other considerations.

This is one problem, but usually only a problem for satellites in earth
orbit, as the magnetic field seems to create more intense particle fields
around the earth as the solar wind comes under the influence of the field.
Satellites which get beyond the earths influence have lower requirements in
radiation hardness, even when being put in a position closer to the sun than
the earth is. For example the SOHO satellite that is at the L1 point between
the earth and sun had a radiation requirement of 10k Rads for a 3 year
mission life, and has been working for over twice that now, on the
instrument that my colleagues produced. Compared to that an instrument that
I was involved in making had a requirement of 100k Rad for a 5 year mission
life in low earth orbit.

I would expect that items taken on the shuttle for an experiment that was to
run for the length of a particular shuttle mission would have almost no
specification for radiation hardness, but anything that was to go on the
space station would probably require a reasonable specification. However
unless there was a requirement to mount it on the outside (such as some form
of sensor or detector), the requirements would not be very stringent.
Aluminium is a reasonable shield against such radiation, with tantalum being
the best for radiation shielding against weight trade-offs.

Thank you

Alan B. Pearce
R25 Rm 1-122
Rutherford Appleton Laboratory
Chilton
Didcot
OXON OX11 OQX
United Kingdom

Tel +44 1235 44 6532
Fax +44 1235 44 5848

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