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Re: RAD-Hardening Spacecraft

Bob Bruninga wrote:

Hi, Bob!  I'm not an expert at all about this, but I want make some
comments that could be interesting to you.

> 1)  The Final RF Power Amps will be directly connected to the power
> bus.  Can a high energey particle cause conduction of the final PA
> junctions, thus shorting the power bus, causing a current peak,
> avalanche breakdown and thus total failure of the system?  If such a
> scenario is possible, then resettable circuit breakers of some sort
> will be required and I dont have any simple ideas...  Help?

Power transistors have a large silicon volume and seems rare that a
single particle could store in the junction enought energy during
enought time to generate a long pulse that will destroy the device.
The circuit inductance will limit the current pulse. Anyway when
appling RF input to it you are making it conductive and aren't
damaged becouse current are limited. Power semiconductor should be
less susceptible to radiation than i.e. a memory cell that easily
could be toggled. Also resettable circuit breakers must be very
fast to avoid the problem if really exist.

> 2)  We need RAD-HARDENED chips for our two KPC-3+ TNC's.  Can anyone
> help locate a source?  Here are the chips needed:

Standard parts could work if choseen the right ones.

> My local guru says that even normal parts from different manufactures vary
> by as much as 1000:1 in radiation sensitivity depending on manufacturing
> tolerences.  Who makes the best parts?

I'm sure you are aware bout those sites, but could check:

NASA/GSFC Radiation Effects and Analysis Home Page

There is available a list of tested device that could help you to
select the better available for you.

The Radiation Effects Data EXchange by the Naval Research Laboratory
Radiation Dynamics Section. http://redex.nrl.navy.mil/ 

Also there you can find link to other resources.
> 3) Looks like we can do without the 14C88 if we dont use the serial port
> on Orbit.  Does anyone see any other power savers?  We could replace the
> voltage vairable pots in the AD8402 with fixed voltage dividers.  How much
> power will we save?

Really, RS232 levels aren't a must even in home computers, that will
work with TTL ones in a relatively noisy environment. Probably with
a good design, shielding, etc. won't need RS232 levels.
Anyway there is plenty of low power parts with autoshutdown that will
be a better choice than a standard 14C88, like Maxim MAX3212 and others,
even high realiability hermetic ones under MIL-STD-883.

Just my thoughts, I havn't any experience about.

73's de Luis

mail: melus@esi.us.es
Ampr: eb7gwl.ampr.org []
AX25: (sorry shut down)

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