[time-nuts] OT - but of interest?

Jim Lux jimlux at earthlink.net
Fri Apr 26 20:59:21 EDT 2013


On 4/26/13 9:18 AM, Chuck Forsberg WA7KGX N2469R wrote:
> On 04/26/2013 06:01 AM, Bob Smither wrote:
>> As many on this list are amateur radio operators the following might
>> be of interest:

>> to track the satellites in real time."
> Will radiation fry the cell phones before thy burn up on re-entry?
> They are expected to re-enter within weeks so there is a good
> chance they will not see a radiation event before they burn up.
>

Total dose will be very small (after all astronauts live in LEO)

So you'd worry about cosmic rays and single event effects.

A lot of modern parts are pretty latchup immune for a variety of reasons.

Things that tend to die are FETs that are switching power.. they don't 
have much voltage margin on the gates and dumping a bunch of charge from 
a single event might push it over the threshold and you get a gate 
rupture (SEGR).

SEU and related SEFI are probably pretty unlikely.  Feature size is 
small, and the odds of hitting one that's actually being used are low. 
There's an external watchdog to reset it as well. The camera will 
probably show some speckles.

They fly a lot of unmodified commercial equipment on ISS (and on 
Shuttle, when we still flew it) and they typically have MTBF of a month 
or so for the really soft parts.  Most stuff will last a year before it 
dies.

It's unclear whether there has ever been a documented case of a 
satellite failing due to latchup in space.  Surrey is pretty cagey about 
their on-orbit performance at that level of detail, but they use mostly 
commercial parts.


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