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Resurrecting NEAR
JoeRobe writes "Space.com is reporting that John Hopkins researchers are going to attempt to revive the NEAR-Shoemaker spacecraft at the end of the year. The spacecraft, designed to orbit asteroid Eros, finished its mission by successfully landing on the surface of the asteroid in February 2001, resting on its body and two solar panels. Now, after NEAR has been silent and cold for over a year, researchers are going to try to make contact with it and possibly try to turn on its scientific instruments one last time . How long can silent electronics last in space?"
methinks you mean Johns Hopkins....
The /. article of the NEAR touchdown can be found here.
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And my guess would be they have three bootable setups: a mask ROM of version 1.0 flight software, and two flash images.
The hardware first tries to boot flash image 1, if that fails then it tries flash image 2, and finally if that fails it falls back to the mask ROM image.
--Rob
Remember the last Hubble maintenance mission? They had to wrap an electric heating blanket around some parts and complete their work in much less than one day to prevent freezing of parts. It is likely very possible to design parts to survive long shutdown, but the HST wasn't designed that way because nobody expected to do it (the module they replaced was not one of the pieces designed to be repaired in space). NEAR was not designed for shutdown either.
They have to schedule time on the DSN (Deep Space Network) to communicate with the spacecraft. Time on a global satellite tracking network is not cheap. There are probably additional costs for people and support services.
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There is a hard limit... Since theoretically almost every atom does decay eventually, an electronic object can sit in space until enough of it's constituent atoms decay away to break the electrical connections. Then it's broken. This limit is generally much longer than the age of the universe so far.
Then there is chemical/mechanical stability. Some compounds do degrade over time, such as plastics. Plastic parts become brittle, crumble, or otherwise age. Batteries and RTG's degrade or wear out. The same goes for moving parts. The time for this to happen is much less than atomic stability of the actual device. If cheap parts are used, even ten years is easily possible, sometimes much less. Chemical degredation is heavily dependant on the temperature of the object in question. It would also more affect the support systems of the electronics worse than the electronics itself. Batteries, fuel cells, electrical shielding for moving parts such as gyros, for example.
Since empty space is not really empty, we also have degradation due to interaction with the spacecraft's environment. Micrometeorites abrade the suface of the craft, but larger ones behave like bullets, and these can definately cause harm to electronics inside. Then there is the radiative environment. Cosmic rays, or other exotic forms of radiation can be really nasty to electronics. At the least, they can cause random noise in running electronics, and say, flip 1's into 0's or vice versa every now and then. The much harder rays can permanently damage or fuse microcircuits. As any overclocker knows, simple heat kills electronics very nicely, so objects closer to the sun may have much shorter lifespans. Radio wave radiation from solar storms, if intense enough, can have the same effect on electronics as a highly statically charged cat rubbing against my motherboard when I took off the case.. (you don't wanna know.) There's a fair amount of redundancy in space based electronics for this reason, but there is a limit to how much abuse these systems can bear. Engineers can't insure against every eventuality, such as ET cats.
In my opinion, the practical limit of a spacecraft is balanced between chemical/mechanical degradation, and environmental hazards. I feel that right now, mechanical degradation is much worse than environmental effects, but as durable solid state devices become more prevalent, this will tip the scale in the other direction. I'd be interested to see statistical information on the reason satellites fail.
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