>I'm also thinking perhaps of some of these spacecraft
>(eg Voyager) that might have a very long life. Do they
>not use EPROMs of the day ? If so, what's to stop their
>programming just fading away - or are they not expected
>to retain it anyway and are simply space junk with some
>transmitting capability ? Do they have special long-
>retention NASA cells ?

I think you will find that spacecraft of the Pioneer/Voyager age would use
bipolar fusible link proms, as EEPROMS were in their infancy then (I
remember having to deal with the very earliest National EEPROMS, brought out
before the venerable 1702, which had a programmed life of 6 months).

EEPROMS that we use now get tantalum sheet glued over them to shield from
radiation (at least for stuff that is low to geosyncronous earth orbit). The
major problem seems to be radiation from the sun which gets concentrated to
some degree by the earths magnetic field.

I do not know what they did for Soho and other spacecraft that live at the
L1 point. They certainly get hit every so often by radiation when there is a
sunspot, as evidenced by the "snow" effect on the sensors that look at the
sun. On this basis I imagine the same precautions were taken as for earth
orbit.

Stuff going deep space does have lower radiation requirements in the
specification. Earth orbit is usually speced at 100k to 300k Rad, but for
other items I have seen as low as 10k Rad.

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