On Mon, 16 Jan 2006, Alan B. Pearce wrote:

>> 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.

See Wikipedia article about the Apollo guidance computers:

http://www.answers.com/topic/apollo-guidance-computer

wire wrapped socketed chips + epoxy, and core rope memory. The Voyagers 
predated that and likely used similar technology ?

Peter
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