On 1/16/06, Peter 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 ? The Voyager probes were later (Voyager 1 was launched in 1977). As a data point, the original Shuttle computers were core memory, with programs loaded from a redundant tape system. (I used to work on them). Bill -- Psst... Hey, you... Buddy... Want a kitten? straycatblues.petfinder.org -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist