Satgen237 Radiation and Satellites Part 1 by GM4IHJ 9th Oct 93 BID of this msg is SGEN237 Please use that BID if you retransmit the msg We live in a unique environment. Almost everywhere in the Universe around us the level of radiation is deadly. Go 1200 kms above the earth ( or lower in places) and you will encounter strong radiation. Go anywhere between 3000 and 26000 kms above the temperate or equatorial regions of the Earth and you will be advised to restrict your stay to a few minutes. On the Earth's surface we are protected by the Atmosphere and the Earth's Magnetic field. Leave that cover and you will not survive for long. Satellite electronics and solar cells have the same vulnerability to radiation as human beings. Most of our early amsats succumbed to Battery failure, but once ground controllers learnt how to regulate battery loading by good house keeping, it became clear that while satellites below 1000 kms altitude were generally safe, those above that height ( RS1 to RS8 ) mostly died from radiation damage to their onboard electronics. What about Phase 3 satellites - they go to 36000 kms plus ? Yes but their original design orbit aimed for 60 degrees inclination enabling them to dodge most of the radiation by climbing up through the polar holes in the radiation belts. All very good if your Phase 3 sat gets to 60 degree inclination. Oscar 10 did not, and within 2 year it began to quietly go mad as its electronics were beaten up on its twice a day trips through the densest part of the radiation belts which fit like a donut with a hole in the middle for the Earth, and a big hole over either pole . So it is vital that any future Phase 3 satellites get to high inclination, even though their modern electronics has far better radiation shielding than was the case with the chips aboard Oscar 10. At first sight Pacsat Lusat Webersat Fuji Uosat etc all look pretty safe. All but Fuji orbit around 1000 kms altitude. But they are much bigger electronic targets, with many more chips than the voice transponding satellites. In particular their large store and forward memory capacity is very vulnerable. So it was no surprise when a system of electronically washing and refreshing these memory circuits was included in the design. Fortunately this memory repair facility for correcting data changes resulting from Single Event Upset (SEUs radiation hits which corrupt a single bit) was made flexible , because ,in space operation, soon proved that the incidence of SEUs was higher than expected. So the wash and refresh routine had to be done much more often, something which the design flexibility permitted. It did not take much guessing to work out where most of the radiation hits were occuring. For years satellite users had known that for some reason the near earth space above eastern Brazil and the adjacent South Atlantic Ocean was " Radiation Hot". At first no one understood why . Then it became clear that the donut shaped radiation belts where shaped by the earths magnetic field , and that field was not centred around the rotation centre of the earth. In fact the magnetic field is centre 600 kms away from the rotation centre towards Malaysia, and because of this Brazil opposite Malaysia on the other side of the world is therefore 600 kms further from the magnetic centre which makes it 600 kms nearer the Earths Van Allen Radiation Belts. Anything flying over Brazil meets the bottom edges of the radiation belts at about 600 kms altitude, unlike most of the rest of the world where the belts only come down to about 1200 kms . Have just been reading G3LDIs excellent " Packet BBS survival for the Beginner". Thanks Roger, I learnt a lot . 73 de GM4IHJ @ GB7SAN