Satgen238 Radiation and Satellites Part 2 by GM4IHJ 16 Oct 93 BID of this msg is SGEN238 Please use this BID if you retransmit this msg Satgen237 discussed radiation problems in near earth space, caused by the Earth's Van Allen Radiation Belts. This report discusses radiation which originates outside earth space. The Sun is the major source of radiation near the earth, and we notice its effects on the Ionosphere - higher solar radiation usually means higher ionisation and hence higher usable HF propagation frequencies, a process generally in step with the Sun's " Sunspot cycle". But the Sun can also throw out enormous clouds of radiating plasma in massive FLARES. The biggest of these are not dangerous to us on the earth's surface, but 40 kms above our heads the radiation can get down to the D layer of the ionosphere in immense bursts which produce Sudden Ionospheric Disturbances (SIDs) whereby HF radio propagation can be lost for minutes or hours. It is therefore no surprise that Mir and Shuttle crews up around 350 km altitude must take precautions in solar storms. Fortunately most solar radiation is lightweight particles , so metal bulkheads and engines provide some protection if placed between the Cosmonauts and the Sun. But Astronauts on Apollo Moon flights were in much greater danger, outside the protection of the earth's magnetic field. So precautions were necessary to ensure that no flights occured when solar flares were likely Equally at risk in Solar Flares are the Geostationary satellites. They normally orbit inside the earth's magnetic field. But big Solar Flares compress the field pushing it inside the geostationary orbit and thereby exposing geosats to severe radiation damage. Several older geosats electrocuted themselves , when static build up in solar storms caused local lightning flashes across their frameworks. Eventually designers found out that this could be countered by using special outer covering material, which avoided electrostatic build up. Meanwhile, now well beyond the outer planets, the Voyager spacecraft are still reporting the passage of the very heavy solar burst that rush past them every few years or so. It is slightly ironic that when the Sun is most active , its output keeps out some of the Galactic Cosmic Radiation (GCR) , which is constantly bombarding the solar system. This GCR can be a long term problem. Anyone going say to Mars could get a 50 RAD dose per year, which on a standard 4 year visit Mars and return trip, amounts to a cumulative radiation dose of perhaps 200 RAD. Certainly a sickness dose, and not far short of the 300 to 600 RAD dose which proved fatal to so many unfortunate people exposed at Hiroshima. However bad as it is, this is only half the problem. Most GCR is very different from the lightweight Hydrogen particle radiation from the Sun. GCR is composed of much heavier material such as the nuclei of iron atoms cast out by supernova explosions, and as will be explained in Part 3 of this report , this is bad news for Cosmonauts and satellites 73 de GM4IHJ @ GB7SAN