6. SPECIAL STUDIES Three brief special studies were conducted during the contract to address the key issues of nuclear radiation design requirements, the potential problems of spacecraft charging, and microwave radiation effects. The results are documented in this section. 6.1 NUCLEAR RADIATION AT GEOSYNCHRONOUS ORBIT The nuclear radiation environment at geosynchronous orbit consists of the Van Allen belt particles (electrons and protons), solar space particles (protons and alpha particles) and galactic (cosmic ray) particles (protons, alpha particles, and heavier nuclei). The Van Allen and galactic particles are always present, even though their fluxes and energies do vary with time (primarily because of solar activity), as shown in Table 6.1-1. The solar flare particles are present only after a significant solar flare has occurred on the western portion of the visible solar disk. It requires a few hours for the first particles emitted during a solar flare to reach the vicinity of the earth, and the particles from a single large flare are often present for two to three days. Typically, there are only a few large solar flares a year which'produce particle radiation near the earth. At synchronous earth orbit, both the Van Allen protons and the electrons have energies of a few Mev, the energy spectra being monotonic (the higher the energy, the fewer particles which have such energies). The Van Allen belt particle dose is shown in Figure 6.1-1. The average particle fluxes are on the order of 10$ cm" 2 sec"^, although this can increase an order of magnitude Table 6.1-1. Time Dependences of Nuclear Radiations
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