C.l Nuclear Weapon Effects on Satellite Power Systems This section discusses the relative nuclear vulnerability and survivability of power satellites and other SPS elements. Nuclear confrontations or even some nuclear weapons tests could damage or destroy elements of the SPS. C.1.1 Basic Nuclear Effects of Concern Nuclear weapons produce x-rays and gamma rays, neutrons, and a large electromagnetic pulse (EMP) in addition to the expected thermal radiation and blast. In space, the thermal radiation and blast will not be the main threats. If the weapon is close enough for thermal or blast damage to be significant, the system will have already been killed by other nuclear radiation. X-rays and gamma rays constitute 60 to 90 percent of the total explosive energy. For example, a one megaton device will produce lO^15 calories of electromagnetic radiation of very short wavelength. In space, the intensity of this radiation falls off as 1/R^2 from the burst point. X-rays are photons with energies in the 1 to 100 keV range and gammas are in the 100 to 10,000 keV range. Both can be approximated by a single blackbody spectrum, so the total fluence of gamma rays is about two orders of magnitude lower than for x-rays. Total energy fluence is given in units of cal/cm^2 , the total absorbed dose is in rads,* and the transient dose rate is given in rads/sec assuming silicon as the absorber. As x-rays and gamma rays interact with matter, they deposit energy by ionization (i.e., the creation of hole-electron pairs) and by disturbing the molecular or crystalline structure of the material (i.e., heat). The energy deposited is a strong function of the x-ray/gamma energy and the atomic number of the material. The predominant damage effect, especially in more dense material, is thermal shock due to the rapid heating of materials. Transient radiation environment effects (TREE), due to the sudden change in conductivity resulting from the creation of a large number of excess hole-electron pairs, can induce large transient currents which can be severely damaging in circuits containing semiconductor devices. Total ionization damage can also occur due to charge buildup and crystalline changes. This latter effect is a function of the total accumulated ionization dose. ♦Absorbed radiation is usually specified in terms of the energy deposited in a givengmass. Thus 1 rad = 100 ergs of absorbed energy per gram of absorber, or 2.39 x 10 calories per gram.
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