optics is assumed to be 1 pr, which severely degrades the short wavelength systems. Thermal blooming, which may further degrade the irradiance, is ignored. C. 3.3 Strategic Use of an SPS Laser System Possible targets for an SPS laser based in synchronous orbit include ballistic missiles (both ICBM and SLBM), satellites, aircraft, ships, military installations, and personnel. The nominal laser threat (see Section C.3.2) would probably not present any significant hazard to targets within the atmosphere. The irradiance values are such that a combination of shielding, convective cooling for moving targets, and time requirements, would severly degrade laser effectiveness. There is some threat, however, to satellites. Analysis on solar cells indicates a threat to low Earth orbit satellites at laser wavelengths of 1.3 micrometers or less. For higher orbit satellites, the threat would extend to higher wavelengths and would be even more pronounced at the lower wavelengths. The optimistic laser threat extends hazards to atmospheric targets, except where atmospherics degrade propagation. For wavelengths less than about 1 micrometer, the irradiance values are such that metal surfaces could be melted in reasonable times. This could bring the entire spectrum of targets into the hazard category, especially at the shorter wavelengths where, in addition to much higher incident irradiance values, the thermal coupling of radiation into bare metal targets is significant (see Figure C.3-4). There is a definite threat to satellites at wavelengths in the near IR and below. For wavelengths in the visible and UV region, it would be extremely difficult to protect against the irradiance values experienced by satellites. c.3.4 SPS Vulnerability to HEL The vulnerability of SPS lasers is assessed here relative to continuous- wave laser irradiation of wavelengths between 0.25 and 2.0 micrometers. The assessment is for thermal damage and is considered to be equally valid for pulsed laser threats within the present state of knowledge of pulsed laser effects and the scenarios under consideration. As the system design is conceptual, and as the vulnerability analyses are based on simplified first order principles, the resulting vulnerability assessments are not intended to establish exact criteria, but rather to provide indications of SPS and component vulnerability.
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