Indirect hazards can either occur unpredictably, many miles from the origin of the hazard or else its origin cannot be unequivocally identified with a particular piece of equipment. The ground hazards posed by a crash of a space shuttle being used to build an SPS can occur hundreds of miles from the launch site or the SPS ground station. Pollution problems also fall into this category. Air pollution standards are enforced by the Environmental Protection Agency, not via the mechanism of making the polluter liable for the damages caused by the pollution, because it is usually impossible to prove a direct cause and effect relationship between the hazard and the incremental pollution caused by specific polluters. Interference of the SPS microwave beams with other users of the electromagnetic spectrum (RFI) may be similar to air pollution problems. RFI could cause a reduction in the signal to noise ratio in equipment located thousands of miles from the SPS rectenna. Because of the distance, it may be Impossible to prove a direct cause and effective relationship between the RFI and the microwave beam of any particular SPS. Interference of Microwave Beam with Other Users While several studies of how the Microwave Beam might affect other users of the radio spectrum have been performed, there is still no definitive list of what equipment might be affected and how far from the rectenna site these effects might be observed. Various lists of the types of effects that might be observed have been compiled but the experiments that will indicate the magnitude of these effects and the resulting magnitude of the Radio Frequency Interference (RFI) have not been performed. Even the optimistic estimates indicate that the SPS Microwave Beam will interfer strongly with the following units:
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