control commands would then be sent to the spacecraft, with potentially damaging consequences for missions that took years to prepare. It is important to examine these effects for both financial and intellectual reasons. The United States, and the rest of the world, have made a cumulative capital investment in radio astronomy of approximately $400,000,000, with the U.S. share being about half of that total. The capital investment in space research is even larger. For example, as part of the U.S. space program, NASA presently launches major interplanetary probes at the rate of one every year or so, each mission costing an amount comparable to the total capital investment in radio astronomy. Beyond the direct investment cost, however, is the intellectual value of the knowledge gained by this research. Study of the philosophical implications of cosmology, the examination and testing of basic physical laws, the exploration of the solar system to which the earth belongs, and the possibility of finding if there is other intelligent life in the universe are intellectual activities beyond price. Radio astronomy and space research are recognized radio services as defined in the Radio Regulations of the International Telecommunication Union, with recognized frequency bands that are protected by allocations and by footnotes in the treaty documents. Definitions of harmful interference to these services have been developed by the International Radio Consultative Committee (the usual abbreviation, CCIR, is derived from its name in French). CCIR Report 224-4 describes these criteria for radio astronomy, and CCIR Reports 365-3 and 685 give the criteria for the space research service. These reports are included in the Appendices A and B, respectively. The harmful flux spec- 2 tral densities, specified in dB W/m -Hz, have been established as reasonable and measurable quantities, and an SPS must conform to those specifications in order to avoid harmful interference to those services. The harmful interference can come from production of harmonic radiation, or generation of noise-like radiation throughout the spectrum. All microwave power generating devices inevitably produce both types of radiation in some quantity that can be measured. This radiation is produced both by normal operation and in potentially more damaging quantities by various failure modes.
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