120 V DC, 3-15 kV DC, 400 Hz AC, 20 kHz AC, and other power modes should not impose any undue burden or risk on the central-station power concept. User Spacecraft Constraints. Specific missions of customer spacecraft could impose major constraints on the central-station power supply concept. The most obvious of these is to maintain receiving antenna orientation toward the power (or relay) station, which may compromise pointing and tracking requirements of optical instruments and communications antennas, as well as introducing undesirable mechanical contrivances such as universal joints and sliding electrical contacts. Another set of obvious constraints are the launch, operational, and maintenance needs of the receiving antenna, power reconversion system (for laser transmission), and power conditioning subsystem, which the customer spacecraft must carry into orbit and operate along with his satellite. Although these systems are almost certainly less massive and in general impose fewer operational problems than the onboard power supply of conventional spacecraft systems, they nevertheless represent a concern to the customer that must be dealt with as part of the power delivery service. A third constraint is imposed by unique operating conditions of the customer spacecraft; e.g. maneuvering, specification of the degree of microgravity and acceptable vibration levels that might be affected by power-system antenna slewing or dynamic power reconversion systems, etc. The use of central-station power for electric or laser propulsion also implies more stringent tracking, slewing, and beam stability requirements on the central-station system than would a nonmaneuvering spacecraft traveling in a gravity-controlled orbit. Variable-thrust needs or power on/power off operation, in addition to provisions for eclipse periods, would also impose operational constraints in the central-station system. One very important consideration for military satellites is survivability. These spacecraft must operate for years both in and outside the Van Allen radiation belts and in orbits with high debris density, and they must also be able to protect themselves, either passively or actively, against potential enemy offensive action which might involve nuclear radiation, electronic warfare (including massive electromagnetic pulses), lasers, high-power microwaves, particle-beam weapons, kinetic-kill missiles, and ‘shotgun-cloud' kinetic weapons. Although their primary areas of vulnerability are their sensors and electronic circuitry, power supplies, because of their large size (solar arrays or the thermal radiators of nuclear-powered systems), are also susceptible to damage or destruction. Hence removal to a remote location of the most vulnerable elements of the power supplies, which are also the most difficult to protect, could have significant survivability benefits to the military customer. Conversely, the power satellite itself would make an ideal target for an enemy whose intent is to disrupt his adversary's satellite systems, whether they be surveillance, reconnaissance, C3, or strategic defense assets. Hence the central-station powerplant operator must be able to assure his military customers that he can protect his power sources against all modes of attack, either by shielding, hardening, jamming of electromagnetic radiation, or onboard defensive missiles. Performing this function to the degree necessary to satisfy military customers could constitute a major technical risk (e.g. how to define and validate the real potential threat that must be countered) and very substantial cost risk. Declining to meet customer survivability needs, however, would almost certainly preclude military organizations' willingness to rely on central-station power supply services. Schedule. Based on current market estimates, it would not make economic sense to consider deployment of space-based central-station power systems until at least the
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