proved in the next phase of the program. Greater coordination is required between the various contractor efforts. In view of the large number of design areas now needing work, it is possible that the concept of two parallel programs has outlived its usefulness. There should be a single NASA program office in charge of the SPS system which could oversee the development of the entire project. 4. BEAM FORMING AND CONTROL Phase control for beam forming is crucial to successful operation of the SPS. Phase control is more critical than many of the other subsystems and components because failure to function within tolerances can cause a sudden and complete loss of power transfer to the ground. The design must have some kind of redundancy or protection at the subsystem level to prevent catastrophic failure. The Reference System The present LinCom scheme for achieving reference phase control has a major disadvantage. The power transmitters at 2.45 GHz tend to interfere with the onboard pilot receiver. This interference is suppressed by the use of a high rejection rationarrow band notch filter, by separating the sidebands of the pilot waveform, and by the use of the spread spectrum anti-jamming improvement ratio. This approach is unacceptable because long-term stability of the deep notch filter is unlikely with real world technology. Use of the spread spectrum to achieve rf interference suppression is very useful. Spread spectrum should also be added to the system for anti-jamming and anti-spoofing. It is recommended that this approach be continued provided that the notch filter problem can be solved, and the use of spread spectrum be expanded for anti-jamming protection also. Alternative Phase and Control Systems The broadcast onboard reference signal idea presented by Rockwell International looks good — it looks as if it will work. It is rugged, resilient, and relatively simple. It should be pursued. Any scheme which will lower the microwave parts count in the phase control system should be given a high priority for further study. It would be desirable, if possible, to eliminate the uplink pilot system for beam forming. This would eliminate possible ionosphere problems and reduce the possibility that the SPS would suffer sudden and complete loss of function if the uplink should suddenly fail or be interrupted. Ground-based pilot systems, that have most of the sophisticated hardware and subsystems on the ground, are the best of the pilot signal types and should be pursued further. There are two very severe problems, however. First, on the order of 150-200 dB isolation is needed from the downlink signal. This is an extremely difficult task. Secondly, as the system ages, tuning drifts and changes in impedance levels will take place. As many components as possible should be under closed-loop control to compensate for phase changes due to drift. Every circuit shown to the review panel had some open loop parts in the phase control scheme. It must be demonstrated that any proposed system can overcome these problems. An even more subtle phase drift problem exists. Certain components under the closed loop subsystem will, when they age and mistune, produce phase changes in the larger part of the system to which they belong; for example, the VCO phaselock
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