analog processor can thus determine the propagation phase to each pickup reflector and command phase shifter settings via modulation on the 2.445-MHz reference signal. The other aspect of phase front control is the phase shift of each klystron. Because the klystrons are high-Q devices and operate at high temperatures, and because the SPS will be subject to periodic eclipsing which introduces thermal transient effects, the use of phase control at each of the 138,000 klystrons appears essential at this time. The output of each klystron can be phase-locked to the subarray input signal as indicated in Figure 2.3-22. The above phase control methods will correct the time-varying phase errors in the SPS array. When first started, however, the bias errors will have to be measured and corrected. For this purpose, the phase shifters at all klystron inputs of a single subarray can be modulated in unison in a variation of the ''bit wiggle" approach proposed by Raytheon. If the received beam is monitored near the edges where the energy is -30 dB below beam peak, the modulation will be about -50 dB below carrier and the correct subarray phase is indicated at the peak of the modulation envelope. 2.3.5 Conclusions The power transmission study effort resulted in the following findings and conclusions: 1. Adaptive phase control studies should be evaluated further for amplitron and klystron systems — Various adaptive phase control techniques can be used for the SPS; however, because of the complex nature of this subsystem, future studies or breadboard ground tests should be initiated to determine performance characteristics of such a design. Applications of amplitrons and klystrons to these networks should be included. 2. DC-dc conversion efficiency goal of 65 percent is a reasonable goal — based on Rockwell's studies and other NASA-sponsored studies, 65 percent dc-dc efficiency goal can be established as a realistic design goal. 3. DC-RF Conversion Device Power Output Optimization — Studies indicate that for increased weight/cost savings and design simplicity, variations in tube output power should be examined. 4. High-Temperature Problems Critical — The high-temperature problems associated with the array design is a key design issue. Satisfactory solutions to material of waveguide for high-temperature operation without sacrifice of efficiency do not exist, therefore requiring future studies. Thermal transients during startup, shutdown, and eclipse must be studied. 5. RCR Offers Potential Solutions to Improved Efficiency, Weight, and Temperature Over Conventional Array — The Rockwell studies indicated that new solutions were required to optimize the waveguide design.