will be vital to alleviate concerns over safety and satellite interference effects. Because the rectenna has a much higher ballistic coefficient, its orbit will decay much more rapidly than that of the Astro-SPAS. (This is the reverse of the Microwave Solution discussed in PART I.) Two ion thrusters, identical to the RIT thruster on Eureca-1, would be used to provide the same net effect, as shown schematically in Figure 5.2-3. During each microwave beaming session, lasting as much as one or two orbits, the ion thrusters would be operated continuously to ensure the two satellites remained about 3 km apart within a tolerance of 100 m, for example. A radar ranging and Doppler device would be required to measure the separation distance and determine the location of the rectenna. Alternatively, a GPS receiver could be placed on the rectenna. Depending on how much the rectenna orbit decays, the Shuttle may need to lower its orbit in order to facilitate recovery and avoid significant orbit phasing manoeuvres later. After a certain number of beaming tests, formation orbit raising would be attempted. This would involve simultaneously operating the cold gas thrusters on both the rectenna and Astro-SPAS. The Astro-SPAS propulsion system would need to be modified or augmented with a separate system for these translational manoeuvres. Once the orbit raising had been completed, the Astro-SPAS would need to make up any differences within one or two orbits until it is once again situated 3 km in front of the rectenna. The rectenna would then automatically re-orient itself to face the Astro-SPAS and further power beaming experiments could continue. The cycle of power beaming followed by orbit-raising would be repeated a number of times until the batteries had been depleted. The entire mission would last only two or three days, depending on whether problems were encountered. Then Astro-SPAS would be recovered by the Shuttle for return to
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