Microwave Beam Reflector There are four challenges that have to be faced in deploying a large reflector in GEO: • A feasible structural design approach capable of producing an ultra-lightweight space structure, packaging for delivery to orbit, and high surface precision after deployment. • A concept for telerobotic assembly of the reflector in space. • Economic space transportation within the available state-of-the-art. • On-orbit station keeping, attitude control and pointing requirements and means of meeting the requirements. The active reflector size is about 2.2 km in diameter. The surface area is 4.15 km2. The actual design is slightly larger as dictated by the need to have attitude control systems at its periphery that do not interfere with the beam. At 0.175 kg/m2, a unit mass calculated to be attainable, the total mass is 722-t (metric tons). At present-day transportation costs to GEO, the cost of delivering a 1000-t. reflector would be prohibitive. Economies of scale can reduce cost, because the large mass delivery requirement can justify- development of a tailored space transportation system. The reflector must maintain its reflecting surface within 1/20 wavelength, or approximately 0.6 cm. This precision is about 1 in 3 x 10^, not exceptional for an optical surface but challenging for an ultra-lightweight space structure. The active reflector is made up of resonant conductive rings of copper or silver plated on an insulating substrate such as Kapton film. The rings are about one wavelength (e.g., 12.24 cm) diameter and are laid in an hexagonal pattern with about 1/4 wave edge separation. The reflector must maintain its assigned location in GEO. While the ground- based transmitter could be designed for electronic steering to track the reflector, minimizing electromagnetic interference with other space assets will require that the uplink power beam be directed to a specific location in GEO. The cost of the rectenna can be minimized if it is fixed-aimed at a particular point in orbit, and is required to maintain its latitude and longitude within 1/4 degree. The reflector must maintain accurate attitude control to keep the downlink power beam centered on the rectenna. Retrodirective phase control can be used to keep the uplink beam centered on the reflector, but this cannot be extended to centering the downlink beam since the reflector is electronically passive. A centering requirement of about 1% of the estimated receiver diameter was assumed. The angle subtended at GEO by 100 m on Earth is about 0.5 arc second. The reflector attitude error must be held to half this value. An on board attitude reference system can use inertial reference and star
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