which are basically identical to those of a direct broadcast satellite, exist and are qualified for a decade of space operations. These types of TWTs are normally also qualified to be repeatedly switched on/off 20.000-30.000 times, equivalent to 5 years on orbit. Although the use of TWTs might lead to a heavier design that is more expensive to launch, this would be off-set by the cost of not having to develop and qualify a microwave generator source. Another advantage of the TWT solution is that it enables a graceful degradation of the Powersat’s capability as each tube failure would eliminate only 250 W7 of power. This degradation would be forestalled by the incorporation of a number of redundant tubes. Groups of TWTs can also be linked, via appropriate phase-shifters, to a feed horn array which would, therefore, be able to electronically control the shape and pointing of the beam. Alternatively, an active subreflector could be used. Power is provided by two 80 m long by 8 m wide solar array wings similar to the Space Station Freedom arrays, alsos similar to the arrays proposed for the SOLA experiment described in the previous Eurospace Powersat study.[8] This array size would provide between 120-150 kW of total power. For propulsion, a high-performance bipropellant system would be used. This systems would be needed to reboost the Powersat when Freedom performs a similar reboost manoeuvre. In addition, a continuously operating ion propulsion system is also necessary to ensure the Powersat always tracks closely behind Freedom as the orbital pair spiral in toward Earth. A deployable mesh-type reflector is configured for the Powersat, and it is sized at around 15 m. Alternatively, a phased-array system could be used, although it would be more difficult to package the required large aperture. With regard to the rectenna, this could potentially use an inflatable torus-type
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