Most heat is radiated directly to deep space, which makes the thermal control quite simple. This would also provide an interesting pointing capability, using an infrared camera on the receiving antenna, focused on the hot TWT collector. Regarding the cost aspect, the ROM price of a present space qualified TWTA ranges around .3 - .5 MAU, but would probably be reduced by a factor of 1.5 to 2, with much less requirements than for a 10-years mission life. The micro wave transmitter would then represent 5 to 10% of the demonstrator cost For the above reasons, the last solution seems quite attractive for these Ariane 4 options. 6.2 EURECA Option For this option, the constraints are still more severe than for the Ariane 4 ones. The product Da.Dr is definitively 1 m2 or below, and the available power is only a few hundred Watts, limiting the microwave experiment to around 50-100 W. This is why Thomson Tubes Electroniques will recommend to use only two microwave generators, which are: • At 30 GHz (transmission distance = 50 m). A 50 Watt, 30 % inefficiency, TWT. • At 12 GHz (transmission distance - 20 m). A 130 Watt, 60% inefficiency, TWT with radiated heat toward deep space (same as for the Ariane 4 option) It is worth noting here that a 30 GHz TWT with more power (100-200 Watts), although available on ground, would require additional R&D to be
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