Figure C.8. Total rectenna area (LEO) Factors driving the choice of the orbit We will try to summarize the advantages and the drawbacks of a LEO constellation, per comparison mainly to the big GEO solar power satellite design: Advantages 1- Design benefits: • Smaller and lighter structures than for GEO SPS (moreover, we do not need fuel for a GEO transfer). • We need fewer launches to bring one small SPS in LEO orbit (but it is also a trade-off with the number of spacecraft to launch). • We need also less EVA and/or robotic operations in orbit (and even none, if we can ensure completely autonomous deployment in space). • Therefore, a higher percentage of on-earth operations and verifications greatly improves reliability and cost. • A constellation is more tolerant to failures (if one SPS breaks down, it will not affect too much the total power output of that constellation). • In LEO, we can use passive gravity gradient stabilization of the spacecraft. • We do not have the interference problems of GEO, and we can avoid slot allocation committees and politics. • With the same antenna and microwave frequency, the receiving rectennas are smaller if the spacecraft is in LEO (if the power transmitted is similar, the average power density will be higher and we will be able to ensure more easily densities above the rectenna's threshold). 2- Commercial benefits: • Shorter construction delays for small SPS and small rectennas. • The power is available quicker from space, therefore early sales of electricity generates funds. • Early demonstration of the validity of this commercial concept • A rapid success of the firsts phases makes it easier to raise funds to continue the project.
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