In these figures, the equatorial orbit is covered by a complete network ranging from 5 to 30 rectennas (for each curve, the total number of rectennas is incremented by 5). For the calculations, we have chosen a reference antenna of 1 km (diameter), and a frequency of 2.45 GHz. To compare these results with other values, we just need to multiply the y-axis by the corresponding factor. For our rough estimations, we have use this well known approximate relation (with elevation and deflection corrections): Then, we can estimate the rectenna area (assuming an elliptical shape): According to these figures, the minimum total rectenna area (7 km2) occurs with a network of 30 rectennas and an orbit of 900 km altitude. For comparison, the same spacecraft in GEO require 90 km2 of rectenna. However, we must notice that many networks (10 to 25 rectennas, 1000 to 2200 km of altitude) offer similar small rectenna areas (8 up to 21 km2). The total area grows rapidly with altitude, and this factor can be a major driver if the rectennas construction costs prove to be a main contribution to the total project cost. Similarly, if the antenna cost is the major driver, we could compare antenna diameters required at each altitude to feed a network of rectennas with similar total area. For instance, if we use a network of 10 rectennas with a total area equal to the area required by the GEO option, and a circular orbit 2200 km high, our antenna will be 4 times smaller than for GEO (Da = 0.48 Dgeo and Aa = 0.23 Ageo)- This means a significant saving on construction costs. We should analyse and optimize all the parameters (antenna, rectenna, power) together, but in this case also, LEO proves to be very interesting. Figure C.1. Total illumination of the SPS by the Sun (per orbit)
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