thus is more suitable for energy transmission in space. For tranmitting energy through the Earth’s atmosphere it is better to use microwaves. The choice of optimal frequency, however, will depend on a variety of factors as well as the choice of how much importance to place on each. While we do not pretend to completely solve the problem, we attempt to determine a method of solution, and analyze the effect of different factors on the final result. First, since at present and for the forseeable future most aerospace projects operate under the idea of minimum mass and size, we should also follow these criteria. Second, as to why microwaves should be used, they can be focused more easily than longer-waved radiation. For energy transfer from a stationary orbit to the Earth’s surface—for example, solar and nuclear orbital power stations—the frequencies from 2.5 GHz to 3 GHz have been chosen. These frequencies fit the requirements for the above projects, namely weak influence of the Earth’s atmosphere on beam propagation and being able to both generate and focus radiation at these frequencies. In this case, it is assumed that the ground receiving antenna has a diameter equal to 10 km while the diameter of the orbiting transmitting antenna, equals 1 km. Let us investigate the possible microwave frequency ranges for all similar space-Earth projects, exemplified by already-designed projects which use orbital power stations for ground power supply. The characteristics of space power station projects can be found in numerous papers and reports written by P. Glaser, J. Mockovciak, J. Patha, G. Woodcock, D. Gregory, K. Ehricke, K. Schritmoller and others, published since 1968 (Table 1). Examining the mass and size of these projects, it is seen that the mass of the transmitting orbital antenna varies from 15% to 30% of the total mass of the orbital power station. For nuclear orbital power stations it varies from 15% to 40% of the total mass. The dimensions (i.e., mass) of the orbiting antenna were chosen by taking into account the fact that, considering the size of the ground recieving antenna, the altitude of a stationary orbit, and assuming a working electromagnetic wavelength on the order of 10 cm, the transmitting antenna must have a diameter on the order of I km to provide an energy transfer efficiency between the two antennas of close to 100%. This is calculated assuming no losses occur due to the microwaves passing through the Earth’s atmosphere. Such a high efficiency requires the following condition (Figure 1).
RkJQdWJsaXNoZXIy MTU5NjU0Mg==