such experiments may come the closest in the near term to demonstrating commercial applicability (that is to say, they would have to be subsidized the least). But more importantly, a series of ground- based demonstrations and applications would both reduce the high costs of beaming technology and establish an infrastructure that can then be utilized in space-based experiments. If this plan is adopted now, then eventually, perhaps as soon as 10 years, space to Earth demonstrations on the US $800 Million level can be justified. An example of such a technology-improvement dependent demonstration is proposed below. Mid term 1 MW Class Space to Earth We have considered a 1 MW class commercial precursor system in the context of existing or nearly existing construction technology and slightly longer-term beaming technology. The mass of the spacecraft is 80 T at launch and 65 T in operational orbit. The shape (Figure 8) is a triangular prismatic structure built with three square elements 100m x 100m wide, a configuration similar to the SPS 2000 concept proposed by ISAS. After being deployed by an Energya launcher in a 28.5° inclination orbit in LEO, the satellite would be assembled manually by a Space Shuttle crew. After assembly, the satellite would propel itself to an equatorial orbit. An electric propulsion system is used for both orbital transfer and station keeping, though a conventional cryogenic system might be employed in order to traverse the Van Allen belts at the beginning of the orbital transfer. Since the assembly operations and the final orbit are not in the same plane, there is a mass penalty required to enact this maneuver. Performing this maneuver at final apogee minimizes this penalty, especially when using electric propulsion. Equatorial orbits were found to be desirable because of the extremely poor ground traces of platforms in non-equatorial orbits, particularly at low orbital altitudes The choice of the altitude of the final orbit has been driven by operational considerations, which are mainly to deliver power for a significant amount of time each day and to provide power density levels on the rectenna compatible with good efficiency. These are actually competing requirements because visibility is maximized in high orbits near GEO and power density is maximized in LEO. Hence we selected a compromise orbit at 20,309 km altitude, which avoids the difficult problem of obtaining an orbital slot in GEO. The orbit is sufficiently high to require concentrating devices at ground level to compensate for the low power densities. The technical and cost considerations lead us to choose static concentrators arranged as parabolic cylinders where the dipole rectifiers are located along the focus line. We believe that this rectenna design would not be much more expensive because the added cost of concentrators is balanced by the smaller number of rectifiers. We chose the frequency of 35 GHz in order to reduce antenna and rectenna dimensions, since a much larger ground facility some kilometers wide would be needed to accommodate the more conservative 2.45 GHz frequency. A possible alternative to 35 GHz transmitters could be the development of integrated solar array/transmitter 2.45 GHz technology, which could significantly decrease the size and complexity of transmitters required at this frequency. It is important to note that both the mass and particularly the costs of the phased array transmitter utterly dominate the platform design. In order to construct the first platform element for less than US $1 Billion, it is necessary for the antenna costs to drop a factor of 10-100. To a lesser extent, the solar arrays also contribute significantly to the cost, though their price is expected to drop appreciably within the next decade. Also, advances in electric propulsion technology would significantly reduce the unit costs of each element. The main conclusion is that from a technical standpoint a conservative demonstration for less than US $1 Billion is feasible— provided that the necessary phased array antenna and rectenna systems are available in the next 10 to 15 years. While this development may take place of its own accord, we believe that a dedicated ground-based testing program will help to ensure the occurrence of this vitally needed advancement in transmitting technology.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==