pick up. On the next higher power level, a light bulb could serve as a flash bright enough to illuminate a printed logo (“Eat at Joe's,” for instance) long enough for a photograph to be taken. At the kilowatt level (using a dish about 100 m in diameter), given a capacitor and some fluorescent paint, a sign could be set to flash on and off and could even be visible from Earth with a small telescope. It has been pointed out that such a demonstration might not be popular with astronomers, but the controversy itself would be great publicity. The determining factor for all of these possibilities is, of course, the area of the microwave collector. The equipment necessary for monitoring received power levels and frequency dispersion and transmitting the data back to Earth can easily be made compact and lightweight, so it does not impose any real restrictions. For reception on the order of a single watt, the rectenna need only be about 2 meters square. Such a rectenna could be easily deployed from a small package using existing, well- tested technology. To get the larger receiver area necessary for demonstrations on the 100 watt scale, inflatable technology as described below would probably have to be used. Reception on the kilowatt scale with a collector deployed from a microsatellite is probably not feasible in the near term. 10.1.4 Vehicle Configuration The choice of an ASAP platform puts rather stringent restrictions on the size, shape, and mass of the receiving satellite. The ASAP ring lies on top of the Ariane H10 upper stage, and is capable of carrying up to six separate payloads of up to 50 kg each. Each of these positions can accommodate a payload with dimensions equal to a 45 cm cube, though exceptions are sometimes made allowing the payload's height to be up to 60 cm or so depending on the nature of the mission's main payload. Individual payloads on the ring can be connected to each other by wires. [Arianespace, 1990] Working within the above constraints, a two-section spacecraft is envisioned. One position on the ASAP platform would be taken up by the main satellite equipment, including sensors, data-handling equipment, a transponder for data transmission, an independent power supply, and whatever else is necessary for the demonstration chosen. The other position would be connected to the main satellite bus by wires strung along the ASAP ring, and would be used to house an inflatable reflector. When deployed, the spacecraft would look something like the one shown in Figure 10.1.6 below. The inflatable reflector would be transparent on one side with a reflective parabolic inner surface. Connected by wires to the main bus about 12 m away, the satellite would be gravity-gradient stabilized and would always point toward Earth. Microwaves transmitted from Arecibo would be collected by the reflector and focused on a small rectenna on the surface of the main spacecraft. Mass restrictions should not be a problem; designs for a 10 m inflatable rigidizable antenna for the QUSAT VLBI mission quote a total mass of 42.05 kg, which includes the main chamber torus, pressurization subsystem, and stowage elements. [Bemasconi, 1984] As the reflector is being used to collect rather than transmit, much less accuracy is needed in manufacturing, so it may be possible to fit an even larger structure within the mass limits. However, detailed numbers are not available for the volume of such an inflatable in its stowed configuration. A simple calculation does indicate that at the density of mylar, a 42 kg payload would take up only about a third of the volume of an ASAP fairing. This would leave two-thirds of the volume for consideration of packing constraints and storage of the inflation gas. Table 10.1.1 shows the relevant statistics for such a satellite flying in the 785 km ERS-1 orbit. Power received averages about 60 W over the diameter of the first minimum for 2.38 GHz, and 10 W for the 430 MHz radar. Times of passage are about 0.1 and 0.6 seconds, respectively. Ilie 60 W figure is enough to power a photograph flash as described above. A corporate or departmental logo could be printed on the outer surface of the reflector with something transparent to microwaves but opaque to visible light, and bids could be taken from various companies to use their logo. It is conceivable that the entire project could be funded by taking the offer of the highest bidder; it might even make a profit.
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