GEO relay. The power in the beam as it leaves the GEO relay is 845 MW, for an average intensity of about 1 MW/m2. If line-of-sight transmission from the power satellite to a GEO relay satellite is not possible, then the beam is directed first to a LEO relay, which reflects it to the GEO relay that reflects it to the ground station. At the ground station, the beam is concentrated by a system of mirrors and harnessed to generate electricity by the same kind of absorbing-cavity/energy-exchanger/binary- cycle/turbine-system as used in the power satellite. Table 3 summarizes some of the important characteristics of the Lockheed system. The efficiency claimed for the energy-exchange/binary-cycles in the power satellite is 73.5% and that claimed for the ground energy-exchanger/binary-cycle is 75.5% (21). As described in Ref. 21, the Lockheed system lases on one of the 10.6 m lines of CO2. However, that reference does not specify which of the several isotopes of CO2 would be used. If it is the most common isotope, l2C16O2, then atmospheric transmission for all lines in the 10.6 ^im band is poor (18). For example, it is less than 40% for the 10.593 /im line (29). Taking 12C16O2 to be the lasant and the atmospheric transmission of the laser beam to 0.5 km elevation with the beam at 50° from vertical to be less than 40% for any of the 10.6 /zm lines of that lasant, the overall efficiency of the Lockheed system is < 3%. By modifying the Lockheed system to use l2Cl8O2 as a lasant instead of 12C16O2, overall efficiency is increased from < 3% to 7%, and this increase is due to the increase in atmospheric transmission (to 0.5 km elevation) from < 40% to 93% (the 93% is from Ref. 18). The transmission is greater with the 12C18O2 lines, because they are offset from the absorption lines of atmospheric 12CI8O2. The advantages of the Lockheed system are that its power satellite is in low-Earth, sun-synchronous orbit (this avoids Earth shadow and substantial weight in GEO), CO2 lasers are well understood and can be phase-locked with no power loss, and overall efficiency is 7% (i.e., as high as that of the microwave Reference Concept) if l2C'8O2 is used. However, the Lockheed concept does have problem areas: the claimed 73.5% binary cycle efficiency appears unrealistically high, energy exchanger dependability has not been established and is very much open to question, etc. See Ref. 27, a report on which most of this paper is based, for a detailed discussion of these and other problem areas.
RkJQdWJsaXNoZXIy MTU5NjU0Mg==