m2 radiator, is made up of 5,926 individual laser diode amplifiers, all phase-locked to produce a single coherent beam, which is focused by the gas lens onto the lunar rover receiver. Figure 4 shows the first- and second-stage amplifiers. A well stabilized master oscillator injects 9 watts into a beam-splitter chain. The beam splitters divide the beam into nine 1-watt separate beams that are applied to the first-stage amplifiers. Each amplified beam (9 watts), is then split into nine 1-watt beams, which are then injected into the second-stage amplifiers. The second stage amplifies each beam to 8 watts. The result is 81 beams, each at 8 watts, which are now sent to the output diode arrays. Figure 5 is one of the 9x9 output arrays. Each 8-watt beam is split into eight 1-watt beams and applied to the third amplifier stage. The output of each third-stage amplifier is split into eight beams and injected into the final fourth amplifier stage (gain of 10). The output of all 9 X 9 amplifier arrays is a phase-locked, single beam with a power of approximately 50 kW. This beam has an aperture of 8 m x 8 m. A gas lens is used to focus this beam onto the lunar rover laser-to-electric receiver producing a 0.62-m-square spot size at the lunar rover over a maximum transmission distance of 3,100 km. One complete amplifier chain is shown in figure 6. Additional optical isolation and focusing elements are shown to ensure that there is no unwanted optical feedback through the amplifier chain. Focusing optics are needed to input the beam into the small diode amplifier region. The pointing accuracy is assumed to be 0.2 radians. Ion thrusters or reaction wheels could be used for pointing and tracking the lunar rover target. The laser transmitter system has a mass breakdown as shown in table I. The total mass of the laser diode array is 850 kg. This mass is then added to the other laser transmitter component masses, as shown in table II, for a total laser transmitter mass of 5,000 kg. Calculations were performed to determine the effect of the gamma and fast neutron effects on the GaALAs laser device. Our calculations indicate that the laser diode array will not be severely affected by the low gamma and neutron fluences over the 7-year, full-power reactor lifetime. The reactor produces 100 kW of electrical power for the laser diode array transmitter operating at approximately 50-percent efficiency, producing 50 kW of emitted laser power. System heat (50 kWT) must be radiated away by the 10-m diameter by 4-m long thermal radiator (2.7 kg/m2) operating at 305 K [8]. Figure 7 shows a power-flow diagram for the laser-transmitter system. The emitted laser-beam profile is a square beam which produces a square diffraction-limited pattern at the rover receiver. The pattern length along one side is given by
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