A 50-kW Module Power Station of Directly Solar-Pumped Iodine Laser

The conceptual design of a 50 kW directly solar-pumped iodine laser ( DSPIL ) modulewas developed for a space-based power station which transmits its coherent-beampower to users such as the moon, Martian rovers, or other satellites with large ( >25kW) electric power requirements. Integration of multiple modules would provide anamount of power that exceeds the power of a single module by combining anddirecting the coherent beams to the user's receiver. The model developed for theDSPIL system conservatively predicts the laser output power (50 kW) that appearsmuch less than the laser output (93 kW) obtained from the gain volume ratio extrapo-lation of experimental data. The difference in laser outputs may be attributed toreflector configurations adopted in both design and experiment. Even though thephoton absorption by multiple reflections in experimental cavity' setup was moreefficient, the maximum secondary absorption amounts to be only 24. 7 percent of theprimary. However, the gain volume ratio shows 86 percent more power output thantheoretical estimation that is roughly 60 percent more than the contribution by thesecondary absorption. Such a difference indicates that the theoretical model adoptedin the study underestimates the overall performance of the DSPIL. This fact maytolerate more flexible and radical selection of design parameters than used in thisdesign study. The design achieves an overall specific power of approximately 5 W/kg and total mass of 10 metric tons.IntroductionLasers permit efficient long-range transmission of electro-magnetic wave energy because of their small beam divergence.Accordingly, numerous conceptual and experimental studieshave been performed to explore laser systems for power trans-mission in space (DeYoung et al., 1988). Among them is thedirect solar-pumped iodine laser (DSPIL) (Lee et al., 1988;Hwang and Tabibi, 1990). An early design study of DSPILshowed that a megawatt power output is feasible in space(DeYoung et al., 1987).In the present study, a 50-kW DSPIL power module wasconsidered since (a) the development of such a small unit istechnologically and economically feasible, (b) the combinationof several modules, as shown in Fig. 1, can be adopted forhigher power demand, and (c) each module could be designedto provide power according to a user's need. The power levelof the module is suitable for powering a lunar or Martian surfacerover which requires a roughly 25-kW power for operation,and for powering other spacecraft. Power availability can bemultiplied by directing the beams from many modules (Fig. 1 ).The laser within a module is based on the master oscillatorpower amplifier (MOPA) principle and is composed of a masteroscillator (MO), a pre-amplifier (PreAmp), a power amplifier(PA) (Fig. 2). An output of 10 W from the MO is amplifiedto 4 kW at the PreAmp, then this 4-kW laser beam is amplifiedto 50 kW at the PA for transmission. The lasant chosen for thisMOPA is perfluoro-t-butyl iodide (t-C, Fgl) which is the most-promising lasant for solar pumping (Lee et al., 1988). Thepumping wavelength for this lasant ranges of 250 nm to 350nm with its peak at 290 nm (Fig. 3). Laser emission is at 1.315