Utilization of Polychromatic Laser System for Satellite Power Beaming

Electrical power generation is an important aspect of a successful space mission. Bigger spacecraft with large solar panels are able to generate enough power to perform their missions, but there are other mass and volume limited spacecraft that are also power-limited in their mission capability. Examples include small satellites with high-power payloads and deployed platforms such as rovers on the lunar surface. These platforms have limited available solar panel area and may have to operate in extended eclipse conditions. For these missions, a power beaming satellite can augment their power generation, greatly enhancing mission capabilities. Space Solar Power (SSP) systems have been investigated for over 50 years. Its potential to deliver energy to any location or to remotely power unmanned vehicles is worthy of development. Recent demonstrations have shown the practicality of transferring power in the terrestrial environment. Two major methods to beam power have been proposed using either microwave or laser energy. Microwave energy has minimal losses due to atmospherics and has a slightly better end-to-end transfer efficiency. When applied to space assets, where mass and volume is a premium, microwave system has a major drawback of requiring a dedicated receiving system just for energy reception that does not serve any other purpose. In contrast, the receivers for laser power beaming are solar cells where the receiving panel can also utilize the natural sunlight to generate electrical power. For space systems where the primary power generation is achieved using solar panels, this method of power beaming is ideal. This method becomes especially attractive for satellite-to-satellite or satellite-to-rover power beaming. Most modern space systems use multi-junction solar cells to better utilize the entire solar spectrum. Since a monochromatic laser does not match the solar spectrum, a multi-junction solar cell would not generate power efficiently from a single wavelength laser. This paper addresses the design for a polychromatic laser system to beam power to a multi-junction solar cell for space applications and the power levels needed of the different laser wavelengths to optimize the spectral response of a space-grade solar cell. Since the wavelengths will be selected to best match the spectral response of each junction and the currents matched across all junctions, the efficiency of the multi-junction cell would increase to 51% without concentration while still being able to use the solar spectrum for power production. Three matched lasers were able to beam power at a 38% increase over a single wavelength laser.