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GT ECE 6390 - Sandwich Module Development for Space Solar Power

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Sandwich Module Development for Space Solar Power Paul Jaffe, John Pasour, Maria Gonzalez, Sheleen Spencer, Michael Nurnberger, Jeremy Dunay, Marty Scherr1, and Phillip Jenkins U.S. Naval Research Laboratory, Washington, DC 20375 202-767-6616 1Thomas Jefferson High School of Science and Technology Abstract. The concept of Space Solar Power (SSP) is broadly defined to be the collection in space of energy from the sun and its wireless transmission from space for use on earth. It has been observed that the implementation of such a system could offer energy security, environmental, and technological advantages to those who would undertake its development. Among recent implementations commonly proposed for SSP, the Integrated Symmetrical Concentrator and Modular Symmetrical Concentrator concepts have received considerable attention. They each employ an array of modules for performing conversion of concentrated sunlight into microwaves for transmission to earth. While prototypes of such modules have been developed previously, none have been subjected to the challenging conditions inherent to the space environment in which an array of modules would be required to operate. The research described herein details our team’s efforts to evaluate the trade studies associated with the development of a sandwich module and its planned implementation and testing. Among the primary concerns is the dissipation of waste heat, as at least two of the three layers of the sandwich are expected to have significant heat generated by conversion inefficiencies. The sandwich is partitioned into layers for photovoltaic conversion, direct current to radiofrequency conversion, and radiofrequency emission. Our focus has been on trades concerning these three layers, as well as those examining module geometry and thermal control. Keywords: Space Solar Power, sandwich module, microwave power transfer PACS: 84.40.Lj, 84.40.Fe, 88.40.H-, 89.20.Kk INTRODUCTION Space Solar Power is generally considered to be the collection in space of energy from the sun and its wireless transmission from space for use on earth (Brown, 1992). This approach would overcome the atmospheric and diurnal limitations associated with terrestrial solar power. The concept itself has been around for many decades, and has been periodically revisited as technology has evolved and components that potentially would be used in an SSP system have seen performance gains. It has been posited not only as a means of providing utility grid power but also for military or other specialized applications (Johnson, et al., 2009). Regardless of the potential of this technology, SSP has been criticized as economically infeasible (Fetter, 2004). The costs associated with putting the large amount of mass that an SSP system would almost invariably require are prohibitive. The possibility of efficient large-scale energy storage that could be paired with ground-based clean energy systems threatens even the most optimistic economic analyses for SSP. Counter-arguments include the point that the spacefaring infrastructure associated with the development of SSP would present a tremendous space resource development advantage to the first implementer (Globus, 2009). One means of reducing launch mass is to use lightweight reflectors to concentrate sunlight collected over a large area on a smaller area photovoltaic (PV) array, effectively reducing the proportion of higher density components required in orbit. Additionally, if the photovoltaic function is directly paired with a means of direct current (DC) to radiofrequency (RF) conversion and an antenna, the collected energy can be transmitted with minimal power distribution complexity. This complexity arises in some implementations because of the need to keep the photovoltaics pointed at the sun and the transmission antenna simultaneously pointed at the earth. Large amounts ofcurrent may need to be routed across a harness network and possibly a rotating conductive joint. The approach described above that avoids these problems has been referred to variously as an Integrated Symmetrical Concentrator (ISC) and Modular Symmetrical Concentrator (MSC) (Mankins, 2003). One such implementation is pictured in Figure 1. FIGURE 1. Modular Symmetrical Concentrator concept (NSSO, 2007). One of the key components in these concepts is the sandwich module. This component integrates the functions of photovoltaic collection, DC to RF conversion, and RF emission into three layers configured as depicted in Figure 2. FIGURE 2. Functional components and notional configuration of a sandwich module for space solar power. This configuration has been examined previously by a number of investigators. Owen Maynard of Raytheon considered trades following the NASA/DOE SSP effort of the late seventies (Maynard, 1980) and several Japanese efforts appear in the literature of the early 2000’s, including those of H. Matsumoto and N. Kaya. In our research effort, we endeavor to execute trades for the sandwich module layers and architecture, based on current and near-term available technology, to culminate in the production of a prototype to be tested in a realistic thermal and vacuum environment. Out of necessity, we have made assumptions about the system context of the module based on having limited resources and lacking a point design from which to derive requirements; the development of which is beyond the scope of our effort. This paper describes the status of this effort as of September, 2010, following the initial year of the investigation.KEY IMPLEMENTATION TRADES As expected, the component choices for the three layers (photovoltaics, DC-RF conversion, and antennas) figure prominently in our trade evaluation. Additionally, the formidable challenge of managing thermal control permeates each of these trades as well as being a trade unto itself. Likewise, the configuration and geometry of the module itself have a massive effect on final module performance and interplay with the other trades. Following are overviews of each of these trades. Photovoltaics (PV) One of the greatest limitations on our research effort is the near-term availability of the components to support a prototype build that meets our system requirements. Several PV materials were considered during the course of this work, resulting in the choice of current state-of-the-art (SOA) III-V multijunction technology. In these devices,


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GT ECE 6390 - Sandwich Module Development for Space Solar Power

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