SPS Feasability Study SD76SA0239-2

Required Capability: Thin high-efficiency polycrystaline cells must be able to resist the effects of radiation at GEO for 30 years, plus a transfer through the Van Allen belts. Development Plan: More testing is required to understand the basic annealing process. Lower temperature capability is desired. Item ~ High Temperature Cell Covers Criticality — Greatly enhance probability of program success For high concentration ratios, the cells can operate at high temperatures. Cell covers must be able to withstand these higher temperatures, and thermal shock from eclipsing. Present Capability: Existing cell covers can safely operate at temperatures up to 85°C. Above that temperature, they are susceptible to failure, particularly in the bond. Required Capability: Cell covers must be able to withstand temperatures of 125°C or more in high concentration ratio designs and designs using selfannealing. Development Plan: The first step is to define the cover requirements at high temperatures. Suitable materials must then be developed and tested to verify performance. Item — Low Cost Mass Production of Arrays Criticality — Critical to program success SPS requires large areas of solar cell blankets per satellite. These must be produced at low cost and high rates consistent with the deployment schedule. As an example, if SPS were constructed with 2-cm square cells, a total of 1.26 x 1011 cells are required per vehicle at a rate of four or more vehicles per year. Present Capability: The present capability for producing solar arrays is limited to small quantities of small, high cost arrays such as are used on existing satellites. Typical cells are on the order of 2 cm x 2 cm square sizes. Costs are of the order of $400/watt. Required Capability: Mass production techniques must be developed that provide high volume, low cost solar cell arrays. If four SPS satellites are constructed per year, a total of 200 km^ solar arrays must be fabricated per year at a cost of less than $.50/watt. Development Plan: First, techniques of fabricating solar arrays at high rate and low cost must be identified. Promising concepts should be tested until a suitable method is demonstrated that reduces costs to acceptable levels and provides high production rates.