Towards an Early Profitable PowerSat, Part II

Al Globus

San Jose State University Research Foundation

Abstract

Development of space solar power (SSP) suffers from the extremely large dimensions and mass of traditional designs driven by the size of on-orbit microwave antennas (typically one km). [1] This leads to huge up-front capital requirements and long, complex development cycles. This paper explores progress since the publication of Part I [3] in the design of a relatively small, simple, single-launch SSP system suitable for niche markets by delivering around 5mw to the ground using:

1. low-mass, thin-film solar cells based the power system of the Ikaros heliogyro solar sail [2] currently en route to Venus. Heliogyros keep their sail shape by rotational forces rather than relatively heavy masts.

2. infra-red (IR) power beaming using fiber lasers. Fiber lasers are optical cable doped to lase.

Since IR wave lengths are approximately 30,000x shorter than microwave and beam spreading is a linear function of wavelength, geosynchronous IR power beam radius can be a few meters, making small PowerSats practical. Fiber lasers are advantageous because they:

1. can lase at about the right frequency (1 - 2µ).
2. have high power output.
3. have excellent thermal properties (high surface to volume ratio).
4. provide their own waveguides.
5. may be able to run from the outer edge of the sail all the way to the center, where the beams can be combined and directed to Earth by a system of mirrors.
6. can be pumped at many points along the fiber.
7. add stiffness to the sail.

References:
[1] "Satellite Power System Concept Development and Evaluation Program Reference System Report," Tech. Rep. DOE/ER-0023, Department of Energy, 10 1978.
[2] Westlake, M., "Japan's Solar Sail Heads Starward," Aerospace America, July-August 2010, pp. 24-25.
[3] Globus, A., "Towards an Early Profitable PowerSat," Space Manufacturing 14: Critical Technologies for Space Settlement, Space Studies Institute, October 2010.

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