Laying the Foundation for Space Solar Power: An Assessment of NASA's Space Solar Power Investment Strategy (2001)

A space solar power system requires integration of many technologies in order to generate electricity from the Sun. Figure D-1 depicts a generic solar power system, from collection of the solar power to receipt of the solar power on Earth and delivery to the grid. This concept is based on the use of microwaves. Options using lasers would involve constellations of small individual satellites, each with its own transmitter, as depicted in Figure D-2. The National Aeronautics and Space Administration’s (NASA’s) Space Solar Power (SSP) Exploratory Research and Technology (SERT) program, as of the date of this report, has not yet chosen a baseline system. Several possible variations of flight demonstrations and systems have been presented to the committee, each classified according to four model system categories (MSCs). Refer to Section 2–1 for a more detailed description of these demonstrations and program milestones.

Despite the differences in these concepts, all space solar power systems have a set of common technology areas and work in the same general manner. Solar energy is collected in geosynchronous Earth orbit (GEO) by a solar power generation technology, probably consisting of photovoltaic (PV) arrays that capture radiation from the Sun and convert it (using the photovoltaic process) into direct electric current. These PV arrays blanket a surface that faces the Sun at all times. The electric current is collected and transformed through the power management and distribution system. Transmitters then beam the power via wireless power transmission to a specific collector (either on Earth’s surface or in space). Receivers (on Earth’s surface or in space) collect the incoming microwave or laser transmission energy and convert it into electricity. For microwave systems, this collector is referred to as a rectenna. For laser-based transmission, the collector is constructed from solar arrays. For space-to-space systems, the collector is application specific. The construction of such SSP systems, each on the order of several square kilometers in size, is handled almost entirely through autonomous robotic assembly, inspection, and maintenance in GEO and requires numerous launches of heavy payloads into space. In-space transportation of SSP components is also required to move payloads from low Earth orbit to GEO. Various risk management and systems design tools also need to be developed during the design stages of any SSP system.

NASA’s SERT program mainly involves research on technologies and design methods that is necessary for such a huge undertaking. The program has identi-

fied several flight demonstration milestones in order to test technologies and concepts in the near-term and mid-term in preparation for transferring the technologies to industry for final full-scale development and implementation. A more specific treatment of these flight demonstrations and key program milestones can be found in Section 2–1.

NASA has chosen to break its research into 12 areas for funding:

1. Systems integration, analysis, and management

2. Solar power generation

3. Wireless power transmission

4. Space power management and distribution

5. Structural concepts, materials, and controls

6. Thermal management and materials

7. Space assembly, inspection, and maintenance

8. Platform systems

9. Ground power systems (GPS)

10. Space transportation (Earth-to-orbit and in-space)

11. Environmental, health, and safety

12. Economic analysis

Each area (with the exception of economic analysis) has been allocated a portion of the earmarked government funding provided to the SERT program for technology roadmap development and prioritization and was charged with (1) developing a set of cost and technology goals, (2) compiling a list of important technology challenges, (3) developing potential applications of technology advancements, (4) developing a breakdown of the specific work necessary for advancement, and (5) developing a schedule of technology milestones that parallel the milestones of the total program. An example of these roadmaps and goals for the solar power generation portion of the program can be found in Appendix C. The program has identified an investment portfolio for a future SSP program with planned resource allocation through 2016 (see Table D-l). This allocation will be affected by choices made by NASA and the President’s Office of Management and Budget in space solar power. Technology flight demonstrations (referred to by NASA as MSCs) are scheduled in FY 2006–2007, FY 2011–2012, and FY 2016.

The SERT program has several levels of organization stemming from management at the NASA Office of Space Flight. A schematic of this organizational structure, which incorporates many NASA field centers as well as industry and academia, is shown in Chapter 3, Figure 3-1. The program has created several levels of oversight through its Senior Management Oversight Committee and various technical and systems working groups. The program has also obtained various external evaluations from groups such as the National Research Council; Resources for the Future, an economic research group; and professional technical societies such as the American Institute of Aeronautics and Astronautics. External comment has also been provided through involvement in various international organizations and symposiums such as the International Forum on Space Solar Power.

Dickinson, Richard. 2000. “Wireless Power Transmission.” Briefing by Richard Dickinson, Jet Propulsion Laboratory, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., September 13.

Mankins, John and Joe Howell. 2000. “Strategic Research and Technology Roadmap.” Briefing by John Mankins and Joe Howell, National Aeronautics and Space Administration, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., December 14.

Nansen, Ralph. 2000. “The Space Solar Power Solution: An Industry/Government Partnership.” Briefing by Ralph Nansen, Solar Space Industries, to the Committee for the Assessment of NASA’s Space Solar Power Investment Strategy, National Academy of Sciences, Washington, D.C., October 23.