Space Solar Power(SSP)

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Space Solar Power (SSP) is the name commonly given to the concept of deploying a system of satellites and ground receivers that would collect the sun’s energy at GeoSynchronous Earth Orbit (GEO is an orbit 35,000 km above the Earth's equator) [1] and beam that energy, via wireless power transmission (WPT) to Earth for use. Many names have been given to such satellites and systems since Peter Glaser first invented the concept in 1968: Solar Power Satellites (SPS), Satellite Solar Power Systems (SSPS), Space-Based Solar Power (SBSP), Power Satellites, Sunsats, etc.,

The numerous existing communication satellites (comsats) differ from the envisioned SSP Satellites, or sunsats, in that sunsats would optimize for efficient power transfer, while comsats have been optimized for their signal to noise ratio.

Fig.1 Integrated Symmetric Concentrator - a 2001 NASA SSP design, developed under the SERT Program

The first major “reference study” of SSP was done by DOE and NASA in 1978-1981[2] [3] [4]. Massive improvements in many fields key to SSP led to NASA’s much smaller “Fresh Look” (1995-1997)[5] and SSP Exploratory Research and Technology (SERT) (1997-2002)[6] studies on SSP.

Numerous technologies key to SSP continue to mature. Microwave Wireless Power Transfer continues to be well funded in Japan. There are many SSP activities that are ongoing today, including both government research and development, several start-up companies, and a variety of not-for-profit organizations.

Of many companies working on SSP development, the leader is an eighteen company Japanese consortium at the Institute of Unmanned Space Experiment Free Flyer (USEF), with an estimated $21 Billion in funding.[7][8] The Japanese group intends to launch a small test satellite in 2015, to test beaming power through the ionosphere using microwaves. A team at Kyoto University recently beamed microwave power from an airship.[9] Kobe University is developing technologies for generation and control of such WPT systems including a retrodirective phased array.

Fig.2 Current JAXA USEF SSPS Concepts

Japanese researchers are targeting a one gigawatt system, equivalent to a medium-sized atomic power plant, that would produce electricity at eight yen (nine cents) per kilowatt-hour, six times cheaper than its current cost in Japan."[10][11] The Japan Aerospace Exploration Agency leads these consortium working on both microwave and laser WPT.

There are also SSP activities underway by Chinese, European and a half dozen other start-up American and international companies working to build SSP satellites. The International Academy of Astronautics (IAA) is currently undertaking the first international assessment of the SSP concept; the results are to be published in late 2010. Astrium, Europe’s largest aerospace company, and the University of Surrey, developer of the laser diode used in DVD players worldwide, is leading a plan to build a demonstration power satellite using infrared laser power beaming. [12] Boeing’s Rocketdyne received the sole source award for Marshall Space Flight Center’s laser-photovoltaic WPT R&D in 2003. [13]

In 2009 the California utility PG&E contracted with Solaren for the first 200 MW Space Solar Power Delivery in 2016. PG&E emphasizes that they are not at risk in that contract [14], since public utilities, as public trusts, are legally constrained from engaging in high risk power production projects.

Building SSP is considered a stretch challenge, both financially and technically. [15][16] The Space Solar Power Institute [17] has proposed that the most rapid development of SSP would be enabled through an act of the US Congress. As Congress chartered the public/private Comsat Corp. through the Comsat Act of 1962, which created our robust commercial satellite communications industry, similar Congressional legislation could charter a public/private corporation to create a power satellite industry.

This draft legislation has been entitled the Sunsat Act, or Sunsat bill.[18] A private Congressionally chartered corporation has all the requisite advantages. Comsat Corp. opened space for communication satellites - when we knew little about space, rockets or space communications. Communications satellites are now a $100+ Billion industry per year. The “Sunsat Act” would accomplish the same task, creating a Sunsat Corp. to build a space solar power industry of much greater size in the same fashion as Comsat Corp. did.

Sunsat Corp. would also create an "instant" market for a huge volume of orbital space transportation, since a major challenge of SSP is lowering the cost of orbital space transportation to about one tenth of the lowest cost now on the space transportation horizon. President Obama's current initiative to commercialize space transportation speaks to this market. Lower cost space transportation is enabled by increasing flight volume, which requires lower costs.

SSP Attributes Compared with Other Energy Alternatives

By collecting the solar energy at GEO, using a photovoltaic (PV) panel of a given size, SSP would collect about 9.6 times as much energy per day as the same PV panel would at an average location in the US (or Europe, Japan, or similar latitude) [19], summarizing various intermittent difficulties reducing terrestrial solar power collection efficiency. By comparison all satellites at GEO, including SSP, receive continuous power, 24/7 except for 72 minutes in shadow at midnight during the spring and fall equinoxes. It is independent of weather conditions at the receiving site, and is dispatchable, meaning that it can be distributed to locations within the satellite's field of view depending on real-time demand for power.

That schedule for SSP also corresponds to a minimum in annual energy for typical utilities, which is quite helpful. By comparison wind energy, for example, typically is available in an inverse relation to when electric power is demanded. This means that during hot summer afternoons or cold winter nights, wind power is unlikely to be available. During the spring or autumn, when power demand is at a minimum, wind power is more frequently available. This is less desirable. ERCOT, for example, which has significant experience with Wind Power, rates Wind power's capacity factor (when it is available for use) at 7.85% during the summer.

Figure 3. CO2 Intensity of Various Power Systems.

U.S. Senate climate bills under discussion, such as Senators Kerry and Lieberman's American Power Act,have assumed a price of $15 a ton of carbon dioxide equivalent, making large CO2-emitting generation fleets potentially vulnerable to large costs associated with purchasing emission allowances, according to a study based on that Senate climate legislation by Point Carbon.[20] Utility power from SSP would emit little CO2, similar to hydroelectric plants or wind.[21] SSP could, therefore be a vital tool in addressing global climate change by providing another clean, powerful, baseload and dispatchable energy alternative. Being dispatchable means that SSP can be used by the contracting utilities customer's whenever that utility wishes to schedule it, unlike more intermittent power sources such as wind, ground solar, or even hydroelectric; which has many other higher priority considerations from flood control and drought to recreation.

Summer heat waves and drought, for example, have restricted the operation of thermal power plants, such as coal or nuclear, due to low river water or exceeding high temperature limits when thermal plants return water to rivers. Conflicts regarding water use are therefore of growing interest. The Department of Energy's Sandia lab reported to Congress on the interdependency of energy and water focusing on threats to national energy production resulting from limited water supplies.[22] This is also a global problem. SSP would use no water in operation.

There are two primary options for wirelessly transferring power from the spacecraft to a customer's receiver on the ground: microwave and laser. The key system trade-offs that must be considered to select the optimum technology are a) conversion efficiency (solar to microwave or laser, and microwave or laser to prime electrical power at the receiver), b) transmitter size and mass, c) receiver size and mass, d) transmission losses due to attenuation, diffraction, scattering, etc., and e) safety and environmental issues. Current technical availability limits SSP WPT options to microwave, but research on the laser option is progressing rapidly. Comments in this paper assume microwave power transfer.

The power receiving antenna (or rectifying antenna, "rectenna", the technical term) could have green farms underneath, which would mean that SSP could effectively use little-to-no land and contribute no environmental pollutant in operation. An SSP rectenna would have about 90% light penetration, similar to chain link fencing. Arecibo, for example, the world's largest (1000 feet) and most sensitive radio antenna in Puerto Rico, is a rough example.[23]



  1.  "Wikipedia: GeoSynchronous"
  2.  "Solar Power Satellites. Office of Technology Assessment, August 1981."
  3.  "Satellite Power System Concept Development and Evaluation Program: Space Transportation. NASA Technical Memorandum 58238, November 1981."
  4.  "Satellite Power System Concept Development and Evaluation Program: Power Transmission and Reception Technical Summary and Assessment"
  5.  "A Fresh Look at Space Solar Power: New Architectures, Concepts, and Technologies. John C. Mankins. International Astronautical Federation IAF-97-R.2.03."
  6.  "[{{{url}}} Overview of the space solar power exploratory research and technology program—AIAA 2000–3060, J.C. Mankins, J. Howell, in: 35th Intersociety Energy Conversion Engineering Conference; Las Vegas, Nevada, 24–28 July, 2000.]"
  7.  "USEF [Online.]"
  8.  "S. Sato and Y. Okada. (2009, Nov. 9). Mitsubishi, IHI to Join $21 Bln Space Solar Project (Update1). [Online.]"
  9.  "Experiments with Microwave Power Transmission from an Airship. Research Institute for Sustainable Humanosphere (RISH), Kyoto University, Kyoto, Japan. T. Mitani, K. Hashimoto, and N. Shinohara. (2009, Mar.)."
  10.  "Land of the Rising Sun Power! Japan May Build a Solar Station in Space by 2030. A. Williams. (2009, Nov 10) Scientific American [Online.]"
  11.  "Japan eyes solar station in space as new energy source(AFP). K. Poupee. (2009 Nov. 8). [Online.]"
  12.  "Astrium Seeks Partners To Help Fund Solar-power Beaming Demonstration. Space News, P. B. de Selding. (2010, Jan. 22). [Online.]"
  13.  "Laser-Photovoltaic Wireless Power Transmission Research & Development. Marshall Space Flight Center Status Report. R. L. Martin. (2003, May 9). [Online.]"
  14.  "PG&E makes deal for space solar power Utility to buy orbit-generated electricity from Solaren in 2016, at no risk, Alan Boyle, April 13, 2009 [Online.]"
  15.  "Space-Based Solar Power: Possible Defense Applications and Opportunities for NRL Contribution Final Report 23 November 2008, Naval Research Laboratory, Washington DC [Online.]"
  16.  "European Space Solar Power Studies."
  17.  "Presentations by Space Solar Power Workshop [Online.]"
  18.  "The Sunsat Act - Transforming our Energy, Economy and Environment by Darel Preble."
  19.  "Photovoltaics(Solar Cells). page 18. Space Solar Power Workshop. 2006. [Online.]"
  20.  "Southern Co To Lose, Exelon To Gain Under US Cap And Trade-Study. (Dow Jones Newswires). (2009, Nov. 30). Available: [Online.]"
  21.  "SSPS: Space Solar Power System project (2009, Dec. 12). CO2 Emission Intensity. Institute for Unmanned Space Experiment Free Flyer(USEF) Available: [Online.]"
  22.  "Energy Demands On Water Resources. Sandia Report to Congress. (2006, December). [Online.]"
  23.  "Arecibo radio telescope. A National Science Foundation facility. Available: [Online.]"

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 "New directions for space solar power, Elsevier; Acta Astronautica, Volume 65, Issue 1-2, July 2009, Pages 146-156, Mankins, J.C., (received December 2006)"