Space solar power

Space-based solar power (SBSP or SSP) is the conversion of solar energy into power, usable either in space or on earth, from a location in space, usually geosynchronous orbit (GSO).
Photovoltaics (PV) would generally be utilized for energy conversion and microwave technology could be applied for wireless energy transmission through space, and to the planet's surface. Dynamic solar thermal power systems are also being investigated. [ [http://www.grc.nasa.gov/WWW/tmsb/secondaryconc/doc/rsc_ssp.html Refractive Secondary Concentrators for Space Solar Power (SSP), NASA Thermo-Mechanical Systems] NASA Glenn Research Center] In space, the sun shines constantly and has greater intensity than on earth. Many problems associated with weight and atmospheric corrosion are eliminated, but other problems take their place like radiation damage to a solar cell limiting its lifetime, or micrometeoroids impacting the fragile solar cells. On earth, diurnal rotation and the associated change from day to night allows collection only during daylight hours. Outside of earth's atmosphere, average solar energy per unit area is on the order of ten times that available on earth and increases as the sun is approached, although there are increased maintenance problems beyond acceptable solar radiation limits.

Producing electricity from sunlight in space is not a new or untried technology. It has been utilized by hundreds of operating satellites. The major difference would be that SSP would capture much more energy and beam it to earth for our use. [ [http://gltrs.grc.nasa.gov/reports/2000/TM-2000-210210.pdf Space Solar Power Satellite Technology Development at the Glenn Research Center—An Overview] James E. Dudenhoefer and Patrick J. George]

Future space solar power has the potential to solve global socioeconomic and environmental problems associated with reliance on finite fossil fuels and nuclear energy. It promises to use space outside of the earth's ecology system and has essentially no by-product waste, once established.

History

1968: Dr. Peter Glaser introduces the concept of a large solar power satellite system of square miles of solar collectors in high geosynchronous orbit (GSO is an orbit 36,000 km above the equator), for collection and conversion of sun's energy into an electromagnetic microwave beam to transmit usable energy to large receiving antennas (rectennas) on earth for distribution on the national electric power grid.

1970's: DOE and NASA examines the Solar Power Satellite (SPS) concept extensively

1994: The United States Air Force conducts the Advanced Photovoltaic Experiment using a satellite launched into low Earth orbit by a Pegasus rocket.

1995-1997: NASA conducts a “Fresh Look” study of space solar power (SSP) concepts and technologies.

1998: Space Solar Power Concept Definition Study (CDS) identifies commercially viable SSP concepts which are credible, with technicaland programmatic risks identified.

1999: NASA's Space Solar Power Exploratory Research and Technology program (SERT see section below) program initiated.

2000: John Mankins of NASA testifies in the U.S. House "Large-scale SSP is a very complex integrated system of systems that requires numerous significant advances in current technology and capabilities... A technology roadmap has been developed that lays out potential paths for achieving all needed advances - albeit over several decades... Ongoing and recent technology advances have narrowed many of the technology gaps, but major technical, regulatory and conceptual hurdles continue to exist... This NASA-funded SSP activity has made significant contributions to narrowing the technology gap (e.g. a three-fold reduction in mass at the solar array level over current state-of-the-art)... An incremental and evolutionary approach to developing needed technologies and systems has been defined, with significant and broadly applicable advances with each increment... The technologies and systems needed for SPS have highly leveraged applicability to needs in space science, robotic and human exploration, and the development of space... The decades-long time frame for SPS technology development is consistent with the time frame during which new space transportation systems, commercial space markets, etc. could advance... Power relay concepts appear technically viable using space solar power technologies, but may depend upon higher frequency power beaming... The question of ultimate large-scale solar power satellite economic viability remains open." [ [http://www.hq.nasa.gov/office/legaff/mankins9-7.html Statement of John C. Mankins] U.S. House Subcommittee on Space and Aeronautics Committee on Science, Sep 7, 2000]

2001: Dr. Neville Marzwell of NASA states "We now have the technology to convert the sun's energy at the rate of 42 to 56 percent... We have made tremendous progress. ...If you can concentrate the sun's rays through the use of large mirrors or lenses you get more for your money because most of the cost is in the PV arrays... There is a risk element but you can reduce it... You can put these small receivers in the desert or in the mountains away from populated areas. ...We believe that in 15 to 25 years we can lower that cost to 7 to 10 cents per kilowatt hour. ...We offer an advantage. You don't need cables, pipes, gas or copper wires. We can send it to you like a cell phone call -- where you want it and when you want it, in real time." [ [http://science.nasa.gov/headlines/y2001/ast23mar_1.htm Beam it Down, Scotty!] Mar, 2001 "from [http://science.nasa.gov/ Science@NASA] "]

Future

From 1995 through 1997, NASA undertook a study effort utilizing teams from government, academia and industry to develop space transportation vehicle concepts intended to drive recurring operations costs $200 or less per pound of payload delivered to low earth orbit(LEO). [ [http://science.ksc.nasa.gov/shuttle/nexgen/Nexgen_Downloads/OpsRepExSum.pdf Concepts and Technologies for Highly Reusable Space Transportation] ] The cost of transporting materials for the construction of future space solar power systems may be significantly reduced [ [http://science.ksc.nasa.gov/shuttle/nexgen/rlvhp.htm NASA KSC Next Gen Site] ] by implementing reusable launch systems [ [http://science.ksc.nasa.gov/shuttle/nexgen/hrst_main.htm#HRST%20Main HRST - Highly Reusable Space Transportation Project] NASA] such as the proposed Maglifter or Star Tram. These launch systems would utilize superconducting magnetic propulsion and levitation to propel reusable launch vehicles RVL's into orbit. Maglifter could reduce launch cost per pound of payload to one tenth of that of the Space Shuttle's $10,000 per pound. Star Tram might reduce the cost to as low as $100 per pound. The Mag Lifter would eliminate the weight of the first stage of the reusable flight vehicle, using permanent ground based magnetic propulsion to reach a horizontal speed of 550 mi/hr, then use onboard propulsion systems for the remaining acceleration to reach orbit. The Star Tram system would accelerate (using gigawatts of electrical power in superconducting magnetic energy storage) a vehicle to 8 km/second (17,800 mi/hr) in 5.3 minutes through a 1,000 mile long evacuated tube that lies on the ground for the first 800 miles, with the remaining tethered (for stability) portion magnetically levitated above the ground tangentially to the earth, rising to its 72,000 ft. end where the space vehicle exits the tube. [ [http://science.ksc.nasa.gov/shuttle/nexgen/Nexgen_Downloads/Spaceport_Visioning_Final_Report.pdf Spaceport Visoning Concept Study Oct 2002] ]

Supplying materials from the Moon is more than ten times easier than lifting materials out of the gravity well of the Earth, and the lunar base could easily become the supplier of power sources for commercial applications in geosynchronous or even low Earth orbit. Later, the moonbase could provide solar arrays for solar power systems for satellites, for missions to Mars, for prospecting missions to the near-Earth asteroids, and beyond. [op cit: "Photovoltaic Power for the Moon"]

The Pentagon's National Security Space Office (NSSO) issued a report [ [http://www.nss.org/settlement/ssp/library/final-sbsp-interim-assessment-release-01.pdf National Security Space Office Interim Assessment Phase 0 Architecture Feasibility Study, October 10, 2007] ] on October 10th, 2007 that states they intend to collect solar energy from space to help the United States' ongoing relationship with the Middle East and the battle for oil. Solar power is a clean source of energy that has no effect on the environment. The International Space Station is most likely to be the first test ground for this new idea, even though it is in a low-earth orbit.

Military personnel could particularly gain from this technology as they are as of 2007 paying around $1/kWh. In principle by beaming power on demand to a location it could eliminate the need to deliver fuel for the field, and hence significantly reduce supply line issues. The American government is eager that private companies will get involved with the launching of the new scheme. Companies that get involved will receive tax and other political benefits that have not been disclosed.

pace solar cells

Although costs are generally reduced for obtaining off the shelf products, solar cells utilized in space may have some different or additional requirements than typical terrestrial application solar cells. Due to the high cost of payload delivery into space, an important measure of power system performance is the specific power (power output per unit mass). This is typically specified for Earth orbit conditions. It is possible to measure specific power at the cell level, blanket level, array level or power system level. Specific power at the cell level does not include array structure and is many times higher than array level specific power. At the blanket level, specific power includes the coverglass, interconnections, and the backing material, but not the array structure.

Total power generation system mass (excluding storage) in currently designed space power systems may be described as follows. Photovoltaic blanket weight is only about a quarter of the total. The array structure and the power management and distribution (PMAD) system account for three-quarters of the power system mass. If the system were to include conversion and transmission of microwave power to earth or other receivers, both total weight and proportions would differ due to additional PMAD hardware and larger arrays required.

Thin solar cells have greater flexibility and so are better suited to construction of a flexible or semi-flexible array capable of being unrolled and/or inflated, to reduce both transportation packing space and weight. In the 1980s considerable research was devoted to development and commercialization of thin-film photovoltaics for terrestrial power generation. Here, thin films of photovoltaic material are deposited on a supporting substrate. This approach has lower conversion efficiencies, but due to the low amount of the active material used, has the potential for high specific power.

In addition to low mass, thin-film photovoltaics are also projected to have considerably lower costs. Materials cost is reduced due to the small amount of materials required; the cost of labor and assembly is reduced by the fact that large-area, integrated assemblies are produced directly on the substrate sheet. One option is to use a thin layer of photovoltaic material deposited onto a flexible substrate.

Efficiencies over 10% have been achieved with three thin-film materials: amorphous silicon (a-Si), copper indium diselenide (CuInSe2), and cadmium telluride (CdTe). However, very little current research is aimed at depositing thin-film cells on lightweight substrates, since most of the applications being considered are terrestrial, where weight is not as critical. To enable their use in space, technology for deposition on extremely lightweight substrates will need to be developed. Thin film solar cells have not yet been demonstrated in space. [op cit: "Photovoltaic Power Options for Mars"]

Concentrator systems

Another alternative is to use a concentrator system to focus light onto small, extremely high efficiency solar cells. This approach has been tested in space only on small-scale experiments. Conversion efficiencies of over 30% have been demonstrated using such concentrator systems. Concentrator systems will not be practical on planets such as Mars, where under worst-case conditions most of the incident sunlight is diffuse, and concentrator systems can focus only the direct component of the solar radiation.

olar power satellites

Solar power satellites would be vast assemblies of large solar modules for producing large scale space solar power. Energy generated from sunlight could be converted into microwaves and beamed to a rectifier-antenna, called a rectenna on earth, where the microwave power is rectified and converted to electric power.

The device necessary to convert the solar energy collected by the satellite to microwave form is called a transmitter. Good transmitters will convert energy from DC to radiofrequency (RF) form efficiently, with adequate control and minimal losses. NASA’s SERT program (discussed below) mandated that transmitters be 500 meters in diameter and emit at a frequency of 5.8 GHz. Three main types of transmitters are frequently considered: klystron, magnetron, and solid-state amplifiers. All of these options have relatively similar specific masses (mass per unit area) at a given power output and thus are approximately equally suitable for these applications. Solid-state amplifiers offer the most opportunity for improvement, as the materials used are capable of a range of different power amplified efficiencies (PAEs) when converting to different frequencies. Materials currently being explored for use in solid-state amplifying transmitters are InGaAs, GaN, and SiC [Mankins, McSpadden. Space Solar Power Programs and Microwave Wireless Power Transmission Technology. IEEE Microwave Magazine. Dec 2002: p 46-57] . Of these, GaN appears have the highest efficiencies. Further improvements on GaN and other materials for these devices are required to improve efficiencies. Goals include reducing contact and channel resistances in the devices as well as reducing the cost of the substrate, surface traps, and charge and interface effects. With sufficient funding and research efforts, these challenges can be overcome.

A 1996 estimate [ [http://www.nas.nasa.gov/About/Education/SpaceSettlement/Contest/Results/96/winner/siete.html NASA: Tango III : A Space Settlement Design] ] for the production of 5 billion watts (equivalent to five large nuclear power plants) would require several square km of solar collectors (weighing approximately 5 million kg) and an earth-based antenna 5 miles in diameter.

Terrestrial solar energy

An average of approximately 0.1 and 0.2 kW/m² of solar energy can be received from the Sun on the Earth's surface. Solar energy (total global insolation) striking the earth's surface consists of 2 components, direct and diffuse (diffuse light may be further subdivided into several other categories). [ [http://joseph-bartlo.net/articles/042797.htm "Basic Origin of Solar Energy and Atmospheric Influence"] 1997 Bartlo, Joseph] Due to influences of the atmosphere (reflection, absorption and scattering), including man made gases and particulates only 10% to 13% of the total incident energy approaching the earth's cross sectional area from the sun is available on earth.

Extraterrestrial solar energy

Extraterrestrial solar power is that collected outside of the earth's atmosphere. Besides man-made satellites in GSO, locations for this conversion may be sun-synchronous (near-polar, always facing the Sun) orbit, space probes, the moon, [ [http://powerweb.grc.nasa.gov/pvsee/programs/solarmoon.html "Photovoltaic Power for the Moon"] ] or other planets. [ [http://powerweb.grc.nasa.gov/pvsee/publications/mars/marspower.html "Photovoltaic Power Options for Mars"] ] There is little loss of microwave energy passing through the Earth’s atmosphere and there is no contribution to the global warming problem by the addition of CO₂ during the production stage. In addition, the orbit of rotation can be selected such that sunlight is received by the satellite ~96% of the time. In near Earth space the average ~1 to 2 kW/m² of energy that can be collected is approximately ten times as much the solar energy available on earth. (Earth's orbit causes varying extraterrestrial S flux between approximately 1329 and 1421 W/m². 1370 W/m² is the solar constant, i.e., mean flux perpendicular with the solar beam in outer space, at the mean distance from the Earth to the Sun. [op cit: Bartlo, Joseph] ) Unaffected by atmospheric gases, particulate matter and cloud cover, photovoltaic arrays in a geostationary Earth orbit (at an altitude of 22,300 miles) would receive, on average, eight times as much sunlight as they would on Earth's surface. [Electric Power Research Institute (EPRI) Journal, April 2000] In addition, they would be unaffected by the Earth's day-night cycle.

ERT

In 1999 NASA's Space Solar Power Exploratory Research and Technology program (SERT) was initiated for the following purpose:

* Perform design studies of selected flight demonstration concepts;
* Evaluate studies of the general feasibility, design, and requirements.
* Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications.
* Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative.
* Construct technology development and demonstration roadmaps for critical Space Solar Power (SSP) elements.

It was to develop a solar power satellite (SPS) concept for a future gigawatt space power systems to provide electrical power by converting the Sun’s energy and beaming it to the Earth's surface. It was also to provide a developmental path to solutions for current space power architectures. Subject to studies it proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar dynamic engines to convert solar flux into electricity. Collection systems were assumed to be in sun-synchronous orbit.

Some of SERT's conclusions include the following:

* The increasing global energy demand is likely to continue for many decades resulting in new power plants of all sizes being built.
* The environmental impact of those plants and their impact on world energy supplies and geopolitical relationships can be problematic.
* Renewable energy is a compelling approach, both philosophically and in engineering terms.
* Many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements.
* Based on their Concept Definition Study, space solar power concepts may be ready to reenter the discussion.
* Solar power satellites should no longer be envisioned as requiring unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin.
* Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches.
* The economic viability of space solar power systems depends on many factors and the successful development of various new technologies (not least of which is the availability of exceptionally low cost access to space) however, the same can be said of many other advanced power technologies options.
* Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century. [ [http://gltrs.grc.nasa.gov/reports/2000/TM-2000-210210.pdf Space Solar Power Satellite Technology Development at the Glenn Research Center—An Overview] James E. Dudenhoefer and Patrick J. George, NASA Glenn Research Center, Cleveland, Ohio]

Laser power beaming

A large-scale demonstration of power beaming is a necessary step to the development of solar power satellites. Laser power beaming was envisioned by some at NASA as a stepping-stone to further industrialization of space.

In the 1980s researchers at NASA worked on the potential use of lasers for space-to-space power beaming, focussing primarily on the development of a solar-powered laser. In 1989 it was suggested that power could also be usefully beamed by laser from Earth to space. In 1991 the SELENE project (SpacE Laser ENErgy) was begun, which included the study of laser power beaming for supplying power to a lunar base.

In 1988 the use of an Earth-based laser to power an electric thruster for space propulsion was proposed by Grant Logan, with technical details worked out in 1989. His proposal was a bit optimistic about technology (he proposed using diamond solar cells operating at six-hundred degrees to convert ultraviolet laser light, a technology that has yet to be demonstrated even in the laboratory, at a wavelength that will not easily transmit through the Earth's atmosphere). His ideas, with the technology scaled down to be possible with more practical, nearer-term technology, were adapted.

The SELENE program was a serious research effort for about two years, but the cost of taking the concept to operational status was quite high and the official project was ended in 1993, before reaching the goal of demonstrating the technology in space. However, some research is was still continuing. There was some hope that an array for a laser-powered aircraft demonstration might be developed. [ [http://powerweb.grc.nasa.gov/pvsee/programs/pvlaser_overview.html Glenn Involvement with Laser Power Beaming-- Overview] NASA Glenn Research Center]

Energy in global winters

Space solar power would be the only means of acquiring direct solar energy to supplement the burning of fossil fuels or nuclear energy sources under the most extreme conditions of a global catastrophic volcanic winter (or similarly, nuclear winter). This could include the massive energy increases necessary to grow food crops and for increased heating requirements under ice age conditions. Such could be the case after a rhyolitic supervolcano at one of the earth's few dozen hotspots. One at Lake Toba, Indonesia 75,000 years ago caused the Millennial Ice Age lasting 1000 years, wiping out 60% of the global population. Ejecta on this scale could occur at the Yellowstone Caldera which 640,000 years ago (one also occurred 2.2 million years ago), released 800 times more (but only one third of that released at Lake Toba and one fifth of that released at the world's largest known at La Garita Caldera in the San Juan Mountains of Colorado 27.8 million years ago) ejecta than Mount St. Helens did in 1980. [Caldera]

ee also

* Future energy development
* Photovoltaics
* Project Earth
* Satellite
* Solar power
* Solar power satellite
* Solar panels on spacecraft

References

External links

* [http://www.spacefuture.com/archive/conceptual_study_of_a_solar_power_satellite_sps_2000.shtml "Conceptual Study of A Solar Power Satellite, SPS 2000"] Makoto Nagatomo, Susumu Sasaki and Yoshihiro Naruo
* [http://blog.wired.com/wiredscience/2008/09/visionary-beams.html Researchers Beam 'Space' Solar Power in Hawaii] (Wired Science)