Space solar power
Encyclopedia
Space-based solar power (SBSP) is the concept of collecting solar power
in space
for use on Earth
. It has been in research since the early 1970s.
SBSP would differ from current solar collection methods in that the means used to collect energy would reside on an orbit
ing satellite
instead of on Earth's surface. Some projected benefits of such a system are:
SBSP also introduces several new hurdles, primarily the problem of transmitting energy from orbit to Earth's surface for use. Since wires extending from Earth's surface to an orbiting satellite
are neither practical nor feasible with current technology, SBSP designs generally include the use of some manner of wireless power transmission. The collecting satellite would convert solar energy into electrical energy on-board, powering a microwave
transmitter or laser
emitter, and focus its beam toward a collector (rectenna
) on the Earth's surface. Radiation
and micrometeoroid
damage could also become concerns for SBSP.
was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g., from an SPS to Earth's surface) using microwave
s from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a rectenna
, on the ground.
Glaser then was a vice president at Arthur D. Little
, Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems—chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space, it showed enough promise to merit further investigation and research.
Between 1978 and 1981, the Congress
authorized the Department of Energy
and NASA
to jointly investigate the concept. They organized the Satellite Power System Concept Development and Evaluation Program. The study remains the most extensive performed to date (budget 50 millions $). Several reports were published investigating the engineering feasibility of such an engineering project. They include:
The project was not continued with the change in administrations after the 1980 US Federal elections.
The Office of Technology Assessment
concluded
In 1997 NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility. In assessing "What has changed" since the DOE study, NASA asserted that:
Conversely, Dr. Pete Worden claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Dr. Worden referred to possible solutions as speculative, and that would not be available for decades at the earliest.
(SERT) (budget 22 millions $) was initiated for the following purposes:
SERT went about developing a solar power satellite (SPS) concept for a future gigawatt space power system, to provide electrical power by converting the Sun’s energy and beaming it to Earth's surface, and provided a conceptual development path that would utilize current technologies. SERT proposed an inflatable
photovoltaic gossamer structure with concentrator lenses or solar heat engine
s to convert sunlight
into electricity. The program looked both at systems in sun-synchronous orbit
and geosynchronous orbit
.
Some of SERT's conclusions:
The space-based portion will not need to support itself against gravity (other than relatively weak tidal stresses). It needs no protection from terrestrial wind or weather, but will have to cope with space hazards such as micrometeors and solar flares.
Two basic methods of conversion have been studied: photovoltaic (PV) and solar dynamic
(SD). Most analyses of SBSP have focused on photovoltaic conversion (commonly known as “solar cells”). Photovoltaic conversion uses semiconductor
cells to directly convert photons into electrical power.
Wireless power transmission was proposed early on as a means to transfer energy from collection to the Earth's surface, using either microwave or laser radiation at a variety of frequencies
.
demonstrated in 1964, during Walter Cronkite
's CBS
News program, a microwave-powered model helicopter
that received all the power it needed for flight from a microwave beam. Between 1969 and 1975, Bill Brown was technical director of a JPL Raytheon
program that beamed 30 kW of power over a distance of 1 miles (1.6 km) at 84% efficiency.
Microwave power transmission of tens of kilowatts has been well proven by existing tests at Goldstone
in California (1975) and Grand Bassin on Reunion Island (1997).
More recently, microwave power transmission has been demonstrated, in conjunction with solar energy capture, between a mountain top in Maui and the main island of Hawaii (92 miles away), by a team under John C. Mankins.
Technological challenges in terms of array layout, single radiation element design, and overall efficiency, as well as the associated theoretical limits are presently a subject of research, as it is demonstrated by the upcoming Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" to be held in the 2010 IEEE Symposium on Antennas and Propagation.
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, focusing 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) had begun, which included the study of laser power beaming for supplying power to a lunar base. The SELENE program was a two-year research effort, but the cost of taking the concept to operational status was too high, and the official project ended in 1993 before reaching a space-based demonstration.
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. He proposed using diamond solar cells operating at 600 degrees to convert ultraviolet
laser light, a technology that has yet to be demonstrated even in the laboratory.
A collection of LEO (Low Earth Orbit
) space power stations has been proposed as a precursor to GEO (Geostationary Orbit
) space-based solar power.
would likely consist of many short dipole
antennas connected via diode
s. Microwaves broadcasts from the satellite would be received in the dipoles with about 85% efficiency. With a conventional microwave antenna, the reception efficiency is better, but its cost and complexity is also considerably greater. Rectennas would likely be multiple kilometers across.
Reusable launch system
s are predicted to provide lower launch costs to low Earth orbit (LEO).
Much of the material launched need not be delivered to its eventual orbit immediately, which raises the possibility that high efficiency (but slower) engines could move SPS material from LEO to GEO at an acceptable cost. Examples include ion thruster
s or nuclear propulsion
.
Power beaming from geostationary orbit
by microwaves carries the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although they have increased atmospheric absorption
and even potential beam blockage by rain or water droplets. Because of the thinned array curse
, it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.
To give an idea of the scale of the problem, assuming a solar panel mass of 20 kg per kilowatt (without considering the mass of the supporting structure, antenna, or any significant mass reduction of any focusing mirrors) a 4 GW power station would weigh about 80,000 metric tons, all of which would, in current circumstances, be launched from the Earth. Very lightweight designs could likely achieve 1 kg/kW, meaning 4,000 metric tons for the solar panels for the same 4 GW capacity station. This would be the equivalent of between 40 and 150 heavy-lift launch vehicle
(HLLV) launches to send the material to low earth orbit, where it would likely be converted into subassembly solar arrays, which then could use high-efficiency ion-engine style rockets to (slowly) reach GEO (Geostationary orbit
). With an estimated serial launch cost for shuttle-based HLLVs of $500 million to $800 million, and launch costs for alternative HLLVs at $78 million, total launch costs would range between $11 billion (low cost HLLV, low weight panels) and $320 billion ('expensive' HLLV, heavier panels). For comparison, the direct cost of a new coal http://www.netl.doe.gov/technologies/coalpower/cctc/ccpi/pubs/2006_program_update.pdf or nuclear power plant ranges from $3 billion to $6 billion dollars per GW (not including the full cost to the environment from CO2 emissions or storage of spent nuclear fuel, respectively); another example is the Apollo missions
to the Moon cost a grand total of $24 billion (1970's dollars), taking inflation into account, would cost $140 billion today, more expensive than the construction of the International Space Station
.
s or Lofstrom loops, which would launch using electrical power, or the geosynchronous orbit space elevator
. However, these require technology that is yet to be developed. John Hunter
of Quicklaunch is working on commercialising the 'Hydrogen Gun', a new form of mass driver which proposes to deliver unmanned payloads to orbit for around 5% of regular launch costs (i.e. $500/lb or US$1,000/kg) and perform 5 launches per day.
, noting the problem of high launch costs in the early 1970s, proposed building the SPS's in orbit with materials from the Moon
. Launch costs from the Moon are potentially much lower than from Earth, due to the lower gravity. This 1970s proposal assumed the then-advertised future launch costing of NASA's space shuttle. This approach would require substantial up front capital investment to establish mass driver
s on the Moon.
Nevertheless, on 30 April 1979, the Final Report ("Lunar Resources Utilization for Space Construction") by General Dynamics' Convair Division, under NASA contract NAS9-15560, concluded that use of lunar resources would be cheaper than Earth-based materials for a system of as few as thirty Solar Power Satellites of 10GW capacity each.
In 1980, when it became obvious NASA's launch cost estimates for the space shuttle were grossly optimistic, O'Neill et al. published another route to manufacturing using lunar materials with much lower startup costs. This 1980s SPS concept relied less on human presence in space and more on partially self-replicating systems on the lunar surface under remote control
of workers stationed on Earth. The high Net energy gain
of this proposal derives from the Moon's much shallower gravitational well.
Having a relatively cheap per pound source of raw materials from space would lessen the concern for low mass designs and result in a different sort of SPS being built. The low cost per pound of lunar materials in O'Neill's vision would be supported by using lunar material to manufacture more facilities in orbit than just solar power satellites.
Advanced techniques for launching from the Moon may reduce the cost of building a solar power satellite from lunar materials. Some proposed techniques include the lunar mass driver and the lunar space elevator
, first described by Jerome Pearson. It would require establishing silicon
mining and solar cell manufacturing facilities on the Moon
.
suggests the Moon is the optimum location for solar power stations, and promotes lunar solar power. The main advantage he envisions is construction largely from locally available lunar materials, using in-situ resource utilization
, with a teleoperated
mobile factory, a crane to assemble the microwave reflectors, and rovers to assemble solar cells, which would significantly reduce launch costs compared to SBSP designs. Power relay satellites orbiting around earth and the Moon reflecting the microwave beam are also part of the project. Another design combined the rovers with the factory and directly paves the Moon with a thin film of solar cells. The Shimizu Corporation
proposed using combination of lasers and microwave for the lunar ring concept, along with power relay satellites.
has also been seriously considered. A NASA design study evaluated a 10,000 ton mining vehicle (to be assembled in orbit) that would return a 500,000 ton asteroid fragment to geostationary orbit. Only about 3,000 tons of the mining ship would be traditional aerospace-grade payload. The rest would be reaction mass for the mass-driver engine, which could be arranged to be the spent rocket stages used to launch the payload. Assuming that 100% of the returned asteroid was useful, and that the asteroid miner itself couldn't be reused, that represents nearly a 95% reduction in launch costs. However, the true merits of such a method would depend on a thorough mineral survey of the candidate asteroids; thus far, we have only estimates of their composition.
At the Earth's surface, a suggested microwave beam would have a maximum intensity at its center, of 23 mW/cm2 (less than 1/4 the solar irradiation constant), and an intensity of less than 1 mW/cm2 outside of the rectenna fenceline (the receiver's perimeter). These compare with current United States Occupational Safety and Health Act
(OSHA) workplace exposure limits for microwaves, which are 10 mW/cm2, - the limit itself being expressed in voluntary terms and ruled unenforceable for Federal OSHA enforcement purposes. A beam of this intensity is therefore at its center, of a similar magnitude to current safe workplace levels, even for long term or indefinite exposure. Outside the receiver, it is far less than the OSHA long-term levels Over 95% of the beam energy will fall on the rectenna. The remaining microwave energy will be absorbed and dispersed well within standards currently imposed upon microwave emissions around the world. It is important for system efficiency that as much of the microwave radiation as possible be focused on the rectenna. Outside of the rectenna, microwave intensities rapidly decrease, so nearby towns or other human activity should be completely unaffected.
Exposure to the beam is able to be minimized in other ways. On the ground, physical access is controllable (e.g., via fencing), and typical aircraft flying through the beam provide passengers with a protective metal shell (i.e., a Faraday Cage
), which will intercept the microwaves. Other aircraft (balloon
s, ultralight, etc.) can avoid exposure by observing airflight control spaces, as is currently done for military and other controlled airspace.
The microwave beam intensity at ground level in the center of the beam would be designed and physically built into the system; simply, the transmitter would be too far away and too small to be able to increase the intensity to unsafe levels, even in principle.
In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Experiments with deliberate microwave irradiation at reasonable levels have failed to show negative effects even over multiple generations.
Some have suggested locating rectennas offshore, but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.
A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective phased array
antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal. This forces the transmitted beam to be centered precisely on the rectenna and to have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused. Such a system would be physically incapable of focusing its power beam anywhere that did not have a pilot beam transmitter.
The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied, but nothing has been suggested which might lead to any significant effect.
, it can form nitrogen compounds. These nitrogen compounds are problematic when they form in the stratosphere, as they can damage the ozone layer. However, the environmental effect of rocket launches is negligible compared to higher volume polluters, such as airplanes and automobiles.
Solar power
Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
in space
Space
Space is the boundless, three-dimensional extent in which objects and events occur and have relative position and direction. Physical space is often conceived in three linear dimensions, although modern physicists usually consider it, with time, to be part of a boundless four-dimensional continuum...
for use on Earth
Earth
Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets...
. It has been in research since the early 1970s.
SBSP would differ from current solar collection methods in that the means used to collect energy would reside on an orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
ing satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
instead of on Earth's surface. Some projected benefits of such a system are:
- Higher collection rate: In space, transmission of solar energy is unaffected by the filtering effects of atmospheric gasses. Consequently, collection in orbit is approximately 144% of the maximum attainable on Earth's surface.
- Longer collection period: Orbiting satellites can be exposed to a consistently high degree of solar radiationRadiationIn physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
, generally for 24 hours per day, whereas surface panels can collect for 12 hours per day at most. - Elimination of weatherWeatherWeather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
concerns, since the collecting satellite would reside well outside of any atmospheric gasses, cloudCloudA cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...
cover, wind, and other weather events. - Elimination of plantPlantPlants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
and wildlifeWildlifeWildlife includes all non-domesticated plants, animals and other organisms. Domesticating wild plant and animal species for human benefit has occurred many times all over the planet, and has a major impact on the environment, both positive and negative....
interference. - Redirectable power transmission: A collecting satellite could possibly direct power on demand to different surface locations based on geographical baseload or peak load power needs.
SBSP also introduces several new hurdles, primarily the problem of transmitting energy from orbit to Earth's surface for use. Since wires extending from Earth's surface to an orbiting satellite
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
are neither practical nor feasible with current technology, SBSP designs generally include the use of some manner of wireless power transmission. The collecting satellite would convert solar energy into electrical energy on-board, powering a microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
transmitter or laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
emitter, and focus its beam toward a collector (rectenna
Rectenna
A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional...
) on the Earth's surface. Radiation
Radiation damage
Radiation damage is a term associated with ionizing radiation.-Causes:This radiation may take several forms:*Cosmic rays and subsequent energetic particles caused by their collision with the atmosphere and other materials....
and micrometeoroid
Micrometeoroid
A micrometeoroid is a tiny meteoroid; a small particle of rock in space, usually weighing less than a gram. A micrometeor or micrometeorite is such a particle that enters the Earth's atmosphere or falls to Earth.-Scientific interest:...
damage could also become concerns for SBSP.
History
The SBSP concept, originally known as Satellite Solar Power System (SSPS), was first described in November 1968. In 1973 Peter GlaserPeter Glaser
Peter Edward Glaser is an American scientist and aerospace engineer. He served as Vice President, Advanced Technology , was employed at Arthur D. Little, Inc., Cambridge, MA ; subsequently he served as a consultant to the company . He was president of Power from Space Consultants...
was granted U.S. patent number 3,781,647 for his method of transmitting power over long distances (e.g., from an SPS to Earth's surface) using microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
s from a very large antenna (up to one square kilometer) on the satellite to a much larger one, now known as a rectenna
Rectenna
A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional...
, on the ground.
Glaser then was a vice president at Arthur D. Little
Arthur D. Little
Arthur D. Little is an international management consulting firm originally headquartered in Boston, Massachusetts, United States, and formally incorporated by that name in 1909 by Arthur Dehon Little, an MIT chemist who had discovered acetate. Arthur D. Little pioneered the concept of contracted...
, Inc. NASA signed a contract with ADL to lead four other companies in a broader study in 1974. They found that, while the concept had several major problems—chiefly the expense of putting the required materials in orbit and the lack of experience on projects of this scale in space, it showed enough promise to merit further investigation and research.
Between 1978 and 1981, the Congress
United States Congress
The United States Congress is the bicameral legislature of the federal government of the United States, consisting of the Senate and the House of Representatives. The Congress meets in the United States Capitol in Washington, D.C....
authorized the Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
and NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
to jointly investigate the concept. They organized the Satellite Power System Concept Development and Evaluation Program. The study remains the most extensive performed to date (budget 50 millions $). Several reports were published investigating the engineering feasibility of such an engineering project. They include:
- Resource Requirements (Critical Materials, Energy, and Land)
- Financial/Management Scenarios
- Public Acceptance
- State and Local Regulations as Applied to Satellite Power System Microwave Receiving Antenna Facilities
- Student Participation
- Potential of Laser for SBSP Power Transmission
- International Agreements
- Centralization/Decentralization
- Mapping of Exclusion Areas For Rectenna Sites
- Economic and Demographic Issues Related to Deployment
- Some Questions and Answers
- Meteorological Effects on Laser Beam Propagation and Direct Solar Pumped Lasers
- Public Outreach Experiment
- Power Transmission and Reception Technical Summary and Assessment
- Space Transportation
The project was not continued with the change in administrations after the 1980 US Federal elections.
The Office of Technology Assessment
Office of Technology Assessment
The Office of Technology Assessment was an office of the United States Congress from 1972 to 1995. OTA's purpose was to provide Congressional members and committees with objective and authoritative analysis of the complex scientific and technical issues of the late 20th century, i.e. technology...
concluded
Too little is currently known about the technical, economic, and environmental aspects of SPS to make a sound decision whether to proceed with its development and deployment. In addition, without further research an SPS demonstration or systems-engineering verification program would be a high-risk venture.
In 1997 NASA conducted its "Fresh Look" study to examine the modern state of SBSP feasibility. In assessing "What has changed" since the DOE study, NASA asserted that:
US National Space Policy now calls for NASA to make significant investments in technology (not a particular vehicle) to drive the costs of ETO [Earth to Orbit] transportation down dramatically. This is, of course, an absolute requirement of space solar power.
Conversely, Dr. Pete Worden claimed that space-based solar is about five orders of magnitude more expensive than solar power from the Arizona desert, with a major cost being the transportation of materials to orbit. Dr. Worden referred to possible solutions as speculative, and that would not be available for decades at the earliest.
SERT
In 1999, NASA's Space Solar Power Exploratory Research and Technology programSpace Solar Power Exploratory Research and Technology program
The Space Solar Power Exploratory Research and Technology program program, conducted by NASA, was initiated by John Mankins and led by Joe Howell in March 1999 for the following purpose:...
(SERT) (budget 22 millions $) was initiated for the following purposes:
- 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.
SERT went about developing a solar power satellite (SPS) concept for a future gigawatt space power system, to provide electrical power by converting the Sun’s energy and beaming it to Earth's surface, and provided a conceptual development path that would utilize current technologies. SERT proposed an inflatable
Inflatable space structures
Inflatable space structures are structures which use pressurized air to maintain shape and rigidity. Notable examples of terrestrial inflatable structures include inflatable boats, and some military tents. Inflatable structures are also candidates for space structures, given their low weight, and...
photovoltaic gossamer structure with concentrator lenses or solar heat engine
Heat engine
In thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance...
s to convert sunlight
Sunlight
Sunlight, in the broad sense, is the total frequency spectrum of electromagnetic radiation given off by the Sun. On Earth, sunlight is filtered through the Earth's atmosphere, and solar radiation is obvious as daylight when the Sun is above the horizon.When the direct solar radiation is not blocked...
into electricity. The program looked both at systems in sun-synchronous orbit
Sun-synchronous orbit
A Sun-synchronous orbit is a geocentric orbit which combines altitude and inclination in such a way that an object on that orbit ascends or descends over any given point of the Earth's surface at the same local mean solar time. The surface illumination angle will be nearly the same every time...
and geosynchronous orbit
Geosynchronous orbit
A geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...
.
Some of SERT's conclusions:
- 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 much lower cost access to space than has been available), 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.
- Launch costsComparison of orbital launch systemsThis page exposes the full list of orbital launch systems. For the short simple list of launchers families, see Comparison of orbital launchers families....
in the range of $100-$200 per kilogram of payload to low-Earth orbit are needed if SPS are to be economically viable.
Advantages
The SBSP concept is attractive because space has several major advantages over the Earth's surface for the collection of solar power.- There is no air in space, so the collecting surfaces could receive much more intense sunlight, unobstructed by weather.
- A satellite could be illuminated over 99% of the time, and be in Earth's shadowShadowA shadow is an area where direct light from a light source cannot reach due to obstruction by an object. It occupies all of the space behind an opaque object with light in front of it. The cross section of a shadow is a two-dimensional silhouette, or reverse projection of the object blocking the...
on only 75 minutes per night at the spring and fall equinoxEquinoxAn equinox occurs twice a year, when the tilt of the Earth's axis is inclined neither away from nor towards the Sun, the center of the Sun being in the same plane as the Earth's equator...
es. - Relatively quick redirecting of power directly to areas that need it most.
- Higher collection rate: In space, transmission of solar energy is unaffected by the filtering effects of atmospheric gasses. Consequently, collection in orbit is approximately 144% of the maximum attainable on Earth's surface.
- Longer collection period: Orbiting satellites can be exposed to a consistently high degree of solar radiationRadiationIn physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
, generally for 24 hours per day, whereas surface panels can collect for 12 hours per day at most. - Elimination of weatherWeatherWeather is the state of the atmosphere, to the degree that it is hot or cold, wet or dry, calm or stormy, clear or cloudy. Most weather phenomena occur in the troposphere, just below the stratosphere. Weather refers, generally, to day-to-day temperature and precipitation activity, whereas climate...
concerns, since the collecting satellite would reside well outside of any atmospheric gasses, cloudCloudA cloud is a visible mass of liquid droplets or frozen crystals made of water and/or various chemicals suspended in the atmosphere above the surface of a planetary body. They are also known as aerosols. Clouds in Earth's atmosphere are studied in the cloud physics branch of meteorology...
cover, wind, and other weather events. - Elimination of plantPlantPlants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
and wildlifeWildlifeWildlife includes all non-domesticated plants, animals and other organisms. Domesticating wild plant and animal species for human benefit has occurred many times all over the planet, and has a major impact on the environment, both positive and negative....
interference. - Redirectable power transmission: A collecting satellite could possibly direct power on demand to different surface locations based on geographical baseload or peak load power needs.
Disadvantages
The SBSP concept also has a number of problems.- The space environment is hostile; panels suffer about 10 times the degradation they would on Earth. System lifetimes on the order of a decade would be expected, which makes it difficult to produce enough power to be economical.
- Space debrisSpace debrisSpace debris, also known as orbital debris, space junk, and space waste, is the collection of objects in orbit around Earth that were created by humans but no longer serve any useful purpose. These objects consist of everything from spent rocket stages and defunct satellites to erosion, explosion...
are a major hazard to large objects in space, and SBSP systems have been singled out as a particularly hazardous activity. - The broadcast frequency of the microwave downlink (if used) would require isolating the SBSP systems away from other satellites. GEO space is already well used and it is considered unlikely the ITUItuItu is an old and historic municipality in the state of São Paulo in Brazil. The population in 2009 was 157,384 and the area is 641.68 km². The elevation is 583 m. This place name comes from the Tupi language, meaning big waterfall. Itu is linked with the highway numbered the SP-75 and are flowed...
would allow an SPS to be launched. - Only about half the power generated by the SSP would be delivered to the grid, once all losses are factored in. These losses are on the same order as modern fossil fuel plants.
Design
Space-based solar power essentially consists of three elements:- a means of collecting solar power in space, for example via solar cellSolar cellA solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
s or a heat engineHeat engineIn thermodynamics, a heat engine is a system that performs the conversion of heat or thermal energy to mechanical work. It does this by bringing a working substance from a high temperature state to a lower temperature state. A heat "source" generates thermal energy that brings the working substance... - a means of transmitting power to earth, for example via microwave or laser
- a means of receiving power on earth, for example via a microwave antenna (rectenna)
The space-based portion will not need to support itself against gravity (other than relatively weak tidal stresses). It needs no protection from terrestrial wind or weather, but will have to cope with space hazards such as micrometeors and solar flares.
Two basic methods of conversion have been studied: photovoltaic (PV) and solar dynamic
Solar thermal energy
Solar thermal energy is a technology for harnessing solar energy for thermal energy . Solar thermal collectors are classified by the United States Energy Information Administration as low-, medium-, or high-temperature collectors. Low-temperature collectors are flat plates generally used to heat...
(SD). Most analyses of SBSP have focused on photovoltaic conversion (commonly known as “solar cells”). Photovoltaic conversion uses semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
cells to directly convert photons into electrical power.
Wireless power transmission was proposed early on as a means to transfer energy from collection to the Earth's surface, using either microwave or laser radiation at a variety of frequencies
Electromagnetic spectrum
The electromagnetic spectrum is the range of all possible frequencies of electromagnetic radiation. The "electromagnetic spectrum" of an object is the characteristic distribution of electromagnetic radiation emitted or absorbed by that particular object....
.
Microwave power transmission
William C. BrownWilliam C. Brown
William C. Brown was an American electrical engineer who helped to invent the crossed-field amplifier in the 1950s and also pioneered microwave power transmission in the 1960s....
demonstrated in 1964, during Walter Cronkite
Walter Cronkite
Walter Leland Cronkite, Jr. was an American broadcast journalist, best known as anchorman for the CBS Evening News for 19 years . During the heyday of CBS News in the 1960s and 1970s, he was often cited as "the most trusted man in America" after being so named in an opinion poll...
's CBS
CBS
CBS Broadcasting Inc. is a major US commercial broadcasting television network, which started as a radio network. The name is derived from the initials of the network's former name, Columbia Broadcasting System. The network is sometimes referred to as the "Eye Network" in reference to the shape of...
News program, a microwave-powered model helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
that received all the power it needed for flight from a microwave beam. Between 1969 and 1975, Bill Brown was technical director of a JPL Raytheon
Raytheon
Raytheon Company is a major American defense contractor and industrial corporation with core manufacturing concentrations in weapons and military and commercial electronics. It was previously involved in corporate and special-mission aircraft until early 2007...
program that beamed 30 kW of power over a distance of 1 miles (1.6 km) at 84% efficiency.
Microwave power transmission of tens of kilowatts has been well proven by existing tests at Goldstone
Goldstone Deep Space Communications Complex
The Goldstone Deep Space Communications Complex — commonly called the Goldstone Observatory — is located in California's Mojave Desert. Operated by ITT Corporation for the Jet Propulsion Laboratory, its main purpose is to track and communicate with space missions. It includes the Pioneer...
in California (1975) and Grand Bassin on Reunion Island (1997).
More recently, microwave power transmission has been demonstrated, in conjunction with solar energy capture, between a mountain top in Maui and the main island of Hawaii (92 miles away), by a team under John C. Mankins.
Technological challenges in terms of array layout, single radiation element design, and overall efficiency, as well as the associated theoretical limits are presently a subject of research, as it is demonstrated by the upcoming Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" to be held in the 2010 IEEE Symposium on Antennas and Propagation.
Laser power beaming
LaserLaser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
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, focusing 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) had begun, which included the study of laser power beaming for supplying power to a lunar base. The SELENE program was a two-year research effort, but the cost of taking the concept to operational status was too high, and the official project ended in 1993 before reaching a space-based demonstration.
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. He proposed using diamond solar cells operating at 600 degrees to convert ultraviolet
Ultraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
laser light, a technology that has yet to be demonstrated even in the laboratory.
Orbital location
The main advantage of locating a space power station in geostationary orbit is that the antenna geometry stays constant, and so keeping the antennas lined up is simpler. Another advantage is that nearly continuous power transmission is immediately available as soon as the first space power station is placed in orbit; other space-based power stations have much longer start-up times before they are producing nearly continuous power.A collection of LEO (Low Earth Orbit
Low Earth orbit
A low Earth orbit is generally defined as an orbit within the locus extending from the Earth’s surface up to an altitude of 2,000 km...
) space power stations has been proposed as a precursor to GEO (Geostationary Orbit
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
) space-based solar power.
Earth-based receiver
The Earth-based rectennaRectenna
A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional...
would likely consist of many short dipole
Dipole
In physics, there are several kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some distance. A permanent electric dipole is called an electret.*A...
antennas connected via diode
Diode
In electronics, a diode is a type of two-terminal electronic component with a nonlinear current–voltage characteristic. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals...
s. Microwaves broadcasts from the satellite would be received in the dipoles with about 85% efficiency. With a conventional microwave antenna, the reception efficiency is better, but its cost and complexity is also considerably greater. Rectennas would likely be multiple kilometers across.
In space applications
A laser sbsp could also power a base or vehicules on the surface of the moon or mars, saving on mass costs to land the power source. A spacecraft or another satellite could also be powered by the same means.Dealing with launch costs
One problem for the SBSP concept is the cost of space launches and the amount of material that would need to be launched.Reusable launch system
Reusable launch system
A reusable launch system is a launch system which is capable of launching a launch vehicle into space more than once. This contrasts with expendable launch systems, where each launch vehicle is launched once and then discarded.No true orbital reusable launch system is currently in use. The...
s are predicted to provide lower launch costs to low Earth orbit (LEO).
Much of the material launched need not be delivered to its eventual orbit immediately, which raises the possibility that high efficiency (but slower) engines could move SPS material from LEO to GEO at an acceptable cost. Examples include ion thruster
Ion thruster
An ion thruster is a form of electric propulsion used for spacecraft propulsion that creates thrust by accelerating ions. Ion thrusters are categorized by how they accelerate the ions, using either electrostatic or electromagnetic force. Electrostatic ion thrusters use the Coulomb force and...
s or nuclear propulsion
Nuclear propulsion
Nuclear propulsion includes a wide variety of propulsion methods that fulfil the promise of the Atomic Age by using some form of nuclear reaction as their primary power source.- Surface ships and submarines :...
.
Power beaming from geostationary orbit
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
by microwaves carries the difficulty that the required 'optical aperture' sizes are very large. For example, the 1978 NASA SPS study required a 1-km diameter transmitting antenna, and a 10 km diameter receiving rectenna, for a microwave beam at 2.45 GHz. These sizes can be somewhat decreased by using shorter wavelengths, although they have increased atmospheric absorption
Water absorption
During the transmission of electromagnetic radiation through a medium containing water molecules, portions of the electromagnetic spectrum are absorbed by water molecules...
and even potential beam blockage by rain or water droplets. Because of the thinned array curse
Thinned array curse
The thinned array curse is a theorem in electromagnetic theory of transmitters. It states that a transmitting aperture which is synthesized by a coherent phased array of smaller apertures that are spaced apart will have a smaller minimum beam spot size The thinned array curse (sometimes, sparse...
, it is not possible to make a narrower beam by combining the beams of several smaller satellites. The large size of the transmitting and receiving antennas means that the minimum practical power level for an SPS will necessarily be high; small SPS systems will be possible, but uneconomic.
To give an idea of the scale of the problem, assuming a solar panel mass of 20 kg per kilowatt (without considering the mass of the supporting structure, antenna, or any significant mass reduction of any focusing mirrors) a 4 GW power station would weigh about 80,000 metric tons, all of which would, in current circumstances, be launched from the Earth. Very lightweight designs could likely achieve 1 kg/kW, meaning 4,000 metric tons for the solar panels for the same 4 GW capacity station. This would be the equivalent of between 40 and 150 heavy-lift launch vehicle
Heavy Lift Launch Vehicle
A Heavy Lift Launch Vehicle, or HLLV, is a launch vehicle capable of lifting more mass into Low Earth Orbit than Medium Lift or Mid-Heavy Lift Launch Vehicles.There is no universally accepted capability requirements for heavy-lift launch vehicles....
(HLLV) launches to send the material to low earth orbit, where it would likely be converted into subassembly solar arrays, which then could use high-efficiency ion-engine style rockets to (slowly) reach GEO (Geostationary orbit
Geostationary orbit
A geostationary orbit is a geosynchronous orbit directly above the Earth's equator , with a period equal to the Earth's rotational period and an orbital eccentricity of approximately zero. An object in a geostationary orbit appears motionless, at a fixed position in the sky, to ground observers...
). With an estimated serial launch cost for shuttle-based HLLVs of $500 million to $800 million, and launch costs for alternative HLLVs at $78 million, total launch costs would range between $11 billion (low cost HLLV, low weight panels) and $320 billion ('expensive' HLLV, heavier panels). For comparison, the direct cost of a new coal http://www.netl.doe.gov/technologies/coalpower/cctc/ccpi/pubs/2006_program_update.pdf or nuclear power plant ranges from $3 billion to $6 billion dollars per GW (not including the full cost to the environment from CO2 emissions or storage of spent nuclear fuel, respectively); another example is the Apollo missions
Project Apollo
The Apollo program was the spaceflight effort carried out by the United States' National Aeronautics and Space Administration , that landed the first humans on Earth's Moon. Conceived during the Presidency of Dwight D. Eisenhower, Apollo began in earnest after President John F...
to the Moon cost a grand total of $24 billion (1970's dollars), taking inflation into account, would cost $140 billion today, more expensive than the construction of the International Space Station
International Space Station
The International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
.
Non-conventional launch methods
SBSP costs might be reduced if a means of putting the materials into orbit were developed that did not rely on rockets. Some possible technologies include ground launch systems such as mass driverMass driver
A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. All existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets. Sequential...
s or Lofstrom loops, which would launch using electrical power, or the geosynchronous orbit space elevator
Space elevator
A space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
. However, these require technology that is yet to be developed. John Hunter
John Hunter (scientist)
John Hunter is a projectile researcher, who developed the 1994 "supergun" Super High Altitude Research Project at the Lawrence Livermore National Laboratory...
of Quicklaunch is working on commercialising the 'Hydrogen Gun', a new form of mass driver which proposes to deliver unmanned payloads to orbit for around 5% of regular launch costs (i.e. $500/lb or US$1,000/kg) and perform 5 launches per day.
From lunar materials launched in orbit
Gerard O'NeillGerard O'Neill
Gerard Kitchen O'Neill was an American physicist and space activist. As a faculty member of Princeton University, he invented a device called the particle storage ring for high-energy physics experiments. Later, he invented a magnetic launcher called the mass driver...
, noting the problem of high launch costs in the early 1970s, proposed building the SPS's in orbit with materials from the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. Launch costs from the Moon are potentially much lower than from Earth, due to the lower gravity. This 1970s proposal assumed the then-advertised future launch costing of NASA's space shuttle. This approach would require substantial up front capital investment to establish mass driver
Mass driver
A mass driver or electromagnetic catapult is a proposed method of non-rocket spacelaunch which would use a linear motor to accelerate and catapult payloads up to high speeds. All existing and contemplated mass drivers use coils of wire energized by electricity to make electromagnets. Sequential...
s on the Moon.
Nevertheless, on 30 April 1979, the Final Report ("Lunar Resources Utilization for Space Construction") by General Dynamics' Convair Division, under NASA contract NAS9-15560, concluded that use of lunar resources would be cheaper than Earth-based materials for a system of as few as thirty Solar Power Satellites of 10GW capacity each.
In 1980, when it became obvious NASA's launch cost estimates for the space shuttle were grossly optimistic, O'Neill et al. published another route to manufacturing using lunar materials with much lower startup costs. This 1980s SPS concept relied less on human presence in space and more on partially self-replicating systems on the lunar surface under remote control
Telepresence
Telepresence refers to a set of technologies which allow a person to feel as if they were present, to give the appearance of being present, or to have an effect, via telerobotics, at a place other than their true location....
of workers stationed on Earth. The high Net energy gain
Net energy gain
Net Energy Gain is a concept used in energy economics that refers to the difference between the energy expended to harvest an energy source and the amount of energy gained from that harvest. The net energy gain, which can be expressed in joules, differs from the net financial gain that may result...
of this proposal derives from the Moon's much shallower gravitational well.
Having a relatively cheap per pound source of raw materials from space would lessen the concern for low mass designs and result in a different sort of SPS being built. The low cost per pound of lunar materials in O'Neill's vision would be supported by using lunar material to manufacture more facilities in orbit than just solar power satellites.
Advanced techniques for launching from the Moon may reduce the cost of building a solar power satellite from lunar materials. Some proposed techniques include the lunar mass driver and the lunar space elevator
Lunar space elevator
A lunar space elevator is a proposed cable running from the surface of the Moon into space.It is similar in concept to the better known Earth space elevator idea...
, first described by Jerome Pearson. It would require establishing silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...
mining and solar cell manufacturing facilities on the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
.
On the Moon
David CriswellDavid Criswell
David R. Criswell, Ph.D is currently the Director of the Institute for Space Systems Operations at the University of Houston. ISSO is the operational agent for the Houston Partnership for Space Exploration....
suggests the Moon is the optimum location for solar power stations, and promotes lunar solar power. The main advantage he envisions is construction largely from locally available lunar materials, using in-situ resource utilization
In-Situ Resource Utilization
In space exploration, in-situ resource utilization describes the proposed use of resources found or manufactured on other astronomical objects to further the goals of a space mission....
, with a teleoperated
Remote manipulator
A remote manipulator, also known as a telefactor, telemanipulator, or waldo , is a device which, through electronic, hydraulic, or mechanical linkages, allows a hand-like mechanism to be controlled by a human operator...
mobile factory, a crane to assemble the microwave reflectors, and rovers to assemble solar cells, which would significantly reduce launch costs compared to SBSP designs. Power relay satellites orbiting around earth and the Moon reflecting the microwave beam are also part of the project. Another design combined the rovers with the factory and directly paves the Moon with a thin film of solar cells. The Shimizu Corporation
Shimizu Corporation
is a leading architectural, engineering and general contracting firm, offering an integrated, comprehensive planning, design and build solutions for a broad range of construction and engineering projects worldwide...
proposed using combination of lasers and microwave for the lunar ring concept, along with power relay satellites.
From an asteroid
Asteroid miningAsteroid mining
Asteroid mining refers to the possibility of exploiting raw materials from asteroids and planetoids in space, including near-Earth objects. Minerals and volatiles could be mined from an asteroid or spent comet to provide space construction material , to extract water and oxygen to sustain the lives...
has also been seriously considered. A NASA design study evaluated a 10,000 ton mining vehicle (to be assembled in orbit) that would return a 500,000 ton asteroid fragment to geostationary orbit. Only about 3,000 tons of the mining ship would be traditional aerospace-grade payload. The rest would be reaction mass for the mass-driver engine, which could be arranged to be the spent rocket stages used to launch the payload. Assuming that 100% of the returned asteroid was useful, and that the asteroid miner itself couldn't be reused, that represents nearly a 95% reduction in launch costs. However, the true merits of such a method would depend on a thorough mineral survey of the candidate asteroids; thus far, we have only estimates of their composition.
Safety
The use of microwave transmission of power has been the most controversial issue in considering any SPS design.At the Earth's surface, a suggested microwave beam would have a maximum intensity at its center, of 23 mW/cm2 (less than 1/4 the solar irradiation constant), and an intensity of less than 1 mW/cm2 outside of the rectenna fenceline (the receiver's perimeter). These compare with current United States Occupational Safety and Health Act
Occupational Safety and Health Act
The Occupational Safety and Health Act is the primary federal law which governs occupational health and safety in the private sector and federal government in the United States. It was enacted by Congress in 1970 and was signed by President Richard Nixon on December 29, 1970...
(OSHA) workplace exposure limits for microwaves, which are 10 mW/cm2, - the limit itself being expressed in voluntary terms and ruled unenforceable for Federal OSHA enforcement purposes. A beam of this intensity is therefore at its center, of a similar magnitude to current safe workplace levels, even for long term or indefinite exposure. Outside the receiver, it is far less than the OSHA long-term levels Over 95% of the beam energy will fall on the rectenna. The remaining microwave energy will be absorbed and dispersed well within standards currently imposed upon microwave emissions around the world. It is important for system efficiency that as much of the microwave radiation as possible be focused on the rectenna. Outside of the rectenna, microwave intensities rapidly decrease, so nearby towns or other human activity should be completely unaffected.
Exposure to the beam is able to be minimized in other ways. On the ground, physical access is controllable (e.g., via fencing), and typical aircraft flying through the beam provide passengers with a protective metal shell (i.e., a Faraday Cage
Faraday cage
A Faraday cage or Faraday shield is an enclosure formed by conducting material or by a mesh of such material. Such an enclosure blocks out external static and non-static electric fields...
), which will intercept the microwaves. Other aircraft (balloon
Balloon
A balloon is an inflatable flexible bag filled with a gas, such as helium, hydrogen, nitrous oxide, oxygen, or air. Modern balloons can be made from materials such as rubber, latex, polychloroprene, or a nylon fabric, while some early balloons were made of dried animal bladders, such as the pig...
s, ultralight, etc.) can avoid exposure by observing airflight control spaces, as is currently done for military and other controlled airspace.
The microwave beam intensity at ground level in the center of the beam would be designed and physically built into the system; simply, the transmitter would be too far away and too small to be able to increase the intensity to unsafe levels, even in principle.
In addition, a design constraint is that the microwave beam must not be so intense as to injure wildlife, particularly birds. Experiments with deliberate microwave irradiation at reasonable levels have failed to show negative effects even over multiple generations.
Some have suggested locating rectennas offshore, but this presents serious problems, including corrosion, mechanical stresses, and biological contamination.
A commonly proposed approach to ensuring fail-safe beam targeting is to use a retrodirective phased array
Phased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
antenna/rectenna. A "pilot" microwave beam emitted from the center of the rectenna on the ground establishes a phase front at the transmitting antenna. There, circuits in each of the antenna's subarrays compare the pilot beam's phase front with an internal clock phase to control the phase of the outgoing signal. This forces the transmitted beam to be centered precisely on the rectenna and to have a high degree of phase uniformity; if the pilot beam is lost for any reason (if the transmitting antenna is turned away from the rectenna, for example) the phase control value fails and the microwave power beam is automatically defocused. Such a system would be physically incapable of focusing its power beam anywhere that did not have a pilot beam transmitter.
The long-term effects of beaming power through the ionosphere in the form of microwaves has yet to be studied, but nothing has been suggested which might lead to any significant effect.
Atmospheric damage due to launches
When hot rocket exhaust reacts with atmospheric nitrogenNitrogen cycle
The nitrogen cycle is the process by which nitrogen is converted between its various chemical forms. This transformation can be carried out by both biological and non-biological processes. Important processes in the nitrogen cycle include fixation, mineralization, nitrification, and denitrification...
, it can form nitrogen compounds. These nitrogen compounds are problematic when they form in the stratosphere, as they can damage the ozone layer. However, the environmental effect of rocket launches is negligible compared to higher volume polluters, such as airplanes and automobiles.
Timeline
- 1968: Dr. Peter GlaserPeter GlaserPeter Edward Glaser is an American scientist and aerospace engineer. He served as Vice President, Advanced Technology , was employed at Arthur D. Little, Inc., Cambridge, MA ; subsequently he served as a consultant to the company . He was president of Power from Space Consultants...
introduces the concept of a "solar power satellite" system with square miles of solar collectors in high geosynchronous orbitGeosynchronous orbitA geosynchronous orbit is an orbit around the Earth with an orbital period that matches the Earth's sidereal rotation period...
for collection and conversion of sun's energy into a microwaveMicrowaveMicrowaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
beam to transmit usable energy to large receiving antennas (rectennaRectennaA rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional...
s) on Earth for distribution.
- 1973: Dr. Peter Glaser is granted United States patent number 3,781,647 for his method of transmitting power over long distances using microwaves from a large (one square kilometer) antenna on the satellite to a much larger one on the ground, now known as a rectenna.
- 1978-81: The United States Department of EnergyUnited States Department of EnergyThe United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
and NASANASAThe National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
examine the solar power satellite (SPS) concept extensively, publishing design and feasibility studies. - 1982: BoeingBoeingThe Boeing Company is an American multinational aerospace and defense corporation, founded in 1916 by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Boeing Corporate headquarters has been in Chicago, Illinois since 2001...
proposal - 1987: Stationary High Altitude Relay PlatformStationary High Altitude Relay PlatformSHARP, short for Stationary High Altitude Relay Platform, was an experimental aircraft using beam-powered propulsion designed by the Communications Research Centre Canada and built by the University of Toronto Institute for Aerospace Studies during the 1980s...
a canadian experiment - 1994: The United States Air ForceUnited States Air ForceThe United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...
conducts the Advanced Photovoltaic ExperimentAdvanced Photovoltaic ExperimentThe Advanced Photovoltaic Experiment was a satellite-based science mission launched into Low Earth orbit on 1994-08-03 by a Pegasus rocket. The mission successfully tested the use of photovoltaic and electronic components in space....
using a satellite launched into low Earth orbit by a Pegasus rocketPegasus rocketThe Pegasus rocket is a winged space launch vehicle capable of carrying small, unmanned payloads into low Earth orbit. It is air-launched, as part of an expendable launch system developed by Orbital Sciences Corporation . Three main stages burning solid propellant provide the thrust...
. - 1995–97: NASA conducts a “Fresh Look” study of space solar power (SSP) concepts and technologies.
- 1998: The Space Solar Power Concept Definition Study (CDS) identifies credible, commercially viable SSP concepts, while pointing out technical and programmatic risks.
- 1998: Japan's space agency begins developing a Space Solar Power System (SSPS), a program that continues to the present day.
- 1999: NASA's Space Solar Power Exploratory Research and Technology programSpace Solar Power Exploratory Research and Technology programThe Space Solar Power Exploratory Research and Technology program program, conducted by NASA, was initiated by John Mankins and led by Joe Howell in March 1999 for the following purpose:...
(SERT, see below) begins.
- 2000: John Mankins of NASA testifies in the U.S. House of RepresentativesUnited States House of RepresentativesThe United States House of Representatives is one of the two Houses of the United States Congress, the bicameral legislature which also includes the Senate.The composition and powers of the House are established in Article One of the Constitution...
, saying "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.
- 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."
- 2001: NASDA (Japan's national space agency) announces plans to perform additional research and prototyping by launching an experimental satellite with 10 kilowatts and 1 megawatt of power.
- 2003: ESA studies
- 2007: The US Pentagon's National Security Space Office (NSSO) issues a report on October 10, 2007 stating they intend to collect solar energy from space for use on Earth to help the United States' ongoing relationship with the Middle EastMiddle EastThe Middle East is a region that encompasses Western Asia and Northern Africa. It is often used as a synonym for Near East, in opposition to Far East...
and the battle for oil. The International Space StationInternational Space StationThe International Space Station is a habitable, artificial satellite in low Earth orbit. The ISS follows the Salyut, Almaz, Cosmos, Skylab, and Mir space stations, as the 11th space station launched, not including the Genesis I and II prototypes...
may be the first test ground for this new idea, even though it is in a low-earth orbit.
- 2007: In May 2007 a workshop is held at the US Massachusetts Institute of Technology (MIT)Massachusetts Institute of TechnologyThe Massachusetts Institute of Technology is a private research university located in Cambridge, Massachusetts. MIT has five schools and one college, containing a total of 32 academic departments, with a strong emphasis on scientific and technological education and research.Founded in 1861 in...
to review the current state of the SBSP market and technology.
- 2009: Several companies announce future SBSP partnerships and commitments, including Pacific Gas and Electric (PG&E) & SolarenSolarenSolaren, Inc. is a Southern California startup corporation created to utilize solar energy for terrestrial electricity usage. The company has a contract under negotiation with Pacific Gas and Electric Company of California to deliver 200 megawatts of power for at least 15 years., starting in 2016...
, Mitsubishi ElectricMitsubishi Electricis a multinational electronics and information technology company headquartered in Tokyo, Japan. It is one of the core companies of the Mitsubishi Group....
Corp. & IHI Corporation, Space Energy, Inc., and Japan Aerospace Exploration AgencyJapan Aerospace Exploration AgencyThe , or JAXA, is Japan's national aerospace agency. Through the merger of three previously independent organizations, JAXA was formed on October 1, 2003, as an Independent Administrative Institution administered by the Ministry of Education, Culture, Sports, Science and Technology and the...
.
- 2010: Europe's EADS AstriumEADS AstriumAstrium Satellites is one of the three business units of Astrium, a subsidiary of EADS. It is a European space manufacturer involved in the manufacture of spacecraft used for science, Earth observation and telecommunication, as well as the equipment and subsystems used therein and related ground...
announces SBSP plans.
- 2010: Professors Andrea Massa and Giorgio Franceschetti announce a special session on the "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" at the 2010 Institute of Electrical and Electronics EngineersInstitute of Electrical and Electronics EngineersThe Institute of Electrical and Electronics Engineers is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence...
International Symposium on Antennas and Propagation.
In fiction
- Space stations transmitting solar power have appeared in science-fiction works like Isaac AsimovIsaac AsimovIsaac Asimov was an American author and professor of biochemistry at Boston University, best known for his works of science fiction and for his popular science books. Asimov was one of the most prolific writers of all time, having written or edited more than 500 books and an estimated 90,000...
's Reason (1941), that centers around the troubles caused by the robotsIsaac Asimov's Robot SeriesIsaac Asimov's Robot Series is a series of short stories and novels by Isaac Asimov featuring positronic robots.- Short stories :Most of Asimov's robot short stories are set in the first age of positronic robotics and space exploration...
operating the station. Asimov's short story "The Last QuestionThe Last Question"The Last Question" is a science fiction short story by Isaac Asimov. It first appeared in the November 1956 issue of Science Fiction Quarterly and was reprinted in the collections Nine Tomorrows , The Best of Isaac Asimov , Robot Dreams , the retrospective Opus 100 , and in Isaac Asimov: The...
" also features the use of SBSP to provide limitless energy for use on Earth. - In the novel "Skyfall" (1976) by Harry HarrisonHarry HarrisonHarry Harrison is an American science fiction author best known for his character the Stainless Steel Rat and the novel Make Room! Make Room! , the basis for the film Soylent Green...
an attempt to launch the core of powersat from Cape Canaveral ends in disaster when the launch vehicle fails trapping the payload in a decaying orbit. - Solar Power Satellites have also been seen in the work of author Ben BovaBen BovaBenjamin William Bova is an American science-fiction author and editor. He is the recipient of six Hugo Awards for Best Professional Editor for his work at Analog Science Fiction in the 1970's.-Personal life:...
's novels "Powersat" and "Colony". - In Sid MeierSid MeierSidney K. "Sid" Meier is a Canadian programmer and designer of several popular computer strategy games, most notably Civilization. He has won accolades for his contributions to the computer games industry...
's Alpha CentauriSid Meier's Alpha CentauriSid Meier's Alpha Centauri is the critically acclaimed science fiction 4X turn-based strategy video game sequel to the Civilization series. Sid Meier, designer of Civilization, and Brian Reynolds, designer of Civilization II, developed Alpha Centauri after they left MicroProse to join the newly...
, an endgame 'building' that fulfills the same function as an SPS is the 'Orbital Power Transmitter' which provides every city that you own with a unit of energy per satellite launched, providing the city has an Aerospace Command building or your faction controls the space elevatorSpace elevatorA space elevator, also known as a geostationary orbital tether or a beanstalk, is a proposed non-rocket spacelaunch structure...
. Building multiple Orbital Power Transmitters provides massive bonuses to energy generation and soon pay for themselves many times over. - In a 1981 storyline from the Iron ManIron ManIron Man is a fictional character, a superhero in the . The character was created by writer-editor Stan Lee, developed by scripter Larry Lieber, and designed by artists Don Heck and Jack Kirby, first appearing in Tales of Suspense #39 .A billionaire playboy, industrialist and ingenious engineer,...
comic book (issues #142-144), a rogue microwave transmission from a secret Solar Power Satellite is responsible for numerous deaths in Allentown, Iowa. - In the computer games SimCity 2000SimCity 2000SimCity 2000 is a simulation/city building video game and the second installment in the SimCity series. SimCity 2000 was first released by Maxis in 1994 for computers running Apple Macintosh Operating System...
and 3000SimCity 3000SimCity 3000 is a city building simulation personal computer game and the third major installment in the SimCity series. It was published by Electronic Arts and developed by series creator Maxis, a wholly owned subsidiary of EA...
, plants that implemented solar satellite technology called microwave powerplants were available in the future. One disaster scenario involved the beam missing the receiver and hitting the city's infrastructure. The plant was discontinued in SimCity 4SimCity 4SimCity 4 is a city-building/urban planning simulation computer game developed by Maxis, a subsidiary of Electronic Arts. It was released on January 14, 2003. It is the fourth installment in the SimCity series. SimCity 4 has a single expansion pack called Rush Hour which adds features to the game...
but several fan-made microwave powerplants were available on various SimCity 4 fan sites. - In the film Die Another DayDie Another DayDie Another Day is the 20th spy film in the James Bond series, and the fourth and last film to star Pierce Brosnan as the fictional MI6 agent James Bond; it is also the last Bond film of the original timeline with the series being rebooted with Casino Royale...
, a satellite weapon is disguised as a solar power satellite. - In Mobile Suit Gundam 00Mobile Suit Gundam 00is an anime TV series, the eleventh incarnation of Sunrise's long-running Gundam franchise consisting of two seasons. It is directed by Seiji Mizushima and written by Yōsuke Kuroda, and features character designs by Yun Kōga. The twenty-five episode season was officially announced by Sunrise...
, a solar power satellite array is constructed around the Earth and is used to harness solar energy for use. They play a critical plot role in the superpowers' power balanceBalance of power in international relationsIn international relations, a balance of power exists when there is parity or stability between competing forces. The concept describes a state of affairs in the international system and explains the behavior of states in that system...
. - In After War Gundam XAfter War Gundam XAfter War Gundam X, known in Japan as , is an anime television series from Japan. It is a part of the Gundam franchise that started in 1979, but takes place in an alternate universe called After War Era. The series has 39 episodes, aired in Japan from April 5, 1996 to December 28, 1996 across TV...
, a solar power station is built on the Moon, and is used to supply energy via microwave to various mobile suits, to energise their powerful "Satellite Cannons". - In Cadillacs and Dinosaurs (TV series)Cadillacs and Dinosaurs (TV series)Cadillacs and Dinosaurs is an American Saturday morning animated television series which aired on CBS Kids in the United States from 1993 to 1994. Based on the comic book of the same name by Mark Schultz, the show was created by screenwriter Steven E...
, space solar power is one of the lost technologies of the ancients.
See also
- Attitude controlAttitude dynamics and controlSpacecraft flight dynamics is the science of space vehicle performance, stability, and control. It requires analysis of the six degrees of freedom of the vehicle's flight, which are similar to those of aircraft: translation in three dimensional axes; and its orientation about the vehicle's center...
- Future energy development
- Orbital station-keeping in GEO
- PhotovoltaicsPhotovoltaicsPhotovoltaics is a method of generating electrical power by converting solar radiation into direct current electricity using semiconductors that exhibit the photovoltaic effect. Photovoltaic power generation employs solar panels composed of a number of solar cells containing a photovoltaic material...
- Project Earth
- SatelliteSatelliteIn the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
- Solar powerSolar powerSolar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar radiation, along with secondary solar-powered resources such as wind and wave power, hydroelectricity and biomass, account for most of the available...
- Solar panels on spacecraftSolar panels on spacecraftSpacecraft operating in the inner solar system usually rely on the use of photovoltaic solar panels to derive electricity from sunlight. In the outer solar system, where the sunlight is too weak to produce sufficient power, radioisotope thermal generators are used as a power source.-History:The...
- Space FountainSpace fountainA space fountain is a proposed form of space elevator that does not require the structure to be in geostationary orbit, and does not rely on tensile strength for support. In contrast to the original space elevator design , a space fountain is a tremendously tall tower extending up from the ground...
- Friis transmission equationFriis transmission equationThe Friis transmission equation is used in telecommunications engineering, and gives the power received by one antenna under idealized conditions given another antenna some distance away transmitting a known amount of power. The formula was derived in 1945 by Danish-American radio engineer Harald T...
equation for beamed wireless power efficiency
External links
- William Maness on why alternative energy and power grids aren’t good playmates and his plans for beaming solar power from space. in Seed (magazine)Seed (magazine)Seed is an online science magazine published by Seed Media Group. The magazine looks at big ideas in science, important issues at the intersection of science and society, and the people driving global science culture...
- Information about Space Solar Power
- The World Needs Energy from Space Space-based solar technology is the key to the world's energy and environmental future, writes Peter E. GlaserPeter GlaserPeter Edward Glaser is an American scientist and aerospace engineer. He served as Vice President, Advanced Technology , was employed at Arthur D. Little, Inc., Cambridge, MA ; subsequently he served as a consultant to the company . He was president of Power from Space Consultants...
, a pioneer of the technology. - Reinventing the Solar Power Satellite", NASA 2004-212743, report by Geoffrey A. LandisGeoffrey A. LandisGeoffrey A. Landis is an American scientist, working for the National Aeronautics and Space Administration on planetary exploration, interstellar propulsion, solar power and photovoltaics...
of NASA Glenn Research Center - Japan's plans for a Solar Power Station in Space - the Japanese government hopes to assemble a space-based solar array by 2040.
- Space Energy, Inc. - Space Energy, Inc.
- Whatever happened to solar power satellites? An article that covers the hurdles in the way of deploying a solar power satellite.
- Solar Power Satellite from Lunar and Asteroidal Materials Provides an overview of the technological and political developments needed to construct and utilize a multi-gigawatt power satellite. Also provides some perspective on the cost savings achieved by using extraterrestrial materialsExtraterrestrial materialsMost atoms on Earth came from the interstellar dust and gas from which the Sun and Solar System formed. However, in the space science community, "extraterrestrial materials" generally refers to objects now on Earth that were solidified prior to arriving on earth...
in the construction of the satellite. - A renaissance for space solar power? by Jeff Foust, Monday, August 13, 2007 Reports on renewed institutional interest in SSP, and a lack of such interest in past decades.
- PowerSat Corporation / PowerSat Limited website Commercial space based solar power companies in Europe and the United States.
- "Conceptual Study of A Solar Power Satellite, SPS 2000" Makoto Nagatomo, Susumu Sasaki and Yoshihiro Naruo
- Researchers Beam 'Space' Solar Power in Hawaii (WiredWired (magazine)Wired is a full-color monthly American magazine and on-line periodical, published since January 1993, that reports on how new and developing technology affects culture, the economy, and politics...
Science) - http://www.nss.org/settlement/ssp/library/index.htm — The National Space SocietyNational Space SocietyThe National Space Society is an international nonprofit 501, educational, and scientific organization specializing in space advocacy...
's Space Solar Power Library - Special Session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" 2010 IEEE International Symposium on Antennas and Propagation
- The future of Energy is on demand? Special Session at the 2010 Festival delle Città Impresa featuring John Mankins (Artemis Innovation Management Solutions LLC, USA), Nobuyuki Kaya (Kobe UniversityKobe UniversityShindai is one of the leading universities in Japan. It can be seen in the several rankings such as shown below.-General Rankings:The university is ranked 10th in 2010 in the ranking "Truly Strong Universities" by Toyo Keizai...
, Japan), Sergio Garribba (Italian Ministry of Economic DevelopmentMinistry of Economic DevelopmentMinistry of Economic Development may refer to:* Ministry of Economic Development * Ministry of Economic Development * Ministry of Finance and Economic Development * Ministry of Economy and Sustainable Development...
, Italy), Lorenzo Fiori (FinmeccanicaFinmeccanicaFinmeccanica S.p.A. is an Italian conglomerate. Finmeccanica is the second largest industrial group and the largest of the hi-tech industrial groups based in Italy. It works in the fields of defence, aerospace, security, automation, transport and energy...
Group, Italy), Andrea Massa (University of TrentoUniversity of TrentoThe University of Trento is an Italian university located in the cities of Trento and Rovereto. It has been able to achieve considerable results in didactics, research and international relations, as shown by Censis University Guide and by the Italian Ministry of...
, Italy) and Vincenzo Gervasio (Consiglio Nazionale dell'Economia ed del Lavoro, Italy). White Paper- History of SPS Developpements International Union of Radio ScienceInternational Union of Radio ScienceThe International Union of Radio Science is one of 26 international scientific unions affiliated to the International Council for Science.- History and objectives :...
2007
Videos
- Powering the Planet 20-minute streaming video from The Futures Channel that provides a "101" on space-based solar power
- Space Solar Power NewSpace 2010 Panel, 72 minutes
- Space Solar Power and Space Energy Systems SSI - Space Manufacturing 14 Panel - 2010 - 27 min
- NASA DVD in 16 Parts Exploring New Frontiers for Tomorrow's Energy Needs
- Space Solar Power Press Conference September 12, 2008 (71 minutes) National Space SocietyNational Space SocietyThe National Space Society is an international nonprofit 501, educational, and scientific organization specializing in space advocacy...