Space-based solar energy

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NASA Integrated Symmetrical Concentrator SPS concept

Space-based solar power ( English space-based solar power , SBSP ) is the concept that solar energy in space to collect and distribute them to the earth. Potential benefits of extracting solar energy in space include a higher collection rate and collection time due to the lack of a diffuse atmosphere, as well as the ability to place a solar collector in orbit where there is no night. A significant part of the incoming solar radiation (55–60%) is lost on its way through the earth's atmosphere due to the effects of reflection and absorption. Space-based solar power systems convert sunlight into microwaves outside of the atmosphere and avoid these losses and the downtime caused by the earth's rotation , but at a high cost due to the cost of launching material into orbit. SBSP is considered to be a form of renewable energy and is occasionally considered among the proposals for geoengineering . It is attractive to those seeking large-scale solutions to anthropogenic climate change or fossil fuel depletion (e.g. peak oil ).

Various SBSP proposals have been explored since the early 1970s, but none are economically viable with today's space launch infrastructure. Some technologists speculate that this could change in the distant future if an off-earth industrial base were to be developed that could manufacture solar power satellites from asteroids or lunar material, or if radically new space launch technologies other than rocket technology were to become available in the future.

In addition to the cost of implementing such a system, SBSP also introduces several technological hurdles, including the problem of transferring energy from orbit to the surface of the earth for use. Since wires that extend from the earth's surface to an orbiting satellite are neither practical nor feasible with current technology, SBSP concepts generally involve the use of some form of wireless power transmission with the associated conversion inefficiencies, as well as land use for the necessary antenna stations to receive the energy on the earth's surface. The collecting satellite would convert solar energy into electrical energy, operate a microwave transmitter or laser transmitter , and transmit that energy to a collector (or microwave rectenna ) on the earth's surface. In contrast to the appearance of SBSP in popular novels and video games, most designs suggest radiation energy densities that are not harmful if humans are accidentally exposed, such as when a transmitter satellite beam goes off course. But the enormous size of the receiving antennas required would still require large blocks of land near the end users to be procured and used for this purpose. The lifespan of space-based collectors, given the challenges of long-term exposure to the space environment, including radiation degradation and damage from micrometeorites , could also become an issue for SBSP.

SBSP is actively operated by Japan, China and Russia. In 2008, Japan passed its Basic Space Law, making space solar energy a national target, and JAXA has a roadmap for the commercial SBSP. In 2015, the Chinese Academy of Space Technology (CAST) presented its roadmap at the International Space Development Conference.

history

A laser pilot beam guides the microwave power transmission to a rectenna.

In 1941, the science fiction author Isaac Asimov published the science fiction short story " Reason ", in which a space station uses microwave rays to transmit the energy collected by the sun to different planets. The SBSP concept, originally known as Satellite Solar Power Plant (SSPS), was first described in November 1968. In 1973 Peter Glaser received US patent number 3,781,647 for his method of transmitting energy over long distances (for example from a PLC to the earth's surface) using microwaves from a very large antenna (up to a square kilometer) on the satellite to to a much larger antenna on the ground, now known as the "rectenna".

Glaser was then Vice President of Arthur D. Little , Inc. NASA signed a contract with ADL in 1974 to lead four other companies in a large-scale study. They found that while the concept had several major problems - most notably the cost of getting the materials it needed in orbit and the lack of experience on projects of this scale in space - it was promising enough to encourage further study and research to justify.

Between 1978 and 1986, the US Congress authorized the Department of Energy (DoE) and NASA to study the concept together. They organized the concept development and evaluation program for satellite power plants. The study is still the largest ever carried out (budget: 50 million dollars). Several reports have been published examining the technical feasibility of such an engineering project. This includes:

Artistic concept of the solar power satellite in action. The arrangement of a microwave transmission antenna is shown. The solar power satellite should be in geosynchronous orbit 22,236 miles above the earth's surface. NASA 1976
  • Resource requirements (critical materials, energy and land)
  • Finance and management scenarios
  • Public acceptance
  • State and local regulations for satellite power systems. Microwave receiving antenna systems
  • Student participation
  • Potential of the laser for SBSP power transmission
  • International agreements
  • Centralization / decentralization
  • Mapping of exclusion areas for Rectenna locations
  • Economic and demographic issues related to the provision
  • Some questions and answers
  • Meteorological effects on the propagation of laser beams and directly solar pumped lasers
  • Public relations experiment
  • Technical summary and evaluation of energy transmission and reception
  • Space transport

attitude

The project was not continued with the change of government after the 1980 US federal elections. The Technology Assessment Bureau concluded that “too little is currently known about the technical, economic and environmental aspects of PLCs to make an informed decision on whether to proceed with development and deployment. In addition, without further research, a PLC demonstration or systems verification program would be a high risk program. "

In 1997, NASA carried out its “Fresh Look” study to examine the current status of SBSP feasibility. In assessing “What has changed” since the DOE study, NASA found that the “US National Space Policy now requires NASA to make significant investments in technology (not in a specific vehicle) to cover the cost of the Dramatically lowering transportation from the earth's surface to orbit. Of course, this is an absolute requirement for solar energy in space. "

Conversely, NASA's Pete Worden claimed that space-based solar cells are about five orders of magnitude more expensive than solar power from the Arizona desert, with the largest cost being to get materials into orbit. Worden described possible solutions as speculative that would not be available for decades at the earliest.

On November 2, 2012, China proposed space cooperation with India, the SBSP mentioned, “can be a space-based solar energy initiative so that both India and China can work with other willing space nations for long-term cooperation with adequate funding To bring space solar energy to earth ".

In February 2019, China (CAST) announced long-term plans to build propulsion satellites.

Research and technology program to explore space solar energy

NASA SERT Integrated Symmetrical Concentrator PLC concept.

In 1999 the NASA Space Solar Power Exploratory Research and Technology Program (SERT) was launched for the following purposes:

  • Execution of design studies of selected flight demonstration concepts.
  • Evaluation of studies on general feasibility, design and requirements.
  • Conceptual designs of subsystems that use advanced SSP technologies to take advantage of future space or terrestrial applications.
  • Formulate a preliminary plan of action for the US (in collaboration with international partners) to launch an aggressive technology initiative.
  • Creation of technology development and demonstration roadmaps for critical elements of space solar energy (SSP).

SERT developed a concept for a solar power satellite (PLC) for a future gigawatt space system to provide electrical energy by converting solar energy and radiating it to the earth's surface, and provided a conceptual development path that utilizes current technologies. SERT proposed an inflatable photovoltaic gossamer structure with concentrator lenses or thermal engines to convert sunlight into electricity. The program looked at systems in both sun-synchronous orbit and geosynchronous orbit . Some of the SERT conclusions:

  • The increasing global energy demand is expected to continue for many decades, with new power plants of all sizes being built.
  • The environmental impact of these facilities and their impact on world energy supplies and geopolitical relationships can be problematic.
  • Renewable energies are a compelling approach, both philosophically and technically.
  • Many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity due to their inherent land and water needs.
  • Based on their concept definition study, space solar power concepts may be ready to re-enter the discussion.
  • Solar power satellites should no longer be viewed as an unimaginably large initial investment in fixed infrastructure before the installation of productive power plants can begin.
  • Space solar systems appear to have many significant environmental benefits compared to alternative approaches.
  • The profitability of space solar systems depends on many factors and the successful development of various new technologies (not least on the availability of a much cheaper access to space than before); however, the same is true of many other options in advanced energy technologies.
  • Space solar energy may well prove to be a serious candidate among the options for meeting the energy needs of the 21st century.
  • Launch costs in the range of $ 100– $ 200 per kilogram of payload from low earth orbit to geosynchronous orbit are necessary if SPS is to be economically viable.

Japanese Aerospace Exploration Agency

The IEEE Spectrum magazine from May 2014 carried an extensive article "It's Always Sunny in Space" by Susumu Sasaki. The article read: “It has been the subject of many previous studies and sci-fi material for decades, but space-based solar energy could finally become a reality within 25 years, according to a proposal from researchers at Japan Aerospace Exploration Agency (JAXA) in Tokyo . "

JAXA announced on March 12, 2015 that it had wirelessly transmitted 1.8 kilowatts over 50 meters to a small receiver by converting electricity into microwaves and then back into electricity. This is the standard plan for this type of energy production. On March 12, 2015, Mitsubishi Heavy Industries demonstrated the transmission of 10 kilowatts (kW) of power to a receiver unit located 500 meters away.

Advantages and disadvantages

advantages

The SBSP concept is attractive because space has several major advantages over the earth's surface in generating solar energy:

  • It is always sunny noon in space and full sun.
  • The quilts could receive much more intense sunlight due to the lack of obstacles such as atmospheric gases, clouds, dust and other weather events. As a result, the intensity in orbit is about 144% of the maximum achievable intensity on the earth's surface.
  • A satellite could be illuminated 99% of the time and be in the shadow of the earth for a maximum of 72 minutes per night in spring and at midnight in autumn. Orbiting satellites can be exposed to consistently high levels of solar radiation, usually 24 hours a day, while surface solar cells currently provide electricity on average 29% of the day.
  • The electricity could be diverted relatively quickly to the areas that need it most. A collective satellite could potentially deliver electricity on demand to different surface locations depending on geographic base load or peak load electricity needs .
  • Eliminate disturbance from plants and wildlife.
  • With very large-scale implementations, especially at lower altitudes, it can reduce the amount of sunlight incident on the earth's surface. This would be desirable in order to counteract the effects of global warming .

disadvantage

The SBSP concept also has a number of problems:

  • The high cost of launching a satellite into space. For 6.5 kg / kW, the cost of placing a power satellite in GEO cannot exceed $ 200 / kg if the cost of electricity is to be competitive.
  • Microwave optics require a GW scale due to the diffraction disk beam defocusing. Typically, a 1 km long transmission plate at 2.45 GHz extends up to 10 km within range of the earth.
  • Inability to restrict power transmission within tiny radiation angles. For example, it takes a 0.002 degree (7.2 arc seconds) beam to stay within a one kilometer receive antenna target from geostationary altitude. The most advanced directional wireless energy transmission systems as of 2019 distribute their power beam half-width over at least 0.9 arc degrees.
  • Inaccessibility: Maintaining an earth-based solar panel is relatively simple, but building and maintaining a solar panel in space would typically be telerobotic. Astronauts who work in GEO (geosynchronous earth orbit) are exposed to unacceptably high radiation hazards and risks in addition to the costs and cost about a thousand times more than the same telerobotic task.
  • The space environment is hostile; PV modules (if used) suffer about 8 times the degradation they would on earth (with the exception of orbits protected by the magnetosphere).
  • Space debris is a major threat to large objects in space, especially large structures like SBSP systems that are under 2000 km on their way through the debris. The collision risk is greatly reduced with GEO, since all satellites move in the same direction and are very close to the same speed.
  • The microwave downlink transmission frequency (if used) would require isolation of the SBSP systems from other satellites. The GEO memory space is already well used and it is considered unlikely that the ITU would allow a PLC to start.
  • The large size and the corresponding cost of the receiving station on the ground. SBSP researcher Keith Henson estimated the cost to be $ 1 billion for 5 GW.
  • Energy losses during several phases of the conversion of photons to electrons to photons back to electrons.
  • The waste disposal in space systems is anyway difficult, but is insoluble if the entire spacecraft is designed to absorb as much sunlight as possible. Conventional temperature control systems for spacecraft , such as radiation blades, can interfere with the closure of the solar module or the power transmission.

design

Artistic concept of a solar panel on an electrically operated LEO-to-GEO space tug.

Space-based solar energy essentially consists of three elements:

  • Collecting solar energy in the room with reflectors or inflatable mirrors on solar cells or heating devices for thermal systems
  • Wireless power transmission to earth via microwave or laser
  • Receiving energy on earth via a rectenna, a microwave antenna

The space-based part does not have to support itself against gravity (with the exception of relatively weak tidal tensions). It doesn't need protection from terrestrial wind or weather, but it does have to deal with space hazards such as micrometeors and solar flares . Two basic methods of conversion were investigated: photovoltaics (PV) and solar thermal (ST). Most of SBSP's analysis has focused on photovoltaic conversion using solar cells that convert sunlight directly into electricity. The solar dynamics use mirrors to concentrate the light on a boiler. The use of solar dynamics could reduce the mass per watt. Wireless energy transfer was proposed early on to transfer energy from the collection to the surface of the earth using either microwave or laser radiation at a variety of frequencies.

Microwave power transmission

William C. Brown demonstrated, during Walter Cronkite's CBS News program in 1964, a microwave-powered model helicopter that received all of the power it needed to fly from a microwave beam. Between 1969 and 1975, Bill Brown was the technical director of a JPL - Raytheon program that radiated 30 kW of electricity over a distance of 1.6 km with an efficiency of 9.6%.

Dozens of kilowatts of microwave transmission has been well demonstrated in existing tests at Goldstone , California (1975) and Grand Bassin, Réunion (1997).

Comparison of laser and microwave power transmission. NASA diagram

Recently, a team led by John C. Mankins demonstrated microwave transmission in conjunction with solar energy sensing between a mountain top in Maui and the island of Hawaii (92 miles away) . Technological challenges in terms of array layout, individual radiation element design and overall efficiency as well as the associated theoretical limits are currently the subject of research, as the special session "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" during the IEEE Symposium 2010 on Antennas and Propagation shows. In 2013, a useful overview was published covering technologies and issues related to microwave energy transfer from space to the ground. In addition, the Proceedings of the IEEE gave an overview of current methods and technologies for the design of antenna arrays for microwave power transmission.

Laser power beams

The laser beam process was seen by some at NASA as a stepping stone to further industrialization of space. In the 1980s, researchers at NASA looked at the possible use of lasers for space-to-space power beaming, focusing primarily on the development of a solar-powered laser. In 1989 it was assumed that energy could also usefully be radiated from earth into space by laser. In 1991 the SELENE project (SpacE Laser ENErgy) began, which included the investigation of laser power transmission to supply a lunar base. The SELENE program was two years of research, but the cost of getting the concept up and running was too high and the official project ended in 1993 before a space-based demonstration took place.

In 1988, Grant Logan proposed the use of an earth-based laser to drive an electric thruster for space propulsion, with technical details being worked out in 1989. He suggested using diamond solar cells with an operating temperature of 600 degrees to convert ultraviolet laser light.

Orbital location

The main advantage of positioning a space power plant in geostationary orbit is that the antenna geometry remains constant, making it easier to align the antennas. Another advantage is that almost continuous energy transfer is immediately available as soon as the first space power plant is put into orbit, LEO (Low Earth Orbit) requires several satellites before they produce almost continuous energy.

The power radiation from the geostationary orbit by microwaves harbors the difficulty that the required sizes of the “optical aperture” are very large. For example, the NASA-SPS study of 1978 required a transmitting antenna with a diameter of 1 km and a receiving rectangle with a diameter of 10 km for a microwave beam at 2.45 GHz . These sizes can be reduced somewhat by using shorter wavelengths, although they have increased absorption in the atmosphere and even possible beam blockage by rain or water droplets. Due to the thinned array curse, it is not possible to create 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 performance of a PLC will inevitably be high; small PLC systems are possible, but uneconomical.

A collection of LEO space power plants has been proposed as the precursor to the space-based solar energy GEO (Geostationary Earth Orbit).

Earthbound receiver

The earth-based rectenna would likely consist of many short dipole antennas connected by diodes . Microwave transmissions from the satellite would be received in the dipoles with an efficiency of around 85%. With a conventional microwave antenna, the reception efficiency is better, but its cost and complexity are also significantly higher. Rectennas would probably be several kilometers wide.

In space applications

A laser SBSP could also power a base or vehicles on the surface of the moon or Mars, saving the bulk of the cost of landing the power source. A spaceship or other satellite could also be operated by the same means. In a 2012 report submitted to NASA on space solar energy, the author mentions another possible use of the technology behind space solar energy for solar electric propulsion systems that could be used for interplanetary human exploration missions.

Startup costs

One problem for the SBSP concept is the cost of space starts and the amount of material to be started.

Much of the imported material does not need to be immediately put into its final orbit, which opens up the possibility that highly efficient (but slower) motors can move PLC material from LEO to GEO at a reasonable cost. Examples are ion or atomic propulsion .

To give an idea of ​​the extent of the problem, a 4 GW power plant with a mass of the solar module of 20 kg per kilowatt (without taking into account the mass of the supporting structure, the antenna or a significant reduction in the mass of the focusing mirrors) would weigh around 80,000 tons, which under the circumstances, they would all be launched from Earth. However, this is far from the state of the art for flown spacecraft, which was 150 W / kg (6.7 kg / kW) as of 2015 and has improved rapidly. Very light constructions could probably reach 1 kg / kW, which is 4,000 tons for the solar panels of the same 4 GW capacity station. In addition to the mass of the panels, overcapacities (including increasing the desired orbit and maintaining position) must also be taken into account.

Starting costs for 4 GW up to LEO
1 kg / kW 5 kg / kW 20 kg / kW
$ 1 / kg (minimum costs at ≈ $ 0.13 / kWh output, 100% efficiency) $ 4 million $ 20 million $ 80 million
$ 2000 / kg (e.g. Falcon Heavy ) $ 8 billion $ 40 billion $ 160 billion
$ 10,000 / kg (e.g. Ariane 5 ) $ 40 billion $ 200 billion $ 800 billion

In addition to these costs, there is the environmental impact of heavy-space launch missions if these costs are to be used in comparison to ground-based energy generation. For comparison: the direct costs for a new coal or nuclear power plant are between 3 billion and 6 billion dollars per GW (excluding the full costs for the environment through CO 2 emissions or the storage of spent nuclear fuel).

Build from space

Made from lunar materials launched into orbit

Gerard O'Neill noticed the problem of high startup costs in the early 1970s and suggested building the SPS 'in orbit using materials from the Moon. The launch cost from the moon may be much lower than from Earth due to lower gravity and the lack of air resistance . This proposal from the 1970s took over the future start-up cost calculation for NASA's space shuttle announced at the time. This approach would require significant up-front investment to build electromagnetic catapults on the moon. Nevertheless, the final report ("Lunar Resources Utilization for Space Construction") from General Dynamics' Convair Division on April 30, 1979 under NASA contract NAS9-15560 concluded that the use of lunar resources for a system of only thirty solar power satellites each with 10 GW capacity would be cheaper than earthbound materials.

In 1980, when it became clear that NASA were very optimistic about the cost estimates for the launch of the space shuttle, O'Neill et al. a. another way to manufacture with lunar materials with significantly lower startup costs. This PLC concept of the 1980s was based less on the presence of humans in space and more on partially self-replicating systems on the lunar surface under the remote control of workers stationed on earth. The high net energy gain of this proposal results from the moon's much shallower gravity source.

Having a relatively cheap source of raw materials per pound from space would reduce concerns about low mass designs and lead to another type of PLC being built. The low cost per pound of lunar material in O'Neill's vision would be helped by the use of lunar material to make more orbital equipment than just solar power satellites. Advanced moon launch techniques can reduce the cost of building a solar power satellite from lunar materials. Some of the proposed techniques include the lunar mass drive and lunar space elevator , first described by Jerome Pearson, which would require the establishment of silicon mining and solar cell production facilities on the moon.

On the moon

Physicist David Criswell suggests that the moon is the optimal location for solar power plants and promotes lunar-based solar energy. The main advantage he envisions is the construction largely from locally available lunar materials, the use of on-site resources, with a teleoperative mobile factory and a crane to assemble the microwave reflectors, as well as rovers to assemble and install solar cells, which is the start-up cost significantly reduce compared to SBSP designs. Power relay satellites orbiting the earth and the moon reflecting the microwave beam are also part of the project. A 1 GW demo project starts at $ 50 billion. The Shimizu Corporation uses a combination of lasers and microwaves for the Luna Ring concept, along with power relay satellites.

From an asteroid

Also, the asteroid mining has been seriously considered. A NASA design study evaluated a 10,000-tonne mining vehicle (to be assembled in orbit) that would bring a 500,000-tonne asteroid fragment back into geostationary orbit. Only around 3,000 tons of the mine ship would be traditional aerospace-grade payloads. The rest would be the reaction mass for the mass driver engine, which could be arranged as spent rocket stages to launch the payload. Assuming 100% of the asteroid returned was useful and that the asteroid miner itself could not be reused, that translates to a nearly 95% reduction in startup costs. The real merits of such a method, however, would depend on a thorough mineral study of the candidate asteroids; so far we only have estimates of their composition. One proposal is to trap the asteroid Apophis into orbit and convert it into 150 5 GW solar power satellites or the larger 1999 AN10 asteroid, which is 50 times the size of Apophis and large enough to build 7,500 5 GW solar power satellites .

gallery

  • A lunar base with a mass drive (the long structure that leads to the horizon). Conceptual illustration of NASA

  • An artist's idea of ​​a "self-growing" robot moon factory

  • Microwave reflectors on the moon and teleoperative robotic built-in rover and crane.

  • “Crawler” crosses the surface of the moon, smooths and melts a top layer of regolith and then places elements of silicon PV cells directly on the surface

  • Sketch of the lunar crawler for the production of lunar solar cells on the lunar surface.

  • Seen here is a series of solar collectors that convert electricity into microwave rays that are directed towards the earth

  • A solar power satellite built from a mined asteroid

safety

The use of energy transfer by means of microwaves was the most controversial topic when considering a PLC concept. At the earth's surface, a proposed microwave beam would have a maximum intensity in its center of 23 mW / cm 2 (less than 1/4 of the solar irradiation constant) and an intensity of less than 1 mW / cm 2 outside the rectangular window (circumference of the receiver). These are compared with the current limit values ​​of the United States Occupational Safety and Health Act (OSHA) for exposure at the workplace for microwaves, which are 10 mW / cm 2. A beam of this intensity is therefore in its center, in a similar order of magnitude as the current one safe workplace, even with long-term or indefinite exposure. Outside the receiver it is far lower than the OSHA long-term values. Over 95% of the beam energy will fall on the front. The remaining microwave energy is absorbed and largely distributed within the standards that currently apply to microwave emissions around the world. It is important for system efficiency that as much of the microwave radiation as possible is focused on the rectennas. Outside of the rectenna, microwave intensities decrease rapidly, so nearby cities or other human activities should be completely unaffected.

There are other ways to minimize exposure to the beam. Physical access is controllable on the ground (e.g. via fences), and typical aircraft flying through the beam provide passengers with a protective metal shell (e.g. a Faraday cage ) that will intercept the microwaves. Other aircraft (balloons, microlights, etc.) can avoid exposure by observing air control rooms, as is currently the case for military and other controlled airspaces. The microwave beam intensity at the bottom in the center of the beam would be designed and physically built into the system; the transmitter would simply be too far away and too small to be able to increase the intensity to uncertain values, also in principle.

In addition, it is a design restriction that the microwave beam must not be so intense that it injures wild animals, especially birds. Experiments with conscious microwave irradiation to a reasonable extent have shown no negative effects even over several generations. Proposals have been made to locate rectennas offshore, but this poses serious problems including corrosion, mechanical stress and contamination.

A frequently proposed approach for ensuring fail-safe beam guidance is the use of a retro-directional phased array antenna / rectenna. A “pilot” microwave beam, which is emitted from the center of the rectennas on the ground, forms a phase front on the transmitting antenna. There circuits in each of the antenna's subarrays compare the phase front of the pilot beam with an internal clock phase in order to control the phase of the outgoing signal. This forces the transmitted beam to center precisely on the rectal needle and to achieve a high level of phase equality; if the pilot beam is lost for any reason (for example if the transmitting antenna is turned away from the rectal needle), the phase control value fails and the microwave power beam is automatically defocused. Such a system would not be physically able to focus its power beam wherever there is no pilot beam transmitter. The long-term effects of radiation from the ionosphere in the form of microwaves have not yet been studied, but nothing has been suggested that could lead to a significant effect.

time beam

In the 20th century

  • 1941: Isaac Asimov published the science fiction short story "Reason", in which a space station transmits the energy collected by the sun to different planets using microwave rays.
  • 1968: Peter Glaser introduces the concept of a "solar power satellite" system with square miles of solar panels in a high geosynchronous orbit to collect solar energy and convert it into a microwave beam to deliver usable energy to large receiving antennas (rectennas) on earth Transfer distribution.
  • 1973: Peter Glaser receives U.S. Patent No. 3,781,647 for his method of transmitting energy over long distances using microwaves from a large (one square kilometer) antenna on the satellite to a much larger antenna on the ground, now known as the rectenna is.
  • 1978–81: The United States Department of Energy and NASA scrutinize the concept of the solar power satellite (SPS) and publish design and feasibility studies.
  • 1987: Stationary High Altitude Relay Platform (SHARP) - a Canadian experiment.
  • 1995–97: NASA conducts a “fresh look” study on the concepts and technologies of space solar energy (SSP).
  • 1998: The Space Solar Power Concept Definition Study (CDS) identifies credible, economically viable SSP concepts and points out technical and programmatic risks.
  • 1998: Japan's space agency begins development of a Space Solar Power System (SSPS), a program that continues to this day.
  • 1999: NASA's Space Solar Power Exploratory Research and Technology (SERT, see below) research and technology program begins.
  • 2000: NASA's John Mankins testifies in the US House of Representatives : “Large-scale SSP is a very complex integrated system of systems that requires many significant advances in current technology and performance. A technology roadmap was developed that shows possible ways to achieve all the necessary advances - albeit over several decades. "

In the 21st century

  • 2001: NASDA (one of Japan's national space agencies prior to joining JAXA) announces plans for additional research and prototyping by launching a 10 kilowatt, 1 megawatt experimental satellite.
  • 2003: ESA studies
  • 2007: The Pentagon's National Security Space Office (NSSO) released a report on October 10, 2007 declaring that it intends to collect solar energy from space for use on Earth to help support ongoing United States relations with the Support the Middle East and the fight for oil. A demo plant could cost $ 10 billion, produce 10 megawatts and be operational in 10 years.
  • 2007: In May 2007, a workshop will be held at the US Massachusetts Institute of Technology (MIT) to review the current state of the SBSP market and technology.
  • 2010: Andrea Massa and Giorgio Franceschetti announce a special session on "Analysis of Electromagnetic Wireless Systems for Solar Power Transmission" at the 2010 Institute of Electrical and Electronics Engineers International Symposium on Antennas and Propagation.
  • 2010: The Indian Space Research Organization and the US National Space Society established a joint forum to strengthen the partnership in the use of solar energy through space-based solar collectors. The forum, named the Kalam NSS Initiative after former Indian President APJ Abdul Kalam , will lay the foundation for the space-based solar power program, which other countries could also join.
  • 2010: Sky's No Limit: Space-Based Solar Power, the next big step in the strategic partnership between Indo-US and the USA by USAF Col Peter Garretson was published at the Institute for Defense Studies and Analysis.
  • 2012: China proposed a joint development between India and China to develop a solar power satellite during a visit by former Indian President APJ Abdul Kalam.
  • 2015: The Space Solar Power Initiative (SSPI) is established between Caltech and Northrop Grumman Corporation. An estimated $ 17.5 million will be made available in a three-year project to develop a space-based solar power system.
  • 2015: JAXA announced on March 12, 2015 that they would wirelessly radiate 1.8 kilowatts 50 meters to a small receiver by converting electricity into microwaves and then converting it back into electricity.
  • 2016: Gen. Zhang Yulin, deputy head of the armaments development division of the Central Military Commission, suggested that China would next begin using Earth-Moon space for industrial development. The goal would be to build space-based solar energy satellites that would radiate energy back to Earth.
  • 2016: A team made up of members from the Naval Research Laboratory (NRL), Defense Advanced Projects Agency (DARPA), Air Force Air University, Joint Staff Logistics (J-4), Department of State, Makins Aerospace, and Northrop Grumman won the Secretary of Defense (SECDEF) / Secretary of State (SECSTATE) / USAID Director's Agency-wide D3 (Diplomacy, Development, Defense) Innovation Challenge with a proposal that the US must lead solar energy in space. A vision video followed the suggestion.
  • 2016: Citizens for Space-Based Solar Power has the D3 proposal in active petitions on the White House website "America Must Lead the Transition to Space-Based Energy" and Change.org "USA Must Lead the Transition to Space-Based Energy." “Converted along with the following video.
  • 2016: Erik Larson and others from NOAA produce a paper entitled “Global Atmospheric Response to Emissions from a Proposed Reusable Spacecraft System”. The paper says that up to 2 TW / year propulsion satellites could be built without causing unbearable damage to the atmosphere. Prior to this paper, there was concern that re-entry NOx would destroy too much ozone.
  • 2016: Ian Cash from SIAC offers CASSIOPeiA (Constant Aperture, Solid State, Integrated, Orbital Phased Array) a new concept PLC.
  • 2017: NASA selects five new research proposals that focus on investing in space. The Colorado School of Mines focuses on "21st Century Trends in Space-Based Solar Power Generation and Storage".

Unusual configurations and architectural considerations

The typical reference system of the systems consists of a significant number (several thousand multi-gigawatt systems to cover all or a significant part of the earth's energy needs) of individual satellites in the GEO. The typical reference concept for the individual satellite is in the range of 1 to 10 GW and usually includes planar or concentrated solar photovoltaics as an energy collector / conversion. The most typical transmission concepts work in the high frequency range between 1 and 10 GHz (2.45 or 5.8 GHz), where there are minimal losses in the atmosphere. The materials for the satellites will be obtained from Earth and manufactured on Earth and will probably be transported to LEO via a reusable rocket launch and transported between LEO and GEO by chemical or electrical propulsion. In summary, the architectural choices are:

  • Location: GEO
  • Energy generation: PV
  • Satellite: monolithic structure
  • Transmission: RF
  • Materials & Manufacturing: Earth
  • Installation: RLVs to LEO, chemistry to GEO

Location of alternative energy generation

While GEO is most typical because of its advantages such as proximity to earth, simplified pointing and tracking, very short time in coverage and scalability to meet the entire global demand multiple times, other locations have been suggested:

  • Sun Earth L1: Robert Kennedy III, Ken Roy & David Fields have proposed a variant of the L1 sunshade called "Dyson Dots" in which a multi-terawatt primary collector would radiate the energy back onto a number of LEO solar synchronous receiver satellites . The far greater distance to the earth requires a correspondingly larger transmission opening.
  • Lunar surface: David Criswell has suggested using the lunar surface itself as a collection medium and transferring the energy to the ground through a series of microwave reflectors in orbit around the earth. The main benefit of this approach would be the ability to manufacture the solar collectors in-situ without the energy costs and the complexity of commissioning. Disadvantages are the much greater distance, which requires larger transmission systems, the necessary "overbuilding" for the moonlit night and the difficulty of sufficient production and alignment of reflector satellites.
  • MEO: MEO systems have been proposed for in-space utilities and jet engines. For example, see Royce Jones' paper.
  • High Elptic Orbits: Molniya, Tundra, or Quazi Zenith orbits have been suggested as early locations for niche markets that require less energy to access and offer good persistence.
  • Solar Synchronization LEO: In this near polar orbit, the satellites process themselves at a speed that enables them to always face the sun when they orbit the earth. This is an easily accessible orbit that uses much less energy, and its proximity to Earth requires smaller (and therefore less massive) transmission ports. However, disadvantages of this approach are the constant relocation of the receiving stations or the storage of energy for a burst transmission. This orbit is already crowded and has significant space debris.
  • Equatorial LEO: The Japanese SPS 2000 proposed an early demonstrator in the equatorial LEO, where several equatorial participating nations could get some power.
  • The Earth's Surface: Narayan Komerath proposed a space power grid that would allow excess energy from an existing grid or power plant on one side of the planet to be channeled into orbit, to another satellite, and to receivers.

Energy generation

Photovoltaics is one of the typical designs for solar power satellites. These can be planar (and usually passively cooled), concentrated (and perhaps actively cooled). However, there are several interesting variants:

  • Solar thermal: Proponents of solar thermal have suggested using concentrated heating to cause a change of state in a fluid to generate energy via rotating machinery, followed by cooling in coolers. The advantages of this method can be the total mass of the system (controversial), the non-degradation due to solar wind damage and the radiation tolerance. A new design of a solar thermal power satellite by Keith Henson and others was visualized in a video. A related concept can be found here: The proposed radiators are thin-walled plastic pipes filled with low pressure (2.4 kPa) and temperature (20 degrees Celsius) steam.
  • Solar Pumped Laser: Japan has pursued a solar pumped laser in which sunlight directly excites the laser medium that is used to create the coherent beam to earth.
  • Fusion decay: This version of a power satellite is not "solar". Rather, the vacuum of space is seen as a "feature rather than a flaw" for traditional fusion. According to Paul Werbos, after the merger, neutral particles also disintegrate into charged particles that would enable a direct conversion into electricity in a sufficiently large volume.
  • Solar wind loop: Also called the Dyson-Harrop satellite. The satellite does not use the sun's photons, but rather the charged particles in the solar wind, which generate a current in a large loop via an electromagnetic coupling.
  • Direct mirrors: Early concepts for direct mirror deflection of light onto planet earth suffered from the problem that the rays coming from the sun are not parallel, but extend from a disk and thus the size of the point on earth is quite large. Lewis Fraas has studied a number of parabolic mirrors to add to existing solar systems.

Alternative satellite architecture

The typical satellite is a monolithic structure made up of a structural truss, one or more collectors, one or more transmitters, and occasionally primary and secondary reflectors. The entire structure can be stabilized with a gravity gradient. Alternative concepts include:

  • Swarms of Smaller Satellites: Some designs suggest swarms of free-flying smaller satellites. This is the case with several laser concepts and apparently also with CALTECH's flying carpets. With RF concepts, a technical limitation is the problem of the sparse arrangement.
  • Free-floating components: Solaren has proposed an alternative to the monolithic structure in which the primary reflector and the transmitted light reflector fly freely.
  • Spin stabilization: NASA examined a spin stabilized thin film concept.
  • Photonic Laser Thruster (PLT) Stabilized Structure: Young Bae has suggested that photonic printing can replace the printing elements in large structures.

transmission

The most typical concept for energy transfer is via an RF antenna at less than 10 GHz to a rectenna on the ground. There are disputes among the benefits of klystrons, gyrotrons, magnetrons, and solid state. Alternative approaches to transfer include:

  • Lasers: Lasers offer the advantage of much lower cost and mass over initial performance, however, there is controversy over the benefits of efficiency. Lasers enable much smaller transmission and reception openings. However, a highly concentrated beam has concerns about eye safety, fire safety, and gun possession. Proponents believe they have answers to all of these concerns. A laser-based approach must also find alternative ways to deal with clouds and precipitation.
  • Atmospheric Waveguide: Some have suggested that it might be possible to use a short pulse laser to create an atmospheric waveguide through which concentrated microwaves could flow.
  • Nuclear Synthesis: Particle accelerators based in the inner solar system (whether in orbit or on a planet like Mercury) could use solar energy to synthesize nuclear fuel from naturally occurring materials. While this would be very inefficient with current technology (in terms of the amount of energy needed to make the fuel versus the amount of energy contained in the fuel) and would raise obvious nuclear safety issues, the basic technology on which Such an approach would support itself has been in use for decades and makes it possibly the most reliable means of transferring energy, especially over very long distances - especially from the inner solar system to the outer solar system.

Materials and Manufacturing

Typical concepts use the developed industrial manufacturing system on earth and use earth-based materials for both the satellite and the propellant. The variants include:

  • Lunar materials: There are designs for solar satellites that obtain> 99% of the material from lunar regolith with very low levels of “vitamins” from other places. The use of materials from the moon is attractive because theoretically launching from the moon is far less complicated than from the earth. There is no atmosphere, so components don't have to be tightly packed in an aeroshell and can withstand vibration, pressure and temperature loads. The start can be done via a magnetic mass driver and the requirement to use all of the propellant for the start. When starting from the moon, the GEO also requires far less energy than the much deeper gravity source on earth. The production of all solar power satellites to fully supply the entire planet with the energy it needs requires less than a millionth of the mass of the moon.
  • Self-replication on the moon: NASA investigated a self-replicating factory on the moon in 1980. Recently, Justin Lewis-Webber proposed a method of custom manufacturing core elements based on John Mankins' SPS-Alpha design.
  • Asteroidal Materials: Some asteroids are said to have even lower Delta-Vs for mining materials than the Moon, and some particular materials of interest, such as metals, may be more concentrated or more accessible.
  • In-space / in-situ manufacturing: With the advent of space-consuming additive manufacturing, concepts such as SpiderFab could enable the mass launch of raw materials for local extrusion.

Method of installation / transport of material to the place of energy production

In the reference designs, the component material is launched via well-understood chemical rockets (mostly completely reusable carrier systems) after LEO, whereupon either a chemical or an electric drive is used to transport it to the GEO. The desired properties for this system are a very high mass flow rate at a low overall cost. Alternative concepts include:

  • Lunar Chemical Launch: ULA recently presented a concept for a fully reusable chemical lander XEUS to transport materials from the lunar surface to an LLO or GEO.
  • Lunar mass driver: Launch of materials from the lunar surface with a system similar to an electromagnetic catapult on an aircraft carrier. An unexplored compact alternative would be the Slingatron.
  • Lunar Space Elevator: An equatorial or near-equatorial cable extends to and through the Lagrangian point. This is what proponents claim is that they are lower in mass than a conventional mass rider.
  • Space elevator : A band of pure carbon nanotubes extends from its center of gravity in geostationary orbit so that lifts can ascend into a GEO. Problems include the physical challenge of creating a belt of this length with sufficient strength, managing collisions with satellites and space debris, and lightning strikes.
  • MEO Skyhook: Roger Lenard suggested a MEO Skyhook as part of an AFRL study. It seems that a gradient stabilized rope with its center of gravity in the MEO can be constructed from available materials. The bottom of the sky hook is in a "non-Keplerian orbit" near the atmosphere. A reusable missile can launch in height and speed at the bottom of the line, which is in a non-Keplerian orbit (which is much slower than typical orbital speed). The payload is transmitted and rises over the cable. The cable itself is protected from entorbtion by an electric drive and / or electromagnetic effects.
  • MAGLEV Start / StarTram: John Powell has a concept for a very high mass flow system. In a first generation system built into a mountain, it accelerates a payload through an evacuated MAGLEV orbit. A small on-board missile circulates the payload.
  • Beamed Energy Launch: Kevin Parkin and Escape Dynamics both have concepts for the ground-based irradiation of a monofuel launcher with RF energy. The RF energy is absorbed and directly heats the propellant, not unlike the NERVA-style nuclear thermal. LaserMotive has a concept for a laser-based approach.

Fictitious

Space stations that transmit solar energy appear in science fiction works such as Isaac Asimov's "Reason" (1941), which revolves around the problems caused by the robots operating the station. Asimov's short story " The Last Question " also covers the use of SBSP to provide limitless energy for use on Earth.

In Ben Bova's novel PowerSat (2005), an entrepreneur attempts to prove that his company's near-completed power satellite and spacecraft (a means of efficiently getting maintenance teams to the satellite) are both safe and economically viable while terrorists have ties to oil producers Nations try to derail these attempts through deception and sabotage.

Various aerospace companies have also featured imaginative future solar power satellites in their corporate vision videos, including Boeing, Lockheed Martin, and United Launch Alliance.

The solar satellite is one of three ways to produce energy in the browser-based game OGame .

Individual evidence

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