Space Solar Power Exploratory Research and Technology program
Encyclopedia
The Space Solar Power
Exploratory Research and Technology program (SERT) program, conducted by NASA
, was initiated by John Mankins and led by Joe Howell in March 1999 for the following purpose:
It was to develop a solar power satellite (SPS) concept for a future gigawatt space power systems to provide electrical power by converting the Sun’s energy and beaming it to the Earth's surface. It was also to provide a developmental path to solutions for current space power architectures. Subject to studies it proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar dynamic engines to convert solar flux
into electricity. The initial program looked at systems in sun-synchronous orbit
, but by the end of the program, most of the analysis looked at geosynchronous orbit
.
Some of SERT's conclusions include the following:
s were considered too heavy, expensive and hard to deploy. Flexible thin film cells promised one viable future option for low mass, low cost, and high production capability by depositing special materials in very thin (micrometers) layers. Flexibility promotes deposition on lightweight inflatable structures needed for packaging large arrays in launch vehicles. The materials considered (kapton
) did not have the high temperature properties needed to allow cell growth deposition so development of a low temperature growth process for thin film solar cell
s was pursued. In the year 2000 the production of 5% efficient prototype small-area cells was followed by a 10% efficient prototype on kapton.
s of specific ranges of sunlight focused through a prism
. 2) An ensemble of quantum
dots in a size range to capture most of the radiation from the solar energy spectrum
. The collection would be equivalent to an array of semiconductor
s individually size tuned for optimal absorption at their bandgaps throughout the solar energy emission spectrum. Theoretical efficiencies were in the range of 50–70%.
's 160v photovoltaic arrays. Development of design and manufacturing techniques to prevent 1000v self-destructive arcing continued. Several arc mitigation techniques were evaluated. Samples incorporating the most promising techniques were acquired and tested to achieve a non-arcing “rad” hard high voltage (greater than 300v) array. Initial development was performed at 300v to utilize existing facilities and equipment.
for conversion to electrical power. Brayton
heat engines utilize a turbine
, compressor
, and rotary alternator
to produce power using an inert gas
working fluid
. Such a system was devised for use on an SSP.
Cost, mass, and technical risk of various Solar Power Generation (SPG) options for a solar dynamic system were studied. For a 10MW SD system, at high power levels this technology was shown to be competitive with projected photovoltaic systems. Testing was performed to determine the characterization of high temperature secondary concentrator refractive materials in an SD environment. A prototype refractive secondary concentrator with a concentration ratio of 10:1 was designed. This, combined with a primary concentrator of 1000:1 would result in a very high 10,000:1 ratio which permits a reasonable pointing accuracy requirement of 0.1°. The performance of the sapphire
concentrator was evaluated via an on-sun calorimeter
test.
. Studies were being conducted to determine sensible technologies this size and scope. All of the switches, conductors and converters were immense compared to current spacecraft. Questions such as using alternating current
vs direct current
power distribution, grounding schemes, standard current conductors vs high and/or low temperature superconductors, system voltage level vs environmental arcing mitigation strategies, types of power converters
and system protection devices, and high temperature radiation
resistant circuit
elements. Results were to be published by the Systems Analysis and Technology Working Group (SATWG) at the culmination of FY 98–99 SERT. Meanwhile, technologies were selected, wherever possible, to leverage other government technology investigations:
impact and specialized connectors at segment, switch and power converter interfaces. It was shown that the tremendous magnetic repulsion force (on the order of 3.5 MT/meter radially at 1 Megamp) could be used for deployment and to present an extremely rigid structure.
could currently be manufactured with acceptably small numbers of micropipe defects, the next goal was to reduce other defects that can harm the performance of power devices. An objective was to demonstrate the high temperature operation of high-voltage SiC diode
s, MOSFET
s, and JFET
s in a DC-DC power converter and develop models for predicting the influence of defects on device performance.
Milestones/products 1999: Demonstrated a 2 kW SiC thyristor
operating at 300C; breadboard
ed 300 volt switch and 600 volt switch; completed dynamic characterization of SiC thyristors. 2000: Completed converter topology vs device study with a breadboard converter prototype; Tested 600v/100amp solid body fuse
.
s are an enabling technology for SSP Low Earth Orbit
(LEO) to Geostationary Orbit
(GEO) orbit transfer and station keeping. Studies showed that advanced electric propulsion can provide a factor of 5 increase in payload for Earth to orbit transfer when compared to storable biprop and cryogenic biprop thrusters
; payload mass
that normally would be manifested for propellant
. Comparisons made to gridded ion thrusters, magnetoplasmadynamic and pulsed inductive thrusters showed that Hall thruster
technology provides overall greater benefits, including quicker trip times, good power density, a good contemporary technology base and good flight history, all translating into commercial industry acceptance. Advances such as direct power drive from the solar arrays and single and/or two-stage operation will allow payloads of 13 to 15 metric tons per 20 metric tons to LEO from launch as opposed to only 2 metric tons using chemical propulsion. Trip times from LEO to GEO are also reasonable at 120 to 230 days depending on performance setpoint. The proposed Hall thruster system consisted of four 50 kW krypton
Hall thrusters directly driven from a 200 kW solar array. The propulsion system will be included on each SSP segment. Performance required from the Hall thruster units is 2000 to 3500 sec ISP with an overall system efficiency of 52% to 57%. Due to the mass of fuel required to place the entire system into geostationary orbit, propellants besides xenon
(normally used), such as krypton and noble gas mixtures were proposed. Additional work on alternative fuels would eventually need to be conducted.
In 2000: tested high power Hall thruster; evaluated 1st generation domestic 50 kW breadboard engine in GRC high power Hall thruster test bed and high current cathode development
Space solar power
Space-based solar power is the concept of collecting solar power in space for use on Earth. It has been in research since the early 1970s....
Exploratory Research and Technology program (SERT) program, conducted by 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...
, was initiated by John Mankins and led by Joe Howell in March 1999 for the following purpose:
- Perform design studies of selected flight demonstration concepts;
- Evaluate studies of the general feasibility, design, and requirements.
- Create conceptual designs of subsystems that make use of advanced SSP technologies to benefit future space or terrestrial applications.
- Formulate a preliminary plan of action for the U.S. (working with international partners) to undertake an aggressive technology initiative.
- Construct technology development and demonstration roadmaps for critical Space Solar Power (SSP) elements.
It was to develop a solar power satellite (SPS) concept for a future gigawatt space power systems to provide electrical power by converting the Sun’s energy and beaming it to the Earth's surface. It was also to provide a developmental path to solutions for current space power architectures. Subject to studies it proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar dynamic engines to convert solar flux
Flux
In the various subfields of physics, there exist two common usages of the term flux, both with rigorous mathematical frameworks.* In the study of transport phenomena , flux is defined as flow per unit area, where flow is the movement of some quantity per time...
into electricity. The initial program looked 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...
, but by the end of the program, most of the analysis looked at 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 include the following:
- The increasing global energy demand is likely to continue for many decades resulting in new power plants of all sizes being built.
- The environmental impact of those plants and their impact on world energy supplies and geopolitical relationships can be problematic.
- Renewable energy is a compelling approach, both philosophically and in engineering terms.
- Many renewable energy sources are limited in their ability to affordably provide the base load power required for global industrial development and prosperity, because of inherent land and water requirements.
- Based on their Concept Definition Study, space solar power concepts may be ready to reenter the discussion.
- Solar power satellites should no longer be envisioned as requiring unimaginably large initial investments in fixed infrastructure before the emplacement of productive power plants can begin.
- Space solar power systems appear to possess many significant environmental advantages when compared to alternative approaches.
- The economic viability of space solar power systems depends on many factors and the successful development of various new technologies (not least of which is the availability of exceptionally low cost access to space) however, the same can be said of many other advanced power technologies options.
- Space solar power may well emerge as a serious candidate among the options for meeting the energy demands of the 21st century.
Program
Model System Categories (MSC's) were defined and ranged from relatively small-scale demonstrations to very large-scale operational SPS systems. In broad terms, each MSC represented an idea of what scale, technology, missions, etc. might be achievable in a particular future timeframe. The technology investment plan uses a time phased methodology to develop hardware and systems starting at 600 volts, followed by 10,000v, and ending with 100,000v to spread development and testing infrastructure costs over the life of the program rather than incur them from the beginning. The 600v technology had immediate application for the Advanced Space Transportation Program (ASTP).- 2005: ~100 kW, Free-flyer, demo-scale commercial space
- 2010: ~100 kW Planetary Surface System, demo-scale, space exploration
- 2015: ~10 MW Free-flyer, Transportation; Large demo, solar clipper
- 2020: 1 GW Free-flyer, Full-scale solar power satellite commercial space
Solar power generation
Current solar cellSolar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
s were considered too heavy, expensive and hard to deploy. Flexible thin film cells promised one viable future option for low mass, low cost, and high production capability by depositing special materials in very thin (micrometers) layers. Flexibility promotes deposition on lightweight inflatable structures needed for packaging large arrays in launch vehicles. The materials considered (kapton
Kapton
Kapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -273 to +400 °C...
) did not have the high temperature properties needed to allow cell growth deposition so development of a low temperature growth process for thin film solar cell
Thin film solar cell
A thin-film solar cell , also called a thin-film photovoltaic cell , is a solar cell that is made by depositing one or more thin layers of photovoltaic material on a substrate...
s was pursued. In the year 2000 the production of 5% efficient prototype small-area cells was followed by a 10% efficient prototype on kapton.
Very high efficiency photovoltaics
Two longer range investigations into high efficiency solar cells was undertaken. 1) “Rainbow” cells to be tailored to the wavelengthWavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
s of specific ranges of sunlight focused through a prism
Prism (optics)
In optics, a prism is a transparent optical element with flat, polished surfaces that refract light. The exact angles between the surfaces depend on the application. The traditional geometrical shape is that of a triangular prism with a triangular base and rectangular sides, and in colloquial use...
. 2) An ensemble of quantum
Quantum
In physics, a quantum is the minimum amount of any physical entity involved in an interaction. Behind this, one finds the fundamental notion that a physical property may be "quantized," referred to as "the hypothesis of quantization". This means that the magnitude can take on only certain discrete...
dots in a size range to capture most of the radiation from the solar energy spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...
. The collection would be equivalent to an array of 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...
s individually size tuned for optimal absorption at their bandgaps throughout the solar energy emission spectrum. Theoretical efficiencies were in the range of 50–70%.
High voltage arc mitigation
The arrays for an SSP platform would have to operate at 1000 volt or higher, as compared to the current International Space StationInternational 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...
's 160v photovoltaic arrays. Development of design and manufacturing techniques to prevent 1000v self-destructive arcing continued. Several arc mitigation techniques were evaluated. Samples incorporating the most promising techniques were acquired and tested to achieve a non-arcing “rad” hard high voltage (greater than 300v) array. Initial development was performed at 300v to utilize existing facilities and equipment.
Solar dynamics
Solar Dynamic (SD) power systems concentrate sunlight into a receiver where the energy is transferred to a heat engineHeat 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...
for conversion to electrical power. Brayton
Brayton cycle
The Brayton cycle is a thermodynamic cycle that describes the workings of the gas turbine engine, basis of the airbreathing jet engine and others. It is named after George Brayton , the American engineer who developed it, although it was originally proposed and patented by Englishman John Barber...
heat engines utilize a turbine
Turbine
A turbine is a rotary engine that extracts energy from a fluid flow and converts it into useful work.The simplest turbines have one moving part, a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades, or the blades react to the flow, so that they move and...
, compressor
Gas compressor
A gas compressor is a mechanical device that increases the pressure of a gas by reducing its volume.Compressors are similar to pumps: both increase the pressure on a fluid and both can transport the fluid through a pipe. As gases are compressible, the compressor also reduces the volume of a gas...
, and rotary alternator
Alternator
An alternator is an electromechanical device that converts mechanical energy to electrical energy in the form of alternating current.Most alternators use a rotating magnetic field but linear alternators are occasionally used...
to produce power using an inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
working fluid
Fluid
In physics, a fluid is a substance that continually deforms under an applied shear stress. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids....
. Such a system was devised for use on an SSP.
Cost, mass, and technical risk of various Solar Power Generation (SPG) options for a solar dynamic system were studied. For a 10MW SD system, at high power levels this technology was shown to be competitive with projected photovoltaic systems. Testing was performed to determine the characterization of high temperature secondary concentrator refractive materials in an SD environment. A prototype refractive secondary concentrator with a concentration ratio of 10:1 was designed. This, combined with a primary concentrator of 1000:1 would result in a very high 10,000:1 ratio which permits a reasonable pointing accuracy requirement of 0.1°. The performance of the sapphire
Sapphire
Sapphire is a gemstone variety of the mineral corundum, an aluminium oxide , when it is a color other than red or dark pink; in which case the gem would instead be called a ruby, considered to be a different gemstone. Trace amounts of other elements such as iron, titanium, or chromium can give...
concentrator was evaluated via an on-sun calorimeter
Calorimeter
A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical reactions or physical changes as well as heat capacity. Differential scanning calorimeters, isothermal microcalorimeters, titration calorimeters and accelerated rate calorimeters are among the most common...
test.
Power management & distribution
Power Management and Distribution (PMAD) covers the entire power system between the source or power generator and the load, which in this case is the transmitterTransmitter
In electronics and telecommunications a transmitter or radio transmitter is an electronic device which, with the aid of an antenna, produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating...
. Studies were being conducted to determine sensible technologies this size and scope. All of the switches, conductors and converters were immense compared to current spacecraft. Questions such as using alternating current
Alternating current
In alternating current the movement of electric charge periodically reverses direction. In direct current , the flow of electric charge is only in one direction....
vs direct current
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
power distribution, grounding schemes, standard current conductors vs high and/or low temperature superconductors, system voltage level vs environmental arcing mitigation strategies, types of power converters
Switched-mode power supply
A switched-mode power supply is an electronic power supply that incorporates a switching regulator in order to be highly efficient in the conversion of electrical power...
and system protection devices, and high temperature radiation
Radiation
In 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...
resistant circuit
Electrical network
An electrical network is an interconnection of electrical elements such as resistors, inductors, capacitors, transmission lines, voltage sources, current sources and switches. An electrical circuit is a special type of network, one that has a closed loop giving a return path for the current...
elements. Results were to be published by the Systems Analysis and Technology Working Group (SATWG) at the culmination of FY 98–99 SERT. Meanwhile, technologies were selected, wherever possible, to leverage other government technology investigations:
Superconductors
A contracted study was continued for the implementation of superconductors on the SSP. Initial studies showed that transmission voltages could be reduced to less than 300 Volts, mitigating arcing effects. Superconductor complications included cryogenic cooling systems with armor to protect against micrometeoroidMicrometeoroid
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:...
impact and specialized connectors at segment, switch and power converter interfaces. It was shown that the tremendous magnetic repulsion force (on the order of 3.5 MT/meter radially at 1 Megamp) could be used for deployment and to present an extremely rigid structure.
Silicon carbide power electronics
Silicon carbide technologies leading to power devices continued to be pursued. This leveraged work previously funded to develop defect free and thick SiC epitaxial substrates. Although substratesWafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...
could currently be manufactured with acceptably small numbers of micropipe defects, the next goal was to reduce other defects that can harm the performance of power devices. An objective was to demonstrate the high temperature operation of high-voltage SiC 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, MOSFET
MOSFET
The metal–oxide–semiconductor field-effect transistor is a transistor used for amplifying or switching electronic signals. The basic principle of this kind of transistor was first patented by Julius Edgar Lilienfeld in 1925...
s, and JFET
JFET
The junction gate field-effect transistor is the simplest type of field-effect transistor. It can be used as an electronically-controlled switch or as a voltage-controlled resistance. Electric charge flows through a semiconducting channel between "source" and "drain" terminals...
s in a DC-DC power converter and develop models for predicting the influence of defects on device performance.
Milestones/products 1999: Demonstrated a 2 kW SiC thyristor
Thyristor
A thyristor is a solid-state semiconductor device with four layers of alternating N and P-type material. They act as bistable switches, conducting when their gate receives a current trigger, and continue to conduct while they are forward biased .Some sources define silicon controlled rectifiers and...
operating at 300C; breadboard
Breadboard
A breadboard is a construction base for prototyping of electronics. The term is commonly used to refer to solderless breadboard ....
ed 300 volt switch and 600 volt switch; completed dynamic characterization of SiC thyristors. 2000: Completed converter topology vs device study with a breadboard converter prototype; Tested 600v/100amp solid body fuse
Fuse (electrical)
In electronics and electrical engineering, a fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit...
.
Ion thrusters
Ion thrusterIon 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 are an enabling technology for SSP 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...
(LEO) to 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...
(GEO) orbit transfer and station keeping. Studies showed that advanced electric propulsion can provide a factor of 5 increase in payload for Earth to orbit transfer when compared to storable biprop and cryogenic biprop thrusters
Rocket engine
A rocket engine, or simply "rocket", is a jet engineRocket Propulsion Elements; 7th edition- chapter 1 that uses only propellant mass for forming its high speed propulsive jet. Rocket engines are reaction engines and obtain thrust in accordance with Newton's third law...
; payload mass
Mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
that normally would be manifested for propellant
Propellant
A propellant is a material that produces pressurized gas that:* can be directed through a nozzle, thereby producing thrust ;...
. Comparisons made to gridded ion thrusters, magnetoplasmadynamic and pulsed inductive thrusters showed that Hall thruster
Hall effect thruster
In spacecraft propulsion, a Hall thruster is a type of ion thruster in which the propellant is accelerated by an electric field. Hall thrusters trap electrons in a magnetic field and then use the electrons to ionize propellant, efficiently accelerate the ions to produce thrust, and neutralize the...
technology provides overall greater benefits, including quicker trip times, good power density, a good contemporary technology base and good flight history, all translating into commercial industry acceptance. Advances such as direct power drive from the solar arrays and single and/or two-stage operation will allow payloads of 13 to 15 metric tons per 20 metric tons to LEO from launch as opposed to only 2 metric tons using chemical propulsion. Trip times from LEO to GEO are also reasonable at 120 to 230 days depending on performance setpoint. The proposed Hall thruster system consisted of four 50 kW krypton
Krypton
Krypton is a chemical element with the symbol Kr and atomic number 36. It is a member of Group 18 and Period 4 elements. A colorless, odorless, tasteless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionally distilling liquified air, and is often used with other...
Hall thrusters directly driven from a 200 kW solar array. The propulsion system will be included on each SSP segment. Performance required from the Hall thruster units is 2000 to 3500 sec ISP with an overall system efficiency of 52% to 57%. Due to the mass of fuel required to place the entire system into geostationary orbit, propellants besides xenon
Xenon
Xenon is a chemical element with the symbol Xe and atomic number 54. The element name is pronounced or . A colorless, heavy, odorless noble gas, xenon occurs in the Earth's atmosphere in trace amounts...
(normally used), such as krypton and noble gas mixtures were proposed. Additional work on alternative fuels would eventually need to be conducted.
In 2000: tested high power Hall thruster; evaluated 1st generation domestic 50 kW breadboard engine in GRC high power Hall thruster test bed and high current cathode development
See also
- Brayton cycleBrayton cycleThe Brayton cycle is a thermodynamic cycle that describes the workings of the gas turbine engine, basis of the airbreathing jet engine and others. It is named after George Brayton , the American engineer who developed it, although it was originally proposed and patented by Englishman John Barber...
- Future energy development
- 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...
- Ion thrusterIon thrusterAn 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...
- 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...
- Rankine cycleRankine cycleThe Rankine cycle is a cycle that converts heat into work. The heat is supplied externally to a closed loop, which usually uses water. This cycle generates about 90% of all electric power used throughout the world, including virtually all solar thermal, biomass, coal and nuclear power plants. It is...
- 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 cellSolar cellA solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
- 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 power satellite
- Stirling cycleStirling cycleThe Stirling cycle is a thermodynamic cycle that describes the general class of Stirling devices. This includes the original Stirling engine that was invented, developed and patented in 1816 by Reverend Dr...
- Superconductor