Solar panels on spacecraft
Encyclopedia
Spacecraft operating in the inner solar system
usually rely on the use of photovoltaic solar panel
s to derive electricity from sunlight
. In the outer solar system, where the sunlight is too weak to produce sufficient power, radioisotope thermal generators (RTGs) are used as a power source.
satellite, launched by the US in 1958. This was largely because of the influence of Dr. Hans Ziegler
, who can be regarded as the father of spacecraft solar power.. Of his 30 year tenure at Fort Monmouth
(1947–1976), Ziegler spent 12 years in the top position as Chief Scientist.
For both uses, the figure of merit
of the solar panels (and RTGs) is the power generated per kilogram, as an upper limit of the power the spacecraft has at its disposal per kg spacecraft (including solar panels).
To increase the power generated per kg, typical solar panels on spacecraft use close-packed solar cell rectangles that cover nearly 100% of the sun-visible area of the solar panels,
rather than the solar wafer circles which, even though close-packed, cover about 90% of the sun-visible area of typical solar panels on earth. However, some solar panels on spacecraft have solar cells that cover only 30% of the sun-visible area.
All electrical circuits generate waste heat
; in addition, solar arrays act as optical and thermal as well as electrical collectors. Heat must be radiated from their surfaces. High-power spacecraft may have solar arrays that compete with the active payload itself for thermal dissipation. The innermost panel of arrays may be "blank" to reduce the overlap of views to space. Such spacecraft include the higher-power communications satellites (e.g., later-generation TDRS) and Venus Express
, not high-powered but closer to the Sun.
Spacecraft are built so that the solar panels can be pivoted as the spacecraft moves. Thus, they can always stay in the direct path of the light rays no matter how the spacecraft is pointed. Spacecraft are usually designed with solar panels that can always be pointed at the Sun, even as the rest of the body of the spacecraft moves around, much as a tank turret can be aimed independently of where the tank is going. A tracking mechanism is often incorporated into the solar arrays to keep the array pointed towards the sun.
Sometimes, satellite operators purposefully orient the solar panels to "off point," or out of direct alignment from the Sun. This happens if the batteries are completely charged and the amount of electricity needed is lower than the amount of electricity made; off-pointing is also sometimes used on the International Space Station for orbital drag reduction
.
than the orbit of Mars
. For example, Magellan
, Mars Global Surveyor
, and Mars Observer
used solar power as does the Earth-orbiting, Hubble Space Telescope
. The Rosetta space probe, launched March 2, 2004, will use solar panels as far as the orbit of Jupiter
(5.25 AU
); previously the furthest use was the Stardust spacecraft
at 2 AU. Solar power for propulsion was also used on the European lunar mission SMART-1
with a Hall effect thruster
.
The upcoming Juno mission will be the first mission to Jupiter to use solar panels instead of the traditional RTGs that are used by previous outer solar system missions.
, which takes a large area of sunlight and concentrates it onto a smaller spot. The same principle is used to start fires with a magnifying glass
on a sunny day.
Solar concentrators put one of these lenses over every solar cell. This focuses light from the large concentrator area down to the smaller cell area. This allows the quantity of expensive solar cells to be reduced by the amount of concentration. Concentrators work best when there is a single source of light and the concentrator can be pointed right at it. This is ideal in space, where the Sun is a single light source. Solar cells are the most expensive part of solar arrays, and arrays are often a very expensive part of the spacecraft. This technology may allow costs to be cut significantly due to the utilization of less material.
It has been proposed that it may be possible to develop space-based solar plants — solar power satellites with large arrays of photovoltaic cells—that would beam the energy they produce to Earth using microwaves or lasers. This could, in principle, be a significant source of electrical power generated using non-fossil fuel sources. Japanese and European space agencies, among others, are analyzing the possibility of developing such power plants in the 21st century.
Solar System
The Solar System consists of the Sun and the astronomical objects gravitationally bound in orbit around it, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. The vast majority of the system's mass is in the Sun...
usually rely on the use of photovoltaic solar panel
Photovoltaic module
A solar panel is a packaged, connected assembly of solar cells, also known as photovoltaic cells...
s to derive electricity from 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...
. In the outer solar system, where the sunlight is too weak to produce sufficient power, radioisotope thermal generators (RTGs) are used as a power source.
History
The first spacecraft to use solar panels was the Vanguard 1Vanguard 1
Vanguard 1 was the fourth artificial Earth satellite launched and the first satellite to be solar powered. Although communication with it was lost in 1964, it remains the oldest manmade satellite still in orbit...
satellite, launched by the US in 1958. This was largely because of the influence of Dr. Hans Ziegler
Hans Ziegler
Hans K. Ziegler was a pioneer in the field of communication satellites and the use of photovoltaic solar cells as a power source for satellites. -Life:Hans Ziegler was born in Munich, Germany...
, who can be regarded as the father of spacecraft solar power.. Of his 30 year tenure at Fort Monmouth
Fort Monmouth
Fort Monmouth was an installation of the Department of the Army in Monmouth County, New Jersey. The post is surrounded by the communities of Eatontown, Tinton Falls and Oceanport, New Jersey, and is located about 5 miles from the Atlantic Ocean. The post covers nearly of land, from the Shrewsbury...
(1947–1976), Ziegler spent 12 years in the top position as Chief Scientist.
Uses
Solar panels on spacecraft supply power for 2 main uses:- power to run the sensors, active heating and cooling, and telemetry.
- power for spacecraft propulsionSpacecraft propulsionSpacecraft propulsion is any method used to accelerate spacecraft and artificial satellites. There are many different methods. Each method has drawbacks and advantages, and spacecraft propulsion is an active area of research. However, most spacecraft today are propelled by forcing a gas from the...
-- electric propulsion, sometimes called solar-electric propulsion. See also energy needed for propulsion methods.
For both uses, the figure of merit
Figure of merit
A figure of merit is a quantity used to characterize the performance of a device, system or method, relative to its alternatives. In engineering, figures of merit are often defined for particular materials or devices in order to determine their relative utility for an application...
of the solar panels (and RTGs) is the power generated per kilogram, as an upper limit of the power the spacecraft has at its disposal per kg spacecraft (including solar panels).
To increase the power generated per kg, typical solar panels on spacecraft use close-packed solar cell rectangles that cover nearly 100% of the sun-visible area of the solar panels,
rather than the solar wafer circles which, even though close-packed, cover about 90% of the sun-visible area of typical solar panels on earth. However, some solar panels on spacecraft have solar cells that cover only 30% of the sun-visible area.
Implementation
Solar panels need to have a lot of surface area that can be pointed towards the Sun as the spacecraft moves. More exposed surface area means more electricity can be converted from light energy from the Sun. Since spacecraft have to be small, this limits the amount of power that can be produced .All electrical circuits generate waste heat
Waste heat
Waste heat sometimes called Secondary heat or Low-grade heat refers to heat produced by machines, electrical equipment and industrial processes for which no useful application is found. Energy is often produced by a heat engine, running on a source of high-temperature heat...
; in addition, solar arrays act as optical and thermal as well as electrical collectors. Heat must be radiated from their surfaces. High-power spacecraft may have solar arrays that compete with the active payload itself for thermal dissipation. The innermost panel of arrays may be "blank" to reduce the overlap of views to space. Such spacecraft include the higher-power communications satellites (e.g., later-generation TDRS) and Venus Express
Venus Express
Venus Express is the first Venus exploration mission of the European Space Agency. Launched in November 2005, it arrived at Venus in April 2006 and has been continuously sending back science data from its polar orbit around Venus. Equipped with seven science instruments, the main objective of the...
, not high-powered but closer to the Sun.
Spacecraft are built so that the solar panels can be pivoted as the spacecraft moves. Thus, they can always stay in the direct path of the light rays no matter how the spacecraft is pointed. Spacecraft are usually designed with solar panels that can always be pointed at the Sun, even as the rest of the body of the spacecraft moves around, much as a tank turret can be aimed independently of where the tank is going. A tracking mechanism is often incorporated into the solar arrays to keep the array pointed towards the sun.
Sometimes, satellite operators purposefully orient the solar panels to "off point," or out of direct alignment from the Sun. This happens if the batteries are completely charged and the amount of electricity needed is lower than the amount of electricity made; off-pointing is also sometimes used on the International Space Station for orbital drag reduction
Night Glider mode
Night Glider mode is one of the procedures for orienting the solar arrays on the International Space Station.Normally the photovoltaic solar arrays of the space station track the sun...
.
Types of solar cells typically used
Gallium arsenide-based solar cells are typically favored over silicon in industry, because they have a higher efficiency. The most efficient solar cells currently in production are multi-junction cells. These use a combination of several layers of both gallium arsenide and silicon to capture the largest spectrum of light possible. Leading edge multi-junction cells are capable of nearly 29% efficiency under ideal conditions.Spacecraft that have used solar power
To date, solar power, other than for propulsion, has been practical for spacecraft operating no farther from the sunSun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
than the orbit of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
. For example, Magellan
Magellan probe
The Magellan spacecraft, also referred to as the Venus Radar Mapper, was a 1,035-kilogram robotic space probe launched by NASA on May 4, 1989, to map the surface of Venus using Synthetic Aperture Radar and measure the planetary gravity...
, Mars Global Surveyor
Mars Global Surveyor
The Mars Global Surveyor was a US spacecraft developed by NASA's Jet Propulsion Laboratory and launched November 1996. It began the United States's return to Mars after a 10-year absence. It completed its primary mission in January 2001 and was in its third extended mission phase when, on 2...
, and Mars Observer
Mars Observer
The Mars Observer spacecraft, also known as the Mars Geoscience/Climatology Orbiter, was a 1,018-kilogram robotic space probe launched by NASA on September 25, 1992 to study the Martian surface, atmosphere, climate and magnetic field...
used solar power as does the Earth-orbiting, Hubble Space Telescope
Hubble Space Telescope
The Hubble Space Telescope is a space telescope that was carried into orbit by a Space Shuttle in 1990 and remains in operation. A 2.4 meter aperture telescope in low Earth orbit, Hubble's four main instruments observe in the near ultraviolet, visible, and near infrared...
. The Rosetta space probe, launched March 2, 2004, will use solar panels as far as the orbit of Jupiter
Jupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
(5.25 AU
Astronomical unit
An astronomical unit is a unit of length equal to about or approximately the mean Earth–Sun distance....
); previously the furthest use was the Stardust spacecraft
Stardust (spacecraft)
Stardust is a 300-kilogram robotic space probe launched by NASA on February 7, 1999 to study the asteroid 5535 Annefrank and collect samples from the coma of comet Wild 2. The primary mission was completed January 15, 2006, when the sample return capsule returned to Earth...
at 2 AU. Solar power for propulsion was also used on the European lunar mission SMART-1
SMART-1
SMART-1 was a Swedish-designed European Space Agency satellite that orbited around the Moon. It was launched on September 27, 2003 at 23:14 UTC from the Guiana Space Centre in Kourou, French Guiana. "SMART" stands for Small Missions for Advanced Research in Technology...
with a Hall effect 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...
.
The upcoming Juno mission will be the first mission to Jupiter to use solar panels instead of the traditional RTGs that are used by previous outer solar system missions.
Power available
In 2005 Rigid-Panel Stretched Lens Arrays were producing 7 kW per wing. Solar arrays producing 300 W/kg and 300 W/m² from the sun's 1366 W/m² power near the Earth are available. Entech Inc. hopes to develop 100 kW panels by 2010 and 1 MW panels by 2015.Future uses
For future missions, it is desirable to reduce solar array mass, and to increase the power generated per unit area. This will reduce overall spacecraft mass, and may make the operation of solar-powered spacecraft feasible at larger distances from the sun. Solar array mass could be reduced with thin-film photovoltaic cells, flexible blanket substrates, and composite support structures. Solar array efficiency could be improved by using new photovoltaic cell materials and solar concentrators that intensify the incident sunlight. Photovoltaic concentrator solar arrays for primary spacecraft power are devices which intensify the sunlight on the photovoltaics. This design uses a flat lens, called a Fresnel lensFresnel lens
A Fresnel lens is a type of lens originally developed by French physicist Augustin-Jean Fresnel for lighthouses.The design allows the construction of lenses of large aperture and short focal length without the mass and volume of material that would be required by a lens of conventional design...
, which takes a large area of sunlight and concentrates it onto a smaller spot. The same principle is used to start fires with a magnifying glass
Magnifying glass
A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle ....
on a sunny day.
Solar concentrators put one of these lenses over every solar cell. This focuses light from the large concentrator area down to the smaller cell area. This allows the quantity of expensive solar cells to be reduced by the amount of concentration. Concentrators work best when there is a single source of light and the concentrator can be pointed right at it. This is ideal in space, where the Sun is a single light source. Solar cells are the most expensive part of solar arrays, and arrays are often a very expensive part of the spacecraft. This technology may allow costs to be cut significantly due to the utilization of less material.
It has been proposed that it may be possible to develop space-based solar plants — solar power satellites with large arrays of photovoltaic cells—that would beam the energy they produce to Earth using microwaves or lasers. This could, in principle, be a significant source of electrical power generated using non-fossil fuel sources. Japanese and European space agencies, among others, are analyzing the possibility of developing such power plants in the 21st century.
See also
- Space solar powerSpace solar powerSpace-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....
- Solar cells
- Photovoltaic arrays
- For solar arrays on 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...
, see ISS Solar Arrays or Electrical system of the International Space StationElectrical system of the International Space StationThe electrical system of the International Space Station is a critical resource for the International Space Station because it allows the crew to live comfortably, to safely operate the station, and to perform scientific experiments. The ISS electrical system uses solar cells to directly convert...