Sunshade
Encyclopedia
A space sunshade or sunshield can be described as analogous to a parasol that diverts or otherwise reduces some of a star's rays, preventing them from hitting a planet and thereby reducing its insolation
, which results in less heating of the planet.
A sunshade is of particular interest towards mitigating
global warming
through solar radiation management
. Such shades could also be used to produce space solar power
, acting as solar power satellites. Proposed shade designs include a single-piece shade and a shade made by a great number of small objects.
, 1.5 million kilometers above Earth. Each disk is proposed to have a 0.6 meter diameter and a thickness of about 5 micrometers. The weight of such a sunshade would be about a gram, adding up to a total weight of almost 20 million tonnes. Such a group of small sunshades that blocks 2% of the sunlight, reflecting it off into space, would be enough to halt global warming, giving us ample time to cut our emissions back on earth.
The individual autonomous flyers building up the cloud of sunshades are proposed to not reflect the sunlight but be transparent lenses, deflecting the light slightly so it does not hit earth. This minimizes the effect of solar radiation pressure on the units, requiring less effort to be put into holding them in place at the L1 point. An optical prototype has been constructed by Roger Angel with funding from NIAC
.
The remaining solar pressure and the fact that the L1 point is an unstable position easily disturbed by the wobble of the earth due to gravitational effects from the moon, requires the small autonomous flyers to be capable of maneuvering themselves to keep their position. A suggested solution to this problem is the placement of mirrors capable of rotation on the surface of the flyers. By using the solar radiation pressure on the mirrors and tilting them in the right direction, the flyer will be capable of altering its speed and direction to keep in position.
Such a group of sunshades would need to occupy an area of about 3.8 square kilometers if placed at the L1 point.
The deployment of the flyers is an issue that requires new technology. It has been proposed that this would be accomplished most easily with large railgun
s or coilgun
s firing a capsule containing a million shades into space every 5 minutes for 10 years using 20 separate launch sites. The estimated total cost of such an operation is 5 trillion US dollars, with a believed lifetime of 50 years.
Even so, it would still take years to launch enough of the disks into orbit
before they have any effect. Thus, if using this technology should become essential, enough time would be needed to implement it.
Roger Angel of the University of Arizona presented the idea for the Sunshade at the U.S. National Academy of Sciences
in April, 2006 and won a NASA
Institute for Advanced Concepts grant for further research in July, 2006.
Creating this sunshade in space was estimated to cost in excess of US$5 trillion, thus leading Professor Angel to conclude that "[t]he sunshade is no substitute for developing renewable energy, the only permanent solution. A similar massive level of technological innovation and financial investment could ensure that. But if the planet gets into an abrupt climate crisis that can only be fixed by cooling, it would be good to be ready with some shading solutions that have been worked out."
Several authors have proposed dispersing light before it reaches the Earth by putting a very large lens in space, perhaps at the L1 point between the Earth and the Sun. This plan was proposed in 1989 by J. T. Early.
In 2004, physicist and science fiction author Gregory Benford
calculated that a concave rotating Fresnel lens
1000 kilometres across, yet only a few millimeters thick, floating in space at the point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%. Side-effects include that, if this lens were built and global warming were avoided, there would be less incentive to reduce greenhouse gases, and humans might continue to produce too much carbon dioxide until it caused some other environmental catastrophe, such as a chemical change in ocean water
that could be disastrous to ocean life
.
The cost of such a lens has been disputed. At a global warming summit in 2004, Benford estimated that it would cost around US$
10 billion
up front, and another $10 billion in supportive cost during its lifespan.
(thin wire mesh) in space, perhaps at the L1 point between the Earth and the Sun. Such a proposal was made in 1997 by Edward Teller
, Lowell Wood
, and Roderick Hyde, although in 2002 these same authors argued for blocking solar radiation in the stratosphere rather than in orbit.
Insolation
Insolation is a measure of solar radiation energy received on a given surface area in a given time. It is commonly expressed as average irradiance in watts per square meter or kilowatt-hours per square meter per day...
, which results in less heating of the planet.
A sunshade is of particular interest towards mitigating
Mitigation of global warming
Climate change mitigation is action to decrease the intensity of radiative forcing in order to reduce the potential effects of global warming. Mitigation is distinguished from adaptation to global warming, which involves acting to tolerate the effects of global warming...
global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
through solar radiation management
Solar radiation management
Solar radiation management projects are a type of geoengineering which seek to reflect sunlight and thus reduce global warming. Examples include the creation of stratospheric sulfur aerosols. They do not reduce greenhouse gas concentrations in the atmosphere, and thus do not address problems...
. Such shades could also be used to produce space solar power
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....
, acting as solar power satellites. Proposed shade designs include a single-piece shade and a shade made by a great number of small objects.
Cloud of small spacecraft near L1
One proposed such sunshade for use towards that effect would be composed of 16 trillion small disks at the Sun-Earth L1 Lagrangian pointLagrangian point
The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...
, 1.5 million kilometers above Earth. Each disk is proposed to have a 0.6 meter diameter and a thickness of about 5 micrometers. The weight of such a sunshade would be about a gram, adding up to a total weight of almost 20 million tonnes. Such a group of small sunshades that blocks 2% of the sunlight, reflecting it off into space, would be enough to halt global warming, giving us ample time to cut our emissions back on earth.
The individual autonomous flyers building up the cloud of sunshades are proposed to not reflect the sunlight but be transparent lenses, deflecting the light slightly so it does not hit earth. This minimizes the effect of solar radiation pressure on the units, requiring less effort to be put into holding them in place at the L1 point. An optical prototype has been constructed by Roger Angel with funding from NIAC
NASA Institute for Advanced Concepts
right|200pxNASA Institute for Advanced Concepts was a NASA-funded program that was operated by the Universities Space Research Association for NASA from 1998 until its closure on 31 August 2007. NIAC sought proposals for revolutionary aeronautics and space concepts that could dramatically impact...
.
The remaining solar pressure and the fact that the L1 point is an unstable position easily disturbed by the wobble of the earth due to gravitational effects from the moon, requires the small autonomous flyers to be capable of maneuvering themselves to keep their position. A suggested solution to this problem is the placement of mirrors capable of rotation on the surface of the flyers. By using the solar radiation pressure on the mirrors and tilting them in the right direction, the flyer will be capable of altering its speed and direction to keep in position.
Such a group of sunshades would need to occupy an area of about 3.8 square kilometers if placed at the L1 point.
The deployment of the flyers is an issue that requires new technology. It has been proposed that this would be accomplished most easily with large railgun
Railgun
A railgun is an entirely electrical gun that accelerates a conductive projectile along a pair of metal rails using the same principles as the homopolar motor. Railguns use two sliding or rolling contacts that permit a large electric current to pass through the projectile. This current interacts...
s or coilgun
Coilgun
A coilgun is a type of projectile accelerator that consists of one or more coils used as electromagnets in the configuration of a synchronous linear motor which accelerate a magnetic projectile to high velocity...
s firing a capsule containing a million shades into space every 5 minutes for 10 years using 20 separate launch sites. The estimated total cost of such an operation is 5 trillion US dollars, with a believed lifetime of 50 years.
Even so, it would still take years to launch enough of the disks into orbit
Orbit
In physics, an orbit is the gravitationally curved path of an object around a point in space, for example the orbit of a planet around the center of a star system, such as the Solar System...
before they have any effect. Thus, if using this technology should become essential, enough time would be needed to implement it.
Roger Angel of the University of Arizona presented the idea for the Sunshade at the U.S. National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
in April, 2006 and won a 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...
Institute for Advanced Concepts grant for further research in July, 2006.
Creating this sunshade in space was estimated to cost in excess of US$5 trillion, thus leading Professor Angel to conclude that "[t]he sunshade is no substitute for developing renewable energy, the only permanent solution. A similar massive level of technological innovation and financial investment could ensure that. But if the planet gets into an abrupt climate crisis that can only be fixed by cooling, it would be good to be ready with some shading solutions that have been worked out."
Sunshade consisting of one Fresnel lens
In 2004, physicist and science fiction author Gregory Benford
Gregory Benford
Gregory Benford is an American science fiction author and astrophysicist who is on the faculty of the Department of Physics and Astronomy at the University of California, Irvine...
calculated that a concave rotating Fresnel lens
Fresnel 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...
1000 kilometres across, yet only a few millimeters thick, floating in space at the point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%. Side-effects include that, if this lens were built and global warming were avoided, there would be less incentive to reduce greenhouse gases, and humans might continue to produce too much carbon dioxide until it caused some other environmental catastrophe, such as a chemical change in ocean water
Ocean acidification
Ocean acidification is the name given to the ongoing decrease in the pH and increase in acidity of the Earth's oceans, caused by the uptake of anthropogenic carbon dioxide from the atmosphere....
that could be disastrous to ocean life
Marine biology
Marine biology is the scientific study of organisms in the ocean or other marine or brackish bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather...
.
The cost of such a lens has been disputed. At a global warming summit in 2004, Benford estimated that it would cost around US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
10 billion
1000000000 (number)
1,000,000,000 is the natural number following 999,999,999 and preceding 1,000,000,001.In scientific notation, it is written as 109....
up front, and another $10 billion in supportive cost during its lifespan.
Sunshade consisting of one diffraction grating
A similar approach involves placing a very large diffraction gratingDiffraction grating
In optics, a diffraction grating is an optical component with a periodic structure, which splits and diffracts light into several beams travelling in different directions. The directions of these beams depend on the spacing of the grating and the wavelength of the light so that the grating acts as...
(thin wire mesh) in space, perhaps at the L1 point between the Earth and the Sun. Such a proposal was made in 1997 by Edward Teller
Edward Teller
Edward Teller was a Hungarian-American theoretical physicist, known colloquially as "the father of the hydrogen bomb," even though he did not care for the title. Teller made numerous contributions to nuclear and molecular physics, spectroscopy , and surface physics...
, Lowell Wood
Lowell Wood
Lowell Wood is an American astrophysicist who has been involved with the Strategic Defense Initiative and with geoengineering studies. He has been affiliated with Lawrence Livermore National Laboratory and the Hoover Institution, and chaired the EMP Commission. Wood invented the Mosquito laser.-...
, and Roderick Hyde, although in 2002 these same authors argued for blocking solar radiation in the stratosphere rather than in orbit.