Space sunshade

Lagrange Points L1-L5 of Earth-Sun 2-body system. L1 & L2 are both ~1.5 million km from Earth. L1: current SOHO location & potential location of Space sunshade. L2: James Webb Space Telescope location. (NASA/WMAP image)

A space sunshade or sunshield is something that diverts or otherwise reduces some of the Sun's radiation, preventing it from hitting the Earth and thereby reducing its insolation, which results in reduced heating.

Quotes

Ways to Spaceflight (1970) Tr. Wege zur Raumschiffahrt (1929)

by Hermann Oberth, Ways to Spaceflight is a public domain Creative Commons translation of Oberth's Wege zur Raumschiffahrt (1929) for NASA, by the Agence Tunisienne de Public-Relations, Tunis, Tunesia (1970). Excerpts are from Ch. 20 Stations in Interplanetary Space pp. 477-506.

• I could have restricted myself in this book to only the most sober physical calculations. But in order to create the necessary respect for my idea (otherwise a realization of this idea is unthinkable), I felt impelled to draw a few pictures of the future... and I have set up some fantastic claims. Naturally, here also, I have said nothing that might not be possible by present scientific standards, and I will now show that I am also on completely scientific ground with this idea of a reflector.

• A rocket with the necessary equipment is sent aloft and there given a lateral propulsion which puts it into an elliptical orbit around the earth. I will call this rotation about the earth "revolution". Major axis perpendicular to the ecliptic, perigee in the south 1,000 km above the earth's surface, apogee in the north 5,000 km above the earth's surface.

• The miniature facets are adjusted by hand... It is sufficient to simply let the sun shine on the miniature reflector and then turn the facets so that the reflected light strikes those parts of the globe corresponding to the region to be irradiated.

• Whether we must seek to constantly reflect the light on the earth vertically or are, in fact, able to is another question. I will assume that we can in order to study the single elements which determine the path of the reflector. (Imaginary numbers are also used in calculations, although it is known that they do not exist.)

• In the south... the main task of large reflectors... of making polar regions arable, is not feasible. If the glaciers of Antarctica were melted, the level of the ocean would rise uncomfortably (6-8 m). Hopefully, by then man will be sensible enough at least to leave a cold zone for the protection of nature.

• So for the southern hemisphere and the tropics there would only remain the illumination of large cities at night and perhaps supplying solar plants with more light as well as the influencing of the weather.

• In the north, on the other hand, outside of Greenland, there are no such masses of land-ice (however much ice there may be, no danger arises from melting ice that floats in the water), and the glaciers of Greenland will remain because if their high location and because there will be more snowfall on Greenland if the polar sea melts.

• The cultural tasks are... possible to fulfill. For example, if a sea route to the ports of Siberia is to be kept ice-free, a route must only be chosen that runs approximately in the direction of the winter wind from the Gulf Stream... light is thrown on a relatively narrow and short strip running from east to west... to the extent that the sky clouds over at this place. ...[T]he direction of the wind and ...the earth's rotation coincide. Hereby the earth always rotates as we need it ...By the time the light patch has passed along the whole stretch, the fog at the beginning will either have settled or been blown away... Then one can begin at the beginning again, Since the clouds hold the heat above the shipping lane... a reflector 100 km in diameter is... sufficient.

• Enough of this. They are only dreams of the future. Bold ones? Perhaps, but we have already experienced... bolder ideas. Who would have believed in 1894 that, a few years later, one would see through a person by means of Roentgen rays? PHILANDER's statement (Medical Fairy Tales), "Man will be made transparent like a jelly-fish", was bolder than this dream of the future; that required finding something completely new, while here we are dealing with laws of nature already known.—Accomplishing these things will certainly require the conversion of enormous energies. But were not hundred times greater sums of money expended during the World War? In one year, the nations of Europe spend more on smoking and drinking than the whole sodium reflector would cost. War and narcotics are quite unnecessary things, yet more money is spent on them than on something useful. Should not mankind, in an exceptional case, also save something for constructive work?
• Ref: Philander, Medizinische Märchen

"Space-based Solar Shield to Offset Greenhouse Effect" (1989)

Journal of The British Interplanetary Society Vol. 42, pp. 567-569, by James T. Early, Lawrence Livermore National Laboratory.

• Terraforming shields for planets such as Venus or Mars would... be large, complex structures requiring vast amounts of lunar or asteroidal material... space manufacturing and long-range transportation... One... stepping stone to understanding and mastering the technologies and processes... would be the construction of a shield to offset the greenhouse effect on... Earth. Such... would not require interplanetary capabilities.

• The time required for the removal of... [greenhouse] gases from the atmosphere by natural processes is... uncertain: current estimates are several centuries.
  The uncertainties... [have] led to calls for... restrictions on the generation of greenhouse gases. ...The existence of a possible technical solution could... have a major short-term impact in influencing short term consumption restrictions, even if the solution could not be implemented until the next century.

• A conceptually simple method for offsetting the greenhouse radiation trapping effects would be to decrease the solar heating by the use of a space-based solar shield.

• Approximately 2% of the solar radiation reaching Earth must be blocked to offset the predicted greenhouse trapping in the next century.

• An ideal opaque shield would scatter the Earth bound solar energy into diffuse infrared energy.

Space Fresnel lens

• The shield may also be transparent and simply scatter the visible photons away from the Earth. ...A glass shield may act as a prism to deflect the sunlight away from the planet in accordance with Snell's Law.

• Lunar soil can be formed into glass for either a transparent or opaque shield.

• The glass may be launched to the shield location by a mass driver. A number of studies have indicated that mass drivers are feasible and economical for launching unmanned payloads from the lunar surface. If the glass sheet is sufficiently flexible it may be formed into sheet on the lunar surface and launched in rolls.

Hermann Oberth: the father of space flight, 1894-1989 (1994)

by Boris V. Rauschenbach

• Oberth... began the book Men in Outer Space: New Projects for Rockets and Space Travel... written in the style accessible to the general reader. ...Published in 1955 in German, it was translated into English, French, Italian, Dutch, and even in Croatian! ...Oberth's new book was indeed "cosmic," and this gave it a cardinal distinction from his classic book of the 1920s. ...A supplemental chapter ...is devoted to "space mirrors," a theme which occupied Oberth all his life. A short description ...is already present in the 1923 book. In 1929, when he published his fundamental work, Ways to Space Travel, he included a much more comprehensive description... in the chapter... "Space Stations." ...[A]lmost the entire chapter is devoted to space mirrors. In the 1954 book... a new varient... is presented. Eventually in Bucharest in 1978, an entire book (in German) was devoted to this theme. ...[T]he primary purpose for the space mirror would today be called an ecological one ...At the time ...there was ...no robotics technology, and he assumed all the work after ...erection ...would ...be carried out manually by astronauts.

• [A] giant net (similar to a trawl) would be erected in outer space, constructed in a hexagonal mesh pattern. This net would be stretched out and a tension sufficient to rotate the entire net would be maintained by centripetal force. The rotation would be begun by special rockets and... continue because it was in a vacuum. The diameter of each hexagon would be about 10 kilometers, and the entire mirror would have a circular disk shape with a diameter of about 100 to 200 kilometers. Within each hexagon, a round mirror approximately 10 kilometers in diameter, would be installed. ...[Each] single mirror would be capable of being [independently] tilted... initiated by... electric actuators.

• Such a mirror, he asserted, could not only light up the cities at night... but could also have a decisive influence on weather and climate.

• [T]he ice in the usable areas of the north polar seas could be melted... to navigate the northern coasts of Europe and Siberia year round. The warming of the Caspian Sea could... produce rain in arid regions of Central Asia. Directing... rays... where spring and autumn frosts are expected would allow... increase[d] fertility... Oberth claimed... it would open up... predicting the weather, but also... determining the weather.

• Oberth proposed to shade planets located close to the sun... with gigantic cosmic shields... Vice versa, the planets... further from the sun... would be warmed... with... gigantic cosmic mirrors.

• [H]is belief... a reduction in the cost of building large structures in outer space could be achieved by delivering the necessary materials from the moon... [H]e presupposed the existence of the necessary industrial plants on the moon, but the end result would be a thousand-fold reduction in the cost of building large structures in space.

Global Warming and Ice Ages (August 15, 1997)

:I. Prospects For Physics-Based Modulation Of Global Change by E. Teller, L. Wood, Roderick Hyde, paper prepared for submittal to the 22nd International Seminar on Planetary Emergencies Erice (Sicily), Italy August 20-23, 1997. UCRL-JC-128715 PrePrint. Lawrence Livermore National Laboratory.

• [T]he problem of possible changes in climate may be better solved by cooperative application of modern technologies rather than by international measures focused on prohibitions.
  • Introduction, p. 3.

Solar Geoengineering Techniques

• Greenhouse warming of the Earth due to human activities is a possibility, moreover one for which mitigative/remedial actions of the types proposed here can be at once deliberate and effective. In contrast, Ice Age-severity cooling... that have occurred quasi-periodically many times during the last 1.2 million years, is a practical certainty. Moreover, a several-decade duration cold snap of Ice Age Maximum temperature-drop is known to have occurred in the Northern Hemisphere with essentially no warning during the last interglacial period, under precursor climatic conditions only slightly warmer than the present-day one.
  • Conclusions, p. 17.

A contour plot of the effective potential due to gravity and the centrifugal force of a two-body system in a rotating frame of reference. The arrows indicate the downhill gradients of the potential around the five Lagrange points, toward them (red) and away from them (blue). Counterintuitively, the L₄ and L₅ points are the high points of the potential. At the points themselves these forces are balanced.

Was breaking the taboo on research on climate engineering via albedo modification a moral hazard, or a moral imperative? (Nov 17, 2016)

Open Access Article by Mark G. Lawrence, Paul J. Crutzen

• A wide range of techniques has been proposed for increasing the planetary albedo, ranging from painting surfaces white to placing mirrors in orbit between the Earth and the sun.

• This sense of taboo was based on a range of arguments against research on albedo modification that have been raised by the broader scientific community, including:
  1. the so-called moral hazard issue, that is, the possibility that research on climate engineering could be perceived as an implicit legitimization, and thus reduce the motivation for mitigating anthropogenic emissions;
  2. the concern that reducing temperatures by albedo modification could distract from other impacts of a fossil-fuel-based economy and the resulting CO2 emissions, such as ocean acidification;
  3. the “slippery slope” concern that research into understanding the potential effectiveness could cascade toward the development and deployment of the techniques under investigation; and
  4. contention about the perceived “techno-fix” approach to address environmental challenges, that is, the notion that technology-caused problems can simply be fixed with more and better technology.

• [G]iven the balance of results of model studies over the last decade... and the challenging directions that this implies both for future research and also for sociopolitical aspects, especially public perception and the development of good governance principles, we have to conclude that the overall verdict is still out. The responsibility still resides with the scientific community to conduct research and engage in the broader dialogue in a responsible way, so that whatever the outcome, historians will hopefully look back and conclude that it was indeed of value—and in that sense a moral imperative—to begin carefully investigating this topic... Perhaps this will already be clear by the time of the next special section like this one, which, following those in 1996 and 2006, should be due in 2026.

See also

• Climate action
• Climate Action Network
• Climate change denial
• Global warming
• Green New Deal
• How to Avoid a Climate Disaster by Bill Gates
• Scientific consensus on climate change
• Space exploration
• Sun

External links

• YouTube videos
  • Can We Block the Sun to Stop Climate Change @Real Engineering channel
  • A huge sun shade in space? @BBC Studios channel