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Space sunshade

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A space sunshade or sunshield is a parasol that diverts or otherwise reduces some of the Sun's radiation, preventing it from hitting a spacecraft or planet and thereby reducing its insolation, which results in reduced heating. Light can be diverted by different methods. The concept of the construction of sunshade as a method of climate engineering dates back to the years 1923, 1929, 1957 and 1978 by the physicist Hermann Oberth.[1][2][3][4] Space mirrors in orbit around the Earth with a diameter of 100 to 300 km, as designed by Hermann Oberth, are intended to focus sunlight on individual regions of the Earth’s surface or deflect it into space so that the solar radiation is weakened in a specifically controlled manner for individual regions on the Earth’s surface. First proposed in 1989, another space sunshade concept involves putting a large occulting disc, or technology of equivalent purpose, between the Earth and Sun.

A sunshade is of particular interest as a climate engineering method for mitigating global warming through solar radiation management. Heightened interest in such projects reflects the concern that internationally negotiated reductions in carbon emissions may be insufficient to stem climate change.[5][6] Sunshades 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. Most such proposals contemplate a blocking element at the Sun-Earth L1 Lagrangian point.

Modern proposals are based on some form of distributed sunshade composed of lightweight transparent elements or inflatable "space bubbles" manufactured in space to reduce the cost of launching massive objects to space.[7][8]

Designs for planetary sunshade

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Cloud of small spacecraft

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One proposed sunshade would be composed of 16 trillion small disks at the Sun-Earth L1 Lagrangian point, 1.5 million kilometers from Earth and between it and the Sun. Each disk is proposed to have a 0.6-meter diameter and a thickness of about 5 micrometers. The mass of each disk would be about a gram, adding up to a total of almost 20 million tonnes.[9] Such a group of small sunshades that blocks 2% of the sunlight, deflecting it off into space, would be enough to halt global warming.[10] If 100 tonnes of disks were launched to low Earth orbit every day, it would take 550 years to launch all of them.

The individual autonomous flyers building up the cloud of sunshades are proposed not to reflect the sunlight but rather to 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 hold them in place at the L1 point. An optical prototype has been constructed by Roger Angel with funding from NIAC.[11]

The remaining solar pressure and the fact that the L1 point is one of unstable equilibrium, 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 hold position. A suggested solution is to place mirrors capable of rotation on the surface of the flyers. By using the solar radiation pressure on the mirrors as solar sails and tilting them in the right direction, the flyer will be capable of altering its speed and direction to keep in position.[12]

Such a group of sunshades would need to occupy an area of about 3.8 million square kilometers if placed at the L1 point[12] (see other lower disc size estimates below).

It would still take years to launch enough of the disks into orbit to have any effect. This means a long lead time. Roger Angel of the University of Arizona[9] presented the idea for a 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$130 billion over 20 years with an estimated lifetime of 50-100 years.[13] Thus leading Professor Angel to conclude that "the 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."[12][14]

Lightweight solutions and "Space bubbles"

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A more recent design has been proposed by Olivia Borgue and Andreas M. Hein in 2022, proposing a distributed sunshade with a mass on the order of 100,000 tons, composed of ultra-thin polymeric films and SiO2 nanotubes.[7] The author estimated that launching such mass would require 399 yearly launches of a vehicle such as SpaceX Starship for 10 years.[7]

A 2022 concept by MIT Senseable City Lab proposes using thin-film structures ("space bubbles") manufactured in outer space to solve the problem of launching the required mass to space.[15] MIT scientists led by Carlo Ratti believe deflecting 1.8 percent of solar radiation can fully reverse climate change. The full raft of inflatable bubbles would be roughly the size of Brazil and include a control system to regulate its distance from the Sun and optimise its effects.[16] The shell of the thin-film bubbles would be made of silicon, tested in outer space-like conditions at a pressure of .0028 atm and at -50 degrees Celsius.[16] They plan to investigate low vapor-pressure materials to rapidly inflate the bubbles, such as a silicon-based melt or a graphene-reinforced ionic liquid.[16]

One Fresnel lens

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The basic function of a space lens to mitigate global warming. A 1,000-kilometre diameter lens is sufficient, and much smaller than what is shown in this simplified image. As a Fresnel lens it would be only a few millimeters thick.

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.[17] His design involved making a large glass (2,000 km) occulter from lunar material and placing at the L1 point. Issues included the large amount of material needed to make the disc and also the energy to launch it to its orbit.[6]

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 L1 point, would reduce the solar energy reaching the Earth by approximately 0.5% to 1%.[18]

The cost of such a lens has been disputed. At a science fiction convention in 2004, Benford estimated that it would cost about US$10 billion up front, and another $10 billion in supportive cost during its lifespan.[18]

One diffraction grating

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A similar approach involves placing a very large diffraction grating (thin wire mesh) in space, perhaps at the L1 point between the Earth and the Sun. A proposal for a 3,000 ton diffraction mesh was made in 1997 by Edward Teller, Lowell Wood, and Roderick Hyde,[19] although in 2002 these same authors argued for blocking solar radiation in the stratosphere rather than in orbit given then-current space launch technologies.[20]

Other Lower Disc Size Estimates

Recent work by Feinberg (2022)[21] illustrate that lower disc area sizes (factor of approximately 3.5 reduction) are feasible when the background climate response is considered. For example, the background Earth climate would yield less re-radiation and feedback. In addition, disc area sizes can be further reduced by 50 times using an Annual Solar Geoengineering approach as indicated by Feinberg (2024).[22]

Spacecraft sunshades

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The James Webb Space Telescope (JWST) infrared telescope has a layered sunshade to keep the telescope cold.

For spacecraft approaching the Sun, the sunshade is usually called a heatshield. Notable spacecraft [designs] with heatshields include:

  • Messenger, launched 2004, orbited Mercury until 2015, had a ceramic cloth sunshade
  • Parker Solar Probe (was Solar Probe Plus), launched 2018 (carbon, carbon-foam, carbon sandwich heatshield)
  • Solar Orbiter, launched Feb 2020
  • BepiColombo, to orbit Mercury, with Optical Solar Reflectors (acting as a sunshade) on the Planetary Orbiter component.

See also

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  • Solar sail – Space propulsion method using Sun radiation
  • Space mirror (geoengineering) – Artificial satellites designed to change the amount of solar radiation that impacts Earth
  • Space-based solar power – Concept of collecting solar power in outer space and distributing it to Earth
  • Spacecraft thermal control – Process of keeping all parts of a spacecraft within acceptable temperature ranges
  • Starshade – Proposed occulter
  • Sunshield (JWST) – Main cooling system for the infrared observatory

References

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  1. ^ Oberth, Hermann (1984) [1923]. Die Rakete zu den Planetenräumen (in German). Michaels-Verlag Germany. pp. 87–88.
  2. ^ Oberth, Hermann (1970) [1929]. ways to spaceflight. NASA. pp. 481–506. Retrieved 21 December 2017 – via archiv.org.
  3. ^ Oberth, Hermann (1957). Menschen im Weltraum (in German). Econ Duesseldorf Germany. pp. 125–182.
  4. ^ Oberth, Hermann (1978). Der Weltraumspiegel (in German). Kriterion Bucharest.
  5. ^ Hickman, John (2018). "The Political Economy of a Planetary Sunshade". Astropolitics. 16 (1): 49–58. Bibcode:2018AstPo..16...49H. doi:10.1080/14777622.2018.1436360. S2CID 148608737.
  6. ^ a b Gorvett, Zaria (26 April 2016). "How a giant space umbrella could stop global warming". BBC. Archived from the original on 20 December 2016. Retrieved 7 December 2016.
  7. ^ a b c Borgue, Olivia; Hein, Andreas M. (2022). "Transparent occulters: A nearly zero-radiation pressure sunshade to support climate change mitigation". Acta Astronautica. 203 (in press): 308–318. doi:10.1016/j.actaastro.2022.12.006. S2CID 254479656.
  8. ^ "Space Bubbles Could Be the Wild Idea We Need to Deflect Solar Radiation". Popular Mechanics. 7 July 2022. Retrieved 23 May 2023.
  9. ^ a b "Space sunshade might be feasible in global warming emergency". EurekAlert. 3 November 2006. Archived from the original on 23 October 2020. Retrieved 11 November 2010.
  10. ^ "Global Sunshade". BBC News. 19 February 2007. Archived from the original on 1 March 2007. Retrieved 11 November 2010.
  11. ^ Tnenbaum, David (23 April 2007). "Pies in the Sky: A Solution to Global Warming". Astrobiology Magazine. Archived from the original on 2 February 2016. Retrieved 14 November 2010.
  12. ^ a b c Angel, Roger (18 September 2006). "Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1)". Proceedings of the National Academy of Sciences of the United States of America. 103 (46). PNAS: 17184–9. Bibcode:2006PNAS..10317184A. doi:10.1073/pnas.0608163103. PMC 1859907. PMID 17085589.
  13. ^ Konecny, Pavel (6 December 2018). "We need SpaceX BFR not just get us to MARS but to save EARTH from Global Warming". Medium. Archived from the original on 22 November 2021. Retrieved 11 March 2019.
  14. ^ "Space Sunshade Might Be Feasible In Global Warming Emergency" (Press release). University of Arizona. 6 November 2006. Archived from the original on 16 March 2010. Retrieved 29 April 2009.
  15. ^ "Space bubbles". MIT Senseable City Lab. Retrieved 24 May 2023.
  16. ^ a b c "Space Bubbles Could Be the Wild Idea We Need to Deflect Solar Radiation". Popular Mechanics. 7 July 2022. Retrieved 23 May 2023.
  17. ^ J. T. Early (1989), "Space-Based Solar Shield To Offset Greenhouse Effect", Journal of the British Interplanetary Society, vol. 42, pp. 567–569, Bibcode:1989JBIS...42..567E. This proposal is also discussed in footnote 23 of Edward Teller; Roderick Hyde & Lowell Wood (1997), Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change (PDF), Lawrence Livermore National Laboratory, archived (PDF) from the original on 27 January 2016, retrieved 30 October 2010.
  18. ^ a b See Russell Dovey, "Supervillainy: Astroengineering Global Warming Archived 4 August 2012 at archive.today and Bill Christensen, "Reduce Global Warming by Blocking Sunlight" Archived 2009-04-17 at the Wayback Machine.
  19. ^ Edward Teller; Roderick Hyde & Lowell Wood (1997), Global Warming and Ice Ages: Prospects for Physics-Based Modulation of Global Change (PDF), Lawrence Livermore National Laboratory, archived (PDF) from the original on 27 January 2016, retrieved 30 October 2010. See pages 10–14 in particular.
  20. ^ Edward Teller, Roderick Hyde & Lowell Wood (2002), Active Climate Stabilization: Practical Physics-Based Approaches to Prevention of Climate Change (PDF), Lawrence Livermore National Laboratory, archived (PDF) from the original on 13 May 2009, retrieved 30 October 2010
  21. ^ Feinberg, Alec (2022). "Solar Geoengineering Modeling and Applications for Mitigating Global Warming: Assessing Key Parameters and the Urban Heat Island Influence". Frontiers in Climate. 4. doi:10.3389/fclim.2022.870071. ISSN 2624-9553.
  22. ^ Feinberg, Alec (February 2024). "Annual Solar Geoengineering: Mitigating Yearly Global Warming Increases". Climate. 12 (2): 26. doi:10.3390/cli12020026. ISSN 2225-1154.
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