Editing Space sunshade (section)

{{Merge|Space mirror
| date = May 2025
| discuss = Talk:Space_sunshade#Second_merge_proposal
}}

{{use dmy dates |date=October 2020}}
{{Short description|Earth shield to reduce sunlight}}[[Image:Space lens.png|thumb|right|300px|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.]]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.  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]].<ref>{{Cite book |last=Oberth |first=Hermann |date=1984 |orig-date=1923 |title=[[Die Rakete zu den Planetenräumen]] |language=german |publisher=Michaels-Verlag Germany |pages=87–88}}</ref><ref>{{Cite book |last=Oberth |first=Hermann |title=ways to spaceflight |url=https://archive.org/details/nasa_techdoc_19720008133 |via=archiv.org |publisher=NASA |access-date=21 December 2017 |language=en |date=1970 |orig-year=1929 |pages=481–506}}</ref><ref>{{Cite book |last=Oberth |first=Hermann |date=1957 |title=Menschen im Weltraum |language=german  |publisher=Econ Duesseldorf Germany |pages=125–182}}</ref><ref>{{Cite book |last=Oberth |first=Hermann |date=1978 |title=Der Weltraumspiegel |language=german |publisher=Kriterion Bucharest}}</ref>{{Request quote|date=January 2025|reason=what exactly did Oberth say about climate engineering?}} [[Space mirror|Space mirrors]] in orbit around the Earth with a diameter of 100 to 300 km, as designed by Hermann Oberth, were 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 could potentially be one [[climate engineering]] method for [[Climate change mitigation|mitigating]] [[global warming]] through [[solar radiation management]], because internationally negotiated reductions in carbon emissions may be insufficient to stem climate change.<ref>{{cite journal |doi=10.1080/14777622.2018.1436360 |title=The Political Economy of a Planetary Sunshade |year=2018 |last1=Hickman |first1=John |journal=Astropolitics |volume=16 |issue=1 |pages=49–58 |bibcode=2018AstPo..16...49H |s2cid=148608737}}</ref><ref name=":0">{{cite web |last=Gorvett |first=Zaria |date=26 April 2016 |title=How a giant space umbrella could stop global warming |url=http://www.bbc.com/future/story/20160425-how-a-giant-space-umbrella-could-stop-global-warming |url-status=live |archive-url=https://web.archive.org/web/20161220163623/http://www.bbc.com/future/story/20160425-how-a-giant-space-umbrella-could-stop-global-warming |archive-date=20 December 2016 |access-date=7 December 2016 |website=BBC}}</ref> 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" [[Space manufacturing|manufactured in space]] to reduce the cost of launching massive objects to space.<ref name=":1">{{cite journal |last1=Borgue |first1=Olivia |last2=Hein |first2=Andreas M. |date=2022 |title=Transparent occulters: A nearly zero-radiation pressure sunshade to support climate change mitigation |journal=Acta Astronautica |volume=203 |issue=in press |pages=308–318 |doi=10.1016/j.actaastro.2022.12.006 |s2cid=254479656 |doi-access=free }}</ref><ref>{{Cite web |date=2022-07-07 |title=Space Bubbles Could Be the Wild Idea We Need to Deflect Solar Radiation |url=https://www.popularmechanics.com/space/a40486004/space-bubbles-climate-change/ |access-date=2023-05-23 |website=Popular Mechanics |language=en-US}}</ref> However it would cost trillions of dollars and no prototype has yet been launched.<ref>{{Cite web |last=Surkes |first=Sue |title=Israeli scientist proposes massive space sunshade to cut global temperatures by 1.5ºC |url=https://www.timesofisrael.com/israeli-scientist-proposes-massive-space-sunshade-to-cut-global-temperatures-by-1-5oc/ |access-date=2025-01-16 |website=www.timesofisrael.com |language=en-US}}</ref> Critics also argue that building it would be too slow to prevent dangerous levels of global warming.<ref>{{Cite news |last=Buckley |first=Cara |date=2024-02-02 |title=Could a Giant Parasol in Outer Space Help Solve the Climate Crisis? |url=https://www.nytimes.com/2024/02/02/climate/sun-shade-climate-geoengineering.html |access-date=2025-01-17 |work=The New York Times |language=en-US |issn=0362-4331}}</ref>