Space mirror
They were theorised as a method of climate engineering through shading the Earth by creating a space sunshade to deflect sunlight and counter global warming.
[5][7] The concept of constructing space mirrors as a method of climate engineering dates to the years 1923, 1929, 1957 and 1978 by the physicist Hermann Oberth and the 1980s by other scientists.
In 1923, Hermann Oberth first described his space mirrors with a diameter of 100 to 300 km in his book Die Rakete zu den Planetenräumen,[1] which are said to consist of a grid network of individually adjustible facets.
These giant mirrors in orbit could be used to illuminate individual cities, as a means of protection against natural disasters, to control weather and climate, to create additional living space for tens of billions of people, Hermann Oberth writes.
[citation needed] The physicist Hermann Oberth followed his first suggestion in 1923[1] with further publications, in which he took into account the technical progress achieved up to that point: 1929 „Ways to Spaceflight“,[2] 1957 „Menschen im Weltraum.
[citation needed] Other scientists proposed in the 1980s to cool Venus’ climate to provide for a theoretical future where humans occupy other planets.
[8] In 1989, James Early, working at the Lawrence Livermore National Laboratory, proposed using a "space shade" 2,000 kilometres (1,200 miles) in diameter orbiting at Lagrangian Point L1.
][2][need quotation to verify] The concept is to reflect enough sunlight to reduce the Earth's temperature thereby balancing out the warming effect of greenhouse gases.
][2][need quotation to verify] Most past proposals for the development of space mirrors are specifically to slow the progression of global warming on Earth.
Geoengineering research efforts to mitigate or reverse global warming can be separated into two different categories, carbon dioxide removal and solar radiation management.
[7] Solar radiation management works to directly mitigate the effects of atmospheric warming due to the burning of fossil fuels and subsequent release of greenhouse gases.
[7] Space mirrors fall under this category of geoengineering as they work to block solar radiation and lower the warming effects from the Sun.
[13] The most straightforward is to have mirrors orbiting around the Earth—an idea first suggested even before the wider awareness of climate change, with rocketry pioneer Hermann Oberth considering it a way to facilitate terraforming projects in 1923.
[18] In an attempt to deal with this problem, other researchers have proposed Inner lagrangian point between the Earth and the Sun as an alternative to near-Earth orbits, even though this tends to increase manufacturing or delivery costs instead.
In 1989, a paper suggested founding a lunar colony, which would produce and deploy diffraction grating made out of a hundred million tonnes of glass.
Two other proposals from the early 2000s advocated the use of thin metallic disks 50–60 cm in diameter, which would either be launched from the Earth at a rate of once per minute over several decades, or be manufactured from asteroids directly in orbit.
Report author and Star Technology president Jerome Pearson calculated it would take 5 million spacecraft to achieve the desired result, and even if each individual craft could last 100 years, that means 137 ships would have to be replaced or repaired per day.
[24] Lowell Wood, a researcher at the Lawrence Livermore National Laboratory, proposed sending a single, massive mirror into orbit at Lagrange point L1, approximately one million miles away from Earth.
[27][28] In addition to the space mirror, suggested sunlight-reducing techniques included launching thousands of highly reflective balloons and pumping sulphate droplets into the upper atmosphere to emulate volcanic emissions.
