Editing Space colonization (section)

====Energy====
[[Solar energy]] in orbit is abundant, reliable, and is commonly used to power satellites today. There is no night in free space, and no clouds or atmosphere to block sunlight. Light intensity obeys an [[inverse-square law]]. So the solar energy available at distance ''d'' from the Sun is ''E'' = 1367/''d''<sup>2</sup> W/m<sup>2</sup>, where ''d'' is measured in [[astronomical unit]]s (AU) and 1367 watts/m<sup>2</sup> is the energy available at the distance of Earth's orbit from the Sun, 1 AU.<ref>McGraw-Hill Encyclopedia of Science & Technology, 8th Edition 1997; vol. 16, p. 654.</ref>

In the weightlessness and vacuum of space, high temperatures for industrial processes can easily be achieved in [[solar ovens]] with huge parabolic reflectors made of metallic foil with very lightweight support structures. Flat mirrors to reflect sunlight around radiation shields into living areas (to avoid line-of-sight access for cosmic rays, or to make the Sun's image appear to move across their "sky") or onto crops are even lighter and easier to build.

Large solar power photovoltaic cell arrays or thermal power plants would be needed to meet the electrical power needs of the settlers' use. In developed parts of Earth, electrical consumption can average 1 kilowatt/person (or roughly 10 [[watt-hour|megawatt-hours]] per person per year.)<ref>[http://www.unescap.org/esd/energy/information/ElectricPower/1999-2000/access.htm UNESCAP Electric Power in Asia and the Pacific], {{webarchive|url=https://web.archive.org/web/20110213083253/http://www.unescap.org/esd/energy/information/ElectricPower/1999-2000/access.htm|date=13 February  2011}}.</ref> These power plants could be at a short distance from the main structures if wires are used to transmit the power, or much farther away with [[wireless power transmission]].

A major export of the initial space settlement designs was anticipated to be large [[solar power satellite]]s (SPS) that would use wireless power transmission (phase-locked [[microwave]] beams or lasers emitting wavelengths that special solar cells convert with high efficiency) to send power to locations on Earth, or to colonies on the Moon or other locations in space. For locations on Earth, this method of getting power is extremely benign, with zero emissions and far less ground area required per watt than for conventional solar panels. Once these satellites are primarily built from lunar or asteroid-derived materials, the price of SPS electricity could be lower than energy from fossil fuel or nuclear energy; replacing these would have significant benefits such as the elimination of [[greenhouse gases]] and [[nuclear waste]] from electricity generation.<ref>{{Cite web|url=http://large.stanford.edu/courses/2015/ph240/gaertner1/|title=Solar vs. Traditional Energy in Homes|website=large.stanford.edu |first=Ryan|last=Gaertner|date=9 November 2015|access-date=26 February 2019|archive-url=https://web.archive.org/web/20181024050207/http://large.stanford.edu/courses/2015/ph240/gaertner1/|archive-date=24 October 2018|url-status=live}}</ref>

Transmitting solar energy wirelessly from the Earth to the Moon and back is also an idea proposed for the benefit of space colonization and energy resources. Physicist Dr. David Criswell, who worked for NASA during the Apollo missions, proposed the idea of using power beams to transfer energy from space. These beams, microwaves with a wavelength of about 12&nbsp;cm, would be almost untouched as they travel through the atmosphere. They could also be aimed at more industrial areas to keep away from humans or animal activities.<ref name="i2massociates.com">{{Cite web |url=http://www.i2massociates.com/downloads/AAPG_Memoir_101-July18-2012.pdf |title=Nuclear Power and Associated Environmental Issues in the Transition of Exploration and Mining on Earth to the Development of Off-World Natural Resources in the 21st Century |access-date=18 September 2017 |archive-url=https://web.archive.org/web/20150214125331/http://i2massociates.com/downloads/AAPG_Memoir_101-July18-2012.pdf |archive-date=14 February 2015 |url-status=live }}</ref> This would allow for safer and more reliable methods of transferring solar energy.

In 2008, scientists were able to send a 20 watt microwave signal from a mountain on the island of Maui to the island of Hawaii.<ref>{{Cite journal|last=Dance|first=Amber|date=16 September 2008|title=Beaming energy from space|journal=Nature|doi=10.1038/news.2008.1109|issn=0028-0836}}</ref> Since then [[JAXA]] and Mitsubishi have been working together on a $21&nbsp;billion project to place satellites in orbit which could generate up to 1 gigawatt of energy.<ref>{{cite web|url=https://www.popsci.com/technology/article/2011-06/satellites-could-gather-energy-sun-and-beam-it-down-earth/ |title=Space Based Solar Power |first=Corey|last=Binns|archive-url=https://web.archive.org/web/20170927054041/http://www.popsci.com/technology/article/2011-06/satellites-could-gather-energy-sun-and-beam-it-down-earth |archive-date=27 September 2017|publisher=Popular Science| date=2 June 2011}}</ref> These are the next advancements being done today to transmit energy wirelessly for space-based solar energy.

However, the value of SPS power delivered wirelessly to other locations in space will typically be far higher than to Earth. Otherwise, the means of generating the power would need to be included with these projects and pay the heavy penalty of Earth launch costs. Therefore, other than proposed demonstration projects for power delivered to Earth,<ref name="NatSecSpaceOffice2007">{{cite web |date=10 October 2007 |title=Space-Based Solar Power As an Opportunity for Strategic Security: Phase 0 Architecture Feasibility Study |url=https://apps.dtic.mil/sti/pdfs/ADA473860.pdf |url-status=live |archive-url=https://web.archive.org/web/20220926134325/https://apps.dtic.mil/sti/pdfs/ADA473860.pdf |archive-date=26 September 2022 |access-date=26 September 2022 |website= |publisher=U.S. National Security Space Office}}</ref> the first priority for SPS electricity is likely to be locations in space, such as communications satellites, fuel depots or "orbital tugboat" boosters transferring cargo and passengers between low Earth orbit (LEO) and other orbits such as [[geosynchronous orbit]] (GEO), [[lunar orbit]] or [[Highly elliptical orbit|highly-eccentric Earth orbit]] (HEEO).<ref name="Lewis-1996"/>{{rp|132}} The system will also rely on satellites and receiving stations on Earth to convert the energy into electricity. Because this energy can be transmitted easily from dayside to nightside, power would be reliable 24/7.<ref>{{cite web|url=https://www.wired.co.uk/article/moon-solar-energy-power |title=Beaming solar energy from the Moon could solve Earth's energy crisis |archive-url=https://web.archive.org/web/20171011044359/http://www.wired.co.uk/article/moon-solar-energy-power |archive-date=11 October 2017 |date=29 March 2017 |website=Wired |first=David |last=Warmflash}}</ref>

[[Nuclear power]] is sometimes proposed for colonies located on the Moon or on Mars, as the supply of solar energy is too discontinuous in these locations; the Moon has nights of two Earth weeks in duration. Mars has nights, relatively high gravity, and an atmosphere featuring [[Climate of Mars#Effect of dust storms|large dust storms]] to cover and degrade solar panels. Also, Mars' greater distance from the Sun (1.52 astronomical units, AU) means that only ''1/1.52<sup>2</sup>'' or about 43% of the solar energy is available at Mars compared with Earth orbit.<ref>{{cite web|url=https://www.sciencedaily.com/releases/2009/10/091004020806.htm |title='Trash Can' Nuclear Reactors Could Power Human Outpost On Moon Or Mars |archive-url=https://web.archive.org/web/20170918154323/https://www.sciencedaily.com/releases/2009/10/091004020806.htm|archive-date=18 September 2017 |date=4 October 2009 |website=ScienceDaily}}</ref> Another method would be transmitting energy wirelessly to the lunar or Martian colonies from solar power satellites (SPSs) as described above; the difficulties of generating power in these locations make the relative advantages of SPSs much greater there than for power beamed to locations on Earth. In order to also be able to fulfill the requirements of a Moon base and energy to supply life support, maintenance, communications, and research, a combination of both nuclear and solar energy may be used in the first colonies.<ref name="i2massociates.com"/>

For both solar thermal and nuclear power generation in airless environments, such as the Moon and space, and to a lesser extent the very thin Martian atmosphere, one of the main difficulties is dispersing the [[Carnot cycle|inevitable heat generated]]. This requires fairly large radiator areas.