Editing Space colonization (section)

====Moons of outer planets====
[[File:Cryobot.jpg|thumb|Artist's impression of a hypothetical ocean [[cryobot]] in [[Europa (moon)|Europa]]]]
Human missions to the outer planets would need to arrive quickly due to the effects of space radiation and microgravity along the journey.<ref name=Palaszewski>{{cite conference |url=https://arc.aiaa.org/doi/10.2514/6.2015-1654 |title=Solar System Exploration Augmented by In-Situ Resource Utilization: Human Mercury and Saturn Exploration |last1=Palaszewski |first1=Bryan |date=2015 |publisher= |book-title= |pages= |doi=10.2514/6.2015-1654 |location=Kissimmee, Florida |conference=8th Symposium on Space Resource Utilization |id=|hdl=2060/20150004114 |hdl-access=free }}</ref> In 2012, Thomas B. Kerwick wrote that the distance to the outer planets made their human exploration impractical for now, noting that travel times for round trips to Mars were estimated at two years, and that the closest approach of Jupiter to Earth is over ten times farther than the closest approach of Mars to Earth. However, he noted that this could change with "significant advancement on spacecraft design".<ref name=Kerwick/> [[Nuclear thermal rocket|Nuclear-thermal]] or nuclear-electric engines have been suggested as a way to make the journey to Jupiter in a reasonable amount of time.<ref name=UTJupiter/> Another possibility would be plasma [[Magnetic sail|magnet sails]], a technology already suggested for rapidly sending a probe to Jupiter.<ref>{{Cite journal |last1=Freeze |first1=Brent |last2=Greason |first2=Jeff |last3=Nader |first3=Ronnie |last4=Febres |first4=Jaime Jaramillo |last5=Chaves-Jiminez |first5=Adolfo |last6=Lamontagne |first6=Michel |last7=Thomas |first7=Stephanie |last8=Cassibry |first8=Jason |last9=Fuller |first9=John |last10=Davis |first10=Eric |last11=Conway |first11=Darrel |date=1 February 2022 |title=Jupiter Observing Velocity Experiment (JOVE): Introduction to Wind Rider Solar Electric Propulsion Demonstrator and Science Objectives |journal=Publications of the Astronomical Society of the Pacific |volume=134 |issue=1032 |pages=023001 |doi=10.1088/1538-3873/ac4812 |issn=0004-6280|doi-access=free |bibcode=2022PASP..134b3001F }}</ref> The cold would also be a factor, necessitating a robust source of heat energy for spacesuits and bases.<ref name=Kerwick/> Most of the larger moons of the outer planets contain [[Ice|water ice]], [[liquid water]], and organic compounds that might be useful for sustaining human life.<ref name="icemoons">{{cite journal|first=G. J. |last=Consalmagno |title=Ice-rich moons and the physical properties of ice |journal=Journal of Physical Chemistry |volume=87 |number=21 |date=1 October 1983 |pages=4204–4208 |doi=10.1021/j100244a045 |url=https://pubs.acs.org/doi/10.1021/j100244a045 }}</ref><ref name="liftveil">{{cite book|first1=Ralph |last1=Lorenz |first2=Jacqueline |last2=Mitton |title=Lifting Titan's veil: exploring the giant moon of Saturn |publisher=Cambridge University Press |date=2002 |isbn=978-0-521-79348-3 |url=https://books.google.com/books?id=VLDG5awUsPoC}}</ref>

[[Robert Zubrin]] has suggested Saturn, Uranus, and Neptune as advantageous locations for colonization because their atmospheres are good sources of fusion fuels, such as [[deuterium]] and [[helium-3]]. Zubrin suggested that Saturn would be the most important and valuable as it is the closest and has an extensive satellite system. Jupiter's high gravity makes it difficult to extract gases from its atmosphere, and its strong radiation belt makes developing its system difficult.<ref name=UTSaturn/> On the other hand, fusion power has yet to be achieved, and fusion power from helium-3 is more difficult to achieve than conventional [[deuterium–tritium fusion]].<ref>{{cite news |last1=Day |first1=Dwayne | author-link = Dwayne A. Day |title=The helium-3 incantation |url=http://www.thespacereview.com/article/2834/1 |access-date=11 January 2019 |work=The Space Review |date=28 September 2015}}</ref> Jeffrey Van Cleve, Carl Grillmair, and Mark Hanna instead focus on Uranus, because the [[delta-v]] required to get helium-3 from the atmosphere into orbit is half that needed for Jupiter, and because Uranus' atmosphere is five times richer in helium than Saturn's.<ref name="He3U">{{cite web |first1=Jeffrey |last1=Van Cleve |first2=Carl |last2=Grillmair |first3=Mark |last3=Hanna |url=http://www.mines.edu/research/srr/2001abstracts/vancleve.PDF |title=Helium-3 Mining Aerostats in the Atmosphere of Uranus |archive-url=https://web.archive.org/web/20060630164712/http://www.mines.edu/research/srr/2001abstracts/vancleve.PDF|archive-date=30 June 2006 |access-date=10 May 2006}}</ref>

Jupiter's [[Galilean moons]] (Io, Europa, Ganymede, and Callisto) and Saturn's [[Titan (moon)|Titan]] are the only moons that have gravities comparable to Earth's Moon. The Moon has a 0.17g gravity; Io, 0.18g; Europa, 0.13g; Ganymede, 0.15g; Callisto, 0.13g; and Titan, 0.14g. Neptune's [[Triton (moon)|Triton]] has about half the Moon's gravity (0.08g); other [[planetary-mass moon|round moons]] provide even less (starting from Uranus' [[Titania (moon)|Titania]] and [[Oberon (moon)|Oberon]] at about 0.04g).<ref name=Kerwick/>