Editing Space exploration (section)

==Targets of exploration==
Starting in the mid-20th century probes and then human missions were sent into Earth orbit, and then on to the Moon. Also, probes were sent throughout the known Solar System, and into Solar orbit. Uncrewed spacecraft have been sent into orbit around Saturn, Jupiter, Mars, Venus, and Mercury by the 21st century, and the most distance active spacecraft, ''Voyager 1'' and ''2'' traveled beyond 100 times the Earth-Sun distance. The instruments were enough though that it is thought they have left the Sun's heliosphere, a sort of bubble of particles made in the Galaxy by the Sun's [[solar wind]].

===The Sun===
The [[Sun]] is a major focus of space exploration. Being above the atmosphere in particular and Earth's magnetic field gives access to the solar wind and infrared and ultraviolet radiations that cannot reach Earth's surface. The Sun generates most [[space weather]], which can affect power generation and transmission systems on Earth and interfere with, and even damage, satellites and space probes. Numerous spacecraft dedicated to observing the Sun, beginning with the [[Apollo Telescope Mount]], have been launched and still others have had solar observation as a secondary objective. [[Parker Solar Probe]], launched in 2018, will approach the Sun to within 1/9th the orbit of Mercury.

===Mercury===
{{main|Exploration of Mercury}}
[[File:MESSENGER EN0108828359M.png|thumb|A ''MESSENGER'' image from 18,000&nbsp;km showing a region about 500&nbsp;km across (2008)]]
[[Mercury (planet)|Mercury]] remains the least explored of the [[Terrestrial planets]]. As of May 2013, the [[Mariner 10]] and ''[[MESSENGER]]'' missions have been the only missions that have made close observations of Mercury. ''MESSENGER'' entered orbit around Mercury in March 2011, to further investigate the observations made by Mariner 10 in 1975 (Munsell, 2006b). A third mission to Mercury, scheduled to arrive in 2025, [[BepiColombo]] is to include two [[space probe|probes]]. BepiColombo is a joint mission between Japan and the [[European Space Agency]]. ''MESSENGER'' and BepiColombo are intended to gather complementary data to help scientists understand many of the mysteries discovered by Mariner 10's [[Gravitational slingshot|flybys]].

Flights to other planets within the Solar System are accomplished at a cost in energy, which is described by the net change in velocity of the spacecraft, or [[delta-v]]. Due to the relatively high delta-v to reach Mercury and its proximity to the Sun, it is difficult to explore and orbits around it are rather unstable.

===Venus===
{{Main|Observations and explorations of Venus}}
[[Venus]] was the first target of interplanetary flyby and lander missions and, despite one of the most hostile surface environments in the Solar System, has had more landers sent to it (nearly all from the Soviet Union) than any other planet in the Solar System. The first flyby was the 1961&nbsp;[[Venera 1]], though the 1962&nbsp;[[Mariner 2]]&nbsp;was the first flyby to successfully return data. Mariner 2 has been followed by several other flybys by multiple space agencies often as part of missions using a Venus flyby to provide a [[Gravity assist|gravitational assist]] en route to other celestial bodies. In 1967, [[Venera 4]] became the first probe to enter and directly examine the atmosphere of Venus. In 1970, [[Venera 7]] became the first successful lander to reach the surface of Venus and by 1985 it had been followed by eight additional successful Soviet Venus landers which provided images and other direct surface data. Starting in 1975, with the Soviet orbiter [[Venera 9]], some ten successful orbiter missions have been sent to Venus, including later missions which were able to map the surface of Venus using [[radar]] to pierce the obscuring atmosphere.

===Earth===
{{Main|Earth observation satellite}}
[[File:TIROS-1-Earth.png|244x244px|thumb|First television image of Earth from space, taken by [[TIROS-1]] (1960)]]Space exploration has been used as a tool to understand Earth as a celestial object. Orbital missions can provide data for Earth that can be difficult or impossible to obtain from a purely ground-based point of reference.

For example, the existence of the [[Van Allen radiation belt]]s was unknown until their discovery by the United States' first artificial satellite, ''[[Explorer 1]]''. These belts contain radiation trapped by Earth's magnetic fields, which currently renders construction of habitable space stations above 1000&nbsp;km impractical. Following this early unexpected discovery, a large number of Earth observation satellites have been deployed specifically to explore Earth from a space-based perspective. These satellites have significantly contributed to the understanding of a variety of Earth-based phenomena. For instance, the [[Ozone depletion|hole in the ozone layer]] was found by an artificial satellite that was exploring Earth's atmosphere, and satellites have allowed for the discovery of archeological sites or geological formations that were difficult or impossible to otherwise identify.

==== Moon ====
{{Main|Exploration of the Moon}}
[[File:Apollo 16 LM Orion.jpg|thumbnail|[[Apollo 16]] LEM Orion, the [[Lunar Roving Vehicle]] and astronaut [[John Young (astronaut)|John Young]] (1972)]]
The [[Moon]] was the first celestial body to be the object of space exploration. It holds the distinctions of being the first remote celestial object to be flown by, orbited, and landed upon by spacecraft, and the only remote celestial object ever to be visited by humans.

In 1959, the Soviets obtained the first images of the [[far side of the Moon]], never previously visible to humans. The U.S. exploration of the Moon began with the [[Ranger 4]] impactor in 1962. Starting in 1966, the Soviets successfully deployed a number of [[Lander (spacecraft)|landers]] to the Moon which were able to obtain data directly from the Moon's surface; just four months later, ''[[Surveyor 1]]'' marked the debut of a successful series of U.S. landers. The Soviet uncrewed missions culminated in the [[Lunokhod programme|Lunokhod program]] in the early 1970s, which included the first uncrewed rovers and also successfully [[Sample return mission|brought lunar soil samples to Earth]] for study. This marked the first (and to date the only) automated return of extraterrestrial soil samples to Earth. Uncrewed exploration of the Moon continues with various nations periodically deploying lunar orbiters. China's [[Chang'e 4]] in 2019 and [[Chang'e 6]] in 2024 achieved the world's first landing and sample return on the [[far side of the Moon]]. India's [[Chandrayaan-3]] in 2023 achieved the world's first landing on the [[lunar south pole]] region.

Crewed exploration of the Moon began in 1968 with the [[Apollo 8]] mission that successfully orbited the Moon, the first time any extraterrestrial object was orbited by humans. In 1969, the [[Apollo 11]] mission marked the first time humans set foot upon another world. Crewed exploration of the Moon did not continue for long. The [[Apollo 17]] mission in 1972 marked the sixth landing and the most recent human visit. [[Artemis II]] is scheduled to complete a crewed flyby of the Moon in 2025, and [[Artemis III]] will perform the first lunar landing since Apollo 17 with it scheduled for launch no earlier than 2026. Robotic missions are still pursued vigorously.

===Mars===
{{Main|Exploration of Mars}}[[File:Spirit rover tracks.jpg|thumb|220x220px|Surface of Mars by the [[Mars Exploration Rover|''Spirit'' rover]] (2004)]]
The exploration of [[Mars]] has been an important part of the space exploration programs of the Soviet Union (later Russia), the United States, Europe, Japan and India. Dozens of [[robotic spacecraft]], including [[orbiter]]s, [[Lander (spacecraft)|landers]], and [[rover (space exploration)|rovers]], have been launched toward Mars since the 1960s. These missions were aimed at gathering data about current conditions and answering questions about the history of Mars. The questions raised by the scientific community are expected to not only give a better appreciation of the Red Planet but also yield further insight into the past, and possible future, of Earth.

The exploration of Mars has come at a considerable financial cost with roughly two-thirds of all spacecraft destined for Mars failing before completing their missions, with some failing before they even began. Such a high failure rate can be attributed to the complexity and large number of variables involved in an interplanetary journey, and has led researchers to jokingly speak of ''The Great Galactic Ghoul''<ref name="space-232">{{cite web |last=Dinerman |first=Taylor |url=http://www.thespacereview.com/article/232/1 |title=Is the Great Galactic Ghoul losing his appetite? |work=The space review |date=27 September 2004 |access-date=27 March 2007 }}</ref> which subsists on a diet of Mars probes. This phenomenon is also informally known as the "[[Mars Curse]]".<ref name="cnn-20061223">{{cite news |last=Knight |first=Matthew |url=http://www.cnn.com/2006/TECH/science/12/23/mwonders.mars/index.html |title=Beating the curse of Mars |work=Science & Space |access-date=27 March 2007 }}</ref> In contrast to overall high failure rates in the exploration of Mars, [[India]] has become the first country to achieve success of its maiden attempt. India's [[Mars Orbiter Mission]] (MOM)<ref>{{cite news |date=24 September 2014 |title=India becomes first Asian nation to reach Mars orbit, joins elite global space club |url=https://www.washingtonpost.com/world/india-is-the-first-asian-nation-to-touch-mars-orbit-joins-elite-global-space-club/2014/09/23/b6bc6992-a432-4f1e-87ad-5d6fc4da3460_story.html |access-date=24 September 2014 |newspaper=The Washington Post |quote=India became the first Asian nation to reach the Red Planet when its indigenously made unmanned spacecraft entered the orbit of Mars on Wednesday.}}</ref><ref>{{cite news |url=https://edition.cnn.com/2014/09/23/world/asia/mars-india-orbiter/index.html |title=India's spacecraft reaches Mars orbit ... and history |work=CNN |date=24 September 2014 |access-date= |quote=India's Mars Orbiter Mission successfully entered Mars' orbit Wednesday morning, becoming the first nation to arrive on its first attempt and the first Asian country to reach the Red Planet. |last = Park|first = Madison }}</ref><ref name="NYT-20140924-GH">{{cite news |last=Harris |first=Gardiner |title=On a Shoestring, India Sends Orbiter to Mars on Its First Try |url=https://www.nytimes.com/2014/09/25/world/asia/on-a-shoestring-india-sends-orbiter-to-mars.html |date=24 September 2014 |work=[[The New York Times]]|access-date=25 September 2014 }}</ref> is one of the least expensive interplanetary missions ever undertaken with an approximate total cost of {{INR}} 450 [[Crore]] ({{US$|73 million}}).<ref name="ibtimes20131105">{{cite news |url=http://www.ibtimes.co.in/india-successfully-launches-first-mission-to-mars-pm-congratulates-isro-team-photos-519719 |title=India Successfully Launches First Mission to Mars; PM Congratulates ISRO Team |work=[[International Business Times]] |date=5 November 2013 |access-date=13 October 2014}}</ref><ref name="ndtv20131105">{{cite news |url=http://www.ndtv.com/article/cheat-sheet/india-s-450-crore-mission-to-mars-to-begin-today-10-facts-441410 |title=India's 450-crore mission to Mars to begin today: 10 facts |work=[[NDTV]] |first=Abhinav |last=Bhatt |date=5 November 2013 |access-date=13 October 2014}}</ref> The first mission to Mars by any Arab country has been taken up by the United Arab Emirates. Called the [[Emirates Mars Mission]], it was launched on 19 July 2020 and went into orbit around Mars on 9 February 2021. The uncrewed exploratory probe was named "Hope Probe" and was sent to Mars to study its atmosphere in detail.<ref>{{Cite web |title=Hope Mars Probe |url=http://mbrsc.ae/en/page/mars-probe |publisher=Mohammed Bin Rashid Space Centre |website=mbrsc.ae |access-date=22 July 2016 |archive-date=25 July 2016 |archive-url=https://web.archive.org/web/20160725185416/http://mbrsc.ae/en/page/mars-probe |url-status=dead }}</ref>

==== Phobos ====
{{Main|Exploration of Phobos}}
The Russian space mission [[Fobos-Grunt]], which launched on 9 November 2011, experienced a failure leaving it stranded in [[low Earth orbit]].<ref name="noburn">{{cite web |url=http://www.satobs.org/seesat/Nov-2011/0069.html |title=Phobos-Grunt – serious problem reported |first=Ted |last=Molczan |publisher=[[SeeSat-L]] |date=9 November 2011 |access-date=9 November 2011 }}</ref> It was to begin exploration of the [[Phobos (moon)|Phobos]] and Martian circumterrestrial orbit, and study whether the moons of Mars, or at least Phobos, could be a "trans-shipment point" for spaceships traveling to Mars.<ref name="yt-W0cUvK0Dgy8">{{cite web|url=https://www.youtube.com/watch?v=W0cUvK0Dgy8 |title=Project Phobos-Grunt |publisher=YouTube |date=22 August 2006 |access-date=24 May 2012 }}</ref><!-- Remove groundless conjecture: It will study Phobos as a target of colonization, too.{{Citation needed|date=November 2008}}-->

===Asteroids===
{{Main|Exploration of the asteroids}}
[[File:Dawn-image-070911.jpg|thumb|Asteroid [[4 Vesta]], imaged by the [[Dawn (spacecraft)|''Dawn'' spacecraft]] (2011)]]
Until the advent of [[Spaceflight|space travel]], objects in the [[asteroid belt]] were merely pinpricks of light in even the largest telescopes, their shapes and terrain remaining a mystery. Several asteroids have now been visited by probes, the first of which was ''[[Galileo (spacecraft)|Galileo]]'', which flew past two: [[951 Gaspra]] in 1991, followed by [[243 Ida]] in 1993. Both of these lay near enough to ''Galileo'''s planned trajectory to Jupiter that they could be visited at acceptable cost. The first landing on an asteroid was performed by the ''[[NEAR Shoemaker]]'' probe in 2000, following an orbital survey of the object, [[433 Eros]]. The dwarf planet [[Ceres (dwarf planet)|Ceres]] and the asteroid [[4 Vesta]], two of the three largest asteroids, were visited by NASA's [[Dawn (spacecraft)|''Dawn'' spacecraft]], launched in 2007.

''[[Hayabusa (spacecraft)|Hayabusa]]'' was a [[robotic spacecraft]] developed by the [[Japan Aerospace Exploration Agency]] to [[Sample return mission|return a sample of material]] from the small near-Earth asteroid [[25143 Itokawa]] to Earth for further analysis. Hayabusa was launched on 9 May 2003 and rendezvoused with Itokawa in mid-September 2005. After arriving at Itokawa, ''Hayabusa'' studied the asteroid's shape, spin, topography, color, composition, density, and history. In November 2005, it landed on the asteroid twice to collect samples. The spacecraft returned to Earth on 13 June 2010.

===Jupiter===
{{Main|Exploration of Jupiter}}
[[File:Io Tupan Patera.jpg|thumb|[[Tupan Patera]] on Jupiter's moon Io]]
The exploration of [[Jupiter]] has consisted solely of a number of automated NASA spacecraft visiting the planet since 1973. A large majority of the missions have been "flybys", in which detailed observations are taken without the probe landing or entering orbit; such as in [[Pioneer program|Pioneer]] and [[Voyager program|Voyager]] programs. The ''[[Galileo spacecraft|Galileo]]'' and ''[[Juno spacecraft|Juno]]'' spacecraft are the only spacecraft to have entered the planet's orbit. As Jupiter is believed to have only a relatively small rocky core and no real solid surface, a landing mission is precluded.

Reaching Jupiter from Earth requires a delta-v of 9.2&nbsp;km/s,<ref name="delta-v">{{cite web |last=Wong |first=Al |date=28 May 1998 |url=http://www2.jpl.nasa.gov/galileo/faqnav.html |archive-url=https://web.archive.org/web/19970105184300/http://www.jpl.nasa.gov/galileo/faqnav.html |url-status=dead |archive-date=5 January 1997 |title=Galileo FAQ: Navigation |publisher=NASA |access-date=28 November 2006 }}</ref> which is comparable to the 9.7&nbsp;km/s delta-v needed to reach low Earth orbit.<ref name="pma-delta">{{cite web |last=Hirata |first=Chris |url=http://www.pma.caltech.edu/~chirata/deltav.html |title=Delta-V in the Solar System |publisher=California Institute of Technology |access-date=28 November 2006 |archive-url=https://web.archive.org/web/20060715015836/http://www.pma.caltech.edu/~chirata/deltav.html |archive-date=15 July 2006 }}</ref> Fortunately, [[Gravitational slingshot|gravity assists]] through [[planetary flyby]]s can be used to reduce the energy required at launch to reach Jupiter, albeit at the cost of a significantly longer flight duration.<ref name="delta-v" />

Jupiter has 95 [[Moons of Jupiter|known moons]], many of which have relatively little known information about them.

===Saturn===
{{Main|Exploration of Saturn}}
[[Saturn]] has been explored only through uncrewed spacecraft launched by NASA, including one mission (''[[Cassini–Huygens]]'') planned and executed in cooperation with other space agencies. These missions consist of flybys in 1979 by ''[[Pioneer 11]]'', in 1980 by ''[[Voyager 1]]'', in 1982 by ''[[Voyager 2]]'' and an orbital mission by the ''Cassini'' spacecraft, which lasted from 2004 until 2017.

Saturn has at least 62 [[Moons of Saturn|known moons]], although the exact number is debatable since Saturn's rings are made up of vast numbers of independently orbiting objects of varying sizes. The largest of the moons is [[Titan (moon)|Titan]], which holds the distinction of being the only moon in the Solar System with an atmosphere denser and thicker than that of Earth. Titan holds the distinction of being the only object in the Outer Solar System that has been explored with a lander, the ''Huygens'' probe deployed by the ''Cassini'' spacecraft.

===Uranus===
{{Main|Exploration of Uranus}}
The exploration of [[Uranus]] has been entirely through the ''[[Voyager 2]]'' spacecraft, with no other visits currently planned. Given its [[axial tilt]] of 97.77°, with its polar regions exposed to sunlight or darkness for long periods, scientists were not sure what to expect at Uranus. The closest approach to Uranus occurred on 24 January 1986. ''Voyager 2'' studied the planet's unique atmosphere and [[magnetosphere]]. ''Voyager 2'' also examined its [[Rings of Uranus|ring system]] and the [[moons of Uranus]] including all five of the previously known moons, while discovering an additional ten previously unknown moons.

Images of Uranus proved to have a uniform appearance, with no evidence of the dramatic storms or atmospheric banding evident on Jupiter and Saturn. Great effort was required to even identify a few clouds in the images of the planet. The magnetosphere of Uranus, however, proved to be unique, being profoundly affected by the planet's unusual axial tilt. In contrast to the bland appearance of Uranus itself, striking images were obtained of the Moons of Uranus, including evidence that [[Miranda (moon)|Miranda]] had been unusually geologically active.

===Neptune===
{{main|Exploration of Neptune}}The exploration of Neptune began with the 25 August 1989 ''[[Voyager 2]]'' flyby, the sole visit to the system as of {{CURRENTYEAR}}. The possibility of a [[Neptune Orbiter]] has been discussed, but no other missions have been given serious thought.

Although the extremely uniform appearance of Uranus during ''Voyager 2''{{'}}s visit in 1986 had led to expectations that Neptune would also have few visible atmospheric phenomena, the spacecraft found that Neptune had obvious banding, visible clouds, [[Aurora (astronomy)|auroras]], and even a conspicuous [[Great Dark Spot|anticyclone storm system]] rivaled in size only by Jupiter's [[Great Red Spot]]. Neptune also proved to have the fastest winds of any planet in the Solar System, measured as high as 2,100&nbsp;km/h.<ref name="Suomi1991">{{cite journal |last1=Suomi |first1=V. E. |last2=Limaye |first2=S. S. |last3=Johnson |first3=D. R. |year=1991 |title=High winds of Neptune: A possible mechanism |journal=Science |volume=251 |issue=4996 |pages=929–932 |bibcode=1991Sci...251..929S |doi=10.1126/science.251.4996.929 |pmid=17847386 |s2cid=46419483}}</ref> ''Voyager 2'' also examined [[Rings of Neptune|Neptune's ring]] and [[Moons of Neptune|moon system]]. It discovered 900 complete rings and additional partial ring "arcs" around Neptune. In addition to examining Neptune's three previously known moons, ''Voyager 2'' also discovered five previously unknown moons, one of which, [[Proteus (moon)|Proteus]], proved to be the last largest moon in the system. Data from ''Voyager 2'' supported the view that Neptune's largest moon, [[Triton (moon)|Triton]], is a captured [[Kuiper belt]] object.<ref name="Agnor06">{{cite journal |last1=Agnor |first1=C. B. |last2=Hamilton |first2=D. P. |year=2006 |title=Neptune's capture of its moon Triton in a binary-planet gravitational encounter |journal=Nature |volume=441 |issue=7090 |pages=192–194 |bibcode=2006Natur.441..192A |doi=10.1038/nature04792 |pmid=16688170 |s2cid=4420518}}</ref>

===Pluto===
{{main|Pluto#Exploration}}The [[dwarf planet]] Pluto presents significant challenges for spacecraft because of its great distance from Earth (requiring high velocity for reasonable trip times) and small mass (making capture into orbit difficult at present). ''[[Voyager 1]]'' could have visited Pluto, but controllers opted instead for a close flyby of Saturn's moon Titan, resulting in a trajectory incompatible with a Pluto flyby. ''[[Voyager 2]]'' never had a plausible trajectory for reaching Pluto.<ref name="jpl-faq">{{cite web |url=http://voyager.jpl.nasa.gov/faq.html |title=Voyager Frequently Asked Questions |access-date=8 September 2006 |publisher=Jet Propulsion Laboratory |date=14 January 2003 |url-status=dead |archive-url=https://web.archive.org/web/20110721050617/http://voyager.jpl.nasa.gov/faq.html |archive-date=21 July 2011}}</ref>

After an intense political battle, a mission to Pluto dubbed ''[[New Horizons]]'' was granted funding from the United States government in 2003.<ref name="s4p">{{cite web |last=Britt |first=Robert Roy |date=26 February 2003 |title=Pluto mission gets green light at last |url=http://www.space4peace.org/articles/plutomissiongetsok.htm |access-date=26 December 2013 |work=space.com |publisher=Space4Peace.org}}</ref> ''New Horizons'' was launched successfully on 19 January 2006. In early 2007 the craft made use of a [[gravity assist]] from [[Jupiter]]. Its closest approach to Pluto was on 14 July 2015; scientific observations of Pluto began five months prior to closest approach and continued for 16 days after the encounter.

===Kuiper Belt Objects===
The ''New Horizons'' mission also performed a flyby of the small planetesimal [[Arrokoth]], in the [[Kuiper belt]], in 2019. This was its first extended mission.<ref>{{cite conference |title=New Horizons Kuiper Belt Extended Mission |url=http://pluto.jhuapl.edu/News-Center/Press-Conferences/2017-12-12/resources/2017_NH_AGU_PA.pdf |first1=Jim |last1=Green |first2=S. Alan |last2=Stern |date=12 December 2017 |conference=2017 AGU Fall Meeting |publisher=Applied Physics Laboratory |pages=12–15 |access-date=26 December 2018 |archive-url=https://web.archive.org/web/20181226234838/http://pluto.jhuapl.edu/News-Center/Press-Conferences/2017-12-12/resources/2017_NH_AGU_PA.pdf
|archive-date=26 December 2018 |url-status=dead |df= dmy-all}}</ref>

===Comets===
{{Main|List of missions to comets}}
[[File:Comet Hartley 2.jpg|thumb|Comet [[103P/Hartley]] (2010)]]

Although many comets have been studied from Earth sometimes with centuries-worth of observations, only a few comets have been closely visited. In 1985, the ''[[International Cometary Explorer]]'' conducted the first comet fly-by ([[21P/Giacobini-Zinner]]) before joining the [[Halley Armada]] studying the famous comet. The [[Deep Impact (spacecraft)|''Deep Impact'' probe]] smashed into [[9P/Tempel]] to learn more about its structure and composition and the [[Stardust (spacecraft)|''Stardust'' mission]] returned samples of another comet's tail. The [[Philae (spacecraft)|''Philae'' lander]] successfully landed on [[67P/Churyumov–Gerasimenko|Comet Churyumov–Gerasimenko]] in 2014 as part of the broader [[Rosetta (spacecraft)|''Rosetta'' mission]].

===Deep space exploration===
{{main|Deep space exploration}}
[[Image:Hubble ultra deep field high rez edit1.jpg|thumb|This high-resolution image of the [[Hubble Ultra Deep Field]] includes galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies, are some of the most distant galaxies to have been imaged by an optical telescope.]]

Deep space exploration is the branch of [[astronomy]], [[astronautics]] and [[space technology]] that is involved with the exploration of distant regions of outer space.<ref>{{cite web|url=http://adc.gsfc.nasa.gov/adc/education/space_ex/exploration.html |title=Space and its Exploration: How Space is Explored |work=NASA.gov |access-date=2009-07-01 |url-status=dead |archive-url=https://web.archive.org/web/20090702153058/http://adc.gsfc.nasa.gov/adc/education/space_ex/exploration.html |archive-date=2 July 2009 }}</ref> Physical exploration of space is conducted both by [[human spaceflight]]s (deep-space astronautics) and by [[robotic spacecraft]].

Some of the best candidates for future deep space engine technologies include [[anti-matter]], [[nuclear power]] and [[beam-powered propulsion|beamed propulsion]].<ref>{{cite web |url=http://www.bbc.co.uk/science/space/exploration/futurespaceflight/index.shtml |title=Future Spaceflight |work=BBC |access-date=2009-07-01 |archive-date=22 April 2009 |archive-url=https://web.archive.org/web/20090422162750/http://www.bbc.co.uk/science/space/exploration/futurespaceflight/index.shtml |url-status=dead }}</ref> Beamed propulsion, appears to be the best candidate for deep space exploration presently available, since it uses known physics and known technology that is being developed for other purposes.<ref name="Forward1996">{{cite journal |last=Forward |first=Robert L. |date=January 1996 |title=Ad Astra! |journal=Journal of the British Interplanetary Society |volume=49 |pages=23–32 |bibcode=1996JBIS...49...23F}}</ref>