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Space explorationis thediscoveryandexplorationofouter spaceby means ofspace technology.[1]Physical exploration of space is conducted both byhuman spaceflightsand byrobotic spacecraft.

While the observation of objects in space, known asastronomy, predates reliablerecorded history, it was the development of large and relatively efficientrocketsduring the early 20th century that allowed physical space exploration to become a reality. Common rationales for exploring space include advancing scientific research, uniting different nations, ensuring the future survival of humanity and developing military and strategic advantages against other countries.

Space exploration has often been used as a proxy competition for geopolitical rivalries such as theCold War. The early era of space exploration was driven by a "Space Race" between theSoviet Unionand theUnited States, the launch of the first man-made object to orbit theEarth, the USSR'sSputnik 1, on 4 October 1957, and the firstMoonlanding by the AmericanApollo 11craft on 20 July 1969 are often taken as the boundaries for this initial period. TheSoviet space programachieved many of the first milestones, including the first living being in orbit in 1957, the firsthuman spaceflight(Yuri GagarinaboardVostok 1) in 1961, the firstspacewalk(byAleksei Leonov) on 18 March 1965, thefirst automatic landingon another celestial body in 1966, and the launch of the firstspace station(Salyut 1) in 1971.

After the first 20 years of exploration, focus shifted from one-off flights to renewable hardware, such as theSpace Shuttle program, and from competition to cooperation as with theInternational Space Station(ISS).

With the substantial completion of the ISS[2]followingSTS-133in March 2011, plans for space exploration by the USA remain in flux.Constellation, a Bush Administration program for a return to the Moon by 2020[3]was judged inadequately funded and unrealistic byan expert review panelreporting in 2009.[4]The Obama Administration proposed a revision of Constellation in 2010 to focus on the development of the capability for crewed missions beyondlow earth orbit(LEO), envisioning extending the operation of theISSbeyond 2020, transferring the development of launch vehicles for human crews fromNASAto the private sector, and developing technology to enable missions to beyond LEO, such asEarth/Moon L1, the Moon,Earth/Sun L2, near-earth asteroids, andPhobosor Mars orbit.[5]As of March 2011, the US Senate and House of Representatives are still working towards a compromise NASA funding bill, which will probably terminate Constellation and fund development of aheavy lift launch vehicle(HLLV).[6]In the 2000s, the People's Republic of China initiated asuccessful manned spaceflight program, while theEuropean Union, Japan, andIndiahave also planned future manned space missions. China, Russia, Japan, and India have advocated manned missions to the Moon during the 21st century, while the European Union has advocatedmanned missions to both the Moon and Marsduring the 21st century. From the 1990s onwards, private interests began promotingspace tourismand then private space exploration of the Moon (seeGoogle Lunar X Prize).

The first steps of putting a man-made object into space were taken by German scientists duringWorld War IIwhile testing theV-2rocket, which became the first man-made object in space on 3 October 1942 with the launching of theA-4. After the war, the U.S.used German scientistsand their captured rockets in programs for both military and civilian research. The first scientific exploration from space was the cosmic radiation experiment[which?]launched by the U.S. on a V-2 rocket on 10 May 1946.[citation needed]The first images of Earth taken from space followed the same year[2][7]while thefirst animal experimentsaw fruit flies lifted into space in 1947, both also on modified V-2s launched by Americans. Starting in 1947, the Soviets, also with the help of German teams, launched sub-orbital V-2 rockets and their own variant, theR-1, including radiation and animal experiments on some flights. Thesesuborbitalexperiments only allowed a very short time in space which limited their usefulness.

First flights

The first successful orbital launch was of theSovietunmannedSputnik 1("Satellite 1")mission on 4 October 1957. The satellite weighed about 83kg (184 pounds), and is believed to have orbited Earth at a height of about 250km (160mi). It had two radio transmitters (20 and 40MHz), which emitted "beeps" that could be heard by radios around the globe. Analysis of the radio signals was used to gather information about the electron density of the ionosphere, while temperature and pressure data was encoded in the duration of radio beeps. The results indicated that the satellite was not punctured by ameteoroid. Sputnik 1 was launched by anR-7rocket. It burned up upon re-entry on 3 January 1958.

This success led to an escalation of the Americanspace program, which unsuccessfully attempted to launcha Vanguard satelliteinto orbit two months later. On 31 January 1958, the U.S. successfully orbitedExplorer 1on a Juno rocket. In the meantime, the Soviet dogLaikabecame the first animal in orbit on 3 November 1957.

First human flights

The first successful human spaceflight wasVostok 1("East 1"), carrying 27 year old RussiancosmonautYuri Gagarinon 12 April 1961. The spacecraft completed one orbit around the globe, lasting about 1 hour and 48 minutes. Gagarin's flight resonated around the world; it was a demonstration of the advancedSoviet space programand it opened an entirely new era in space exploration:human spaceflight.

The U.S. first launched a person into space within a month ofVostok 1withAlan Shepard's suborbital flight inMercury-Redstone 3. Orbital flight was achieved by the United States whenJohn Glenn'sMercury-Atlas 6orbited the Earth on 20 February 1962.

Valentina Tereshkova, the first woman in space, orbited the Earth 48 times aboardVostok 6on 16 June 1963.

China first launched a person into space 42 years after the launch of Vostok 1, on 15 October 2003, with the flight ofYang Liweiaboard theShenzhou 5(Spaceboat 5) spacecraft.

First planetary explorations

The first artificial object to reach another celestial body wasLuna 2in 1959.[8]The first automatic landing on another celestial body was performed byLuna 9[9]in 1966.Luna 10became the first artificial satellite of the Moon.[10]The first manned landing on another celestial body was performed byApollo 11in its lunar landing on 20 July 1969.

The first successful interplanetary flyby was the 1962Mariner 2flyby ofVenus(closest approach 34,773 kilometers). Flybys for the other planets were first achieved in 1965 forMarsbyMariner 4, 1973 forJupiterbyPioneer 10, 1974 forMercurybyMariner 10, 1979 forSaturnbyPioneer 11, 1986 forUranusbyVoyager 2, and 1989 forNeptuneby Voyager 2.

The first interplanetary surface mission to return at least limited surface data from another planet was the 1970 landing ofVenera 7on Venus which returned data to earth for 23 minutes. In 1971 theMars 3mission achieved the first soft landing on Mars returning data for almost 20 seconds. Later much longer duration surface missions were achieved, including over 6 years of Mars surface operation byViking 1from 1975 to 1982 and over 2 hours of transmission from the surface of Venus byVenera 13in 1982, the longest ever Soviet planetary surface mission.

Key people in early space exploration

The dream of stepping into the outer reaches of the Earth's atmosphere was driven by the fiction ofJules Verne[11]

HYPERLINK "http://en.wikipedia.org/wiki/Space_exploration" \l "cite_note-12" [12]

HYPERLINK "http://en.wikipedia.org/wiki/Space_exploration" \l "cite_note-13" [13]andH.G.Wells,[14]and rocket technology was developed to try to realise this vision. The GermanV-2was the first rocket to travel into space, overcoming the problems of thrust and material failure. During the final days of World War II this technology was obtained by both the Americans and Soviets as were its designers. The initial driving force for further development of the technology was a weapons race for intercontinental ballistic missiles (ICBMs) to be used as long-range carriers for fastnuclear weapondelivery, but in 1961 whenUSSRlaunched the first man into space, the U.S. declared itself to be in a "Space Race" with the Soviets.

Apollo 11was thespaceflightthatlandedthe first humans on theMoon, AmericansNeil ArmstrongandBuzz Aldrin, on July 20, 1969, at 20:18UTC. Armstrong became the first to step onto the lunar surface six hours later on July 21 at 02:56 UTC. Armstrong spent about two and a half hours outside the spacecraft, Aldrin slightly less, and together they collected 47.5 pounds (21.5kg) of lunar material for return to Earth. A third member of the mission,Michael Collins, piloted thecommand spacecraftalone in lunar orbit until Armstrong and Aldrin returned to it just under a day later for the trip back to Earth. TheNational Aeronautics and Space Administration(NASA) is the agency of theUnited States governmentthat is responsible for the nation's civilianspace programand foraeronauticsandaerospaceresearch.

PresidentDwight D. Eisenhowerestablished the National Aeronautics and Space Administration (NASA) in 1958[5]with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. TheNational Aeronautics and Space Actwas passed on July 29, 1958, disestablishing NASA's predecessor, theNational Advisory Committee for Aeronautics(NACA). The new agency became operational on October 1, 1958.[6]

HYPERLINK "http://en.wikipedia.org/wiki/NASA" \l "cite_note-NacaNASA-7" [7]Since that time, most U.S. space exploration efforts have been led by NASA, including theApollomoon-landingmissions, theSkylabspace station, and later theSpace Shuttle. Currently, NASA is supporting theInternational Space Stationand is overseeing the development of theOrion Multi-Purpose Crew VehicleandCommercial Crewvehicles. The agency is also responsible for theLaunch Services Program(LSP) which provides oversight of launch operations and countdown management for unmanned NASA launches. Most recently, NASA announced a newSpace Launch Systemthat it said would take the agency's astronauts farther into space than ever before and lay the cornerstone for future human space exploration efforts by the U.S.[8]

HYPERLINK "http://en.wikipedia.org/wiki/NASA" \l "cite_note-NASA_Briefing_on_Deep_Space_Launch_System-9" [9]

HYPERLINK "http://en.wikipedia.org/wiki/NASA" \l "cite_note-Space_.26_Cosmos-10" [10]NASA science is focused on better understanding Earth through theEarth Observing System,[11]advancingheliophysicsthrough the efforts of the Science Mission Directorate's Heliophysics Research Program,[12]exploring bodies throughout theSolar Systemwith advanced robotic missions such asNew Horizons,[13]and researchingastrophysicstopics, such as theBig Bang, through theGreat Observatoriesand associated programs.[14]NASA shares data with various national and international organizations such as from theGreenhouse Gases Observing Satellite.

NASA'sSpace Shuttle Program, officially called theSpace Transportation System(STS), was the United States government'smannedlaunch vehicleprogram from 1981 to 2011, with the program officially beginning in 1972. The wingedSpace Shuttle orbiterwas launched vertically, usually carrying four to sevenastronauts(although two and eight have been carried) and up to 50,000lb(22,700kg) ofpayloadintolow Earth orbit(LEO). When its mission was complete, theShuttlecould independently move itself out of orbit using itsOrbital Maneuvering System(it oriented itself heads down and tail first, firing its OMS engines, thus slowing it down) andre-entertheEarth's atmosphere. During descent and landing the orbiter acted as a re-entry vehicle and a glider, using its RCS system and flight control surfaces to maintain altitude until it made an unpowered landing at either Kennedy Space Center or Edwards Air Force Base.

The Shuttle is the only winged manned spacecraft to have achieved orbit and land, and the only reusable manned space vehicle that has ever made multiple flights into orbit (the Russian shuttleBuranwas very similar and had the same capabilities but made only one unmanned spaceflight before it was cancelled). Itsmissionsinvolved carrying large payloads to various orbits (including segments to be added to theInternational Space Station), providing crew rotation for the International Space Station, and performing service missions. The orbiter also recoveredsatellitesand other payloads (e.g. from the ISS) from orbit and returned them to Earth, though its use in this capacity was rare. Each vehicle was designed with a projected lifespan of 100 launches, or 10 years' operational life.

The program formally commenced in 1972, although the concept had been explored since the late 1960s, and was the sole focus of NASA's manned operations after the finalApolloandSkylabflights in the mid-1970s. The Shuttle was originally conceived of and presented to the public in 1972 as a 'Space Truck' which would, among other things, be used to build a United States space station inlow Earth orbitduring the 1980s and then be replaced by a new vehicle by the early 1990s. When the concept of the U.S. space station evolved into that of theInternational Space Station, which suffered from long delays and design changes before it could be completed, the service life of the Space Shuttle was extended several times until 2011 when it was finally retired serving at least 15 years longer than it was originally designed to do. In 2004, according to the President George W. Bush'sVision for Space Exploration, use of the Space Shuttle was to be focused almost exclusively on completing assembly of the ISS, which was far behind schedule at that point.

The first experimental orbiter "Enterprise", built only forinitial atmospheric landing tests (ALT), was delivered for those test flights in 1976, and the first launch to space took place on April 12, 1981, withColumbiaflying onSTS-1. The Space Shuttle program finished with its last mission,STS-135flown byAtlantis, in July 2011, retiring the final Shuttle in the fleet. The Space Shuttle program formally ended on August 31, 2011.[1]Retirement of the Shuttle - the most complex vehicle ever built - ended the era in which all of America's varied space activities were performed by one craft -or even one organization. Functions performed by the Shuttle for 30 years will be done by not one but many different spacecraft currently flying or in advanced development. Secret military missions are being flown by the US Air Force's "highly successful" unmanned mini-space plane, theX-37B[citation needed]. By 2012, cargo supply to the International Space Station began to be flown by privately owned commercial craft under NASA'sCommercial Resupply Servicesby SpaceX's successfully tested and partially reusableDragon spacecraft, followed by Orbital Sciences'Cygnus spacecraftin late 2013. Crew service to the ISS will be flown exclusively by the RussianSoyuzwhile NASA works on theCommercial Crew Development program. For missions beyondlow Earth orbit, NASA is building theSpace Launch Systemand theOrion spacecraft.

TheSpace Transportation System(STS) was a proposed system of reusable manned space vehicles envisioned byNASAin 1969 to support extended operations beyond theApollo program. (NASA appropriated the name for itsSpace Shuttle Program, the only component of the proposal to survive Congressional funding approval.) The purpose of the system was twofold: to reduce the cost of spaceflight by replacing the current method of launching "capsules" on expendable rockets with reusable spacecraft; and to support ambitious follow-on programs including permanent orbitingspace stationsaround the Earth and Moon, and a human landing mission to Mars.

In February 1969, PresidentRichard Nixonappointed a Space Task Group headed by Vice PresidentSpiro Agnewto recommend human space projects beyond Apollo. The group responded in September with the outline of the STS, and three different program levels of effort culminating with a human Mars landing by 1983 at the earliest, and by the end of the twentieth century at the latest. The system's major components consisted of:

a permanentspace stationmodule designed for 6 to 12 occupants, in a 270-nautical-mile (500km) Earth orbit, and as a permanent lunar orbit station. Modules could be combined in Earth orbit to create a 50 to 100 person permanent station.

a chemically fueledlow-Earth orbit(100-to-270-nautical-mile (190 to 500km))shuttle a chemically fueledspace tugto move crew and equipment between Earth orbits (includinggeosynchronous), and which could be adapted for use as a lunar orbit-to-surface shuttle

anuclear-poweredvehicle using theNERVAengine to ferry crew, spacecraft and supplies between low Earth orbit and lunar orbit, geosynchronous orbit, or to other planets in the solar system.

The tug and ferry vehicles would be of a modular design, allowing them to be clustered and/orstagedfor large payloads or interplanetary missions. The system would be supported by permanent Earth and lunar orbitalpropellant depots.[1]TheSaturn Vmight still have been used as aheavy lift launch vehiclefor the nuclear ferry and space station modules. A special "Mars Excursion Module" would be the only remaining vehicle necessary for a humanMarslanding.

As Apollo accomplished its objective of landing the first men on the Moon, political support for further manned space activities began to wane, which was reflected in unwillingness of the Congress to provide funding for most of these extended activities. Based on this, Nixon rejected all parts of the program except theSpace Shuttlewhich inherited the STS name. As funded, the Shuttle was greatly scaled back from its planned degree of reusabliilty, and deferred in time. The Shuttle first flew in 1981, and was retired in 2011.

A second part of the system,Space Station Freedom, was approved in the early 1980s and announced in 1984 by presidentRonald Reagan. However, this also became politically unviable by 1993, and was replaced with theInternational Space Station, with substantial contribution byRussia. The ISS was completed in 2010.2.

The International Space Station (ISS) is a space station, or a habitable artificial satellite in low Earth orbit. The ninth space station to be inhabited by crews, it follows the Soviet and later Russian Salyut, Almaz, and Mir stations, andSkylab from the U.S. The ISS is a modular structure whose first component was launched in 1998.[7] Now the largest artificial body in orbit, it can often be seen at the appropriate time with the naked eye from Earth.[8] The ISS consists of pressurised modules, external trusses, solar arrays and other components. ISS components have been launched by American Space Shuttles as well as Russian Proton and Soyuz rockets.[9] Budget constraints led to the merger of three space station projects with the Japanese Kib module and Canadian robotics. In 1993 the partially built components for a Soviet/Russian space station Mir-2, the proposed American Freedom, and the proposed EuropeanColumbus merged into a single multinational programme.[9] The ISS is arguably the most expensive single item ever constructed.[10]

The ISS serves as a microgravity and space environment research laboratory in which crew members conduct experiments in biology, human biology, physics, astronomy, meteorology and other fields.[11][12][13] The station is suited for the testing of spacecraft systems and equipment required for missions to the Moon and Mars.[14]

Since the arrival of Expedition 1 on 2 November 2000, the station has been continuously occupied for 13 years and 51 days, the longest continuous human presence in space. (In 2010, the station surpassed the previous record of almost 10 years (or 3,634 days) held by Mir.) The station is serviced by a variety of visiting spacecraft: Soyuz, Progress, the Automated Transfer Vehicle, the H-II Transfer Vehicle,[15] Dragon, and Cygnus. It has been visited by astronauts and cosmonauts from 15 different nations.[16]

The ISS programme is a joint project among five participating space agencies: NASA, Roskosmos, JAXA, ESA, and CSA.[15][17] The ownership and use of the space station is established by intergovernmental treaties and agreements.[18] The station is divided into two sections, the Russian Orbital Segment (ROS) and the United States Orbital Segment (USOS), which is shared by many nations. The ISS maintains an orbit with an altitude of between 330 km (205 mi) and 435 km (270 mi) by means of reboost manoeuvres using the engines of the Zvezda module or visiting spacecraft. It completes 15.50 orbits per day.[19] The ISS is funded until 2020, and may operate until 2028.[20][21][22] The Russian Federal Space Agency, Roskosmos (RKA) has proposed using the ISS to commission modules for a new space station, called OPSEK, before the remainder of the ISS is deorbited. According to the original Memorandum of Understanding between NASA and Rosaviakosmos, the International Space Station was intended to be a laboratory, observatory and factory in space. It was also planned to provide transportation, maintenance, and act as a staging base for possible future missions to the Moon, Mars and asteroids.[23] In the 2010 United States National Space Policy, the ISS was given additional roles of serving commercial, diplomatic[24] and educational purposes.[25]Aspaceplaneis a vehicle that operates as anaircraftin Earth's atmosphere, as well as aspacecraftwhen it is inspace. It combines features of an aircraft and a spacecraft, which can be thought of as an aircraft that can endure and maneuver in the vacuum of space or likewise a spacecraft that can fly like an airplane. Typically, it takes the form of a spacecraft equipped withwings, althoughlifting bodieshave been designed and tested as well. The propulsion to reach space may be purely rocket based or may use the assistance of air-breathing engines.

However, for anaircraftto successfully fly inEarth's atmosphere, it must be able to successfullycontrol,powerandsustainits own flight.[1]If a spaceplane cannot successfully control itself, power itself or sustain its flight oncereentering Earth's atmosphere, it cannot be considered successful ataviationin theatmosphere.

Only five spaceplanes have successfully flown to date, havingreentered Earth's atmosphere,returnedtoEarth, andsafely landed theX-15,Space Shuttle,Buran,SpaceShipOne, andX-37. All five arerocket gliders. Onlyrocketsandrocket-powered aircrafthave thus far succeeded in reachingspace. Two of these five (X-15 and SpaceShipOne) arerocket-powered aircraft, having been carried up to an altitude of several tens of thousands of feet by an atmospheric aircraftmother shipbefore release. Three (Space Shuttle, Buran, and X-37) arevertical takeoff horizontal landing (VTHL)vehicles relying uponrocket liftfor the ascent phase in reaching space andatmospheric liftforreentry,descentandlanding. All three of theorbitalspaceplanes successfully flown to date utilize aVTHL(vertical takeoff, horizontal landing) design. They include the pilotedUnited StatesSpace Shuttleand two unmanned spaceplanes: the late-1980sSovietBuranand the early-2010sBoeing X-37.

The early-1980sBOR-4(subscale test vehicle for theSpiral spaceplanethat was subsequently cancelled) was aspacecraftthat did successfullyreenter the atmosphereand fly like anaircraft. But it was not designed tosustain atmospheric flight. It was designed to stop flying, open aparachuteand thensplash in the ocean.

These vehicles have usedwingsto provideaerobrakingto return from orbit and to providelift, allowing them to land on arunwaylike conventional aircraft. These vehicles are still designed to ascend to orbit vertically underrocketpower like conventionalexpendable launch vehicles. One drawback of spaceplanes is that they have a significantly smallerpayload fractionthan a ballistic design with the same takeoff weight. This is in part due to the weight of the wings around 9-12% of the weight of the atmospheric flight weight of the vehicle. This significantly reduces the payload size, but the reusability is intended to offset this disadvantage.

While all spaceplanes have usedatmospheric liftfor thereentry phase, none to date have succeeded in a design that relies on aerodynamic lift for the ascent phase in reaching space (excluding amother shipfirst stage). Efforts such as theSilbervogelandX-30/X-33have all failed to materialize into a vehicle capable of successfully reaching space. ThePegasuswinged booster has had many successful flights to deploy orbital payloads, but since its aerodynamic vehicle component operates only as a booster, and not operate in space as a spacecraft, it is not typically considered to be a spaceplane.[citation needed]On the other hand,OREX[6]is a test vehicle ofHOPE-Xand launched into 450km LEO usingH-IIin 1994. OREX succeeded to reenter, but it was only hemispherical head of HOPE-X, that is, not plane-shaped.

Other spaceplane designs aresuborbital, requiring far less energy for propulsion, and can use the vehicle's wings to provide lift for theascent tospace in addition to the rocket. As of 2010, the only such craft to have successfully flown to and fromspace, back toearth, have been theNorth American X-15andSpaceShipOne. Neither of these craft was capable of entering orbit. The X-15 and SpaceShipOne both began their independent flight only after being lifted to high altitude by a carrier aircraft.

Scaled CompositesandVirgin Galacticunveiled on December 7, 2009, theSpaceShipTwospace plane, theVSS Enterprise, and itsWhiteKnightTwomothership, "Eve". SpaceShipTwo is designed to carry two pilots and six passengers on suborbital flights. On 29 April 2013, after three years of unpowered testing, the spacecraft successfully performed its first powered test flight.[7]XCOR Aerospacesigned a $30 million contract withYecheon Astro Space Centerto build and lease itsLynx Mark IIspaceplane, which would be designed to take off from a runway under its own rocket power, and to reach the same altitude and speed range as SpaceShipOne and SpaceShipTwo, due to the fact that Lynx is propelled by higher specific impulse fuels. Lynx is designed to only carry a pilot and one passenger, although tickets are expected to be around half those quoted for Virgin Galactic services.[8]Hyflex[9]

HYPERLINK "http://en.wikipedia.org/wiki/Spaceplane" \l "cite_note-10" [10]was a miniaturized suborbital demonstrator ofHOPE-Xlaunched in 1996. Hyflex flew to 110km altitude and succeeded inatmospheric reentry, subsequently achievinghypersonic flight. Though Hyflex achieved acontrolledaircraft descent, it was not designed for a plannedaircraft landing, the engineers opting instead for asplashdownwithout aparachute. The Hyflex that flew failed to recover and sank in thePacific Ocean.

What Is The Future Of Space Travel?

Chemical rockets may be a dead end because of their extreme inefficiency. Just to put the space shuttle into earth orbit (to reach 17,500 MPH), the rockets need to carry 15 times its weight in fuel and thats considered extremely efficient among other chemical-based rocket systems. To escape earths gravitational pull and explore our solar system (to reach 25,000 MPH), you would need significantly more fuel. Occasionally, space agencies can mitigate some of the problems by using gravitational assists from planets. They use a planets gravity well to slingshot a probe toward its destination, significantly speeding it up.

The problem with this solution is one of availability. To take advantage of a planets gravity well, the planet has to be in a specific place, at a specific time. This leaves a small window which a probe would need to be launched. Some of these windows can be incredibly rare. The Voyager space probes, which explored the planets in the outer solar system, took advantage of a planet alignment that happens only once every 176 years.

Then there is the cost. The average cost to put the space shuttle into orbit is 450 million USD per mission. Thats a huge price tag just to reach low earth orbit, and its also a big part of the reason the shuttle program was scrapped. If we wanted to leave earth orbit and explore our solar system with such an inefficient technology (without gravitational assists), the problems become severely compounded. Because there arent any fuel stations in space, a spaceship has to carry all its fuel with it, fuel which is not only pricey, but heavy.

If we wanted to leave our solar system and travel to our closest neighboring star in a reasonable time frame (say, 900 years) using standard chemical-based rockets, it would require 10137kilograms of fuel that is more fuel than exists on our planet. Thus, we need to look towards developing a better, more efficient method of propulsion.

Solar sails do exactly as the name suggests; they sail on the solar wind. There is no actual wind in space because space is a vacuum, but there is something similar that a spacecraft could use to propel itself. A craft equipped with a giant sail made out of ultra-thin mirrors can harness a combination of light and high speed ejected gasses from the sun to reach incredible speeds. The pressure of the light and gasses is very small, but since there no friction in the vacuum of space, it allows that small pressure to build up over time. Given enough time, this pressure can propel a craft to a significant fraction of light speed. The time to reach top speeds could be lessened by aiming extremely powerful lasers or masers at the sails from a base on the moon or other satellite without an atmosphere.

However, a solar sail does have its drawbacks. Once far enough away from the sun (and any laser boosting stations we have setup), the craft would no longer be accelerating and instead rely on its own inertia to travel to its destination. The craft would then have to direct its sails towards the destination star to decelerate and slow down.

Solar sail spacecrafts became a reality when, back in May 2010, the Japanese launched the Ikaros probe. It successfully deployed its solar sails and is currently in a wide orbit around the sun. Its expected to reach Jupiter in a few years.

An ion thruster (or ion drive) is a lot less exciting than how it is often portrayed in science fiction books and movies. It operates on similar principle as the solar sail; using very low thrust but over an extended period of time. It achieves this thrust by ejecting charged ions, gas or plasma out of its electric engine which propels the spacecraft. This method of acceleration allows a craft to achieve a very high specific impulse. Such a craft would only work in the vacuum of space since the thrust is so low. However, the fuel required by the engine is significantly less than is required by chemical rockets which maxes out thanks to the Carnot limit (a limit on efficiency).

This technology is being heavily considered for future space missions and has already proven its feasibility in space. In 1998, NASA launched the Deep Space 1 probe which was powered by a xenon gas ion engine and was the first ion drive in space. In 2003, Japan launched the Hayabusa probe which used 4 xenon ion engines. Its mission was to rendezvous with an asteroid and collect samples. It completed its mission and returned to earth in June of 2010.

Like the solar sail, ion drives also have their drawbacks. First, they would need to carry their fuel with them. While the amount required to get the nearest star is technically feasible, it wouldnt be very practical. Travel time is another issue. While an ion drive is significantly more efficient than rocket engines, and is great for jaunts around our solar system, interstellar travel is another matter entirely. With a gravitational assist from our sun, it still would take19,000 yearsto reach Proxima Centauri with a ship using an ion engine.

We need more speed if we want to leave the confines of our solar cradle

If we wanted to get to our nearest neighboring star using the best technology available to usright now, nuclear propulsion is our best option. Its fast, proven and relatively cheap. A ship equipped with nuclear pulse propulsion and could theoretically reach 12% the speed of light. That is so fast, you could travel completely around the earth and end up back at your starting point in just under 2 seconds. Or you could travel to the moon in 13 seconds it took Apollo 11 four days to reach the moon by comparison. While it would take 19,000 years to reach Proxima Centauri with an Ion Drive, it would take a relatively manageable 35 years using nuclear pulse propulsion. A human would be able to travel to our nearest neighboring star within his or her lifetime. And it could be done with technology that already exists.

The way nuclear propulsion works sounds a bit crazy, but it is proven and it is relatively simple. Small nuclear bombs are dropped out of the back of the spacecraft which detonate. The resulting force from the explosion accelerates the craft. This is done repeatedly until the desired speed has been attained. An incredibly large, reinforced pusher plate would shield the craft from damages and radiation while dampeners would be used to mitigate the effects of G force and provide smoothacceleration.

The US military began looking into nuclear pulse propulsion back in 1958 under the project name Orion. The project was shelved in 1963 thanks to the Partial Test Ban Treaty which prevents nuclear devices being detonated in space. The idea wasnt forgotten however. In 1973, the British Interplanetary Society developed a similar concept, called Project Daedalus. Then in 1998, the nuclear engineering department at PSU began developing two improved versions of the Daedalus design known as Project Ican and Project Aimstar.

One of the obvious drawbacks to nuclear pulse propulsion is that you have to carry your fuel with you. This means carrying hundreds or thousands of small nuclear bombs. There is also the problem of ablation of the pusher plate. Repeated exposure to nuclear blasts will cause erosion if not sprayed with a special oil before each detonation. Yet another problem is nuclear fallout. This could be averted if a craft is launched from a polar region, or if a craft is launched into space using conventional rockets, then once far enough away, began using its nuclear propulsion.

The late Carl Sagan once suggested that nuclear pulse propulsion would be an excellent use for our current stockpiles of nuclear weapons.

A spacecraft equipped with a nuclear fusion engine could explore our solar system without the need to carry a large fuel supply thanks to its efficient, long-term acceleration capability. There are two ways a fusion engine could work. The first is using the energy created by a fusion reaction to generate electricity. This electricity could be used to superheat plasma which then would be ejected out the back of the craft, providing thrust. The second method would be more direct. It would use the plasma-based exhaust from the fusion reaction to provide thrust.

The drawbacks of a fusion engine are very similar to that of the ion drive. While fusion is a huge improvement over ion drives, it would be very hard to achieve the higher speeds necessary when traveling between stars. Fusion technology is also still in the experimental stage of development. The technology must overcome hurdles with plasma confinement to become viable, then a reactor would need to be miniaturized to a size manageable for a spacecraft. Currently, experimental laser-based ICF reactors are as large as football stadiums and are struggling to break even with power output.

Antimatter is the most potent fuel source that we currently know of. Its also the most efficient. Antimatter is as the name implies, matter which has its charges reversed. When antimatter comes into contact with normal matter, the two annihilate one another in a ferocious blast of pure energy. A piece of antimatter the size of a small coin contains enough energy to propel a fully loaded space shuttle into orbit. Once in orbit, NASA claims that a trip to Mars would only require as little as 10 milligrams worth of antimatter. n engine using antimatter is pretty simple in its operation. A beam of anti-electrons is released into an engine core where it annihilates the surface of a metal plate. This creates a small explosion which propels the craft forward. Another proposed design uses a sail, similar to the solar sail described above. A cloud of anti-particles is released which then reacts explosively with surface of the sail. This reaction can propel the craft to incredible speeds. According to NASA, an antimatter powered craft would be able to reach speeds up to 70% the speed of light. That means we could reach Proxima Centauri in just under 6 years.

The drawbacks of using antimatter are production and containment. Antimatter is a byproduct of atom-smashing tests done at particle accelerators. Tests which are very expensive to operate. If we wanted to produce a single gram of antimatter, it would cost over a trillion dollars. Containment is also another issue. Since antimatter violently reacts when it comes into contact with normal matter, it would have to be stored in vacuum containers at incredibly low temperatures, suspended by strong magnetic fields. This becomes a challenge because anti-electrons (positrons) repel each other, often explosively. Some solutions have been proposed, one suggests that by combining positrons with electrons, researchers can create an element called positronium which can theoretically store the anti-electrons indefinitely.

Faster than light travel is just the stuff of science fiction, right? After all, didnt Einstein say that the speed of light is the ultimate speed limit? Not necessarily, claim physicists. The devil is in the details. According to physics, there are ways around the universes ultimate speed limit. These technical loopholes could theoretically and potentially allow us to race a beam of light,and win.

NASA researchers know that nothing can accelerate faster than the speed of light, but they also know there is no such restriction regarding space itself. Spacetime has no such limit on how fast it can move, and it is believed that spacetime exceeded the speed of light during the expansion of the big bang. Researchers at NASAs advanced propulsion division have been wondering if spacetime can make a repeat performance.

A warp drive, once the stuff of science fiction, could travel faster than light by riding on a wave of spacetime. It creates this wave by compressing the spacetime in front of the ship and expanding the spacetime behind it. A ship then sits in the middle of this wave, and is propelled through space. Since the ship itself isnt moving, and only the spacetime around the ship is moving, no laws of physics are broken.

At NASA Eagleworks, researchers have begun to attempt to prove the concept of warp drive with lab experiments. There, the researchers set up a mini warp drive called the White-Juday Warp Field Interferometer. The experiment seeks to generate a very tiny instance of a warp field. A warp field that is so small, it is only expected to perturb spacetime by one part in 10 million. While the results will be underwhelming if successful, it will be existence for proof of concept. The location for the new project is the facility that was built for the Apollo program, the very same one that put astronauts on the moon.

The first scientific paper which took warp drives seriously was written in 1994 by Mexican physicist Miguel Alcubierre. Alcubierres paper called for enormous energies to power his theoretical warp drive. The mass-energy equivalent of Jupiter. Harnessing that kind of energy is impractical and virtually impossible, so his paper went largely ignored.

In October of 2012, at the 100 Year Starship Symposium, NASA researcher Harold White gave a presentation where he announced that he discovered loopholes in the mathematical equations. Loopholes which brought down the energy requirements to levels much lower than previously thought. He calculated that by altering the design of the warp engine and the ship itself, he could get the energy requirements down to just a few thousand pounds of mass. This takes warp drives out of the realm of science fiction and puts them in the realm of the plausible.