Moon landing

Stamp with a drawing of the first soft landed probe Luna 9, next to the first view of the lunar surface photographed by the probe.

After the unsuccessful attempt by Luna 1 to land on the Moon in 1959, the Soviet Union performed the first hard Moon landing – "hard" meaning the spacecraft intentionally crashes into the Moon – later that same year with the Luna 2 spacecraft, a feat the U.S. duplicated in 1962 with Ranger 4. Since then, twelve Soviet and U.S. spacecraft have used braking rockets (retrorockets) to make soft landings and perform scientific operations on the lunar surface, between 1966 and 1976. In 1966 the USSR accomplished the first soft landings and took the first pictures from the lunar surface during the Luna 9 and Luna 13 missions. The U.S. followed with five uncrewed Surveyor soft landings.

The Soviet Union achieved the first uncrewed lunar soil sample return with the Luna 16 probe on 24 September 1970. This was followed by Luna 20 and Luna 24 in 1972 and 1976, respectively. Following the failure at launch in 1969 of the first Lunokhod, Luna E-8 No.201, the Luna 17 and Luna 21 were successful uncrewed lunar rover missions in 1970 and 1973.

Many missions were failures at launch. In addition, several uncrewed landing missions achieved the Lunar surface but were unsuccessful, including: Luna 15, Luna 18, and Luna 23 all crashed on landing; and the U.S. Surveyor 4 lost all radio contact only moments before its landing.

More recently, other nations have crashed spacecraft on the surface of the Moon at speeds of around 8,000 kilometres per hour (5,000 mph), often at precise, planned locations. These have generally been end-of-life lunar orbiters that, because of system degradations, could no longer overcome perturbations from lunar mass concentrations ("masscons") to maintain their orbit. Japan's lunar orbiter Hiten impacted the Moon's surface on 10 April 1993. The European Space Agency performed a controlled crash impact with their orbiter SMART-1 on 3 September 2006.

Indian Space Research Organisation (ISRO) performed a controlled crash impact with its Moon Impact Probe (MIP) on 14 November 2008. The MIP was an ejected probe from the Indian Chandrayaan-1 lunar orbiter and performed remote sensing experiments during its descent to the lunar surface.

The Chinese lunar orbiter Chang'e 1 executed a controlled crash onto the surface of the Moon on 1 March 2009. The rover mission Chang'e 3 soft-landed on 14 December 2013, as did its successor, Chang'e 4, on 3 January 2019. All crewed and uncrewed soft landings had taken place on the near side of the Moon, until 3 January 2019 when the Chinese Chang'e 4 spacecraft made the first landing on the far side of the Moon.[5]

On 22 February 2019, Israeli private space agency SpaceIL launched spacecraft Beresheet on board a Falcon 9 from Cape Canaveral, Florida with the intention of achieving a soft landing. SpaceIL lost contact with the spacecraft and it crashed into the surface on 11 April 2019.[6]

Indian Space Research Organization launched Chandrayaan-2 on 22 July 2019 with landing scheduled on 6 September 2019. However, at an altitude of 2.1 km from the Moon a few minutes before soft landing, the lander lost contact with the control room.[7]

The view through the window of the Lunar Module Orion shortly after Apollo 16's landing.

A total of twelve men have landed on the Moon. This was accomplished with two US pilot-astronauts flying a Lunar Module on each of six NASA missions across a 41-month period starting 20 July 1969, with Neil Armstrong and Buzz Aldrin on Apollo 11, and ending on 14 December 1972 with Gene Cernan and Jack Schmitt on Apollo 17. Cernan was the last man to step off the lunar surface.

All Apollo lunar missions had a third crew member who remained on board the command module. The last three missions included a drivable lunar rover, the Lunar Roving Vehicle, for increased mobility.

To get to the Moon, a spacecraft must first leave Earth's gravity well; currently, the only practical means is a rocket. Unlike airborne vehicles such as balloons and jets, a rocket can continue accelerating in the vacuum outside the atmosphere.

Upon approach of the target moon, a spacecraft will be drawn ever closer to its surface at increasing speeds due to gravity. In order to land intact it must decelerate to less than about 160 kilometres per hour (99 mph) and be ruggedized to withstand a "hard landing" impact, or it must decelerate to negligible speed at contact for a "soft landing" (the only option for humans). The first three attempts by the U.S. to perform a successful hard Moon landing with a ruggedized seismometer package in 1962 all failed.[8] The Soviets first achieved the milestone of a hard lunar landing with a ruggedized camera in 1966, followed only months later by the first uncrewed soft lunar landing by the U.S.

The speed of a crash landing on its surface is typically between 70 and 100% of the escape velocity of the target moon, and thus this is the total velocity which must be shed from the target moon's gravitational attraction for a soft landing to occur. For Earth's Moon, the escape velocity is 2.38 kilometres per second (1.48 mi/s).[9] The change in velocity (referred to as a delta-v) is usually provided by a landing rocket, which must be carried into space by the original launch vehicle as part of the overall spacecraft. An exception is the soft moon landing on Titan carried out by the Huygens probe in 2005. As the moon with the thickest atmosphere, landings on Titan may be accomplished by using atmospheric entry techniques that are generally lighter in weight than a rocket with equivalent capability.

The Soviets succeeded in making the first crash landing on the Moon in 1959.[10] Crash landings[11] may occur because of malfunctions in a spacecraft, or they can be deliberately arranged for vehicles which do not have an onboard landing rocket. There have been many such Moon crashes, often with their flight path controlled to impact at precise locations on the lunar surface. For example, during the Apollo program the S-IVB third stage of the Saturn V rocket as well as the spent ascent stage of the Lunar Module were deliberately crashed on the Moon several times to provide impacts registering as a moonquake on seismometers that had been left on the lunar surface. Such crashes were instrumental in mapping the internal structure of the Moon.

To return to Earth, the escape velocity of the Moon must be overcome for the spacecraft to escape the gravity well of the Moon. Rockets must be used to leave the Moon and return to space. Upon reaching Earth, atmospheric entry techniques are used to absorb the kinetic energy of a returning spacecraft and reduce its speed for safe landing. These functions greatly complicate a moon landing mission and lead to many additional operational considerations. Any moon departure rocket must first be carried to the Moon's surface by a moon landing rocket, increasing the latter's required size. The Moon departure rocket, larger moon landing rocket and any Earth atmosphere entry equipment such as heat shields and parachutes must in turn be lifted by the original launch vehicle, greatly increasing its size by a significant and almost prohibitive degree.

The intense efforts devoted in the 1960s to achieving first an uncrewed and then ultimately a human Moon landing become easier to understand in the political context of its historical era. World War II had introduced many new and deadly innovations including blitzkrieg-style surprise attacks used in the invasion of Poland and Finland, and in the attack on Pearl Harbor; the V-2 rocket, a ballistic missile which killed thousands in attacks on London and Antwerp; and the atom bomb, which killed hundreds of thousands in the atomic bombings of Hiroshima and Nagasaki. In the 1950s, tensions mounted between the two ideologically opposed superpowers of the United States and the Soviet Union that had emerged as victors in the conflict, particularly after the development by both countries of the hydrogen bomb.

The first image of another world from space, returned by Luna 3, showed the far side of the Moon in October 1959.

Willy Ley wrote in 1957 that a rocket to the Moon "could be built later this year if somebody can be found to sign some papers".[12] On 4 October 1957, the Soviet Union launched Sputnik 1 as the first artificial satellite to orbit the Earth and so initiated the Space Race. This unexpected event was a source of pride to the Soviets and shock to the U.S., who could now potentially be surprise attacked by nuclear-tipped Soviet rockets in under 30 minutes. Also, the steady beeping of the radio beacon aboard Sputnik 1 as it passed overhead every 96 minutes was widely viewed on both sides as effective propaganda to Third World countries demonstrating the technological superiority of the Soviet political system compared to that of the U.S. This perception was reinforced by a string of subsequent rapid-fire Soviet space achievements. In 1959, the R-7 rocket was used to launch the first escape from Earth's gravity into a solar orbit, the first crash impact onto the surface of the Moon, and the first photography of the never-before-seen far side of the Moon. These were the Luna 1, Luna 2, and Luna 3 spacecraft.

A 1963 conceptual model of the Apollo Lunar Excursion Module

The U.S. response to these Soviet achievements was to greatly accelerate previously existing military space and missile projects and to create a civilian space agency, NASA. Military efforts were initiated to develop and produce mass quantities of intercontinental ballistic missiles (ICBMs) that would bridge the so-called missile gap and enable a policy of deterrence to nuclear war with the Soviets known as mutual assured destruction or MAD. These newly developed missiles were made available to civilians of NASA for various projects (which would have the added benefit of demonstrating the payload, guidance accuracy and reliabilities of U.S. ICBMs to the Soviets).

While NASA stressed peaceful and scientific uses for these rockets, their use in various lunar exploration efforts also had secondary goal of realistic, goal-oriented testing of the missiles themselves and development of associated infrastructure, just as the Soviets were doing with their R-7.

After the fall of the Soviet Union in 1991, historical records were released to allow the true accounting of Soviet lunar efforts. Unlike the U.S. tradition of assigning a particular mission name in advance of a launch, the Soviets assigned a public "Luna" mission number only if a launch resulted in a spacecraft going beyond Earth orbit. The policy had the effect of hiding Soviet Moon mission failures from public view. If the attempt failed in Earth orbit before departing for the Moon, it was frequently (but not always) given a "Sputnik" or "Cosmos" Earth-orbit mission number to hide its purpose. Launch explosions were not acknowledged at all.

Artist's portrayal of a Ranger spacecraft right before impact

One of the last photos of the Moon transmitted by Ranger 8 right before impact

In contrast to Soviet lunar exploration triumphs in 1959, success eluded initial U.S. efforts to reach the Moon with the Pioneer and Ranger programs. Fifteen consecutive U.S. uncrewed lunar missions over a six-year period from 1958 to 1964 all failed their primary photographic missions;[13][14] however, Rangers 4 and 6 successfully repeated the Soviet lunar impacts as part of their secondary missions.[15][16]

Failures included three U.S. attempts[8][15][17] in 1962 to hard land small seismometer packages released by the main Ranger spacecraft. These surface packages were to use retrorockets to survive landing, unlike the parent vehicle, which was designed to deliberately crash onto the surface. The final three Ranger probes performed successful high altitude lunar reconnaissance photography missions during intentional crash impacts between 2.62 and 2.68 kilometres per second (9,400 and 9,600 km/h).[18][19][20]

Model of Luna 16 Moon soil sample return lander

Model of Soviet Lunokhod automatic Moon rover

The Luna 9 spacecraft, launched by the Soviet Union, performed the first successful soft Moon landing on 3 February 1966. Airbags protected its 99 kilograms (218 lb) ejectable capsule which survived an impact speed of over 15 metres per second (54 km/h; 34 mph).[24] Luna 13 duplicated this feat with a similar Moon landing on 24 December 1966. Both returned panoramic photographs that were the first views from the lunar surface.[25]

Luna 16 was the first robotic probe to land on the Moon and safely return a sample of lunar soil back to Earth.[26] It represented the first lunar sample return mission by the Soviet Union, and was the third lunar sample return mission overall, following the Apollo 11 and Apollo 12 missions. This mission was later successfully repeated by Luna 20 (1972) and Luna 24 (1976).

In 1970 and 1973 two Lunokhod ("Moonwalker") robotic lunar rovers were delivered to the Moon, where they successfully operated for 10 and 4 months respectively, covering 10.5 km (Lunokhod 1) and 37 km (Lunokhod 2). These rover missions were in operation concurrently with the Zond and Luna series of Moon flyby, orbiter and landing missions.

Launch of Surveyor 1.

Pete Conrad, commander of Apollo 12, stands next to Surveyor 3 lander. In the background is the Apollo 12 lander, Intrepid.

The U.S. robotic Surveyor program was part of an effort to locate a safe site on the Moon for a human landing and test under lunar conditions the radar and landing systems required to make a true controlled touchdown. Five of Surveyor's seven missions made successful uncrewed Moon landings. Surveyor 3 was visited two years after its Moon landing by the crew of Apollo 12. They removed parts of it for examination back on Earth to determine the effects of long-term exposure to the lunar environment.

Within four months of each other in early 1966 the Soviet Union and the United States had accomplished successful Moon landings with uncrewed spacecraft. To the general public both countries had demonstrated roughly equal technical capabilities by returning photographic images from the surface of the Moon. These pictures provided a key affirmative answer to the crucial question of whether or not lunar soil would support upcoming crewed landers with their much greater weight.

However, the Luna 9 hard landing of a ruggedized sphere using airbags at a 50-kilometre-per-hour (31 mph) ballistic impact speed had much more in common with the failed 1962 Ranger landing attempts and their planned 160-kilometre-per-hour (99 mph) impacts than with the Surveyor 1 soft landing on three footpads using its radar-controlled, adjustable-thrust retrorocket. While Luna 9 and Surveyor 1 were both major national accomplishments, only Surveyor 1 had reached its landing site employing key technologies that would be needed for a crewed flight. Thus as of mid-1966, the United States had begun to pull ahead of the Soviet Union in the so-called Space Race to land a man on the Moon.

A timeline of the space race between 1957 and 1975, with missions from the US and USSR.

Advances in other areas were necessary before crewed spacecraft could follow uncrewed ones to the surface of the Moon. Of particular importance was developing the expertise to perform flight operations in lunar orbit. Ranger, Surveyor and initial Luna Moon landing attempts all flew directly to the surface without a lunar orbit. Such direct ascents use a minimum amount of fuel for uncrewed spacecraft on a one-way trip.

In contrast, crewed vehicles need additional fuel after a lunar landing to enable a return trip back to Earth for the crew. Leaving this massive amount of required Earth-return fuel in lunar orbit until it is used later in the mission is far more efficient than taking such fuel down to the lunar surface in a Moon landing and then hauling it all back into space yet again, working against lunar gravity both ways. Such considerations lead logically to a lunar orbit rendezvous mission profile for a crewed Moon landing.

Accordingly, beginning in mid-1966 both the U.S. and U.S.S.R. naturally progressed into missions featuring lunar orbit as a prerequisite to a crewed Moon landing. The primary goals of these initial uncrewed orbiters were extensive photographic mapping of the entire lunar surface for the selection of crewed landing sites and, for the Soviets, the checkout of radio communications gear that would be used in future soft landings.

An unexpected major discovery from initial lunar orbiters were vast volumes of dense materials beneath the surface of the Moon's maria. Such mass concentrations ("mascons") can send a crewed mission dangerously off course in the final minutes of a Moon landing when aiming for a relatively small landing zone that is smooth and safe. Mascons were also found over a longer period of time to greatly disturb the orbits of low-altitude satellites around the Moon, making their orbits unstable and forcing an inevitable crash on the lunar surface in the relatively short period of months to a few years.

Controlling the location of impact for spent lunar orbiters can have scientific value. For example, in 1999 the NASA Lunar Prospector orbiter was deliberately targeted to impact a permanently shadowed area of Shoemaker Crater near the lunar south pole. It was hoped that energy from the impact would vaporize suspected shadowed ice deposits in the crater and liberate a water vapor plume detectable from Earth. No such plume was observed. However, a small vial of ashes from the body of pioneer lunar scientist Eugene Shoemaker was delivered by the Lunar Prospector to the crater named in his honor – currently the only human remains on the Moon.

Luna 10 became the first spacecraft to orbit the Moon on 3 April 1966.

Zond mounted on top stage of Proton booster in assembly hangar

It is possible to aim a spacecraft from Earth so it will loop around the Moon and return to Earth without entering lunar orbit, following the so-called free return trajectory. Such circumlunar loop missions are simpler than lunar orbit missions because rockets for lunar orbit braking and Earth return are not required. However, a crewed circumlunar loop trip poses significant challenges beyond those found in a crewed low-Earth-orbit mission, offering valuable lessons in preparation for a crewed Moon landing. Foremost among these are mastering the demands of re-entering the Earth's atmosphere upon returning from the Moon.

Inhabited Earth-orbiting vehicles such as the Space Shuttle return to Earth from speeds of around 7,500 m/s (27,000 km/h). Due to the effects of gravity, a vehicle returning from the Moon hits Earth's atmosphere at a much higher speed of around 11,000 m/s (40,000 km/h). The g-loading on astronauts during the resulting deceleration can be at the limits of human endurance even during a nominal reentry. Slight variations in the vehicle flight path and reentry angle during a return from the Moon can easily result in fatal levels of deceleration force.

Achieving a crewed circumlunar loop flight prior to a crewed lunar landing became a primary goal of the Soviets with their Zond spacecraft program. The first three Zonds were robotic planetary probes; after that, the Zond name was transferred to a completely separate human spaceflight program. The initial focus of these later Zonds was extensive testing of required high-speed reentry techniques. This focus was not shared by the U.S., who chose instead to bypass the stepping stone of a crewed circumlunar loop mission and never developed a separate spacecraft for this purpose.

Initial crewed spaceflights in the early 1960s placed a single person in low Earth orbit during the Soviet Vostok and U.S. Mercury programs. A two-flight extension of the Vostok program known as Voskhod effectively used Vostok capsules with their ejection seats removed to achieve Soviet space firsts of multiple person crews in 1964 and spacewalks in early 1965. These capabilities were later demonstrated by the U.S. in ten Gemini low Earth orbit missions throughout 1965 and 1966, using a totally new second-generation spacecraft design that had little in common with the earlier Mercury. These Gemini missions went on to prove techniques for orbital rendezvous and docking crucial to a crewed lunar landing mission profile.

After the end of the Gemini program, the Soviet Union began flying their second-generation Zond crewed spacecraft in 1967 with the ultimate goal of looping a cosmonaut around the Moon and returning him or her immediately to Earth. The Zond spacecraft was launched with the simpler and already operational Proton launch rocket, unlike the parallel Soviet human Moon landing effort also underway at the time based on third-generation Soyuz spacecraft requiring development of the advanced N-1 booster. The Soviets thus believed they could achieve a crewed Zond circumlunar flight years before a U.S. human lunar landing and so score a propaganda victory. However, significant development problems delayed the Zond program and the success of the U.S. Apollo lunar landing program led to the eventual termination of the Zond effort.

Like Zond, Apollo flights were generally launched on a free return trajectory that would return them to Earth via a circumlunar loop if a service module malfunction failed to place them in lunar orbit. This option was implemented after an explosion aboard the Apollo 13 mission in 1970, which is the only crewed circumlunar loop mission flown to date.

Zond 5 was the first spacecraft to carry life from Earth to the vicinity of the Moon and return, initiating the final lap of the Space Race with its payload of tortoises, insects, plants, and bacteria. Despite the failure suffered in its final moments, the Zond 6 mission was reported by Soviet media as being a success as well. Although hailed worldwide as remarkable achievements, both these Zond missions flew off-nominal reentry trajectories resulting in deceleration forces that would have been fatal to humans.

As a result, the Soviets secretly planned to continue uncrewed Zond tests until their reliability to support human flight had been demonstrated. However, due to NASA's continuing problems with the lunar module, and because of CIA reports of a potential Soviet crewed circumlunar flight in late 1968, NASA fatefully changed the flight plan of Apollo 8 from an Earth-orbit lunar module test to a lunar orbit mission scheduled for late December 1968.

In early December 1968 the launch window to the Moon opened for the Soviet launch site in Baikonur, giving the USSR their final chance to beat the US to the Moon. Cosmonauts went on alert and asked to fly the Zond spacecraft then in final countdown at Baikonur on the first human trip to the Moon. Ultimately, however, the Soviet Politburo decided the risk of crew death was unacceptable given the combined poor performance to that point of Zond/Proton and so scrubbed the launch of a crewed Soviet lunar mission. Their decision proved to be a wise one, since this unnumbered Zond mission was destroyed in another uncrewed test when it was finally launched several weeks later.

By this time flights of the third generation U.S. Apollo spacecraft had begun. Far more capable than the Zond, the Apollo spacecraft had the necessary rocket power to slip into and out of lunar orbit and to make course adjustments required for a safe reentry during the return to Earth. The Apollo 8 mission carried out the first human trip to the Moon on 24 December 1968, certifying the Saturn V booster for crewed use and flying not a circumlunar loop but instead a full ten orbits around the Moon before returning safely to Earth. Apollo 10 then performed a full dress rehearsal of a crewed Moon landing in May 1969. This mission orbited within 47,400 feet (14.4 km) of the lunar surface, performing necessary low-altitude mapping of trajectory-altering mascons using a factory prototype lunar module too heavy to land. With the failure of the robotic Soviet sample return Moon landing attempt Luna 15 in July 1969, the stage was set for Apollo 11.

Progress in space exploration has recently broadened the phrase moon landing to include other moons in the Solar System as well. The Huygens probe of the Cassini–Huygens mission to Saturn performed a successful moon landing on Titan in 2005. Similarly, the Soviet probe Phobos 2 came within 120 mi (190 km) of performing a moon landing on Mars' moon Phobos in 1989 before radio contact with that lander was suddenly lost. A similar Russian sample return mission called Fobos-Grunt ("grunt" means "soil" in Russian) launched in November 2011, but stalled in low Earth orbit. There is widespread interest in performing a future moon landing on Jupiter's moon Europa to drill down and explore the possible liquid water ocean beneath its icy surface.[64]

After the failure of the Vikram lander of Chandrayaan-2, the Indian Space Research Organisation (ISRO) plans to re-attempt a soft landing with a third lunar exploration mission, Chandrayaan-3. It is scheduled to launch in late 2021 or early 2022.[65]

The Lunar Polar Exploration Mission is a robotic space mission concept by ISRO and Japan's space agency JAXA[66][67] that would send a lunar rover and lander to explore south pole region of the Moon in 2024.[68][69][70] JAXA is likely to provide launch service using the future H3 rocket, along with responsibility for the rover. ISRO would be responsible for the lander.[67][71]

Russia's Luna-Glob 25 is expected to be launched in May 2021.[72][73]

Many conspiracists hold that the Apollo Moon landings were a hoax;[74] however, empirical evidence is readily available to show that human Moon landings did occur. Anyone on Earth with an appropriate laser and telescope system can bounce laser beams off three retroreflector arrays left on the Moon by Apollo 11,[75] 14 and 15, verifying deployment of the Lunar Laser Ranging Experiment at historically documented Apollo Moon landing sites and so proving equipment constructed on Earth was successfully transported to the surface of the Moon. In addition, in August 2009 NASA's Lunar Reconnaissance Orbiter began to send back high resolution photos of the Apollo landing sites. These photos show the large descent stages of the six Apollo Lunar Modules which were left behind, the tracks of the three Lunar Roving Vehicles, and the paths left by the twelve astronauts as they walked in the lunar dust.[76]In 2016, then President of the United States, Barack Obama, acknowledged that the Moon landing was not a hoax and publicly thanked the members of the television show Mythbusters for publicly proving as much in season 6 episode 2.[77]

• List of Apollo astronauts
• Lunar Escape Systems
• Robert Goddard
• Soyuz 7K-L1
• Zond program
• First on the Moon (disambiguation)

• James Gleick, "Moon Fever" [review of Oliver Morton, The Moon: A History of the Future; Apollo's Muse: The Moon in the Age of Photography, an exhibition at the Metropolitan Museum of Art, New York City, 3 July – 22 September 2019; Douglas Brinkley, American Moonshot: John F. Kennedy and the Great Space Race; Brandon R. Brown, The Apollo Chronicles: Engineering America's First Moon Missions; Roger D. Launius, Reaching for the Moon: A Short History of the Space Race; Apollo 11, a documentary film directed by Todd Douglas Miller; and Michael Collins, Carrying the Fire: An Astronaut's Journeys (50th Anniversary Edition)], The New York Review of Books, vol. LXVI, no. 13 (15 August 2019), pp. 54–58. "'If we can put a man on the moon, why can's we...?' became a cliché even before Apollo succeeded.... Now... the missing predicate is the urgent one: why can't we stop destroying the climate of our own planet?... I say leave it [the moon] alone for a while." (pp. 57–58.)

• NASA's page on Moon landings, missions, etc. (includes information on other space agencies' missions.)
• Moon missions (United States) at Curlie
• Project Apollo Archive Flickr Gallery: an independently organized collection of high-res photos for the Moon Landing and the Apollo Missions.