Moon landing

2008/9 Schools Wikipedia Selection. Related subjects: Space transport

A moon landing is the arrival of an intact manned or unmanned spacecraft on the surface of a planet's natural satellite. The concept has been a goal of humankind since it was first appreciated that the Moon is Earth's closest large celestial body. One of the clearest early examples of the concept in fiction was Jules Verne's novel From the Earth to the Moon, written in 1865. Since the Soviet Union first succeeded in implementing the concept in 1966, this term referred to eighteen spacecraft landings on the Moon through 1976. Nine of these missions returned to Earth bearing samples of moon rocks.

The United States achieved the first manned landing on Earth's Moon as part of the Apollo 11 mission commanded by Neil Armstrong. On July 20, 1969, Armstrong, accompanied by Edwin 'Buzz' Aldrin, landed the lunar module Eagle on the surface of the Moon. Armstrong and Aldrin spent a day on the surface of the Moon before returning to Earth. A total of six such manned moon landings were carried out between 1969 and 1972.

The Soviet Union later achieved sample returns via the unmanned Luna 16, Luna 20 and Luna 24 moon landings. Since this was during the time of the Cold War, the contest to be the first on the Moon was one of the most visible facets of the space race.

Progress in space exploration has since broadened the phrase to include other moons in the solar system as well. The Huygens probe of the Cassini mission to Saturn performed a successful unmanned moon landing on Titan in 2005. Similarly, the Soviet probe Phobos 2 came within 120 miles of performing an unmanned moon landing on Mars' moon Phobos in 1989 before radio contact with that lander was suddenly lost. 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.

Scientific background

The primary concern of any moon landing is the high velocity involved that arises from the effects of gravity. In order to go to any moon, a spacecraft must first leave the gravity well of the Earth. The only practical way of accomplishing this feat is with a rocket. Unlike other airborne vehicles such as balloons or jets, only a rocket can continue to increase its speed at high altitudes in the vacuum outside the Earth's atmosphere.

Once the Earth has been left behind, a moon landing next requires a spacecraft to shed or lose at least an amount of speed equal to the escape velocity of the target moon to overcome its gravitational attraction. For Earth's Moon, this figure is 2.4 kilometers per second or around 5,000 miles per hour. This so-called 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 a moon landing on Titan such as that carried out by the Huygens probe. As the only moon with an atmosphere, landings on Titan may be accomplished by using atmospheric entry techniques that are generally lighter in weight than a rocket with equivalent capability.

Whatever method is used to slow a spacecraft as it nears a moon, the key requirement for a moon landing is to be traveling at a survivable speed upon reaching the moon's surface. Otherwise the space mission ends not in a landing but a crash. Such crashes can occur because of malfunctions in a spacecraft, or they can be deliberately arranged for vehicles that do not have an onboard landing rocket. There have been many such moon crashes. For example, during the Apollo program the S-IVB third stage of the Saturn V moon 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.

If a return to Earth is desired after a moon landing is accomplished, the escape velocities of the moon and Earth must again be overcome for the spacecraft to come to rest on the surface of the Earth. 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 to zero for 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. This necessitates optimizing the sizing of stages in the launch vehicle as well as consideration of using space rendezvous between multiple spacecraft and reaching intermediate orbits prior to landing; in particular, lunar orbit rendezvous. Thus systems engineering and logistics become major factors in the design of any moon landing mission.

Political background

The intense and expensive effort devoted in the 1960s to achieving first an unmanned and then ultimately a manned moon landing can only be understood in the political context of its historical era. World War II with its 60 million dead, half Soviet, was fresh in the memory of all adults. In the 1940s, the war had introduced many new and deadly innovations including blitzkrieg-style surprise attacks used in the invasion of Poland and in the attack on Pearl Harbour; the V-2 rocket, a ballistic missile which killed thousands in attacks on London; and the atom bomb, which killed tens 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.

On October 4, 1957, the Soviet Union launched Sputnik 1 as the first artificial satellite to orbit the Earth and so initiated the Space Age. This unexpected event was a source of pride to the Soviets and shock to the Americans. This dramatic and successful demonstration of the new R-7 Semyorka rocket on only its third test flight meant that the Soviets could use ballistic missiles carrying hydrogen bombs in a surprise attack against any target on Earth, a frightening new capability the Americans did not have. Further, 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 the American one. 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, respectively.

The American response to these Soviet achievements was to greatly accelerate previously languishing space and missile projects. 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 Mutually Assured Destruction or MAD. These newly-developed missiles were made available to civilians of the newly formed NASA space agency for various projects which would demonstrate the payload, guidance accuracy and reliabilities of American 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. The tight schedules and lofty goals selected by NASA for lunar exploration also had an undeniable element of generating counter-propaganda to show to other countries that American technological prowess was the equal and even superior to that of the Soviets.

U.S. unmanned hard landings (1958-1965)

In contrast to Soviet lunar exploration triumphs in 1959, success eluded initial American efforts to reach the Moon with the Pioneer and Ranger programs. Fifteen consecutive U.S. unmanned lunar missions over a six year period from 1958 to 1964 all failed their primary photographic missions; however Rangers 4 and 6 successfully repeated the Soviet lunar impacts as part of their secondary missions. Failures included three American attempts 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 at around 6,000 miles per hour as planned.

U.S. Mission	Mass (kg)	Launch Vehicle	Launched	Mission Goal	Mission Result
Pioneer 0	38	Thor-Able	17 Aug 1958	Lunar orbit	Failure - first stage explosion; destroyed
Pioneer 1	34	Thor-Able	11 Oct 1958	Lunar orbit	Failure - software error; reentry
Pioneer 2	39	Thor-Able	08 Nov 1958	Lunar orbit	Failure - third stage misfire; reentry
Pioneer 3	6	Juno	06 Dec 1958	Lunar flyby	Failure - first stage misfire, reentry
Pioneer 4	6	Juno	03 Mar 1959	Lunar flyby	Failure - targeting error; solar orbit
Pioneer P-1	168	Atlas-Able	24 Sep 1959	Lunar orbit	Failure - pad explosion; destroyed
Pioneer P-3	168	Atlas-Able	29 Nov 1959	Lunar orbit	Failure - payload shroud; destroyed
Pioneer P-30	175	Atlas-Able	25 Sep 1960	Lunar orbit	Failure - second stage anomaly; reentry
Pioneer P-31	175	Atlas-Able	15 Dec 1960	Lunar orbit	Failure - first stage explosion; destroyed
Ranger 1	306	Atlas - Agena	23 Aug 1961	Prototype test	Failure - upper stage anomaly; reentry
Ranger 2	304	Atlas - Agena	18 Nov 1961	Prototype test	Failure - upper stage anomaly; reentry
Ranger 3	330	Atlas - Agena	26 Jan 1962	Moon landing	Failure - booster guidance; solar orbit
Ranger 4	331	Atlas - Agena	23 Apr 1962	Moon landing	Failure - spacecraft computer; crash impact
Ranger 5	342	Atlas - Agena	18 Oct 1962	Moon landing	Failure - spacecraft power; solar orbit
Ranger 6	367	Atlas - Agena	30 Jan 1964	Lunar impact	Failure - spacecraft camera; crash impact
Ranger 7	367	Atlas - Agena	28 Jul 1964	Lunar impact	Success - returned 4308 photos, crash impact
Ranger 8	367	Atlas - Agena	17 Feb 1965	Lunar impact	Success - returned 7137 photos, crash impact
Ranger 9	367	Atlas - Agena	21 Mar 1965	Lunar impact	Success - returned 5814 photos, crash impact

Three different designs of Pioneer lunar probes were flown on three different modified ICBMs. Those flown on the Thor booster modified with an Able upper stage carried an infrared image scanning television system with a resolution of 1 milliradian to study the Moon's surface, an ionization chamber to measure radiation in space, a diaphragm/microphone assembly to detect micrometeorites, a magnetometer, and temperature-variable resistors to monitor spacecraft internal thermal conditions. The first, a mission managed by the United States Air Force, exploded during launch; all subsequent Pioneer lunar flights had NASA as the lead management organization. The next two returned to Earth and burned up upon reentry into the atmosphere after achieved maximum altitudes of around 70,000 and 900 miles, far short of the roughly 250,000 miles required to reach the vicinity of the Moon.

NASA then collaborated with the United States Army's Ballistic Missile Agency to fly two extremely small cone-shaped probes on the Juno ICBM, carrying only photocells which would be triggered by the light of the Moon and a lunar radiation environment experiment using a Geiger-Müller tube detector. The first of these reached an altitude of only around 64,000 miles, serendipitously gathering data that established the presence of the Van Allen radiation belts before reentering Earth's atmosphere. The second passed by the moon at a distance of over 37,000 miles, twice as far away as planned and too far away to trigger either of the onboard scientific instruments, yet still becoming the first American spacecraft to reach a solar orbit.

The final Pioneer lunar probe design consisted of four " paddlewheel" solar panels extending from a one-meter diameter spherical spin-stabilized spacecraft body that was equipped to take images of the lunar surface with a television-like system, estimate the Moon's mass and topography of the poles, record the distribution and velocity of micrometeorites, study radiation, measure magnetic fields, detect low frequency electromagnetic waves in space and use a sophisticated integrated propulsion system for maneuvering and orbit insertion as well. None of the four spacecraft built in this series of probes survived launch on its Atlas ICBM outfitted with an Able upper stage.

Following the unsuccessful Atlas-Able Pioneer probes, NASA's Jet Propulsion Laboratory embarked upon an unmanned spacecraft development program whose modular design could be used to support both lunar and interplanetary exploration missions. The interplanetary versions were known as Mariners; lunar versions were Rangers. JPL envisioned three versions of the Ranger lunar probes: Block I prototypes, which would carry various radiation detectors in test flights to a very high Earth orbit that came nowhere near the Moon; Block II, which would try to accomplish the first Moon landing by hard landing a seismometer package; and Block III, which would crash onto the lunar surface without any braking rockets while taking very high resolution wide-area photographs of the Moon during their descent.

The Ranger 1 and 2 Block I missions were virtually identical. Spacecraft experiments included a Lyman-alpha telescope, a rubidium-vapor magnetometer, electrostatic analyzers, medium-energy-range particle detectors, two triple coincidence telescopes, a cosmic-ray integrating ionization chamber, cosmic dust detectors, and scintillation counters. The goal was to place these Block I spacecraft in a very high Earth orbit with an apogee of 670,000 miles. From that vantage point, scientists could make direct measurements of the magnetosphere over a period of many months while engineers perfected new methods to routinely track and communicate with spacecraft over such large distances. Such practice was deemed vital to be assured of capturing high-bandwidth television transmissions from the Moon during a one-shot fifteen minute time window in subsequent Block II and Block III lunar descents. Both Block I missions suffered failures of the new Agena upper stage and never left low earth parking orbit after launch; both burned up upon reentry after only a few days.

The first attempts to perform a Moon landing took place in 1962 during the Rangers 3, 4 and 5 missions flown by the United States. All three Block II missions carried a 94 pound, two-foot diameter landing sphere (made of balsa wood) designed to withstand a 150 mile per hour impact. This lander (code-named Tonto) was designed to provide impact cushioning using an exterior blanket of crushable balsa wood and an interior filled with incompressible liquid freon. A 56 pound, one-foot diameter metal payload sphere floated and was free to rotate in a liquid freon reservoir contained in the landing sphere. This payload sphere contained six silver-cadmium batteries to power a fifty milliwatt radio transmitter, a temperature sensitive voltage controlled oscillator to measure lunar surface temperatures, and a seismometer that was designed with sensitivity high enough to detect the impact of a five pound meteorite on the opposite side of the Moon. Weight was distributed in the payload sphere so it would rotate in its liquid blanket to place the seismometer into an upright and operational position no matter what the final resting orientation of the external landing sphere. After landing plugs were to be opened allowing the freon to evaporate and the payload sphere to settle into upright contact with the landing sphere. Four pounds of water were also included to provide thermal control for the lander, absorbing heat and boiling off as low-pressure steam during the hot lunar daytime and retaining sufficient heat to allow the lander electronics to avoid freezing temperatures during the cold lunar nighttime. The batteries and water supply were sized to allow up to three months of operation for the payload sphere. Various mission constraints limited the landing site to Oceanus Procellarum on the lunar equator, which the lander ideally would reach 66 hours after launch.

No cameras were carried by the Ranger landers, and no pictures were to be captured from the lunar surface during the mission. Instead, the ten-foot-high, 730 pound Ranger Block II mother ship carried a 200 scan line television camera which was to capture images from 2,400 miles down to 37 miles during the free-fall descent to the lunar surface. The 13 pound camera was designed to transmit a picture every 10 seconds. Other instruments gathering data before the mother ship crashed onto the Moon at 6,500 miles per hour were a gamma ray spectrometer to measure overall lunar chemical composition and a radar altimeter. At eight seconds before impact and 13 miles above the lunar surface, the radar altimeter was to give a signal ejecting the landing capsule and its 236 pound solid-fueled braking rocket overboard from the Block II mother ship. The braking rocket was to slow the landing sphere to a dead stop at 1,100 feet above the surface and separate, allowing the landing sphere to free fall once more and hit the surface at a survivable speed of 100 miles per hour.

On Ranger 3, failure of the Atlas guidance system and a software error aboard the Agena upper stage combined to put the spacecraft on a course that would miss the Moon. Attempts to salvage lunar photography during a flyby of the Moon were thwarted by in-flight failure of the onboard flight computer. This was probably because of prior heat sterilization of the spacecraft by keeping it above the boiling point of water for 24 hours on the ground, to protect the Moon from being contaminated by Earth organisms. Heat sterilization was also blamed for subsequent in-flight failures of the spacecraft computer on Ranger 4 and the power subsystem on Ranger 5. Only Ranger 4 reached the Moon in an uncontrolled crash impact on the far side of the Moon.

Heat sterilization was discontinued for the final four Block III Ranger probes. These replaced the Block II landing capsule and its retrorocket with a heavier, more capable television system to support landing site selection for upcoming Apollo manned moon landing missions. Six cameras weighing a total of 350 pounds were designed to take thousands of high-altitude photographs in the final twenty minute period before crashing on the lunar surface. Camera resolution was 1,132 scan lines, far higher than the 525 lines found in a typical American 1964 home television. The final pictures taken were expected to have a resolution of around two feet. While Ranger 6 suffered a failure of this camera system and returned no photographs despite an otherwise successful flight, the subsequent Ranger 7 mission to Mare Cognitum was a complete success. Breaking the six year string of failure in American attempts to photograph the moon at close range, the Ranger 7 mission was viewed as a national turning point and instrumental in allowing the key 1965 NASA budget appropriation to pass through the United States Congress intact without a reduction in funds for the Apollo manned moon landing program. Subsequent successes with Ranger 8 and Ranger 9 further buoyed American hopes.

U.S.S.R. unmanned hard landings (1958-1966)

While American lunar exploration missions were undertaken in full view of public scrutiny, Soviet moonshots of the 1960s and 1970s were conducted under a policy of extreme governmental secrecy. Only with the coming of glasnost in the late 1980s and the fall of the Soviet Union in 1991 did historical records come to light allowing a true accounting of Soviet lunar efforts. Unlike the American tradition of assigning a particular mission name in advance of launch, the Soviets assigned a public " Luna" mission number only if a launch resulted in a spacecraft going beyond Earth orbit. 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 failure in reaching the Moon. Launch explosions were not acknowledged at all. This policy had the effect of hiding Soviet moonshot failures from public view, making their successes seem even more impressive.

U.S.S.R. Mission	Mass (kg)	Launch Vehicle	Launched	Mission Goal	Mission Result
		Semyorka - 8K72	23 Sep 1958	Lunar Impact	Failure - boooster malfunction at T+ 93 sec
		Semyorka - 8K72	12 Oct 1958	Lunar Impact	Failure - boooster malfunction at T+ 104 sec
		Semyorka - 8K72	04 Dec 1958	Lunar Impact	Failure - boooster malfunction at T+ 254 sec
Luna-1	361	Semyorka - 8K72	02 Jan 1959	Lunar Impact	Failure - missed moon, but first spacecraft to solar orbit
		Semyorka - 8K72	18 Jun 1959	Lunar Impact	Failure - boooster malfunction at T+ 153 sec
Luna-2	390	Semyorka - 8K72	12 Sep 1959	Lunar Impact	Success - first lunar impact
Luna-3	270	Semyorka - 8K72	04 Oct 1959	Lunar Flyby	Success - first photos of lunar far side
		Semyorka - 8K72	15 Apr 1960	Lunar Flyby	Failure - booster malfunction, failed to reach Earth orbit
		Semyorka - 8K72	16 Apr 1960	Lunar Flyby	Failure - boooster malfunction at T+ 1 sec
Sputnik-25		Semyorka - 8K78	04 Jan 1963	Moon landing	Failure - stranded in low Earth orbit
		Semyorka - 8K78	03 Feb 1963	Moon landing	Failure - boooster malfunction at T+ 105 sec
Luna-4	1422	Semyorka - 8K78	02 Apr 1963	Moon landing	Failure - lunar flyby at 5000 miles
		Semyorka - 8K78	21 Mar 1964	Moon landing	Failure - booster malfunction, failed to reach Earth orbit
		Semyorka - 8K78	20 Apr 1964	Moon landing	Failure - booster malfunction, failed to reach Earth orbit
Cosmos-60		Semyorka - 8K78	12 Mar 1965	Moon landing	Failure - stranded in low Earth orbit
		Semyorka - 8K78	10 Apr 1965	Moon landing	Failure - booster malfunction, failed to reach Earth orbit
Luna-5	1475	Semyorka - 8K78	09 May 1965	Moon landing	Failure - lunar impact
Luna-6	1440	Semyorka - 8K78	08 Jun 1965	Moon landing	Failure - lunar flyby at 100,000 miles
Luna-7	1504	Semyorka - 8K78	04 Oct 1965	Moon landing	Failure - lunar impact
Luna-8	1550	Semyorka - 8K78	03 Dec 1965	Moon landing	Failure - lunar impact during landing attempt
Luna-9	1580	Semyorka - 8K78	31 Jan 1966	Moon landing	Success - first lunar hard landing, numerous photos
Luna-13	1580	Semyorka - 8K78	21 Dec 1966	Moon landing	Success - second lunar hard landing, numerous photos

The Luna 9 spacecraft, launched by the Soviet Union, performed the first successful Moon landing on February 3, 1966 using the "hard landing" technique. Airbags protected its 200 pound ejectable capsule which survived an impact speed of over 30 miles per hour—the speed of many automobile accidents causing fatalities on Earth. Luna 13 duplicated this feat with a similar moon landing on December 24, 1966. Both returned panoramic photographs that were the first views from the lunar surface.

American unmanned soft landings (1966-1968)

The American robotic Surveyor program was part of an effort to locate a safe site on the Moon for a human landing and test under actual lunar conditions the radar and landing systems required to make a true controlled touchdown. Five of Surveyor's seven missions made successful unmanned moon landings.

U.S. Mission	Mass (kg)	Booster	Launched	Mission Goal	Mission Result	Landing Zone	Lat/ Lon
Surveyor 1	292	Atlas - Centaur	30 May 1966	Moon landing	Success - 11,000 pictures returned, first American Moon landing	Oceanus Procellarum	002.45S 043.22W
Surveyor 2	292	Atlas - Centaur	20 Sep 1966	Moon landing	Failure - midcourse engine malfunction, placing vehicle in unrecoverable tumble; crashed southeast of Copernicus Crater	Sinus Medii	004.00S 011.00W
Surveyor 3	302	Atlas - Centaur	20 Apr 1967	Moon landing	Success - 6,000 pictures returned; trench dug to 17.5 cm depth after 18 hr of robot arm use	Oceanus Procellarum	002.94S 336.66E
Surveyor 4	282	Atlas - Centaur	14 Jul 1967	Moon landing	Failure - radio contact lost 2.5 minutes before touchdown; perfect automated Moon landing possible but actual outcome unknown	Sinus Medii	unknown
Surveyor 5	303	Atlas - Centaur	08 Sep 1967	Moon landing	Success - 19,000 photos returned, first use of alpha scatter soil composition monitor	Mare Tranquillitatis	001.41N 023.18E
Surveyor 6	300	Atlas - Centaur	07 Nov 1967	Moon landing	Success - 30,000 photos returned, robot arm & alpha scatter science, engine restart, second landing 2.5 m away from first	Sinus Medii	000.46N 358.63E
Surveyor 7	306	Atlas - Centaur	07 Jan 1968	Moon landing	Success - 21,000 photos returned; robot arm & alpha scatter science; laser beams from Earth detected	Tycho Crater	041.01S 348.59E

Transition From Direct Ascent Landings To Lunar Orbit Operations (1966)

Within four months of each other in early 1966 the Soviet Union and the United States had accomplished successful moon landings with unmanned 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 manned landers with their much greater weight.

However, the Luna 9 hard landing of a ruggedized sphere using airbags at a 30 mile-per-hour ballistic impact speed had much more in common with the failed 1962 Ranger landing attempts and their planned 100 mile-per-hour 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.

Advances in other areas were necessary before manned spacecraft could follow unmanned 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 utilized flight paths from Earth that traveled directly to the lunar surface without first placing the spacecraft in a lunar orbit. Such direct ascents use a minimum amount of fuel for unmanned spacecraft on a one-way trip.

In contrast, manned 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 actually 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 manned Moon landing. Accordingly, beginning in mid-1966 both the U.S. and U.S.S.R. naturally progressed into missions which featured lunar orbit operations as a necessary prerequisite to a manned Moon landing.

Soviet lunar orbit satellites (1966-1974)

U.S.S.R Mission	Mass (kg)	Booster	Launched	Mission Goal	Mission Result
Cosmos - 111		Molniya-M	01 Mar 1966	Lunar orbiter	Failure - stranded in low Earth orbit
Luna-10	1582	Molniya-M	31 Mar 1966	Lunar orbiter	Success - 2738 km x 2088 km x 72 deg orbit, 178 m period, 60 day science mission
Luna-11	1640	Molniya-M	24 Aug 1966	Lunar orbiter	Success - 2931 km x 1898 km x 27 deg orbit, 178 m period, 38 day science mission
Luna-12	1620	Molniya-M	22 Oct 1966	Lunar orbiter	Success - 2938 km x 1871 km x 10 deg orbit, 205 m period, 89 day science mission
Cosmos-159	1700	Molniya-M	17 May 1967	Prototype test	Success - high Earth orbit manned landing communications gear radio calibration test
		Molniya-M	07 Feb 1968	Lunar orbiter	Failure - booster malfunction, failed to reach Earth orbit - attempted radio calibration test?
Luna-14	1700	Molniya-M	07 Apr 1968	Lunar orbiter	Success - 870 km x 160 km x 42 deg orbit, 160 m period, unstable orbit, radio calibration test?
Luna-19	5700	Proton	28 Sep 1971	Lunar orbiter	Success - 140 km x 140 km x 41 deg orbit, 121 m period, 388 day science mission
Luna-22	5700	Proton	29 May 1974	Lunar orbiter	Success - 222 km x 219 km x 19 deg orbit, 130 m period, 521 day science mission

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

Soviet Circumlunar Loop Flights (1967-1970)

U.S.S.R Mission	Mass (kg)	Booster	Launched	Mission Goal	Payload	Mission Result
Cosmos-146	5400	Proton	10 Mar 1967	High Earth Orbit	unmanned	Failure - stranded in elliptical high Earth orbit, unable to initiate controlled high speed atmospheric reentry test
Cosmos-154	5400	Proton	08 Apr 1967	High Earth Orbit	unmanned	Failure - stranded in elliptical high Earth orbit, unable to initiate controlled high speed atmospheric reentry test
		Proton	28 Sep 1967	High Earth Orbit	unmanned	Failure - booster malfunction, failed to reach Earth orbit
		Proton	22 Nov 1967	High Earth Orbit	unmanned	Failure - booster malfunction, failed to reach Earth orbit
Zond-4	5140	Proton	02 Mar 1968	High Earth Orbit	unmanned	Failure - launched successfully to 300,000 km high Earth orbit, high speed reentry test guidance malfunction, intentional self-destruct to prevent landfall outside Soviet Union
		Proton	23 Apr 1968	Circumlunar Loop	non-human biological payload	Failure - booster malfunction, failed to reach Earth orbit; launch preparation tank explosion kills three in pad crew
Zond-5	5375	Proton	15 Sep 1968	Circumlunar Loop	non-human biological payload	Success - looped around Moon, returned live biological payload safely to Earth despite landing off-target outside the Soviet Union in the Indian Ocean
Zond-6	5375	Proton	10 Nov 1968	Circumlunar Loop	non-human biological payload	Failure - looped around Moon, successful reentry, but loss of cabin air pressure caused biological payload death, parachute system malfunction and severe vehicle damage upon landing
		Proton	20 Jan 1969	Circumlunar Loop	non-human biological payload	Failure - booster malfunction, failed to reach Earth orbit
Zond-7	5979	Proton	08 Aug 1969	Circumlunar Loop	non-human biological payload	Success - looped around Moon, returned biological payload safely to Earth and landed on-target inside Soviet Union
Zond-8		Proton	20 Oct 1970	Circumlunar Loop	non-human biological payload	Success - looped around Moon, returned biological payload safely to Earth despite landing off-target outside Soviet Union in the Indian Ocean

Zond 5 was the first spacecraft to carry life from Earth to the vicinity of the Moon. Believing a Soviet manned lunar flight was imminent in late 1968, NASA changed the flight plan of Apollo 8 from an Earth-orbit mission to a risky lunar orbit mission.

U.S. lunar orbit satellites (1966-1967)

U.S. Mission	Mass (kg)	Booster	Launched	Mission Goal	Mission Result
Lunar Orbiter 1	386	Atlas - Agena	10 Aug 1966	Lunar orbiter	Success - 1160 km X 189 km x 12 deg orbit, 208 m period, 80 day photography mission
Lunar Orbiter 2	386	Atlas - Agena	06 Nov 1966	Lunar orbiter	Success - 1860 km X 52 km x 12 deg orbit, 208 m period, 339 day photography mission
Lunar Orbiter 3	386	Atlas - Agena	05 Feb 1967	Lunar orbiter	Success - 1860 km X 52 km x 21 deg orbit, 208 m period, 246 day photography mission
Lunar Orbiter 4	386	Atlas - Agena	04 May 1967	Lunar orbiter	Success - 6111 km X 2706 km x 86 deg orbit, 721 m period, 180 day photography mission
Lunar Orbiter 5	386	Atlas - Agena	01 Aug 1967	Lunar orbiter	Success - 6023 km X 195 km x 85 deg orbit, 510 m period, 183 day photography mission

Apollo 8 carried out the first manned orbit of the Moon on December 24, 1968, certifying the Saturn V booster for manned use. Apollo 10 then performed a full dress rehearsal of a manned moon landing in May 1969. This mission stopped short at ten miles altitude above the lunar surface, performing necessary low-altitude mapping of trajectory-altering mascons using a factory prototype lunar module that was too overweight to allow a successful landing. With the failure of the unmanned Soviet sample return moon landing attempt Luna 15 in July 1969, the stage was set for Apollo 11.

American manned Moon landings (1969-1972)

American strategy

The U.S. Moon exploration program originated during the Eisenhower administration. In a series of mid-1950s articles in Collier's magazine, Wernher von Braun had popularized the idea of a manned expedition to the Moon to establish a lunar base. A manned Moon landing posed several daunting technical challenges to the U.S. and USSR. Besides guidance and weight management, atmospheric re-entry without ablative overheating was a major hurdle. After the Soviet Union's launch of Sputnik, von Braun promoted a plan for the United States Army to establish a military lunar outpost by 1965.

After the early Soviet successes, especially Yuri Gagarin's flight, U.S. President John F. Kennedy looked for an American project that would capture the public imagination. He asked Vice President Lyndon Johnson to make recommendations on a scientific endeavor that would prove U.S. world leadership. The proposals included non-space options such as massive irrigation projects to benefit the Third World. The Soviets, at the time, had more powerful rockets than the United States, which gave them an advantage in some kinds of space missions. Advances in U.S. nuclear weapons technology had led to smaller, lighter warheads, and consequently, rockets with smaller payload capacities. By comparison, Soviet nuclear weapons were much heavier, and the powerful R-7 rocket was developed to carry them. More modest potential missions such as flying around the Moon without landing or establishing a space lab in orbit (both were proposed by Kennedy to von Braun) were determined to offer too much advantage to the Soviets, since the U.S. would have to develop a heavy rocket to match the Soviets. A Moon landing, however, would capture world imagination while functioning as propaganda.

Mindful that the Apollo Program would economically benefit most of the key states in the next election—particularly his home state of Texas because NASA's base was in Houston—Johnson championed the Apollo program. This superficially indicated action to alleviate the fictional " missile gap" between the U.S. and USSR, a campaign promise of Kennedy's in the 1960 election. The Apollo project allowed continued development of dual-use technology. Johnson also advised that for anything less than a lunar landing the USSR had a good chance of beating the U.S. For these reasons, Kennedy seized on Apollo as the ideal focus for American efforts in space. He ensured continuing funding, shielding space spending from the 1963 tax cut and diverting money from other NASA projects. This dismayed NASA's leader, James E. Webb, who urged support for other scientific work.

In conversation with Webb, Kennedy said:

Everything we do ought to really be tied in to getting on to the moon ahead of the Russians [...] otherwise we shouldn't be spending that kind of money, because I'm not interested in space [...] The only justification for [the cost] is because we hope to beat [the USSR] to demonstrate that instead of being behind by a couple of years, by God, we passed them.

The Saturn V booster was the key to U.S. moon landings, using more efficient liquid hydrogen fuel instead of kerosene in its upper stages to lift heavier payloads with a launch record of no failures in thirteen launches. The N-1 exploded in flight during four secret test launches and never achieved operational status.

Whatever he said in private, Kennedy needed a different message to gain public support to uphold what he was saying and his views. Later in 1963, Kennedy asked Vice President Johnson to investigate the possible technological and scientific benefits of a Moon mission. Johnson concluded that the benefits were limited, but, with the help of scientists at NASA, he put together a powerful case, citing possible medical breakthroughs and interesting pictures of Earth from space. For the program to succeed, its proponents would have to defeat criticism from politicians on the left, who wanted more money spent on social programs, and on those on the right, who favored a more military project. By emphasizing the scientific payoff and playing on fears of Soviet space dominance, Kennedy and Johnson managed to swing public opinion: by 1965, 58 percent of Americans favored Apollo, up from 33 percent two years earlier. After Johnson became President in 1963, his continuing defense of the program allowed it to succeed in 1969, as Kennedy had originally hoped.

Soviet strategy

Soviet leader Nikita Khrushchev did not relish "defeat" by any other power, but equally did not relish funding such an expensive project. In October 1963 he said that the USSR was "not at present planning flight by cosmonauts to the Moon", while insisting that the Soviets had not dropped out of the race. Only after another year would the USSR fully commit itself to a Moon-landing attempt, which ultimately failed.

At the same time, Kennedy had suggested various joint programs, including a possible Moon landing by Soviet and American astronauts and the development of better weather-monitoring satellites. Khrushchev, sensing an attempt by Kennedy to steal Russian space technology, rejected the idea: if the USSR went to the Moon, it would go alone. Korolyov, the RSA's chief designer, had started promoting his Soyuz craft and the N-1 launcher rocket that would have the capability of carrying out a manned Moon landing. Khrushchev directed Korolyov's design bureau to arrange further space firsts by modifying the existing Vostok technology, while a second team started building a completely new launcher and craft, the Proton booster and the Zond, for a manned cislunar flight in 1966. In 1964 the new Soviet leadership gave Korolyov the backing for a Moon landing effort and brought all manned projects under his direction. With Korolyov's death and the failure of the first Soyuz flight in 1967, the co-ordination of the Soviet moon landing program quickly unraveled. The Soviets built a landing craft and selected cosmonauts for the mission that would have placed Aleksei Leonov on the Moon's surface, but with the successive launch failures of the N1 booster in 1969, plans for a manned landing suffered first delay and then cancellation.

Apollo Moon landings

U.S. Mission	Booster	Launched	Mission Goal	Mission Result
Apollo 1 (AS-204)	Saturn 1B	(21 February 1967)	Manned Earth orbit	Failure - never launched: command module destroyed and three astronauts killed on 27 January 1967 by fire in the module during a test exercise - retroactively called Apollo 1
Apollo 2 (AS-203)	Saturn 1B	5 July 1966	Unmanned Earth orbit	Success - fuel tank behaviour test and booster certification - informally known as Apollo 2
Apollo 3 (AS-202)	Saturn 1B	25 August 1966	Unmanned suborbital	Success - command module reentry test successful, even though reentry was very uncontrolled - informally known as Apollo 3
Apollo 4	Saturn V	9 November 1967	Unmanned Earth orbit	Success - first test of new booster and all elements together (except lunar module), successful reentry of command module
Apollo 5	Saturn 1B	22 January 1968	Unmanned Earth orbit	Success - first flight of lunar module, multiple space tests of lunar module, no controlled reentry
Apollo 6	Saturn V	4 April 1968	Unmanned Earth orbit	Partial success - severe oscillations during orbital insertion, several engines failing during flight, successful reentry of command module (though mission parameters for a 'worst case' reentry scenario could not be achieved)
Apollo 7	Saturn 1B	11 October 1968	Manned Earth orbit	Success - eleven-day manned Earth orbit, command module testing (no lunar module), some minor crew issues
Apollo 8	Saturn V	21 December 1968	Manned lunar orbit	Success - ambitious mission profile (changed relatively shortly before launch), first human lunar orbit (no lunar module), first earthrise seen by men and major publicity success, some minor sleeping and illness issues
Apollo 9	Saturn V	3 March 1969	Manned Earth orbit	Success - ten-day manned Earth orbit, with EVA and successful manned flight / docking of lunar module
Apollo 10	Saturn V	18 May 1969	Manned lunar orbit	Success - second manned lunar orbit, test of lunar module in lunar orbit, coming as close as 8.4 nautical miles (15.6 km) to the Moon's surface
Apollo 11	Saturn V	16 July 1969	Manned lunar landing	Success - first manned landing on the Moon (manual landing required), exploration on foot in direct vicinity of landing site
Apollo 12	Saturn V	14 November 1969	Manned lunar landing	Success - mission almost aborted in-flight after lightning strike on takeoff caused telemetry loss, successful landing within walking distance (less than 200 meters) of the Surveyor 3 probe
Apollo 13	Saturn V	11 April 1970	Manned lunar landing	Failure - problematic oscillations on start, unrelated explosion in service module during Earth-Moon transition caused mission to be aborted - crew took temporary refuge in lunar module and eventually returned to Earth with command module after single pass around Moon
Apollo 14	Saturn V	31 January 1971	Manned lunar landing	Success - software and hardware problems with lunar module almost caused landing abort during lunar orbit, first colour video images from the Moon, first materials science experiments in space
Apollo 15	Saturn V	26 July 1971	Manned lunar landing	Success - first longer (3 days) stay on Moon, first use of lunar rover to travel (total of 17.25 miles / 27.76 km), more extensive geology investigations
Apollo 16	Saturn V	16 April 1972	Manned lunar landing	Success - malfunction in a backup yaw gimbal servo loop almost aborted landing (and reduced stay duration on Moon by one day to three for safety reasons), only mission to target lunar highlands
Apollo 17	Saturn V	7 December 1972	Manned lunar landing	Success - last (and still most recent) manned landing on the Moon, only mission with geologist
Apollo 18+	Saturn V	-	Manned lunar landings	Cancelled - Several more missions (with detailed planning for up to Apollo 20) were cancelled

In total twenty-four American astronauts have traveled to the Moon, with twelve walking on its surface and three making the trip twice. Apollo 8 was a lunar-orbit-only mission, Apollo 10 included powered descent and then an abort-mode ascent of the LM, while Apollo 13, originally scheduled as a landing, ended up as a lunar fly-by by means of free return trajectory; thus, none of these missions made landings. Apollo 7 and Apollo 9 never left Earth orbit. Apart from the inherent dangers of manned moon expeditions as seen with Apollo 13, one reason for their cessation according to astronaut Alan Bean is the cost it imposes in government subsidies."

Other aspects of the Apollo Moon landings

Unlike other international rivalries, the Space Race has remained unaffected in a direct way regarding the desire for territorial expansion. After the successful landings on the Moon, the U.S. explicitly disclaimed the right to ownership of any part of the Moon.

President Richard Nixon had speechwriter William Safire prepare a condolence speech for delivery in the event that Armstrong and Aldrin became marooned on the Moon's surface and could not be rescued.

In the 1940s writer Arthur C Clarke forecast that man would reach the Moon by 2000.

On August 16, 2006, the Associated Press reported that NASA is currently missing the original Slow-scan television tapes (which were made before the scan conversion for conventional TV) of the Apollo 11 Moon walk. Some news outlets have mistakenly reported that the SSTV tapes were found in Western Australia, but those tapes were only recordings of data from the Apollo 11 Early Apollo Surface Experiments Package.

Soviet unmanned soft landings (1969-1976)

U.S.S.R. Mission	Mass (kg)	Booster	Launched	Mission Goal	Mission Result	Landing Zone	Lat/ Lon
		Proton	19 Feb 1969	Lunar rover	Failure - booster malfunction, failed to reach Earth orbit
		Proton	14 Jun 1969	Sample return	Failure - booster malfunction, failed to reach Earth orbit
Luna-15	5700	Proton	13 Jul 1969	Sample return	Failure - lunar crash impact	Mare Crisium	unknown
Cosmos-300		Proton	23 Sep 1969	Sample return	Failure - stranded in low Earth orbit
Cosmos-305		Proton	22 Oct 1969	Sample return	Failure - stranded in low Earth orbit
		Proton	06 Feb 1970	Sample return	Failure - booster malfunction, failed to reach Earth orbit
Luna-16	5600	Proton	12 Sep 1970	Sample return	Success - returned 0.10 kg of moon dust back to Earth	Mare Fecunditatis	000.68S 056.30E
Luna-17	5700	Proton	10 Nov 1970	Lunar rover	Success - Lunokhod-1 rover traveled 10.5 km across lunar surface	Mare Imbrium	038.28N 325.00E
Luna-18	5750	Proton	02 Sep 1971	Sample return	Failure - lunar crash impact	Mare Fecunditatis	003.57N 056.50E
Luna-20	5727	Proton	14 Feb 1972	Sample return	Success - returned 0.05 kg of moon dust back to Earth	Mare Fecunditatis	003.57N 056.50E
Luna-21	5950	Proton	08 Jan 1973	Lunar rover	Success - Lunokhod-2 rover traveled 37.0 km across lunar surface	LeMonnier Crater	025.85N 030.45E
Luna-23	5800	Proton	28 Oct 1974	Sample return	Failure - Moon landing achieved, but malfunction prevented sample return	Mare Crisium	012.00N 062.00E
		Proton	16 Oct 1975	Sample return	Failure - booster malfunction, failed to reach Earth orbit
Luna-24	5800	Proton	09 Aug 1976	Sample return	Success - returned 0.17 kg of moon dust back to Earth	Mare Crisium	012.25N 062.20E

Future plans

The current U.S. Vision for Space Exploration calls for a lunar sortie mission called Orion 15 as part of Project Constellation that will include humans landing on the Moon in 2019.

Russia plans to send cosmonauts to the Moon by 2025 and establish a permanent manned base there in 2027-2032.

ISRO, the Indian National Space agency, has announced the Chandrayaan program for Lunar exploration. The second mission Chandrayaan II plans to land a motorised rover by 2010/ 2011.

Other nations, including China, have expressed interest in pursuing human landings on the Moon, but none have currently announced formal plans.

The Google Lunar X Prize competition offers a $20 million award for the first privately-funded team to land a robotic probe on the Moon. Like the Ansari X Prize before it, the competition aims to advance the state of the art in private space exploration.

Hoax accusations

Conspiracy theorists insist that the Apollo moon landings were a hoax. These accusations flourish in part because predictions by enthusiasts that Moon landings would become commonplace have not yet come to pass. Some claims can be empirically discredited by three retroreflector arrays left on the Moon by Apollo 11, 14 and 15. Today, anyone on Earth with an appropriate laser and telescope system may bounce laser beams off these devices, verifying deployment of the Lunar Laser Ranging Experiment at historically documented Apollo moon landing sites.

In addition, close scrutiny of film footage of the EVAs shows clearly something that could not be replicated in an Earth sound-stage. Lunar dust kicked up by the astronauts and the Lunar Rovers shoots up quite high because of the low gravity, but settles just as rapidly as there is no air resistance. Watching this film footage, and comparing it to footage from the Tom Hanks miniseries, From the Earth to the Moon—which does show dust clouds resulting from the actors' spacesuits kicking up dust—shows this difference clearly.

Since the first hoax accusations were made - albeit by non-scientists pursuing the conspiracy accusations in part for monetary gain - and although they have been repeatedly debunked by many independent scientists - a small minority of the global population continues to believe the now-obsolete allegations, which has bothered NASA and the astronauts who flew the missions. However, it has recently become apparent that from the multiple scheduled or proposed governmental and private efforts to send landers or orbiters to the Moon, it is likely that independent infallible proof will be returned, and conclude any conspiracies. The next lunar orbiter currently scheduled for launch is NASA's Lunar Reconnaissance Orbiter mission, due to launch in November 2008, and will have the ability to photograph the historic landing sites.