In orbital mechanics, a circumlunar trajectory, trans-lunar trajectory or lunar free return is a type of free return trajectory which takes a spacecraft from Earth, around the far side of the Moon, and back to Earth using only gravity once the initial trajectory is set.
The first spacecraft to fly a circumlunar trajectory was Luna 3. Circumlunar trajectories were also used by Apollo missions prior to lunar orbit insertion, [1] to provide a free return to Earth in the event of a propulsion system malfunction on the way to the Moon. This was used on Apollo 13, when an oxygen tank rupture necessitated return to Earth without firing the Service Module engine, although a number of course corrections using the Lunar Module descent engine were used to refine the trajectory. [2]
A number of proposed, but not flown, crewed missions have been planned to intentionally conduct circumlunar flybys, including the Soviet Soyuz 7K-L1 or Zond programme, and several US proposals, including Gemini-Centaur and an early Apollo proposal. [3]
The latest circumlunar mission was 2022 NASA Artemis 1.
Apollo 8 was the first crewed spacecraft to leave Earth's gravitational sphere of influence, and the first human spaceflight to reach the Moon. The crew orbited the Moon ten times without landing and then returned to Earth. The three astronauts—Frank Borman, James Lovell, and William Anders—were the first humans to see and photograph the far side of the Moon and an Earthrise.
The Apollo program, also known as Project Apollo, was the United States human spaceflight program carried out by the National Aeronautics and Space Administration (NASA), which succeeded in preparing and landing the first men on the Moon in 1969. It was first conceived in 1960 during President Dwight D. Eisenhower's administration as a three-person spacecraft to follow the one-person Project Mercury, which put the first Americans in space. Apollo was later dedicated to President John F. Kennedy's national goal for the 1960s of "landing a man on the Moon and returning him safely to the Earth" in an address to Congress on May 25, 1961. It was the third US human spaceflight program to fly, preceded by the two-person Project Gemini conceived in 1961 to extend spaceflight capability in support of Apollo.
Apollo 10 was the fourth human spaceflight in the United States' Apollo program and the second to orbit the Moon. NASA, the mission's operator, described it as a "dress rehearsal" for the first Moon landing. It was designated an "F" mission, intended to test all spacecraft components and procedures short of actual descent and landing.
A trans-lunar injection (TLI) is a propulsive maneuver, which is used to send a spacecraft to the Moon. Typical lunar transfer trajectories approximate Hohmann transfers, although low-energy transfers have also been used in some cases, as with the Hiten probe. For short duration missions without significant perturbations from sources outside the Earth-Moon system, a fast Hohmann transfer is typically more practical.
Luna 15 was a robotic space mission of the Soviet Luna programme, that was in lunar orbit together with the Apollo 11 Command module Columbia.
The Apollo Lunar Module, originally designated the Lunar Excursion Module (LEM), was the lunar lander spacecraft that was flown between lunar orbit and the Moon's surface during the United States' Apollo program. It was the first crewed spacecraft to operate exclusively in the airless vacuum of space, and remains the only crewed vehicle to land anywhere beyond Earth.
Zond was the name given to two distinct series of Soviet robotic spacecraft launched between 1964 and 1970. The first series, based on the 3MV planetary probe, was intended to gather information about nearby planets.
Zond 8, also known as L-1 No.14, was the last in the series of circumlunar spacecraft, a member of the Soviet Zond program, designed to rehearse a piloted circumlunar flight, an uncrewed version of Soyuz 7K-L1 crewed circumlunar flight spacecraft. The project was initiated in 1965 to compete with the Americans in the race to the Moon but lost its importance once three astronauts orbited the Moon on the Apollo 8 mission in December 1968.
Gemini 11 was the ninth crewed spaceflight mission of NASA's Project Gemini, which flew from September 12 to 15, 1966. It was the 17th crewed American flight and the 25th spaceflight to that time. Astronauts Pete Conrad and Dick Gordon performed the first direct-ascent rendezvous with an Agena Target Vehicle, docking with it 1 hour 34 minutes after launch; used the Agena rocket engine to achieve a record high-apogee Earth orbit; and created a small amount of artificial gravity by spinning the two spacecraft connected by a tether. Gordon also performed two extra-vehicular activities for a total of 2 hours 41 minutes.
The Constellation program was a crewed spaceflight program developed by NASA, the space agency of the United States, from 2005 to 2009. The major goals of the program were "completion of the International Space Station" and a "return to the Moon no later than 2020" with a crewed flight to the planet Mars as the ultimate goal. The program's logo reflected the three stages of the program: the Earth (ISS), the Moon, and finally Mars—while the Mars goal also found expression in the name given to the program's booster rockets: Ares. The technological aims of the program included the regaining of significant astronaut experience beyond low Earth orbit and the development of technologies necessary to enable sustained human presence on other planetary bodies.
The Soviet crewed lunar programs were a series of programs pursued by the Soviet Union to land humans on the Moon, in competition with the United States Apollo program. The Soviet government publicly denied participating in such a competition, but secretly pursued two programs in the 1960s: crewed lunar flyby missions using Soyuz 7K-L1 (Zond) spacecraft launched with the Proton-K rocket, and a crewed lunar landing using Soyuz 7K-LOK and LK spacecraft launched with the N1 rocket. Following the dual American successes of the first crewed lunar orbit on 24–25 December 1968 and the first Moon landing on July 20, 1969, and a series of catastrophic N1 failures, both Soviet programs were eventually brought to an end. The Proton-based Zond program was canceled in 1970, and the N1-L3 program was de facto terminated in 1974 and officially canceled in 1976. Details of both Soviet programs were kept secret until 1990 when the government allowed them to be published under the policy of glasnost.
A Moon landing or lunar landing is the arrival of a spacecraft on the surface of the Moon, including both crewed and robotic missions. The first human-made object to touch the Moon was Luna 2 in 1959.
Deep Space Expedition Alpha (DSE-Alpha), is the name given to the mission proposed in 2005 to take the first space tourists to fly around the Moon. The mission is organized by Space Adventures Ltd., a commercial spaceflight company. The plans involve a modified Soyuz capsule docking with a booster rocket in Earth orbit which then sends the spacecraft on a free return circumlunar trajectory that circles around the Moon once. While the price was originally announced in August 2005 to cost US$100 million per seat, Space Adventures founder Eric Anderson announced in January 2011 that one of the two available seats had been sold for $150 million.
In orbital mechanics, a free-return trajectory is a trajectory of a spacecraft traveling away from a primary body where gravity due to a secondary body causes the spacecraft to return to the primary body without propulsion.
In astronomy and spaceflight, a lunar orbit is an orbit by an object around Earth's Moon. In general these orbits are not circular. When farthest from the Moon a spacecraft is said to be at apolune, apocynthion, or aposelene. When closest to the Moon it is said to be at perilune, pericynthion, or periselene. These derive from names or epithets of the moon goddess.
The Saturn C-2 was the second rocket in the Saturn C series studied from 1959 to 1962. The design was for a four-stage launch vehicle that could launch 21,500 kg (47,300 lb) to low Earth orbit and send 6,800 kg (14,900 lb) to the Moon via Trans-Lunar Injection.
The C-2 design concept was for a proposed crewed circumlunar flight and the Earth orbit rendezvous (EOR) missions. It was initially considered for the Apollo lunar landing at the earliest possible date (1967).
A trans-Earth injection (TEI) is a propulsion maneuver used to set a spacecraft on a trajectory which will intersect the Earth's sphere of influence, usually putting the spacecraft on a free return trajectory.
Advanced Gemini was a series of proposals that would have extended the Gemini program by the addition of various missions, including crewed low Earth orbit, circumlunar and lunar landing missions. Gemini was the second crewed spaceflight program operated by NASA, and consisted of a two-seat spacecraft capable of maneuvering in orbit, docking with uncrewed spacecraft such as Agena Target Vehicles, and allowing the crew to perform tethered extra-vehicular activities.
Artemis II is a scheduled mission of the NASA-led Artemis program. It will use the second launch of the Space Launch System (SLS) rocket and include the first crewed mission of the Orion spacecraft. The mission is scheduled for no earlier than September 2025. Four astronauts will perform a flyby of the Moon and return to Earth, becoming the first crew to travel beyond low Earth orbit since Apollo 17 in 1972. Artemis II will be the first crewed launch from Launch Complex 39B of the Kennedy Space Center since STS-116 in 2006.
Chang'e 5-T1 was an experimental robotic spacecraft that was launched to the Moon on 23 October 2014, by the China National Space Administration (CNSA) to conduct atmospheric re-entry tests on the capsule design planned to be used in the Chang'e 5 mission. As part of the Chinese Lunar Exploration Program, Chang'e 5, launched in 2020, was a Moon sample return mission. Like its predecessors, the spacecraft is named after the Chinese Moon goddess Chang'e. The craft consisted of a return vehicle capsule and a service module orbiter.
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