A trans-Earth injection (TEI) is a propulsion maneuver used to set a

spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...

on a

trajectory A trajectory or flight path is the path that an object with mass in motion follows through space as a function of time. In classical mechanics, a trajectory is defined by Hamiltonian mechanics via canonical coordinates; hence, a complete tra ...

which will intersect the

Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

sphere of influence In the field of international relations, a sphere of influence (SOI) is a spatial region or concept division over which a state or organization has a level of cultural, economic, military, or political exclusivity. While there may be a formal a ...

, usually putting the spacecraft on a free return trajectory. The maneuver is performed by a

rocket A rocket (from , and so named for its shape) is a vehicle that uses jet propulsion to accelerate without using any surrounding air. A rocket engine produces thrust by reaction to exhaust expelled at high speed. Rocket engines work entirely ...

engine.

From the Moon

The spacecraft is usually in a

parking orbit A parking orbit is a temporary orbit used during the launch of a spacecraft. A launch vehicle follows a trajectory to the parking orbit, then coasts for a while, then engines fire again to enter the final desired trajectory. An alternative trajec ...

around the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

at the time of TEI, in which case the burn is timed so that its midpoint is opposite the Earth's location upon arrival. Uncrewed space probes have also performed this maneuver from the Moon starting with Luna 16's direct ascent traverse from the lunar surface in 1970. On the

Apollo Apollo is one of the Twelve Olympians, Olympian deities in Ancient Greek religion, ancient Greek and Ancient Roman religion, Roman religion and Greek mythology, Greek and Roman mythology. Apollo has been recognized as a god of archery, mu ...

missions, it was performed by the restartable Service Propulsion System (SPS) engine on the

Service Module A service module (also known as an equipment module or instrument compartment) is a component of a crewed space capsule containing a variety of support systems used for spacecraft operations. Usually located in the uninhabited area of the spacec ...

after the undocking of the (LM)

Lunar Module The Apollo Lunar Module (LM ), 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 s ...

if provided. An Apollo TEI burn lasted approximately 150 seconds, providing a posigrade velocity increase of 1,000 m/s (3,300 ft/s). It was first performed by the

Apollo 8 Apollo 8 (December 21–27, 1968) was the first crewed spacecraft to leave Sphere of influence (astrodynamics), Earth's gravitational sphere of influence, and the first human spaceflight to reach the Moon. The crew orbited the Moon ten times ...

mission on December 25, 1968. It was last performed by the propulsion module of

Chandrayaan-3 Chandrayaan-3 ( ) is the third mission in the Chandrayaan programme, a series of Exploration of the Moon, lunar-exploration missions developed by the ISRO, Indian Space Research Organisation (ISRO). The mission consists of a Chandrayaan-2#Vikra ...

mission during 13 October 2023

List of missions that performed a Trans-Earth injection

Total 17 missions have performed such a maneuver.

NASA The National Aeronautics and Space Administration (NASA ) is an independent agencies of the United States government, independent agency of the federal government of the United States, US federal government responsible for the United States ...

has performed it the most (10 times), followed by Soviet Union (3 times), China (3 times), and India (once). These missions are in order, *

* Apollo 10 *

Apollo 11 Apollo 11 was a spaceflight conducted from July 16 to 24, 1969, by the United States and launched by NASA. It marked the first time that humans Moon landing, landed on the Moon. Commander Neil Armstrong and Lunar Module pilot Buzz Aldrin l ...

* Apollo 12 * Luna 16 *

Apollo 14 Apollo 14 (January 31February 9, 1971) was the eighth crewed mission in the United States Apollo program, the third to Moon landing, land on the Moon, and the first to land in the Geology of the Moon#Highlands, lunar highlands. It was the las ...

Apollo 15 Apollo 15 (July 26August 7, 1971) was the ninth crewed mission in the Apollo program and the fourth Moon landing. It was the first List of Apollo missions#Alphabetical mission types, J mission, with a longer stay on the Moon and a greate ...

* Luna 20 *

Apollo 16 Apollo 16 (April 1627, 1972) was the tenth human spaceflight, crewed mission in the United States Apollo program, Apollo space program, administered by NASA, and the fifth and penultimate to Moon landing, land on the Moon. It was the second o ...

Apollo 17 Apollo 17 (December 7–19, 1972) was the eleventh and final mission of NASA's Apollo program, the sixth and most recent time humans have set foot on the Moon. Commander Gene Cernan and Lunar Module Pilot Harrison Schmitt walked on the Moon, ...

* Luna 24 *'' Clementine'' * Chang'e 5-T1 * Chang'e 5 * Artemis 1 *

Chang'e 6 Chang'e 6 () was the sixth robotic lunar exploration mission by the China National Space Administration (CNSA) and the second CNSA lunar sample-return mission. Like its predecessors in the Chinese Lunar Exploration Program, the spacecraft is ...

From outside the Earth-Moon system

In 2004, from outside the Earth-Moon system, the Stardust probe comet dust return mission performed TEI after visiting Comet Wild 2.

References

Astrodynamics Spacecraft propulsion Exploration of the Moon Apollo program {{spacecraft-stub

From the Moon

List of missions that performed a Trans-Earth injection

From outside the Earth-Moon system

See also

References