A trans-Earth injection (TEI) is a propulsion

maneuver Maneuver (American English), manoeuvre (British English), manoeuver, manœuver (also spelled, directly from the French, as manœuvre) denotes one's tactical move, or series of moves, that improves or maintains one's strategic situation in a compet ...

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. The maneuver is performed by a rocket engine.

From the Moon

The spacecraft is usually in a parking orbit around the Moon 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 missions, it was performed by the restartable Service Propulsion System (SPS) engine on the Service Module 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 ...

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 low Earth orbit and the first human spaceflight to reach the Moon. The crew orbited the Moon ten times without landing, and then departed safely back to Earth. These ...

mission on December 25, 1968.

From outside the Earth-Moon system

In 2004, from outside the Earth-Moon system, the

Stardust probe ''Stardust'' was a 385-kilogram robotic space probe launched by NASA on 7 February 1999. Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust, and return them to Earth for analysi ...

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

From outside the Earth-Moon system

See also

References