Trans Lunar Injection

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A Trans Lunar Injection (TLI) is propulsive maneuver used to set a spacecraft on a trajectory which will intersect the Moon. Historically most TLIs have been Hohmann transfers, but the Hiten probe used a low energy transfer for this purpose.^[1] For spacecraft with high thrust engines, a Hohmann transfer is almost always the most economical way to get from one circular orbit to another.

The spacecraft is usually in a parking orbit around Earth at the time of TLI.

The maneuver is usually performed by a rather large rocket engine. On the Apollo missions it was performed by the restartable J-2 engine in the third (S-IVB) stage of the Saturn V rocket. This particular TLI burn lasted approximately 346 seconds, providing 10,000 to 10,600 ft/s (3.05 to 3.25 km/s) of delta-v, at which point the spacecraft was travelling at approximately 10.95 km/s (24,500 mph or 39,420 km/h).

The burn is timed so that the mid-point of the TLI is opposite the moon (or more precisely, the moon's location upon arrival). The first space probe to successfully perform this maneuver was the Soviet Union's Luna 1 on January 2, 1959. The first manned mission to successfully perform this procedure, and thus becoming the first humans to leave the Earth's influence, was the crew of Apollo 8 on December 21, 1968.

[edit] See also

• Trans Earth Injection

[edit] References

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