What does TLI mean in NASA

Trans Lunar Injection, also known as TLI, is a maneuver used to propel a spacecraft from Earth orbit into an orbit around the Moon. It involves accelerating the spacecraft to high speeds and redirecting it toward the Moon's gravity field. TLI typically requires relatively large amounts of propellant, and as such is usually only performed once in a mission.

Spacecraft typically use TLI when they are attempting to reach lunar orbit or explore other planetary bodies in the solar system beyond Earth's orbit. Additionally, some unmanned missions to comets and asteroids may use TLI as one stage of their journey.

Since Trans Lunar Injection requires accelerating a spacecraft to very high speeds, it generally requires significant amounts of fuel for propellant. The exact amount of fuel required will depend on the size of the spacecraft, its mass and orbit velocity before TLI is initiated, as well as other factors like engine efficiency.

Not every space mission uses TLI; if a craft does not need to change orbits or escape Earth's gravity field - such as with some satellites - then no maneuver like TLI will be necessary. Additionally, if a mission needs to reach destinations within Earth's orbit (like some near-Earth satellites) then maneuvers other than TLI may be used instead.

As with any space maneuver that involves accelerating craft at high velocities and redirecting them through gravitational fields, there are associated risks when performing TLI. Proper planning must be done prior to initiating the burn in order to reduce these risks significantly.

Not all probes employ Trans Lunar Injection (TLI); those that do not need to escape from Earth's gravity field or otherwise change their orbits can operate without carrying out this maneuver in most cases. Generally speaking, only those probes whose objectives involve lunar orbit or deeper-space exploration would utilize TLI during their mission lifetime.

The duration of time taken for a spacecraft launch using trans lunar injection depends on several variables including thrust power, total mass of the payload being launched on board and initial orbital velocity among others. Generally speaking, a successful trans lunar injection can take from anywhere between 1 hour up to several days depending upon these factors.