Translunar injection (TLI): the burn that changes the spacecraft's orbit from a closed loop around Earth into an elongated path that reaches the Moon's distance.
- TLI is the one large departure burn of the outbound trip. It is performed near the end of the Earth parking orbit, where the spacecraft is already moving fast.
- Because the burn raises the orbit, the spacecraft leaves Earth's vicinity with less speed than it had in parking orbit — the extra energy went into climbing away from Earth.
- After TLI the engine shuts down and the coast begins. No further large burn is needed to reach the Moon.
Why one burn is enough: the burn sets the trajectory once; inertia carries the spacecraft along it.