The placement of a spacecraft into orbit around the Moon. Apollo 11 used a retroburn (see retrorocket) to enter an elliptical LOI and, after one orbit, fired another retroburn to circularize the orbit. NASA's Lunar Prospector probe, launched in 1998, changed its spin axis before encountering the Moon in order to prepare for LOI. At LOI, it fired its thrusters to begin an initial 12-hour orbit and within a few days settled into a circular polar orbit 100 km above the lunar surface.
Subjects: Astronomy and Astrophysics.