Halo orbit

A halo orbit is a periodic, three-dimensional orbit near the L1, L2, or L3 gravitational equilibrium points in the three-body problem of orbital mechanics. A spacecraft in a halo orbit does not technically orbit the L point itself (which is just an equilibrium point with no mass), but travels in a closed, repeating path near the L point. Halo orbits are the result of a complicated interaction between the gravitational pull of the two planetary bodies and the coriolis and centrifugal accelerations on a spacecraft. Halo orbits exist in many three-body systems. Because halo orbits tend to be unstable, stationkeeping is required to keep a spacecraft on the orbit.