Every orbit is an ellipse. The point farthest from the body being orbited is the apoapsis. Its opposite, the closest point, is the periapsis. Together they define the shape and size of the orbit.

Spacecraft operators care about the apoapsis because it is where orbital velocity is lowest and where manoeuvres often happen. A burn at apoapsis raises the periapsis efficiently. A burn at periapsis raises the apoapsis. Mission planners choose the point that saves the most fuel.

Named variants

• Apogee around Earth
• Apoapsis around the Moon or a planet
• Aphelion around the Sun

Geostationary transfer orbits use a low periapsis and a high apoapsis. A single burn at apoapsis circularizes the orbit and places the satellite in its working position.