Apogee, Perigee, and Why They Matter for Every Satellite

Every elliptical orbit has two extremes. Apogee is the farthest point from Earth — where the satellite moves most slowly. Perigee is the closest — where it moves fastest. Together they determine the orbit's shape and most of its operational properties.

Why orbits are elliptical

Newton's law of gravity, applied to two bodies, has only one stable solution: a conic section. Below escape velocity, the conic is an ellipse. Circular orbits are a special case where eccentricity equals zero. Most natural and engineered orbits are slightly elliptical, with eccentricity between 0 and 1.

Apogee and perigee for famous orbits

ISS

Apogee ~420 km, perigee ~415 km — nearly circular

Hubble

Apogee ~547 km, perigee ~535 km

Geostationary

Apogee = perigee = 35,786 km (perfectly circular)

Molniya orbits

Apogee ~40,000 km, perigee ~600 km

Geostationary Transfer Orbit

Apogee ~35,786 km, perigee ~200 km

How apogee and perigee are used

• Communications satellites in Molniya orbits spend most of their time over high latitudes by parking their slow apogee over Russia or Canada.
• GTO (Geostationary Transfer Orbit) is an elliptical orbit launched first, with the satellite raising its perigee at apogee with onboard propulsion.
• Sun-synchronous orbits use precise inclination and eccentricity to maintain a constant local solar time on the surface below.

How they change over time

Atmospheric drag pulls perigee down and circularizes orbits. Solar pressure and lunar gravity perturb high orbits. Active satellites perform station-keeping maneuvers to maintain their target apogee and perigee. Without maintenance, orbits drift and eventually decay.