Satellite Orbit-Raising Manoeuvres

A satellite reaches its working orbit by using controlled thrust to change the orbit in which its launcher places it. These orbit-raising manoeuvres change the satellite's velocity and orbital energy, converting a transfer orbit into the required operational orbit.

From launch injection to a transfer orbit

A launcher may place a satellite directly into its operational orbit or first inject it into an intermediate orbit. After separation, a satellite requiring further orbit changes uses its onboard propulsion system under ground-commanded or automated control.

• For many high-altitude missions, the intermediate orbit is elliptical: perigee is its closest point to Earth, while apogee is its farthest point.
• A geostationary transfer orbit (GTO) typically has a low perigee and an apogee near geostationary altitude; it is not itself a geostationary orbit.
• The required manoeuvres depend on the starting orbit and the target altitude, shape and inclination.

How propulsion raises and reshapes the orbit

Before a burn, the satellite is oriented so that thrust acts in the required direction. A velocity change, called delta-v, alters its subsequent path under Earth's gravity.

• A prograde burn, directed along the satellite's motion at perigee, raises the apogee.
• A prograde burn at apogee raises the perigee; this is central to converting an elongated GTO into a nearly circular high-altitude orbit.
• Inclination correction changes the tilt of the orbital plane and can be combined with other manoeuvres; plane changes generally require less delta-v where orbital speed is lower.
• Chemical propulsion commonly uses separate burns with coasting intervals, whereas electric propulsion can reshape an orbit gradually through prolonged low thrust.

Reaching and maintaining the operational orbit

Orbit determination from tracking data allows controllers to assess the achieved trajectory and plan corrections. Final manoeuvres establish the required orbital parameters and, where applicable, the assigned position relative to Earth.

• For a geostationary orbit, the satellite must follow a circular, prograde equatorial orbit with a period equal to Earth's rotation period, so that it appears stationary above one longitude.
• Not every mission targets geostationary orbit: navigation and other satellites may operate in inclined orbits.
• After insertion, station-keeping manoeuvres counter orbital disturbances; these maintain the operational orbit rather than perform the initial orbit raising.