Thrust Subsystem

The thrust subsystem comprises the propulsion elements used to place a satellite into its final operational orbit and to maintain or adjust that orbit throughout the mission. It typically includes an apogee boost (or apogee kick) motor used to circularise the orbit after launch, together with smaller thrusters used for orbit maintenance, relocation to a different orbital slot, and end-of-life disposal. These orbital maneuvers are distinct from attitude control, which maintains spacecraft orientation.

For geostationary satellites, the majority of propellant consumption is associated with north–south station keeping to counteract perturbations caused primarily by the Sun and Moon, while a much smaller fraction is required for east–west station keeping to control longitude drift. Satellite operational life may be extended by reducing or ceasing north–south station keeping, allowing the spacecraft to drift into an inclined orbit; this saves propellant at the expense of increased Earth-station tracking complexity and additional coordination requirements.

A reserve of propellant is retained for end-of-life maneuvers, enabling the satellite to be transferred to a disposal or graveyard orbit a few hundred kilometers above the geostationary arc to mitigate long-term interference and collision risk.