A spacecraft having east/west orbit control during a north or south stationkeeping manoeuvre

摘要

A 3-axis stabilised spacecraft (10) has primary and secondary attitude control thruster strings (A,B,38,40,42) thrusters (2A to 7A and 2B to 7B) in each string exerting roll, pitch and yaw torques. The primary and secondary thruster strings are similar and exhibit paired thrusters oriented on opposite sides of an East/West axis passing through the spacecraft. A stationkeeping input (36) energizes the North or South thrusters (6B,7B,6A,7A) to cause a manoeuvre of the spacecraft along a North/South axis, the thrusters effecting a perturbation in the spacecraft's attitude. An attitude control system energizes at least a primary string thruster (2A to 5A) to counteract the attitude perturbation, the thruster being oriented so as also to cause a change in the spacecraft's East/West orbit velocity. A processor (30) is responsive to the change in East/West orbit velocity reaching a deadband limit value to deactivate the primary string thruster and to activate the secondary string thruster (2B to 5B) which exhibits a similar torque effect on the spacecraft as the primary string thruster but is oriented so as to cause an oppositely directed change in the spacecraft's East/West orbit velocity. The spacecraft further includes a system for enabling all primary and secondary thrusters that exert a force in one direction (i.e. East or West) for attitude control during limit cycling and during the North or South stationkeeping manoeuvre. The like directed thrusters both provide attitude stabilization and cause a predetermined change in orbit velocity. IMAGE IMAGE