On-orbit jitter control in momentum actuators using a three-flywheel system

Vibrations on-board a spacecraft have degrading effects on the performance of certain payloads like astronomical telescopes, Earth observation systems, optical communication equipment, etc. The major source of these vibrations include momentum actuators used for attitude control, thrusters, solar array drives and other rotary mechanical equipment. The effect of these vibrations is spacecraft jitter which causes for example, smearing of images in a telescope. Spacecraft jitter due to rotor imbalance in momentum actuators is considered. Publications to date have researched isolation and suppression of vibration thus caused. This paper investigates the dynamics of jitter due to rotor imbalance and proposes a modification to the momentum actuators that provides a long term jitter management solution. The modification involves replacing a flywheel/rotor in the momentum actuator by a three-flywheel system. This method overcomes the need for prior precision balancing of individual flywheels and is capable of achieving a balanced system on orbit. It also provides limited redundancy against flywheel failure and may help accelerate testing and calibration. The dynamics of the three-flywheel system are developed and elaborate simulations are performed to verify the validity of the method. The performances of the proposed three-flywheel system and an equivalent single-flywheel system are compared. The effect of single/multiple flywheel failure in the three-flywheel system is investigated. An indicative design of the three-flywheel system and other implementation aspects are discussed to evidence its practicality. The potential increase in the mass, and power consumption of the three-flywheel system is discussed using a power and mass analysis based on the indicative design.