The replacement Reaction Wheel Actuator for the Hubble Space Telescope arrives at the Vertical Processing Facility.

The replacement Reaction Wheel Actuator for the Hubble Space Telescope arrives at the Vertical Processing Facility. Part of Hubble's Pointing Control System, the actuators receiving information from sensors and physically adjust Hubble's position and orientation so that Hubble can view the required celestial bodies. The reaction wheels work by rotating a large flywheel up to 3000 rpm or braking it to exchange momentum with the spacecraft which will make Hubble turn. The RWA is part of the payload on mission STS-109, the Hubble Servicing Mission, scheduled to launch Feb. 28, 2002