1. Block II spacecraft were 3-axis stabilized, with ground pointing using reaction wheels . 2. To control satellite orientation, several magnetorquer coils and reaction wheels were added. 3. The problem had cropped up in one of the craft's reaction wheels . 4. Attitude control was achieved using the hydrazine thrusters and four reaction wheels . 5. Designers therefore supplement reaction wheel systems with other attitude control mechanisms. 6. It is 3-axis body stabilised using Sun and Earth sensors, momentum and reaction wheels . 7. The reaction wheels slowly move the 25, 000-pound telescope from one point to another. 8. The reaction wheels can only provide a certain amount of change in angular momentum. 9. Over time, reaction wheels may build up stored momentum that needs to be cancelled. 10. One of Hubble's four reaction wheels briefly malfunctioned in November.
