Thrusters and Spinning Wheels

HOW DO YOU CONTROL ATTITUDE IN SPACE?

Because the control surfaces that an airplane uses cannot work in airless space, a spacecraft relies on a different form of attitude control. To change orientation, a spacecraft applies torque (a twisting force) by firing small rockets or by spinning internal wheels.

To rotate a spacecraft, a pair of thruster rockets on opposite sides of the vehicle are fired in opposite directions. To stop the rotation, a second pair is fired to produce an opposing force. The Space Shuttle’s Reaction Control System provides the thrust for attitude maneuvers (roll, pitch, and yaw), and for small velocity changes along the Shuttle’s longitudinal axis (front to back). See the Space Shuttle Discovery at the National Air and Space Museum's Steven F. Udvar-Hazy Center.

Credit: National Air and Space Museum, Smithsonian Institution

Some satellites use a system of reaction wheels—basically gyroscopes—to change their attitude in space. The rapidly spinning wheels carry a lot of rotational momentum that the spacecraft can tap to change its own orientation. To do this in all three dimensions of space, the spacecraft must use three rotating wheels oriented at right angles to one another.

HOW CAN THRUST HELP CHANGE ATTITUDE?                     

Most spacecraft use small thruster rockets to control their attitude. To rotate a spacecraft, a pair of thruster rockets on opposite sides of the vehicle are fired in opposite directions. To stop the rotation, a second pair is fired to produce an opposing force.