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.
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.