Slew (spacecraft)

A spacecraft is either spin stabilized or 3 axis stabilized (The very first "Sputnik" was an exception, it was wobbling).

For a spin stabilized spacecraft a slew means a change of the direction of the spin axis relative to space. This can be done by applying a (significant) torque to the spacecraft, in general by operating a thruster in pulsed mode synchronous to the spin. This results in a precession and slews for this kind of spacecraft are therefore also called "precession manoeuvre"

The attitude of 3 axis stabilized spacecraft is typically in closed loop control with actuators maintaining a certain attitude based on attitude sensor measurements. The attitude stabilisation can use stars as reference and aim for an attitude that is fixed relative to inertial space. With a slew is then meant that the actuators are operated such that the attitude of the spacecraft is changed. A typical example is a space telescope that should be turned to observe a new celestial object. But also for 3 axis stabilized spacecraft for which the normal attitude is not inertially fixed the spacecraft is said to make a slew if the attitude is changed in another way and with another, mostly higher, rate then when in the basic attitude control mode. An example is the Magellan probe that once per orbit interupted the scanning of the Venus surface making a large turn to direct its high gain antenna to the Earth for data transmission