Slew and slewing are terms which can refer to a spacecraft's orientation or movement in reference to a plane or fixed position such as

Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

, the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

, another celestial body or other point in space. During space flight, a craft's attitude must be controlled for reasons dependent upon the craft's mission. Keeping a spacecraft slewed properly is vital toward ensuring that its high-gain antenna remains oriented toward Earth for sending and receiving data and commands. Additionally with many craft, keeping their solar arrays angled toward the Sun optimizes their power absorption and reduces the craft's reliance on internal power systems. Thermal heating and cooling of a craft and its subsystems can also be controlled by the craft's orientation. Cameras or other sensing equipment that are fixed into position upon the craft need to be aimed by slewing the craft. A spacecraft can either be spin stabilized or 3-axis stabilized to maintain proper orientation. For spin-stabilized spacecraft, slewing is accomplished by applying a (significant) torque to the spacecraft, in general by operating a thruster in synchronous or asynchronous direction to its spin to adjust its spin rate. This results in a

precession Precession is a change in the orientation of the rotational axis of a rotating body. In an appropriate reference frame it can be defined as a change in the first Euler angle, whereas the third Euler angle defines the rotation itself. In oth ...

and slews for this kind of spacecraft are therefore also called "precession manoeuvre." The slew of

3-axis stabilized spacecraft Attitude control is the process of controlling the orientation of an aerospace vehicle with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, etc. Controlling vehicle ...

is typically in

closed loop control Control theory is a field of mathematics that deals with the control of dynamical systems in engineered processes and machines. The objective is to develop a model or algorithm governing the application of system inputs to drive the system to a ...

with thrusters or electrically-powered reaction wheels maintaining or altering the craft's attitude based on sensor measurements. 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 than when in the basic attitude control mode. An example is the

Magellan probe The ''Magellan'' spacecraft was a robotic space probe launched by NASA of the United States, on May 4, 1989, to map the surface of Venus by using synthetic-aperture radar and to measure the planetary gravitational field. The ''Magellan'' p ...

that once per orbit interrupted the scanning of the Venus surface making a large turn to direct its high gain antenna to the Earth for data transmission.

References

{{Reflist Spaceflight concepts

See also

References