The slew of a

spacecraft A spacecraft is a vehicle that is designed spaceflight, to fly and operate in outer space. Spacecraft are used for a variety of purposes, including Telecommunications, communications, Earth observation satellite, Earth observation, Weather s ...

is its orientation 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 Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...

, the

Sun The Sun is the star at the centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

, another celestial body or other point in space. When moving to assume such an orientation, the spacecraft is slewing. During

spaceflight Spaceflight (or space flight) is an application of astronautics to fly objects, usually spacecraft, into or through outer space, either with or without humans on board. Most spaceflight is uncrewed and conducted mainly with spacecraft such ...

, a craft's attitude must be controlled for reasons depending on the craft's mission. Keeping a spacecraft slewed properly is vital for ensuring that its 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 o ...

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

3-axis stabilized spacecraft Spacecraft attitude control is the process of controlling the orientation of a spacecraft (vehicle or satellite) with respect to an inertial frame of reference or another entity such as the celestial sphere, certain fields, and nearby objects, ...

is typically in closed loop control with thrusters or electrically-powered

reaction wheel A reaction wheel (RW) is an electric motor attached to a flywheel, which, when its rotation speed is changed, causes a counter-rotation proportionately through conservation of angular momentum. A reaction wheel can rotate only around its center ...

s 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 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