Slew (spacecraft)
Encyclopedia
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 interrupted the scanning of the Venus surface making a large turn to direct its high gain antenna to the Earth for data transmission
Spin-stabilized satellite
A spin-stabilized satellite is a satellite which has the motion of one axis held fixed by spinning the satellite around that axis, using the gyroscopic effect.The attitude of a satellite or any rigid body is its orientation in space...
or 3 axis stabilized
3 axis stabilized spacecraft
3 axis stabilization is a design feature of most modern spacecraft whereby the spacecraft utilizes sensor readings to determine how actuators on the spacecraft can be used to keep it in a desired attitude, or orientation in space.-See also:...
(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
Precession
Precession is a change in the orientation of the rotation axis of a rotating body. It can be defined as a change in direction of the rotation axis in which the second Euler angle is constant...
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
Control theory
Control theory is an interdisciplinary branch of engineering and mathematics that deals with the behavior of dynamical systems. The desired output of a system is called the reference...
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
Inertial space
In physics, the expression inertial space refers to the background reference that is provided by the phenomenon of inertia.Inertia is opposition to change of velocity, that is: change of velocity with respect to the background, the background that all physical objects are embedded in....
. 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
Magellan probe
The Magellan spacecraft, also referred to as the Venus Radar Mapper, was a 1,035-kilogram robotic space probe launched by NASA on May 4, 1989, to map the surface of Venus using Synthetic Aperture Radar and measure the planetary gravity...
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