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{{Short description|Spacecraft orientation}}
{{Other uses|Slew (disambiguation){{!}}Slew}}The '''slew''' of a [[spacecraft]] is its orientation in reference to a plane or fixed position such as [[Earth]], the [[Sun]], another celestial body or other point in space. When moving to assume such an orientation, the spacecraft is '''slewing.'''<ref name=messenger_pj>{{cite web|url=http://photojournal.jpl.nasa.gov/catalog/PIA14805|title=PIA14805: A Sideways Glance|publisher=Jet Propulsion Laboratory|accessdate=2012-01-01}}</ref><ref name=NASA_LSI>{{cite web|url=http://lunarscience.nasa.gov/articles/tycho-central-peak-spectacular|title=Tycho Central Peak Spectacular!|publisher=NASA's Lunar Science Institute|accessdate=2012-01-01}}</ref><ref name=gcn>{{cite web|url=http://gcn.gsfc.nasa.gov/gcn3/3590.gcn3|title=GCN GRB Observation Report|publisher=NASA's Goddard Space Flight Center|accessdate=2012-01-01}}</ref>

During [[spaceflight]], 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.<ref name=Basics11>{{cite web|url=http://www2.jpl.nasa.gov/basics/bsf11-2.php|title=Basics of Space Flight: Section II|publisher=Jet Propulsion Laboratory|accessdate=2012-01-01}}</ref>

For [[Spin-stabilized satellite|spin-stabilized spacecraft]], slewing is accomplished by applying a (significant) torque to the spacecraft, in general by operating a [[Vernier thruster|thruster]] in synchronous or asynchronous direction to its spin to adjust its spin rate.<ref name=dictionary1>{{cite web|url=http://er.jsc.nasa.gov/seh/s.html#slewing|title=Dictionary of Technical Terms for Space|publisher=NASA's Software, Robotics and Simulation Division|accessdate=2012-01-01}}</ref> This results in a [[precession]] and slews for this kind of spacecraft are therefore also called "precession manoeuvre."

The slew of [[3-axis stabilized spacecraft]] is typically in [[Control theory|closed loop control]] with thrusters or electrically-powered [[reaction wheel]]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.

==See also==
* [[Attitude control (spacecraft)]]
* [[Flight dynamics (spacecraft)]]
* [[Reaction control system]]

==References==
{{Reflist}}

[[Category:Spaceflight concepts]]

Slew (spacecraft) - Revision history

Ajay Kumar: Created a new article