Editing Guidance system (section)

{{Short description|Device used to guide vehicles}}{{More citations needed|date=May 2017}}

A '''guidance system''' is a virtual or physical device, or a group of devices implementing a controlling the movement of a [[ship]], [[aircraft]], [[missile]], [[rocket]], [[satellite]], or any other moving object. Guidance is the process of calculating the changes in position, velocity, [[altitude control|altitude]], and/or rotation rates of a moving object required to follow a certain trajectory and/or altitude profile based on information about the object's state of motion.<ref>{{cite book 
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|first3=Angus P.
|date=2007
|title=Global Positioning Systems, Inertial Navigation, and Integration
|url=https://archive.org/details/globalpositionin00grew_526
|url-access=limited
|edition=2nd
|location=Hoboken, New Jersey, USA
|publisher=Wiley-Interscience, John Wiley & Sons, Inc.
|page=[https://archive.org/details/globalpositionin00grew_526/page/n49 21]
|isbn=978-0-470-04190-1
}}</ref><ref>{{cite book 
|last1=Farrell
|first1=Jay A.
|date=2008
|title=Aided Navigation: GPS with High Rate Sensors
|url=https://archive.org/details/aidednavigationg00farr
|url-access=limited
|location=USA
|publisher=The McGraw-Hill Companies
|pages=[https://archive.org/details/aidednavigationg00farr/page/n27 5] et seq
|isbn=978-0-07-164266-8
}}</ref><ref>
{{Cite report
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 | date       = June 1965
 | title      = Apollo Guidance and Navigation
 | url        = http://www.ibiblio.org/apollo/hrst/archive/1713.pdf
 | publisher  = Massachusetts Institute of Technology, Instrumentation Laboratory
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 | access-date = October 12, 2014
}}</ref>

A guidance system is usually part of a [[Guidance, navigation and control]] system, whereas navigation refers to the systems necessary to calculate the current position and orientation based on sensor data like those from [[compass]]es, [[GPS|GPS receivers]], [[Loran-C]], [[star tracker]]s, [[inertial measurement unit]]s, [[altimeter]]s, etc. The output of the [[navigation system]], the navigation solution, is an input for the guidance system, among others like the environmental conditions (wind, water, temperature, etc.) and the vehicle's characteristics (i.e. mass, control system availability, control systems correlation to vector change, etc.). In general, the guidance system computes the instructions for the control system, which comprises the object's actuators (e.g., [[Spacecraft propulsion|thrusters]], [[reaction wheels]], [[Flap (aeronautics)|body flaps]], etc.), which are able to manipulate the path and orientation of the object without direct or continuous human control.

One of the earliest examples of a true guidance system is that used in the German [[V-1 flying bomb|V-1]] during [[World War II]]. The navigation system consisted of a simple [[gyroscope]], an [[airspeed]] sensor, and an altimeter. The guidance instructions were target altitude, target velocity, cruise time, and engine cut off time.

A guidance system has three major sub-sections: Inputs, Processing, and Outputs. The input section includes [[sensor]]s, [[Course (navigation)|course]] data, [[radio]] and [[satellite link]]s, and other information sources. The processing section, composed of one or more [[Central processing unit|CPUs]], integrates this data and determines what actions, if any, are necessary to maintain or achieve a proper [[Aircraft heading|heading]]. This is then fed to the outputs which can directly affect the system's course. The outputs may control [[speed]] by interacting with devices such as [[turbine]]s, and [[Fuel pump (engine)|fuel pump]]s, or they may more directly alter course by actuating [[aileron]]s, [[rudder]]s, or other devices.