Guidance and Control Systems

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Guidance and Control Systems

Guidance and control systems determine and regulate everything from the trajectory of a vehicle to how much fuel it burns and when. Thus, these systems are vital to the performance of satellites, rockets , and spacecraft in orbit and when moving through space. Space travel and the use of communications and other types of satellites would be impossible without the thousands of individual components that constitute guidance and control systems.

Piloted and Unpiloted Guidance

In piloted spacecraft, guidance control is usually an automatic processthat is, controlled by the ground-based support crew. But astronauts also have the capability of guiding their craft, in order to fine-tune their orbit or interstellar path, maneuver the spacecraft to a target, and as a fallback system in case of ground-based guidance failure.

Unpiloted craft, such as a rocket (essentially a tube mounted on an explosive motor), has to be oriented correctly and kept going in the desired direction. Longitudinal and lateral guidance and control processes are important.

Longitudinal guidance, along the long axis of the rocket, prevents potentially catastrophic end-over-end tumbling. Fins are sometimes used for this purpose. Passive fins, which do not move, can be positioned toward the front or, most commonly, towards the rear of the rocket. Passive fins cannot correct for changes from the desired route caused by things such as a cross-wind. Such directional control, which is important in the targeting of military weapons, for example, can be achieved by active fins, which are pivoted in a manner similar to the rudder on an airplane. Proper lateral guidance, or guidance around the cylinder, is ensured by small rockets called thrusters. They are positioned along the side of the craft and help prevent or control spinning.


Satellites intended for orbit can have various guidance and control systems, depending on the design of the satellite, the height of the orbit, and the satellite's function. Many satellites are stabilized in their orbits by spinning. Things that spin are naturally stable. Cylindrical satellites often spin slowly, at about one revolution per second, to keep them in their predetermined orbit. If a satellite has a communications dish, the dish must remain stationary to keep pointing at its target on Earth. The satellite has to be designed to maintain its stability even with a nonmoving portion present, and the dish must be designed to prevent the satellite from wobbling out of orbit. Satellites with protruding solar panels require another means of guidance and control, which is provided by gyroscopes or small spinning wheelsflywheelsthat are part of the main body of the satellite. If sensors detect an orbital change, a signal is relayed to the flywheels to spin faster or slower to correct the deviation.

Forces associated with Earth, such as gravity and the magnetic field, provide other means of guidance, serving to position the orbiting spacecraft or satellite in a certain orientation or maintain the desired flight path.

see also Flight Control (volume 3); Inertial Measurement Units (volume 3); Navigation (volume 3).

Brian Hoyle


Macaulay, David. "Harnessing the Elements." In The Way New Things Work. Boston:Houghton Mifflin, 1988.

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Guidance and Control Systems

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