Satellite Altitude and Orbit Control( AOCS)

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Satellite Altitude and Orbit Control AOCS

Satellite Altitude and Orbit Control: In this post, Altitude Control & Orbit Control of Satellite is explained.

Satellite Altitude and Orbit Control

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Altitude of a satellite

The attitude of a satellite refers to its orientation in space.

Much of the equipment carried aboard a satellite is meant for the purpose of controlling its attitude. Attitude control is necessary, to ensure that directional antennas point in the proper directions.

In the case of earth environmental satellites, the earth-sensing instruments must cover the required regions of the earth, which also requires attitude control.

A number of forces, referred to as disturbance torques, can alter the attitude, some examples being the gravitational fields of the earth and the moon, solar radiation, and meteorite impacts.

Attitude control must not be confused with station keeping, which is used for maintaining a satellite in its correct orbital position, although the two are closely related.

To exercise attitude control, there must be available some measure of a satellite’s orientation in space and of any tendency for this to shift.

In one method, infrared sensors, referred to as horizon detectors, are used to detect the rim of the earth against the background of space.

Satellite Altitude and Orbit Control AOCS
Satellite Altitude and Orbit Control AOCS

With the use of four such sensors, one for each quadrant, the center of the earth can be readily established as a reference point.

The attitude-control process takes place aboard the satellite, but it is also possible for control signals to be transmitted from earth, based on attitude data obtained from the satellite.

Whenever a shift in attitude is desired, an attitude maneuver is executed. The control signals needed to achieve this maneuver may be transmitted from an earth station.

Controlling torques may be generated in a number of ways. Passive attitude control refers to the use of mechanisms which stabilize the satellite without putting a drain on the satellite’s energy supplies; at most, infrequent use is made of these supplies, for example, when thruster jets are impulsed to provide corrective torque.

xamples of passive attitude control are spin stabilization and gravity gradient stabilization.

The other form of attitude control is active control.

With active attitude control, there is no overall stabilizing torque present to resist the disturbance torques. Instead, corrective torques are applied in response to disturbance torques. Methods used to generate active control torques include momentum wheels, electromagnetic coils, and mass expulsion devices, such as gas jets and ion thrusters.

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