Position sensor

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Position sensors (also position control sensors ) are used in space technology and are an essential part of position control in almost every larger satellite or spacecraft ( s / c ). By means of measurements of reference fields or reference points (e.g. earth's magnetic field or stars), they determine the position and orientation of a satellite in three-dimensional space , mostly relative to the earth . This information is then used by other position control components such as actuators or Torqrods to stabilize or change the position and position of the satellite.

Orbit and attitude control system of a spacecraft

function

Position sensors are components of the orbit and position control system of a spacecraft, also called ADCS ( A ttitude D etermination and C ontrol S ystem) or AOCS (English A ttitude and O rbit C ontrol S ystem). This is responsible for the alignment of the satellite relative to a reference point (position control), e.g. B. a point on the earth's surface, as well as for the stabilization or change of its current orbit, the so-called orbit .

Components

Path and attitude control systems mainly consist of:

  • Position sensors for determining position and position
  • Torque and force generating units (e.g. actuators ) for changing path and position
  • Telemetry and command interface
  • Arithmetic unit

Sensor types

The most important types of position sensors are:

Each type of sensor has specific advantages and disadvantages. In practice today, due to their high accuracy, star sensors are mainly used on satellites , mostly in combination with sun sensors and a fluxgate magnetometer .

Star sensor

Star sensors make images of the starry sky and compare the geometric arrangement of the recorded stars with an internal database. By evaluating this comparison,the position of a satellite relative to the starry sky can then be clearlydetermined using suitable algorithms .

Sun sensor

Sun sensors determine the position of a satellite relative to the sun . This is basically only possible if the sun is in the field of view (FOV ) of the sensor. A distinction is made between digital and analog sun sensors.

Earth sensor

Earth sensors determine the position of a satellite relative to the earth . Due to the lack of accuracy, mainly due to the albedo influence , earth sensors are being displaced more and more by the more precise but more expensive star sensors.

GPS

GPS is used on satellites to determine position. A GPS unit suitable for space usually consists of 2 components: the receiver and the antenna . The accuracy range of the position determination is usually in the range of 100 meters.

Magnetometer

A magnetometer determines the direction and strength of the earth's magnetic field . With the help of this data, among other things, the position relative to the earth is determined. The most common design for space applications is that of the fluxgate magnetometer .

Gyroscope (rotation rate sensors)

Gyroscopes or gyroscopes determine the rate of rotation of a satellite compared to its inertial state . A distinction is made between mechanical gyroscopes and - more modern - optical gyroscopes; in recent years fiber optic gyroscopes ( laser gyroscopes ) havealso been used increasingly.

application

Position sensors are used in both near -earth and geostationary satellites. Such sensors are also used in interplanetary missions, for example Mars Express .

Manufacturer

The Thuringian company Jena-Optronik GmbH is a leading supplier of position sensors .

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