Ensuring a satellite's correct positioning on its axes is a tricky business. There is no simple guide in space, and yet pin-point accuracy is needed, especially with observation satellites, or satellites that communicate with one another. Recently, however, solid-state charge-coupled device, or CCD image sensors have been providing a convenient and reliable solution to the problem by accurately locating light sources-distant stars or a laser-on which the satellite's attitude may be referenced. The concept used is quite simple. The CCD contains a two-dimensional array of light-sensing elements that receives an image focused by a lens pointing approximately towards the reference light source. Assuming that it is a star seen as a bright point, its image will fall on one, or a few, of the CCD's elements. The CCD integrates the light received by the array during a given exposure period and then reads out the contents of each element. The element or elements that received the star's image will give a strong signal, while the others will give a low background level. In this way, position of the image on the sensor can be located. If the sensor is at a well-defined position in the satellite, the correct attitude can be obtained. This is achieved by coupling the sensor to the thruster controls to maintain the image targeted on a specific location of the sensor array.
CCDs point the way
CCDs zeigen den Weg
Satellite Communications ; 12 , 10 ; 25-29
1988
5 Seiten
Article (Journal)
English
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