Navigation telescope
The navigation telescope is an instrument for monitoring and controlling photogrammetric image flights . The approximately 50 cm long telescope was used in survey aircraft until around 1990 (the advent of GPS ) and was mounted vertically downwards next to the serial camera . On the terrain passing in the field of vision , the operator was able to use line marks and time intervals to check the correct distances between the recorded aerial images and to compensate for the drift caused by the cross wind by panning the camera .
One device to be coupled with this was the overlap regulator for maintaining the usual longitudinal overlap of the aerial images (mostly 60 percent). A spatial evaluation ( stereo photogrammetry) can only be carried out with the terrain areas that have been photographed twice .
In manned space travel
The scanning telescope in manned space travel functions in a similar way to the navigation telescope , see also Space Sextant . It was used in the Gemini and Apollo spacecraft to visually measure the direction of flight over the earth's surface or the moon .
Comparable but automated measuring instruments are also available for interplanetary navigation .