Automatic satellite tracking system for the NASA Satellite Photometric Observatory
The development of an Automatic TV Tracking System for NASA's mobile 61 cm aperture Satellite Photometric Observatory is described. The analysis techniques used to match the FOV and resolutions to changing seeing conditions are covered in details. Theoretical reasons for such matching of general interest are discussed. It is shown that the energy density in a satellite image is 11 times greater during good seeing conditions than during typical seeing conditions. The Z7987 image tube is shown to be able to detect 16th magnitude objects under ideal seeing conditions using only 8 percent of the light collected by the main telescope. Experimental results show that the SPO equipped with a Z7987 camera can track a satellite at any orbital velocity with less than 0.14 mr accuracy using the DBA Series 606 TV Tracker. The manual system used prior to the installation of the Automatic TV Tracking System could maintain track at 1.1 mr accuracy for comparison.
Television System Optimization For Astronomy And Special Applications
The predominance of television systems which operate at standard broadcast rates tend to mask several system optimization techniques which can improve performance of nonstandard systems. Astronomical systems, in particular, benefit by use of nonstandard frame rates, line numbers, and a proper balance between exposure time and sensor gain. Resolution and signal-to-noise from a given sensor can be maximized by proper selection of the number of TV lines and the frame time. In addition, the signal-to-video noise for a given TV resolution has a peak value for the video bandwidth picked from sensor and system parameters.
Transfer Characteristics and Spectral Response of Television Camera Tubes
It is the intention of this chapter to describe methods of presenting television camera tube characteristics that will cover all camera tubes regardless of their spectral sensitivity. Although the majority of present-day camera tubes are sensitive only in the near-ultraviolet, the visible, and the near-infrared spectrum, it is felt that a general method of presenting television camera tube characteristics that can be used for any spectral region will be more useful than a method that is applicable only to the visible spectrum. The major application for television camera tubes has been, and probably still is, the entertainment field. The need for precise definition of the tube characteristic does not exist for the entertainment field or a few similar applications. Consequently, a certain amount of subjectivity has been evident in the stating of television camera tube characteristics. However, television camera tubes are now being used more and more for scientific, engineering, and defense applications, where the need exists for objective and relatively accurate means of stating the tube characteristics. For this reason, the more general radiometric units for input signal are preferred over the more common photometric units. Measurements will be given in radiometric units, and I shall show how to transfer from either set of units to the other. The output signal will be given both in terms of signal current and in signal-to-noise ratio.