TV Optical Scanner

Description

The TV optical scanner flown on Explorer 6 was an improved version of the TV system first employed on Pioneer 2. The experiment consisted of an optical unit containing a concave spherical mirror and phototransistor, a video amplifier, timing and logic circuits, and telemetry. The experiment was designed to test the feasibility of using such instrumentation to obtain low-resolution daylight cloudcover photographs. The Explorer 6 scanner also served as a forerunner to the TV camera systems carried on later, more advanced satellites. The scanner's optical axis was directed 45 deg away from the spacecraft spin axis, which was parallel to the orbital plane. The vehicle's spin furnished the line scanning, and the spacecraft's forward motion along its trajectory provided the frame scanning. During a scan (one spacecraft revolution), a single scan spot (element) on earth was viewed and transmitted back to earth. During the next spacecraft revolution, an adjacent spot was scanned. This procedure was repeated until a line of 64 such spots was formed. Then the process was repeated to form an adjacent line of elements, and so on, until a frame, or picture, was obtained. The system could produce useful photographs only when the spacecraft's velocity and orbital position were such that successive lines overlapped. (At apogee, for example, the TV lines were separated by a distance about equal to their length, and hence no meaningful picture could be obtained.) Data obtained from this experiment are limited and of extremely poor quality. Proper spacecraft orientation was never achieved, resulting in a considerable amount of blank space between successive scan lines. The scanner's logic circuits also failed to operate normally (only every fourth scan spot could be successfully reproduced), further reducing the resolution. The last useful data were obtained on August 25, 1959.