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Descent Imaging on the Lunar Surveyor Missions

In the 1990s and 2000s, we have come to think of "Surveyor" as being a Mars exploration program. However, during the 1960s there was another "Surveyor" program that was designed to determine whether the U.S. could safely land a spacecraft on the surface of the Moon. The Lunar Surveyor program was conducted between 1966 and 1968. Five of seven landers were successful: Surveyor 1 (1966), Surveyor 3 (1967), Surveyor 5 (1967), Surveyor 6 (1967), and Surveyor 7 (1968). Of these, only Surveyors 1 and 2 had descent cameras. Surveyor 1 successfully landed but Surveyor 2 crashed.

The Surveyor 1 and 2 "approach" cameras were vidicon-based like their surface cameras. Little information about these cameras is available today. From the Surveyor 1 Mission Report we read:

   The approach camera is intended to provide overlapping
   photography of the lunar surface during the terminal phase
   of the trajectory and is turned on nominally 1000 nautical
   miles above the lunar surface. Because of the complexity of
   the terminal descent phase of the mission, the approach camera
   was not utilitized.
Since the only communication during landing was via a low-rate omnidirectional antenna, competition for bandwidth between the camera and other engineering subsystems probably squeezed out camera operations. The approach camera was deleted from the later Surveyor missions and replaced with other experiments.

Presumably, though, the TV camera consisted of a vidicon tube, lens of unknown (possibly 25-mm) focal length and a shutter. The 200-line mode of the landed camera would probably have been used. The 200-line mode transmitted over the omnidirectional antenna and scanned one frame every 61.8 sec. Each 200-line picture required 20 sec for a complete video transmission and utilized a bandwidth of 1.2 kHz.

Surveyor data transmissions were converted to a standard television signal for closed-circuit and public broadcast television. The television images were displayed on Earth on a slow scan monitor coated with a long persistency phosphor. The persistency was selected to optimally match the nominal maximum frame rate. One frame of TV identification was received for each incoming TV frame and was displayed in real time at a rate compatible with the incoming image. These data were recorded on a video magnetic tape recorder.




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