Mars TV Camera

Description

The Mars television experiment was designed to obtain photographs of the Martian surface and telemeter them to earth. The TV subsystem consisted of (1) a Cassegrain narrow-angle reflecting telescope with a 30.5-cm effective focal length and a 1.05- by 1.05-deg field of view, (2) a shutter and filter assembly that had 0.08- and 0.20-s exposure times and used red and green filters, (3) a slow scan vidicon tube, with a 0.22- by 0.22-in. sq target, which translated the optical image into an electrical video signal, and (4) related electronics including a TV data encoder. On July 14, 1965, at 0018 UT, the picture recording sequence commenced. Vidicon output underwent analog-to-digital conversion and data were stored at 240,000 bits per picture (each picture was 200 lines by 200 pixels, 6 bits per pixel)on a wo-track, 1/4-in., 330-ft long, magnetic tape loop on the spacecraft. Two of every three pictures taken were recorded on the tape, resulting in a chain of pairs of overlapping, alternately filtered pictures extending across the disk of Mars. Data were transmitted after occultation of the spacecraft by Mars by the radio subsystem from July 15 to 24, 1965, and were processed in real time by a 7044/7094 system to format magnetic tapes of the image data for processing by the Ranger television processing programs and for conversion to a film record. Conversion from electrical signals to an optical image was performed by the video-to-film recorder using 64 shades. The experiment yielded 21 pictures plus 21 lines of picture 22. This performance indicated a normal recording sequence. Computer processing programs yielded photographs with greater contrast than the raw image data. A detailed description of the television experiment, data processing, and the various versions of the photography can be found in the JPL "Mariner Mars 1964 Project Report, Television Experiment, Part I, Investigators' Report," of the Mariner IV Pictures of Mars, TR 32-884, 1967.