The ATS 3 Multicolor Spin-Scan Cloudcover Camera (MSSCC) represented a significant advance over a similar but monochromatic spin-scan camera on ATS 1. The MSSCC was mounted with its optical axis perpendicular to the spacecraft’s spin axis and viewed the earth through a special aperture in the spacecraft’s side. The camera consisted of a high-resolution telescope, three photomultiplier light detectors (red, blue, and green), and a precision latitude step mechanism. Light entering the system was focused alternately on a set of three 0.038-mm aperture plates and then passed through various filters to impinge on the appropriate photodetector. The telescope multiplier assembly could be tilted in discrete steps to provide pole-to-pole coverage in 2400 scan lines. East-to-west scan was provided by the spin of the satellite itself. A total time of 24 min was required to scan one frame and 2.4 min to retrace with a nominal satellite rotation of 100 rpm. From its geosynchronous orbit, the camera had a ground resolution of better than 4 km at nadir. The experiment was successful, with ATS 3 being the first spacecraft to transmit operational multicolor earth-cloud photographs. Approximately 3 months after launch, however, the red and blue channels failed, and the system subsequently was limited to producing black-and-white pictures. Good quality black-and-white pictures were received daily until December 11, 1974, when operations were curtailed to three pictures a week. Experiment operation was completely discontinued on October 30, 1975.

From National Space Science Data Center, NSSDC ID: 1967-111A-01