While early color television systems faced challenges on Earth, one particular technology, the field-sequential color system, found an unexpected and crucial application in space exploration. In the late 1960s, NASA revived a modified version of the Goldmark-CBS system to broadcast color video from the Apollo Command Modules. This adaptation by Westinghouse Electric Corporation allowed for the transmission of color images from space, including eventually
from the lunar surface itself, marking a unique chapter in the history of color television.
Adapting an Older Technology for Space
Color broadcast studio television cameras in the 1960s, such as the RCA TK-41, were large, heavy, and consumed a lot of energy. These cameras typically used three imaging tubes to generate red, green, and blue (RGB) video signals, which were then combined to produce a composite color picture. Such systems required complex optics to keep the tubes aligned, and were susceptible to misalignment due to temperature variations and vibration. For the demanding environment of space, and particularly for lunar surface operations, a more robust and simpler system was needed.
Recognizing these limitations, Stanley Lebar and his Westinghouse team, who were project managers for NASA's Apollo television cameras, began exploring options for adding color to their cameras as early as 1967. They determined that the CBS field-sequential system, despite its earlier commercial struggles, would likely be the best system to study. This system, originally invented by CBS Laboratories in the 1940s, utilized a color wheel with six filter segments rotating in front of a single video camera tube to generate the RGB signal. It was simpler, more reliable, and more power-efficient than the standard three-tube color camera systems.
The Westinghouse Lunar Color Camera
The Westinghouse lunar color camera used a modified version of CBS's field-sequential color system. A color wheel, featuring six filter segments, was positioned behind the lens mount and rotated at 9.99 revolutions per second. This rotation produced a scan rate of 59.94 fields per second, which matched the NTSC video standard. Synchronization between the color wheel and the pickup tube's scan rate was achieved through a magnet on the wheel, which controlled the sync pulse generator governing the tube's timing. The camera incorporated the same SEC video imaging tube as the monochrome lunar camera flown on Apollo 9.
This specialized camera was larger than its monochrome counterpart, measuring 17 inches (430 millimeters) long, including its new zoom lens. The zoom lens offered a variable focal length from 25 mm to 150 mm, providing a 6:1 zoom ratio. Its field of view ranged from 43 degrees at its widest angle to 7 degrees in its extreme telephoto mode, with an aperture range from F4 to F44 and a T5 light transmittance rating. Starting with Apollo 10 in May 1969, these sequential color TV cameras were flown on all NASA human spaceflight missions until the late 1980s, when they were eventually replaced by CCD-based cameras. This marked a remarkable second life for a technology that had been deemed commercially unviable for terrestrial broadcasting.
