Hawes Mechanical Television Archive by James T. Hawes, AA9DT
Col-R-Tel on the Moon (Part 1)

Astronaut descends ladder from LEM to lunar surface. (NASA photo)

NASA photo

Illusion Generator

The moon landings transported humanity to a new frontier. This grand adventure also offered a personal scale. Each viewer shared the astronauts' observations. Each of us beheld the lunar landscape for himself. For the worldwide audience, the Apollo astronauts became our Apollo astronauts. As they spoke with us, we all joined Mission Control. We saw what they saw. We delighted in their personal words and thoughts. Newsmen and engineers explained to us technical details that college physics students had never heard. For a brief moment, each of us had a seat on the world's most powerful spacecraft.

Only through television could this event be possible. Here's a true example of television, not as a box of electronics, but as illusion generator. The Apollo astronauts took a rocket to the moon and back. Via television, the rest of us soared through 500,000 miles of virtual space. Illusion generator though it was, television was our true distant vision. Television portrayed the moon as it grew close. At the television, we drew a sigh of relief as our LEM touched down. And by television, we matched our footfalls to the first steps on the lunar surface. Our friend with the camera was there. And this camera brought us all along. In television history, we have found no more compelling use for the medium.

Moon tech. Apollo moon television differs from the TV that we watched in our homes on Earth. NASA briefed the media on the differences.

Spinning wheel. We heard about the spinning wheel in front of color moon TV cameras. Electronics brought us the black-and-white part of the picture. But the color wheel brought us the hues. Mechanical TV had returned to open another technical outback!

Not the CBS color TV system. Newspaper stories mentioned that this mechanical color system was really the CBS color system: The very same system that the US had abandoned in 1951. Quaint, but inaccurate. The CBS color TV system didn't really go to the moon. A CBS color set couldn't lock the moon color picture. In fact, a CBS set couldn't even lock a monochrome picture from the moon. With a CBS color TV, at best, all you'd see would be flipping streaks.

FACT: Apollo moon TV was really Col-R-Tel.

Terrestrial Col-R-Tel

What is Col-R-Tel? Let's define some terms and recount some related TV technical history...
Photo: 1955 Col-R-Tel converter (back view)
1955 Col-R-Tel converter from back of TV. (Luckett, 1955, p. 137)
  • Col-R-Tel (for our purposes, terrestrial Col-R-Tel) is field-sequential color TV that operates at NTSC scanning rates. This is standard black-and-white TV with a non-standard, color switching circuit. When you view the TV through a color wheel, the picture comes out in full color. The Col-R-Tel brand color converter debuted in 1955. For several more years, Color Converter, Inc., a small Indiana company, manufactured Col-R-Tel kits. At $150, the kits allowed do-it-yourselfers to convert their black-and-white TV sets for color reception.

  • Apollo mooncams that produced color pictures first flew on Apollo 10. Astronaut Tom Stafford promoted the use of these cameras. After Apollo 10, every Command Module carried a color mooncam. Starting with Apollo 12, every Lunar Module carried a hardened color camera for use on the lunar surface.

  • Compatible with Col-R-Tel. These moon cameras produced a field-sequential, color signal that was compatible with the 1955 Col-R-Tel output. Apparently Westinghouse and RCA developed their mooncams independently of and without knowledge of Col-R-Tel (Lebar, 2006). Despite this fact, Col-R-Tel and Apollo mooncams are parallel and compatible technologies.

  • Field-sequential color is a form of TV where colors play across the screen one by one, instead of simultaneously. The CBS color TV system, Col-R-Tel and color mooncams all use field-sequential color technology.

  • CBS color is a color TV method that Peter Goldmark invented in the 1940s. The FCC approved the final version in 1950. CBS became the U.S. color TV standard in 1951. Yet after only a few months, it flopped commercially. The CBS system is a field-sequential color system that operates at non-NTSC scanning rates. This system is incompatible with NTSC TV. The most famous features of the CBS system are the color wheels (scanning discs) at both the TV camera and TV receiver.

  • NTSC stands for National Television System Committee. With considerable help from industry engineers at various companies, RCA invented our NTSC color system. NTSC color TV is compatible with black-and-white TV. In NTSC color, combinations of three primary colors, red, green and blue, make up all the colors in a picture. The three primaries transmit simultaneously. In 1953, the FCC (Federal Communications Commission) approved this system. NTSC broadcasts began in December, 1953. NTSC remained the U.S. system of television until digital TV took over in 2009.

Connections. There are several connections between Col-R-Tel and the color mooncams that debuted some 14 years later...

  • Like terrestrial Col-R-Tel, mooncams (lunar Col-R-Tel) produce field-sequential pictures. These pictures are compatible with the output of terrestrial Col-R-Tel.

  • Both terrestrial Col-R-Tel and the mooncams conserve picture bandwidth and equipment complexity. (For our purposes, bandwidth is the amount of data that can simultaneously pass through the system.)

  • The cost of the Col-R-Tel process (whether on Earth or the moon) is a decrease in image quality. The resulting picture is dim and flickers slightly. The mooncams pose another problem: Normal TV sets can't properly decode and display mooncam pictures.

  • Apollo downlink stations solve the display problem with complex electromechanics: The downlinks contain equipment that converts the R-B-G (red-blue-green) sequential signal to NTSC. This NTSC is viewable on a home TV. Fortunately the conversion process eliminates both the dimness and flicker problems of terrestrial Col-R-Tel pictures. Conversion takes 12 seconds and slightly blurs the edges of moving objects. (Spacecraft Films, Men On the Moon, “TV Transmission 33:59 GET” and “Probe & Drogue TV.”)

How Terrestrial Col-R-Tel Works

Only the wheel. Col-R-Tel adopted the CBS color wheel, the CBS system's most distinctive feature. The CBS system uses one wheel before the studio camera. A matching and synchronized wheel rotates in front of the home receiver, painting colors over the TV picture.

Differences. Unlike the CBS system, Col-R-Tel only needs a color wheel at the receiver. Col-R-Tel electronics differ markedly from CBS system circuits. On screen, the difference is obvious: Col-R-Tel can reproduce standard, off-air, NTSC color TV signals. The CBS system can't. CBS electronics are proprietary. Col-R-Tel electronics are a unique design, too, but that design borrows heavily from NTSC color.

The mechanical part of a Col-R-Tel kit is a plastic color wheel. Six transparent, colored wedges make up the wheel. You mount the wheel in front of the picture tube. Viewers watch the picture through the spinning wheel. As the wheel spins, it adds hues to the picture.

Block diagram: Terrestrial Col-R-Tel system (Farbfernsehen, mechanisches 

Col-R-Tel kit electronics add color saturation values to the picture. Normally, CRT brightness (luminance) is the sum of three color values. The kit's color saturation values add or subtract from this sum. Of course, the display is still monochrome. Yet when watching through the color disc, the viewer perceives true color pictures. Another circuit alters incoming NTSC-standard color signals to produce field-sequential color signals. The electronics also keep the wheel in step with station color signals.

From Col-R-Tel to Mooncams

Mooncams must travel through space, pulling multiple G-forces during takeoffs and landings. They must operate over a 500-degree temperature range. Despite all this abuse, mooncams must be reliable. And there's more: Mooncams have to use as little power and bandwidth as possible. Mooncams must be lightweight and portable. They can't be temperamental. Complicated tube alignment and optical balancing procedures are out of the question. With all these requirements, no studio color camera of the 1960s can measure up. Eventually Westinghouse designers find a solution in field-sequential technology, the stuff of Col-R-Tel and the CBS color system. This technology only requires one tube, so out go the tube-alignment procedures. Meanwhile, the weight and power requirements drop to one-third or one-fourth. Bandwidth reduction is possible, since only one color transmits at a time. (Mooncams don't transmit chroma, burst, or separate monochrome signals.) Specialized camera tubes (the SEC from Westinghouse and the SIT from RCA) can operate in extreme lighting conditions. Special reflective coatings protect the cameras from the temperature extremes of lunar days and nights. New integrated circuits and transistors shrink the electronics. And like Col-R-Tel, every color mooncam sports a color wheel.

Lunar Col-R-Tel

Westinghouse Moon cameras. For the early Apollo missions, Westinghouse designed and supplied monochrome and color cameras. At Westinghouse, the TV camera program manager for Apollo was Stanley Lebar. Stan led the camera development group. Larkin Niemyer directed engineering efforts on the color cameras. Beginning with Apollo 10, lunar missions included a color model for the Command Module.

Westinghouse logo

Stan Lebar and WEC color camera for CM

On Apollo 10, astronaut Thomas Stafford enthusiastically promoted the cabin color camera. The results from the Westinghouse field-sequential color system were nothing but spectacular. After the mission, NASA decided to include color cameras on future missions. These missions transmitted color TV pictures from Westinghouse (WEC) cameras in their command modules. Apollo 12 was the first mission to deploy a color camera on the lunar surface. Yet due to an operator error early in the mission, Apollo 12's surface camera failed. Apollo 13 developed serious equipment problems, and couldn't land. Apollo 14 achieved the first successful color TV transmissions from the lunar surface.

Left: Stan Lebar holds the Westinghouse color camera for use onboard the Command Module.

SEC Tube. Westinghouse (WEC) used a type WL30691 SEC (Secondary Electron Conduction) pickup tube in its TV mooncams. According to Westinghouse, SEC advantages include “...its size, weight, power requirements, ruggedness, stability, and simplicity of operation.” Low-light capability and lack of lag are particularly important characteristics of the SEC. “Lag is a problem when viewing a moving scene, generally resulting in a loss of resolution...” (Niemyer paper, 5)

Right: Mechanical drawing of SEC tube from color mooncam manual, as retouched by the author (Westinghouse, Manual, 3-8)

Drafting drawing: SEC tube, including internal features

Moon color wheel. Moon cameras include a small color wheel in front of the camera lens. This wheel measures some three inches across. It rotates at 599.94 rpm. To the left of the wheel you can see the three-to-one driver wheel. The driver rotates in the reverse direction (clockwise here, from behind the lens) at 1799.82 rpm. The motor shaft, rotating counterclockwise, appears to the left of the driver. The color wheel is practically the same as the terrestrial Col-R-Tel wheel. The main difference is that moon wheels have broader borders between color wedges. Otherwise, both terrestrial and lunar Col-R-Tel wheels resemble the original, CBS wheel. Stanley Lebar tells me that the mooncams scanned the tube in R-B-G order. This is the order that CBS inventor Peter Goldmark specified. Col-R-Tel also follows this CBS color order spec. (CBS research with test audiences proved that R-B-G was the preferred order.) Yet in both terrestrial and lunar Col-R-Tel, the electronics differ from the CBS electronics.

See the photo at top-right, above: This is the back of the Westinghouse color wheel assembly from an Apollo mooncam. This part of the color wheel faces the camera body. The photo originally appeared in “The Color War Goes to the Moon” by Stanley Lebar. Note: The colors on this wheel appear to be cyan, yellow and magenta. As Stan explained to me, these are the complements of the filtered colors red, blue and green. The glass dichroic filters reflect complements and pass filtered colors. Notice the six filter wedges on the color wheel: The convex sides of each filter wedge are the leading edges. This disc would turn counterclockwise. A retouched negative picture shows the actual filter colors. To see these colors, click the photo.

             Electric color wheel for mooncam

Goldmark's CBS patent for color wheel

Goldmark's CBS patent (U.S. patent 2,304,081) includes his color wheel drawing, bottom-right, above. Note the similarity to the mooncam color wheel. Goldmark's color wheel turns counterclockwise, the same way as the Lebar wheel does. (See the direction arrow in the center.) To view a color version of Goldmark's wheel, click the drawing.

Moon color wheel differences. I mentioned the moon color wheel's broad borders between color wedges. These opaque borders allow time to finish scanning one color video field. Afterward, the next color filter swings into place. Colors scan across the camera at the standard NTSC vertical frequency, 59.94 Hz.

RCA cameras. RCA supplied color cameras for Apollo 15, 16 and 17. One of RCA's important contributions was that it corrected the picture gamma (brightness in relation to signal strength).

RCA logo

Less blooming. The result of this change was less blooming or clipping of bright picture details. Gone were the Smurf-like astronaut pictures! Since Mission Control could remotely operate the RCA camera, the camera could follow the lunar liftoff. RCA dubbed the camera the Ground-Controlled Television Assembly or GCTA. Soon after the camera's introduction, astronauts shortened the name to “gotcha.” Robert G. Horner managed the engineering design team. Sam Russell was RCA's project engineer for the Apollo cameras. A link to his story appears at the end of this article.

Right: RCA's GCTA camera for Apollo missions 15 - 17. The moon rover telecasts used this type of camera.
             GCTA camera

Noise Reduction

Image Transform received a NASA contract to reduce noise in lunar video. This extra processing smoothed and sharpened mooncam pictures during Apollo 16 and 17. Image Transform was a North Hollywood, California concern. In nearly real time, it polished video feeds from lunar surface EVAs (extravehicular activities). After this processing, the video returned to Houston for dissemination to worldwide TV networks.

Right: Mechanical drawing of SIT tube from RCA color mooncam manual. Retouched by the author (RCA, Manual, 1-23)
Mechanical drawing: RCA 
             SIT tube

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