The black-and-white TV system

Apollo’s implementation of black-and-white television w as, by far, the simpler of the tw;o systems, and the less greedy of radio bandwidth. The camera, as used on Apollos 8, 9 and 11 had just one imaging tube and operated at scan rates that would normally be called slow-scan television. The frame rate used was only 10 frames per second with 320 lines per frame. There was no interlace. The bandwidth of the signal (which dictated how well the image handled fine detail) was restricted to a very low value of 0.4 MHz (as compared to about 5 MHz for contemporary broadcast TV). The camera used a vidicon type of imaging tube that was notorious at the time for its excessive image lag, and this caused a ghostly smear to trail behind the moving image.

When the pictures reached Earth at this non-standard frame rate, they were electronically incompatible with just about every TV system on the planet. Converters were installed at chosen ground stations to generate standard US television signals from the lunar TV. The converter worked in two stages. The first simply consisted of another vidicon TV camera aimed at a small television screen. The screen displayed the images from the Moon at 10 frames per second while the camera, which ran at 60 fields per second, was allowed to capture the screen only when a full image had been completed, which was every tenth of a second. In other words, only one field in six from the camera contained a picture.

The second stage was to recreate the missing five fields. The single good frame from the TV camera was recorded onto a magnetic disk which then replayed it five times to reconstruct the full 60-fields-per-second TV signal, ready for distribution to Houston. The repetition of the fields and additional lag from the second camera added to the ghostly impression left by Apollo ll’s moonwalk coverage.

A question that is often asked is, if Neil Armstrong was the first man on the Moon, who operated the TV camera? ft is a spurious question because it assumes that all cameras must have a cameraman behind them. In fact, Eagle’s camera was mounted inside a fold-down panel next to the ladder. At the top of the ladder, Armstrong pulled a lanyard to open the panel and thereby reveal the camera. The most ergonomic and lightweight way to mount the camera on this panel was upside – down, so on Earth, the conversion equipment had a switch which the operator flicked to right the upside-down picture. Once both crewmen were on the surface, Armstrong lifted the camera from its mount and placed it on a stand from where the TV audience could watch proceedings. The operator threw his switch back to restore the image’s orientation.