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Through Telemetry and Data

Apollo 11 was also equipped with other imaging systems whose original high-resolution data survive, notably the 16mm Maurer Data Acquisition Camera, which recorded Armstrong's descent down the ladder and approximately 86 minutes of the lunar EVA, as well as Hasselblad 70mm still cameras.

To broadcast the SSTV transmission on standard television, NASA ground receiving stations performed real-time scan conversion to the NTSC television format. The moonwalk's converted video signal was broadcast live around the world on July 21, 1969 (2:56 UTC). At the time, the NTSC broadcast was recorded on many videotapes and kinescope films. Many of these low-quality recordings remain intact. As the real-time broadcast worked and was widely recorded, preservation of the backup video was not deemed a priority in the years immediately following the mission. In the early 1980s, NASA's Landsat program was facing a severe shortage of data tapes and it is likely the tapes were erased and reused at this time.

A team of retired NASA employees and contractors tried to find the tapes in the early 2000s but was unable to do so. The search was sparked when several still photographs appeared in the late 1990s that showed the visually superior raw SSTV transmission on ground-station monitors. The research team conducted a multi-year investigation in the hopes of finding the most pristine and detailed video images of the moonwalk. If copies of the original SSTV format tapes were to be found, more modern digital technology could make a higher-quality conversion, yielding better images than those originally seen. The researchers concluded that the tapes containing the raw unprocessed Apollo 11 SSTV signal were erased and reused by NASA in the early 1980s, following standard procedure at the time.

Although the researchers never found the telemetry tapes, they did discover the best visual quality NTSC videotapes as well as Super 8 movie film taken of a video monitor in Australia, showing the SSTV transmission before it was converted. These visual elements were processed in 2009, as part of a NASA-approved restoration project of the first moonwalk. At a 2009 news conference in Washington, D.C., the research team released its findings regarding the tapes' disappearance. They also partially released newly enhanced footage obtained during the search. Lowry Digital completed the full moonwalk restoration project in late 2009.

Background

Apollo 11 was the spaceflight that landed the first two people on the Moon. Neil Armstrong became the first person to step onto the lunar surface on July 21, 1969, at 02:56 UTC. Buzz Aldrin joined him 19 minutes later. Only limited radio bandwidth was available to transmit the video signal from the lunar landings, which needed to be multiplexed with other communication and telemetry channels beamed from the Lunar Module Eagle, back to Earth.

Therefore, Apollo 11's moonwalk video was transmitted from the Apollo TV camera in a monochrome SSTV format at 10 frames per second (fps) with 320 lines of resolution, progressively scanned. These SSTV signals were received by radio telescopes at Parkes Observatory in Australia, the Goldstone tracking station in California, and Honeysuckle Creek tracking station, also in Australia.

The camera's video format was incompatible with existing NTSC, PAL, and SECAM broadcast television standards. It needed to be converted before it could be shown on broadcast television networks. This live conversion was crude, essentially using a video camera pointing at a high-quality 10-inch (25 cm) TV monitor.

Video signal processing

Since the camera's scan rate was much lower than the approximately 30 fps for NTSC video, the television standard used in North America at the time, a real-time scan conversion was needed to be able to show its images on a regular TV set. NASA selected a scan converter manufactured by RCA to convert the black-and-white SSTV signals from the Apollo 7, 8, 9 and 11 missions.

When the Apollo TV camera radioed its images, the ground stations received its raw unconverted SSTV signal and split it into two branches. One signal branch was sent unprocessed to a 14-track analog data tape recorder, where it was recorded onto 14-inch (36 cm) diameter reels of one-inch-wide (25 mm) analog magnetic data tapes at 120 inches (3.0 m) per second. The other raw SSTV signal branch was sent to the RCA scan converter, where it was processed into an NTSC broadcast television signal.

The RCA scan converter operated on an optical conversion principle. The conversion process started when the signal was sent to a high-quality 10-inch (25 cm) video monitor, where a conventional RCA TK-22 television camera—using the NTSC broadcast standard of 525 scanned lines interlaced at 30 fps—merely re-photographed its screen. The monitor had persistent phosphors that acted as a primitive framebuffer. An analog disk recorder, based on the Ampex HS-100 model, was used to record the first field from the camera.

It then fed that field, and an appropriately time-delayed copy of the first field, to the NTSC Field Interlace Switch (encoder). The combined original and copied fields created the first full 525-line interlaced frame and the signal was then sent to Houston. The disk recorder repeated this sequence five more times, until the camera imaged the next SSTV frame. The converter then repeated the whole process with each new frame downloaded from space in real time. In this way, the RCA converter produced the extra 20 frames per second needed to produce flicker-free images to the world's television broadcasters.

This live conversion was crude compared to early-21st-century electronic digital conversion techniques. Image degradation was unavoidable with this system as the monitor and camera's optical limitations significantly lowered the original SSTV signal's contrast, brightness and resolution. If the scan converter's settings were incorrectly set, as they were at the Goldstone station during the first few minutes of Apollo 11's moonwalk, the negative impact on the image could be very obvious.

When Armstrong first came down the Lunar Module's ladder, he was barely visible because the contrast and the vertical phase were not set correctly by the scan converter operator. The video seen on home television sets was further degraded by the very long and noisy analog transmission path.

The converted signal was sent by satellite from the three receiving ground stations to Houston. Then the network pool feed was sent by microwave relay to New York, where it was broadcast live to the United States and the world. Because all of these links were analog, each one added additional noise and distortion to the signal.

NTSC broadcast tapes

This low-quality optical conversion of the Apollo 11 moonwalk video images—made with a TV camera taking pictures of a video monitor—is what was widely recorded in real-time onto kinescope film and NTSC broadcast-quality two-inch quadruplex videotape. Recordings of this conversion were not lost and have long been available to the public, along with much higher-quality video from later Apollo missions. If the one-inch (25 mm) data tapes, containing the raw unprocessed Apollo 11 SSTV signals, were to be found, modern digital technology would allow for significantly better conversion and processing. The quality would be similar to that viewed by a few technicians and others at SSTV-receiving ground stations before the video was converted to NTSC.

In 2005, an amateur Super 8 movie with about 15 minutes of Apollo 11 images was rediscovered. The footage had been taken by Ed von Renouard at Honeysuckle Creek tracking station during or immediately after the Apollo 11 moonwalk. The images show mainly the scan converted monitor and briefly the slow-scan monitor. This is some of the best quality recording of brief segments of the Apollo 11 moonwalk available. The images are available on DVD.

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