We’ve been treated to some new Earthrise images from NASA’s Artemis program. Those spectacular digital HD color images are almost taken for granted these days, but at the dawn of the Space Age in the 1960s the imaging was quite primitive. The image above shows the first-ever Earthrise image captured by Lunar Orbiter 1, 380,000 km from Earth, on August 23, 1966 — and that’s the digitally enhanced image. Below is the original:
Those vertical dark lines you see are an artifact of the imaging process. Back in the Lunar Orbiter days digital cameras didn’t yet exist. The original image was a physical film photograph taken by an analog camera. It was a very good camera of course — a Hasselblad 600EL using 70 mm B&W film. But after taking the photo, it had be developed onboard the craft, and then sent through an optical scanner.
The scanner would focus a bright beam of light on the frame of film. It scanned the frame in vertical strips from left to right. A photodetector behind the film would register the amount of light that got through. Variations in scanning accuracy and scanner brightness is what created those dark lines.
This analog data was then sent by radio to mission control, where it was recorded on 2-inch magnetic tapes. Then it was reassembled slice by slice. The analog signal was used to drive a specialized cathode-ray tube (CRT) kinescope that would beam light at a piece of film, again slice by slice, exposing it and producing a copy of the original photo. The process was pretty much like fax machines worked back in the day. It stripped out much of the dynamic range and fine details, hence the comparatively crude quality of the originals.
Then, in 2008, at the NASA Ames Research Center, the Lunar Orbiter Image Recovery Project (LOIRP) was launched. The restoration project was famously nicknamed “McMoon’s” because the team set up shop in an abandoned, empty McDonald’s building on the base.
The first step was to find some working 2-inch tape players (by then obsolete) to extract the analog recordings. That alone was quite the project, but after scavenging around for junked machines and parts, they managed to get a few working. They played the tapes and fed the signal to modern analog-to-digital converters, creating digital vertical strips. Finally, they used advanced imaging software to stitch together the strips. The software was also able to compensate for the brightness variations and eliminate the dark strips. They could even have “colorized” it but decided to stay with the original B&W format.
The Lunar Orbiter Image Recovery Project is ongoing. They have 1500 of those original 2-inch tapes, and are slowly converting the data into digital form to restore the images. This Earthrise image confirms their method works: data from the original tapes can be retrieved with the newly-restored 1960s tape players, and enhanced when processed by software from 2008 (and later).
A lot of old film, audio, documents and artwork have been digitized for the sake of preservation. Digital files are not subject to the ravages of time or natural disasters. Digitization is a long tedious process, even using modern technology. But the results will preserve for posterity some of the classic media of the past.
Next Week in Sky Lights ⇒ Earth’s Mini-Moon