Fifty years ago, 5 unmanned lunar orbiters circled the moon, taking extremely high resolution photos of the surface. They were trying to find the perfect landing site for the Apollo missions. They would be good enough to blow up to 40 x 54ft images that the astronauts would walk across looking for the great spot. After their use, the images were locked away from the public, as at the time they would have revealed the superior technology of the USA's spy satellite cameras, which the orbiters cameras were designed from. Instead the images from that time were grainy and low resolution, made to be so by NASA.
Comparison of the Earthrise image shown to the public in 1966 on top, and the restored image directly from the tape on the bottom. The bottom image was released in 2008, 42 years after it was taken. Credit: NASA/LOIRP.
These spacecraft were Lunar Orbiter I to V, and they were sent by NASA during 1966 and 67. In the late 1960's, after the Apollo era, the data that came back on analog tapes was placed in storage in Maryland. In the mid 1980's they were transferred to JPL, under the care of Nancy Evans, co-founder of the NASA Planetary Data System (PDS). The tapes were moved around for many years, until Nancy found Dennis Wingo and Keith Cowing. They decided they needed to be digitised for future generations, and brought them to NASA Ames Research Centre. They set up shop in an abandoned McDonalds, offered to them as free space. They christened the place McMoon. The aim was to digitise these tapes before the technology used to read them disappeared, or the tapes destroyed.
The Lunar Orbiters never returned to Earth with the imagery. Instead, the Orbiter developed the 70mm film (yes film) and then raster scanned the negatives with a 5 micron spot (200 lines/mm resolution) and beamed the data back to Earth using lossless analog compression, which was yet to actually be patented by anyone. Three ground stations on earth, one of which was in Madrid, another in Australia and the other in California recieved the signals and recorded them. The transmissions were recorded on to magnetic tape. The tapes needed Ampex FR-900 drives to read them, a refrigerator sizes device that costed $300,000 to buy new in the 1960's.
The FR-900 that was used to restore the old images. A mix of old and new equipment to get the images to modern PC's. Credit: MIT Technology Review.The back of the first FR-900 has been signed by the people who brought the project to life, including Nancy Evans. Credit: MIT Technology Review.
The tape drive that they found first had to be restored, beginning with a wash in the former restaurants sink. The machine needed a custom built demodulator to extract the image, an analog to digital converter, and a monitor connection to view what was happening. As the labelling system of the tapes had been forgotten, and documentation was not readily available, they had to hand decode the coordinates on the tapes. They also had a big collection from parts of other FR-900's and similar designs. The spare parts were constantly needed to keep the recorder going, there was good reason that the format didn't continue for for long.
In order to read the tapes, the heads of the FR-900 apply a magnetic field to the tape inducing a current through it. The current can be measured and run through the demodulator. This pulls out the image signal, that is then run through an analog to digital converter. The data is then processed on a computer using the custom system they set up. They made custom software that interfaced with Photoshop to link the relevant parts of the image together. The orbiters sent out each image in multiple transmissions, with each strip (one tin) making up part of the image. the software manages to link up the images nearly seamlessly at the full potential resolution. The best of the images can show the lunar surface at a resolution less than 1m, much better than any other orbiter that has been there.
They were huge files, even by today's standards. One of the later images can be as big as 2GB on a modern PC, with photos on top resolution DSLRs only being in the region of 10MB you can see how big these images are. One engineer said you could blow the images up to the size of a billboard without losing any quality. When the initial NASA engineers printed off these images, they had to hang them in a church because they were so big. The below images show some idea of the scale of these images. Each individual image when printed out was 1.58m by 0.4m.
This image shows the large thin strip images being laid out on the floor of a large room so the engineers could look for good landing spots. Credit: NASA.The image shows a NASA technician with a ream of photograph printouts used to assemble the overall image. Credit: NASA.
Orbiter IV was there to produce a single big image of the front side of the moon. In pictures taken between May 11-25, 1967 the Orbiter took a number of images that span the area from the north pole to the south pole and from the eastern limb to the western limb. The complete mosaic of an image stretched 40 by 45 ft. The engineers laid it out on the floor and all the observers including the astronauts had to crawl over it and take off their shoes. The images were so good, even at this size that some astronomers used magnifying glasses. This giant image was the primary source to select the sites for Orbiter V to photograph in a higher resolution. The images taken by Orbiter V decided the exact locations for Apollo 11 to land.
The very prominent feature in this image is the Tsiolkovskiy Crater on the far side of the moon. Taken by Orbiter 3 on 19 February 1967. Credit: NASA/LOIRP.
Since 2007 the Lunar Orbiter Image Recovery Project has brought back 2000 images from 1500 analog tapes. The first ever picture of an earthrise. As Keith Cowing said "an image taken a quarter of a fucking million miles away in 1966. The Beatles were warming up to play Shea Stadium at the moment it was being taken." To find more of those images go to their website, but I warn you those images are huge.