This week in rocket history is Lunar Orbiter 3, one of the missions that prepared for the Apollo moon landings.

Following on from the Ranger series of impactors, the Lunar Orbiter spacecraft were a series of spacecraft that NASA sent into lunar orbit to survey the surface for candidate landing sites for the future Apollo missions. They weighed 385 kilograms and consisted of a cone with four fixed solar panels, a propulsion system, and a camera system that used two lenses to expose images onto the same frame of 70-mm film – an 80-mm lens for medium resolution and a 610-mm lens for high resolution. The film was developed in the spacecraft using a process from a then classified reconnaissance satellite called Samos E-1 and transmitted digitally back to Earth for analysis.

Lunar Orbiter 3 launched on February 5, 1967, on an Atlas-Agena rocket on a three-day trip to the Moon. Its primary mission was to survey candidate landing sites identified by Orbiters 1 and 2 at a higher resolution to confirm their suitability.

The spacecraft’s mission lasted from February 8 to 23, 1967. Four days into the mission, the spacecraft lowered its perilune – the lowest point in its orbit around the Moon – from 200 kilometers to 55 kilometers to obtain higher resolution images. After all the images were captured, most were developed and transmitted back to Earth. However, the mechanism which advanced the film into the developer failed on March 4, leaving about a quarter of the images unable to be developed and scanned. Despite this failure, the spacecraft still returned almost 500 high-resolution images and 149 medium-resolution images. One of these showed the Surveyor 1 spacecraft at its landing site.

Besides its imagery mission, the spacecraft also carried radiation and micrometeoroid detection instruments, which returned data on the lunar environment.

The spacecraft was tracked from Earth for several months for lunar geodesy and communication tracking purposes before being commanded to deorbit and impact the Moon in October 1967. All Lunar Orbiters were commanded to deorbit before their maneuvering thrusters were depleted to avoid becoming navigation hazards to crewed Apollo spacecraft. Lunar Orbiters 1, 2, 3, and 5 were commanded to deorbit in 1967 and 1968, while Lunar Orbiter 4’s orbit naturally decayed after contact was lost.

Decades later, a small team of dedicated nerds who met on an Internet forum rescued the 1,498 data tapes full of downlinked images from all five Lunar Orbiters. The goal in reprocessing the 40-year-old images was to compare them to new images taken by the Lunar Reconnaissance Orbiter, launched in 2009.

The tapes were supposed to have been destroyed in the 1980s but were fortunately saved and left in a barn. The team refurbished old tape drives the size of a refrigerator to be able to read the tapes. In all, they had four tape drives and were able to restore two to working condition.

In addition to the tape drives, they needed to recreate from scratch the hardware used to convert the raw signal data into images, a process called demodulation.

The original Lunar Orbiter images were just as good as the modern ones, but digital processing techniques in the 1960s were quite primitive compared to modern techniques. One of the more significant images, the first “Earthrise”, was taken in 1966, and the scan at that time was low quality. The Lunar Orbiter Image Recovery Project was able to reprocess the original data and produce a much higher quality image, which was released in 2008.

The program was heavily supported by NASA, totaling $700,000 plus hardware and facilities. They also got additional crowdfunding to finish the process. The work was carried out in a former McDonald’s at NASA Ames Research Center, named McMoon by the project.

More Information

Lunar Orbiter 3 (NASA)