The Lunar Orbiter spacecraft were designed primarily to photograph areas of the lunar surface for selection and verification of safe landing sites for the Surveyor and Apollo missions. It was also equipped to collect selenodetic, radiation intensity, and micrometeoroid impact data.
Lunar Orbiter (1966 – 1967)
Five Lunar Orbiter missions were launched in 1966 through 1967 with the purpose of mapping the lunar surface before the Apollo landings. All five missions were successful, and 99% of the Moon was photographed with a resolution of 60 m or better. The first three missions were dedicated to imaging 20 potential lunar landing sites, selected based on Earth-based observations. These were flown at low inclination orbits. The fourth and fifth missions were devoted to broader scientific objectives and were flown in high altitude polar orbits. Lunar Orbiter 4 photographed the entire nearside and 95% of the farside, and Lunar Orbiter 5 completed the farside coverage and acquired medium (20 m) and high (2 m) resolution images of 36 pre-selected areas. The images at the top of the page show the Lunar Orbiter spacecraft with the high and medium resolution cameras at the center, and an image of the crater Tycho taken with the Lunar Orbiter 5 medium resolution camera.
The Lunar Orbiters had an ingenious imaging system, which consisted of a dual-lens camera, a film processing unit, a readout scanner, and a film handling apparatus. Both lenses, a 610-mm narrow angle high-resolution (HR) lens and an 80-mm wide-angle medium resolution (MR) lens, placed their frame exposures on a single roll of 70 mm film. The axes of the two cameras were coincident so the area imaged in the HR frames were centered within the MR frame areas. The film was moved during exposure to compensate for the spacecraft velocity, which was estimated by an electric-optical sensor. The film was then processed, scanned, and the images transmitted back to Earth.