NASA launched five Lunar Orbiter missions from 1965 to 1967. Each was designed to image a large portion of the lunar surface to help Apollo mission planners select good landing sites for astronauts. Each orbiter shot its images on film, developed the film, scanned the images, and transmitted them to Earth in strips. The technology was based in part on that developed for Earth-orbiting spy satellites. All five Lunar Orbiter missions were successful. Scientists combined their images to produce the best maps of the Moon to that time, and the images continue to provide an important resource for lunar scientists.