The Lunar Orbiter program consisted of five spacecraft which returned photography of 99 percent of the surface of the Moon (near and
far side) with resolution down to . Altogether the Orbiters returned 2180 high resolution and 882 medium resolution frames. The micrometeoroid experiments recorded 22 impacts showing the average micrometeoroid flux near the Moon was about two orders of magnitude greater than in interplanetary space, but slightly less than in the near-Earth environment. The radiation experiments confirmed that the design of Apollo hardware would protect the astronauts from average and greater than average short term exposure to solar particle events. The use of Lunar Orbiters for tracking to evaluate the
Manned Space Flight Network tracking stations and Apollo Orbit Determination Program was successful, with three of the Lunar Orbiters (2, 3, and 5) being tracked simultaneously from August through October 1967. The Lunar Orbiters were all eventually commanded to crash on the Moon before their attitude control fuel ran out so they would not present navigational or communications hazards to later Apollo flights. The Lunar Orbiter program was managed by NASA
Langley Research Center at a total cost of roughly $200 million. Doppler tracking of the five orbiters allowed mapping of the gravitational field of the Moon and discovery of
mass concentrations (mascons), or gravitational highs, which were located in the centers of some (but not all) of the lunar maria. Below is the flight log information of the five Lunar Orbiter photographic missions: •
Lunar Orbiter 1 • Launched August 10, 1966 • Imaged Moon: August 18 to 29, 1966 • Impact with Moon: October 29, 1966 • Apollo landing site survey mission •
Lunar Orbiter 2 • Launched November 6, 1966 • Imaged Moon: November 18 to 25, 1966 • Impact with Moon: October 11, 1967 • Apollo landing site survey mission •
Lunar Orbiter 3 • Launched February 5, 1967 • Imaged Moon: February 15 to 23, 1967 • Impact with Moon: October 9, 1967 • Apollo landing site survey mission •
Lunar Orbiter 4 • Launched May 4, 1967 • Imaged Moon: May 11 to 26, 1967 • Impact with Moon: Approximately October 31, 1967 • Lunar mapping mission •
Lunar Orbiter 5 • Launched August 1, 1967 • Imaged Moon: August 6 to 18, 1967 • Impact with Moon: January 31, 1968 • Lunar mapping and hi-res survey mission
Data availability The Lunar Orbiter orbital photographs were transmitted to Earth as analog data after onboard scanning of the original film into a series of strips. The data were written to magnetic tape and also to film. The film data were used to create hand-made mosaics of Lunar Orbiter frames. Each LO exposure resulted in two photographs: medium-resolution frames recorded by the 80-mm focal-length lens and high-resolution frames recorded by the 610-mm focal length lens. Due to their large size, HR frames were divided into three sections, or sub-frames. Large-format prints () from the mosaics were created and several copies were distributed across the U.S. to NASA image and data libraries known as Regional Planetary Information Facilities. The resulting outstanding views were of generally very high spatial resolution and covered a substantial portion of the lunar surface, but they suffered from a "venetian blind" striping, missing or duplicated data, and frequent saturation effects that hampered their use. For many years these images have been the basis of much of lunar scientific research. Because they were obtained at low to moderate Sun angles, the Lunar Orbiter photographic mosaics are particularly useful for studying the morphology of lunar topographic features. Several atlases and books featuring Lunar Orbiter photographs have been published. Perhaps the most definitive was that of Bowker and Hughes (1971); it contained 675 photographic plates with approximately global coverage of the Moon. In part because of high interest in the data and in part because that atlas is out of print, the task was undertaken at the Lunar and Planetary Institute to scan the large-format prints of Lunar Orbiter data. These were made available online as the Digital Lunar Orbiter Photographic Atlas of the Moon.
Data recovery and digitization . In 2000, the
Astrogeology Research Program of the US Geological Survey in Flagstaff, Arizona was funded by NASA (as part of the Lunar Orbiter Digitization Project ) to scan at 25 micrometer resolution archival LO positive film strips that were produced from the original data. The goal was to produce a global mosaic of the Moon using the best available
Lunar Orbiter frames (largely the same coverage as that of Bowker and Hughes, 1971). The frames were constructed from scanned film strips; they were digitally constructed, geometrically controlled, and map-projected without the stripes that had been noticeable in the original photographic frames. Because of its emphasis on construction of a global mosaic, this project only scanned about 15% of the available Lunar Orbiter photographic frames. Data from Lunar Orbiter missions
III,
IV and
V were included in the global mosaic. In addition, the USGS digitization project created frames from very high resolution Lunar Orbiter images for several 'sites of scientific interest.' These sites had been identified in the 1960s when the Apollo landing sites were being selected. Frames for sites such as the
Apollo 12 landing site, the
Marius Hills, and the Sulpicius Gallus rille have been released. In 2007, the
Lunar Orbiter Image Recovery Project (LOIRP) began a process to convert the Lunar Orbiter Images directly from the original
Ampex FR-900 analog video recordings of the spacecraft data to digital image format, a change which provided vastly improved resolution over the original images released in the 1960s. The first of these restored images were released in late 2008. Almost all of the Lunar Orbiter images had been successfully recovered and were undergoing digital processing before being submitted to NASA's
Planetary Data System. ==See also==