The Moon is Earth’s nearest neighbor. Since the dawn of intelligence, our eyes have seen the Moon, puzzling over its shady figures, its phases, its motions in the sky, and its relation to tides. Even the smallest telescopes resolve the shadows into a heavily cratered surface, stimulating the imagination. Each advance of the astronomer’s art has revealed new insights into the nature of the lunar surface, until curiosity and competition led the American and Russian space programs to send orbital cameras, robotic landers and rovers, and the Apollo astronaut exploration teams to the Moon.
The Lunar Orbiter program, a series of five photographic spacecraft launched in 1966 and 1967, was motivated by the need to find and certify safe and interesting landing sites for the Apollo spacecraft. When the Lunar Orbiter program was started (1964), no spacecraft had landed on the Moon, but the Apollo program was committed to safely land the Lunar Module, with two astronauts on board. At the time, I was working in the lunar environment group of Bellcomm, Inc. AT&T established Bellcomm at the request of NASA to support the Apollo project headquarters group. Our responsibility included the challenging assignment of finding a safe landing site for a vehicle about the size of a helicopter, with a half-meter (0.5-m, 20-inch) ground clearance and limited ability to land on a slope. Of course, we had very little information about the lunar surface at such scales. There was some information from lunar photometry and radar scatter measurements, but there were strong uncertainties about what aspects of the surface were being measured; in particular, the soil strength was an unknown. Speculation raised possibilities of dust floated by static electricity or fragile glass-like lava.
The requirements for Lunar Orbiter were established to achieve the best possible resolution within the state of the art and to obtain imagery of that resolution over a significant percentage of the area available for Apollo landings. Targeted Apollo landing sites had to be as smooth as possible over a large enough area to accommodate the down-range and cross-range navigation errors, determined by the tracking and control uncertainties associated with factors such as the largely unknown gravity anomalies.
NASA’s Langley Research Center was chosen to manage the Lunar Orbiter program. I had the pleasure of drafting the specifications and participating in the selection of contractors. The resulting spacecraft and camera designs of Boeing Aircraft and Eastman Kodak (respectively) were capable of enormous data collection capacity, even in today’s terms. All together, about 1000 pairs of medium- and high-resolution exposures were made during the five missions. The negatives were developed in orbit, scanned, and transmitted to photographic and magnetic tape recorders in the three stations of the Deep Space Network operated by the Jet Propulsion Laboratory in California, Spain, and Australia. Each exposure results in one medium-resolution frame and one long high-resolution frame, usually presented as three subframes
Although five missions were planned to compensate for possible failures, either of spacecraft or rejection of initial target sites, the survey for early Apollo landing sites was completed in the first three missions. As a result, the fourth mission was used for a comprehensive survey of the nearside of the Moon; these are the photographs that are the primary contents of this book. The fifth mission examined many scientific sites at very high resolution, surveyed a few additional landing sites for later Apollo missions, and improved coverage of the farside of the Moon. Since the Lunar Orbiter missions returned their extensive photographic coverage of Earth’s Moon, the pictures have been the basic reference for high-resolution topographic information. The most often referenced images are the comprehensive set of about 600 images selected by Bowker, 1971 and the nearside set of about 450 images selected by Whitaker, 1970.
Following the thorough coverage of the Lunar Orbiter program, the Apollo Command and Service Module, in orbit during landing missions, provided additional coverage of the equatorial regions with its mapping and panoramic cameras. The Clementine mission provided a comprehensive survey of altitude, albedo (intrinsic brightness) and multispectral data in 1994. Lunar Prospector provided gamma ray spectroscopy in 1998. The data from these spacecraft has added insight into the mineral composition of nearly all the lunar surface, extending surveys of the equatorial region by Apollo. The interpretation of the remote sensing data has been supported by ground truth from analysis of lunar rocks and soil returned by Apollo and Luna missions. Despite the advances of these later missions, the Lunar Orbiter photographs, taken at a low sun angle, remain the primary source of topographic images and are used extensively in current scientific presentations, papers, and books.
At the time of Lunar Orbiter’s design, image scanning technology was much less advanced than it is today. The methods used resulted in artifacts in the images that distract a viewer. Scanning and transmission limitations required the subframes to be reassembled from 20 to 30 framelets of 35-millimeter film. There are fine bright lines running across each subframe between the framelets and there are brightness variations from the spacecraft’s scanner that appear as streaks within the framelets. The artifacts are particularly distracting when the images are printed at high contrast in order to show subtle topographic features and brightness variations. Lunar scientists have become used to these artifacts, but they detract from their value to students and casual observers.
Since the first photos were received, I have wanted to clean up the scanning artifacts, but at the time it would have been very expensive. The priorities were to examine the photos and start using them, rather than to improve their visual quality. Advances in the art of computation and the capacity of modern computers have enabled processing of the photos to remove nearly all of the scanning artifacts, resulting in clear images that are much easier to view. Drawing on an understanding of the nature of the artifacts, I have written programs that measure and compensate for the systematic artifacts and in addition apply filtering techniques similar to those published by Lisa Gaddis of the United States Geological Survey (Gaddis, 2001).
Lunar Orbiter photography has been archived as hard copy photographs, each about 60 cm (about 2 feet) wide, at each NASA Regional Planetary Image Facility, including one at the Lunar and Planetary Institute (LPI) in Houston, Texas. LPI has digitized this important archival source and published the images in the Digital Lunar Orbiter Photographic Atlas of the Moon on the LPI web site (www.lpi.usra.edu/research/lunar_orbiter/). Further, the LPI staff has added annotations to the photos, clearly outlining many of the features and labeling them with their internationally recognized names.
A team led by Jeff Gillis carried out this important work; Jeff was supported by Washington University at St. Louis and LPI. He is currently with the University of Hawaii. LPI technical and Administrative support was provided by Michael S. O'Dell, Debra Rueb, Mary Ann Hager, and James A. Cowan with assistance from Sandra Cherry, Mary Cloud, Renee Dotson, Kin Leung, Jackie Lyon, Mary Noel, Barbara Parnell, and Heather Scott. The selection of photos on the LPI Digital Archive is that selected for "Lunar Orbiter Photographic Atlas of the Moon" by Bowker and Hughes (see the Reference section for details).
The annotated photos in this atlas provide full coverage of the nearside, including nearly all of the features whose names have been approved by the International Astronomical Union (IAU). All of the high- and medium-resolution photos of Lunar Orbiter 4 (except for a few that were found unacceptable for Bowker, 1971) have been cleaned and are in the enclosed compact disk. Most of these, selected for non-redundancy and interest of features, are printed along with the annotated photos. All of the photos (prior to processing by the author) are courtesy of NASA and LPI.
Photos with annotated overlays label the major features within each of the photos, including the landing sites of manned and unmanned spacecraft. These overlays were extracted digitally from those published by LPI. I added additonal annotations to provide lattitude, longitude and scale information and also to bring the set of features up to date with the Gazetteer of Planetary Nomenclature, the list maintained for the IAU by the United States Geological Survey Astrogeology Program. Notes with each photo point out salient aspects of the features. The combination of cleaned photos, labeled features, and notes are intended to serve as powerful aids to learning the geography and geology of the nearside of the Moon as well as valuable reference material.
Throughout the project of cleaning the photos and writing this book helpful suggestions and comments were made by Jeff Gillis, Mary Ann Hager, Paul Spudis, Lisa Gaddis, Debbie Martin, Michael Martin, Ewen Whitaker, and Brad Jolliff.
My dear wife Mary worked long and patiently as system administrator, picture processor, and reviewer.
Special gratitude goes to Don Wilhelms, USGS Astrogeology (retired) whose books have been major sources and who was kind enough to review this book and set me straight on lunar geology.
Charles J. Byrne
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