Lunar Orbiter 1, launched on August 10, 1966, was the first photograph-taking spacecraft to orbit a celestial body other than Earth. Its photographs of the lunar surface, and the pictures of other Lunar Orbiters that soon followed, profoundly changed the way humans would see and imagine the Moon.
On May 25, 1961, President John F. Kennedy made a famous speech, stating, “I believe this nation should commit itself to achieving the goal, before this decade is out, of landing a man on the Moon and returning him safely to Earth.” In the light of the state of space technology at that time, this was a quite remarkable statement to make, and it would serve as a challenge to the scientists and engineers to make it happen.
Landing an astronaut on the Moon and ensuring a safe return was not going to be an easy task. A whole new technology had to be developed. It must be remembered that the space age was merely four years old at that time and reaching the Moon seemed to be a dream. To make it a reality would require a systematic approach that would progress in stages. The National Aeronautics and Space Administration
A photograph of the far side of the Moon taken by Lunar Orbiter 3. The dark circle in the center is a mare inside the Tsiolkovsky crater.
Firsthand exploration of the Moon began with the Soviet flyby mission of Luna 1 in January, 1959. It was a crude mission by today’s standards, but it did return a photograph of the previously unseen far side of the Moon. This mission was closely followed in September, 1959, by another Soviet probe (Luna 2), which hard-landed on the lunar surface. The United States’ answer to the Soviet achievements began with the Ranger program. These spacecraft were designed to obtain high-resolution photographs of the Moon right up to the point of impact. Ranger 3 first passed by the Moon in late January, 1962, and it was followed by a hard-lander (Ranger 4) in April, 1962. Prior to this time, scientists had to be content with what Earth-based telescopes could provide. The clarity of the photographs returned by the Ranger spacecraft ushered in a new age in planetary exploration.
The second step in the U.S. program of lunar exploration was the Surveyor series. These spacecraft were designed to soft-land on the Moon and analyze the surface material. Photography was also a high priority. Surveyor 1 safely landed on the Ocean of Storms on June 2, 1966, and transmitted back high-quality photographs and other important scientific data. It provided scientists with thousands of sharp close-up views and answered many questions about the lunar surface material.
In conjunction with Surveyor was the third step in NASA’s plan, the Lunar Orbiter project. It was initially assigned to the Jet Propulsion Laboratory (JPL) in Pasadena, California, but JPL’s heavy workload with the Ranger and Surveyor programs forced a management change. Surveyor was reassigned to the Langley Research Center
The basic mission for the Lunar Orbiter spacecraft was to photograph the lunar surface in high resolution and to test the capabilities of a spacecraft in lunar orbit. Many of the techniques and procedures later used by the Apollo astronauts were first attempted by the Lunar Orbiters. The principal goal of the Lunar Orbiter program was to obtain the highest quality photographs for selection of potential landing sites for Apollo. The Lunar Orbiter series employed five separate spacecraft to accomplish its mission. Later, based upon the success of the first three flights, the overall mission objective was expanded. The final two spacecraft would be placed in nearly polar orbits that permitted them to take overlapping photographs of almost the entire near side of the Moon. These high-resolution photographs were used later to make a photograph-map of the Moon.
All the Lunar Orbiter spacecraft were launched from Cape Canaveral, Florida. The launch vehicle was the reliable Atlas-Agena rocket. The time involved from lift-off to lunar orbital insertion required four days. Once in lunar orbit, the spacecraft would be tracked for several days to determine its exact position. Eventually, Lunar Orbiter 1 was positioned in a highly elliptical orbit with an approximate altitude of 56 kilometers at its closest distance and 1,853 kilometers at its most distant point. This orbit allowed for maximum use of its solar panels for electrical energy, and less reliance on the spacecraft’s battery. Photography would be maximized when the spacecraft was at its lowest altitude.
Compared to more modern spacecraft, Lunar Orbiter was relatively small. It weighed only 385 kilograms and, when its solar panels were extended, had dimensions of 5.7 meters by 3.7 meters. Electrical energy was supplied to the various instruments from its solar panels when it was in sunlight, and it relied on its battery when in darkness. Changes in the spacecraft’s orbital altitude were made from small nitrogen-gas jets. These were used also to realign the spacecraft’s orientation periodically. To function properly, it had to keep one sensor aligned on the Sun and the other on the star Canopus.
The photographic subsystem onboard Lunar Orbiter had the capabilities of taking pictures, processing them, and then converting the optical images into electronic signals for transmission back to Earth. The camera system employed both a wide-angle and a telephotographic lens. The camera operated each simultaneously, thereby taking both a close-up and wide-angle image of the same feature. This proved to be extremely valuable for determining the relationship between widely separated features. One very basic problem that the Lunar Orbiter’s camera subsystem had to overcome was the motion of the spacecraft. Traveling at almost 7,000 kilometers per hour would cause the image to blur. This problem was solved through the use of a sensor that determined the velocity-to-height ratio of the spacecraft. It would then command the film platen to follow the image and thereby compensate for the spacecraft’s motion. It was a very remarkable device that proved to be most effective and resulted in clear, crisp images.
Film that was processed on board the spacecraft was never intended to be returned to Earth. Instead, the film was scanned by a device that “read” the density (dark versus light intensity) of the images as a beam of light passed through them. These changes in intensity were then converted to electronic signals that were proportional to the beam’s strength. These signals were then transmitted back to Earth and reconstructed into an image much like that of a conventional television set. Then, enlargements and even stereoscopic pairs were made from these images. It was a very effective procedure that produced good results.
The Lunar Orbiter 1 mission was an important step toward landing a human on the Moon. In its basic accomplishments, it proved that a spacecraft could perform complicated maneuvers in orbit and gather valuable data in the process. In addition, it provided a detailed examination of nine potential Apollo landing sites and mapped a large portion of the lunar surface, thus setting the standard for future missions.
Lunar Orbiter 1 was launched on August 10, 1966, and achieved lunar orbit on August 14. In total, it spent seventy-six days in orbit and completed 547 revolutions of the Moon. After completing its mission, the spacecraft was deliberately crashed into the lunar surface to prevent any possible interference with future spacecraft.
During its time in lunar orbit, Lunar Orbiter 1 accomplished all of its primary goals, and more. Wide-area photographic coverage of nine potential Apollo landing sites was made, as well as extensive far side and limited near side photographic coverage. This included detailed examination of the Surveyor landing sites, future Lunar Orbiter photograph targets, and important landmarks for the Apollo astronauts to use. Lunar Orbiter 1 became the first spacecraft to photograph Earth from beyond the Moon. The photographs proved to be so successful that a decision was made to modify the missions of the later orbiters. Several of the sites to be examined by Lunar Orbiter 2 were eliminated from consideration, thereby freeing the spacecraft to look for more acceptable sites.
Lunar Orbiter 1 photographs were both exciting and valuable to science. They provided scientists with their first detailed look at another world in space. The images showed an alien environment pocked by uncountable numbers of craters of every size. For years, Earth-based telescopes revealed their presence, but no one had guessed how important impact cratering had been to the history of the Moon. By photographing on a much smaller scale, Lunar Orbiter 1 images revealed a remarkable amount of detail concerning the nature of impact craters. Earlier Ranger and Surveyor images hinted at the complexity of an impact crater, but it was Lunar Orbiter 1 that detailed the patterns of small craters made from the secondary impacts of ejected debris. Also, the evidence provided by these photographs helped establish the distinction between young and older craters. Where the two coexist, a relationship can be made that suggests a certain weathering process at work.
Studies of the Lunar Orbiter 1’s photographs helped establish the three basic types of lunar terrain: level, gently rolling, and rough. The dark lunar maria proved to be the relatively level features, but they did exhibit a higher crater population than previously thought. In contrast to the maria, the highlands are much rougher and are dominated by much larger craters. The highlands also exhibited features that are often associated with mountain-building processes on Earth, but their origin remains uncertain.
Many of the achievements of Lunar Orbiter 1 were technical in nature. It had to achieve its predicted lunar orbit accurately by executing a series of precise orbital maneuvers. To accomplish this, it had to demonstrate the multiple-restart capability of a liquid-propellant rocket system that would operate for extended periods. This had never been done before in space. In addition, Lunar Orbiter 1 demonstrated the ability to command and control its altitude reliably during 374 maneuvers. Without such an ability, precision photography would not have been possible. Finally, by performing all of its mission, Lunar Orbiter 1 broke new ground in understanding the problems encountered in lunar navigation. This, in turn, greatly aided all future missions.
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Greeley, Ronald. Planetary Landscapes. London: Allen & Unwin, 1985. Offers readers both the fundamentals of planetary geology and an in-depth look at specific topics. The chapter discussing the Moon is very comprehensive and utilizes many of the Lunar Orbiter photographs. An extremely well-illustrated book and readable for post-high school levels. -
Kopal, Zdenek. A New Photographic Atlas of the Moon. New York: Taplinger, 1971. The introductory chapters provide a good overview of the Moon’s geological history and its surface features. An extensive collection of lunar photographs, many from the Lunar Orbiter series, illustrate the text. A valuable reference for lunar studies. -
Kosofsky, L. J., and Farouk El-Baz. The Moon as Viewed by Lunar Orbiter. Washington, D.C.: Government Printing Office, 1970. A good review of the results of the Lunar Orbiter series. Includes a representation of the photographs taken. Serves as a useful reference work. -
Levin, Ellis, D. D. Viele, and Lowell B. Eldrenkamp. “The Lunar Orbiter Missions to the Moon.” Scientific American, May, 1968, 58-78. Published shortly after the completion of the Lunar Orbiter series. Serves as a good review of those missions. Provides a detailed presentation of the spacecraft’s design and purpose. Contains several of the best images. -
Moore, Patrick, and Garry Hunt. Atlas of the Solar System. Chicago: Rand McNally, 1983. Provides one of the most comprehensive reviews of the solar system available in one book. Combines knowledge gained from spacecraft investigations with that of ground-based observations. The content is very readable and well illustrated. The chapter on the Moon is extensive and uses several Lunar Orbiter photographs as examples of specific features. -
Mutch, Thomas A. Geology of the Moon. Rev. ed. Princeton, N.J.: Princeton University Press, 1972. This work represents one of the first attempts to combine pre-Apollo lunar studies with the early results from the piloted missions. Lunar features are discussed in great detail, with numerous Lunar Orbiter photographs used as illustrations. The bibliography is an excellent reference guide for further study. -
Siddiqi, Asif A. Deep Space Chronicle: Robotic Exploration Missions to the Planets. NASA SP-2002-4524. Washington, D.C.: National Aeronautics and Space Administration, 2002. Offers readers a good reference to planetary missions, including the Lunar Orbiter and Surveyor programs. -
Trask, N. J., and L. C. Rowan. “Lunar Orbiter Photographs: Some Fundamental Observations.” Science 158, no. 3808 (1967): 1529-1535. One of the first reports on the results of Lunar Orbiter to appear in the professional journals. Presented in a more technical manner, but provides good insight into the importance of the mission. Readable at the college level. -
Ulivi, Paolo, and David M. Harland. Lunar Exploration: Human Pioneers and Robotic Surveyors. New York: Springer Praxis, 2004. Provides a good review of the Lunar Orbiter program.
Pioneer Space Program Is Launched
NASA Launches Project Gemini
Luna 2 Becomes the First Human-Made Object to Impact on the Moon
Luna 3 Provides the First Views of the Far Side of the Moon
Ranger Program
Luna 9 Makes the First Successful Lunar Soft Landing
Surveyor Program Prepares NASA for Piloted Moon Landings
First Humans Land on the Moon
Soviet Rover Lunokhod 1 Lands on the Moon