Key Figures
Benjamin Milwitzky, Surveyor program manager, NASA
Walker E. “Gene” Giberson, Surveyor project manager until 1965, Jet Propulsion Laboratory (JPL)
Robert Parks, JPL Surveyor program manager, 1965-1966
Howard H. Haglund, JPL Surveyor program manager, 1966-1968
R. G. Forney, JPL Spacecraft Systems manager
Leonard Jaffe, Survey Scientific Evaluation Advisory Team chairperson
Eugene M. Shoemaker (1928-1997), principal investigator, imaging science experiment
A. L. Turkevich, principal investigator, alpha scattering experiment
Ronald F. Scott, principal investigator, soil mechanics surface sampler experiment
Summary of the Program
In May, 1960, the National Aeronautics and Space Administration (NASA) approved a Surveyor Program consisting of two parts: a Lunar Orbiter for photographic coverage of the Moon’s surface and a lunar lander to obtain scientific information on the Moon’s environment and structure. Before human beings could safely be sent to the Moon, the Surveyors were to provide spacecraft designers with information on the load-bearing limits of the lunar surface, its magnetic properties, and its radar and thermal reflectivity.
The Jet Propulsion Laboratory (JPL) was assigned project responsibility, and four Surveyor study contracts were awarded in July, 1960, to Hughes Aircraft, North American, Space Technology Laboratories, and McDonnell Aircraft. On January 19, 1961, NASA chose Hughes Aircraft’s proposal for the Surveyor and began planning at JPL for seven lunar-landing flights, the first of which was planned for launch on an Atlas-Centaur booster in 1963.
Because of development problems with the Centaur, early failures of the Ranger lunar impactor, and increasing demands for information on the lunar surface to support the Apollo Program, the orbiter portion of Surveyor was dropped in 1962 and replaced by the Lunar Orbiter project, managed by NASA’s Langley Research Center. Problems with the Centaur upper stage forced postponement of the first Surveyor launch and required a reduction in the spacecraft’s weight—from an original 1,134 kilograms with a 156-kilogram payload to 953 kilograms carrying only 52 kilograms of instruments.
The Atlas-Centaur became operational in 1966, and Surveyor 1 was launched from Launch Pad Complex 36A at Cape Kennedy, Florida, on May 30, 1966. Surveyor 1, the first test model of the series, carried more than one hundred engineering sensors to monitor spacecraft performance. No instrumentation was carried specifically for scientific experiments, but the spacecraft was outfitted with a survey television system and with instrumentation to measure the bearing strength, temperature, and radar reflectivity of the lunar surface.
Photograph of the Surveyor 3 spacecraft resting on the surface of the Moon, taken by Apollo 12 astronauts (descriptions added). Not seen are the main retrorocket and radar unit, which are jettisoned before landing. (NASA)
After injection on a trajectory intersecting the Moon, the Surveyor spacecraft separated from the Centaur upper stage. Midcourse maneuvers, using vernier engines on the spacecraft, were performed to bring it within the desired target area. For the terminal descent, the main retroengine was ignited, by command of an onboard radar altimeter, to provide most of the braking. After this retroengine burned out, at about 10 kilometers above the lunar surface, it was jettisoned. A second radar altimeter, providing measurements of velocity and altitude, was used with the smaller vernier engines, in a closed loop under control of an onboard analog computer, for the final descent phase. To reduce the disturbance to the lunar surface, the vernier engines were extinguished by the computer when the spacecraft was about 4 meters above the surface and the descent rate was about 1.5 meters per second. At 06:17 Coordinated Universal Time (UTC) on June 2, 1966, Surveyor 1 soft-landed in the southwest portion of the Ocean of Storms, becoming the first U.S. spacecraft to soft-land on another celestial body.
During the next two lunar days (28 Earth days each) the Surveyor returned some eleven thousand photographs of the surrounding terrain to Earth. Surveyor 1 completed its primary mission on July 14, 1966, but engineering interrogations were conducted at irregular intervals through January, 1967.
Surveyor 2, launched on September 20, 1966, had essentially the same configuration as Surveyor 1 and was intended to land in the Central Bay, another potential Apollo landing zone. When the midcourse maneuver was attempted on September 21, one of the three vernier engines failed to ignite, and the unbalanced thrust caused the spacecraft to tumble. Although repeated commands were sent in an attempt to salvage the mission, Surveyor 2 crashed on the Moon on September 22, 1966.
Surveyor 3, though similar to the two earlier spacecraft, was equipped with two fixed mirrors to extend the view of its television camera underneath the spacecraft. A remotely controlled surface sampler arm, capable of digging trenches and manipulating the surface material in view of the television camera, was also added. The Surveyor 3 spacecraft was launched on April 17, 1967, from Launch Pad Complex 36B at Cape Kennedy—the first time the two-burn capability of the Centaur was used on an operational mission. After separation from the Atlas, the Centaur engine ignited and burned for approximately five minutes to place the vehicle into a 167-kilometer circular parking orbit. The Centaur coasted for 22 minutes, then reignited to place the spacecraft on a lunar-intercept trajectory. The use of a parking orbit greatly increased the fraction of the lunar surface to which the Surveyor could be targeted.
The midcourse correction maneuver and the firing and jettisoning of the retroengine proceeded as planned. A few seconds before touchdown, however, the onboard radar lost its lock on the surface, apparently because of unexpected reflections from large rocks near the landing site. As a result, the spacecraft guidance system switched to an inertial mode, which prevented the vernier engines from extinguishing about 4 meters above the surface as planned. The spacecraft touched down with its vernier engines still firing, lifted off, touched down a second time, lifted off again, then touched down for a third time after receiving a command from Earth 34 seconds after the initial touchdown. The spacecraft had a lateral velocity of about 1 meter per second at the first touchdown, and the distance between the first and second touchdowns was about 20 meters, while there was a distance of about 11 meters between the second and third touchdowns.
The landing occurred on April 19, 1967, in the southeast part of the Ocean of Storms, a potential Apollo landing region. Surveyor 3 landed in a medium-sized crater and came to rest tilted at an angle of about 14°. This location allowed the crater to be viewed from the inside, and the unplanned tilt permitted the camera to aim high enough to photograph an eclipse of the Sun by Earth, which would not have been possible if the landing had been on a level surface. The spacecraft returned 6,315 television pictures and operated its surface sampler for more than eighteen hours before transmissions ceased shortly after local sunset on May 3, 1967.
Surveyor 4, carrying the same payload as Surveyor 3 had, was launched on July 14, 1967. After a flawless flight to the Moon, radio signals from the spacecraft ceased abruptly during the final descent, approximately 2.5 minutes before touchdown and only two seconds before retroengine burnout. Radio contact with the spacecraft was never reestablished, and Surveyor 4 crashed into the lunar surface, possibly after an explosion.
Surveyor 5 was launched from Cape Kennedy on September 8, 1967. Because of a helium regulator leak that developed during flight, a radically new descent technique was engineered, and the Surveyor 5 performed a flawless descent and soft landing in the Sea of Tranquility on September 11, 1967. The spacecraft was similar to its two immediate predecessors, except that the surface sampler was replaced by an “alpha backscatter instrument,” a device to determine the relative abundances of the chemical elements in the lunar surface material. In addition, a bar magnet was attached to one of the footpads to determine if magnetic material was present in the lunar soil.
During its first lunar day, which ended at sunset on September 24, 1967, Surveyor 5 took 18,006 television pictures, performed chemical analyses of the lunar soil, and fired its vernier engines for 0.55 second to determine the effects of high-velocity exhaust gases impinging on the lunar surface. On October 15, 1967, after exposure to the two-week deep freeze of the lunar night, Surveyor 5 responded to a command from Earth, reactivating, and transmitted an additional 1,043 pictures and data from the lunar surface.
The Surveyor 6 spacecraft, essentially identical to Surveyor 5, was launched on November 7, 1967, and landed on the Moon on November 10, 1967. The landing site, near the center of the Moon’s visible hemisphere in the Central Bay, was the last of four potential Apollo landing sites designated for investigation by the Surveyor Program. From landing until a few hours after lunar sunset on November 24, 1967, the spacecraft transmitted more than 29,000 television pictures, and the alpha backscattering experiment acquired thirty hours of data on the chemical composition of the lunar soil. On November 17, 1967, Surveyor 6’s vernier engines were fired for 2.5 seconds, causing the spacecraft to lift off from the lunar surface and move laterally about 3 meters to a new location. Television pictures showed the effect of rocket firings close to the lunar surface. When combined with images taken from the earlier landing site, the new photographs provided stereoscopic data of the surrounding terrain and surface features.
Because the previous Surveyors had completed the Apollo landing site survey, Surveyor 7 was targeted at the scientifically interesting rock-strewn ejecta blanket of the crater Tycho. Launched on January 7, 1968, the Surveyor 7 spacecraft landed less than 2 kilometers from its target on January 10, 1968. During the first lunar day, 21,046 pictures of the lunar surface were acquired, but the alpha backscatter package failed to deploy. The surface sampler arm was programmed from Earth to force the package into position and subsequently to move it to two additional sites. Laser beams from Earth were also detected by the television camera during a test. Forty-five more photographs and additional surface chemical data were obtained during the second lunar day of operation, before the spacecraft was deactivated on February 21, 1968.
Having met all the Apollo survey objectives, follow-on Block 2 missions were canceled because of budget constraints, and the Surveyor Project Office at JPL was closed on June 28, 1968.
Contributions
The surface sampler arms on Surveyors 3 and 7 made measurements of how much weight the lunar surface soil could bear before being penetrated as well as how depth affected the bearing capacity and shear strength in trenches up to 20 centimeters deep. The strength and density of individual lunar rocks were also determined. Strain gauges on the shock absorbers determined the loads on the legs of the spacecraft during the touchdown on the lunar surface. The radar reflectivity and dielectric constant of the lunar surface material were determined by the landing radar system. Thermal sensors determined the surface temperatures, thermal inertia, and directional infrared emission at all five landing sites.
At the mare landing sites, firings of the vernier rocket engines on Surveyors 3, 5, and 6 and the attitude control rockets on Surveyors 1 and 6 against the lunar surface provided information on the permeability of the surface to gases, the cohesion of the soil, its response to gas erosion, and its adhesion to spacecraft surfaces.
The alpha backscattering experiments on Surveyors 5, 6, and 7 determined the abundances of the major chemical elements from carbon to iron on six surface samples and one subsurface sample at two mare sites and one highland site. These analyses indicated that the most abundant element of the lunar surface is oxygen (57 atomic percent), followed by silicon (20 atomic percent), and aluminum (7 atomic percent). These are the same elements, and in the same order, that are most common in Earth’s crust. The major chemical elements at the mare sites are generally similar to those found in terrestrial basaltic rocks. The similarity to basalts, as well as the morphology of the surface features determined from the Lunar Orbiter images, provides strong circumstantial evidence that some melting and chemical separation of the lunar material had occurred in the past. This surface composition is significantly different from primordial solar system material. It is also different from most known meteorites, indicating that the Moon is not a major source of the meteorites that hit Earth.
The magnets carried on Surveyors 5, 6, and 7 provided information on the magnetic particles at two mare sites and one highland site. The single highland site showed a lower abundance of iron and other chemically similar elements, demonstrating that the lunar surface is not homogeneous. These chemical differences were suggested as an explanation for the difference in albedo, or surface reflectivity, between the highland and mare regions.
Five successful Surveyor spacecraft returned 87,700 television pictures of the lunar surface, Earth, the solar corona, Mercury, Venus, Jupiter, and stars to the sixth magnitude. Lunar surface images provided information on the size-frequency distribution of lunar craters ranging from a few centimeters to tens of meters in diameter. Observations were consistent with the distribution predicted from prolonged bombardment by meteorites, and therefore allowed for the size distribution of the incoming meteoroids to be inferred.
Two and a half years after its landing, Surveyor 3 was visited by the Apollo 12 astronauts, who cut off the video camera, some camera cable, aluminum tubing, and a glass filter and returned these items to Earth for analysis to determine the extent of lunar weathering, micrometeorite impacts, and ion bombardment from the Sun.