The Surveyor Program
The Surveyor program consisted of seven unmanned lunar missions that were launched between May 1966 and January 1968. Five of these spacecraft, Surveyor 1, 3, 5, 6, and 7 successfully soft-landed on the lunar surface. In addition to demonstrating the feasibility of lunar surface landings, the Surveyor missions obtained lunar and cislunar photographs and both scientific and technological information needed for the Apollo manned landing program. Four spacecraft, Surveyor 1, 3, 5, and 6, returned data from selected mare sites from Apollo program support, and Surveyor 7 provided data from a contrasting rugged highland region. For more on the individual missions, select from the list below.
Launch: 30 May, 1966
Landed: 2 June, 1966, 06:17:37 UT
Landing Site: Flamsteed P (2.45°S latitude, 316.79°E longitude)
In addition to proving a variety of new equipment and spacecraft design and validating the technique for landing on the Moon, Surveyor 1, the first U.S. spacecraft to land softly on the Moon, returned a large quantity of scientific data during its first two days of operation on the lunar surface. Following its landing the spacecraft transmitted 11,240 high-resolution television pictures. Surveyor 1 completed its primary mission on July 14, 1966, after transmitting, in addition to the television pictures, data on the bearing strength, temperatures, and radar reflectivity of the Moon. Subsequent engineering interrogations of the spacecraft were conducted through January 1967.Selection of the Target Site
All Surveyor landing sites, except for the last one, were selected primarily because they were being considered as Apollo landing sites. The landing site selected for Surveyor 1 was in the southwest part of Oceanus Procellarum. The spacecraft came to rest within about 15 kilometers of the target point, on a flat surface inside a 100-kilometer crater, one radius from the edge of a rimless 200-meter crater.
Launch: 20 September, 1966
Surveyor 2 was intended to land in Sinus Medii, a different area of the Apollo zone. When the midcourse maneuver was attempted, one of the vernier engines failed to ignite, and the unbalanced thrust caused the spacecraft to tumble. Although repeated efforts were made to salvage the mission, none was successful. Surveyor 2 crashed into the Moon southeast of Copernicus Crater on September 22, 1966.
Launched: 17 April, 1967
Landed: 20 April, 1967, 00:04:53 UT
Landing Site: Oceanus Procellarum (2.94°S latitude, 336.66°E longitude)
The data from Surveyor 3 showed that it touched down on the lunar surface three times before landing because the engines did not shut down as intended. The spacecraft moved 20 meters between the first and second touchdowns and about 11 meters between the second and third. A final translation movement of about 30 centimeters occurred following the third touchdown. The engines finally shut down prior to the third touchdown.
Like its predecessors, this mission carried a survey television camera, as well as other instrumentation for determining various properties of the lunar surface material. In addition, it carried a surface sampler instrument for digging trenches, making bearing tests, and otherwise manipulating the lunar material in view of the television system. During its operation, which ended May 4, 1967, Surveyor 3 acquired a large volume of new data and took 6326 pictures. In addition, the surface sampler accumulated 18 hours of operation, which yielded significant new information on the strength, texture, and structure of the lunar material to a depth of 17.5 centimeters.
Selection of the Target Site
All Surveyor landing sites, except for the last one, were selected primarily because they were being considered as Apollo landing sites. The site selected for Surveyor 3 was in the southeast part of Oceanus Procellarum. The spacecraft came to rest in a subdued, rounded crater about 200 meters in diameter approximately 370 kilometers south of the crater Copernicus. Later, this site was indeed the landing site of an Apollo mission. Apollo 12 landed nearby and the crew visited the Surveyor 3 landing site and conducted an investigation of the spacecraft.
Launch: 14 July, 1967
This mission carried the same payload as Surveyor 3. After a flawless flight to the Moon, radio signals from the spacecraft abruptly ceased during the terminal-descent phase, approximately 2 and 1/2 minutes before its touchdown in Sinus Medii. Contact with the spacecraft was never reestablished.
Launch: 8 September, 1967
Landed: 11 September, 1967, 00:46:44 UT
Landing Site: Mare Tranquillitatus (1.41°N latitude, 23.18°E longitude)
This spacecraft was basically similar to its predecessor, except that the surface sampler was replaced by an alpha-backscatter instrument. In addition, a small bar magnet was attached to one of the footpads. Because of a critical helium regulator leak, a radically new descent profile had to be designed for the spacecraft. Surveyor 5 performed it flawlessly and landed softly. Once safely on the Moon, the spacecraft functioned well, outperforming the previous missions. During its first lunar day, 18,006 television images of exceptional quality and high scientific content were returned to Earth. On October 15, 1967, after having spent two weeks in the deep freeze of a lunar night, Surveyor 5 responded immediately to the first turn-on command and resumed operation, returning 1048 additional pictures and 22 hours of additional data.
Selection of the Target Sites
All Surveyor landing sites, except the last one, were selected primarily because they were being considered as Apollo landing sites. The site selected for Surveyor 5 was in the southwest part of Mare Tranquillitatis. Surveyor 5 landed in a dimple-shaped, 9-by-12-meter rimless crater, the largest of a small chain of rimless craters.
Launch: 07 November, 1967
Landed: 10 November, 1967, 01:01:06 UT
Landing Site: Sinus Medii (0.46°N latitude, 358.63°E longitude)
The performance of Surveyor 6 on the lunar surface was virtually flawless. From touchdown until a few hours after sunset on November 24, 1967, the spacecraft transmitted 29,952 television pictures and the alpha-scattering instrument acquired 30 hours of data on the chemical composition of the lunar material.
As part of the surface mechanical properties investigation, Surveyor 6 performed a “hop” maneuver, moving 2.5 meters away from its original landing area. This maneuver provided excellent views of the surface disturbances produced by the initial landing and the effects of firing rocket engines close to the lunar surface. Photography obtained after the hop contributed to the soil mechanics investigation.
On November 26, 1967, the spacecraft was placed in hibernation for the two-week lunar night. Contact with the spacecraft was resumed for a short period on December 14, 1967.
Selection of the Target Site
The landing site chosen for this mission was in Sinus Medii, in the center of of the Moon’s visible hemisphere, the last of four potential Apollo landing areas designated for investigation by the Surveyor program. The spacecraft came to rest on a nearly flat, heavily cratered mare area, about 200 meters northwest of the base of a ridge about 30 meters high.
Launch: 07 January 1968
Landed: 10 January 1968, 01:05:36 UT
Landing Site: Tycho Crater North Rim (41.01°S latitude, 348.59°E longitude)
Despite the more hazardous terrain in the landing area, Surveyor 7 landed without incident. During the first lunar day, 20,993 television pictures were obtained. An additional 45 pictures were obtained during the second lunar day. One potential problem developed when the alpha-scattering instrument failed to fully deploy on its own. The surface sampler was then used to place the instrument on the surface and later to move it twice. In addition to acquiring a wide variety of lunar surface data, Surveyor 7 also obtained pictures of Earth and performed star surveys. Laser beams from Earth were successfully detected by the television camera in a special test of laser-pointing techniques.
Post-sunset operations were conducted for 15 hours after local sunset at the end of the first lunar day. During these operations, additional Earth and star pictures were obtained, as were observations of the solar corona. Operation of the spacecraft was terminated 80 hours after sunset. The spacecraft was reactivated for the second lunar day on February 12, 1968, and operated until February 21, 1968.
Selection of the Target Site
The investigations in the Apollo landing zone having been satisfactorily accomplished, Surveyor 7 could be sent to an area of primarily scientific interest. The site selected was a rugged, rock-strewn ejecta blanket near Tycho Crater. The spacecraft landed less than 1.5 miles from the center of the target circle, about 18 miles north of the rim of Tycho.
Each spacecraft weighed 1000 kilograms at launch, was 3.3 meters high, and had a 4.5-meter diameter. The tripod structure of aluminum tubing provided mounting surfaces for scientific and engineering equipment. Onboard equipment consisted of a 3-meter-square solar panel that provided approximately 85-watt output, a main battery and 24-volt non-rechargeable battery that together yielded a 4090-watt total output, a planar array antenna, two omnidirectional antennas, and a radar altimeter. The soft landing was achieved by the spacecraft free falling to the lunar surface after the engines were turned off at a 3.5-meter altitude. Operations began shortly after landing.
Four Surveyor spacecraft landed in the lunar maria near the equator. These sites were selected primarily because they were being considered for Apollo manned lunar landings. Surveyor 7, the last in the series, landed in the highland region close to Tycho Crater, a site chosen primarily for its scientific interest. The suitability of each site for making a safe landing was also evaluated as part of the site selection process.
The Scientific Investigations
In addition to the objectives of developing and validating the technology for landing softly on the Moon and providing data on the compatibility of the Apollo spacecraft design with conditions on the lunar surface, the Surveyor program had the objective of adding to our scientific knowledge of the Moon. Toward that end, the following investigations were performed by the Surveyor spacecraft (note that not all investigations were carried out on every mission).
Each Surveyor spacecraft carried a television camera, and more than 86,000 70-millimeter pictures were obtained at very high resolution (to 1 millimeter). This photography provided information on the nature of the surface terrain in the immediate vicinity of the spacecraft as well as the number, distribution, and sizes of the craters and boulders in the area. In addition to lunar terrain studies, the photography supported investigations of soil mechanics, magnetic properties, and composition of the surface material.
Lunar Surface Mechanical Properties
Mechanical property estimates are the result of interpretations of landing telemetry data and television pictures as noted above. Measurements from strain gauges mounted on the spacecraft landing gear were analyzed. The surface sampler, flown on Surveyor 3 and Surveyor 7, also obtained data on mechanical properties. To study soil erosion effects and to determine soil properties, the vernier engines and attitude jets were operated after the landings and the results observed with the television camera.
Lunar Surface Soil Mechanics
The soil mechanics investigation was performed by the surface sampler carried on Surveyor 3 and 7. The sampler proved to be an extremely versatile and useful piece of equipment. Using this device, operators performed a number of bearing and impact tests and trenching operations. All these operations were monitored using the television camera, and photography of the results provided information for this investigation.
Lunar Surface Temperature and Thermal Characteristics
None of the Surveyor spacecraft carried any instruments, as such, to measure lunar surface temperatures or thermal characteristics. However, there were temperature sensors on the outer surfaces of two electronic compartments, on the solar panel, and on the planar array, which were highly dependent on the local thermal radiation environment.
Lunar Surface Electromagnetic Properties
Surveyor 5, 6, and 7 had a magnet attached to one of the spacecraft footpads to determine magnetic properties and composition of the soil. Surveyor 7 had additional magnets on a second footpad and the surface sampler. Photographs showing the amount of dust adhering to magnets indicated the amount of magnetic particles in the soil and allowed estimates of the lunar soil compositions when compared with premission experiment photographs of magnets in terrestrial soils of various compositions.
Alpha-Scattering Chemical Analysis
Composition of surface materials was also determined from data obtained by the alpha-scattering instrument. This instrument was carried by Surveyor 5, 6, and 7 to allow chemical analysis of the lunar surface material. The performance of the alpha-scattering equipment and operational system during the three missions was excellent. In all, six lunar samples were examined. The Surveyor 5, 6, and 7 missions provided the first chemical analysis of lunar surface material.
In summary, five Surveyor spacecraft landed successfully on the lunar surface. Four of these examined widely separated mare sites in the Moon’s equatorial belt. The fifth investigated a region within the southern highlands. Four spacecraft survived the extreme cold of the lunar night and operated for more than one day/night cycle. In total, the five spacecraft operated for a combined elapsed time of about 17 months, transmitted 87,000 pictures, performed 6 separate chemical analyses of surface and near-surface samples, dug into and otherwise manipulated and tested lunar material, measured its mechanical properties, and obtained a wide variety of other data that greatly increased our knowledge of the Moon.