The Surveyor Spacecraft
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.
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.
Surveyor Landing Sites
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).
Television Observations
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.
Program Summary
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.