Surveyor 1, 2, 3, 4, 5, 6, 7

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. 

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 spacecraft carrierd a Star-37 retro motor for breaking. After the Star-37 has burned out, it was separated and the Surveyor descended on its three hydracine engines (Thiokol TD-339). 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 to avoid contamination of the landing site. 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. 

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.