Surveyor 3 was the third lander of the American uncrewed Surveyor program sent to explore the surface of the Moon in 1967. It was the first mission to carry a surface-soil sampling-scoop.

Surveyor 3 was visited by Apollo 12 astronauts Pete Conrad and Alan Bean in November 1969, and remains the only probe visited by humans on another world. The Apollo 12 astronauts excised several components of Surveyor 3, including the television camera, and returned them to Earth for study.

History
Launched on April 17, 1967, Surveyor 3 landed on April 20, 1967, at the Mare Cognitum portion of the Oceanus Procellarum (S3° 01' 41.43" W23° 27' 29.55"), in a small crater that was subsequently named Surveyor. It transmitted 6,315 TV images to the Earth, including the first images to show what planet Earth looked like from the Moon's surface.

As Surveyor 3 was landing in the crater highly reflective rocks confused the spacecraft's lunar descent radar. The engines failed to cut off at  in altitude as called for in the mission plans, and this delay caused the lander to bounce on the lunar surface twice. Its first bounce reached the altitude of about . The second bounce reached a height of about . On the third impact with the surface – from the initial altitude of 3 meters, and velocity of zero, which was below the planned altitude of , and very slowly descending – Surveyor 3 settled down to a soft landing as intended.

This Surveyor mission was the first that carried a surface-soil sampling-scoop, which can be seen on its extendable arm in the pictures. This mechanism was mounted on an electric-motor-driven arm and was used to dig four trenches in the lunar soil. These trenches were up to 7 inches (17.8 centimeters) deep. Samples of soil from the trenches were placed in front of the Surveyor's television cameras to be photographed and the pictures radioed back to the Earth. When the first lunar nightfall came on May 3, 1967, Surveyor 3 was shut down because its solar panels were no longer producing electricity. At the next lunar dawn (after 14 terrestrial days, or about 336 hours), Surveyor 3 could not be reactivated, because of the extremely cold temperatures that it had experienced. This is in contrast with the Surveyor 1, which was able to be reactivated twice after lunar nights, but then never again.

Surveyor 3 became famous after the crew of Apollo 12 used it as a landing target site. Landing within walking distance on November 19, 1969, the astronauts took several pictures of the probe and removed a scoop from the probe's soil mechanics-surface sampler, a section of unpainted aluminum tube from a strut supporting the Surveyor's radar altimeter and Doppler velocity sensor, another section of aluminum tube that was coated with inorganic white paint and a segment of television cable wrapped in aluminized plastic film and the Surveyor 3's television camera which were returned to Earth. Surveyor 3 is the only probe visited by humans on another world.

Science instruments

Television
The television camera on Surveyor 3 consisted of a vidicon tube, two 25 and 100 millimeter focal length lenses, shutters, filters, and an iris mounted along an axis inclined about 16 degrees to the central axis of the spacecraft. The TV camera was mounted under a mirror that could be moved in azimuth (horizontally) and elevation (vertically). The operation of the camera was completely dependent upon the receipt of proper commands from the Earth. Frame-by-frame coverage of the lunar surface was obtained over the complete 360 degrees in azimuth, and from +40 degrees above the plane normal to the camera's Z-axis to −65 degrees below this plane. Both 600-line and 200-line modes of TV camera operation were used. The 200-line mode transmitted over an omnidirectional antenna and scanned one frame every 61.8 seconds. A complete video transmission of each 200-line picture required 20 seconds and used a bandwidth of 1.2 kHz. The 600-line pictures were transmitted over a directional antenna. These pictures were scanned as often as once every 3.6 seconds. Each 600-line picture required a nominal one second to be read from the image vidicon, and its transmission required a 220 kHz bandwidth, using digital picture transmission. The TV photos were displayed back on the Earth on a slow-scan TV monitor that was coated with a long-persistence phosphor. Its persistence had been selected to match the nominal maximum frame rate. One frame of TV identification was received for each incoming TV photo, and the picture was displayed in real-time at a rate compatible with that of the incoming image. These data were recorded on a video magnetic-tape recorder. The camera returned 6315 pictures between April 20 and May 3, 1967, including views of the spacecraft itself, panoramic lunar surveys, views of the mechanical surface digger at work, and of an April 24 eclipse of the Sun by the Earth.

The Apollo 12 Lunar Module landed near Surveyor 3 on November 19, 1969. Astronauts Conrad and Bean examined the spacecraft, and they brought back about  of parts of the Surveyor to the Earth, including its TV camera, which is now on permanent display in the National Air and Space Museum in Washington, D.C.

Soil mechanics surface sampler
The soil mechanics surface sampler was designed to dig, scrape, and trench the lunar surface and to transport lunar surface material while being photographed so that the properties of the lunar surface could be determined. The sampler was mounted below the television camera and consisted primarily of a scoop approximately 120 mm long and 50 mm wide. The scoop consisted of a container, a sharpened blade, and an electric motor to open and close the container. A small footpad was attached to the scoop door to present a flat surface to the lunar surface. The scoop was capable of holding a maximum quantity of approximately 32 mm diameter of solid lunar material and a maximum of 100 cm³ of granular material. The scoop was mounted on a pantograph arm that could be extended about 1.5 m or retracted close to the spacecraft motor drive. The arm could also be moved from an azimuth of +40 to -72 degrees or be elevated 130 mm by motor drives. It could also be dropped onto the lunar surface under force provided by gravity and a spring. The surface sampler performed seven bearing tests, four trench tests, and 13 impact tests. The total operating time was 18 hours, 22 minutes on 10 separate occasions. Measurements of motor currents and forces applied to the surface were not obtained due to the state of the spacecraft telemetry following landing on the lunar surface. However, estimations were possible. The small spring constant of the torque spring precluded the determination of density from the impact tests. Penetrations of 38 to 50 mm were obtained from the bearing tests, and a 175 mm depth was reached during trenching operations. The design of the mechanism and its electronic auxiliary was more than adequate for the lunar surface operations. The scoop was also returned to Earth by the Apollo 12 astronauts and is currently on display at JPL.

Apollo 12 and the possibility of interplanetary contamination

The Surveyor 3 landing site was later selected also as the landing target for the Lunar Module of the Apollo 12 crewed lunar mission in 1969. Several components of the Surveyor 3 lander were collected and returned to the Earth for study of the long-term exposure effects of the harsh lunar environment on human-made objects and materials. Although space probes have returned to Earth in the decades since Apollo 12, this remains the only occasion on which humans have visited a probe that had been sent off-world.

It is widely claimed that a common type of bacterium, Streptococcus mitis, accidentally contaminated the Surveyor's camera prior to launch, and that the bacteria survived dormant in the harsh lunar environment for two and a half years, supposedly then to be detected when Apollo 12 brought the Surveyor's camera back to the Earth. This claim has been cited by some as providing credence to the idea of interplanetary panspermia, but more importantly, it led NASA to adopt strict abiotic procedures for space probes to prevent contamination of the planet Mars and other astronomical bodies that are suspected of having conditions possibly suitable for life. Most dramatically, the Galileo space probe was deliberately destroyed at the end of its mission by crashing it into Jupiter, to avoid the possibility of contaminating the Jovian moon Europa with bacteria from Earth. The Cassini probe also impacted Saturn at the end of its mission in 2017.

However, independent investigators have challenged the claim of surviving bacteria on Surveyor 3 on the Moon. There is a possibility the contamination was caused by using a non-airtight container, or by scientists not covering their arms in the clean room after Apollo 12.

Lunar Reconnaissance Orbiter

In 2009, the Lunar Reconnaissance Orbiter (LRO) photographed the Surveyor 3 landing site in some detail, in which surrounding astronaut foot tracks could also be seen. In 2011, the LRO returned to the landing site at a lower altitude to take higher resolution photographs.

See also

 Planetary protection
 List of artificial objects on the Moon

References

External links
 Surveyor Program Results (PDF) 1969
 Analysis of Surveyor 3 material and photographs returned by Apollo 12 (PDF, 24 MB) 1972
 Surveyor 3 images at Lunar and Planetary Institute
 Surveyor Site III Lunar Map at Lunar and Planetary Institute
 Surveyor Site III Lunar Photomap at Lunar and Planetary Institute

3
Spacecraft launched in 1967
Missions to the Moon
Apollo 12
Spacecraft launched by Atlas-Centaur rockets
Soft landings on the Moon
Alan Bean
Pete Conrad
1967 on the Moon