Second crewed Moon landing
Apollo 12 (November 14–24, 1969) was the sixth crewed flight in the United States Apollo program and the second to land on the Moon. It was launched on November 14, 1969, by NASA from the Kennedy Space Center in Florida. Commander Charles "Pete" Conrad and Lunar Module Pilot Alan L. Bean completed just over one day and seven hours of lunar surface activity while Command Module Pilot Richard F. Gordon remained in lunar orbit.
Apollo 12 would have attempted the first lunar landing had Apollo 11 failed, but after the success of the earlier mission, Apollo 12 was postponed by two months, and other Apollo missions also put on a more relaxed schedule. More time was allotted for geologic training in preparation for Apollo 12 than for Apollo 11, Conrad and Bean making several geology field trips in preparation for their mission. Apollo 12's spacecraft and launch vehicle were almost identical to Apollo 11's. One addition was a set of hammocks, designed to provide Conrad and Bean with a more comfortable resting arrangement inside the Lunar Module during their stay on the Moon.
Shortly after being launched on a rainy day at Kennedy Space Center, Apollo 12 was twice struck by lightning, causing instrumentation problems but little damage. The crew found that switching to the auxiliary power supply resolved the data relay problem, which helped save the mission. The outward journey to the Moon otherwise saw few problems. On November 19, Conrad and Bean achieved a precise landing at their expected location within walking distance of the Surveyor 3 robotic probe, which had landed on April 20, 1967. In making a pinpoint landing, they showed that NASA could plan future missions in the expectation that astronauts could land close to sites of scientific interest. Conrad and Bean carried the Apollo Lunar Surface Experiments Package, a group of nuclear-powered scientific instruments, as well as the first color television camera taken by an Apollo mission to the lunar surface, but transmission was lost after Bean accidentally pointed the camera at the Sun and its sensor was burned out. On the second of two moonwalks, they visited Surveyor 3 and removed parts for return to Earth.
Lunar Module "Intrepid" lifted off from the Moon on November 20 and docked with the command module, which subsequently traveled back to Earth. The Apollo 12 mission ended on November 24 with a splashdown.
Crew and key Mission Control personnel.
The commander of the all-Navy Apollo 12 crew was Charles "Pete" Conrad, who was 39 years old at the time of the mission. After receiving a bachelor's degree in aeronautical engineering from Princeton University in 1953, he became a naval aviator, and completed United States Naval Test Pilot School at Patuxent River Naval Air Station. He was selected in the second group of astronauts in 1962, and flew on Gemini 5 in 1965, and as command pilot of Gemini 11 in 1966. Command Module Pilot Richard "Dick" Gordon, 40 years old at the time of Apollo 12, also became a naval aviator in 1953, following graduation from the University of Washington with a degree in chemistry, and completed test pilot school at Patuxent River. Selected as a Group 3 astronaut in 1963, he flew with Conrad on Gemini 11.
The original Lunar Module pilot assigned to work with Conrad was Clifton C. Williams Jr., who was killed in October 1967 when the T-38 he was flying crashed near Tallahassee. When forming his crew, Conrad had wanted Alan L. Bean, a former student of his at the test pilot school, but had been told by Director of Flight Crew Operations Deke Slayton that Bean was unavailable due to an assignment to the Apollo Applications Program. After Williams's death, Conrad asked for Bean again, and this time Slayton yielded. Bean, 37 years old when the mission flew, had graduated from the University of Texas in 1955 with a degree in aeronautical engineering. Also a naval aviator, he was selected alongside Gordon in 1963, and first flew in space on Apollo 12. The three Apollo 12 crew members had backed up Apollo 9 earlier in 1969.
The Apollo 12 backup crew was David R. Scott as commander, Alfred M. Worden as Command Module pilot, and James B. Irwin as Lunar Module pilot. They became the crew of Apollo 15. For Apollo, a third crew of astronauts, known as the support crew, was designated in addition to the prime and backup crews used on projects Mercury and Gemini. Slayton created the support crews because James McDivitt, who would command Apollo 9, believed that, with preparation going on in facilities across the US, meetings that needed a member of the flight crew would be missed. Support crew members were to assist as directed by the mission commander. Usually low in seniority, they assembled the mission's rules, flight plan, and checklists, and kept them updated; For Apollo 12, they were Gerald P. Carr, Edward G. Gibson and Paul J. Weitz. Flight directors were Gerry Griffin, first shift, Pete Frank, second shift, Clifford E. Charlesworth, third shift, and Milton Windler, fourth shift. Flight directors during Apollo had a one-sentence job description, "The flight director may take any actions necessary for crew safety and mission success." Capsule communicators (CAPCOMs) were Scott, Worden, Irwin, Carr, Gibson, Weitz and Don Lind.
Preparation.
Site selection.
The landing site selection process for Apollo 12 was greatly informed by the site selection for Apollo 11. There were rigid standards for the possible Apollo 11 landing sites, in which scientific interest was not a major factor: they had to be close to the lunar equator and not on the periphery of the portion of the lunar surface visible from Earth; they had to be relatively flat and without major obstructions along the path the Lunar Module (LM) would fly to reach them, their suitability confirmed by photographs from Lunar Orbiter probes. Also desirable was the presence of another suitable site further west in case the mission was delayed, and the Sun would have risen too high in the sky at the original site for desired lighting conditions. The need for three days to recycle if a launch had to be scrubbed meant that only three of the five suitable sites found were designated as potential landing sites for Apollo 11, of which the Apollo 11 landing site in the Sea of Tranquility was the easternmost. Since Apollo 12 was to attempt the first lunar landing if Apollo 11 failed, both sets of astronauts trained for the same sites.
With the success of Apollo 11, it was initially contemplated that Apollo 12 would land at the site next further west from the Sea of Tranquility, in Sinus Medii. However, NASA planning coordinator Jack Sevier and engineers at the Manned Spaceflight Center at Houston argued for a landing close enough to the crater in which the Surveyor 3 probe had landed in 1967 to allow the astronauts to cut parts from it for return to Earth. The site was otherwise suitable and had scientific interest. Given that Apollo 11 had landed several miles off-target, though, some NASA administrators feared Apollo 12 would land far enough away that the astronauts could not reach the probe, and the agency would be embarrassed. Nevertheless, the ability to perform pinpoint landings was essential if Apollo's exploration program was to be carried out, and on July 25, 1969, Apollo Program Manager Samuel Phillips designated what became known as Surveyor crater as the landing site, despite the unanimous opposition of members of two site selection boards. 
To locate Surveyor 3, NASA invited Ewen Whitaker, who together with Gerard Kuiper worked on multiple Moon atlases. Whitaker had found the Surveyor 1 landing site with better precision than NASA. By studying images from Surveyor 3 and comparing them with photographs of thousands of similar craters under the microscope, he identified two rocks near Surveyor 3, that led to the identification of the probe's location.
Training and preparation.
The Apollo 12 astronauts spent five hours in mission-specific training for every hour they expected to spend in flight on the mission, a total exceeding 1,000 hours per crew member. Conrad and Bean received more mission-specific training than Apollo 11's Neil Armstrong and Buzz Aldrin had. This was in addition to the 1,500 hours of training they received as backup crew members for Apollo 9. The Apollo 12 training included over 400 hours per crew member in simulators of the Command Module (CM) and of the LM. Some of the simulations were linked in real time to flight controllers in Mission Control. To practice landing on the Moon, Conrad flew the Lunar Landing Training Vehicle (LLTV), training in which continued to be authorized even though Armstrong had been forced to bail out of a similar vehicle in 1968, just before it crashed.
Soon after being assigned as Apollo 12 crew commander, Conrad met with NASA geologists and told them that the training for lunar surface activities would be conducted much as Apollo 11's, but there was to be no publicity or involvement by the media. Conrad felt he had been abused by the press during Gemini, and the sole Apollo 11 geology field trip had turned into a near-fiasco, with a large media contingent present, some getting in the way—the astronauts had trouble hearing each other due to a hovering press helicopter. After the return of Apollo 11 in July 1969, more time was allotted for geology, but the astronauts' focus was on getting time in the simulators without being preempted by the Apollo 11 crew. On the six Apollo 12 geology field trips, the astronauts would practice as if on the Moon, collecting samples and documenting them with photographs, while communicating with a CAPCOM and geologists who were out of sight in a nearby tent. Afterwards, the astronauts' performance in choosing samples and taking photographs would be critiqued. To the frustration of the astronauts, the scientists kept changing the photo documentation procedures; after the fourth or fifth such change, Conrad required that there be no more. After the return of Apollo 11, the Apollo 12 crew was able to view the lunar samples, and be briefed on them by scientists.
As Apollo 11 was targeted for an ellipse-shaped landing zone, rather than at a specific point, there was no planning for geology traverses, the designated tasks to be done at sites of the crew's choosing. For Apollo 12, before the mission, some of NASA's geology team met with the crew and Conrad suggested they lay out possible routes for him and Bean. The result was four traverses, based on four potential landing points for the LM. This was the start of geology traverse planning that on later missions became a considerable effort involving several organizations.
The stages of the lunar module, LM–6, were delivered to Kennedy Space Center (KSC) on March 24, 1969, and were mated to each other on April 28. Command module CM–108 and service module SM–108 were delivered to KSC on March 28, and were mated to each other on April 21. Following installation of gear and testing, the launch vehicle, with the spacecraft atop it, was rolled out to Launch Complex 39A on September 8, 1969. The training schedule was complete, as planned, by November 1, 1969; activities after that date were intended as refreshers. The crew members felt that the training, for the most part, was adequate preparation for the Moon mission.
Hardware.
Launch vehicle.
There were no significant changes to the Saturn V launch vehicle used on Apollo 12, SA–507, from that used on Apollo 11. There were another 17 instrumentation measurements in the Apollo 12 launch vehicle, bringing the number to 1,365. The entire vehicle, including the spacecraft, weighed at launch, an increase from Apollo 11's . Of this figure, the spacecraft weighed , up from on Apollo 11.
Third stage trajectory.
After LM separation, the third stage of the Saturn V, the S-IVB, was intended to fly into solar orbit. The S-IVB auxiliary propulsion system was fired, with the intent that the Moon's gravity would slingshot the stage into solar orbit. Due to an error, the S-IVB flew past the Moon at too high an altitude to achieve Earth escape velocity. It remained in a semi-stable Earth orbit until it finally escaped Earth orbit in 1971, but briefly returned to Earth orbit 31 years later. It was discovered by amateur astronomer