Apollo 12 | Universe Today

Written by Jerry Coffey

Normally being second is a bad thing, but in the case of Apollo 12 that isn't true. Apollo 12 was the second lunar landing and the sixth manned Apollo spacecraft. The mission was launched a short four months after Apollo 11. The landing site for the mission was the Ocean of Storms. Some of the key objectives of the mission were to achieve a more precise landing , something that had not been achieved by Apollo 11, and to visit the Surveyor 3 probe. The mission needed to bring back a part of it for analysis.

Despite a rain storm, Apollo 12 launched on time. Interestingly enough, just 36.5 seconds after lift-off from Kennedy Space Center, the vehicle triggered a lightening discharge through itself and down to Earth through the Saturn's ionized plume. A second strike at 52 seconds after launch knocked out the attitude indicator. The telemetry at Mission Control was garbled nonsense. However, the Saturn V continued to fly correctly. This meant that the strikes had not affected the Saturn V's Instrument Unit. The mission did lose all three fuel cells which caused almost all of the command module's instruments to fail, but by switching to auxiliary power, the crew avoided having to abort the mission.

After lunar module separation, the Apollo 12 S-IVB was intended to fly into solar orbit. The S-IVB auxiliary propulsion system was fired and the remaining propellants vented to slow it down to fly past the moon's trailing edge. The moon's gravity would then slingshot the stage into solar orbit; however, a small error in the state vector in the Saturn's guidance system caused the S-IVB to fly past the Moon at too high an altitude to achieve Earth escape velocity. It remained in a semi-stable Earth orbit after passing the Moon on November 18, 1969. It finally escaped Earth orbit in 1971 but was briefly recaptured in Earth orbit 31 years later. It was discovered by amateur astronomer Bill Yeung who gave it the temporary designation J002E3 before it was determined to be an artificial object.

The lunar landing was an exercise in precision targeting, using a doppler effect radar technique developed to allow the pinpoint landings needed for the future Apollo missions. Most of the descent was automatic, with manual control assumed by Conrad during the final few hundred feet of descent. Apollo 12 succeeded in landing within walking distance (less than 200 meters) of its intended target, which was the Surveyor 3 probe, which had landed on the Moon in April 1967.

The Apollo 12 mission was a great success. Here is a nice article on the mission. Here on Universe Today we have a good article that includes images of the Apollo 12 landing sites. Astronomy Cast offers a cool episode about losing contact with rovers.

Filed under: Astronomy

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Tags: Apollo 12, apollo missions, astronauts