It included three lunar EVAs: 7.2 hours, 7.4 hours, 5.7 hours and one trans-earth EVA of 1.4 hours. Despite a malfunction in the Command Module which almost aborted the lunar landing, Apollo 16's lunar module landed successfully in the Descartes Highlands on April 21. Commander John W. Young and Lunar Module Pilot Charles Duke spent nearly three days on the lunar surface while Command Module Pilot Ken Mattingly orbited the Moon.
A subsatellite was released from the Service Module while in lunar orbit to carry out experiments on magnetic fields and solar particles (the first subsatellite had been released from Apollo 15).
The crew splashed down in the Pacific Ocean on April 27.
The original launch date in March 1971 was scrubbed well in advance due to an issue with a fuel tank supplying the RCS on the command module. The location of the problem forced a rolback to the VAB on January 27, 1971. The stack was returned after repairs well before the final countdown had initiated.[3]
A malfunction in a backup yaw gimbal servo loop in the main propulsion system of the CSM Casper caused concerns about firing the engine to adjust the CSM's lunar orbit, and nearly caused the Moon landing to be aborted. After a delayed first landing attempt, it was determined that the malfunction presented relatively little risk, and Young and Duke (who were already undocked, and flying LM Orion when the problem occurred) were permitted to land on the Moon.
Young and Duke spent three days exploring the Descartes highland region, while Mattingly circled overhead in Casper. This was the only one of the six Apollo landings to target the lunar highlands. On the first day of lunar surface operations, news was relayed to them that the House of Representatives had approved the Space Shuttle program. Young stated that it was needed.[4]
The astronauts discovered that what was thought to have been a region of volcanism was actually a region full of impact-formed rocks (breccias). Their collection of returned specimens included a 25-pound (11 kg) chunk that was the largest single rock returned by the Apollo astronauts[5] (nicknamed "Big Muley" after Bill Muehlberger, principal investigator for the mission's geology activities[6]). The scientific results of Apollo 16 caused planetary geologists to revise previous interpretations of the lunar highlands, concluding that meteorite impacts were the dominant agent in shaping the Moon's ancient surfaces.
Young and Duke set up their Apollo Lunar Surface Experiments Package (ALSEP), which included an experiment to measure heat flow between two probes they were to insert into holes drilled in the surface. Young, however, accidentally got one foot tangled up in the cable to one of the probes, detaching it and rendering the experiment useless.
The astronauts also conducted performance tests with the lunar rover, Young at one time getting up to a top speed of 11 miles per hour (18 kilometers per hour), which still stands as the record speed for any wheeled vehicle on the Moon (listed as such in the Guinness Book of Records).
Apollo 16 was originally scheduled for splashdown at 3:30 pm EST on April 28. The mission was shortened by a day (reducing the time in orbit around the Moon after the LM left the Moon and docked with the CSM) because of the problems with the command module prior to landing. As Duke described on the Apollo Lunar Surface Journal website: "The more you waited up there - if you did have a problem - the less time you had to think of something brilliant to fix it. They got a little nervous and brought us home a day early, I think, just to make sure we could have some ample time to fix any problems."[7] There were no problems encountered during the return flight.
The aircraft carrier USS Ticonderoga delivered the Apollo 16 command module to the North Island Naval Air Station, near San Diego, California on Friday, May 5, 1972. On Monday, May 8, 1972, ground service equipment being used to empty the residual toxic RCS fuel in the command module tanks, exploded in a Naval Air Station hanger. A total of 46 people were sent to the hospital for 24 to 48 hours observation, most suffering from inhalation of toxic fumes. Most seriously injured was a technician who suffered a fractured kneecap when the GSE cart overturned on him. A hole was blown in the NAS hangar roof 250 feet above, and about 40 windows in the hanger were shattered. The command module suffered a three-inch gash in one panel.[8][9][10]
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