Shepard was designated as the commander of the first crewed Project Gemini mission, but was grounded in 1963 due to Ménière's disease, an inner-ear ailment that caused episodes of extreme dizziness and nausea. This was surgically corrected in 1969, and in 1971, Shepard commanded the Apollo 14 mission, piloting the Apollo Lunar Module "Antares". At age 47, he became the fifth, the oldest, and the earliest-born person to walk on the Moon, and the only one of the Mercury Seven astronauts to do so. During the mission, he hit two golf balls on the lunar surface.