After flying the Apollo Lunar Module to the Moon's surface on April 21, Young and Duke spent 71 hours—just under three days—on the lunar surface, during which they conducted three extra-vehicular activities or moonwalks, totaling 20 hours and 14 minutes. The pair drove the Lunar Roving Vehicle (LRV), the second produced and used on the Moon, for . On the surface, Young and Duke collected of lunar samples for return to Earth, including Big Muley, the largest Moon rock collected during the Apollo missions. During this time Command Module Pilot Ken Mattingly orbited the Moon in the command and service module (CSM) and performed observations. Mattingly, staying with the command module, spent 126 hours and 64 revolutions in lunar orbit. After Young and Duke rejoined Mattingly in lunar orbit, the crew released a subsatellite from the service module (SM). During the return trip to Earth, Mattingly performed a one-hour spacewalk to retrieve several film cassettes from the exterior of the service module.