Roving Vehicle made unnecessary any further maneuvering. Lunar surface Stand-up EVA and first EVA With Falcon due to remain on the lunar surface for almost three days, Scott deemed it important to maintain the circadian rhythm they were used to, and as they had landed in the late afternoon, Houston time, the two astronauts were to sleep before going onto the surface. But the time schedule allowed Scott to open the lander's top hatch (usually used for docking) and spend a half hour looking at their surroundings, describing them, and taking photographs. Lee Silver had taught him the importance of going to a high place to survey a new field site, and the top hatch served that purpose. Deke Slayton and other managers were initially opposed due to the oxygen that would be lost, but Scott got his way. During the only stand-up extravehicular activity (EVA) ever performed through the LM's top hatch on the lunar surface, Scott was able to make plans for the following day's EVA. He offered Irwin a chance to look out as well, but this would have required rearranging the umbilicals connecting Irwin to Falcon'''s life support system, and he declined. After repressurizing the spacecraft, Scott and Irwin removed their space suits for sleep, becoming the first astronauts to doff their suits while on the Moon. Throughout the sleep period Mission Control in Houston monitored a slow but steady oxygen loss. Scott and Irwin eventually were awakened an hour early, and the source of the problem was found to be an open valve on the urine transfer device. In post-mission debriefing, Scott recommended that future crews be woken at once under similar circumstances. After the problem was solved, the crew began preparation for the first Moon walk. After donning their suits and depressurizing the cabin, Scott and Irwin began their first full EVA, becoming the seventh and eighth humans, respectively, to walk on the Moon. They began deploying the lunar rover, stored folded up in a compartment of Falcons descent stage, but this proved troublesome due to the slant of the lander. The experts in Houston suggested lifting the front end of the rover as the astronauts pulled it out, and this worked. Scott began a system checkout. One of the batteries gave a zero voltage reading, but this was only an instrumentation problem. A greater concern was that the front wheel steering would not