Apollo 15 (July 26 – August 7, 1971) was the fourth crewed mission to land on the Moon. It was the first of three J missions, with a longer stay on the Moon, a greater focus on science, and the use of the first Lunar Roving Vehicle (LRV). David Scott and James Irwin landed near Hadley Rille and spent 18 and a half hours on extravehicular activity (EVA), collecting 170 pounds (77 kg) of surface material. During the return trip, Alfred Worden performed the first spacewalk in deep space. The mission included the collection of the Genesis Rock, thought to be part of the Moon's early crust, and Scott used a hammer and a feather to demonstrate Galileo's theory that, absent air resistance, objects fall at the same rate regardless of mass. The mission was later marred when it was found that the crew had carried unauthorized postal covers to the lunar surface, some of which were sold by a West German stamp dealer. The crew was reprimanded for poor judgment, and none flew in space again. This photograph, taken by Scott during an EVA on August 2, shows Irwin giving a military salute beside the U.S. flag. The Lunar Module Falcon is in the center, with the LRV on the right.Photograph credit: David Scott; restored by Bammesk and Basile Morin