Harrison Schmitt cancelled in September 1970, the community of lunar geologists supporting Apollo felt so strongly about the need to land a professional geologist on the Moon, that they pressured NASA to reassign Schmitt to a remaining flight. As a result, Schmitt was assigned in August 1971 to fly on the last mission, Apollo 17, replacing Joe Engle as Lunar Module Pilot. Schmitt landed on the Moon with commander Gene Cernan in December 1972. Schmitt claims to have taken the photograph of the Earth known as "The Blue Marble", possibly one of the most widely distributed photographic images in existence. NASA officially
Far side of the Moon 17 missions since that time, and photographed by multiple lunar probes. Spacecraft passing behind the Moon were out of direct radio communication with the Earth, and had to wait until the orbit allowed transmission. During the Apollo missions, the main engine of the Service Module was fired when the vessel was behind the Moon, producing some tense moments in Mission Control before the craft reappeared. Geologist-astronaut Harrison Schmitt, who became the last to step onto the Moon, had aggressively lobbied for his landing site to be on the far side of the Moon, targeting the lava-filled crater Tsiolkovskiy. Schmitt's ambitious