Apollo 15 Mission Overview
Left: Jim Irwin and the lunar rover on the rim of Hadley Rille. Right: Jim Irwin, the Lunar Module Falcon, and the Lunar Rover in front of the Apennine Mountains.
Apollo 15 was launched on July 26, 1971, and successfully completed the fourth human landing on the Moon. It was the first of the “J series” of Apollo missions, which featured longer stays on the surface and in lunar orbit and more extensive science operations than was possible on the earlier Apollo missions. Commander David Scott and Lunar Module Pilot James Irwin landed the lunar module Falcon about 0.5 km from the planned landing location at Hadley-Apennine. Hadley Rille is a lunar lava channel, and the Apennine Mountains form part of the rim of the Imbrium impact basin. The Imbrium basin, more than 1100 km in diameter, is the second largest and one of the youngest impact basins on the Moon. This landing site had the dual purposes of sampling volcanic material from Hadley Rille and the adjacent mare basaltic plains and obtaining materials from the lower slopes of Mount Hadley Delta, which is part of the Apennine Mountains. It was hoped that the Imbrium impact had uplifted material from deep in the lunar crust which would then be accessible on the surface of Mount Hadley Delta. The primary alternative landing site that was considered was the unusual volcanic domes in the Marius Hills. However, it was felt that the geologic objectives at Hadley-Apennine were more important. Moreover, Hadley-Apennine provided a better overall distribution for the geophysical experiments that were deployed on each Apollo mission. The Apennine Mountains are 3 km high to the east of the landing site, requiring an unusually steep landing approach.
Scott and Irwin spent a total of 67 hours on the Moon and performed three extra-vehicular activities (EVAs, or “moonwalks”), totaling 18 hours and 35 minutes. In addition, Scott performed a 33 minute long “stand up EVA”, looking out of the top hatch of Falcon to obtain a complete photo panorama of the landing site and using a 500 mm telephoto lens for high resolution closeups of selected features. At the start of the first EVA, lasting 6 hours 33 minutes, the crew deployed the Lunar Rover, a 210 kg vehicle capable of driving at a top design speed of 13 km/hr. Each wheel was independently powered, and the front and rear wheels could be steered separately for maximum mobility on the lunar surface. The rover extended the distance the crew could travel away from the Lunar Module and increased the amount of science equipment and samples that they could carry. In addition, a television camera that was controlled from Earth provide Mission Control with enhanced ability to monitor and direct the crew’s exploration at each sample collection site. Scott and Irwin then drove to locations along the rille and at the base of the mountain scarp southwest of the landing site. At one point, the crew made an unplanned stop so that Scott could “adjust his seat belt”; in fact, he collected an unusual looking basalt (sample 15016), which is now known informally as the Seatbelt Basalt. The basalts collected at the Apollo 15 landing site are chemically similar to those from Apollo 12 and formed about 3.3 billion years ago. During the final part of the EVA, the crew began deployment of the ALSEP experiment package, which included a seismometer, magnetometer, equipment to measure the solar wind, and a new experiment to measure the heat coming out of the Moon’s interior. The Heat Flow Experiment required drilling a deep core into the Moon, but this proved unexpectedly difficult and required time from the crew on all three EVAs to complete the necessary work.
On the second EVA, lasting 7 hours and 12 minutes, the crew drove south from the landing site onto Mount Hadley Delta, reaching an elevation of about 100 meters above the plains where they landed. Although the rover handled the climb easily, the crew found it difficult to work on the steep slope. Nevertheless, this was a geologically very productive traverse. The crew collected two rocks that consist of a mixture of material that melted during the Imbrium basin impact and material that formed at least 20 km deep in the crust prior to the Imbrium impact. The crew also collected “Genesis Rock”, so named because it is an anorthosite (nearly 100% plagioclase, which likely from the magma ocean very early in lunar history), although Apollo 16 later collected better and larger examples of anorthosites.
On the third EVA, lasting 4 hours and 50 minutes, the crew first completed extraction of the deep core sample and then drove the rover to locations along Hadley Rille west of the landing site. Because of the time required to collect the core sample and the need to keep the scheduled lunar liftoff time, a planned stop at the North Complex, a possible volcanic structure, had to be cancelled. However, the consensus of the mission science team was that the effort required to collect the deep core was worth the time it took. Analysis of the core in the Lunar Sample Laboratory showed at least 42 distinct layers down to a depth of 2.4 meters below the surface. The deepest and oldest layer formed between 420 and 750 million years ago. During the three EVAs combined, Scott and Irwin collected 77.3 kilograms of lunar samples. They drove the lunar rover for a total distance of 27.8 km and reached a maximum distance of 5 km from the landing site.
During the moon landing, Command Module Pilot Alfred Worden remained in lunar orbit in the Command Module, Endeavour, operating a new set of orbital experiments, including high resolution mapping cameras, a laser altimeter to measure the Moon’s topography, and several experiments to map regional variations in the Moon’s chemical composition. Worden also made visual observations of the lunar surface, which played a key role in the selection of the landing site for Apollo 17. Apollo 15 spent a total of 6 days and 1 hour in lunar orbit, circling the Moon 74 times. On the last orbit prior to departing the Moon, the crew deployed a small subsatellite, which remained at the Moon to continue making measurements of the Moon’s gravity and magnetic fields and of charged particles. While on the return voyage to Earth, Worden made a 39-minute spacewalk to collect the film cassettes from the mapping cameras, which were located in the Scientific Instrument Module, which was part of the spacecraft’s Service Module. The crew landed in the Pacific Ocean north of Hawaii on August 7 after a flight of 12 days and 7 hours. Although one parachute did not fully deploy, the remaining two parachutes provided a safe landing. Prior lunar landing crews had been required to remain in biological quarantine for 21 days to avoid possible contamination of Earth by lunar organisms. This requirement was waived beginning on Apollo 15 because the earlier missions had provided no evidence of living lunar organisms.