Apollo 15, which launched on July 26, 1971, marked the beginning of NASA's most challenging missions to the moon. It featured the longest stay yet on the lunar surface, three moonwalks and the first use of a "moon buggy," or lunar rover.
In training for Apollo 15, the three astronauts put an emphasis on geological work. They spent many hours in the field learning how to identify different types of rocks and formations. The crew — all Air Force pilots — had trained together in the past, with all of them serving as backups for the Apollo 12 mission.
Commander Dave Scott had two missions of space experience behind him. He was the command module pilot on Apollo 9, which featured the first Apollo docking in space. He also flew on an eventful Gemini mission in 1966. Gemini 8 had a malfunctioning thruster that spun the spacecraft around so quickly that the astronauts almost lost consciousness; crewmate Neil Armstrong managed to pull them out of the lurch by activating the re-entry system.
A rocky test drive
After several missions of choosing progressively less conservative landing sites, NASA wanted to aim even higher for Apollo 15. The site they came up with for the landing — Hadley Rille, on the edge of Mare Imbrium — is described as "spectacularly beautiful" on a NASA website. More importantly, it was a treasure trove of geologic treasure, including mountains, craters and Hadley — a large canyon.
Unlike the other crews, Apollo 15 astronauts chose to sleep after landing July 30 before doing the first moonwalk. It was to preserve energy for the longer mission. But before hitting the sack, Scott opened the hatch at the top of the lander Falcon and took a series of camera shots to get a panorama view of the site.
The next morning, Scott hopped down the ladder and looked at the field site surrounding him. "Man must explore. And this is exploration at its greatest," he proclaimed. Then he and Irwin got to work unfolding the lunar roving vehicle from the side of Falcon.
Next came a test drive. It was no surprise that driving was a bumpy experience, given all the rocks and mini-divots in the moon's surface. While the front wheel drive wasn't working, Scott found he could manage all right with the rear wheel drive system.
The astronauts drove the rover a total of 17.5 miles (28 kilometers). The crew's main complaint was the seatbelts, which were difficult to get on and off because the suits weren't pushed down very much when the astronauts sat in the light lunar gravity. [Driving on the Moon: The 40-Year Legacy of NASA's First Lunar Car]
Irwin and Scott were on the hunt for anorthosites, which are believed to be the moon's oldest rocks, and they found them in spades during the second day on the surface. At Spur Crater, the astronauts picked up four of these types of rocks. The most well-known of the bunch was later dubbed the Genesis Rock because of its ancient age, some 4.5 billion years old.
Back at Falcon, Scott was supposed to drill down below the moon's surface to get a "core sample" that would show the layers of rock underneath. The regolith was packed tight, and it was hard to get the drill in far enough. Scott, who was tired from seven hours of work outside, then didn't have the energy to pull it back out.
NASA ordered him to leave it until the next day. After the astronauts went outside for the third spacewalk, both of them struggled to withdraw the core, but they succeeded.
After a geologic trip to Hadley Rille, the astronauts returned to Antares. Scott then did a mini scientific experiment in front of the TV camera in honor of Galileo Galilei. In the 1600s, Galileo is said to have dropped weights from the Leaning Tower of Pisa to demonstrate that objects of different mass fall at the same rate.
When Scott's feather and hammer struck regolith at the same time, mission controllers applauded. "Nothing like a little science on the moon," Scott said.
While Scott and Irwin toiled on the surface, Worden contributed his own observations from above. From the command module Endeavour, Worden excitedly a described an area called Littrow, which some believed was a volcanic region. Later, Littrow was where Apollo 17 landed.
The crew left the surface of the moon on Aug. 2 and for the first time, the liftoff was seen on Earth via the television camera on the lunar rover. Just before they left lunar orbit, the crew launched the Particles and Fields satellite. The satellite was designed to investigate the moon's mass and gravitational variations, particle composition of space near the moon and the interaction of the moon's magnetic field with that of Earth.
All told, Apollo 15's moon-roving astronauts spent 18 hours, 37 minutes working on the lunar surface — almost the total time spent in lunar orbit by the Apollo 8 crew. They set other records as well, including longest time in lunar orbit — about 145 hours; and longest lunar mission — 295 hours. They returned to Earth Aug. 7, bringing back a geologic bonanza for scientists and positioning NASA for more ambitious missions to come.