EVA-2
The target of the second EVA was Mount Hadley Delta again, but the crew drove via a more direct route and to a site east of where they had travelled the previous day. Travelling at 5.5 mph (9 km/h) they made good time across the plain. The first stop of the day, Station 4 was cancelled to give them more time to finish the drilling the holes for the heat flow experiment. This was at a crater Dune, on the western edge of the South Cluster.
After making a navigation stop at Spur, they started to travel the 1.9 mi (3 km) along the base of the Delta to reach Station 5, at a site named Front. Scott found there was little variation in the surroundings and decided that Front was going to offer little difference, so it was decided to stop at a site about 1.9 mi (3 km) from St George and 320 ft (100 m) up to the Delta. It was interesting work, with the slope being about 10 degrees. Not reaching Front cancelled Station 5, placing them instead at Station 6.
They first sampled a fresh looking 1 meter crater, that was part of the rim of the older 3 meter crater. More samples were made above the area where they had parked the Rover. Most were breccias, but they did find one porphyritic basalt.
Scott decided to move down to a 40 ft (12 m) crater, which was the largest one nearby. He went down inside it to sample, but found most of the rocks to be too large. Mission Control called up and said they would like the crew to dig a trench to study the soil mechanics and take a core sample. Irwin dug the trench, which Scott photographed. Then the core sample was taken from inside the crater.
Returning the Rover, they drove 650 ft (200 m) to a large boulder. Even walking short distances on the slope was time consuming so it was easier to just have the crew use the Rover to get there. The boulder was 10 ft (3 m) across. It was necessary for one crewmember to stay by the Rover, holding it to make sure it didn't slide down the hill, which was now had a 15 degrees slope. With time running out on the stop, Scott was able to confirm what Irwin had seen earlier — the rock had a greenish tinge. The color was found to come from magnesium oxide.
Back on the Rover, they travelled onwards to Spur crater, which was 320 ft (100 m) across and 66 ft (20 m) deep. Reaching the crater's rim they found small fragments, including one with a white vein. At first Irwin thought he had kicked up some green soil, but Scott found it was just caused by the visors of the helmets which were coated gold.
It was then that they saw what would become the most famous lunar sample collected during the entire Apollo program — sample #15415 or as it was dubbed by the media, the "Genesis Rock". It looked at first just like a partially crystalline rock, but the closer they looked they realised it was almost pure plagioclase, meaning it was anorthosite. It was originally thought they had found a piece of the Moon's primordial crust, but later analysis would show that the rock was only 4.1 ± 0.1 billion years old, which is younger than the Moon itself, and was formed after the Moon's crust solidified. But it was still an extremely old sample, and was from the pre-Imbrian era.
With time running out, and the walk-back constraint approaching, the geology backroom decided that they wanted the astronauts to collect as many small fragments as they could from the area. Irwin had wanted to sample a large breccia but after spending so much time on #15415, there was little time left at the site. They also took some rake samples, netting 78 fragments from the regolith. With only three minutes before they had to move on, Irwin hit a large rock with his scoop, breaking it along one of its fracture lines. The chip they collected would be the second largest rock collected on the mission.
They returned to Falcon along the same path as they came. Passing the South Cluster and Dune, Scott decided to stop and collect some samples. Joe Allen, the CapCom, warned them that they only had ten minutes to spend here. Irwin's camera jammed, forcing Scott to take all the documentation photography. Quickly working they collected a couple of samples.
On returning to the LM, Scott began another attempt at drilling holes for the heat-flow experiment. Irwin took some manual core samples from around the ALSEP site. Again like the previous day the drill continued to get stuck, refusing to go any further. Scott was able to advance a few centimeters by pulling the drill up to clear the flutes on the drill bit and then letting the drill advance only using its own weight. This process however would cause the drill bit sections to come apart, meaning that what Scott was really doing was creating a new obstruction below the surface without realizing it. When he tried to emplace the probes they only went in 3 ft (1 m). Post-flight analysis would find that the drill design was flawed, with the flutes too close together at the joint joining the sections of the stem.
A soil mechanics experiment was undertaken by digging a trench and using a penetrometer to measure the strength of the regolith. Scott began drilling another hole, this time for a deep core sample. At 2.4 meters, Scott decided to this was far enough as they were well below the depth of the heat-flow probes, the main reason for taking the core sample. Not wanting to lose time the next day returning to remove the core, he started to pull it out. He managed to get it up 20 cm but then it refused to move any further.
The last task of the day was to set up the flag of the United States. They were outside Falcon for 7 hours and 12 minutes.
Read more about this topic: Apollo 15, Lunar Surface