EVA-3
Overnight, Mission Control decided to cancel the traverse to the North Complex. Time saved not going there would be spent on pulling out the deep core sample. Although annoyed by this, Scott understood that although he was in command of the Mission, he was part of a team, and the mission scientists had decided that the core sample was more important than sampling the North Complex.
Before setting off to the ALSEP site, the crew took some customary publicity shots of them and the flag.
Back at the core sample drill both Scott and Irwin grabbed hold of the drill and tried to pull it out. Slowly but surely they managed to work it out of the ground by getting up under the drill. A few more tries and it was completely out of the ground. When they came to break the stem apart they found that a vice built into the Rover for the purpose had been installed backwards. Scott by this time was becoming more and more annoyed at the amount of time being spent on this sample and said "How many hours do you want to spend on this drill, Joe?"
Analysis of the core samples found that pebble concentration and density varied dramatically. Along the 7.9 ft (2.4 m) length of the sample, there were more than 50 distinct layers, varying in thickness from 0.2 to 8.2 inches (0.5 to 21 cm). Of particular interest was the fact that the deepest portions of the core samples were too deep for cosmic rays to penetrate, meaning that they had not been affected by recent cosmic ray activity.
The Rover TV camera was having problems. Any attempt to pan up or down would cause it to flop down, leaving it pointing uselessly at the ground and requiring an astronaut to repoint it.
After making a 16 mm film of the Rover driving for the engineers on Earth, they set off for the main target of their last EVA, Hadley Rille. On the way they stopped to photograph a rock they suspected had formed a crater nearby. Unfortunately there was no time to stop and sample it.
They arrived at a 50 ft (15 m) crater near to their original target crater, Scarp. Scott decided to stop here as it met the original objective of Scarp which was to collect debris from near the rille. After taking a panorama of the site, Scott took some samples finding them to be extremely soft. It is thought that the area around them was the youngest ever walked on by an astronaut.
Moving on they travelled to the Rille. One of the objectives of Apollo 15 was to sample exposed bedrock at its point of origin. On previous missions, the basalt collected had been thrown there by impacts. As Irwin took the site panaroma, Scott used the 500 mm telephoto lens to image the far side of the Rille, which was about 0.6 mi (1 km) across. They were looking for layering in the wall of the Rille, which could help geologists to find if the lava flows that had filled Palus Putredinis came in one go or over time.
Irwin started a radial sample. He found a rectangular rock that was too large to return to Earth. Due to the slope of the surrounding area he was able to see some bedrock below the rim of the Rille that appeared to be above them further along. They walked to a 10 ft (3 m) crater and sampled the meter sized rocks that it had thrown up.
It was meant to be time to move on again, but the geology backroom decided that the loss of another sampling station was offset by the chance of sampling true bedrock. So they were given more time. Moving down to the very edge of the Rille they sampled a large 7 ft (2 m) rock. Back at the Rover they took another rake sample and a core sample. Scott then decided to sample a vuggy, coarsely grained basalt. He decided to take the whole football shaped rock. Dubbed "Great Scott" the 21 lb (9.5 kg) sample would be the biggest returned on Apollo 15. They moved onto the last station of the Mission, Station 10. With little time left, all they could do was photograph the site at a 200 ft (60 m) crater.
Scott had one more thing to do once he returned to the LM:
- "Well, in my left hand, I have a feather; in my right hand, a hammer. And I guess one of the reasons we got here today was because of a gentleman named Galileo, a long time ago, who made a rather significant discovery about falling objects in gravity fields. And we thought where would be a better place to confirm his findings than on the Moon. And so we thought we'd try it here for you. The feather happens to be, appropriately, a falcon feather for our Falcon. And I'll drop the two of them here and, hopefully, they'll hit the ground at the same time."
And they did. Scott then drove the Rover for the last time to a point 300 ft (90 m) from the LM so that it could observe the liftoff. He placed a small Bible on the hand controller and then walked about 20 ft (6 m) to a small hollow where he placed a plaque bearing the names of the fourteen known astronauts and cosmonauts to have lost their lives (two cosmonaut deaths had not been made public at the time — Valentin Bondarenko and Grigori Nelyubov). Beside it he placed a "Fallen Astronaut" statuette.
They were outside the LM for 4 hours and 50 minutes.
Read more about this topic: Apollo 15, Lunar Surface