Head wrote a memo to NASA managers identifying five areas of scientific interest along Hadley Rille. One of those, which turned out to be the eventual landing site, was particularly interesting from a scientific perspective, but would also require a landing angle far steeper than any that had been attempted previously. Scott, who was mission commander, agreed that the mission should attempt to land where the best science could be done.

“So Dave jumps in the simulator to try this steep landing,” Head recalled. “He tries it; says we’re good to go, and that’s where we ended up going.”

Once on the surface, the real scientific work began. Scott and Irwin would perform over 19 hours of extravehicular activities (EVAs), twice the EVA time logged on previous missions. The solar-powered Lunar Roving Vehicle, a remarkable feat of engineering in its own right, enabled the astronauts to traverse a previously unthinkable 17 miles across the lunar surface. The mission returned to Earth with 170 pounds of lunar material. Apollo 11, by contrast, brought home a little over 47 pounds.

Head was among the scientists whose job it was to teach two test pilots how to do geology on another world. Head said that Scott in particular was a natural geologist and became engrossed in the subject.   

“One of the best compliments I ever had,” Head said, “was from Dave’s wife at the time, who took me aside and said, ‘Jim, you've absolutely ruined Dave. I had to take a night school course in geology just to be able to talk to him at dinner.’”

The training paid big dividends. In addition to the green volcanic glass, Scott and Irwin gathered one of the big stars in NASA’s lunar sample collection, known as the “genesis rock.” One of the reasons Head and other scientists wanted to land in the lunar highlands was the potential for finding samples of the original deep lunar crust. When Scott spotted the ancient chunk an anorthosite sitting on the surface, he recognized it instantly, enthusiastically radioing to mission control: “Guess what we just found! I think we found what we came for.”

Later in the mission, another important specimen caught Scott’s eye: a basalt that was full of holes, or vesicles, left behind by gas escaping from rising lava. EVA time was quickly drawing to a close and mission managers were ever wary of staying out too long. But Scott knew he had to have that rock: He and Head had discussed the importance of vesicular basalts in understanding what gases were present in the lunar interior. Rather than ask for a time extension, Scott simply jumped off the rover and grabbed the rock, while telling Mission Control that he needed to adjust his seatbelt — an action Scott described as “the commander’s prerogative.” The sample would come to be known in the scientific community as the “seatbelt basalt,” another star of NASA’s collection. 

Head and his fellow Apollo scientists were in mission control in Houston during the mission and were able to communicate with the crew. But they weren’t there to micromanage, only to provide expertise when needed.

 “The astronauts did this work on their own,” Head said. “It wasn’t like we were saying, ‘send us a picture of the rock and we’ll tell you if it’s good.’ The mantra was, ‘train them, trust them and turn them loose.’”

Head described the science room in the Mission Operations Center as an incredibly intense and busy place — so busy, in fact, that Head missed it when Scott dropped Head’s name in communications with Mission Control, referring to the valley containing Hadley Rille as “Head Valley.”

“Dave said something like, ‘I’m looking down Head Valley,’ and someone poked me and said, ‘Hey, did you hear that?’” Head recalls. “I was planning the next traverse; I completely missed it. But Dave did that for several of the scientists who worked closely with him and it was really thoughtful.”

Head and Scott remain close friends and collaborators to this day. Scott has worked with Brown students over the years as a visiting professor, and the University awarded him an honorary degree in 2011.  Most recently, on July 31, 2021, Head joined Scott at an event at the San Diego Air and Space Museum to commemorate the mission’s 50th anniversary.

The pair have worked with researchers at the Massachusetts Institute of Technology and elsewhere to show how Apollo 15 could serve as a template for future missions to the Moon and Mars. They refer to the close collaboration between scientists and engineers — the work they say made Apollo 15 possible — as “science-engineering synergism.”

“The geologists and scientists worked together with engineers and managers to optimize the program,” Scott said during a 2013 visit to Brown. “It’s the kind of thing Jim and I are trying to emphasize ... so that the science community understands the engineering and the engineers understand the science. Working together, we get better science and better engineering.”