final lunar excursion, they were to explore North Ray crater, the largest of any of the craters any Apollo expedition had visited. After exiting Orion, the pair drove to North Ray crater. The drive was smoother than that of the previous day, as the craters were shallower and boulders were less abundant north of the immediate landing site. After passing Palmetto crater, boulders gradually became larger and more abundant as they approached North Ray in the lunar rover. Upon arriving at the rim of North Ray crater, they were away from the LM. After their arrival, the duo took photographs of the wide and deep crater. They visited a large boulder, taller than a four-story building, which became known as 'House Rock'. Samples obtained from this boulder delivered the final blow to the pre-mission volcanic hypothesis, proving it incorrect. House Rock had numerous bullet hole-like marks where micrometeoroids from space had impacted the rock. About 1hour and 22 minutes after arriving at the North Ray crater, they departed for Station 13, a large boulder field about from North Ray. On the way, they set a lunar speed record, traveling at an estimated downhill. They arrived at a high boulder, which they called "Shadow Rock". Here, they sampled permanently shadowed soil. During this time, Mattingly was preparing the CSM in anticipation of their return approximately six hours later. After three hours and six minutes, they returned to the LM, where they completed several experiments and unloaded the rover. A short distance from the LM, Duke placed a photograph of his family and an Air Force commemorative medallion on the surface. Young drove the rover to a point about east of the LM, known as the 'VIP site,' so its television camera, controlled remotely by Mission Control, could observe Apollo 16's liftoff from the Moon. They then reentered the LM after a 5-hour and 40-minute final excursion. After pressurizing the LM cabin, the crew began preparing to return to lunar orbit. Solo activities After Orion was cleared for the landing attempt, Casper maneuvered away, and Mattingly performed a burn that took his spacecraft to an orbit of in preparation for his scientific work. The SM carried a suite of scientific instruments in its SIM bay, similar to those carried on Apollo 15. Mattingly had compiled a busy schedule operating the various SIM bay instruments, one that became even busier once Houston decided