At this point in their return traverse, Scott and Irwin were relying entirely on the LRV's navigation system. They had followed their outbound traverse tracks around the western edge of Dune Crater, but left them behind as they headed due North. They would not see their original tracks again until they had passed Arbeit Crater on their left, when they could follow them back to the LM. Joe Allen briefed them on the off-loading of the lunar samples and core tubes back at the Lunar Module, and the other steps they would have to take once they got there. Their workday was far from over. Irwin would be busy performing soil mechanics experiments which occupied five detailed pages on his Cuff Check List. These were designed to determine the soil's ability to bear load and its general stability. Scott once again tackled the drilling, but the second drilling exercise to place the other heat flow sensor proved just as difficult as the first. Nevertheless he placed the second sensor, even though it was not as deep as the scientists had hoped. Scott then helped Irwin with the trenching experiment, which achieved a depth of roughly 25 cm before hitting a rock.
Joe Allen then informed the crew that the ALSEP site would become the de facto Station 8 stop, where the deep core sample was originally scheduled to be taken.
Scott was surprised at this, thinking this task had been bypassed by Houston. Nevertheless, he turned to the task of having to drill a deep core sample. Surprisingly, he succeeded in drilling down to a depth of 2.4 m after only a few minutes of effort. However, when it came time to extract the core tube, it could not be removed. Scott spent precious time trying to pull it out but the Moon held its grip on the core tube sections. Houston advised him to leave them there for the time being and another attempt would be made the following day. Meanwhile, Irwin took photographs of the various experiments at the ALSEP site. When both astronauts were back at the LM, Allen asked Scott to give the LRV a good dusting, including the LCRU, the TCU, the battery covers and the top of the TV camera.
Allen once more reminded the crew to dust off the LRV battery covers prior to opening them to let the batteries radiate to deep space. They continued with their closeout of the EVA, getting the lunar samples in the rock bags and core tubes up to the Lunar Module. Scott powered down the LCRU and opened its blankets and made sure that the TV camera was in the down position and powered off. Scott and Irwin climbed back into the Lunar Module, and re-pressurized the cabin at 149 hours and 26 minutes, Ground Elapsed Time (GET). They had set a new EVA record of 7 hours, 12 minutes and 53 seconds. The bad news was that they only had twenty-two hours left on the lunar surface, which was dictated by the limited lunar surface time of the Lunar Module. The next day's EVA would have to be shortened, and that put the hoped-for trek to the North Complex in serious doubt. The crew spent the next several hours going through the detailed closeout procedures with CapCom Gordon Fullerton. During this time, Scott and Irwin had the chance to communicate with their Command Module Pilot, Al Worden. They only had a few minutes to speak, but Scott used it to rave about the performance of the rover.
Certainly, Wernher von Braun was pleased with how well the mission was going, and gratified that the Lunar Rover had performed so well up to this point. Morea and his team were all smiles, as were the engineers and managers at Boeing and GM. Nevertheless, the LRV's thermal team kept a watchful eye on the temperature of the subsystems as Scott and Irwin finally bedded down for the last ''night'' on the Moon.
EVA-3: RECOVERING THE DEEP CORE SAMPLE AND RETURNING TO THE RILLE
CapCom Joe Allen awoke Scott and Irwin at just after 160 hours Ground Elapsed Time. Allen and Scott actually conversed in German for a minute or two, which warmed the hearts of Dr. von Braun, Dr. Kurt Debus, and many of the other original German engineers who worked on Apollo. Both astronauts had slept well and Allen updated the crew, stating that their first task was to retrieve the deep core tube, followed by the planned LRV Grand Prix photography before starting out for Station 9. They exited the Lunar Module, finished preparing the rover, then drove over to the ALSEP site to once more attempt to extract the core tube, which had a design flaw in the flutes at the core tube joints. After repeated strenuous efforts, Scott and Irwin finally succeeded in pulling the core tube from the ground, but at the
cost of a minor shoulder injury for Scott and the eventual blackening and loss of several fingernails. The frustration didn't end there. Scott managed to separate the first three sections of the core tube, but the last three sections were recalcitrant. The device at the back of the rover designed to help separate the sections had actually been manufactured backwards and thus could not properly grip the core tubes. Scott and Irwin spent an exasperating, time-consuming and precious half-hour trying to separate the sections, to no avail. Scott asked Houston if all the effort for this core tube was really worth it and Joe Allen assured him it most certainly was.
''Quite seriously, Dave and Jim,'' Allen told them, ''that's undoubtedly the deepest sample out of the Moon for perhaps as long as the Moon itself has been there.''
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