With the docking successfully completed, Worden pressurised the tunnel between Endeavour and Falcon, then removed the forward hatch and docking equipment to inspect the 12 docking latches. Meanwhile, Irwin copied down a P30 PAD from mission control for a burn that would eventually Lake the jettisoned LM out of lunar orbit to crash on the Moon.
Once the LM’s overhead hatch had been opened, Worden sent the vacuum cleaner through the tunnel to help the LM crew to deal with the dust on their spacesuits. Scott and Irwin then began to transfer all required items to the CSM, with a list in the flight plan indicating where each item should be stored. The list included film magazines, rock and soil samples, food, used urine and faecal bags and one of the oxygen purge system (OPS) packages from the surface. The OPS. w’hich had been mounted on top of one of the PLSSs during the moonw’alks. w’ould be needed by Worden during the coast home to Earth, for his spacewalk to retrieve film magazines from the cameras in the SIM bay. It contained high-pressure oxygen bottles that would provide emergency air to a suited crewman in case of a problem with their primary umbilical air supply.
Items not required by Endeavour for the remainder of its mission, such as used lithium hydroxide canisters, a second OPS and the now-useless docking probe and drogue, were left in the LM to be jettisoned with it. In the light of the Soyuz 11 incident, this jettison was to occur with the crew fully suited up. As Irwin w:as the last to leave Falcon’s cabin, he closed its overhead hatch behind him. Once everyone was inside the command module, the forward hatch was installed and the cabin checked for leaks. At this point. Scott had to deal with a slight pressure leak in his suit. “Okay, we are going to be a few minutes here. We’ve got to pul some LCG plugs in our suits and it’s going to take probably about 10 or 15 minutes to gel all that done.”
This communication was the start of a confused episode which involved checks of the suit and hatch for pressure integrity. Scott’s boss, Deke Slayton, came on to the communications loop, betraying management’s concern at the crew’s deviation from the flight plan. Scott’s use of the plugs in his liquid cooled garment (LCG) w:as a minor remedy for a leak that was probably brought on by the wear and tear from the tenacious and abrasive lunar dust.
“Hey, one quick question. How come you guys need plugs for those suits?’’ asked Slayton.
“Well, because, apparently, the LCG connection on the inside won’t hold an air seal,’’ replied Scott. “So we’re getting them taken care of with these extra little blue plugs we got that are airtight on the inside.”
“Roger. We thought those plugs only were required w’hen the LCG was not on. We’re trying to crack that one for you down here, Dave. There’s something screwy here.’’
“Okay. Well, we’ll put these plugs in and run another pressure integrity cheek and see how it works.’’
Scott’s subsequent successful suit integrity cheek pul the crew slightly behind their timeline, but Slayton’s intervention displayed the start of jitteriness in mission control about the crew and their tiredness when a slightly abnormal situation arose. Then, with only a few minutes to go before LM jettison, another pressure integrity problem became evident when Worden reported the pressure difference between the cabin and the tunnel. “LM/CM dcha-P is 2.5… 2.0, excuse me.”
“Copy, 2.0,” confirmed Bob Parker at the Capcom console.
The crew had used the tunnel vent valve to bleed air out into space from between the two spacecraft. Had it been completely evacuated, this pressure reading, given in pounds per square inch (psi), would show between five and six psi because it indicated the pressure difference across the forward hatch. With a good vacuum in the tunnel, the reading would be essentially the absolute cabin pressure. Their procedures called for the reading to be at least three psi prior to jettison. The fact that it was only two psi, having earlier read three psi, strongly suggested that air was entering the tunnel through the hatch of one or other spacecraft. Compounding the jitters in the MOCR was the knowledge that, on the way to the Moon, there had been confusion between Scott and the MOCR about the settings of this valve, which could either vent the tunnel or allow the crew- to monitor the pressure but not do both.
“Okay, the LM/CM delta-P doesn’t look exactly right to us. What do you think?” asked Scott.
“We’d like to get another pound [per square inch of pressure] out of there.” replied Parker. “We’re showing about 3.5 in there.” But mission control were not reading this directly. They had deduced this figure by subtracting the reading they had been given from the measured cabin pressure (5.5-2.0 = 3.5).
“Okay.” said Scott, as he and his crew looked for answers. “We had a suspicion that possibly the LM overhead dump valve was open, and it might be.” That is, it was possible Irwin had inadvertently left it open a little when he left the LM. Scott tried venting the tunnel further. "It’s up to about 2.3 now,” he reported.
The flight controllers in the MOCR discussed the readings with Scott a bit longer, before reaching a conclusion that was an extreme rarity in the history of flight control a mistaken conclusion. Parker radioed up. “Dave, we think that the increase in the cabin pressure during the suit integrity check could have raised it from your side.” However, adding more air to the cabin by inflating the suits for Scott’s pressure test would have had the opposite effect, increasing the pressure difference across the hatch.
Then Parker let slip about how the ground and the spacecraft had got out of sync with each other. "Stand by. Dave; confusion reigns down here.” In the light of this, mission control decided to hold off on the jettison, back out of the situation they were in, and have the crew disarm the pyrotechnic devices that were about to cut loose the LM. If the crew’ were to remove the hatch to inspect its seal, an accidental detonation of the armed LM jettison explosives would be catastrophic.
Scott and his crew brought the tunnel back up to the same pressure as the cabin, then removed the hatch but found nothing untoward. In any case, it was perfectly possible that contamination to the seal, perhaps from lunar dust, could have been blown off as the hatch was removed. Now that they had an extra two hours before the next jettison attempt, because it had to occur at a specific point in the orbit, mission control decided to use the Lime to test the hatch seal thoroughly. The crew reduced the pressure in the tunnel low enough to give a reading of 3.5 psi and Parker asked them to hold it there throughout their next far-side pass to see whether it had changed when they reappeared 45 minutes later. Scott and his crew were thinking about food and wanted to take their helmets and gloves off to eat: "I guess in that case, we’ll probably break the suits down and then run another suit check before we see you around the corner.”
“Okay, we’ll buy that," replied Parker.
“It’s about time for dinner.’’ said Scott.
“I knew there was a reason.”
By this time, it was 18 hours since Scott and Irwin had suited up for their gruelling final day on the lunar surface. They had not eaten for eight hours, and had been fully suited for much of the time since before launch from the Moon 6 lA hours earlier. The problems with their suit and hatch integrity were compounding their tiredness and they were going to be a further two hours behind. They were keen to get settled down to a much-needed meal break.
“Okay, we’re about 3.2 [psi] now on the delta-P,” reported Scott. “We’ll leave LM [meaning tunnel] in Vent.”
“Roger.” replied Parker. “I understand; 3.2 and still venting.”
The confusion was being compounded. Mission control had asked for the tunnel pressure to be held around the far side, but SeoiL had understood that he was to leave it venting. Then the managers worried whether the crew’ should remove their helmets and gloves in order to eat. Breaking open their suits w’ould necessitate another check of their pressure integrity before LM jettison. Despite having earlier concurred with the request from the crew to do precisely this, the suit integrity check would pump air into the cabin and affect the reading on their pressure gauge, so Parker notified them of a compromise: "You are permitted to break the suits down, but do not do the suit integrity check until you come back around the other side; wfe can Lake another look at that tunnel.”
Once the crew’ reappeared from behind the Moon, Parker quizzed them. “How’ did the hatch integrity check go?’’
‘"Well, we’ve just had it in Tunnel Vent all the way around the back side as I think you suggested," replied Scott.
“Did you have a look at holding it in delta-P to see how it was holding on that?’’ queried Parker.
“No, we just left it in Tunnel Vent all the way around the back side,” reported Scott. “That’s what we’d thought you’d said to do. We can check it now.”
By now’, Glynn Lunney. the flight director on this shift, w’as becoming frustrated at the difficulty his team were having in getting this crew put to bed. Parker called up, “15, why don’t you bring it up to 3.5. and let us watch it for a w’hile. I think w’e garbled something there.’’ Lvcryone was keen that they jettison the LM only when the seal on the forward hatch w’as good.