Long

For their pioneering journey to the surface of the Moon, Armstrong and Aldrin made only a single foray onto the surface before attempting to get some sleep in the uncomfortable confines of the LM. The rendezvous and docking next day were therefore carried out by a crew that were hopefully rested to some extent. As each successive flight became more ambitious and the LM was trusted with a crew for longer periods, the rendezvous and docking day grew increasingly packed. At first, 4-hour, and eventually nearly 6-hour moonwalks were shoe-horned into the day. Then by the time 2 hours had been added for getting into a suit, plus time to prepare for lift-off, meals and the rendezvous itself, the day became especially long and intense.

For mission control, the excessive length of the crew's day became an issue when Scott and Irwin returned from their highly successful stay at Hadley Base near the eastern rim of the mighty Imbrium Basin. This was one of the very few times when the crew in an Apollo spacecraft and the people in mission control managed to get out of sync with one another, probably because managers in the mission operations control room (MOCR) were worried about their perception of the crew's tiredness in the wake of the Soyuz 11 tragedy only a month before the flight of Apollo 15.

With a successful docking completed, Worden pressurised the tunnel between Endeavour and Falcon, then removed the forward hatch and docking equipment to allow him to inspect the 12 docking latches. Meanwhile, Irwin copied down a P30 PAD from mission control for a burn that would eventually take the jettisoned LM out of lunar orbit to crash on the Moon.

Once the LM's overhead hatch had been removed, Worden sent the vacuum cleaner through the tunnel to help the LM crew to deal with the dust on their space suits. Scott and Irwin then began transferring all required items to the CSM, following a list in the flight plan that indicated 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, which had been mounted on top of one of the PLSS during the moonwalks, would be needed by Worden during the coast home to Earth, for his spacewalk to the SIM bay to retrieve film magazines from the cameras there. It contained a high-pressure oxygen bottle that provided emergency air to a suited crewman in case a leak opened up in his suit.

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. Irwin was the last to leave Falcon's cabin, closing its overhead hatch behind him. Once everyone was inside the command module, the forward hatch was installed and a check made 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 got to put some LCG plugs in our suits and it's going to take probably about 10 or 15 minutes to get all that done.''

This communication was the start of a confused episode which involved the checking of suit and hatch integrity. Scott's boss, Deke Slayton, came on to the communications loop, betraying management's sudden concern at the crew's deviation from the flight plan. Scott's problem with the plugs in his liquid cooled garment (LCG) was 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 when 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 check and see how it works.''

Scott's subsequent successful suit integrity check put the crew slightly behind their timeline, but Slayton's intervention displayed the start of management's jitteriness 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.

"Copy, 2.0,'' confirmed Bob Parker at the Capcom console.

The crew could use the tunnel vent valve to bleed air out of the tunnel between the two spacecraft. Had it been completely evacuated, this pressure reading, given in pounds per square inch (psi), would show between 5 and 6 psi, essentially the absolute cabin pressure. Their procedures called for the reading to be at least 3 psi prior to jettison. The fact that it was only 2 psi when it had earlier read 3 psi strongly suggested that air was entering the tunnel through either the LM hatch or the CM hatch. Compounding the jitters in the MOCR was the knowledge that, on the way to the Moon, Scott had misinterpreted the settings of the valve that both vented the tunnel and allowed the crew to monitor the pressure.

"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.'' It was possible that Irwin had inadvertently left it open even a little when he left the LM. Scott tried venting the tunnel further. "It's up to about 2.3 now,'' he informed them.

The flight controllers in the MOCR discussed the readings with Scott a bit longer, before coming to 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 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 light of this confusion, 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 sever the LM. If the crew were to remove the hatch to inspect its seal, then 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; they 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 2 hours before the next jettison attempt, mission control wanted to use the time to test the hatch seal thoroughly. Since the crew had reduced the pressure in the tunnel low enough to give a reading of 3.5 psi, Parker asked them to hold it there throughout their next far-side pass, and see if 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 had been l8 hours since Scott and Irwin suited up for their gruelling work on the lunar surface. They had not eaten for 8 hours and had been sealed in their suits, with helmets and gloves, since before launch from the Moon 6% hours earlier. The problems with their suit and hatch integrity were compounding their tiredness. They were hungry, and 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. The MOCR had asked for the tunnel pressure to be held around the far side but Scott now had the impression that he was to leave it venting. Then the MOCR worried whether the fully suited crew should remove their helmets and gloves to allow them to eat. Breaking open their suits would necessitate another check of their pressure integrity before LM jettison. 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; we can take another look at that tunnel.'' Another suit integrity check would pump more air into the cabin, affecting the reading on their pressure gauge.

Once the crew passed around 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 this time, Glynn Lunney, the flight director on this shift, was becoming somewhat 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 while. I think we garbled something there.''

The integrity check was successful and the crew proceeded with the jettison. It was timed to occur when the stack, which was holding its attitude constant with respect to the stars, had the LM facing away from the Moon, which only happened once per orbit. A guarded push-button sent a signal to the pyrotechnic circuits, detonating an explosive cord around the tunnel which cut its circumference cleanly.

''And, it's away clean, Houston,'' said Worden as the remaining air within the tunnel gave the LM a mild push away from the CSM, along with its tunnel and the disposed-of items inside.

''Roger, copy,'' empathised Parker. ''Hope you let her go gently. She was a nice one.'' ''Oh, she was at that,'' agreed Worden.

But the trials of Apollo 15's rendezvous day were not over. The procedures called on the crew to make an RCS burn to put some more distance between them and the LM, details of which had been entered into the computer earlier. Scott was then to use P41 to execute this burn.

''Houston, 15,'' called Scott. ''Question on the separation manoeuvre. Do you want us to burn residuals in P41, or just make 1-foot-per-second burn?'' ''Roger, Dave,'' replied Parker. ''Burn them in P41, please.'' Scott looked at the DSKY and was not happy with what it was telling them. The size of the burn along the three orthogonal axes was displayed in front of him, and one of them was telling him that the burn would take them forwards, towards the very thing they were trying to avoid. Additionally, the lateness of the whole jettison procedure meant that it was difficult to keep a check on the LM. The discarded spacecraft was nearly in line of sight to the Sun.

''Houston, P41 says seven-tenths forward,'' pointed out Scott. ''Yes, seven-tenths forward, seven-tenths up.''

''Roger, Dave,'' confirmed Parker.

''And forward takes us right back to the LM,'' reminded Scott. ''Stand by, Dave,'' said Parker, the MOCR's only point of contact with the crew. ''We're looking into that, of course.''

''Okay. We got about a minute and 15 seconds or so.'' ''Roger.''

Having pointed out the inconsistency to the MOCR, Scott continued with preparations for the burn, trusting that they would know what was best. After a pause, he announced, ''Average g is on.'' The computer had begun to measure acceleration and was about to begin the burn. ''Ah, hold the burn, Dave.'' ''Okay, we'll hold the burn,'' said Scott.

The confusion between the MOCR and the spacecraft continued as each party began using differing terminology to describe where the LM was sited with respect to the CSM. Terms such as 'in front of, 'dead ahead' and 'trailing' can have multiple meanings in the three-dimensional regime of space. Therefore when mission control suggested that Scott should simply point towards the LM and fire the thrusters to move away from it, Parker compounded the confusion by saying, ''We need you behind him and then a firing of retrograde.'' Unfortunately, the word 'retrograde' has a precise meaning in celestial mechanics: opposite the orbital motion. Since they were leading the LM around the Moon at this point, the instruction's strict meaning required that they manoeuvre the CSM to be trailing it, then slow down their orbital motion slightly to increase the separation, which was not what was intended. The MOCR eventually tightened up its language.

''Okay, Dave,'' called Parker. ''How about 2-foot-per-second posigrade, as long as you're in front of him. Understand?''

''Okay; so that'll be a minus-x delta-v for 2 feet per second at our present attitude, right?'' checked Scott.

"Roger. That affirm, Dave."

"Okay. We're all in the same frequency. We'll do that."

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