Despite the differences between the landings, all had one thing in common: the commander did not allow the computer to land in automatic mode and instead operated the attitude ''manually'' in P66 (table 10.1). David Scott proved most reflexive about
P66/ATT HOLD takeover altitude for six flights (compiled by the author from Apollo mission transcripts).
Flight P66 height (ft.)
his use of the automation, perhaps because of his education at MIT and his comfort with automatic controls. He described a single, integrated system: ''we—as a group flying the machine, the PNGS, AGS, Irwin, and me, we were all flying that thing.'' This ''collective entity'' was organized around the pilot to make it ''safer and more efficient if there was a focal point. And I was the focal point. Jim fed things into my ears. The Moon fed things into my eyes, and I could feel the machine operating.'' Irwin read Scott as much information as possible so the commander could keep his eyes focused on the outside. ''I wasn't going to do any talking.'' Scott said, ''I was doing the flying. I was going to look outside the window, and he [Irwin] was going to tell me what was going on inside.''99
As commonly told in newspapers, astronaut memoirs, and popular books, stories of Apollo landings usually recount how ''the computer was taking us into a bad area,'' necessitating the commander's manual override of the mindless automation. Such accounts fail to acknowledge the heavily mediated nature of the ''manual'' intervention, which was really semiautomatic. Software created the very semblance of ''manual'' control of a complex beast like the LM and maintained a variety of feedback loops to make it flyable. Moreover, until a relatively low altitude of a few hundred feet, the commander could use the LPD to redesignate to a different area. Only below that level would ''manual'' takeover be required. Consider the comments of each of the commanders on their interventions:
Neil Armstrong, Apollo 11:
''The LPD was pointing... just short (and slightly north) a large rocky crater surrounded with the large boulder field with very large rocks covering a high percentage of the surface____Continuing to monitor the LPD, it became obvious that I could not stop short enough to find a safe landing area.''100
Pete Conrad, Apollo 12:
''I didn't like the size of the area short, where we had normally been trying to land, and I looked for a more suitable place.''101
Alan Shepard, Apollo 14:
''Using thirty years of pilot skills, [he] threaded a needle between the hills and ridges along their approach path and dropped his ship down into a narrow valley, craters and boulders everywhere.''102
David Scott, Apollo 15:
''I knew I could land the machine if it would stay upright and the engine kept burning. And all the other things I had was icing on the cake.''103 ''I was very surprised that the general terrain was as smooth and flat as it was.104
John Young, Apollo 16:
''It was working so well I was tempted to let it (the PNGS) do the thing all by itself; but the trouble is, we got down low and I could see that we were going to land in that pothole down there.''105
Gene Cernan, Apollo 17:
''The reason I took over is that I wanted to slow our forward velocity down. I did not want to go any farther west, because there were more blocks and more hummocky terrain.''106
''Finding a place to land wasn't as easy as anticipated. A boulder the size of a house—that wasn't supposed to be there—loomed right in front of me... I scanned for an empty space in a parking lot of boulders as big as automobiles.''107
Each commander describes human control of the mission in the last few moments. Nearly all mention that the LPD was carrying the LM into a rocky, cratered area. Of course, given the rocky nature of the moon, that's not too surprising. But it did happen on every single flight. Fortunately, according to the commanders, on every single flight there was a smooth area suitable for landing a short distance away.
The exception in the comments above are from David Scott, who explained his manual control as preparation for reacting quickly in case something went wrong. ''If I'm in the loop mentally I can respond more quickly than if I have to watch an automatic system and take over and then get my mind into the loop. So I was more comfortable in flying a manual descent than an automatic descent ...my mental computer is already running at full speed.'' As he indicated in the quote at the beginning of this chapter, this apparent safety might have been an illusion—a computer problem would likely have affected the manual control as much as the automatic. But a hand on the stick gave the commander a feeling of confidence and control. Scott admitted that ''mainly, it's a challenge'' to do the landing manually, and being in the loop for emergency response was secondary. Scott was thrilled by the difficulty of the landing. For him, and for the other pilots, it represented the ultimate in flight. ''I don't care what anybody says, that's damn hard. I mean, that takes real aviation. That's flying!''
The astronauts' own comments tend to emphasize visual recognition of the landing spot as the unique human capability, demanding hands-on piloting to land safely. ''You could fly automatically, but it's not likely,'' Armstrong told the SETP, noting, ''one reason is that the auto system doesn't know how to pick an area and it can't change its mind.''108 Armstrong conflated two issues in a way that was common in dis cussions of the landings: the perception and judgment required for selecting a landing site and manual versus automatic control of the LM.
NASA management, and at least some of the astronauts, acknowledged this conflation. Comparisons of the Apollo 11 and 12 landings raised the question of why, once the landing spot had been chosen, the computer should not gently land the LM, given that an instrument landing might be required anyway. Indeed, after Apollo 12 the IL team added software to make an automatic touchdown easier for the commander. Now anywhere below 500 feet the commander could enter could enter ''P66 Auto'' mode (velocity-nulling guidance), in which the computer would bring the LM to a gentle stop, hover, and descend at a constant rate. P66 Auto could land a LM blind, through a dust cloud like the one Conrad had encountered.109 The feature was included on every flight from Apollo 13 to 17. It was never used.
Even P66 Auto did not represent the limit of the computer's capability. Astronaut John Young suggested an additional feature. In P66 Auto mode, the astronaut could ''mark,'' or designate a landing spot as it moved past a particular point across the LPD marker on his window. P66 Auto would then fly the LM to that spot, null the velocities, and land. Young's suggestion (which became known as ''P66 LPD'') would allow the commander to request specific horizontal velocities by jogging his control stick, much as he jogged the stick to move the LPD point around. A left deflection of the stick, for example, would increment the horizontal velocity two feet per second to the left, and a right deflection could cancel it out. Similar motions could move forward and backwards.110 Don Eyles implemented this mode in simulations, demonstrating precise landings, but it was never included in an Apollo flight.111 Given more time, and perhaps more flights, the landings would likely have evolved further computer control, decreasing pilots' workload and the attendant risk during the final descent.
None of this is to say that the astronauts, their perceptions, judgments, or flying skills were irrelevant to the landings. Quite the contrary. The sociotechnical system, including the engineers, flight controllers, and programmers on the ground, as well as pieces of machinery, was impressive, precise, even wondrous, achieving a successful landing on all six attempts. But it was not perfect. Programs alarmed, guidance overshot, boulders appeared, people misspoke, and buttons failed. In each case, human abilities intervened in unplanned ways, made decisions, and landed the spacecraft on the moon.
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