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I remembered that I once read an article about the design of the controller, but now I can't google it out. In short, it talked about the control panel of one Moon landing mission was full of technical number, and not a good design for human. When landing on the surface on the Moon, those numbers went wildly too much that they could not rely on them. In the end, they had to use their own senses to land. In an interview, they said that this would almost kill them.

Does this ever happen?

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closed as unclear what you're asking by Organic Marble, Brian Tompsett - 汤莱恩, Nathan Tuggy, Fred, Gwen Nov 8 '15 at 0:25

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    $\begingroup$ You're probably referring to the Apollo 11 lunar landing but it's really hard to tell. Did you search our Q&A for threads discussing apollo-program? Judging distance on the Moon is incredibly hard or even impossible for the most part of final approach since there's no atmospheric diffraction and distant features appear just as sharp to the eye as close by ones. Only way to judge proximity to the ground without an altimeter would be as the thrusters start kicking up some surface dust around for the final 10 meters or so. $\endgroup$ – TildalWave Nov 7 '15 at 14:38
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    $\begingroup$ To add to TidalWave's comment, as I recall, Buzz Aldrin didn't turn off one of the Apollo 11 lander's devices (I think it was one of the radars) which then caused a memory overflow in the on-board computer. $\endgroup$ – Fred Nov 7 '15 at 14:56
  • $\begingroup$ Sorry, I'm new to everything here (including the knowledge), but if I recall correctly, the article is about the control panel, a design fault, not a technical error. $\endgroup$ – Ooker Nov 7 '15 at 14:59
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    $\begingroup$ What is your actual question? This is probably going to get closed if you don't edit it to make it more specific. $\endgroup$ – Organic Marble Nov 7 '15 at 15:18
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    $\begingroup$ This (doneyles.com/LM/Tales.html) is a great article describing at a very detailed level exactly what the crew saw on the displays and how they used the information. I sorta feel that any judgement on whether this is good or bad UI is opinion based. $\endgroup$ – Organic Marble Nov 10 '15 at 17:22
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The digital computer on the Apollo spacecraft (virtually identical units in the CM and the LM) used a keypad input and numeric display output which was not very intuitive to use, although the intensive training the crews underwent probably helped it feel relatively natural. In theory, the crew could designate a landing point, and the computer could use the ship's radar to watch the surface and land in a completely automatic mode.

However, the LM also had joystick controls and windows, and in practice, for each of the Apollo landings, at around 500 feet altitude the commander switched the computer into a semi-automatic mode called P66 attitude hold. In this mode the commander could adjust the rate of descent by 1 foot-per-second at a time, and adjust the attitude (orientation) of the lander via joystick -- turning it slightly toward any direction would cause it to accelerate in that direction.

The LM didn't have a good view directly downward, however, so P66 required coordination between the commander (looking out the window and flying the ship) and the LM pilot (looking at the computer displays). If you read the transcripts of Apollo 11 around the 04 06 43 11 timestamp, you'll see the LMP (Aldrin) calling out altitude and speed figures, while Armstrong is steering around, looking for a good flat spot to put down.

It was absolutely a challenging and scary process, as evidenced by Armstrong's heart rate at the time, but the crews had practiced it, and managed 6 out of 6 safe landings over the course of the Apollo program.

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  • $\begingroup$ I seem to remember that Armstrong's maximal heart rate was 156. Which is impressive given how challenging and scary the process was...! $\endgroup$ – user2705196 Oct 28 '17 at 22:45
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It seems pretty clear from this photo that everything was visible. There were definitely some difficult aspects of the journey.

enter image description here

The truth is, the LEM was largely computer controlled. Humans helped in the landing spot selection, and could adjust the aimpoint, but that was really all they were doing. There were some adjustments made by virtue of some written numbers that might have been illegible in flight, but they could get used to the numbers in training and adjust, even if they couldn't read the number. Essentially the windows had numbers in them to program into the computer to adjust the landing site.

You might read "Digital Apollo: Human and Machine in Spaceflight", which is where I learned how this works.

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    $\begingroup$ While in theory the LM could land automatically with just aimpoint designation coming from humans, in fact the final part of every lunar landing was done in the semi-automatic P66 Attitude Hold mode, where the commander had control of rate-of-descent and the ship's attitude. The computer held the attitude and rate stable between inputs, but the commander was certainly flying it. My source here is also Digital Apollo, pp. 207, 238, 241, etc. $\endgroup$ – Russell Borogove Nov 7 '15 at 17:51

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