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When landed on the moon, the ladder seems to be in the shadow for each Apollo mission.

For example, on this photo, the ladder is not in the side exposed to the Sun. (the astronaut go out of the LM in the shadow of the LM).

Why did the NASA choose to land the LEM in that direction (exit (and the ladder) in the shadow of the LM)?

NASA photo AS11-40-5869; Buzz Aldrin in the moonhttps://upload.wikimedia.org/wikipedia/commons/a/a5/AldrinOnMoon.jpg

Russell McMahon
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Manu H
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    Bonus: Whenever the Luna Rover is stationary the shadows of the sun-side wheels never fall on the far-side wheels. This is by design and not an astounding coincidence. [Somebody will probably now produce a photos falsifying this :-) , but that was the aim.] – Russell McMahon Jul 08 '19 at 06:53
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    @RussellMcMahon Whaa...? Fascinating. Why was this by design, can you provide references? – KlaymenDK Jul 08 '19 at 08:47
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    Bonus two: The shadow of the LEM is projected on both Aldrin and the lunar ground, why can't we see the ground? – user721108 Jul 08 '19 at 09:21
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    @qqjkztd I think you lack some photographic background. It is not uncommon that the dynamic range of a camera make shadow dark enough to not be able to see details on it while white objects (the astronaut) light by a small reflector (here, the moon regolith) is bright enough to be seen (you can easily find reconstitution made with Lego on photographs' blogs and try to reproduce it yourself) – Manu H Jul 08 '19 at 09:27
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    @qqjkztd This image shows the original plus a lightened version. I suspect that the black shadow has been further darkened - can't have original photos when they can be improved with editing. (I may be wrong). The 'black" is a very dark blue and is not quite homogeneous, but dies not have the variability I'd expect. [I often enough lighten up photos in this manner to check for editing]. || That said, the ground is horizontal and less liable to be highly illuminated by low angle reflected light. – Russell McMahon Jul 08 '19 at 10:43
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    @KlaymenDK I'll see what I can find. The reason was that the shadow area is COLD - a wheel n sun and partly in deep shadow experiences significant differential heating which can lead to failure. That argument would seem to apply to anything shadowed - but that's what I recall I read. The mechanical cyclical load when rolling would not help. || This interesting thesis on bottom of page 7 refers to wheel/shadow issues with the Apollo 14 MET ("handcart" :-) ). That MAY be what I was recalling, but ollld memory says it applied to the Rovers. tbd. – Russell McMahon Jul 08 '19 at 11:08
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    || PhD thesis - Dynamic thermal modeling for moving objects on the Moon || p7 lower - ... During Apollo 14 the MET was used to transport instruments and equipment ... MET was designed to sustain minimal temperatures as low as 216 K. ... during surface operations one wheel fell below that threshold temperature only because it was shadowed by the other parts of the MET ... The Astronauts had to adopt to this unforeseen condition in order not to loose the MET. ... by positioning the MET [so] no shadow was casted on the wheels. – Russell McMahon Jul 08 '19 at 11:12
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    @qqjkztd: because Aldrin is subject to indirect illumination from the surface (moonlight!) while the [convex] surface itself cannot be illuminated by other points of the same surface? – Violet Giraffe Jul 08 '19 at 17:31
  • Because Stanley Kubrick forgot to take the motion of the Moon into account when he built the stage set... :) – RonJohn Jul 10 '19 at 13:07

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All the lunar landings were performed with the sun low in the sky behind the LM, between 5º and 14º above the horizon at the landing site. This provided several advantages:

  • The sun wouldn't be in the crew’s eyes during any portion of the descent (they’d start out oriented feet forward, lying on their backs looking upward, during the braking phase, and progressively pitch downward from that orientation to standing vertically looking forward during the final portion of descent)
  • The terrain would cast sharp shadows, which made it easier to see the shape of the surface
  • The shadow of the LM itself would be cast on the ground ahead in the final moments of descent, which would help the commander judge the LM's altitude.

The descent ladder, being on the front leg of the ship, was therefore always in shadow after touchdown.

Russell Borogove
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  • I think it also helped the astronauts climb down the ladder more easily, since the sun would not shine in their eyes. That's just a minor advantage compared to your reasoning though :) – John Hamilton Jul 08 '19 at 07:18
  • Would the ladder in the sun have been much hotter to the point it would be an issue somehow? – jcaron Jul 08 '19 at 07:32
  • @jcaron I'd guess not because the astronauts would have to handle and step on other things that had been in the sun. But that's just a guess. – David Richerby Jul 08 '19 at 08:40
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    The third bullet point there is the key one - pilots would rather use shadows to judge altitude rather than blindly trusting doppler radar to indicate the descent rate and altitude of the LM. From what I've read, no landing was ever performed under autonomous control. Lovell intended to, but of course that never happened. It make sense for the ladder to be under the only windows on the ascent stage - ergo the ladder is on the dark side. –  Jul 08 '19 at 10:42
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    @Snow: That was my thinking exactly, from KSP landings. I always use the shadow. – dotancohen Jul 08 '19 at 11:22
  • @JohnHamilton: Technically, it's oriented in a way that the astronauts look directly at the sun when using the ladder (if the LM were not blocking it). If you turn the LM 180°, they have their backs to the sun so unless reflection off the LM was a reasonable issue, I don't think visibility while climbing the ladder factors into it. (It may be an issue when turning the LM 90° or 270° though) – Flater Jul 08 '19 at 11:41
  • Now I'm wandering why they put the door (and the ladder) on the front side of the LM. – Manu H Jul 08 '19 at 12:43
  • @ManuH the placement of the windows and the door beneath them makes that side of the LM "the front". –  Jul 08 '19 at 12:55
  • @Snow I meant why put the door and the windows on the same face? – Manu H Jul 08 '19 at 12:58
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    The cabin was very small, and the astronauts stood just behind the window to improve their downward view. There was nowhere else for the exit hatch to be placed. – Russell Borogove Jul 08 '19 at 13:00
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    And it makes sense for the ladder (and any crew members using the ladder) to be visible from inside the lander. –  Jul 08 '19 at 13:03
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    A useful document may be the Apollo Descent Guidance – CGCampbell Jul 08 '19 at 13:49
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    The low sun makes a lot of sense from the point of view of revealing surface relief during the descent. This meant the landing had to be made in the lunar morning or evening. Morning was always chosen because, in the event of any mishap, that gave them the maximum amount of daylight to resolve the issue. – Oscar Bravo Jul 08 '19 at 13:50
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    @CGCampbell, it still makes sense to want to maximize the amount of daylight in case of a problem, even when the period from dawn to dusk lasts 348 hours. I'd rather have 324 hours to work on something if I'm stranded on another world, than just 24 hours. (Or rather, I'd prefer my useful working period to be determined by O2, and not daylight.) – Ghedipunk Jul 08 '19 at 17:42
  • @CGCampbell Eh? didn't get the joke... Landings were always scheduled for local mid-morning (the landing sites are all a bit to the right of the terminator as seen from the Northern Hemisphere of Earth). So the site was in daylight for around 10-12 (Earth) days after landing. – Oscar Bravo Jul 09 '19 at 14:54