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Pictures of NASA spacesuits like the ones below of Neil Armstrong’s Apollo suit (from the Smithsonian) and Gemini suit usually show the right wrist connection red and the left blue.

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Color coding for marine, aviation and spacecraft navigation lights is always green for right (starboard) and red for left (port). It certainly helps make sense out of confusion in the marine world. Faced with a tangle of lines with colored tracers, telling port from starboard is reflexive. Same would apply to donning suit gloves in an emergency.

Is there a reason this convention was not followed for spacesuits? In the beginning, all astronauts were pilots and would have been ingrained with the red/green standard.

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Marine

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Red and green navigation lights on an F-22 Raptor

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Red and green bottom navigation lights on SpaceX Dragon

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    $\begingroup$ Because EVA suit glove connection fittings are not marine, aviation, or spacecraft? Apples, oranges. $\endgroup$ Jan 8 at 21:19
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    $\begingroup$ ... The other thing that could be noted is in the US red is associated with right winged politics (Republicans) & blue is associated with left winged politics (Democrats), whereas in other countries it's the other way around: red is left wing & blue is right wing. The wrist connector colors on NASA suits seem to match US political colors. It would be interesting to know whether that was intentional or not. $\endgroup$
    – Fred
    Jan 8 at 23:16
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    $\begingroup$ @Fred, that association is much newer than the Mercury/Gemini/Apollo missions -- it dates to the 2000 presidential election. In the 1960s, red would be associated with communist (and by extension, left-wing) politics. $\endgroup$
    – Mark
    Jan 8 at 23:30
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    $\begingroup$ ... or it could just be that the "American colors" are red, white, and blue. The suit is white, and the other fittings are red and blue for a sufficiently patriotic look $\endgroup$
    – Dragongeek
    Jan 9 at 13:55
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    $\begingroup$ This anecdotal bit is not very 'aerospace' but it worked for me. I had a set of high performance alpine skis that I needed to set up the bindings differently differently between right and left. There were colored markers in a prominent location and I associated "Red = Right" $\endgroup$
    – BradV
    Jan 9 at 18:49

3 Answers 3

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The wrist fittings' colors matched those of the gloves: the right one was red, the left one was blue. The colors only had to be distinguishable from each other and from the main color of the suit and gloves. No correspondence to any other meaning of colors was needed, although the alliterative "Red = Right" is plausible: that's also used for stereo audio connectors (red right, black or white left).

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Not an answer, purely speculative:

but a series of notes i came across that might be of use:

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Bad picture of Gas inlet and Gas outlet connectors to the suit, circa Apollo 11.

Lunar Outfitters: Making the Apollo Space Suit (Bill Ayrey, 2020; ISBN: 9780813066578) (I do not have access to this book but given the details, it may well have the answer within that the OP is looking for)

Connector color code:

LSS ( life support system ) connectors with the inlet being anodized blue and outlet being anodized red).

ILC Space Suits & Related Products, The Path Leading To Space

Gemini:

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suit was worn by astronaut Deke Slayton during early training and development testing, prior to the final decision being made by NASA as to which suit would be used during the Gemini missions

Red-right, Left-blue already established here circa 1963. With only two major outlets, Out in Red on the Right, and In in Blue on the Left, which matches the wrist colors at this point. Perhaps this was the point at which it made sense that the L/R match the connectors. As more connectors were added to later suits this may have got lost, with the priority being Upper/Lower (see first graphic) instead of Left/Right, until Apollo 17 suit changes.

Whats interesting is that the Outlet colored Red, has the Wrist colored Red closest to it - under High-G or high pressure situations, it is advantageous to have the connector closest to that sides hand; likewise Blue Inlet has the Blue wrist closest. Perhaps if they had changed the internal design of the pressure suit so that the Blue Inlet was on the Right, and the Red on the left, then this would have fitted better visually. Perhaps the design of the Gemini LSS had the Outlet-to-the-suit connection on the right, and the Inlet on the left, therefore dictating the Inlet-Outlet arrangement on the pressure suit.

During development, the suit or parts of it went through color changes - notably with the use of blue - to red.

A5L 1965 developmental blue pressure suit, for example, was mostly blue, including the anodised helmet ring - and during development this was overlaid with the red ring.

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Apollo 11 neck ring suit color variation, perhaps blue is training, red, on right is final.

Another note was that during development some parts - especially the anodised disconnects were cannibalized from one set and used in subsequent variations, carrying through the colors without ever re-evaluating their color code, as they simply already existed and were serving their purpose (ie. the why fix what isn't broken).

by Apollo 17, it looks like there is a R/L color coding re-arrange relating to the major connections - major Outlets in Red, on the Right; with major Inlets in Blue, on the Left, sort of matching the wrist disconnects again:

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Link:

International Latex Corporation (ILC) Dover Space Suits & Related Products

https://history.nasa.gov/alsj/ILC-SpaceSuits-RevA.pdf

As said, entirely speculative, but at one point, with only two connectors it may have been a thought to match the wrist colors, visible to the user, with the R/L connectors on the front of the suit, and then subsequently never changed. And in general, blue=in and red=out still stands as a generic color code in of itself.

So...given the above:

Why does NASA suit color coding not follow conventional navigation color coding?

NASA does, but this coloring was not for navigational conventional left/right, port/starboard indication, but rather limited to Blue-In and Red-Out indicators when it was simply two connectors on the front of the suit and you had to make sure it was easy to distinguish, and access, between the two. The wrist disconnects, which once matched each side, were simply left as they were over time. (speculative)

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    $\begingroup$ Good ideas. +1. I can see choosing blue for breathable air and red for "don't breath this". With suit helmet on, the wearer may have trouble seeing the color of the connectors on his belly, but the wrist colors would be visible. $\endgroup$
    – Woody
    Jan 10 at 1:34
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There's no particular reason to pick any given colors for the suit connectors, as long as they're easy to distinguish. The red/green light standard really has nothing to do with making sure you get the correct glove on the correct arm. Most likely they chose red and blue merely because the suit is white, and "red, white, and blue" are the USA colors.

That said, there are potential reasons to pick blue over green in the suit design. Red and green are the most common colors that colorblind people have difficulty telling apart, while blue and red are almost never confused by anything short of complete colorblindness (which is extremely rare). In other words, if there's going to be any difficulty identifying colors, blue and red are the two least likely to be mixed up, even if there are visual issues or weirdly colored lighting at play.

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