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As noted in this question and this NASA webpage, for more than 40 years U.S. and Russian spacesuits for extra-vehicular activities have been white because

  1. white reflects heat so that the astronaut doesn't get too warm.
  2. white is visible against the black background of space.

However, wouldn't the same arguments hold (perhaps even more so) for a silver spacesuit, such as was used in the Mercury program? Why has silver never been used as an EVA suit color?

(The orange suits used during launch and recovery are not EVA suits, and are thus outside the scope of this question.)

DrSheldon
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    Interesting question! I've never really understood what "silver color" is. I'd guess is's a combination of "gray" and a reduced degree of diffuseness compared to whatever a "white" surface would have. A mirror surface will appear black in space unless oriented in such a way that it reflects light from somewhere, so I'd guess an answer might evolve along those lines. – uhoh Aug 05 '18 at 06:40
  • @uhoh: Pictures of the Mercury suits show diffuse reflection, not the specular reflection of a mirror. So, they should reflect sunlight no matter what angle, and not appear black as space. – DrSheldon Aug 05 '18 at 06:50
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    Ya it's not binary, but anything that's not absolutely black will show some reflectivity. It would be great to find a photo of a Mercury suit in a black room with only a single light source. Anyway, the difference between something that would be called "silver", and something that would be called "gray" is related to "the degree of diffuseness". Silver isn't really a color as much as it is a property. – uhoh Aug 05 '18 at 07:36
  • The difference between white and silver is only the kind of reflection, silver is reflecting more or less like a mirror, white is a fully diffuse reflection. May be the reflections of sunlight from a silver suit were considered bad for photos and the vision of other astronauts. – Uwe Aug 05 '18 at 10:28
  • I wonder if it might be a durability issue, when I see those old silver suits, the coating is always flaking off. Course they are 50 years old at this point. – Organic Marble Aug 05 '18 at 13:52
  • The suits used for Apollo are a little bit younger, but they do look aged now too, see 1. – Uwe Aug 05 '18 at 15:00
  • @uwe: Your linked article notes that the outer layer of Apollo suits is Teflon, which was probably chosen to limit abrasion. Teflon is naturally white, so perhaps the white color instead of silver for Apollo suits was not deliberate, but rather a consequence of the chosen materials. – DrSheldon Aug 05 '18 at 15:21
  • The mercury suits had a very thin deposit of aluminium applied by evaporation in a vacuum. – Uwe Aug 05 '18 at 15:29
  • The outer layer of Apollo suits is Beta cloth made from a woven silica fiber coated with Teflon. The resulting fabric will not burn. – Uwe Aug 05 '18 at 15:50
  • This NASA document about multilayer insulation contains information about several aluminized layers for UV reflection below the top layer. – Uwe Aug 05 '18 at 16:12
  • The silver suit used inside the Mercury capsule was never used for an EVA outside the capsule. – Uwe Aug 05 '18 at 19:44

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NASA's webpage: "The History of Spacesuits" explains that the suits for the Mercury program were an early design and not puncture resistant nor as heavy as the white suits (which contain aluminized mylar underneath). They were also not fire resistant.

"What Were Early Spacesuits Like?

NASA astronauts first flew into space during the Mercury program. NASA’s first spacesuits were made for Mercury. The Mercury suits were only worn inside the spacecraft.

NASA’s first spacewalks took place during its second space program, Gemini. The suits used for Gemini were better than the Mercury suits. But the Gemini suits were simpler than today’s suits.

...

Astronauts wore heavy white spacesuits when going on spacewalks outside the space shuttle. These same heavy white suits are sometimes used when astronauts go on spacewalks outside the space station.".

Mercury Spacesuits

Due to a fire and resulting deaths the suits were improved.

Wikipedia - "Apollo Program":

"Astronauts Grissom, White, and Roger B. Chaffee were wearing A1C suits on January 27, 1967 in a preliminary countdown demonstration test for the planned February 21 Apollo 1 launch, when they were killed in a cabin fire, leading to NASA cancelling manned Block I flights and use of the A1C suit. Since the fire had burned through the suits, NASA added a fireproofing requirement to the new suit, which replaced the outer layer with beta cloth. The Block II suit was designated A7L and manufactured by ILC Dover. The new suit was first used on Apollo 1's replacement flight, Apollo 7 flown by Schirra, Eisele and Cunningham in October 1968.".

NASA has a couple of webpages explaining why the suits are white, but even webpages mentioning aluminized mylar don't say why is is better (or worse) than white.

  1. The reason that spacesuits are white is because white reflects heat in space the same as it does here on Earth. Temperatures in direct sunlight in space can be more than 275 degrees Fahrenheit.

  1. Shuttle spacesuits are made by sewing and cementing various materials together, and then attaching metal parts that let the different components be joined together.

  2. Shuttle spacesuit materials include ortho-fabric, aluminized mylar, neoprene-coated nylon, dacron, urethane-coated nylon, tricot, nylon/spandex, stainless steel, and high-strength composite materials.

Modern suits use multi layer insulation and thermal micrometeoroid garment for the outer layer:

Spacesuit Layers

A NASA Report on the testing of various materials titled: "Space environmental effects on spacecraft: LEO materials selection guide, part 2" on page 10-147 explains that FEP Teflon has a lower erosion from atomic oxygen than many other materials, and has this reflectivity chart on page 10-3:

Spectral Absorption of Some Tested Materials

White is almost as good as aluminized ("silver") color and can be applied to more durable materials, leading to an improved system overall.

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Rob
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  • I think you're missing an important point in this last plot: White color is actually better in radiating waste heat than both black paint and transparent, aluminized material. – asdfex Aug 06 '18 at 21:38