What are the Advantages of having a Double-pane Space Helmet?

Question

In the following image of Exploration Extravehicular Mobility Unit (xEMU) or Artemis Generation Space Suit, it can be seen the helmet contains double-pane of glass (inside the black rectangle)

What is in between the two glass layers - air, inert gases (Helium, Neon, Argon, Krypton, Xenon), or vacuum?

What are the advantages of having a double-pane space helmet? Some of the possible advantages that I could think are as follows:

For additional safety, to avoid accidental decompression in case of damage in the outermost glass layer.
For radiation protection (I can't think how this can happen)?
For thermal insulation (like the double-pane windows used in some houses)?

Or is that any other thing? Are the current generation space-helmets double-paned or single-paned (I can't see any difference clearly)?

I can't post an answer because I have no source, but the need for thermal insulation (if that turns out to be an answer) might be more to prevent condensation of water vapor (especially that exhaled directly on to the surface) than to prevent heat loss, since the suit has to go out of its way to get rid of excess heat (How have space suits dissipated the heat removed from astronauts?). Slightly related: Does sunlight warm an astronaut's face during a spacewalk? — uhoh, Oct 20 '19 at 05:40
If they have ended up with needing divergent properties they may be different materials, separated to avoid problems with thermal expansion. Or possibly to make it easier to service/swap parts. — GremlinWranger, Oct 20 '19 at 05:44
@uhoh, Maybe this could help (See only What is a Double-Pane Window?). It is about double-pane windows, and I don't know whether it's reasonable to superpose the same concept here. — Vishnu, Oct 20 '19 at 05:48
@GremlinWranger, I don't think thermal expansion of the visor is more important than the metal joints (or bearings) at wrist, arms etc. — Vishnu, Oct 20 '19 at 05:50
@Intellex I think that comment means to point out that the visor may be providing several different functions at the same time, and some of those may be best served by glass and others by plastic (just for example). Since the materials have different coefficients of thermal expansion and temperatures can vary wildly in space during use, storage, and transportation, trying to laminate them into a single layer could cause trouble, whereas separating them allows each material to expand/contract on its own, stresses in a bonded bi-material visor could lead to cracks or de-lamination for example. — uhoh, Oct 20 '19 at 05:53
@uhoh, Thanks for your comment. If that is the case, are current generation visors double-pane? I don't think so. — Vishnu, Oct 20 '19 at 05:59
Maybe they could put a HUD on one or both of the panes. I don't know if they do this now but it may be a future enhancement. — Klapterseven, Oct 21 '19 at 12:00
Protection against any facehuggers! (This looks pretty classy.) — David Tonhofer, Oct 21 '19 at 16:48
@OrganicMarble I guess more relevant would be to ask if the Apollo suits were double-paned? If the purpose is to protect against dust, then that's the last time that was an issue. — Darrel Hoffman, Oct 21 '19 at 18:41
@DarrelHoffman Apollo was not double either https://www.apollomaniacs.com/apollo/spacesuit/thum/p552a.png — Organic Marble, Oct 21 '19 at 18:50

score 39 · Accepted Answer · edited Oct 23 '19 at 13:56

39

The outer pane is just a replaceable protection of the inner pane against scratches, dirt, and abrasion.

The helmet on the suits for Artemis missions will also feature a quick-swap protective visor. The clear protective visor is a sacrificial shield that protects the pressurized bubble from any wear and tear or dents and scratches from the abrasive dirt of planetary bodies. The quick-swap function means that astronauts can replace the visor before or after a spacewalk instead of sending an entire helmet back to Earth for repairs.

From this page.

Within the pressurized airlock the gas between the panes is the breathing gas used in the airlock. During an EVA in space the gas would ooze into the vacuum. Using a noble gas between the panes does not make sense.

The outer pane does not protect against radiation and does not provide thermal insulation in a vacuum, but it increases safety by protecting the inner pane against damages.

By the way, I don't think the helmet's material would get dents.

edited Oct 23 '19 at 13:56

Glorfindel

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answered Oct 20 '19 at 07:17

Uwe

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"...breathing gas used in the airlock". Won't the Artemis programme make use of suit-ports to prevent lunar dust from entering the habitat? I think an airlock for astronauts will not be necessary. – Vishnu Oct 20 '19 at 13:24
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@Intellex I suspect that even with a suit port, it would be easier to put on a spacesuit if the pressure on the inside and outside is equal. And it would be safer, too. – Level River St Oct 20 '19 at 13:37
@Intellex But how to replace the gloves of a suit if there is only a suit-port and no airlock? How to clean and lubricate rotatory joints of the arm parts of the suit? – Uwe Oct 20 '19 at 15:07
@Uwe, Yes. Now I understand the necessity of air-locks. But how are they going to prevent lunar-dust entering the habitation module or rover? – Vishnu Oct 20 '19 at 15:24
@Intellex you could make the airlock a water filled tunnel, and have the astronauts surface like divers entering a pressurized deep-sea habitat. Provided you have enough water, swimming for a bit would wash lots of the dust away – Dragongeek Oct 20 '19 at 20:35
@Dragongeek, Thanks for the idea. Now we have two options - wait and see or ask another question here. – Vishnu Oct 21 '19 at 02:49
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@Dragongeek I think the added weight of carrying around that much water (in addition to the water used for drinking, because once you taint that water with lunar dust you probably don't want to drink it) would be prohibitively expensive. – Darrel Hoffman Oct 21 '19 at 14:20
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@Uwe I suppose you could use suit-ports most of the time, and then just bring the suits into a full airlock when they need maintenance? Even if you have to bring them in once every five EVAs, that's still an 80% reduction in the number of opportunities for dust to get inside. – anaximander Oct 21 '19 at 16:02
According to Scott Manley’s video on the subject, Suit Port capability may be dropped from the requirements for the first lunar missions. – CourageousPotato Oct 23 '19 at 03:11
Lunar dust mitigation systems exist - they're more or less space vacuums. Could contract Dyson to build one. – mothman Oct 25 '19 at 08:38

What are the Advantages of having a Double-pane Space Helmet?

1 Answers1