Pneumatically Pressurized Space Suits?

The smallest crewed spacecraft you can get without doing some sci-fi stuff to your astronauts is a spacesuit. The spacesuits used in Extravehicular Activities (EVA) aka spacewalks, these small spacecraft need to provide a micro-environment that will allow astronauts to not just live, but do complicated work. One environmental feature that dictates a large amount of space suit design is the need for pressure. Without pressure pushing against your skin your body risks getting nitrogen narcosis. Unfortunately, that need for pressure against our skin makes the design of spacesuits more complicated. The best way to minimize the risk of the bends is to have air pressure as close to our atmospheric pressure as possible, but the higher the pressure in your spacesuit, the harder it is for an astronaut to move parts of their spacesuit. Think about properly inflated car tires and how hard they are to bend using your bare hands.

During my class on the requirements of human spaceflight, we discussed various technologies used in the creation of spacesuits and how to design them to maximize mobility. A question I raised to my Professor, Dr Garret Reismann, with moving a compressible gas around being such a problem, had there been any investigation into using water to provide pressure inside space suits. At the time he could not think of any examples of investigations into using water to pressurize a space suit. He did opine that one reason, of probably countless, would come down to mass as well as complexities ein donning and doffing (putting something on or taking it off)

Out of continuing curiosity I tried doing some online “research” (aka searching on Google for a few different versions of the query “pressurizing spacesuits in space using water”)

The results were less helpful than I’d hoped, aside from a StackExchange thread, I couldn’t find any meaningful research into why there hadn’t been more research into using water pressure as a means of keeping astronauts from getting the bends.

Regardless I wanted to jot down a few thoughts into a water-pressurized spacesuit. Maybe someone will find it useful (likely for comedic effect in engineering circles, but I’ll take what I can get)

There were some (ok lots but I only want to write some of them) legitimate concerns brought up in my initial inquiries into hydraulic pressurized spacesuits.

Suit Mass

Water Getting in the Way

Donning and Doffing

System Complexity

I believe I have reasonable partial answers for 2 of these concerns.

Suit Mass: As heavy as space suits are, about 113 kg, they are in fact designed to keep their overall mass to a relative minimum as that mass is expensive to get too and from Earth Orbit.

Due to the provisional investigation nature of this blog post I will not lie and claim that I have a good answer just some tools for guestimation. How much mass would our water pressurization system add?

The average American male has about 2.1 square meters of skin. Assuming that NASA sticks with a desire to accommodate astronauts as tall as a 95th percentile height male, that means a proportional 95th percentile male, who is 6% taller than their 50th percentile counterparts, might have about 12% more surface area than a male of average height. Add a generous fudge factor, and we can imagine that our astronauts have about 2.6 sq meters of skin.

If we imagine that their body was wrapped in about 1cm of pressurized water, we have a pretty easy number to estimate. With 1 cubic cm of water having a mass of about 1 gram and 1 square meter having an area of 10,000 square centimeters, our water mass is just 26,000*water thickness.

Water mass: 26 kilograms, other mass, unknown.

Where I have no useful answer is how other mass properties would change, how much lighter/heavier would our astronaut’s clothes get, what types of components need to be added, or if we are lucky could parts be removed due to all of this water.

One element that might be removed from the traditional EVA suit would be that of the Liquid Cooling and Venitation Garment as our space suit is already filled with additional water that could be circulated by suit elements, there would be no need for a discrete garment.

Water getting in the way:

This problem is already being investigated by researchers at UC Berkeley for totally different reasons. What they propose is a spacesuit design where there are two pressurized systems, the helmet and body of the suit, working semi-independently of each other (). This approach should be able to work with a water pressurized lower suit. Pressure in the helmet allows our astronaut to breath as well as providing a “push” against the water filling the body of our proposed suit. Now there is certainly a risk of mechanical mishap allowing water to leak into the helmet volume. This has already happened with our current EVA suits, and we only use water to control temperature and hydrate. What happens when there is even more water to slush around? Great question, I have no perfect answer, but solutions could include, but not be limited to.

Emergency breathing valve (not a great option, but hey transparency is important to me) Think something like the breathing mechanism for scuba diving

Water barriers. As mentioned with the proposed two zones of our space suit, the helmet would ideally already have some barriers to keep the pressure in the helmet semi-independent from the water. By having the air pressure inside the helmet slightly higher than the pressure of the suit body water, I believe you would help reduce the likelihood of water moving around.

Spongy materials to help guide fluids. Assuming water gets from the body into the helmet gas pressure zone, having absorbent materials near any seems would be a good way to prevent small amounts of water transfer.

Donning and Doffing

AKA fancy words for putting on and taking off a space suit.

My supposed argument for a water-filled body cavity for a space suit comes down to the time required for astronauts to prepare for their EVAs. A space suit is most pliable when the interior pressure is as low as possible, unfortunately, the lower the pressure inside the space suit, the more likely our astronaut will suffer from complications associated with depressurizing nitrogen. The general strategy for EVAs is to have astronauts spend many hours acclimating their bodies to lower air pressures to gently remove nitrogen from the blood stream.

A suit that can maintain an interior pressure closer to the air pressure inside of your space ship/station means, in theory, your astronauts can get to work that much faster.

For our imagined water-filled suit, assuming you can get the concept to work, we still need to make sure that the time required for crew members to put on/remove their suit, takes less time than the pressure acclimation currently needed.

If astronauts can’t fill/empty the water volume cleanly and conveniently or somehow not need to swap out water to enter and exit, it doesn’t matter whether it is more flexible (which to be clear I’m not sure of the speed of this process)

Suit Complexity

Now this is one of those topics where I am aware that I lack the necessary depth to say anything meaningful, but hey thought experiments can be helpful.

Broad strokes making a mini-spacecraft that has two pressurized environments with a shared bulkhead, but the pressure source comes from radically different fluids, sounds like a hard problem to crack. To avoid being presumptive I will simply share the few cohesive thoughts I can add.

Research like UC Berkely’s “Advanced Two-System Space Suit” provides a good starting point for the creation of a suit with two distinctive pressurization systems. What should not be discounted is that their efforts are focused on supporting the development of the MIT BioSuit being developed by Professor Dava Newman. As such what makes sense for that design may not necessarily make sense for our water suit.

On that note Professor Newman has been spending far more time researching this space than I have been by orders of magnitude, the fact that I have not yet seen a paper title mentioning using a compressive liquid inside of space suit makes me think there are some very good, probably obvious to subject matter experts, reasons why a liquid filled space suit is not a great idea.

In “Conclusion?”

I wish I had a clearer narrative. While my naïve perspective on things makes me want a bit more study (by peole with research grants) on water filled space suits, I do think by writing this post I have been able to put into words some of the less obvious risks to this idea.

The obvious big problem is just how expensive designing spacesuits is, and no one wants to start from a blank page when we have technologies that do work.

The big one for me is the problematic nature of water in space, unless we can cleanly enter and exit the water pressurized parts of our suit without water getting out of the suit volume, well we’ve introduced too much risk to the rest of the spacecraft. Even if the suit overall would be lighter by using a non-compressible fluid, if that mass savings came at the risk of shorting out electronics near our airlock, well that’s not really an acceptable option.

I hope this long read was at least interesting.

As per usual questions, ideas, and suggestions are always welcome.

Below are links with material I read, but I couldn’t remember if I actually used the material for what I wrote, but they do have some interesting info if you want to check it out.

https://www.re-thinkingthefuture.com/designing-for-typologies/a6628-evolution-of-the-space-suit/

https://www.nasa.gov/feature/spacewalk-spacesuit-basics

https://ieeexplore.ieee.org/document/7500869

https://www.nasa.gov/pdf/188963main_Extravehicular_Mobility_Unit.pdf   

https://phys.org/news/2015-02-spacesuit.html

https://www.smithsonianmag.com/air-space-magazine/space-wear-180964337/

https://www.lpi.usra.edu/publications/reports/CB-1106/ucb01.pdf two zone spacesuit pressurization system