Optimal mobility technique for non-Earth-like terrestrial planets?

[JoeSchmuckatelli]

On 1/10/2022 at 11:08 AM, MKI said:

Running on a curved surface is not directly comparable to running on a flat one due to the angle of impact. 

On 1/10/2022 at 11:08 AM, MKI said:

Otherwise why isn't running up-hill or downhill as easy as running on a flat surface? The gravity is the same

 

https://www.woodway.com/product/curve-treadmill-buy/

 

Running uphill - you are lifting your weight higher... Thus more work.  Running downhill, you are falling more and thus easier 

 

[sevenperforce]

On 1/10/2022 at 5:19 AM, kerbiloid said:

On 1/10/2022 at 4:30 AM, monophonic said:

Okay, so a pressure mask and a pressure diaper.

And a pressure skin to cover the skin pores, ears, nail roots, and other places where the liquid can get outside.
I.e. a whole second skin aka spacesuit.

If you have liquid escaping your body through your nail roots you have a very big problem.

Yes, we have skin pores, but there is no liquid inside our skin that can boil readily through pores. Epidermis is very tough stuff. There might be some mild edema here or there but it wouldn't be significant. And you can have pressure-fitting elements. 

But yes, obviously you'd want to have the ears covered as well. That was assumed to be included with the helmet.

On 1/10/2022 at 5:19 AM, kerbiloid said:

I.e. a whole second skin aka spacesuit.

I'm not saying you won't need an EVA suit at all. But you might not need a pressure suit. That's the difference.

On 1/10/2022 at 5:19 AM, kerbiloid said:

At the altitude the pneumatic pipes (along the back and down) get inflated, pull the rubberized bands which strangle the inner layer making it mechanically press the body around.

And that would still be much less complicated than the giant EVA suits we use now.

14 hours ago, Piscator said:

On 1/8/2022 at 10:26 PM, sevenperforce said:

Only if you're stupid enough to take your mask off.

The Armstrong limit only applies to exposed liquids. Skin is quite tough and can hold in pressure very well. If it couldn't then we'd all simultaneously explode; after all, our blood pressure is 16% higher than atmospheric pressure.

Why would a mask matter? Exposing your lungs to actual Martian atmosphere or to pure oxygen at Martian ambient pressure is - by definition - no difference pressure-wise. That said, I was less worried about your blood starting to boil and more about the drying-out of exposed lung tissues. I'm not quite sure how much this would actually impede the function of the lungs, but a complete evaporation of the water in your exposed mucous membranes would be very uncomfortable to say the least (especially if you take evaporation cooling into account).

Hmm. Okay, yes now I'm seeing what you're saying. The pressure inside the helmet does need to be above the Armstrong limit.

However, as long as the pressure differential between the inside of the lungs and the outside of the lungs isn't too great, you'd be fine.

I wonder if you could lower the Armstrong limit using a high humidity breathing mix. 

[kerbiloid]

Welll, then the fighter pilots don't need the pressure suits they are wearing.-

 

Spoiler

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They just don't know  that they need only a mask.

[monophonic]

3 hours ago, kerbiloid said:

Welll, then the fighter pilots don't need the pressure suits they are wearing.-

 

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They just don't know  that they need only a mask.

Those suits are for far more than just survival in a low pressure environment. They use pressure to force blood towards the head during high G maneuvers, and also to support the ribcage to contain the overpressure gas mix they breathe to increase the oxygen content of the said blood. Both are done just to maximize the amount of oxygen available to the brain during high Gs. They are very extreme measures for a small gain, but that small gain is the difference between life and death when things come to that.

[kerbiloid]

39 minutes ago, monophonic said:

Those suits are for far more than just survival in a low pressure environment. They use pressure to force blood towards the head during high G maneuvers, and also to support the ribcage to contain the overpressure gas mix they breathe to increase the oxygen content of the said blood. Both are done just to maximize the amount of oxygen available to the brain during high Gs. They are very extreme measures for a small gain, but that small gain is the difference between life and death when things come to that.

And they provide the external pressure to let the chest breathe.

[monophonic]

30 minutes ago, kerbiloid said:

And they provide the external pressure to let the chest breathe.

Yes. The external pressure to let the chest breathe against the high internal overpressure used to force extra oxygen into the bloodstream. Absolutely not at all like the situation on Mars that has been the discussion, where the internal overpressure is no more than you experience blowing up a party balloon. That is not a problem for a healthy body to handle without external support, remember the body can itself generate that pressure difference without too much effort.

[kerbiloid]

25 minutes ago, monophonic said:

on Mars that has been the discussion, where the internal overpressure is no more than you experience blowing up a party balloon.

The Martian external pressure is equal to the 35 km above Earth. No party balloons fly so high.

[magnemoe]

12 hours ago, kerbiloid said:

Welll, then the fighter pilots don't need the pressure suits they are wearing.-

 

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They just don't know  that they need only a mask.

This looks like an primitive mechanical over pressure suit or an full body corset including lacing. It should work but your mobility is in an full body corset so is the time to getting it on and off. 
Inflated suits is more practical. 
Now mechanical over pressure makes lots of sense for gloves who is the main issue with eva. 

[wumpus]

19 hours ago, JoeSchmuckatelli said:

https://www.woodway.com/product/curve-treadmill-buy/

 

Running uphill - you are lifting your weight higher... Thus more work.  Running downhill, you are falling more and thus easier 

 

Except that you hit each footfall with more force running downhill.  The downhills of the Boston Marathon are said to be worse than "heartbreak hill".

[JoeSchmuckatelli]

2 hours ago, wumpus said:

you hit each footfall with more force running downhill

Sure - your body has to absorb both the weight of the footfall but also correct for the acceleration, so the force is greater.  

I used to do a LOT of running and the 'shock' sensation felt when running downhill was always more jarring; the 'heave' of running uphill just more taxing on the muscles.  At times, running up a steep hill just felt like placing my foot down for grip, not like the slap you get while trying to retain control on the way down.  So you can catch your breath on the way down, but man it can be physical.

[Piscator]

On 1/12/2022 at 12:59 AM, sevenperforce said:

I wonder if you could lower the Armstrong limit using a high humidity breathing mix. 

I'm a bit hazy on the subject, but doesn't "high humidity" just mean that the partial pressure of water vapor in the atmosphere is close to the vapor pressure of water for a given temperature? In other words, you'd have to have at least the Armstrong pressure in water vapor to achieve saturation, which means that below that pressure there's no such thing as "high humidity".

On the other side, we probably wouldn't have to worry about adding water vapor to our breathing mix (in the loose sense) since our lungs would autogenously pressurize. If my math checks out, you would need as little as 50mg of water per litre of internal cavity to reach Armstrong pressure, which seems quite manageable. I guess, that's where a mask does come in handy.

As has been established, all this would of course rely on finding another way to oxygenate your blood, since the oxygen partial pressure would be too low for your lungs to be much of a help.

 

 

[KerikBalm]

On 1/10/2022 at 11:19 AM, kerbiloid said:

And a pressure skin to cover the skin pores, ears, nail roots, and other places where the liquid can get outside.
I.e. a whole second skin aka spacesuit.

https://en.wikipedia.org/wiki/Mechanical_counterpressure_suit

Quote

The human body can briefly survive exposure to the hard vacuum of space unprotected,^[2] despite contrary depictions in some popular science fiction. Human skin does not need to be protected from vacuum and is gas-tight by itself. Human flesh expands to about twice its size in such conditions, giving the visual effect of a body builder rather than an overfilled balloon. This can be counteracted through mechanical counter-pressure from a suitably designed garment. Consciousness is retained for up to 15 seconds as the effects of oxygen starvation set in. Counteracting this requires a helmet to contain breathing gases and protect the ears and eyes.^[3] These effects have been confirmed through various accidents in very high altitude conditions, outer space, and training vacuum chambers.^[4][2]

You'd need more than a face mask, human flesh swelling to 2x volume doesn't sound great... (bodybuilder rather than overfilled balloon though...)

Quote

Cooling of the astronaut with an SAS is generally achieved with evaporation from body perspiration which is emitted from the suit in all directions. Water, salts, and proteins can deposit on optics and other sensitive surfaces causing damage or degradation. This can limit the usefulness of an SAS.

Evaporation would be much higher, doesn't seem like going out for a stroll on Mars wearing just one of these would be a good idea... but short excursions when neccessary, fine.

[kerbiloid]

53 minutes ago, KerikBalm said:

https://en.wikipedia.org/wiki/Mechanical_counterpressure_suit

The problem with it is in the joints, especially the neck, and in the fact that the skin is an excretory organ, too.

But actually this doesn't change anything, as the classic pressure suit provides exactly the mechanical counterpressure by tightening the inner suit layer pneumatically.
(Not by the air pressure surrounding the body inside the suit, but by pulling the bands on the pneumopipes inflation.)

Edited January 13, 2022 by kerbiloid

[Piscator]

19 hours ago, KerikBalm said:

You'd need more than a face mask, human flesh swelling to 2x volume doesn't sound great... (bodybuilder rather than overfilled balloon though...)

I was worrying about this point as well, but have a bit of a problem finding out why this would be the case. I'm of course aware of the Kittinger incident, but I'm not sure how much of the (apparently quite painful and debilitating) swelling was caused by the low pressure per se and how much was caused by the difference between the pressurized and unpressurized parts of the suit. After all, you can easily imagine body fluids accumulating in the only body part that's not pressurized.

Source link [2] in your quoted passage mentions water in your tissues beginning to boil as a cause, which sounds plausible enough. While your blood may be protected by vessels designed to withstand the pressure differences of a beating heart, other liquids in your body might be not so lucky. Then again, the  descriptions of pressure chamber accidents don't seem to mention this effect. Does it take a while to develop? I'd really love to find a good source.

[sevenperforce]

On 1/14/2022 at 4:10 AM, Piscator said:

Source link [2] in your quoted passage mentions water in your tissues beginning to boil as a cause, which sounds plausible enough. While your blood may be protected by vessels designed to withstand the pressure differences of a beating heart, other liquids in your body might be not so lucky. Then again, the  descriptions of pressure chamber accidents don't seem to mention this effect. Does it take a while to develop? I'd really love to find a good source.

From that source,

"In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim’s mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin."

Author Alan Bellows is a computer programmer but he is not, to my knowledge, a physicist or biologist, so I'm inclined to take this with a grain of salt.

The best corollary I could think of would be cupping "therapy" (I put therapy in scare quotes because it isn't), where a partial vacuum is pulled inside cups attached to your skin, causing the skin to expand into the space. However, the effect here is almost certainly driven by external pressure. According to this systematic review¹, the top end of the typical pressure differential in cupping is 600 mmHg or ~80 kPa. This pressure differential would mean a pressure inside the cup of about 21 kPa, or 0.21 atm. Flight pressure for the Apollo astronauts was just about 0.33 atm, and their skin certainly didn't swell up like they were experiencing cupping all over their bodies at once.

_{1. Yes, I recognize that it's very weird to think about doing a systematic review (which is valid science) of cupping (which is fake science). But oh well.}

I would argue that with the exception of stomach acid, there really is no loose fluid sloshing around anywhere inside us. Obviously if your muscle or soft tissue was exposed to vacuum the moisture would immediately evaporate, but that's not the case here. You would see some tissue expansion due to blood pressure having less external pressure to push against, but as the wiki explains, it would be less like a balloon and more like the transient hypertrophy experienced by a bodybuilder due to the muscle pump phenomenon.

Bodybuilders will typically work out immediately before going on stage because the increased blood flow and buildup of lactic acid in the muscles causes them to swell noticeably:

Spoiler

I simply don't see any reason why there would be any moisture in your body that would "boil" unless it was exposed. Boiling is what happens when the vapor pressure at the surface of a liquid is equal to the atmospheric pressure, and so you can't have "boiling" unless you have exposed liquids. The actual presence of gas bubbles in your tissue, which is what can happen to someone who experiences the bends, would be excruciatingly painful and rapidly fatal.

Note that with the bends it is not evaporation or boiling, but nitrogen molecules leaving solution and forming gas bubbles due to the change in pressure, not unlike what happens when you open a carbonated beverage.

Edited January 19, 2022 by sevenperforce

[kerbiloid]

7 hours ago, sevenperforce said:

I simply don't see any reason why there would be any moisture in your body that would "boil" unless it was exposed. Boiling is what happens when the vapor pressure at the surface of a liquid is equal to the atmospheric pressure, and so you can't have "boiling" unless you have exposed liquids

 

Quote

• 18.9-19.35 - Armstrong line  - the beginning of space for the human body : boiling water at the temperature of the human body. The internal fluids do not boil yet, as the body generates enough internal pressure, but saliva and tears may begin to boil with the formation of foam, the eyes swell.
• <snip>
• OK. 35 km - the beginning of space for water or the triple point of water : at this altitude, the atmospheric pressure is 611.657 Pa and water boils at 0 ° C, and above it cannot be in liquid form.

When a solid body is decaying by turning into gas, it's called "sublimation".

This is what happens to water at 35 km height. It boils/sublimates from solid directly to gas without even getting liquid, so a liquid water can't exist at such pressure at all.

But much sooner, at 19 km, it can't be liquid at the body temperature, it starts evaporating.

So, to stay intact, it's necessary to provide an external pressure.
From 10..12 km - to prevent the dissolved nitrogen and other gases boiling, from 19 - to prevent the water boiling itself.

Edited January 20, 2022 by kerbiloid

[Piscator]

16 hours ago, sevenperforce said:

Author Alan Bellows is a computer programmer but he is not, to my knowledge, a physicist or biologist, so I'm inclined to take this with a grain of salt.

That was the passage I was referring to and I came to the same conclusion pretty much. Which is why I didn't consider the source overly reliable.

16 hours ago, sevenperforce said:

Boiling is what happens when the vapor pressure at the surface of a liquid is equal to the atmospheric pressure, and so you can't have "boiling" unless you have exposed liquids.

I was thinking about the topic quite a bit after my last post and I'm not sure that this is really how it works. Please correct me if you find a flaw with my line of argument, but as I see it, the essential part of boiling vs evaporation is that the pressure throughout the liquid needs to be lower than the current vapor pressure for boiling to occur. Only if this condition is met, cavities or instabilities that form inside the liquid for whatever reason would start accumulating gas from their surroundings instead of collapsing immediately. Or looking at it from a slightly different angle, a vapor bubble in a liquid wouldn't be stable unless its internal pressure (the vapor pressure) is greater than the pressure of the surrounding liquid.

If the total pressure is too high for bubbles to form inside the liquid, the only place where a phase change would occur is the surface of the liquid, where the vapor pressure of the substance might be able to overcome its partial pressure in the gas phase, or in other words evaporate.

Since bubbles form at the bottom of a pot of boiling water and would still form if you covered the surface with a layer of oil for example, this explanation seems to fit the observations rather better.

 

If my line of reasoning is correct so far, the question regarding vacuum exposure would be less whether a liquid is exposed or not, but rather whether it is enclosed by a membrane able to provide the necessary counterpressure. As mentioned, blood vessels are certainly able to do this but I have no idea how regular cell membranes would compare.

Since you would at least expect some readily findable results of animal experiments if bloating was a real concern, my guess is that it probably doesn't happen. I would still consider it imaginable though at this stage.