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

[miklkit]

Boots.  Boots with magnets in them to grip the metal floor better. 

[sevenperforce]

8 hours ago, MKI said:

16 hours ago, K^2 said:

I'm timing a full circle to be about 7s. And the inner diameter of this track is about 5m, which would mean it's about a fifth of Earth's gravity.

First, aren't they in orbit around Earth and just "running up the curved wall?" the whole time? Which I guess would mean your continuously running up a very steep hill that curves toward you. Lot easier than a flag surface, or "downhill" (!!!)

Yes, this was my thought. They're in microgravity; they're just using the curvature of the wall to keep themselves moving. Very different from running across the lunar surface.

On 1/7/2022 at 6:57 PM, cubinator said:

I think you've dropped an order of magnitude somewhere. Mars' pressure is 0.006 atm, humans need a pressure much greater than that to get enough oxygen while preventing our lungs from bursting from positive pressure. They would still need a pressure suit of some kind.

Hmm, yes, I must have dropped an order of magnitude.

The lowest oxygen concentration that can sustain human life is 35.1% of the sea level oxygen concentration, and sea level air is 21% oxygen, so the lowest pressure that would be indefinitely survivable with a pure oxygen atmosphere would be 0.073 atm. Quite low, but still over ten times the atmospheric pressure on Mars.

That being said, I'm not entirely sure that's a problem. As long as you have warm clothes and a firmly-fitted mask, a difference of 0.067 psi between the inside of your body and the outside isn't going to hurt you. Humans take airplane flights every day where the external pressure drops 0.25 atm over ten minutes and it doesn't hurt them. It's gauge pressure that's the problem, and I don't think that wearing a mask pressurized at 1.067 atm would hurt me.

In fact, given that heat transfer in an 0.006 atm environment would be extremely low, I suspect you could even get away with exposed skin, at least for a minute.

19 hours ago, Piscator said:

It's also an order of magnitude below the Armstrong limit/pressure, which would make prolonged survival a bit tricky.

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.

In a near-future world where people are actually living out their entire lives on Mars, I suspect you would rapidly end up with colonies that used different air pressures. Would make for an interesting science fiction setting.

[sevenperforce]

Science fiction gloss:

Short-term visitors to Mars acclimated quickly to "Tourist 50-50", the mixture of 50% nitrogen and 50% oxygen at just under half of Earth's atmospheric pressure. For most, it was no different than relocating from a city near sea level to a higher altitude like Denver or La Paz. The lower pressure helped make EVA operations less challenging and also conserved the precious resources of bottled nitrogen carried by Starship from Earth.

Colonists who were willing to live at 0.1 Earth atmospheres (or 16 Martian atmospheres) were the "lifers", those who had chosen to spend the rest of their days on the Red Planet. At these pressures, the heart and lungs would last for much longer than those of their tourist counterparts, and they could walk freely across the Martian sands with nothing more than warm clothing and a well-fitted breathing helmet. They aged much more slowly, although a slow death from cancer at 150 or 170 years due to elevated radiation levels was inevitable. But the change to their organs was permanent; they could not transition back to 50-50. If they spent more than a few hours at higher pressures, the atrophy in their organs would lead to rapid hypoxia and death.

Edited January 9, 2022 by sevenperforce

[cubinator]

14 minutes ago, sevenperforce said:

0.073 atm. Quite low, but still over ten times the atmospheric pressure on Mars.

That being said, I'm not entirely sure that's a problem. As long as you have warm clothes and a firmly-fitted mask, a difference of 0.067 psi between the inside of your body and the outside isn't going to hurt you.

.073 atm is 1.07 psi, which is most certainly enough to hurt you. Like you said, you'd have ten times the atmospheric pressure of Mars wanting out from inside your fragile lungs.

Edited January 9, 2022 by cubinator

[kerbiloid]

https://ru-m-wikipedia-org.translate.goog/wiki/Космическое_пространство?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=ru

(English wiki lacks the table)

Quote

• 6.6 km - the highest located stone building (Mount Llullillaco , South America) ^[16] .
• 7 km is the limit of a person's adaptability to a long stay in the mountains.
• 7.99 km - the border of a homogeneous atmosphere at 0 ° C and the same density from sea level . The brightness of the sky decreases in proportion to the decrease in the height of a homogeneous atmosphere at a given level ^[17] .
• 8.2 km is the border of death without an oxygen mask: even a healthy and trained person can lose consciousness and die at any time. The brightness of the sky at the zenith is 440–893 cd / m² ^[18] .
• 8.848 km - the highest point of the Earth, Mount Everest - the limit of walking accessibility into space.
• 9 km - the limit of adaptability to short-term breathing of atmospheric air.
• 10-12 km - the border between the troposphere and the stratosphere ( tropopause ) in the middle latitudes. Also, this is the boundary of the rise of ordinary clouds , thinned and dry air extends further.
• 12 km - breathing air is equivalent to being in space (the same time of loss of consciousness ~ 10-20 s) ^[19] ; the limit of short-term breathing of pure oxygen without additional pressure.
  Ceiling of subsonic passenger airliners . The brightness of the sky at the zenith is 280-880 cd / m² ^[14] .
• 15-16 km - breathing pure oxygen is equivalent to being in space ^[20] .
  10% of the mass of the atmosphere remained overhead ^[21] . The sky turns dark purple (10-15 km) ^[22] .
• 16 km - additional pressure is required in the cockpit when wearing a high-altitude suit .
• 18.9-19.35 - Armstrong's line - the beginning of space for the human body : water boiling at the temperature of the human body. Internal fluids do not boil yet, since the body generates enough internal pressure, but saliva and tears may begin to boil with the formation of foam, and the eyes may swell.

Spoiler

20 km =50 mbar

 

https://ru-m-wikipedia-org.translate.goog/wiki/Климат_Марса?_x_tr_sl=auto&_x_tr_tl=en&_x_tr_hl=ru

The highest Martian pressure is ~10 mBar

Edited January 9, 2022 by kerbiloid

[sevenperforce]

2 hours ago, cubinator said:

.073 atm is 1.07 psi, which is most certainly enough to hurt you. Like you said, you'd have ten times the atmospheric pressure of Mars wanting out from inside your fragile lungs.

I'm going to challenge this. Survivability of pressure differentials are a function of the inside vs the outside, and that's a gauge function, not an absolute function.  To your ribcage, there is no difference between trying to hold in 0.073 atm against 0.006 atm and trying to hold in 1.067 atm against 1.000 atm.

For reference, a moderate mechanical ventilator operates at a +/- 2 psi differential.

At the very most, you would have to have an airflow that would cycle pressure with your breathing, which is not terribly difficult to accomplish.

[kerbiloid]

The average pressure on Mars corresponds to 35 km on the Earth, where a full-featured spacesuit or a pressurized cabin are necessary.

[K^2]

17 hours ago, MKI said:

First, aren't they in orbit around Earth and just "running up the curved wall?" the whole time? Which I guess would mean your continuously running up a very steep hill that curves toward you. Lot easier than a flag surface, or "downhill" (!!!)

8 hours ago, sevenperforce said:

Yes, this was my thought. They're in microgravity; they're just using the curvature of the wall to keep themselves moving. Very different from running across the lunar surface.

How exactly? From perspective of the runner, both are accelerating frames of reference. When you're running on the flat surface of the planet, planet's surface might as well just be curving up towards you. There's literally no difference unless you change pace.

[DDE]

Apollo data is "tainted" by the bulky, inflexible suits. Hops seemingly involve less movement than walking.

On 1/7/2022 at 11:34 PM, kerbiloid said:

There is a special moon walk methodics already developed in late 1980s.

  Reveal hidden contents

 

People may be confused as to your intentions.

Spoiler

 

 

[sevenperforce]

6 hours ago, K^2 said:

How exactly? From perspective of the runner, both are accelerating frames of reference. When you're running on the flat surface of the planet, planet's surface might as well just be curving up towards you. There's literally no difference unless you change pace.

I think that when the radius of curvature is close to your stride length, that would change things. 

[sevenperforce]

19 hours ago, kerbiloid said:

The average pressure on Mars corresponds to 35 km on the Earth, where a full-featured spacesuit or a pressurized cabin are necessary.

Only because no one has ever had any need to acclimate humans to walking around at 35 km altitude.

[kerbiloid]

2 hours ago, sevenperforce said:

Only because no one has ever had any need to acclimate humans to walking around at 35 km altitude.

Quote

• 12 km - breathing air is equivalent to being in space (the same time of loss of consciousness ~ 10-20 s) ^[19] ; the limit of short-term breathing of pure oxygen without additional pressure.
  Ceiling of subsonic passenger airliners . The brightness of the sky at the zenith is 280-880 cd / m² ^[14] .
• 15-16 km - breathing pure oxygen is equivalent to being in space ^[20] .
  10% of the mass of the atmosphere remained overhead ^[21] . The sky turns dark purple (10-15 km) ^[22] .
• 16 km - additional pressure is required in the cockpit when wearing a high-altitude suit .
• 18.9-19.35 - Armstrong's line - the beginning of space for the human body : water boiling at the temperature of the human body. Internal fluids do not boil yet, since the body generates enough internal pressure, but saliva and tears may begin to boil with the formation of foam, and the eyes may swell.

Pure physics.

[sevenperforce]

15 minutes ago, kerbiloid said:

"Internal fluids do not boil yet, since the body generates enough internal pressure"

This is the important bit.

As long as you have your eyes, nose, and mouth covered by a pressurized helmet, none of those things will boil. You'll be fine. 

The only question is whether the pressure in your lungs will be too great in comparison to the pressure outside your lungs. If the pressure in your lungs is too great, it will be too much work to exhale and you will suffocate. But I think human lungs and ribcages are capable of handling and exhaling 1.064 atm internal pressure at 1.000 atm external pressure. If that's the case, then they will be equally capable of handling 0.076 atm at 0.006 atm external pressure.

[kerbiloid]

10 minutes ago, sevenperforce said:

As long as you have your eyes, nose, and mouth covered by a pressurized helmet, none of those things will boil. You'll be fine. 

1. There are other openings in the human body.

2. The skin is porous.

3. The hands start swelling at 10 km altitude.

Quote

12 km - breathing air is equivalent to being in space (the same time of loss of consciousness ~ 10-20 s) ^[19] ; the limit of short-term breathing of pure oxygen without additional pressure.

At 10km they have to wear high-altitude suits simulating the air pressure by strangling bands attached to elastic pneumatic pipes,

Edited January 10, 2022 by kerbiloid

[K^2]

13 hours ago, sevenperforce said:

I think that when the radius of curvature is close to your stride length, that would change things.

If you briskly walk at 3.5mph, the radius of curvature of Earth's surface is about 2.5m from perspective of an inertial frame of reference. This is about what it was for the track on Skylab. The pace of astronaut in that Skylab demo is closer to 5mph, or a light jog, which on Earth would give you radius of curvature of a little over 5m, so double that or Skylab track. It's all in the ballpark, though, and certainly comparable to stride length in both cases.

[monophonic]

2 hours ago, sevenperforce said:

The only question is whether the pressure in your lungs will be too great in comparison to the pressure outside your lungs. If the pressure in your lungs is too great, it will be too much work to exhale and you will suffocate. But I think human lungs and ribcages are capable of handling and exhaling 1.064 atm internal pressure at 1.000 atm external pressure. If that's the case, then they will be equally capable of handling 0.076 atm at 0.006 atm external pressure.

That internal overpressure is about what you need to generate to properly blow a party balloon. So that pressure difference is certainly no risk to our ribs.

2 hours ago, kerbiloid said:

1. There are other openings in the human body.

2. The skin is porous.

3. The hands start swelling at 10 km altitude.

At 10km they have to wear high-altitude suits simulating the air pressure by strangling bands attached to elastic pneumatic pipes,

Okay, so a pressure mask and a pressure diaper. Something to keep the water from leaving through skin. How do those pressure suits work? I suppose they are not as bulky as an Apollo suit? Might a rubber jumpsuit suffice? Something akin to a diving dry suit but tighter fit? Or would it have to be too tight to get into? Maybe a gel could help there? Could the moisture in such a gel also help maintain an equilibrium between the water in the skin and between it and the suit?

Okay, I don't know what's got into the tap water this time. But clearly there's too much of it. Or not enough. I'll stop asking questions now. For now.

5 minutes ago, K^2 said:

If you briskly walk at 3.5mph, the radius of curvature of Earth's surface is about 2.5m from perspective of an inertial frame of reference. This is about what it was for the track on Skylab. The pace of astronaut in that Skylab demo is closer to 5mph, or a light jog, which on Earth would give you radius of curvature of a little over 5m, so double that or Skylab track. It's all in the ballpark, though, and certainly comparable to stride length in both cases.

Of course to stay upright on the Skylab track their feet had to move at considerably higher velocity than their heads. That can be handled by the human physique and psyche, though, as is obvious.

[kerbiloid]

48 minutes ago, 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.

48 minutes ago, monophonic said:

How do those pressure suits work? I suppose they are not as bulky as an Apollo suit?

Spoiler

https://en.wikipedia.org/wiki/Pressure_suit
Almost same or a little thinner.
The space crew wears them not to work outside, but to survive a short-time depressurization, a short rescue walk, or just another short trip oudoors, say to take a photo of Apollo from outside.
For multihour sessions (EVA, lunacy) they use much heavier and bulkier suits.

The airplane crew wears them in case of the cabin depressurization.

At the sea level the pressure suit looks like on the photo.
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.

48 minutes ago, monophonic said:

Might a rubber jumpsuit suffice? Something akin to a diving dry suit but tighter fit?

The diving ones don't provide pressure, as the external pressure is vice versa, high.

The jumpsuits are used at much lower altitudes, about a couple of kilometers or so.

The high-altitude jumps get done in the pressure suits like above.

48 minutes ago, monophonic said:

Maybe a gel could help there?

On Mars there is no need to withstand additional pressure from inside and tighten the body volume.

Edited January 10, 2022 by kerbiloid

[MKI]

On 1/9/2022 at 3:49 AM, K^2 said:

How exactly? From perspective of the runner, both are accelerating frames of reference. When you're running on the flat surface of the planet, planet's surface might as well just be curving up towards you. There's literally no difference unless you change pace.

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

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

[kerbiloid]

5 minutes ago, MKI said:

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

Auto-adjustment

Spoiler

 

[K^2]

2 hours ago, MKI said:

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

If your rotational rate matches your forward velocity, as it does on the video, the impact is always normal to the surface, as you can clearly see on the video.

Seriously, the only difference is Coriolis forces on your limbs that you have to correct for. Otherwise, these are mathematically equivalent systems. Like, the equations of motion are identical in their respective frames. Please, stop trying to come up with differences.  This is like trying to invent perpetual motion with magnets. Just because it looks strange, doesn't mean it's magical. The equations are right there.

[MKI]

1 hour ago, K^2 said:

Seriously, the only difference is Coriolis forces on your limbs that you have to correct for. Otherwise, these are mathematically equivalent systems. Like, the equations of motion are identical in their respective frames. Please, stop trying to come up with differences.

I'm not trying to come up with differences only identify that there is one.

The Coriolis forces you mention sound like a difference. So besides the "Coriolis forces" , there is no difference. 

 

1 hour ago, K^2 said:

This is like trying to invent perpetual motion with magnets. Just because it looks strange, doesn't mean it's magical.

Wha? 

[K^2]

3 hours ago, MKI said:

The Coriolis forces you mention sound like a difference. So besides the "Coriolis forces" , there is no difference. 

Which is well documented to be compensated for by motor system, resulting in effectively identical motion after a surprisingly brief acclimatization period. Which is once again, why I'm insisting that a person jogging at effective 0.2G inside a 5m circle on Skylab means it's a good mode of locomotion on a flat surface at the same 0.2G. Outside of things that are involuntarily compensated for by human body, the two experiences are identical.

3 hours ago, MKI said:

Wha? 

It's a very common thing for people to keep trying to come up with arrangement of magnets that results in perpetual motion, which all comes from the fact that they don't understand the fundamental theorems of classical field theory that categorically prevent any such configuration from working. Even conservation laws aside, you don't need to figure out what all the forces are going to be, and solve complicated equations to discover that they cancel out for every single case when you can solve the general problem to show that no work is being done, and therefore, no net forces are possible in the first place.

Same concept. If I can do a change of coordinate system and show that the effective shape of the surface is identical from perspective of the runner, I don't need to puzzle on specific movement of the feet and how they impact the ground. It can't be different, because there is a trivial transformation from one coordinate system to another, preserving equations of motion. If it works for a runner in a circular track on a space station, it will work for flat surface with same effective gravity at the surface. It doesn't matter if the surface curves towards me because I'm moving along a surface that's actually curved, or if I'm moving in time through space-time that's actually curved. It's an identical picture.

[Piscator]

On 1/9/2022 at 4:26 AM, 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).

[MKI]

16 hours ago, K^2 said:

It's a very common thing for people to keep trying to come up with arrangement of magnets that results in perpetual motion, which all comes from the fact that they don't understand the fundamental theorems of classical field theory that categorically prevent any such configuration from working

I didn't realize I brought up magnets for perpetual motion

 

16 hours ago, K^2 said:

It's an identical picture.

Its an identical picture once you factor in that "Coriolis forces" right?

[K^2]

3 hours ago, MKI said:

Its an identical picture once you factor in that "Coriolis forces" right?

It is an identical picture once you correct for Coriolis forces.