Fastest Human Reentry Speeds Possible

[edzieba]

This idea of breathing liquid oxygen: is this a serious thing people are considering? Has anyone ever "breathed a liquid"? That in and of itself sounds pretty weird to me, and how does it make higher G loads less problematic? Is it because the lungs won't collapse if full of liquid? My apologies if I'm a bit dense but this sounds kind of nutty to me (I don't mean that in a bad way).

Not breathing LOX (that would likely be fatal) but breathing an fluid, usually a perfluorocarbon, that readily dissolved Oxygen and CO2.

[laszlo]

Ok, given we'd stay in the 12 - 16 km/s range for just a little bit earlier return form Mars, this might be possible. I wouldn't go that far to let the astronauts drink oxygenated fluid...

BTW, while reading about this, apparently they did actual experiments with suspending someone in fluid (but breathing air). The peak of 31gees for 5 seconds (during a 25 second cycle) was achieved by the researcher just holding his breath while in the water capsule: https://history.nasa.gov/SP-4201/ch2-4.htm

Kind of interesting, but you can get a similar result by using nylon netting and proper restraints. So maybe we can do even better than this but without the weight penalty of water. Like a gee-loading-optimized mechanical counter-pressure suit. (but with something different than nylon, which has a springing effect... may need active compensation?). Could allow tolerance beyond 10gees for significant lengths of time.

At this point, we're talking g-loading higher than a typical spacecraft structure could handle. You're potentially more worried about the spacecraft failing than the person.

https://history.nasa.gov/SP-4201/ch2-4.htm


I kind of think we have more space to explore this area in terms of biomedical adaptation. A lot of these experiences are 70 or even 90 years old, and we haven't had the opportunity to try modern techniques.

I'm reminded of the high-gee adaptations and countermeasures in The Expanse. Gotta get some "juice"...

From Wikipedia article on Colonel John Stapp, USAF flight surgeon:

By riding the decelerator sled, in his 29th and last ride at Holloman Air Force Base in New Mexico, Stapp demonstrated that a human can withstand at least 46.2 g (in the forward position, with adequate harnessing). This is the highest known acceleration voluntarily encountered by a human, set on December 10, 1954.[7][8]

[WTF]

From Wikipedia article on Colonel John Stapp, USAF flight surgeon:

By riding the decelerator sled, in his 29th and last ride at Holloman Air Force Base in New Mexico, Stapp demonstrated that a human can withstand at least 46.2 g (in the forward position, with adequate harnessing). This is the . known acceleration voluntarily encountered by a human, set on December 10, 1954.[7][8]
[/quote]

'This is going to hurt'
Reportedly overheard as he prepared for that last rocket sled run.

Eyecandy?
GOOGLE: Rocket Sled, Sonic Wind I

An uncle. When visiting me at the maternity ward, my mother stated he told me to wear my seatbelt.

[chopsticks]

Not breathing LOX (that would likely be fatal) but breathing an fluid, usually a perfluorocarbon, that readily dissolved Oxygen and CO2.

Yes, I wasn't thinking of breathing the liquid oxygen that's used as rocket propellant!

Even with a breathable liquid, how does that help with surviving higher G forces?

[Asteroza]

Not breathing LOX (that would likely be fatal) but breathing an fluid, usually a perfluorocarbon, that readily dissolved Oxygen and CO2.

Yes, I wasn't thinking of breathing the liquid oxygen that's used as rocket propellant!

Even with a breathable liquid, how does that help with surviving higher G forces?

It's not just keeping the lungs from collapsing, it provides some physical pressure to resist crushing of the rib cage as a liquid is incompressible.

[Pete]

Not breathing LOX (that would likely be fatal) but breathing an fluid, usually a perfluorocarbon, that readily dissolved Oxygen and CO2.

Yes, I wasn't thinking of breathing the liquid oxygen that's used as rocket propellant!

Even with a breathable liquid, how does that help with surviving higher G forces?

Your goal is, as far as possible, to make the human body neutrally buoyant. Both in total and in parts!
So you don't have extra heavy bits that try to sink to the bottom, and extra light bits that try to rise to the top.
And so the whole is gently floating in fluid, rather than being supported on a concrete slab under you, flattening you out to straberry-jam-filled-pancake.

Now obviously we cannot do much about the denser bones being dense. But they are reasonably strong, and the weight is spread so bruising under the bones is not do bad.
But the lungs present a HUGE air void right in the middle of your body, that under heavy gravity wants to float up through your ribs and out. By filling them with something that is the same density as the rest of your body, you prevent this problem. Also, a fluid-filled interior will better resist compression from external forces. Provide interior support. Really, filling you lungs with liquid is *great* for you, aside from that slight issue of, well, breathing.

A grape, on a nice soft sponge bed, "dies" under less than 10g in a centrifuge.
The same grape, in a saline bath, is fine up to 120g, and then only breaks when the seeds float out through the skin.
Strange, i really expected them to sink, but apparently live grape seed are less dense than grape pulp.

[darkenfast]

Reminds me of the COPV tearing loose and shooting up through the LOX tanks on the failed SpaceX CRS mission. Once it is explained, it's obvious, but at first it sounds odd. I wonder what other little surprises would await a liquid-breathing astronaut trying a very high-g maneuver?

[Hog]

Not breathing LOX (that would likely be fatal) but breathing an fluid, usually a perfluorocarbon, that readily dissolved Oxygen and CO2.

Yes, I wasn't thinking of breathing the liquid oxygen that's used as rocket propellant!

Even with a breathable liquid, how does that help with surviving higher G forces?

It's not just keeping the lungs from collapsing, it provides some physical pressure to resist crushing of the rib cage as a liquid is incompressible.

But would add tremendous mass to delicate system that has evolved dealing with gases..  Perhaps more mass coupled with accelerations could possibly cause more issues inside the actual lung structures.
 
Incompressible fluids "could" be detrimental as they transmit forces rather than dissipate them. This is the basis of hydraulics.  If you are relying on the contents of your lungs to resist the crushing of you chest cavity, you've got very big issues at hand.

Breathing liquids can be accomplished.  It's having the human survive after switching back to air.  Respiratory Acidosis and I'd guess the stripping of the surfactants of the lungs could be problematic.

Very interesting topic.

[Genial Precis]

Incompressible fluids "could" be detrimental as they transmit forces rather than dissipate them. This is the basis of hydraulics.  If you are relying on the contents of your lungs to resist the crushing of you chest cavity, you've got very big issues at hand.

Breathing liquids can be accomplished.  It's having the human survive after switching back to air.  Respiratory Acidosis and I'd guess the stripping of the surfactants of the lungs could be problematic.

So, transmitting forces is actually what you want. A contained column of water doesn't rearrange itself. If you add material of different density, such as a bubble, it tries to float. Filling the lungs with a density-matched liquid is a win for acceleration tolerance.

I don't believe existing liquid breathing candidates are density matched. So they are maybe of interest for diving, but not for acceleration tolerance.

ISTM that it would be more realistic to use an artificial o2-co2 exchange rig hooked into the person's blood. That is an existing medical device. Then the requirement is just for the lungs to tolerate whatever they're filled with. And to get enough blood through the device, presumably.
Edit: Ah, the wikipedia state of the art is that you need to administer lots of anti-clotting agents (heparin) the whole time, and that's quite dangerous.

Medical interest seems to be in partially filling lungs with perfluorocarbon fluid to improve gas exchange, somehow, either in premature infants or adults with acute respiratory distress syndrome. Partial liquid ventilation doesn't kill adults with ARDS more effectively than the ARDS, at least, but survival was no different from control. On the other hand partial liquid ventilation isn't relevant here.

The surfactant stripping thing apparently isn't a totally unsolvable problem, because people do sometimes survive partial liquid ventilation.

Edit: This approach with micro/nano capsules full of high pressure oxygen suspended in saline seems more promising than perfluorocarbons:
https://link.springer.com/article/10.1007/s10047-015-0835-z
https://www.nature.com/articles/s41598-020-73768-9

[Robotbeat]

We are born with fluid in our lungs.

It’ll be like being born again.

[Paul451]

We are born with fluid in our lungs.
It’ll be like being born again.

With blood and screaming.

[Genial Precis]

We are born with fluid in our lungs.

It’ll be like being born again.

I mean, that's kind of prescriptive. A fetus gets everything by blood, right? So that's at least one place to look for what you could do to:
1) Ensure tolerance of fluid in the lungs without needing them for gas exchange
2) Exchange gases by extracorporeal exchange with blood without pumping the recipient full of heparin

Biology is hard, so the amount that that prescription solves on its own is nil, but it's a place to look.

[Robotbeat]

We are born with fluid in our lungs.
It’ll be like being born again.

With blood and screaming.

No one said it’d be a picnic.