Upper Altitude Parachuting Survivability

Cafe Society
21

Thank you all for being so enthusiastic about this! Let me answer a few questions that I’ve seen pop up here to hopefully help guide the discussion.

This is not the hardest sci-fi out there. I already wrote an extremely hard sci-fi novel, and have as yet been unable to find a publisher, so this one I winged it and decided for “coolness.” There is antigravity technology, but more vehicle-sized than human implant size, and existing AI. The vehicle which will rescue our heroes is essentially an intelligent flying motorcycle. I had thought that, since I’ve seen parachutists make formations and clasp hands and such, that such a vehicle could get close enough for one person to reach out, take the handlebar, and pull themself onto the seat without causing too much turbulance. As for catching the second person, this hovercycle has a docking clamp, which it has learned to use to also pick things up. My initial idea was that the one person would get onto the flying skycycle, then swoop in, grab the other with the clamp, and barely manage to slow down/pull up so they don’t slam into the ground (and then immediately acquire medical assistance).

Definitely below the Karman line or even the real edge of space. Part of what I’m trying to ascertain here is what a reasonable height would be. I know I’ve read of a case where a woman who was sucked out of a plane at 30,000 feet who survived, no suit or even parachute, so that could be a good baseline altitude, but I’d like to press it as high as I could reasonably go.

The current plan is that the vehicle is intelligent and very loyal to the main character, and when the main character gets sucked out into the air, it goes after him to save him.

It looks like the problems I need to overcome include the pressure, lack of oxygen, and control of the flat spin.

For the pressure, would some sort of skin suit work? I could imagine that a space marine would wear a form-fitting skinsuit as part of their main uniform, especially if they work in areas where depressurization is a distinct possibility. The suit would offer freedom of movement, but then might tighten when it detects low pressure, to compensate. Sound silly, or viable?

The oxygen, I can easily have the space marine carry some small device, a pressure bottle of emergency oxygen, for the same reason as the skinsuit.

The flat spin is harder. I saw Baumgartner went into a spin, but then recovered. Is that something that experienced HALO jumpers can do when they reach lower atmosphere? How would one do that?

And how would someone survive without this, or what injuries would they suffer? I’m assuming a successful catch without the crushing impact. Embolisms were mentioned, but I know those are not immediately lethal. Would a high-altitude embolism go away as the faller entered denser lower-atmosphere air?

22

The problem isn’t just holding one’s breath; it is also that the ambient pressure is so much lower that it will cause the unprotected jumper to become uncoordinated and then lose consciousness. I can personally hold my breath for over four minutes, which is unexceptional by freediving standards, but that is at ambient pressure or higher (when underwater). If you experience sudden decompression, you actually want to exhale to eliminate the pressure in the lungs and sinuses lest they rupture; the oxygen still in the blood can maintain adequate perfusion for at least five minutes before start of nervous tissue damage, and longer if the blood is supersaturated with oxygen, but the loss of pressure will cause a reduction in diastolic pressure (the pressure in between heartbeats) regardless of how hard the heart pumps that will result in a limit of useful consciousness. The time of useful consciousness is 6 to 9 seconds above 50 kft.

As for temperature, the real problem is that the low density of the atmosphere at high altitude will cause all liquids to rapidly evaporate, resulting in fast cooling (the same phenomenon that causes airplanes to ice up). The body is not a particularly efficient radiator of heat so the core temperature will remain stable for the short duration of flight, but you can expect frostbite of exposed dermis and potentially freezing of eyes and mucus membranes as well as rupture of blood vessels near the surface. It isn’t as dramatic as the explosive decompression sometimes portrayed in science-horror movies like Event Horizon, but it certainly isn’t pleasant.

In HALO and HAHO jumping, the jumper pre-breathes pure oxygen for 30-40 minutes to reduce nitrogen concentration and increase oxygen saturation as well as carrying a breathing bottle. On exiting the plan, the jumper has to maintain a fairly rigid body position to avoid spinning in comparison to jumping from standard recreational heights where a jumper can wave arms and do other acrobatics. For HAHO the canopy is deployed at high altitude, which can impart sharp opening impulse due to the rapid descent speed cat high altitude and corresponding high dynamic pressure, often requiring a reefing stage. For HALO, the jumper falls to a much lower altitude–sometimes as low as under 1500 ft–before deploying the canopy, but because of the greater drag the terminal speed is much lower and they deploy as normal.

A gas embolism is not immediately life threatening itself as it will resolve as soon as pressure increases but can result in thrombus or loose tissue embolism (usually fat or plaque) which can be debilitating and rapidly fatal. Since the people who do HALO and HAHO jumps are generally younger and in excellent physical condition and are medically evaluated it isn’t such a concern as it would be with the general population, but it is possible for anyone to have an latent condition that can lead to a fatal embolism. Other injuries are as described above, in addition to whatever trauma or injury might occur in the capture operation.

Stranger

23

The blood stops moving?

24

Since the two people getting sucked out are an active space marine and an athletic warrior emperor, that should reduce the threat of a thrombus or loose tissue embolism.

25

No, diastolic pressure drops, resulting in a lack of adequate oxygen perfusion. The brain is particularly sensitive to drop in perfusion which is why a correctly applied sleeper hold can cause someone to pass out in seconds even though a typical adult can hold their breath of several minutes with training.

Stranger

26

Ah. So I started wondering if adopting a head-down posture would solve the pressure problem (I think it would). Then realized – you’re in free fall. There is no “down”.

27

Once you get to terminal velocity (or even reasonably close to it), there is a “down”.

28

You may be thinking of Vesna_Vulović, but she was inside part of a damaged plane which fell from 33,000 feet, and the remnants of the fuselage probably protected her from the impact. The highest survived real free-fall was probably Ivan Chisov or Alan Magee. (The latter gets bonus points for the extremely cinematic end of his fall, in which he crashed through the glass roof of a railway station.)

29

Little bit of useful info here:

I’ll do something more substantive tomorrow now that we have a few parameters to work with.

30

After ~10 seconds. Too late according to the table cited above.

But it’s a possibility.
(1) The system normally maintains enough pressure to pump blood to your head. At ground level you can maintain a greater pressure by inverting your posture.
(2) Outer space is only a short distance away. Gravity is still around the same value.
(3) Total unconsciousness takes longer than the ~10 seconds cited above, and perhaps you could learn to maintain a head-down posture while in free-fall and drifting out of consciousness. And brain use of oxygen is variable: perhaps some people are better at remaining mentally calm while falling out of a sub-space aircraft.
(4) Although the internet reports that it takes around 14 seconds to reach terminal velocity, I don’t know how long it takes until acceleration is slow enough that gravitational force on (essentially) a 6’ column of water will be enough to maintain perfusion (itself something I’ve never considered before)

31

Maintaining a straight head down position in skydiving is actually pretty difficult; it results in increased speed (since there is lower aspect and therefore less total drag) and a tendency to tumble. Imagine trying to do a handstand while jumping onto a wall and you get some idea of the proprioception required. Skydivers instead tend to arch and streamline which prevents going tumbling through controlled drag on the legs. A trained gymnast or professional high diver might be able to manage it in lower atmosphere, but even most athletic people would find it difficult to the that coordinated, and at upper atmosphere with almost no aeroelastic forces to act upon (not to mention just the difficulty of maintaining orientation in a freefall environment) I don’t think it would be feasible.

The “brain use of oxygen” is not variable; the amount of oxygen that neurons and other critical tissues need to function metabolically has a very well defined threshold. What is variable is the amount of oxygen different people carry in their blood; very aerobically fit people will have more red blood cells and oxygenation capacity, and will probably have a smaller difference between systolic and diastolic pressure, which means a drop in external pressure will have less of an immediate effect. However, the loss of pressure will still result in overall reduced diastolic pressure (regardless of how efficient or powerful the heart is) and it is that loss of pressure that results in interruption of oxygen perfusion. In short, it doesn’t matter how fit you are; loss of blood pressure to the brain will cause rapid onset of confusion and unconsciousness (hypoxia) in seconds, followed in minutes by the necrosis of necrosis of brain tissue (brain damage and death).

The idea of the characters wearing some kind of advanced emergency partial pressure undersuit combined with some means of providing oxygen (perhaps a compressed supply, or even an artificial organ connected to the circulatory system which provides supplemental oxygen) is probably the best way to address this. Being collected by a pursuing rescue ship mid-fall still remains a difficult problem to resolve but given enough handwavium and a willingness to ignore the practical issues of aerodynamic interactions may be sufficient. Or, you could have the characters carrying some miniaturized nanotech version of MOOSE that automagically deploys.

Stranger

32

Would a wetsuit help? It would provide some compression as well as thermal insulation.

Brian

33

Even 7mm thick wetsuit, as constricting as it feels, doesn’t really provide that much compression, and the insulation value is pretty good but wetsuits work in water by using body heat to warm the layer of water near the skin and then insulating that against the outside ocean water. For an altitude suit, you’d want an impermeable outer layer that wind could not cut through and then a compression undersuit that is fitted or laced tight to prevent expansion of the body tissues in event of a loss of pressure. Depending on application, you may have insulating and active thermal management layers in-between. Here is the description of the Shuttle Launch Escape Suit (LES), which was based on the Air Force CSU-4/P partial pressure suit used in numerous high altitude flight applications including the Kittinger in USAF stratosphere jump.

Stranger

34

Neuroimaging - Wikipedia

" Functional magnetic resonance imaging (fMRI) and arterial spin labeling (ASL) relies on the paramagnetic properties of oxygenated and deoxygenated hemoglobin to see images of changing blood flow in the brain associated with neural activity. This allows images to be generated that reflect which brain structures are activated (and how) during the performance of different tasks or at resting state."

35

I’m not clear on the point you are trying to make but the degree of oxygen perfusion and the corresponding metabolic function of neural tissue is as well characterized as anything in functional neuroscience. Without sufficient regular delivery of oxygen to neurons, the necessary cellular metabolism for useful consciousness cannot be maintained, irrespective of the physical conditioning of the subject. The subject can be a couch potato or an Olympic athlete but less than ten seconds of significantly reduced perfusion would result in disorientation and unconsciousness.

Stranger

36

The point is that oxygen use in the brain is variable. It is a well-known variable: visualization has been done for decades.

I’m not trying to make any point about the value of this variation: I just mentioned it as one of the possible variables.

37

What is being viewed with functional magnetic resonance imaging (fMRI) and arterial spin labeling (ASL) is looking at where the brain is most active, i.e. where neurons are undergoing the highest rates of metabolic activity and corresponding rate of action potentiation; in essence, the discharging of neural impulses across the axon membrane. That does not mean that there is wide variability in the threshold of perfusion of oxygen to individual neurons to maintain cognitive functions, and in fact there pretty well defined minimal thresholds of metabolic activity to achieve neuron potentiation.

The problem of maintaining (useful) consciousness at elevated atmosphere is not the availability of oxygen in the bloodstream, but the ability of hemoglobin to bind oxygen molecules and deliver them to the individual cells, which requires the average blood pressure to remain above a minimum threshold. At a partial pressure of oxygen (PO2) of below 70 mmHg ambient, people become hypoxic (oxygen saturation of red blood cells falls below 90%) and below 30 mmHg ambient, oxygen saturation drops off precipitously and well below levels to maintain cellular metabolism; see Figure 20.20.

How quickly this affects the individual depends on some extent how powerful and efficient their cardiovascular system is, but as external pressure drops below the necessary mean blood pressure threshold of ~50 mmHg to bind oxygen and deliver it to tissues, it becomes impossible for both the alveoli to exchange gases (even supplied with pure oxygen at ambient pressure), and for red blood cells to maintain a concentration gradient at the cell membrane to facilitate the passive diffusion of oxygen molecules to neurons. Some cells are pretty tolerant to oxygen deprivation because they can shut down for an extended duration without affecting gross body function, but neurons in general, and particularly the metabolically active neurons of the cerebral cortex, require a constant supply of oxygen molecules (and to be able to exchange waste CO2 back out to the bloodstream) in order to function. An interruption of supply, whether because there is no oxygen coming into the blood supply, because red blood cells are saturated with CO or some other contaminant, or because the average blood pressure is not high enough to achieve the threshold for diffusion of oxygen through the cell membrane causes neurons to stop potentiating within seconds, and to begin destructive catabolism within minutes.

In short, a 6 to 9 second Time of Useful Consciousness is not something that can be physically trained to improve, or is highly variable between individuals, or anything of that nature. It is driven by fundamental cellular metabolism and passive gas diffusion through the cell membrane that requires a minimum pressure.

Stranger

38

What is being measured is typically oxygenation.

I’ve never claimed anything about threshold of perfusion: as I’ve said above, I’d never considered it before.

Since active areas of the brain use more oxygen, there will be more perfusion, but that’s a result, not a cause.

39

It could be worth looking into the story of Ewa Wiśnierska as well - she was a paraglider who was sucked up into a cumulonimbus cloud and survived being at ~32,000 ft elevation, according to her GPS. However, I believe in this case she was suspended at the extreme altitude for ~40 minutes, according to this page, so it won’t necessarily be applicable to a case where your characters are just falling through the upper atmosphere.

40

She survived in large part because the tail section she was in corkscrewed, instead of falling straight down.