I am trying to figure out what kind of liquid, if any, can be used to severely impede or slow human motion without killing or severely damaging their bodies (IE if after being submerged in this liquid they need to spend a long time in the hospital, or are permanently disabled in some way.) Experiencing pain or minor side effects is acceptable, however. I am planning on using this fluid for the following while piloting a mech-type vehicle of approximately 13 feet tall, similar in design to the method-2:

  • Shock Absorption, such that the pilot does not become incapacitated and sustains minimal injury in the event of a crash.
  • Movement Impairment, such that a pilots movements are impaired or prevented in some way by the liquid that does not induce paralysis.
  • Bonus: Nutrition, such that the pilot can use the fluid to satisfy his/her basic nutritional requirements by consuming some amount of it (they don't have to like it though). This is, however, an optional point.

A response to some comments I anticipate getting, in the hopes of being more clear for everyone:

Why do you need to stop the pilot from moving?

The way I envision it, the pilot must be kept relatively still in the sitting position, and would have a specialized suit that utilizes technology similar to this to move the robot. More moving parts means more things that can go wrong, and I figure a setup like you see in pacific rim has significantly more moving parts than some sensors, a filtration system to keep the liquid clean, etc. on the inside of the cockpit.

What you are describing is not possible with current or near future technology!

This is not intended to be near future, and I am basing it on technology that exists today to keep it at least loosely based on science, so please feel free to use more futuristic versions of modern or near future technology.

There are more effective ways of keeping your pilot still/protecting them from crashes/etc.

By all means please share any alternative ideas that accomplish the same goals with these constraints, however please also keep in mind the cost of the idea. Regardless, thank you for your enthusiasm, it is greatly appreciated.

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    A liquid is probably the worst shock absorber you can pick, With no compressibility it will just transmit shocks not absorb them. – John Apr 16 at 21:07
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    If you want a liquid that can “feed” your pilot - I assume for long missions - you’re also going to have to deal with the pilots’ excrement and urine. And have systems that work for men and women. – Richard Cosgrove Apr 16 at 23:26
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    A womb, amniotic fluid and an umbilical cord... :) – RonJohn Apr 16 at 23:35
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    Also, how does your pilot see? – RonJohn Apr 16 at 23:36
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    As far as I understand, any kind of "shock absorption" surrounding a pilot could only really distribute a shock rather than actually absorb it. That means it would work nicely against impacts like bullet shots, but achieve very little against full-on crashes, for the same reason plane crashes are seldom survivable. It depends on how fast your mech is going, but eventually deceleration will just tear apart the pilot's blood vessels on impact. – Siguza Apr 17 at 0:36

13 Answers 13

Edible water bubbles.

edible water bubbles https://www.boredpanda.com/edible-water-bubble-skipping-rocks-lab/

The bubbles, called the Ooho!, are created by encasing a blob of drinking water within an edible membrane made from a natural seaweed extract. Nothing goes to waste, and the product will fully biodegrade in 4-6 weeks if left unconsumed.

Your pilot is encased in these bubbles. He can move but the bubbles get in the way. He breathes through a nose mask with an air supply and has a VR visor on. If he opens his mouth he can eat the bubbles in front of him: the gel has some protein and carbs and the inside is water with electrolytes. Some of these bubbles might have been in the cockpit for quite a while and might taste like prior pilots.

On impact, each bubble resists slightly before breaking, in aggregate absorbing the kinetic energy. Released water drains thru the intact bubbles down to the floor. Slow movement of the pilot displaces the bubbles gently without breaking them.

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    @RonJohn: some of the bubbles are full of butter. – Willk Apr 17 at 1:51
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    I've heard of armies marching on their stomachs but this is ridiculous – Pingcode Apr 17 at 4:21
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    The air between them (spheres don't fully fill space - they don't tessellate) would also help dampen the impact, as they squeeze to fill that space. – Baldrickk Apr 17 at 7:57
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    Bonuses if you fill some bubbles with various drugs to help the pilot. Need to stay awake? The blue bubbles are full of caffeine and amphetamines. Injured? Red bubbles contain morphine. Allergic to butter? Green have concentrated antihistamines. Just make sure not to swallow anything if the bubbles burst... – Joe Bloggs Apr 17 at 8:54
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    +1 even before I read "Some of these bubbles might have been in the cockpit for quite a while and might taste like prior pilots." – arboviral Apr 17 at 13:46

The current answers (other than Willk's) have a perspective issue: they offer suggestions of things that might be good at stopping things from outside the surface getting to the pilot. But crash protection is the opposite of this: you are trying to stop things inside from hitting anything at dangerous velocities. And corn starch type solutions are kind of optimally awful at this: the momentum of the pilot's body during a crash will attempt to carry him forward into the suspension, which then naturally responds as a near-solid. Making your pilot instantly smash into a de facto concrete wall is not going to help.

Crash protection is about dissipating momentum outwards and away from the person(s). Watch modern car racing, for example, and see what happens in a crash: parts go flying everywhere. This is actually exploited as a safety feature: when tires, doors, spoilers, etc. all go flying off they carry away momentum. The parts with the human in them will correspondingly have less momentum and so said human is now in less danger (but not insignificant amounts; that's why they have the very rigid, very not-going-to-fly-away roll cage, for example).

Any fluid suspension system that's going to serve as a crash protection system is going to have to allow that fluid to be shed: it's going to need to squirt or outright explode its own fluid out at sufficient rate to prevent the aforementioned insta-brick-wall disaster. And that's going to be hard, as there's no guarantee that the outer layers being free to move out is sufficient to stop the inner layers from forming a de facto wall-of-death. Indeed, the proposed nature of the fluid makes this highly unlikely: if it was already capable of transmitting forces throughout its body quickly and uniformly, it wouldn't ever act in this "rigid" fashion.

Any system you design that's based on a "make the pilot not go anywhere" principle is, of necessity, going to mean "pilot dies instantly in a crash". You need a system that assumes he'll be moving, allows him to move, and does what it can to dissipate momentum and energy away from the pilot sufficiently fast to offer a meaningful chance of survival (if you're hitting the ground at 200 mph, you're pretty much just as dead as if it was at 400mph). So what you're looking for is a racing car in mech form. A Transformer that easily falls apart would be ideal.

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    This. What kills you is not your just your skull hitting the obstacle, it's also your brain hitting the inside of your skull (more complicated than this but that's the insight you need). – Ben Apr 17 at 8:15
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    Ooblecking the human in means they are braced for any impact, which prevents bouncing and flailing injuries. Plenty of people survive high g maneuvers pressed into non-dissipative nylon straps. Dissipation is only required when you get past what the internals of a human can take which be a lot for short times. – user25818 Apr 17 at 20:47
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    The main problem is acceleration or rather decelleration. Dissipating momentum is quite easy. The problem is actually doing it slowly enough. "It's not the fall that kills, it's the impact" is mostly true because the ground doesn't move (or doesn't move far enough) when you impact it. You will shed all your momentum but in way too little time. That's why car airbags deflate when you hit them and why you still need to wear a seatbelt. The deflation is so that you are decelerated more gently than when hitting the rigid steering wheel. – Adwaenyth Apr 19 at 9:20

Here's an excellent description of the deceleration problem (keeping pilots alive in the case of a crash) on Aviation Stack Exchange: https://aviation.stackexchange.com/questions/16545/even-after-years-of-research-why-are-planes-unable-to-keep-passengers-alive-in/16553#16553

In summary, the goal is to gently slow you down, but this requires distance to work in, which isn't generally possible once you exceed a speed of around 80-100km/hr unless you have an extraordinarily large vehicle. No amount of liquid, foam or cornstarch can change the fundamental problem of reducing velocity to zero with a bounded survivable deceleration needs space to work in, in fact many of these options will make it worse.

Of course, in SciFi, you just introduce an "inertial damper" or some other technomagic and avoid the whole problem using whatever medium best suits your story.

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    Where a fluid would come in handy is for those quick strikes (like artillery) where you have a massive force for a very short time. A compressible fluid (more like a really thick gas than a liquid) would help translate these shocks into something survivable. The trick is to be the exact opposite of cornstarch - typically rigid in the low-force zones and then spongy as the force gets higher. – throx Apr 17 at 2:46
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    @user49634 can't speak for mecha crashes, but being hit by a car at 30mph is fatal in ~20% of occasions. At 40 it goes to 80%. Above that? yeah, we are not built for rigid body collisions with that much energy. – Baldrickk Apr 17 at 8:00
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    @throx If you want non-Newtonian fluid that's opposite to water-starch mix, you're talking about mayo : ) Solid enough to stand on it's own, flows under stress. – Agent_L Apr 17 at 14:47
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    Ok, embedding a mecha pilot in a bath if mayonnaise is a whole novel on its own. That's all kinds of awesome. – throx Apr 18 at 9:35
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    @thanby What happens in mech, stays in mech. – Agent_L Apr 18 at 15:30

Corn starch suspended in water could do the trick for you.

When mixed with a fluid, cornstarch can rearrange itself into a non-Newtonian fluid. For example, adding water transforms cornstarch into a material commonly known as Oobleck while adding oil transforms cornstarch into a Electrorheological fluid. The concept can be explained through the mixture termed "cornflour slime".

As for what a non-newtonian fluid is:

A non-Newtonian fluid is a fluid that does not follow Newton's Law of Viscosity.

In the specific case of corn starch, the last link says that it is "shear thickening", and "Apparent viscosity increases with increased stress". In practice: solid things can only move very slowly in it. The faster something moves, the more the suspension resists the movement.

You can search for some videos in Youtube. Some people have enough sense of humour to fill swimming pools with this suspension. The end result being a whitish mass which you can walk on, and even ride a bicycle or motorcycle on. The liquid resists you getting inside it due to the speed of your feet or wheels.

Dance like there is no tomorrow!

But if you stand still over it you will slowly sink, and pulling you out will require some considerable force.

Stuck

The worst damage being pulled out of it might cause is some minor depilation. Unless your friends are idiotic/drunk enough to try to pull you out by tying you to a car, in which case you might end up starring in the Darwin Awards (if only with for a honorable mention).

Your pilots will need some life support gear for their heads. Corn starch will not allow for breathing. It might help with the nutrition part, though.

The fluid would protect the pilot against blasts (the energy of the blast will be captured by the corn starch, which will temporarily harden). In case of breah, the pilot should also be protected against shrapnel.

Edit: to all who are saying that this would kill the pilot: if the pilot is naked within the fluid, then yes, you are right. I think the question has this as a premise, since OP would like the pilot to breath the fluid. I propose a solution for the sudden deceleration death problem - the pilot needs to wear a suit akin to that of a jet fighter pilot. Some models are even filled with a fluid to help cope with extreme acceleration and deceleration. That would mix the best of both worlds - protection against deceleration from the suit, and protection against blasts and shrapnel from the starch.

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    @Shalvenay, even in a perfluorocarbon base, it'd probably be far too thick to breathe. – Eiríkr Útlendi Apr 16 at 23:00
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    I think this can do with some more explicit verification. It's not immediately clear to me what kind of forces are experienced in the middle of the suspension when the surface is subjected to sufficient force. I would also expect this to go over very badly in a crash scenario, violently violating the OP's desire for this to be a defense against crashes. The person's momentum will carry them forward into the resisting suspension, so they will effectively be smashed into a concrete wall instantly. – zibadawa timmy Apr 17 at 1:06
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    How does it being a nonnewtonian fluid help? I've seen this used in egg-drop (The egg did not survive) . "On impact the Oobleck becomes like concrete", Problem as I see it, is now your pilot might as well be hitting concrete. This trick to making crash safe vehicles is to maximize the amount of time deceleration takes -- which is why having padding (or a spring) works, the pilot does not have to come to a sudden halt. Maybe Ooblek to immobilize the limbs/neck, combined with some other solution to maximizes deceleration time would work. But on its own is the opposite of what you want – Lyndon White Apr 17 at 3:41
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    -1. This will kill your pilot. – Pyritie Apr 17 at 12:27
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    I have a non-newtonian fluid based back protector - As far as I can see nails on all the criteria - I have almost full range of movement (much better than the old plate based ones). As they are actually in use for motorcycle safety gear, snow sports safety gear, martial arts safety gear a larger suspension of it for greater speeds seems logical. Not sure the non-newtonian is still corn starch based - maybe I should try eating it and let you know... – Collett89 Apr 17 at 14:03

Liquids like water compress very little, if at all. This makes them generally a poor choice for a shock absorber. Suspend a pilot in a sphere of water and strike that water with a stick and the impact will propagate through to the pilot relatively undissipated.

There's one thing that liquids are very good at doing, though: moving around. Use this to your advantage. The liquid doesn't absorb impacts directly. Instead, applying a impact force to the liquid causes some of the liquid to flow into an alternate container where a more traditional shock absorber is located. This is how a water hammer arrestor in a building works. Sudden spikes in water pressure can damage plumbing fixtures, so the arrestor provides a low-resistance path for water to take where the extra kinetic energy is absorbed by a spring, air piston, or gravity. The plumbing fixture still feels some of the force, but at a greatly reduced magnitude.

Your fictional vehicle can use whatever sort of dampening devices you want to use. Suspending the pilot in a fluid allows the fluid to transmit the force of an impact to the dampeners regardless of what direction the impact came from (you'd essentially be the piston in a giant hydraulic shock absorber). The contraption would convert bursty impact forces into weaker forces applied over a longer period of time, but with the side effect that the pilot would likely experience a lot of motion. Big impacts become survivable, but potentially disorienting or nausea-inducing. Solving these problems is left up to whatever sort of suit/gear you want to give the pilot.

Just water will suffice right? It slows movement, absorbs kinetic energy and also heat in case of heat-based weapons.

One big problem would be how shocks propagate through water. If a grenade blows under water and you are nearby the shockwave will rip your lungs apart. This is because water doesnt compress very well. So another liquid, something like a non-newtonian fluid that solidifies upon a shock: http://www.snf.ch/en/researchinFocus/newsroom/Pages/news-171108-press-release-liquid-shock-absorbers.aspx

Not only will it absorb energy upon impact, it will protect the wearer from possible injury should spalling or similar occur.

Magnetorheological fluid

Another solution would be the use a magnetorheological fluid. A complicated name to describe a fluid whose viscosity is influenced by magnetic field. This kind of fluid is used in “magnetorheological damper” which are highly appreciated in automotive (mainly for very expensive cars suspensions) for their very good shock absorbance.

What I can imagine is a complex set of electromagnets surrounding a sort of tank in which your pilot is floating. The way magnets are disposed leads the viscosity gradient of the magnetorheological fluid to “adopt the shape” of a seat. Electromagnets adjust their power in reaction to extern stimulus so the seat shape is always conserved.

EDIT :

As @Ruadhan2300 suggested it in comments, an easier and more realistic way to achieve OP’s goal is to opt for a spherical tank. Then to makes the fluid adopts a viscosity gradient from water-like in the center to solid-like in the border. The pilot now floats in the middle of the tank and is prevented from crashing against the border by this responsive viscosity gradient.

The only cons I see here is that your pilot have to wear a suit (I not sure that these kind of fluid is good for health).

  • To expand on this idea, in a crash or sudden deceleration you could have kinetic dynamos which generate the fields in such a way that the fluid forms a thickness gradient from the relatively water-like middle where the pilot is to a near solid at the outer bounds. Essentially wrapping the pilot in a massive cushion. – Ruadhan Apr 17 at 11:37

The solution can be a ROTATING SPHERE filled with a highly VISCOUS liquid.

enter image description here

Two of the above answers pointed out the effects of deceleration to human body. But they assume linear motion. If the impacting object is rotating instead, a much fewer portion of the impact energy is absorbed, most of it being used to further rotate the object.

from https://en.wikipedia.org/wiki/Parachute_landing_fall:

A parachute landing fall (PLF) is a safety technique that allows a parachutist to land safely and without injury. The technique is used to displace the energy of the body contacting the earth at high speeds. The parachutist ideally lands facing the direction of travel [...] while rotating toward the side (generally the direction with the dominant directional speed). When executed properly, this technique is capable of allowing a parachutist to survive uninjured during landing speeds that would otherwise cause severe injury or even death.

The second aspect is related to the viscosity of the fluid. The more viscous a fluid is, the more inertia there is between the contacting layers of the liquid, when it comes to motion. When an outer part of a liquid is put into motion (ex: wind generating waves, making them move), all the bottom layers of the liquid are also put into motion, but at more and more reduced speeds. The rate by which the speeds are slowed down is proportional to the viscosity.

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

Viscosity is a property of the fluid which opposes the relative motion between the two surfaces of the fluid that are moving at different velocities.

enter image description here

In the case of a sphere filled with viscous liquid, the liquid layer next to the sphere walls will have almost the same speed (rotational speed) as the sphere. The inner layers will have gradually lower speeds. The more viscous the fluid is, the lower the rotational speed of the liquid will be, towards the center of the sphere.

You will need to place your human in the center of the sphere. Perhaps a system of inner spheres, all having liquid between them, will be even better. The external most sphere will obviously not be rotating, as it will be fixed firmly to the vehicle.

According to http://www.vp-scientific.com/Viscosity_Tables.htm , various flavors of motor oil seem pretty good candidates for your liquid.

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    Unless you're talking about the pilot inside the sphere(s) spinning along with it, you're still talking about a linear stop. The pilot is travelling linearly and has to come to rest, no matter what fancy spinning stuff you put around him. – throx Apr 19 at 11:46
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    i did mean the pilot spinning inside. that's why i gave the example with the parachutists rolling at landing; actually, the pilot's outer sphere doesn't have to be spinning all the time, but only before the impact, so that the impact moment will catch the sphere already rotating; thus the impact will make the sphere rotate even more – Newton fan 01 Apr 19 at 15:18
  • I'm not sure a pilot spinning at a high enough velocity to spread an impact more smoothly on his body would help him pilot a mech much? – throx Apr 20 at 9:32

There are a lot of shock-absorbing gels in use today that harden on impact. Some are being developed for use as body armour. My smartphone’s case even has some gel in it. As far as I’m aware these are different to non-Newtonian fluids.

For your scenario, a form of this gel (or layers of different gels) could be used for body armour: the outer layers harden and deeper layers distribute shockwaves: like layers of Kevlar. And future scientists can find a way for them to revert to gel after an impact, so they’re reusable.

Also, today there is a liquids that humans could breath: perfluorocarbon (referred to in a comment). It has been tested successfully on mice. If your pilot was a pool of that, contained in gel, it would reduce the mechanics required for the pilot’s cockpit: they’d just be floating in liquid surrounded by the gels. The pilot could use VR goggles for their interface display.

This liquid is used for breathing, so couldn’t help with nutrition though.

I dont think it's a good technology, because most liquids weigh a lot (about 1ml = 1g): imagine you just have a half cubic metre of a liquid - that would be 500 litres, with a weight of half a tonne.

Also crashes with small airplanes are far more survivable - there are videos of small airplanes crashing into the woods and the pilot surviving just fine; I don't think we will ever be able to save a pilot from a 200km/h crash with an 100+ ton vehicle. (and 200km/h and 100 tons are a pretty lucky outcome for commercial flight planes)

But when you think out of the box, and forget the liquid, an airbag is doing exactly this, without a fluid.

  • Air is a Newtonian Fluid (approximately). – Shufflepants Apr 17 at 18:26

Some theoretical thoughts:

you can survive unharmed forces of up to 30g for very short time and about 10g sustained over some seconds.

You stated elsewhere that your maximum expected velocity is about 50 mph so about 80km/h.

When we take these maximums into account, you need at least 80 cm of deceleration space to reduce your 22m/s to 0, even if you accept a 30g shock for about 0.7 seconds (which is a bit much, but maybe some future technology and special training can help).


We can assume that your Mech will have some external buffer-zones that help with deceleration, so you probably don´t need all of that deceleration space around you.

What I could imagine is some form of foam, that dissolves rather quickly and is reproduced by the vehicle constantly. The pilot would probably need some form of suspension straps to keep himself in the middle of that. The foam could be edible - breathing is still a concern though, even if the bubbles would carry oxygen, the co2 would have to go somewhere.

You´d probably still need some kind of egg-shaped capsule of at least 1.5x2.5 meters to keep your squishy human alive.

It will need a Gyroscopic effect and dissipate the vehicle momentum by changing the vector component of the forces. That will keep the human condition a constant. Engine thrust can also be modified to intentionally generate oblique shocks in a safe manner to dissipate energy. There needs to be a mechanism for this. This will be the second layer of protection. This will be expensive today.

As you indicated not near future. You want to use a liquid. This is what I would envision.

  • Human body is floating inside liquid - In a neutral buoyancy state.

  • Build a crude "inertial dampener" by basically putting the human inside a liquid filled capacitor - which is also the liquid the human "floats" in.

  • The liquid plays the role of a dielectric that is much stronger than air to reduce electric arcing due to the high voltages required to build up the required static charges.

  • Because of the extremely high voltages required, maybe the high voltages need to be pulsed and only turned on when injury is imminent.

  • Any mechanical forces that cause motion on the charged plates would be transferred via the electric field to every part of the human at approx the speed of light, making the complete human act like a rigid body that is part of the charge source/plate, while other forces would take around the order of the speed of sound to propogate incase the forces are causing catastrophic damage to the mech and destroying the inertial dampener.

Human damage may be caused by:

  • Toxicity of absorbing the liquid through the skin.

  • The high electric fields the body is exposed to.

  • Potentially being electrocuted if the dielectric breaks down or not have enough dielectric between plate and human)

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