In the vein of the Expanse's juice or the Forever War's submergible tanks, what types of body or cockpit modifications would allow a human to survive high G maneuvers in short impulses in a combat setting? Note in this case I am not looking for major coverage in the vertical (+/- Y axis), rather the lateral planes.

Some context. My mech pilots are basically flying glorified hover tanks that can rocket around quickly. If you've ever played the later Armored Core games, you'll know what I'm talking about. Maneuvering is handled by a series of short high impulse/high G rockets. General movement is a much softer powered flight of sorts, the main takeaway is that the "legs" of the mech never touch the ground in a combat or self-powered transport mode. That said, no one is going to be straight line accelerating at high G for more than a minute at most, such a maneuver would essentially be teetering on the edge of death and not a tactic taught or routinely employed at all. These quick maneuvers happen when an opponent has closed in very close. Engagements don't typically last more than five minutes at max. Rapid direction/vector changing does happen during these moments. Essentially the mechs are zipping around each other like ice skaters.

Some tech level surrounding the pilots/world:

  1. Early cybernetics. Signals from the brain passed into a microchip can allow prosthetics to move in certain predictable ways for daily and limited combat use.
  2. Based on the type of person/ how they were born, their organs, limbs, nerves etc can be regrown with exception of the brain. Decent amount of stem cell research in this world.
  3. The mechs/tanks in general aren't using composite armor all that much for defense. The first layer of defense is essentially a particle shield that slows or disintegrate parts of an incoming warhead. The second layer of defense is copious amounts of explosive reactive armor to defeat stripped/heavily damaged warheads that brute forced their way through the shield. Lastly some mechs/tanks might have a final layer of composite armor. Though there's decent numbers that have just structural metal under ERA blocks.
  4. Low level gene editing.
  5. Advanced recoil dampening systems for weapon systems on all levels. From the lowly rifle up to tank/mech guns.
  6. High impulse thrusters that don't melt or crack under repeated use (near future material science).
  7. A system in place that allows a person or pilot to be flooded with fluids at various points in their body. Requires multiple small tubes throughout the body. System isn't experimental and is routinely used in emergency medical situations.
  8. Virtual prosthesis/bionic eyes. Sight is nearsighted only, however. Significant drop off past a few meters. Good picture quality, however.
  9. Advanced cameras,optics,sensors etc. Pilots, tankers, mech pilots, ship captains etc don't need the use of windows or clear material for navigation. Cameras and visual image stitching has allowed fighter pilots in particular to fly with completely enclosed and more aerodynamically suited cockpits. Basically no one is using glass/clear material for navigation anymore for combat. The screens that are used are optimized for long term visual use and are detailed enough to capture very small detail. Added benefits of image processing are baked in such as zooming in, different encoding/color options etc.

Body modifications can start at or even before birth.


The maneuvering thrusters aren't constantly firing off in a certain direction like a rocket engine, rather there is a massive burst of thrust in a short amount of time. Time could range from less than up to a second and a half. The mechs make heavy use of momentum to "skate" across the battlefield. Thrusters can be toggled/chained to a very limited degree in the same direction at a high thrust output, they however can use a much lower impulse over a longer period of time to essentially glide much more smoothly. In this mode its more akin to general movement than heavy combat maneuvers, it's the equivalent of a fighter jet cruising to combat and then actually pulling high G maneuvers during combat. There's significant drag as well. It can be safely assured that the Mach barrier will not be crossed in sustained flight/chained maneuvers on a single vector.

For the purposes of this question, I am trying to find something that allows a pilot to survive high near instantaneous G forces/jerk.

  • $\begingroup$ Are you asking for body or cockpit modifications? Title says one thing, body another one. $\endgroup$
    – L.Dutch
    Commented Oct 6, 2022 at 10:13
  • $\begingroup$ @L.Dutch Technically it can be both. Based on some previous feedback, the specification of body or cockpit only made system-based answers bad answers which is something that I wanted. For example, something like "juice" from the expanse is a system since it relies on shipboard equipment but interacts with the body. The Forever War relies on shipboard systems but also the human body similarly. So, answers can be system based in that they rely on one part body or cockpit. But it's not necessary to involve both. $\endgroup$
    Commented Oct 6, 2022 at 10:17
  • $\begingroup$ You do know that one minute at 20G is close to orbital velocity, starting from a standstill -- right? $\endgroup$
    – Zeiss Ikon
    Commented Oct 6, 2022 at 11:12
  • $\begingroup$ @ZeissIkon It's more to illustrate the concept. The maneuvering thrusters are designed for fast movement. They fire off very quickly then shut off. They actual horizontal movement is done through momentum. Tere's significant drag and the mech slows down rapidly. For lore reasons, chaining the same thrusters over and over rapidly doesn't work. $\endgroup$
    Commented Oct 6, 2022 at 11:29
  • 3
    $\begingroup$ "The Mach barrier will not be crossed": Which means that if the maneuver takes 6 seconds or more the acceleration is less than 6 g, or if it takes 5 seconds or more the acceleration is less than 7 g, or if it takes 4 seconds of more the acceleration is less than 8 g. All those are survivable without any science-fiction device. Ah, and while the English alphabet has only 26 letters, the Physics alphabet has many more. In the Physics alphabet, G and g are different letters, meaning different things. $\endgroup$
    – AlexP
    Commented Oct 6, 2022 at 11:56

5 Answers 5


This is a fun question for a number of reasons, but I think the biggest reason is the wide range of G force limits depending on impulse duration. With impulses below 0.1s, the sitting human body can withstand up to 35 Gs in the forward direction, and 14Gs in the lateral directions. Now, obviously as we approach 1 minute impulses the limit drops to the subscribed 10Gs, but that’s a physical limit before extreme stress and 20ush Gs the limit before injury. It is likely though that the vehicles will never need to achieve so long an impulse. For each second of impulse at 10Gs, the vehicle is achieving nearly 100m/s velocity. In tactical combat terms, that is very fast. Considering your desire to have these vehicles moving with such constant change in direction, there will likely only be impulses in the range of 0.1 to 0.5 seconds. In this case, the vehicle could safely provide impulses up to 14G in the lateral planes, up to 20 in the forward direction.

Given this information, the real question of the pilot safety measure probably has less to do with the actual speed of the vehicle and more to do with the physical security of the pilot’s body and limbs. At these rates of acceleration, it would be pretty devastating to the body to have arms free to flail around, or head free to get rock violently from side to side. Even the strong human doesn’t have musculature or reactions to control their limbs in these conditions. It stands to reason, then, given the series of technological items you’ve provided, to leverage that tech to keep the pilot as safe as possible in the vehicle.

Cybernetic Controller

Since the user can send commands to the vehicle from their brain with electrical connections, it is not necessary to have the user operating the vehicle with hands or legs. Given this, during combat, the pilot should strap everything down and utilize the remote-control functionality. Normally, this would be problematic for sight-lines, but there are advanced imaging systems that would allow for a full 360 degree display to be pot up on a screen that only takes up the pilot’s static field of view. Alternatively, the orientation of the camera could also be controlled by the remote brain interface.


Blood Flow


One of the big issues with high-acceleration maneuvers is the tendency of blood to pool in unwanted parts of the body. While this is less of an issue in the lateral planes for a sitting human, it can’t hurt to account for it. You have already provided for fluid circulating apparatus effectively built into the human body itself, so take that a step further and use it to recirculate blood to where it needs to be in the event of a high-acceleration maneuver. Using the human-body interfaces and external bypass pumps, the blood flow can be regulated to stay consistent to the brain and the rest of the body regardless of velocity and acceleration. This would be hugely effective in increasing the tolerance of the human body to these kinds of high-thrust situations.


Another major issue to high-acceleration is breath control. The body will weigh X amount more in the opposed direction of acceleration when accelerating and this can impede proper breathing. At lower values of G this can be control with shallow breathing to both eject CO2 and allow room for air to enter the lungs. At higher values, this becomes more difficult. Using external masks/etc. and pumps to extract CO2 and push O2 through the nose and mouth would work. However, it may not be needed here, given that the pilot has access to blood recirculation tech. Using this, the external pumping apparatus could infuse oxygen directly into the bloodstream if O2 Saturation drops below a certain point. The effect of this system would again greatly extend the safe acceleration metric for a human body.

Impact and Bruising

Even using the most effective restraints can leave a human body vulnerable to the forces of impact that would be experienced due to such acceleration. The greatest source of impact will come from the restraints themselves as the body is jerked around. For most vehicles this sort of thing is reduced by a suspension. In the case of our pilot, a suspension should be used around the entire cockpit if at all possible to reduce the relative shock of sudden jerking movements. Given that most combat maneuvers should be relatively short, on the order of 0.5 second impulse or less, a suspension of the cockpit could be very effective. Some methods for achieving include using “floating” the cockpit in a water barrier, electromagnetic field, old-fashioned mechanical springs, the advanced recoil-reduction systems you've already set up, or all four. Since the imaging systems allow for the cockpit to be completely enclosed, there’s not a reason why the suspension system can’t fully encompass the cockpit and assist with all of this thrusting around and jerking.

Potential issues

Marrying all of these technologies would make for a very impressive system to reduce the stress and fatigue on a pilot of one of these vehicles. The biggest issue with a lot of these systems is their complexity and cost. High complexity would mean relatively high probability of malfunction, and cost would limit the throughput of these vehicles in production. We can avoid the malfunction issue somewhat with redundancies, but if we are basing the function of the combat on entirely electronic visual media, if we lose all the cameras or electrical systems or breach the cockpit, the vehicle is out. Of course, at that point, the pilot is likely also dead, so it may not matter.


You’ve already laid the foundation in your setup to provide for these support systems, and I think that merging them with these uses in mind will make for easy resolution to your issue.


If the pilot can be encased in a rigid capsule inside as little as a few centimeters of fluid at body density (i.e. barely denser than water), they can take 10 G or so at right angles to the spine for more than a minute at a time with no further modifications needed (in fact, with training, this is possible with common acceleration couches like those used in, for instance, the Mercury capsules of the early 1960s -- the early Mercury astronauts, flying suborbital on Redstone, took 8-9 G for a couple minutes during reentry and most remained conscious).

I would point out that if you can reach 10 G for a full minute (= 6 km/s less gravity and air drag losses), you have a suborbital spaceship, not a hovertank...

  • $\begingroup$ is air in the lungs the reason for 10 G limitation? I mean would a diver breathing gear with variable breathable gas mixture and pressure allow to tolerate higher G $\endgroup$
    – user35577
    Commented Oct 6, 2022 at 11:33
  • $\begingroup$ at some point there should be spaghettification issues due to turn radius relative to body dimensions too $\endgroup$
    – user35577
    Commented Oct 6, 2022 at 11:40
  • 2
    $\begingroup$ Spaghettification won't happen below the Stapp limits at least. One limitation for 10G duration is the fatigue factor of breathing, but there are others (blood pressure differential is a large part of why this works better "lying down" than "standing up" to begin with). $\endgroup$
    – Zeiss Ikon
    Commented Oct 6, 2022 at 11:43

I am assuming these maneuvers are very brief and made with minimal warning, like to dodge an incoming missile or whatever. In that case, there's not really any way to predict which direction the acceleration will be in. This means the trick space capsules use, where the crew lays almost supine, such that the G's pull toward their back instead of down, isn't feasible.

With this in mind, the most dangerous G's aren't high positive G's, they're negative G's. Instead of pulling blood out of the brain, negative G's push blood into the brain. Permanent damage is much more likely. Wikipedia says the limit is around 2 to 3 negative G's, limited by the strength of blood vessels. Pull too many negative G's, and you risk bursting them.

I have two ideas to remedy this, one cockpit-related one biology-related.

If the pilot sits in a little capsule attached to the rest of the mech via springs, the springs will take some of the acceleration, so long as it's brief. Might be enough to mean the difference between discomfort and an aneurysm.

If the pilot is genetically-modified to have stronger and/or more elastic blood vessels, he'll be able to handle higher negative G's before one bursts.


Head (Brain) in a Jar

enter image description here

You do not say it, but you seem to want something more extreme than the flight suits and chairs that fighter pilots use.

One problem with high G's is it makes blood rush away from the head and go somewhere else. To solve this simply shop off the head so there is no "somewhere else":

. . . the orientation of the camera could also be controlled by the remote brain interface.

nerves etc can be regrown with exception of the brain.

Rather than have their whole body in the robot, the pilot only puts their head or maybe just the brain in the robot. The head or brain has a life-support system that is much more robust than a puny human body. There is also a wire going into the brainstem and into the nervous system of the robot.

While the the pilot is piloting their body is kept alive. When the pilot is finished piloting their head or brain is reattached.

  • 1
    $\begingroup$ When too much or too little blood in the brain is the main problem you want to solve, then a less radical solution could be to implant valves in the blood vessels of the neck which control blood flow during high-g maneuvers. $\endgroup$
    – Philipp
    Commented Oct 7, 2022 at 13:45

The question to ask to decide what the maximum g-force a body can take is not the one you might expect. It is this.

What happens when you drop a wrench on a submarine?

A sub is very nearly neutral buoyancy. This means that with only the tiniest amount of work it can keep the same depth in water. However, the parts of a sub are not neutral because they are of widely varying density. An impact to the sub causes the denser objects to lag behind the rest and slam into the side of the sub.

So too the parts of a human. Bones in particular are denser than the remainder of a human. There are also other organs that are of different density. A concussion results because the brain is different density to the fluid it floats in. Thus an impact to the skull tends to cause the brain to move out-of-place, possibly resulting in serious harm.

You want a body with minimal differences in density. Starting with bones. You need to replace bones with structures of the same density as the rest of the body. Then, to get higher and higher acceptable g-force, you want to reduce the density differences to smaller and smaller values.

You want Kif Kroker. Kif does not have bones. He has a series of fluid filled bladders. In addition, he is pretty squishy. So put him in a form-fitting shell that will hold his normal shape. And give him a ventilation system that will let him breathe out rapidly when he is accelerated. He will simply compress a little. The air will get squeezed out of his lungs. As long as the acceleration lasts no longer than he can go without breathing, he will be fine.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .