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At 1 G, we feel at home.
At 5 G's, normal people can stay awake.
At 9 G's, trained pilots with G-suits can stay awake.
At 25 G's, R.I.P.

Unfortunately, these numbers are limiting for space travel, especially for the astronaut. For example, if you and I wanted to visit Alpha-Centauri (4.2 light-years away) and come back and tell everyone about our trip, at a comfortable 1 G acceleration and deceleration, our round-trip travel time would be 11.64 earth years and 7.06 rocket years. That's 7 years we'll never get back!

We can't save much on the round-trip travel time by earth's standards (traveling at light speed would only save 3.24 earth years from our previous example's earth time).

However, we can really cut down on our perceived time by accelerating at a faster rate. For example, if we accelerated/decelerated at an uncomfortable 9 G's for the whole trip, while earth's perceived time only drops a little (8.82 years, or 76% of the original time), our perceived time drops to 1.6 very uncomfortable years: just 23% of the original time...nice! At 150 G acceleration, our perceived travel time is only 1 month there and 1 month back!

Obviously, a big problem with our 150 G trip is that under normal circumstances we died 125 G's ago. Thus, my questions are:

  1. Can we make 150 G's (or other large G amounts) survivable to humans using levitation techniques (for example, I'm worried that your blood might be "locked" into place and thus be unable to pump)? Note that solutions could involve regulating your internal body composition so that each part "pulls its own weight" in the suspension (as opposed to only your stomach being lifted).
  2. Can we make 150 G's feel like 1 G so that we are not just levitating frogs for our whole trip?
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    $\begingroup$ Inject nano-particles encapsulated with a body-friendly layer of gel layer. Choose ferro-magnetic nano-particles so when enough are in body, an external magnetic field can apply nearly-uniform force to all body. Not just surface. All volume (except brain, the gel should not stick to brain tissue, but all other tissues especially bones.) Note: dont try at home. $\endgroup$ – huseyin tugrul buyukisik Aug 7 '13 at 20:29
  • $\begingroup$ The times you've provided are in a reference frame that is moving with the ship right? $\endgroup$ – Doryan Miller Apr 23 '14 at 17:09
  • $\begingroup$ @DoryanMiller Correct, as without FTL the trip will take a minimum of 8.4 years to an earth observer. $\endgroup$ – Briguy37 Apr 23 '14 at 18:17
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While I'm not sure how the solution using levitation would work, I'm focussing on surviving some more of the acceleration, independent of that, and propose how to handle some problems that may be relevant even with levitation available.


Part of the problem that's killing us is that the body contains compressible parts, which will collapse.

The problem is the air, and we should get rid of it. That's easy, because there are prooven commerial systems for breathing liquids available already.
Sounds a little like scifi, maybe, but seems to work - after getting used to breath a liquid, that is.

It's used for diving in deep areas of the sea under high pressure, wehere pressurized air dos not work. You's breath perfluorocarbon, with some oxygen disolved in it, of course. This creates a pretty uniform pressure in the body during acceleration, which is slightly disturbed by inhomogenous density of the body.

This seems to actually work up to 20G with perfluorocarbon, and even above 20G if a liquid of more similar density to the body could be used.

Apart from making the body incompressible (after filling some other parts with liquids), the original purpose of liquid breathing may help us too - it is related to exchanging oxygen in the lung depending on pressure.
As we now can stand the pressure that is caused by the acceleration, it may help us actually get oxygen into out blood if we should find a way to breath.

Assuming we can not levitate gases like air ot oxygen, and not influence pressure changes in gas volumes inside the body, the above would possibly save us from suffocating. If we happen to havr time to do it, that is.

See Liquid breathing.

Not sure these are the first things that would have killed us, but it is a good start having to eliminate a couple of fatal options every day from now, if we are curious to find out it worked in out lifetime!

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  • $\begingroup$ I looked into liquid oxygen which has a density of 1,141 kg/m^3, 1.141 times that of water, much closer than the twice dense perfluorocarbon. The problem is that it can't be in liquid form above -113C, so it wouldn't be an option in liquid form. However, air at sea level at 15C has a density of 1.225 kg/m^3, so if we increased the pressure 800 times, the air would be the exact density of water. Deep see divers regularly do 10 times, but it would be interesting to know the true limits if the oxygen levels were controlled perfectly. $\endgroup$ – Briguy37 Apr 23 '14 at 19:09
  • $\begingroup$ Breathing liquid oxygen is a bold idea somehow - well matching the whole question, I like it :) And... pretty sure it's a non-smoking flight, right? $\endgroup$ – Volker Siegel Apr 23 '14 at 19:17
  • $\begingroup$ @Briguy37 I'm not clear about how the acceleratioin affects the pressure in the body - any chanche to adjust the acceleration to provide the 800bar? Hmm... sounds too good... :) $\endgroup$ – Volker Siegel Apr 23 '14 at 19:19
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I don't think there are many soft materials that would survive undistorted or intact under 150G force. So no humans will be undergoing that kind of acceleration. In fact it is probably a little worse what you've calculated because you have to ramp up to 150G then turn around and accelerate the other way to ramp back down so either your trip time gets longer because of that or you need more acceleration to make it in 1 month.

So first question: there's no way to "levitate" your way out of being accelerated if the box you're sitting in is accelerating.

Second question: Sci-Fi writers have realized this is a serious problem for frail humans and they invent "inertia dampers" or "inertia negation" which is a fictitious device that negates inertia and removes it from surrounding mass. Unfortunately this ability is only imaginative at this point in time.

You could send humans as zygotes, then take 100 years to get there under low acceleration (less fuel too), and grow them in situ. Not everyone's romanticized idea of space travel, but it's better then getting flattened at 150G.

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  • $\begingroup$ Thanks for the answer. For the time calculations, I was using the "Long Relativistic Journeys" portion from this page for 4.2 ly and multiplying by 2 for the return trip. For the acceleration, yes you still accelerate, but I was thinking that ideally every atom in your body would accelerate equally 149 G's by the "levitation" forces so that you'd only feel 1 G of the 150 G's you actually accelerate at. Obviously getting every atom to participate is the trouble... $\endgroup$ – Briguy37 Aug 8 '13 at 13:24
  • $\begingroup$ "soft materials that would[n't] survive undistorted or intact under 150G force" - for arguments sake what if these materials were in free fall (e.g. falling towards a black whole). Would the 150G have any damaging effect? $\endgroup$ – NPSF3000 Oct 30 '14 at 8:58
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Theory aside, reduction to practice promises some challenges.

Diamagnetic levitation varies as the diamagnetic susceptibility of the material in a huge field gradient (overall field intensity is not the active component). Fatty brain with ionic and electrical currents versus blood and tissue suggests what nurses call an "owie." Moving conductive medium (saline blood) with intense magnetic field induces current. Rather a lot of metabolism involves positively and negatively charged species that will move in opposite directions through the gradient (cross product for Lorentz force). Metabolism also includes free radical species. In a strong magnetic field, unparied spins align and do not form a spin-paired chemical bond. Room temp at one tesla, proton population inversion is a few ppm. Room temp at 50 tesla - calculate it - you're staring down percentage.

Do not wear a conducting ring while moving, ditto magnetic stuff. Oxygen is paramagnetic. Cycling supercon coils through 150 gee is a bad idea. As with a rail gun, the reaction force is in the field is in the coils. Vibrating supercon coils quenches them, as does shifting them. Deep cryogenic specific heat decreases as the cube of absolute temperature.

Two modest constraints before you design the starship by whatever means: conservation of linear momentum and conservation of energy. 1) What will you toss out the rear of the ship to make it accelerate forward, mv vs -mv? 2) How will you power the toss, (mv^2)/2?

1) The best you can do, specific impulse and stuff storage, is photons. Pick a frequency and then a contingent intensity at the emitter. Will you spark the vacuum? Tossing matter is untenable.

2a) Closed system matter-antimatter annihilation falls short. You only get half the 2(mc^2), for hadron-anihadron annihilation (the nuclei, 99.97+ mass-%) lose half the energy as unsteerable neutrinos. Where do you get tonnes of antimatter?

2b) Open system scavenge hydrogen from space then fusion won't do it. In your rest frame, it is coming at you within an epsilon of lightspeed. That is a headwind. A fusion ram jet must first cancel that (ya gotta way compress it, right? Resolve the vector into orthogonal components) before any net thrust obtains. Exhaust is a foot/nanosecond for reaction time. Long ramjet?

Don't just sit there, find work-arounds.

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