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So I want to send a ship to Alpha Centauri very quickly - by this, I mean less than 5 years. This means that the ship will have to accelerate at 50-100 $g$ or even more. But we don't want to turn our astronauts into pancakes, right?

Is spending long time periods in perfluorocarbons saturated with oxygen (or similar stuff) actually healthy or does it pose risks? What are the side effects? Does it neutralize the $g$-forces? How does it feel swimming or sitting in tanks filled with perfluorocarbons while your ship is accelerating at 1000 meters per square second?

Can this only be used on spaceships or can you use that in habitats on high-gravity planets too?

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  • $\begingroup$ See biology.stackexchange.com/questions/23074/…. $\endgroup$
    – HDE 226868
    Aug 30 '15 at 15:54
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    $\begingroup$ Technically you don't need high accelerations to get to AC in 5 years, 1gee will do perfectly. Ignoring relativity for a moment, the speed of light is 3e+8m/s, if you accelerate continuously at 10m/s, you will be reach that velocity in 347 days. Even taking into consideration relativity it will only take about 5 years to reach AC. The only reason to suffer high gforces in interstellar travel is if your drive is only capable of putting out extremely high gees for a short time (such as if your using beamed power and have to do most the accelerating within 30 light days of Sol). $\endgroup$ Sep 2 '15 at 13:06
  • $\begingroup$ @BlakeWalsh Don't forget to decelerate at the other end. : ) $\endgroup$ Sep 2 '15 at 14:44
  • $\begingroup$ @DougWarren 5 years is about how long it takes to travel 4 light years with constant acceleration (the basic formula is 0.5ly in the acceleration year, then 1ly per year, then 0.5ly in the deceleration year). Because AC is 4.37ly you'd need to up the timetable, accelerating at 2gees for 250 days, coasting, then decelerating for 250 days, will get you there in less than 5 years. Personally though I prefer to lithobrake, you get there half a year faster at a fraction of the cost! $\endgroup$ Sep 2 '15 at 19:07
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You probably can survive heavy acceleration while breathing liquids though keeping tabs on infection and ventilator function over longer periods will be definite concerns.

Breathing Fluorocarbons

The Biology SE answer indicates that it's possible for animals (very little human testing has been done) to survive for extended periods while immersed in and breathing fluorocarbons. Animal diaphragms aren't strong enough to move fluids so a ventilator must be used. Due to the dearth of research on the long-term effects of adult humans breathing fluorocarbons for weeks, months or years, everything is speculation though, given the inert nature of fluorocarbons, it would probably be okay.

Suspension in Fluorocarbons

So without a weight belt/suit, a human will tend to "float" towards the top of the tank. Under 1$g$ acceleration, a simple weight belt is sufficient to maintain buoyancy because the strain induced by differences in buoyancy between the human body and water is negligible. However, under 50 to 100$g$ the strain will be considerably more and will need to be accounted for. A full body weighted & pressure suit will be best because the less dense portions of the human body will want to float up and must be restrained.

There is also this article (paywall) about adaptation to acceleration environments.

Yes you probably could suspend a crew in a fluid for the crushing accelerations required by the OP but it doesn't take a ton of handwaving to do so. The only people you're going to really annoy are the buoyancy scientists.

Older Answer:

From the Biology SE answer:

Kylstra, the first pioneer introducing the idea of land animals breathing liquids (Kylstra et al., 1962, found mice could withstand 4 hours of 160 atmospheres of pressure.

So how much acceleration is equivalent to 160 atmospheres?

100kpa is one atmosphere.
100kpa * 160 = 16000kpa
P=F/A
F=P*A
F=16000000 Pa (N/m^2) * 1.7 m^2
F = 27.2 MN

While 27.2 meganewtons seems like a lot, remember that this is across the entire surface of the body and from all directions so the pressures equalize. Free gases in the gut will diffuse in the surrounding tissues so decompressing/decelerating will need to be done slowly to avoid a lethal case of the bends.

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  • $\begingroup$ This answers whether it's plausible for people to breathe fluids, but not whether just breathing fluids would protect you against high Gs. $\endgroup$ Sep 2 '15 at 13:36
  • $\begingroup$ @Whelkaholism, thank you for the correction. I've made edits to better address the question. $\endgroup$
    – Green
    Sep 2 '15 at 14:04
  • $\begingroup$ Very interesting analysis! I was wondering about things like concussion, actually - I just don't have enough physics to know what would happen for sure, but my gut feeling is that being submerged in liquid wouldn't stop your brain bouncing around squishily if the whole tank accelerated at 100g? $\endgroup$ Sep 2 '15 at 14:16
  • $\begingroup$ While 160 atmospheres correspond to 16000000 N/m^2, it's not correct to multiply this by the surface area of a human to get the acceleration. The net acceleration would from pressure would be acording to Archmides principle. The problem is that Kylstra messures a different thing than what OP asks for. To withstand acceleration Perfluorocarbon liquids is a bad choice, because it's density is different from humans. $\endgroup$
    – Taemyr
    Sep 2 '15 at 14:17
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    $\begingroup$ @Whelkaholism Acceleration actually doesn't cause your brain to bounce. It's jerk that does that. Now, granted, acceleration will smoothly press your brain into paste on the back of your head, but the smoothness of it gives the organs more time to adjust to optimal distributions. A jerk (like from hitting your head) leads to a difference in acceleration between your skull and your brain, and that's where the concussions occur. $\endgroup$
    – Cort Ammon
    Sep 2 '15 at 16:37
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Does it neutralize the g-forces?

Being immerged in and breathing a liquid with a density close to that of the human body can aliviat damage from g-forces because in such an environment the forces are applied evenly. However Perfluorocarbon fluids are a bad choice, as they are far too dense - The density differentials in this case is as big as they are when you are immerged in and breathing air, you just change the sign.

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