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If all of the crew and passengers of an interstellar craft were in suspended animation except prior to Earth departure and just before destination arrival, would they need artificial gravity (through some from of spin) for the length of the journey?

Also please let me know if there's a better place to ask this question. I don't want to step out of context.

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  • $\begingroup$ What kind of speeds does the ship fly at ? does it accelarate to them or "magically" jump from 0 speed to 95% of light speed? $\endgroup$ – Soan Jan 13 at 0:23
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    $\begingroup$ Instead of spin, you might look at gravity by linear acceleration, providing artificial gravity as a side effect of your main thrust. $\endgroup$ – Cadence Jan 13 at 0:29
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    $\begingroup$ What form of suspended animation? Cryogenic? Temporal? Something else? $\endgroup$ – Xavon_Wrentaile Jan 13 at 8:10
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    $\begingroup$ What's the expected duration of the trip (time for lack or gravity to affect your passengers)? $\endgroup$ – Nahshon paz Jan 13 at 8:36
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    $\begingroup$ There notes: 1) You do not need a perfect solution. You just need acceptable for travel time, but that is at least 1 year + distrance travelled in LY. 2) But that is with contant 1G accelleration. Speeds archived are very high. Space is not 100% empty. collisions at that speed are going to destroy your ship so you need some handwavium. 3) Nice to read and right here on here on Stack exchange: space.stackexchange.com/questions/840/… $\endgroup$ – Hennes Jan 13 at 11:52
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Need? No. Want? Yes.

From real life:

Science Results for Everyone Maintaining strong muscles is a big enough challenge on Earth. It is much harder to do in space where there is no gravity. Calf muscles biopsies before flight and after a six months mission on the ISS show that even when crew members did aerobic exercise five hours a week and resistance exercise three to six days per week, muscle volume and peak power both still decrease significantly. Overall, the data suggest that current exercise countermeasures are not enough. The addition of a second treadmill and the Advanced Resistive Exercise Device (ARED) along with more rigorous exercise regiment are giving good results in preventing muscle loss and preserving overall muscle health.
-Effect of Prolonged Space Flight on Human Skeletal Muscle (Biopsy) - 08.15.18 -NASA

Unless your sleeper technology can make up for the atrophy of muscles that's normally seen in both comatose patients AND the atrophy seen in Active microgravity residents, the addition of artificial gravity would reduce this problem to coma patient level, which could be treated with neuromuscular electrical stimulation.

But neuromuscular electrical stimulation doesn't work for bone mass losses (Osteoporosis) as well, which is also another problem of microgravity. So your sleeper tech would also need that. Artificial gravity would make it a non-issue.

So need? No, your sleeper tech can adjust for the medical issues or have your travelers arrive skinny and weak. But you probably want it.

Whatever the source of the gravity, it should be about Earth normal 1G. Lower gravity would cause less stress to the body and still lead to skeletal-muscular mass losses (at a lower rate), and high gravity causes issues with blood pumping and stress to tissue. Sustained high gravity force can kill a human.

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  • $\begingroup$ It could be that because of his propulsion system that there already is a "gravity" because the acceleration of the ship causes it. $\endgroup$ – Soan Jan 13 at 0:28
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    $\begingroup$ @Soan then the issue is how fast it's accelerating and how likely that is to be above earth normal 1G. I'd hate to try to travel in a sustained 10G acceleration. Probably be dead. $\endgroup$ – cde Jan 13 at 0:37
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    $\begingroup$ @pelinore most scifi shows suspended animation on ships with artificial gravity activated tho. $\endgroup$ – cde Jan 13 at 3:35
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    $\begingroup$ @pelinore except every film where the crew wake up from cryosleep due to problems on the ship mid flight when no one is supposed to be asleep. Most scifi glosses over alot of realistic effects of space travel, handwaves everywhere. OP is asking for world building reasons and saying "ignore this" does not help that. $\endgroup$ – cde Jan 13 at 3:44
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    $\begingroup$ One reason for "always on" gravity is the usual "problem aboard the ship" issue in SF. If it takes time and energy to spin up a rotating ring around a central shaft, it would probably "come on" too late in an emergency, thus it might make more sense to turn it on and then leave it that way. $\endgroup$ – James Jan 13 at 13:08
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Would a sleeper ship need artificial gravity?

No

There's only one real reason people want artificial gravity during a space journey.

To avoid the muscle atrophy etc arising from micro gravity.

But assuming that the suspended animation suspends (or at least significantly slows) all biological functions at a cellular level (which is the way it's most usually depicted in sci fi) there's no plausible explanation for why there would be any muscle (or other) atrophy from zero g during the journey.

So they wouldn't need it.


Which doesn't mean a sleeper ship won't have it, just that they probably won't have any artificial gravity they have got turned on during the bulk of the journey.

A ship on a regular shuttle run might not have any if no one is expected to spend more than a few hours awake in zero g either end of the journey, while an exploration vessel that might loiter for an extended period above a planet after arriving probably will (if the tech is available).

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    $\begingroup$ It really depends on what's being called "suspended animation" here. If they are put in some sort of timeless stasis field then your answer is correct, but if they are simply put in a comatose state for the duration of the trip then there could be other factors at play. Given that suspended animation itself is still in the realm of science fiction this gives a lot of possible wiggle room for whether it's necessary or not. $\endgroup$ – fluffy Jan 13 at 4:24
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    $\begingroup$ @fluffy : I normally presume suspended animation to involve some form of "cold sleep" (which is stated as a proviso in my answer) so yes, if it doesn't involve suspended animation then my answer won't apply, agreed, but if it doesn't involve suspended animation (of the sort I assume) then they'll age & die long before arriving unless the journey is a very short one or they've very long lifespans so I think I'm on safe ground there :) $\endgroup$ – Pelinore Jan 13 at 4:46
  • $\begingroup$ @fluffy is basically right. Freezing a body solid damages the body. Cyrogenics is the science of lowering the body's temperature to minimize metabolism and no more. $\endgroup$ – JBH Jan 13 at 15:14
  • $\begingroup$ @JBH : Cryogenics in sci fi involves minimizing the bodies temperature to minimize metabolism yes, the minimum metabolism is zero, so your point was? ;p : It's a very common trope that cryosleep involves some form of bio antifreeze pumped into the veins, the OP says they're in cryosleep & asks if they'll need artificial gravity, given that the journey is 100 years or more to assume cryosleep doesn't reduce metabolism to zero (or sufficiently close to to make no difference) is more of an assumption than assuming it does. $\endgroup$ – Pelinore Jan 13 at 15:23
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    $\begingroup$ You might need gravity for the plants and animals which are carried with the suspended humans, but cannot be suspended as well $\endgroup$ – Julian Egner Jan 14 at 12:57
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Absolutely Yes

Humanity was not designed for microgravity.

Life in the microgravity environment of space brings many changes to the human body. The loss of bone and muscle mass, change in cardiac performance, variation in behavior, and body-wide alterations initiated by a changing nervous system are some of the most apparent and potentially detrimental effects of microgravity. Changes to bone are particularly noticeable because they affect an astronaut's ability to move and walk upon return to Earth's gravity. (Source: NASA)

In a nutshell (and building on CDE's excellent answer), all of the following suffer in microgravity, whether you're sleeping or not.

  • Bones
  • Muscles
  • Cardiovascular system
  • Nervous system

And, based on the very brief mention of "variations in behavior," the brain itself suffers for lack of gravity.

The simple reality is that long-term space travel will require 1G gravity or Bad Things happen. Sleeping doesn't solve the problem. In fact, extrapolating from the explanations, thanks to the loss of active psychological and physiological activity, it might be a great deal worse.

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  • $\begingroup$ OP says "Sleep is cryogenic" (see comments below the question), if they're frozen there can be no muscle atrophy, bone density loss or any other biological atrophy of the organism during the suspended animation portion of the journey & the question specifically asks if they need gravity while sleeping during the journey. $\endgroup$ – Pelinore Jan 13 at 14:10
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    $\begingroup$ @Pelinore you're making an assumption about "cryogenic" that may or may not be true. It doesn't necessitate freezing solid. You need only drop the temperature to minimize metabolism. After that, you're just damaging the body. (Look up "freeze drying" and "freezer burn.") $\endgroup$ – JBH Jan 13 at 15:10
  • $\begingroup$ No more assumptions than yours, just in the opposite direction : Consider this, once you've "minimized" metabolism sufficiently to prevent any noticeable aging then you've by necessity minimized it sufficiently to prevent any noticeable atrophy caused by zero g, given the OP has said the journey is at least a hundred years & the sleep is cryogenic I think my assumptions are safe, not so sure about yours though :) $\endgroup$ – Pelinore Jan 13 at 15:14
  • $\begingroup$ @Pelinore, but not the chemistry. cheers. $\endgroup$ – JBH Jan 14 at 3:21
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You probably want your sleeper ship to spin, even if artificial gravity is not a concern. The reason is that a rotating spacecraft has a more stable orientation than a non-spinning one- which will probably begin to tumble erratically after a while.

Space probes like the Voyagers and New Horizons rotate so they can keep their radio dishes oriented towards the Earth. Your sleeper ship might want to send status reports back to Earth and maybe conduct long-distance scans of the destination en route. Keeping a stable orientation makes that easier. It will also make establishing a comfortable artificial gravity easier once you've arrived.

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