It's well established that the human body does not do well in zero gravity. Symptoms such as fluid loss, muscle atrophy, bone mass loss are well known. Less well known problems extend to such mundane activities as urinating. Astronauts on space walks need to be reminded to urinate because their bladders can only tell "fullness" with the help of gravity.

Related to this question about how a human body would adapt to zero gravity. I'm not adapting to, I'm designing for zero gravity.

How would you design a humanoid body to operate in zero gravity?

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    $\begingroup$ Does it need to be humanoid? The ideal structure of the body would most likely shift without gravity to provide an "up" $\endgroup$
    – Cort Ammon
    Sep 2, 2015 at 2:34
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    $\begingroup$ Lois McMaster Bujold's book Falling Free featured "quaddies", humans genetically modified to have an extra pair of arms in place of legs so as to function in zero gravity. There were other changes to their bodies as well. $\endgroup$ Sep 2, 2015 at 8:06
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    $\begingroup$ Farts would evolve to have no odour so humans could jet around like cephalopods whilst still maintaining social mores. $\endgroup$ Sep 2, 2015 at 9:13
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    $\begingroup$ Isn't this almost tantamount to designing a sea creature that can float in the air and is pretty much emulating zero gravity here on earth? $\endgroup$
    – user12258
    Sep 2, 2015 at 11:33
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    $\begingroup$ Have a look on how Scott Bieser invented the Belt Apes in Quantum Vibe. (This and the following pages are an In-universe documentary about belt apes in a funny dialect.) $\endgroup$
    – Turion
    Sep 2, 2015 at 18:00

3 Answers 3


Humanoid (and every other tetrapod on the planet) forms evolved expecting gravity. If you try to take the basic concepts (skeleton, limbs with joints that only bend one way) and rework for a zero gravity environment you will not produce anything useful.

Since you want to start from scratch, look at existing microgravity environments, and then look at Disney to anthropomorphicise the results. End result will be something like a 4-limbed octopus, with bones remaining only in the ribcage, mouth and skull ( and even that's optional, I'm thinking that the brain is worth protecting ).

If I am a truly zero-g creature I would want better (and longer) grasping appendages, suckers would be very useful here. I would not want any directional limitations on said appendages. I would also want panoramic vision, which means we can toss the human head concept right out the airlock. Also need an internal method of propulsion so the being doesn't get "stuck" in the middle of a chamber. This means wings of some sort, or jet propulsion like a cephalopod's hyponome.

Etcetera, etcetera.

In conclusion, redesigning a humanoid for zero g is going to give you a rather poorly adapted creature - you may as well stay with the stock model and just tweak the biochemistry a bit to deal with the known problems.

  • $\begingroup$ I live on earth where I appreciate gravity, but I want longer appendages, panoramic vision and an internal method of propulsion! +1 for not considering a vacuum environment! $\endgroup$
    – Pogrindis
    Sep 2, 2015 at 14:14

I'm going to assume you want to retain the basic human form.

You want the body to gain muscle mass at the drop of a hat, without overdeveloping it either. Muscle mass is part of what helps humans avoid energy, but you need very little effort even to lift huge weights in space - a touch is all it takes to move literally tons (2000 pounds) of mass. If they're not going to spend hours and hours of their productive day doing zero-G workouts, they need to gain muscle mass in response to extremely minor exertions. Such easy gain of muscle would be, wasteful and dangerous if food ever runs short, though.

The heart is a muscle, and that weakens in space, too, meaning that without ensuring that it gains muscle mass, heart problems that were minor, or even negligible on earth, might become critical. We don't know, but the loss of muscle mass might even be an eventual death sentence for the heart.

Next, bone density. Bones lose mass in space. Of course, you're not using them to walk on, but that doesn't reduce the potential stresses a bone might be required to support, especially in an environment where it takes very little force to move you at high speeds.

Spinal development in zero G hasn't been studied in humans because nobody think's it's worth the risk (or wants to be known as the country that risked) screwing a child up for life in the name of science. However, it's known to be related to the stresses a human grows up under. Bad posture can deform the spine over time, so it follows that no gravity can cause the spine to grow malformed. We don't know this, but you will want some controls in place to ensure that the body grows to the proper form without gravitational stresses, especially if you ever want them to walk on a planet.

There are a lot of other unknowns. Astronauts have just not spent a lot of time in space - if they do, because of the muscle loss and bone loss, they just can't walk on earth anymore. Nobody is willing to abandon a human to space forever, just for science.

However, a surprising number of animals have been bred in space, and returned to earth. Being gestated in zero G and returning to G causes serious issues - not knowing up from down, not being able to orient themselves properly, in everything from rats to jellyfish to snails. However, it seems that in rats the inner ear becomes MORE sensetive from being gestated in space, not less - it is exposed not just to downward pull, but constant unexpected yawing and rolling. Therefore, space bred rats rapidly recovered their lost ability to balance, and adapted to gravity.

I haven't found any long-term studies of animals raised from childhood to adulthood in zero-G, but I didn't look too long. Maybe you'll have better luck.

As to changes to the human form . . . I can't see a lot of people wanting to. It sounds cool, but when it comes down to it, humans find humans attractive, and nobody wants to be engineered to be unattractive. Beyond that, our brains are built to handle two arms and two legs - messing with our brains until handling tentacles is natural would go so far that I would suggest it represents a divergence of species - they would be no longer human.

Going back to our roots might be easier - feet that are better for gripping and prehensile tails might be handy in space, might not mess with the 'human' aesthetic so much, and are things that our brains already were once hardwired to handle, and might handle again easily.


Building a bit on user12247's answer, I will suggest there are two environments that need to be looked at, requiring two rather different solutions:

  1. A creature living in 0g volumes such as space stations. Here things like suction cups on the limbs and so on would work rather well. Wings, flaps between the limbs that can work as wings or some sort of jet propulsion system will also be quite useful in getting around. If we are going to play with genetic engineering on that scale, maybe spinnerets like spiders would also be useful, you could stick a string to a wall or surface and cast off, but pull yourself back if you miscalculated somehow.

  2. A creature living in the vacuum of space. Here we need an armoured and protected volume for the biological systems. The creature would have a heavy skin like an elephant (human skin actually survives exposure to vacuum rather well, but for prolonged exposure, we want more protection), or alternatively protection in the form of an exoskeleton like an insect (we need to take growth and shedding old exoskeletons into account if we go this way), or perhaps armoured plates like a turtle's shell or some dinosaurs (with the problem of a mass penalty).

You would want to reduce if not eliminate the expulsion of matter into space, so the creature would have to be symbiotic, with what could best be described as a hyperplant growing from the creature, being nourished by the waste products and feeding back oxygen, carbohydrates, sugars and proteins into the bloodstream. We might possibly want other symbionts in the "ecosystem" to do things like process asteroidal material to make up deficits in the recycling and "top off" raw materials. The circulation of fluids in the hyperplant would also serve as part of the temperature control mechanism for the symbiotic relationship.

To be really exotic, the hyperplant could have reflective leaves, or electrically charged "vines" to provide solar energy and propulsion for the creature in free space; a built in solar or electrostatic sail. A spinneret might be useful, but the potential loss of mass unless it can be recovered and recycled would have to be carefully considered.

When at rest, the creature would be "starfished" out to provide the maximum surface area for the hyperplant, while being able to "reel in or otherwise retract the plant part of the symbiont when needing to do work with the limbs.


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