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https://bigthink.com/starts-with-a-bang/...ity-space/
KEY POINTS: In the microgravity environment of outer space, human bodies suffer an enormous number of maladies: space blindness, bone loss, muscle atrophy, loss of sleep, and much more.
To counteract the long-term effects that zero-gravity (or microgravity) environments have on the human body, many have proposed to use Einstein’s equivalence principle to replace gravitational acceleration with another type of acceleration: a feasible alternative.
However, most plans to create a type of artificial gravity, where rotational motion and centripetal acceleration allow for relatively small-scale structures in space to produce gravity, suffer from an enormous problem: vestibular side-effects. Here’s the big obstacle, biologically, that humans must reckon with.
EXCERPTS: [...] The simplest case is for linear acceleration: where a rocket fires continuously, accelerating everyone inside at a continuous acceleration ... but it also requires using an awful lot of energy in sustained fashion: providing continuous thrust to deliver that linear acceleration.
The alternative is what we’re asked to consider: what if instead of using linear acceleration, we used rotational acceleration? ... the simplest is to have a large cylinder or wheel-like space station that rotated about its central axis: weightless in the center, but with rotation providing an inward-pushing, or centripetal, force everywhere along the outer edge.
[...] The cheapest, lowest-cost version of this, instead of constructing a large structure like a cylinder or wheel, would be as follows:
Simply construct two equal-mass capsules, separate them by a particular distance. Connect them by a tether that cannot be stretched or broken, and then start them in relative motion — uniform circular motion — about their mutual center of mass. And they’ll continue revolving around that fixed point, with an inward, center-seeking acceleration providing a normal force always pointing toward the opposite capsule. Throughout the 20th and 21st centuries, this has provided fertile ground for artists, futurists, and space enthusiasts of all varieties.
But is this actually a feasible solution to the long-term problem of having a sustained human presence in space? [...] Unless you remained perfectly still, you’d feel a violent (but false) sensation of tumbling, known as the Coriolis illusion.
[...] The reason behind this has nothing to do with someone’s toughness, nor is it something that anyone can reasonably adapt to. The issue is physiological in nature, and nearly every human has to reckon with it. As a human being, you have a complex set of organs in your inner ear, including a network of ducts and sacs made of soft tissue with a mythical sounding name: the membranous labyrinth. This labyrinth isn’t hollow, but rather is filled with a fluid known as endolymph, and the motion of this fluid when your body accelerates, rotates, or even when you tilt or turn your head is how you experience that sensation of being oriented, independent of the visual cues you receive from your eyes.
If you’re in an environment that’s rapidly rotating, and the rate of rotation is large — not just in terms of absolute speed, but rather in terms of the number of revolutions-per-minute that you’re experiencing — the flow of the endolymph fluid in your inner ear will be affected, resulting in a mismatch between what your eyes tell you you’re seeing and how the fluid in your ear is behaving. This leads to those sensations of severe discomfort that we described above. The only way to have an artificially rotating space station not lead to those symptoms is to build an extremely large one that’s over a mile (1.6 km) long, and even that is pushing it. You’d really want one that was even longer, perhaps around 5 kilometers (3 miles) in diameter, in order to avoid what would be near-constant and persistent symptoms of disorientation, nausea, and discomfort.
From a scientific perspective, of course, this is possible. You can, in theory, build, launch, and deploy two equal-mass capsules. You can place them as far apart as you want, with a connecting cable — either a soft one, like kevlar, or even a rigid one, like a steel alloy — if you like. [...] The problem, though, is keeping your angular momentum balanced so precisely. The larger your distance is from the center-of-rotation, the more you can perturb your system with even small motions. An act like jumping, doing a single pull-up, or rearranging the items inside the capsule would require a complete recalibration of your spacecraft, which poses an enormous obstacle for habitation. The reason a wheel, cylinder, or torus-like design is preferred to a simple two-mass tether is because the mass distribution is more even, and so is less sensitive to small perturbations or deviations.
The danger of rearranging your mass (changing your moment of inertia) in a large, rotating system is that you’ll start to get differential rotation, which starts exerting torques on the tether or cable. Just as an unbalanced tire can lead to catastrophe if untreated, what will initially begin as vibrations, tremors, or wobbles in the orbit of your capsule can lead to the complete destabilization of your spacecraft. You’d have to make constant corrections to the rotating spacecraft’s motion anytime the masses inside of it were moved or rearranged, and the larger the distance your two tethered masses are separated by, the more complex those corrections are going to be... (MORE - missing details)
KEY POINTS: In the microgravity environment of outer space, human bodies suffer an enormous number of maladies: space blindness, bone loss, muscle atrophy, loss of sleep, and much more.
To counteract the long-term effects that zero-gravity (or microgravity) environments have on the human body, many have proposed to use Einstein’s equivalence principle to replace gravitational acceleration with another type of acceleration: a feasible alternative.
However, most plans to create a type of artificial gravity, where rotational motion and centripetal acceleration allow for relatively small-scale structures in space to produce gravity, suffer from an enormous problem: vestibular side-effects. Here’s the big obstacle, biologically, that humans must reckon with.
EXCERPTS: [...] The simplest case is for linear acceleration: where a rocket fires continuously, accelerating everyone inside at a continuous acceleration ... but it also requires using an awful lot of energy in sustained fashion: providing continuous thrust to deliver that linear acceleration.
The alternative is what we’re asked to consider: what if instead of using linear acceleration, we used rotational acceleration? ... the simplest is to have a large cylinder or wheel-like space station that rotated about its central axis: weightless in the center, but with rotation providing an inward-pushing, or centripetal, force everywhere along the outer edge.
[...] The cheapest, lowest-cost version of this, instead of constructing a large structure like a cylinder or wheel, would be as follows:
Simply construct two equal-mass capsules, separate them by a particular distance. Connect them by a tether that cannot be stretched or broken, and then start them in relative motion — uniform circular motion — about their mutual center of mass. And they’ll continue revolving around that fixed point, with an inward, center-seeking acceleration providing a normal force always pointing toward the opposite capsule. Throughout the 20th and 21st centuries, this has provided fertile ground for artists, futurists, and space enthusiasts of all varieties.
But is this actually a feasible solution to the long-term problem of having a sustained human presence in space? [...] Unless you remained perfectly still, you’d feel a violent (but false) sensation of tumbling, known as the Coriolis illusion.
[...] The reason behind this has nothing to do with someone’s toughness, nor is it something that anyone can reasonably adapt to. The issue is physiological in nature, and nearly every human has to reckon with it. As a human being, you have a complex set of organs in your inner ear, including a network of ducts and sacs made of soft tissue with a mythical sounding name: the membranous labyrinth. This labyrinth isn’t hollow, but rather is filled with a fluid known as endolymph, and the motion of this fluid when your body accelerates, rotates, or even when you tilt or turn your head is how you experience that sensation of being oriented, independent of the visual cues you receive from your eyes.
If you’re in an environment that’s rapidly rotating, and the rate of rotation is large — not just in terms of absolute speed, but rather in terms of the number of revolutions-per-minute that you’re experiencing — the flow of the endolymph fluid in your inner ear will be affected, resulting in a mismatch between what your eyes tell you you’re seeing and how the fluid in your ear is behaving. This leads to those sensations of severe discomfort that we described above. The only way to have an artificially rotating space station not lead to those symptoms is to build an extremely large one that’s over a mile (1.6 km) long, and even that is pushing it. You’d really want one that was even longer, perhaps around 5 kilometers (3 miles) in diameter, in order to avoid what would be near-constant and persistent symptoms of disorientation, nausea, and discomfort.
From a scientific perspective, of course, this is possible. You can, in theory, build, launch, and deploy two equal-mass capsules. You can place them as far apart as you want, with a connecting cable — either a soft one, like kevlar, or even a rigid one, like a steel alloy — if you like. [...] The problem, though, is keeping your angular momentum balanced so precisely. The larger your distance is from the center-of-rotation, the more you can perturb your system with even small motions. An act like jumping, doing a single pull-up, or rearranging the items inside the capsule would require a complete recalibration of your spacecraft, which poses an enormous obstacle for habitation. The reason a wheel, cylinder, or torus-like design is preferred to a simple two-mass tether is because the mass distribution is more even, and so is less sensitive to small perturbations or deviations.
The danger of rearranging your mass (changing your moment of inertia) in a large, rotating system is that you’ll start to get differential rotation, which starts exerting torques on the tether or cable. Just as an unbalanced tire can lead to catastrophe if untreated, what will initially begin as vibrations, tremors, or wobbles in the orbit of your capsule can lead to the complete destabilization of your spacecraft. You’d have to make constant corrections to the rotating spacecraft’s motion anytime the masses inside of it were moved or rearranged, and the larger the distance your two tethered masses are separated by, the more complex those corrections are going to be... (MORE - missing details)
