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Let's say I have a spaceship under construction with a habitation module and I want a reasonably compact means of mimicking the compressive effects of gravity on the body I have two candidate ideas for achieving this both of which boil down to creating a significant downwards acceleration for astronauts inside the module over and over again at a high frequency and with significant G force to make up for more constant force not being feasible and with with the rational that acceleration force will effect the entire body more evenly than simply wearing a magnetic suit and being constantly held down and pushed down by it.

Idea one: The astronauts wear air filled suits and reside in a fluid filled chamber and at a high rate with significant force this fluid is made to suddenly flow down into a drain in the designated floor while replacement fluid comes in from the designated ceiling.

Idea two: The astronauts wear ferromagnetic suits and spring or piston bearing shoes inside the habitation modules and a strong electromagnetic is turned on and off in order to accelerate the crew downwards over and over again dragging them with the ferromagnetic suits and pushing them back up with the springs or inert gas filled pistons.

Would either of these ideas work in theory and if not why and can either be adjusted to be more feasible? Is my reasoning good and what can I do to improve it?

I am trying to design ships for my setting that better justify long term habitation in space without having to be too out there or too large.

I considered trying to channel ultrasonic waves through the bodies of crew members but that seems to not be an option, see: Could a form of acoustic levitation be used as artificial gravity?

Could a vehicle levitate through use of ultrasonic sound waves?

Though I am somewhat skeptical as I was under the impression that ultrasound travels well through most tissues and so could be used to deposit force farther into the body.

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    $\begingroup$ Without the "pulsing" aspect of it, your first idea has been explored worldbuilding.stackexchange.com/questions/237767/… While the question is aimed at using air rather than liquid fluids, in order to achieve the same effective "gravity" it would require comparably (impractical) forces. $\endgroup$
    – KerrAvon2055
    Commented Jan 11 at 6:07
  • $\begingroup$ @KerrAvon2055 That doesn't entirely make sense to me seeing as one just blows and drags the astronaut down to apply external compressive stress while the methods I described rely more on acceleration force to try to better effect the entire body. $\endgroup$
    – ProfessorMoreRight
    Commented Jan 11 at 8:05
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    $\begingroup$ What excatly are you trying to achive? Artifical gravity, like for the purpose of living inside a spaceship but not having to hassle with zero g? Or a kind of "medical gravity chamber" that one goes into for a few hours a day to combat the muscle and bone detoriation in zero g but not being able to do anything in there? Because for the former your high frequency accelaration would not work as for every "down gravity" phase there would ba an equal "up gravity" phase and thus on avarage result in "zero g with parkinsons" instead of a usable artifical gravity. (cont) $\endgroup$
    – datacube
    Commented Jan 11 at 9:41
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    $\begingroup$ (cont) and for the latter we have no idea if that would help at all. Probably not better then just having a physical excercise room like it is done already today. $\endgroup$
    – datacube
    Commented Jan 11 at 9:46
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    $\begingroup$ Constant strong vibrations tend to do unpleasant things to the human body. $\endgroup$
    – Mark
    Commented Jan 12 at 1:02

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What I’m hearing (correct me if I’m wrong) is that you want artificial gravity for long-term space voyages so that your astronaut’s bones stay intact. Generally a good thing.

Here’s the thing: if your ship is accelerating towards its destination, you don’t need artificial gravity.

Consider a high-efficiency ion engine array with a thrust that puts out a few meters-per-second-square of acceleration on the ship. You can burn for as long as you need with Bussard ram hydrogen collectors (technical name for what your astronauts will inevitably call a “billion-dollar vacuum cleaner for space”), and if it’s a spaceship intended to cross great distance, then your propulsion needs are also solved, and at the same time, the occupants of the ship will experience gravity without having to wear huge, bulky, expensive, dangerous oscillating-gravity suits!

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  • $\begingroup$ Less for moving ships and more for small stations and stationary ships. $\endgroup$
    – ProfessorMoreRight
    Commented Jan 11 at 23:15
  • $\begingroup$ In the event that a ship is more stationary then yes continuous acceleration becomes difficult; in that case, spin-gravity is the best bet for stability’s sake. $\endgroup$
    – controlgroup
    Commented Jan 12 at 15:04
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It's extremely unpractical...

You are probably neglecting that the astronauts will not dilly dally while being shaken up and down at high frequency, but if they are there they are supposed to be doing something.

Wearing a spacesuit is already cumbersome in itself, being shaken would surely make any task other than preparing cocktails a nightmare.

Additionally, having an upright stance is not the only position for an astronaut: try bending forward to grab a box while being vigorously shaken...

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  • $\begingroup$ That is why I mentioned a habitation module. If it is still too much then I can perhaps simply restrict it to some kind of exercise and light rest module. One should perhaps also consider the frequency of the applied downwards force and how they feel together as opposed to more isolated jolts. $\endgroup$
    – ProfessorMoreRight
    Commented Jan 11 at 4:50
  • $\begingroup$ Why were the science based and hard science tags removed? As far as I am aware nothing being discussed violates the laws of physics and I want to stay within the boundaries of science (not the same as real world practicality), if this is impossible then I would like to actually know why or in other words be told in a complete fashion why. $\endgroup$
    – ProfessorMoreRight
    Commented Jan 11 at 8:09
  • $\begingroup$ Please read the tag description: you used 3 tags which are mutually exclusive (internal consistency, science based and hard science). AFAIK no science has even been made on "shaking gravity", so I left the one which according to me makes more sense. You can change the tag, but don't put conflicting tags. $\endgroup$
    – L.Dutch ♦
    Commented Jan 11 at 8:30
  • $\begingroup$ How are they mutually exclusive, can you clarify? Furthermore I did not use the term "shaking gravity", is it not scientific fact that if you for instance launch a rocket carrying a space capsule for acceleration for it's duration subjects the occupants to G force? So if I apply similar acceleration to an object and have it return so I could do it again, wouldn't that repeatably subject said object to G force or am I missing something? $\endgroup$
    – ProfessorMoreRight
    Commented Jan 11 at 8:40
  • $\begingroup$ Oh... I checked the internal consistency tag and understand better now. Science based seems like the most accurate tag between the three. $\endgroup$
    – ProfessorMoreRight
    Commented Jan 11 at 9:08
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If you only need the gravity...

Spin the habitat

Didn't you wonder why those monstrous habitats all are cylindrical? It's because they are rotating around the central axis providing a constant acceleration effect on their inner surface. You do just that, and have your astronauts tolerate the acceleration, the harder the farther from the axis. If you need some modules to not rotate, devise a means to transit from rotating part(s) to non-rotating ones, and a means to reach the center from the bottom of your artificial gravity well, and you're set.

If you really need it to be pulsed... This depends on exact frequency. For frequencies of 0.2 Hz or lower you can devise a shaker-type device that has two parts. One, the capsule with the astronaut, is spinning around the mass center of him at half the required frequency; the other works like a piston and accelerates the capsule back and forth while the capsule's leg end is pointed outwards. With correct phasing, this would cause the astronaut to experience short-term acceleration pulses to his "general up" each time the piston applies the force, with length and actual vector spread being equal parts of the half circle and half cycle. So if you'd want artificial gravity to be applied for only the small part of time, this device would not even cause dizziness to the astronaut, as he would experience about the same feelings that happen on a children's two-person swing, if one would stand on it instead of sitting, the longer the part, the steeper the swing. For longer pulses, just make a centrifuge with altered path of the capsule, say a curved polygon instead of a simple circle.

For high frequencies, I assume that applying pulsed gravity would have an unbalancing effect to the vestibular apparatus of the astronaut, as the effect would be very similar to having a very shaky jeep ride, but with that jeep having iron wheels and no amortisators, thus whoever enters the device would have his health damaged; so I'd advise against pulsed gravity with high frequency on a space habitat.

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  • $\begingroup$ The thing is I am trying to be as spacially compact as possible and to avoid even using a tether. Good points about the health effects. $\endgroup$
    – ProfessorMoreRight
    Commented Jan 11 at 12:44
  • $\begingroup$ @ProfessorMoreRight why making it compact? You're in SPAAACE after all, huh? Have it be big and largely separate, and spin to your leisure. Centrifuges provide constant acceleration to whoever is within, allowing doing valuable work while inside as well. Also you might not need to stop the centrifuge once you've spun it up, just make an airlock/spinlock that would spin up and down according to the personnel's desire to go in or out of the device, losing way less energy in the process. $\endgroup$
    – Vesper
    Commented Jan 11 at 13:42
  • $\begingroup$ To keep modules closer together and more interconnected than with a tether constantly, not use as much material as a full ring, present a smaller profile, and as a bonus avoid as Coriolis effect issues with the ears. Though your right that centrifugal gravity is significantly more energy efficient. $\endgroup$
    – ProfessorMoreRight
    Commented Jan 11 at 13:56
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One aspect we must consider about the health effects of zero/micro gravity on the human body, is that gravity must act on the body itself, and not on something we wear in order to keep our feet on the "ground". Even astronauts on the ISS doing runs on a treadmill while tethered to the treadmill itself can mitigate those negative effects but not cancel them out. After all, our blood vessels must carry the weight of our blood. The blood pressure at our feet is higher than that under our scalp just because of that. Bones must feel the weight of the body even when we just lie in our beds. As Vesper said, "Spin the habitat". There are engineering challenges (stress on the ship's fuselage), but is feasible and definitely more practical. There are yet unknown issues like whether women can give birth to a normal child in space. The issue is that babies orient their head downwards in preparation for birth with head out first. How the baby would behave if it was in space? How would you give the babies the benefits of gravity even before they are born?

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