Hard Science Fiction has a gravity problem

I’m interested in looking at scientifically plausible methods for solving the gravity problem for long duration space flight. It seems the two leading candidates are centripetal force and linear acceleration. Both come with a host of problems and neither seem reasonably feasible or practical.

Centripetal force has a few issues that make something like Von Braun rings seem impractical for long duration flight. This artificial gravity is created by a rotating reference frame that spins around a central axis. Anything that is moving along a circular trajectory must feel a centripetal force directed toward the center of the turn. The normal force of the hull will act as the centripetal force, causing the centrifugal force in the rotating frame to point downwards toward the hull along the axis of rotation.

There are several problems with such a system. One is gravity like that which we experience is pulling down toward the center, where centripetal acceleration pulls toward the axis of rotation. Also the force is a product of the size and speed of rotation, smaller radii must turn faster where larger radii would turn slower to achieve the same sense of force. However the smaller radius would create a dramatic difference in the gravity felt at your head versus that felt at your feet. Larger radii or slower speed would have a more balanced effect. The problem there is linear velocity would need to be much higher than the speed at which potential astronauts would move or they could experience increased gravity moving in one direction, and decreased gravity moving in another.

Then there is the Coriolis effect, which is an apparent force that acts at on a body moving relative to a rotating reference frame at right angles to the motion and axis of rotation. This means anyone moving toward or away from the axis of rotation will feel a force in the opposite direction, causing a loss of sense of balance. Restrictions on head movements or a slower rotation can mitigate this effect, but those are not really practical solutions for most design situations. Couple this to a significant difference in the gravity at our head versus our feet and it makes a real problem for any potential astronaut.

A third problem with this design is the distribution of mass, as even small shifts in the weight of the system can destabilize it and cause it to wobble, creating many obvious problems for the stability of the craft.

All of this presents problems for both design and energy consumption, as the craft would have to power the rotation and deal with friction while maintaining conservation of the angular momentum. The most logical design, a larger ring with a slower rotational period, is the most complex, expensive and impractical.

The second method has fewer drawbacks, but is equally complicated. According to the equivalence principle, linear acceleration would be indistinguishable from a gravity field. The force would simply be the consequence of inertial motion following Newton’s law. What’s more unlike artificial rotational gravity the force of linear acceleration would be equally distributed throughout the vehicle. As well there would be no frictional issue or need to power the spinning ring or chamber.

The main issue with linear acceleration is it would need to be constant in order to produce a long term gravitational effect, and for that effect to remain a full 1g for duration you would need a method with a high specific impulse and low thrust for a long period of time. Conventional propulsion systems would mean carrying a lot of fuel, though systems like Hall thrusters or maybe Ram jet systems do show some promise to this end.

Yet all of this is still in the shadow of our general lack of experimental knowledge in what even low gravity or temporary gravity would have on biological systems over long periods of time, but the effect of zero g is well understood and it isn’t good. Without practical information we are left guessing as to whether even centrifuges could mitigate the effects of low gravity over time on the body. Other alternatives like diamagnetism or magnetogravitaion carry yet even more untested potential risks.

It seems like there is no real way to write a story about long term space flight that is scientifically accurate, everything would have to at some point rely on either the theoretical or the hypothetical, which begs the question of if it can actually be done in real life. Perhaps building gravity stations at various points between solar system bodies to reduce to amount of time in zero g while moving throughout the solar system.

Science fiction has a gravity problem, and it seems so does science fact. I would be curious to hear some ideas of how this problem might be overcome, maybe such a conversation could help with both.

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Perhaps the best solution in the long run will be to engineer ourselves rather than trying to emulate gravity in space. Perhaps in the far enough future, with advances in genetic manipulation, nano technology, augmentation etc., we could thrive in a zero-g environment without the adverse biological effects that we would encounter today.

Altering ourselves might ask for even greater advances in technology than the requirements proposed by methods to create an artificial gravity, but it feels to me like more of a long-term solution and less of a ‘band-aiding’ of the problem.

Engineering ourselves would have further benefits that might be essential to a interstellar civilization…Why terraform an entire planet when you could engineer a person to survive it’s current atmosphere?

These are the kinds of questions I’m interested in. For example what would be the net effects of long term 0g, if we mitigate them, can we unmitigate them? If we alter ourselves for long term low gravity, could we then alter back? Would we want to?

These are huge questions that would involve a lot of interdisciplinary fields of science and medicine, much of which would only be hypothetical at this stage. I’m merely pondering concepts I’ve heard of, I wouldn’t have a clue how to begin answering them.

But to ponder further…in regards to altering ourselves, whether we would want/need to revert back afterwards would depend on what we’re doing. For example, are you customizing a person to be able to thrive in a particular air mixture, or are you completely reworking the way breathing works in the body so that it could apply to any atmosphere? If the latter, then why go back?

An example I heard in a documentary on nanotechnology was the possibility of creating artificial red blood cells with 100 times the oxygen capacity of regular red blood cells. Imagine swimming underwater on a single breath for over an hour. If this was possible, I can’t imagine wanting to go back to normal.

In another scenario, and I’m just making this up for an example, imagine we could alter ourselves to be extremely resistant to radiation to better survive a harsh planet. However, if I wanted to return to earth, maybe this means that I can no longer receive enough vitamin D from our sun, and would want to revert back.

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That’s really the question. If we can’t find a practical way to stay acclimated to a planetary environment, can we ever really explore even the edges of our solar system? Even with linear acceleration we’re only talking 1/3 g for extended periods even with theoretical propulsion systems. We can’t even do that for the kinds of time we would need to stay in that environment to make the journey. It seems that if we distribute centrifuge gravity stations at various points in the solar system we could explore it deeper and safer than manufacturing gravity we take with us and still return to our home planet, but can we really build ladders to the stars? If not what truly are our options?

Colonizing the galaxy might mean setting up distant planets before we get there. A hypothetical idea that I’ve read about is letting AI do it. The idea goes something like this:
Create machines and send them off to several nearby stars with planets. These machines would include everything that is required to get to said planets, set up infrastructure (e.g. a habitat for humans that arrive later on. This also might mean terraforming), the ability to acquire resources from the planet to build/maintain the outpost, and the ability to create more machines that can then launch from this planet and continue the process elsewhere.

This process would have a multiplying effect with each initial planet sending several more missions to other planets. From this, the entire galaxy could be colonized within a few million years. Planets scattered throughout the galaxy would be ready to be populated, should we want to occupy them.

Of course, we would still need to get there ourselves and in good health. For a civilization capable of carrying out the idea above, that might be a cakewalk.

The problem I’m seeing is getting there, not in the technological sense. If the craft generates it’s own artificial gravity it becomes enormously complex and fake gravity is a poor substitute over long time scales. If it relies on linear acceleration gravity keeps getting heavier the faster you go over those longer distances. If we acclimate to low G through physiological changes, we can’t set foot on the ground. The overall effect of going from low to high G environments in either short or long periods is not really tested.

So far for our local system the method I’m seeing is a gravity ladder. Groups of autonomous stations periodically spaced, kind of like decompression chambers seeded throughout the solar system at calculated points which allow explorers to have higher gravity environments to stay in during extended missions. We hop from point to point, a few months out a few months in. The whole purpose being to allow astronauts to stay acclimated to gravity so they can go home. Meanwhile allowing the vessels to be less complex amd therefore more reliable, a key factor to any space exploration.

Over larger scales though, beyond our solar system, I’m not seeing an obvious solution.

Hi. This is so cool topic. There is something in one concept I call “space goo” that I just can’t resist to tell mine. So let’s go.
If we decouple us into photons as information packets only thing we’ll be able to do is to achieve the speed of light that we already know. So where we have stuck. We still have lack in our knowledge about what space really is. Space the final frontier.
On the other side we have already running ‘experiment’ in ours earth orbits. GPRS and those nasty little buggers of space goo. OK. Time dilate in those clocks, right? So something is wrong with math on earth or with the ‘atom’ mass in clock. If it run slower than mass rises up. If mass rises up then something internally is going on without us willing that to be at all. Bigger mass means bigger locality means less relativity, less relativity means more independence from outer world.
So intuitive answer in my Disneyland is we need to find a way to find a hack how to avoid ‘that thing’ whatever we can be, 5th dimension or whatsoever.

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