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.