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My setting is based on a blend of "soft" and "hard" sci fi concepts, and one of the softer elements is artificial gravity/inertial compensators. Accelerations in this setting tend to not exceed 50 gees, with most craft not exceeding 30 even in exceptional circumstances. Although there are ways around high gee forces, such as immersing crew in shock absorbing liquid etc, inertial compensators are commonly employed, making use of "virtual" curved space in order to generate gravity.

For artificial gravity generation, ships employ opposed pairs of grav generators each covering a particular axis, which are able to provide trixial inertial dampening as well as providing gravity. The system is not particularly powerful and can't produce extreme amounts of gravity so there are no gravitic weapons or reactionless drives etc.

Whilst this could easily be a handwave, I'd prefer these kept to a minimum and want to at least try and reconcile a fictional device with real physical laws.

Edit: Should add that ships in this setting tend not to have large habitable spaces due to extensive automation, so any of gravity/inertia control only has to operate within a relatively small area rather than cover the whole ship. Other methods of gravity provision are available and also commonly used (spin and thrust).

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    $\begingroup$ What is the perceived conflict between the inertial compensators described in the question and the conservation of momentum? Please edit the question to explain what is the problem to be solved. P.S. Virtual curved space is perfectly good technobabble! $\endgroup$
    – AlexP
    May 15 at 22:04
  • $\begingroup$ Yes, it would probably be better focused on this particular method rather than compensators vs momentum in general, thanks. $\endgroup$
    – Nemactual
    May 15 at 22:36
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    $\begingroup$ Eighteen hours ago I have asked the original poster to please explain how on Earth can conservation of momentum be broken by something, anything which happens strictly inside the ship and has no observable effects outside the ship. The question has not been edited to explain, so I am now downvoting and voting to close as completely unclear what the question even is. $\endgroup$
    – AlexP
    May 16 at 16:56
  • $\begingroup$ Yes, I would prefer to make the question more broad, as there are also elements of conservation of mass/energy at play but I was unsure with the rules of changing question topics to be more broad. $\endgroup$
    – Nemactual
    May 16 at 20:25
  • $\begingroup$ Particularly as I have received some good answers from people and I wouldn't want them to be suddenly less applicable to the question... $\endgroup$
    – Nemactual
    May 16 at 20:46

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Simple. The gravity generators cannot generate a virtual curvature in one direction without generating an "equal and opposite" virtual curvature. This "equal and opposite" curve doesn't need to be "equal" in acceleration to the primary field, nor "opposite" in position. It just needs to generate the same force in the opposite direction. Otherwise, that force comes out in the delicate components of the gravity generator itself.

Or in other words, a gravity generator pulls down on the ship's crew, and pushes up on the ship's structure. The ship's structure pushes up on the crew, which pushes the structure down. Thus, no reactionless drives.

A modern gravity generator is designed with such that it will mostly compensate for changes in mass within its fields, to a certain extent. You can load a ship from a station without turning off gravity on either one. But sudden changes from something like catastrophic damage exceeds the tolerances of the design and breaks the components.

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  • $\begingroup$ A gravity drive that works like a modern ion drive would be powerful; use your gravity generators to form a rocket plume, and push on the ship in the other direction. $\endgroup$
    – Yakk
    May 16 at 14:23
  • $\begingroup$ @Yakk true, but whether you use heat or gravity to propel your remass, you are still constrained by the rocket equation. $\endgroup$
    – ltmauve
    May 18 at 3:37
  • $\begingroup$ Like a bussard ramjet, if you can gather propellant from the interstellar medium, you can violate the constraints of the rocket equation. Because instead of a rocket, you are acting like an interstellar prop plane. Your problem becomes carrying energy and converting it to pushing the medium, and not carrying propellant. Of course, the hard part of the bussard ramjet is collecting the ISM. $\endgroup$
    – Yakk
    May 18 at 13:15
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Continuing to ignore the physics of artifical gravity (or lack thereof), mainly the fact that if you had some device for creating a gravitational field by curving space, it would itself act as a configuration of mass-energy that would similarly curve space, meaning just as difficult to accelerate and transport, making the device itself reduntant. Putting that can of worms aside, if you have inertial dampers it shouldn't be too hard to explain conservation of momentum, just take a leaf out of how satellites do it today with angular momentum.

For a satellite in space that wants to keep its orientation (say to always point to the surface), it needs to maintain a constant angular momentum. However collisions with microjunk, necessary orbital maneuvers, and even uneven lighting change the momentum. To compensate the body has reaction wheels which store a large amount of angular momentum, and so only needs to speed up or slow down slightly in the opposite direction to the outside disturbance. Eventually the reaction wheel can become "oversaturated", i.e. it is spinning at its maximum speed and cannot spin faster to compensate for the addition of external momentum of the opposite magnitude. If the satellite has fuel left, it can eject this fuel to "spin down" the reaction wheels. If the body has no mass to eject whatsoever, it has no choice but to keep the angular momentum it has and can no longer maintain control of its orientation. When the reaction wheel eventually jams from wear, the body will violently begin rotating for the rest of eternity.

Your inertial dampers can do the exact same thing for linear momentum as reaction wheels do for angular. If the spaceship has to suddenly stop, the momentum of the interior is damped so the inhabitants don't go flying into the windshield, but instead of magically annihilating that momentum, the dampers store it. Maybe in some extra-dimensional space or the like. As long as the spaceship wishes to remain stationary it must keep storing this momentum. If the storage reaches its maximum, some mass must be ejected at high speed in the opposite direction to keep things conserved. And if there ever is a catastrophic failure of the linear reaction stores, well then bye-bye ship.

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One limiting factor that would be both straightforward and logical is that the Inertia Dampeners themselves need to be very massive (at least as massive as the object which inertia they are trying to negate + safety limit) to work at all.

But the problem is, this means that the propulsion system is now taxed with pushing that extra mass. Which requires more energy, which, combined with the extra mass, leads to more inertia to dampen.

Its kinda like a mutated twin brother to the Tyranny of The Rocket Equation, only instead of the problem of getting extra energy without extra mass, you want to get rid of energy.

What you end up with, is an equilibrium in which the Inertial Dampeners can only be massive just barely enough to protect the crew, and even then, only to a certain level, beyond which the Dampener mass required simply grows infinitely, with equally growing need for energy to push the whole craft. one could imagine the Dampeners as twin balls of extremely dense metal, weighted perfectly down to micrograms, which provide just enough mass to shift inertia with, but not a microgram more, or it would cause a runaway effect.

This prevents the dampeners not only from completely violating physics (they do not create mass or energy from nothing, just shuffle their own through spacetime shenanigans). It also limits the size of spacecraft crews, the size of spacecraft itself, and speeds starships can achieve and still be able to maneuver sensibly.

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Your gravity generators aren't gravity generators.

Instead, they are fields that couple with matter in a uniform way, and relatively gently nudge it.

Imagine a chamber of low-speed Neutrinos. On each side of the chamber you have "magical" mirrors that make them flip direction. In addition, one of the mirrors makes them more likely to interact with normal matter, and the other one reverses this effect.

In this chamber you create a standing wave of the Neutrinos, bouncing back and forth, sort of like a laser resonance cavity, but for Neutrinos.

As the Neutrinos interact with matter, they transfer momentum to them. As these are low-energy Neutrinos they don't cause exotic particles to appear.

With a huge number of low-energy high-interaction Neutrinos, you can get a huge number of tiny pushes on every single particle uniformly. The trick is to tune it so that the pushes happen proportional to the masses of the particles.

If you can't do this with Neutrinos (and honestly I think you can't), then make it dark matter WIMP particles, tweaked to interact more strongly.

The effect is that the mirrors generate force proportional and opposite to the amount of matter that is gently pushed between them; in effect, you created something that acts like a gravity gradient in the chamber, with the required forces transferred using WIMPs to the chamber walls.

Generating these WIMPs tuned to interact requires the chamber - this might be something analogous to how a laser works in cloning photons, where creating the first tuned WIMP is difficult, but making more once you have that tuned WIMP is easier. It is a WASER - WIMP amplification through stimulated emission of radiation.

The tuned WIMPs aren't suitable for reactionless drives or ranged weapons1. You can use it as a reaction drive, in that you can toss particles into a WASER chamber to accelerate them. You can do the same to make a mass-driver - a WASER cannon is a linear accelerator of mass that uses WASER instead of magnetic field.


1 This is sort of begging the question, why? Well, the "tuning" could fade rapidly, resulting in the WIMP beam produced no longer pushing matter after it leaves the chamber. The resonance should also be key to efficiently producing the WASER effect: setting up a WASER chamber with a given gradient should be expensive and time consuming. This prevents using WASER emissions themselves as an efficient "reactionless" drive (pushing WIMPs out the exhaust pipe instead of baryonic matter).

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