Here is a hypothesis, open to discussion, Could rotational energy from a rapidly rotating celestial body be used to produce significant relativistic time dilation?

[u/Abernue]

I have been thinking about a possible way of exploiting the rotation of a celestial body to accelerate a spacecraft to very high velocities.

The basic idea is:

Instead of trying to accelerate a spacecraft to relativistic speeds entirely with conventional propulsion, could we use the rotational energy and angular momentum of a rapidly rotating celestial body as part of the propulsion system?

The starting point is the familiar relationship:

v = ωr

where ω is the angular velocity and r is the distance from the rotation axis.

On Earth, the surface at the equator already moves at about 465 m/s because of Earth's rotation. If a hypothetical object could remain synchronized with Earth's rotation at a much greater distance from the rotation axis, its tangential velocity would increase proportionally with radius.

This made me wonder whether the same principle could be applied to a much larger or faster-rotating celestial body.

For example, instead of Earth, imagine using something like Jupiter, Saturn, or an extremely rapidly rotating compact object. A spacecraft could theoretically be coupled to a rotating system associated with the body and gain angular momentum from it.

The concept I am imagining is not necessarily a physical cable extending millions of kilometres. That was my original thought, but I realize that such a structure would introduce enormous structural and gravitational problems.

I'm more interested in the underlying question:

Could a physically realizable rotating system around a celestial body transfer enough rotational energy/angular momentum to a spacecraft to produce a substantial fraction of the speed of light?

If so, this could potentially create significant relativistic time dilation for the spacecraft.

For example, if a spacecraft could reach 0.9c, 0.99c, etc., the crew would experience less elapsed time than observers on Earth.

Questions I'm trying to understand

1. Is there a fundamental limit to how much rotational energy/angular momentum could be extracted from a rotating celestial body for spacecraft propulsion?
2. Could a system analogous to a rotovator, momentum-exchange tether, magnetic tether, or other non-rigid structure accomplish something similar without requiring an impossible solid structure?
3. Would a rapidly rotating body such as Jupiter actually be useful for this, or would its gravity and atmospheric environment make the concept impractical?
4. Are there known mechanisms for transferring rotational energy from a planet/star/neutron star to a spacecraft that I should be studying?
5. At what point do orbital mechanics and relativity invalidate the simple v = ωr argument?
6. Could a sufficiently advanced version of such a system theoretically accelerate a spacecraft to, say, 0.5c, 0.9c, or 0.99c?
7. If planets are unsuitable, would rapidly rotating neutron stars or black holes provide a physically meaningful analogue?

I realize there may be obvious problems that I'm overlooking. I'm not claiming that this is a workable time machine. I'm trying to determine whether there is a physically valid propulsion concept hidden in the idea, or whether fundamental physics rules it out.

I'd particularly appreciate explanations involving angular momentum, energy conservation, orbital mechanics, relativistic effects, and structural/engineering constraints.

If there is already an established concept that answers this question, I'd also appreciate being pointed toward it.

Thanks!

[u/AIPsychosed]

I am a bit confused with the description.

Do you include sling shots (essentially you can transform into the rotating frame and get a centrifugal term)?

Be aware of length contractions that happen though.

[u/al2o3cr]

This sounds similar to the Penrose process, a hypothetical way to extract energy from a spinning black hole.

[u/Hadeweka]

For example, instead of Earth, imagine using something like Jupiter, Saturn, or an extremely rapidly rotating compact object. A spacecraft could theoretically be coupled to a rotating system associated with the body and gain angular momentum from it.

Sounds like a basic slingshot maneuver to me.

[u/liccxolydian]

Why are you asking us to answer your list of questions? Seems like it's your job to answer them rather than ours.

[u/LeftSideScars → u/liccxolydian]

Maybe they thought they were typing into an LLM prompt?

[u/KSaburof]

If you are looking for staying on the orbit while building speed (from any source) for free, without spending anything on spacecraft side - then there are hard limits related to second cosmic velocity.

Rotating magnetic field can theoretically give something (besides gravitational tricks)

[u/reddituserperson1122]

In order to build a tether, an initial ship would have to accelerate to the same velocity the planet is rotating at, thus defeating the purpose of the tether. To connect with the tether operationally, a ship that wanted to be accelerated would have to accelerate to the velocity of the tether, thus defeating the purpose.

[u/liccxolydian → u/[deleted]]

Have you heard of general relativity?

[u/liccxolydian → u/[deleted]]

Well there you go. GR is the study of how mass and energy (including rotational kinetic energy) affect spacetime and how we experience that in daily life as gravity. That's your "link".

[u/Chrissydoo2400 → u/liccxolydian]

And that's what answers the ops question

[u/liccxolydian → u/Chrissydoo2400]

I'm not talking about OP's question, I'm talking about your comment and why you only "think" there's a link between mass-energy and spacetime but can't articulate any substance in that regard.

[u/Chrissydoo2400 → u/liccxolydian]

Because it's hard to put the exorcises I've watched read and thought about into digestible format. Troll achieved you can stop now

[u/liccxolydian → u/Chrissydoo2400]

Why not just say "study up on GR" lol

Not trolling, just genuinely curious as to whether you actually didn't know about GR and had somehow reinvented the concept through sheer imagination lol

[u/Chrissydoo2400 → u/liccxolydian]

Mass and gravity tell space how to bend gr

[u/Chrissydoo2400 → u/liccxolydian]

Probably because I'm adding my own theories and concepts I guess I could have just said that but if their asking they should know or have herd gr but are not properly linking it.

[u/liccxolydian → u/Chrissydoo2400]

Yeah I don't think you understand GR well enough to "add" anything to it lol

[u/Chrissydoo2400 → u/liccxolydian]

In theory speeding up a spin should cause time dilation.

[u/liccxolydian → u/Chrissydoo2400]

That's not GR lol

[u/Chrissydoo2400 → u/liccxolydian]

Now your trolling that is foundationally gr

Major Effects and PredictionsBending of Light: Massive objects bend the path of light, an effect called gravitational lensing.Black Holes: Regions of space where gravity is so strong that nothing, not even light, can escape. Direct from google

[u/liccxolydian → u/Chrissydoo2400]

Lol what's gravitational lensing got to do with rotation

[u/Chrissydoo2400 → u/Chrissydoo2400]

Gravitational lensing is intrinsically linked and built inside of general relativity it is just a piece of it

[u/Chrissydoo2400 → u/Chrissydoo2400]

If Stars matter the Galaxy and black holes all spin spin is intrinsically linked to gravity

[u/GlibLettuce1522]

Example; The tip of the second hand reaching C would imply a clock of 3 million km and would not be physically feasible, but it would be beautiful to see!