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There are a few questions regarding the Alcubierre drive here, so I'll pose this one and see what I get.

Currently, our space exploration vehicles, both manned and unmanned, are at the mercy of Kepler and Newton. We have some control over what direction we're pointed and how fast we're going, but our movement through space is governed by slingshotting around the Earth, Sun and other planets and moons, which allow us to gain, lose or maintain our velocity much more efficiently than any rocket could. There's no energy source nor thrust motor we can conceive of that's powerful or long-lived enough to allow us to ignore orbital motion and simply push, against the Sun and any other nearby gravity wells, to take a relatively straight-line path anywhere in our neighborhood.

Editing based on Deer Hunter's comment...

Let's now conceive of a drive system powerful enough that we no longer need to use gravity slingshotting as our primary means of propulsion outside LEO. The Alcubierre Drive is currently the most plausible future tech, but we could imagine virtually any drive system that would allow us to not only "win", handily, against the straight-line pull of anything in the Solar system, but be efficient enough that such a tug-o-war is a drop in the bucket for the fuel capacity of the ship equipped with such a drive. Such a drive system, even if it were subluminal, would be the gateway to the solar system (even half-light speed, impractical for interstellar travel, would make landing on Mars and coming back a day trip).

Here's the question; given a drive system, Alcubierre-based or otherwise, powerful enough that we no longer depend on gravity-based navigation maneuvers to get around, what role would gravity still play in our navigation and maneuvering? Obviously, where gravity helps us out, such as falling toward the Sun to cross the system, we could let it, and there's really no "standing still" (though even that could be possible with such a drive system, depending on your definition of "still"), but given that we'd have the ability to travel much faster than gravity could pull us, I imagine that gravity would be more hindrance than help; we'd simply adjust course to account for the effect of gravity wells as we pass by them, much as we currently do in airplanes to account for wind.

So, would gravity really matter anymore in the post-reactionary thrust engine era of space travel? Or would it, much like the wind to an airplane, simply be something to correct for?

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  • $\begingroup$ Keith, please remember that there are no Alcubierre drives as of now. Idle speculation without any blueprints is not what SEx.SE is for - SciFi can be the place for that, I'd reckon. Note: I'm voting to close as too broad. Please feel free to edit the post. $\endgroup$
    – Deer Hunter
    Aug 9, 2013 at 19:04
  • $\begingroup$ ... Except, of course, there are already Alcubierre drives in Sci-Fi; they're called warp drives, and the Star Trek universe is full of them, along with a healthy dose of "we don't want to deal with real physics so just hand-wave it". The answer would be based on the resulting TV in which the word "orbit" is a throwaway mention. The drive system in question doesn't have to be spacetime-warping; we could hypothesize based on any super-rocket. The question stands; what role will gravity play in navigation and maneuvering once technology advances beyond the dependence on gravity to move around? $\endgroup$
    – KeithS
    Aug 9, 2013 at 19:08
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    $\begingroup$ Alcubierre drives aren't quite science fiction, but (And I hate to say this...), this question might be a better question for Physics than here. It's very much in the theoretical realm for now. $\endgroup$
    – PearsonArtPhoto ♦
    Aug 9, 2013 at 21:37
  • $\begingroup$ "push, against the Sun and any other nearby gravity wells," There's no such pushing whatsoever. It's all action-reaction. $\endgroup$
    – Don Branson
    Sep 27, 2013 at 5:46
  • $\begingroup$ If a warp bubble were to be formed, which is most likely the only way you would ever travel faster than light, it would destroy anything around it with its own gravitational force. Basically, it would destroy the solar system before you started moving. $\endgroup$
    – AndrewMaxwellRockets
    Feb 28, 2019 at 23:04

2 Answers 2

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Let's set aside, for the moment, field-warping, etc., and consider a hypothetical ultra-powerful propulsion system which has no significant effect on space-time beyond the immediate region of the craft itself. Let's also say that your craft can (somehow) negate the effects of extremely high acceleration. Even with this ultimate magic bullet, your trajectories will still be tracing conic sections. Newton and Kepler still apply, merely corrected by relativistic equations at higher speeds.

No matter how fast you go, if you're subluminal, your path is still a curve traced on a gravity well. Kepler and Newton are just providing you with a way to map your journey. Subluminal ultra-high speed will not break the mathematics, but once you get to a substantial percentage of the speed of light, relativistic effects cannot be ignored.

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The Alcubierre drive requires exotic matter to contract space-time behind it. The contraction of space-time in the front requires equal amount of positive energy/matter. The negative mass/energy requirement as proposed by Ramon and Ford is about -10E64Kg. The same amount (10E64Kg) is required on the front. Now let us analyze this mass:

Mass of Sun=1.989E30 Kg=1 Solar Mass Mass of Super Massive Blackhole=A Billion Solar Masses~1.0E40 Kg which is 1.0E24 times less than a SMB.

Now imagine the space time warp created by such amount of mass. We are creating such large warp to achieve FTL travel which is the purpose of our Alcubierre Drive. You can read more here

Your Question:

given a drive system, Alcubierre-based or otherwise, powerful enough that we no longer depend on gravity-based navigation maneuvers to get around, what role would gravity still play in our navigation and maneuvering?

Currently Alcubierre drive is the only realizable approach for FTL which is powerful enough. The utility and correctness of other theories remains to be determined. So, any ship using this drive system must obtain a region of space between source and destination, so that the affect of warp is nil. Otherwise the dominant warping of the ship w.r.t. other masses would attract the surrounding matter towards the warp bubble. So, yes Gravity/Matter would still matter but not in the way it mattered in the case of Gravitational Slingshots.

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    $\begingroup$ "...Gravity/Matter would still matter but not in the way it mattered..." That sentence mattered so much to me. $\endgroup$
    – ThePlanMan
    May 15, 2014 at 13:45

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