Edit: I'm exploring an idea for a hypothetically possible form of propulsion for a sci-fi story. My question is if, based on what I describe below, other folks might have some ideas about how the construction and operation of such vehicles might work.

As some general scope to the question, this isn't describing any kind of warp drive or FTL. Rather, it proposes a what-if scenario where a gravity field/source can be produced artificially on demand in front of a spacecraft.

First, two assumptions. One, gravity has a particle (vs being a side effect of mass on space time. Lot of debate in the physics community around this but supported by the Standard Model). Two, a technology can be created to create gravitons on demand.

Ok, given that imagine a potential kind of reactionless spacecraft propulsion. A ship has a long projection in front of it. At the end of that projection is a gravity generator that produces a gravity well of some amount. Let’s say 1G for the example.

The idea is that such a ship could essentially produce a gravity well in front of it that it falls into. It doesn’t have to be a constant field. Maybe the generator alternates on/off to help move things along.

I have some ideas about the internals of such a craft could be configured. Like, each deck could be built so the floors always point to the front of the ship. To slow down, the ship rotates 180 degrees so the gravity field is now in the inverse direction of travel.

With the exception of the hypothetical gravity generator, I can imagine being able to build spacecraft like this using today's technology. Power sources might be solar, fission, RTG, etc.

What are some other considerations we'd have to make when designing craft like this?


closed as too broad by Ash, Nahshon paz, Cadence, Gryphon, RonJohn Sep 2 '18 at 14:28

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

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    $\begingroup$ Welcome to Worldbuilding, Geuis! If you have a moment, please take the tour and visit the help center to learn more about the site. You'll also find Worldbuilding Meta and The Sandbox useful. Here is a meta post on the culture and style of Worldbuilding.SE, just to help you understand our scope and methods. Have fun! $\endgroup$ – FoxElemental Aug 23 '18 at 0:19
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    $\begingroup$ I'm sorry but could you please clarify a bit more what was your question? I mean, at the bottom of your post write: "So, my question is..." Thanks $\endgroup$ – Ender Look Aug 23 '18 at 0:20
  • $\begingroup$ Thanks @EnderLook. Added some more details and updated the wording a bit. $\endgroup$ – Geuis Aug 23 '18 at 0:32
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    $\begingroup$ I am having a bit of difficulty visualizing this, as the image always becomes one of trying to lift myself up by my bootstraps. Every action occurs equally in opposite directions. Pulling your body up is also pulling your hands down. How do you push something ahead of you which in turn pulls you towards it at the same time? Pushing something ahead also pushes you back equally. But another vision I have is surfing a gravitational wave, where the wave is produced by pushing something ahead of you. $\endgroup$ – Justin Thyme Aug 23 '18 at 2:10
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    $\begingroup$ @Geuis To point at where I think Justin is having trouble, what you are describing is basically an action without an equal and opposite reaction. There is a force on the ship, but there is no corresponding reaction force on the device creating the gravitons. If this was a "real" source of gravity, such as a black hole, it is easy to see that while the ship would be pulled forward, it would also crush the projection because the black hole is "hard to move." $\endgroup$ – Cort Ammon Aug 23 '18 at 6:10

Some Troubles

A trough in space-time in front of your ship will not do anything unless there is a corresponding ridge created behind it. Its more like surfing on a wave of space-time than it is falling. Its also inertialess so its technically not motion at all so much as a change in location that is occurring constantly as you warp space around you. You are basically just proposing a psuedo-scientific handwavey way to create an Alcumbierre drive without using exotic matter, negative mass, or literally astronomical volumes of energy. This comes with a few problems however.

The Trough Catches Stuff

That trough in space time is going to be collecting literally everything that gets in the way and moves it along with the ship. This means every single speck of dust, radioactive particle, hydrogen atom, high energy particle etc etc. Once the ship stops this is going to be propelled on a bow-wave along whatever path you were traveling in at the speed of light. You will obliterate whatever you are trying to reach simply by reaching it. The fact that we aren't detecting such crazy bursts of radiation and catastrophic ripples in space-time means that this method of travel doesn't work, there aren't any intelligent races using it, or that our model for gravity is wrong. (Hint: Our evidence for gravity working the way it does is pretty strong.) But it's Science Fantasy so it doesn't have to be totally accurate, but you do need to mcguffin up a solution to the solar system frying tsunami of gamma rays, relativistic particles, and planet orbit shattering distortions in the local space time.

Catastrophic Gravitational Issues

Turns out the radioactive particle tsunami is actually a minor side effect of something a bit more scary. See, that tidal wave of highly radioactive particles moving at light speed is being borne upon a sort of splash-wave of space-time. So as you exit your "jump" you are going to be releasing such a huge space-time distortion that weird stuff starts happening. Think if you had a bunch of beach balls arranged in a pool and some guy did a cannon-ball into the water. That, except with planets. Also weird temporal distortions I'm not smart enough to explain would happen too, except nobody would be around to see it since they'd be too busy frying to death in all the horrible radiation to notice that their planet was flying off into a new orbit, and since they're stuck in the temporal distortion they wouldn't notice that time wasn't flowing properly anyways. The Horrified crew of your ship are outside observers though so they would get to watch them all die in really funky distorted time-rates, so that's kinda neat. If you don't think watching entire solar systems be destroyed every time you jump then you will need to bust that handwavium out and mgcuffin up a solution for why this doesn't happen too.

Temporal Issues

So even though the Alcumbierre space-time warp method of travel doesn't necessarily move the ship kinetically at faster than light speed, its still subject to a lot of relativistic laws regarding temporal phenomenon. Namely, that if you move past the speed of light time actually starts moving backwards. This means that you would actually show up somewhere before you left. This causes all sorts of crazy time paradoxes that I'm far too unintelligent to understand. But its bad stuff. Bad stuff happens when you break time. You probably need more handwavium and mcguffinite to fix this.

Ultimately it's a Non-issue for the Story

See, thing is, FTL is already not possible. FTl is pretty much literally spcae-magic in any science based story. The idea for your ship can work however you want it to without any of the horrific implications of the big "what if" scenario in which we pretend FTL would work with real physics. Point being, The deck-plan of your fictional ship isn't the biggest part of the story you really need to be worried about if you are going to go for hard science here. I'm only really giving you a blue-collar layman's view of why FTL occurring would be pretty horrific for all involved, but if some guy DID get FTL to work it would basically be a cosmic disaster every time they fired it up.

  • $\begingroup$ Thanks for the response @TCAT117. I'm not sure, but I suspect you started thinking about your response while I was updating the question. What I'm thinking is specifically not a warp drive or FTL system. Rather, its entirely relativistic. At the idea's core, rather than pushing the vehicle its being pulled. By creating an artificial gravity well ahead of the vehicle, the craft falls toward the source and gains acceleration in that manner. $\endgroup$ – Geuis Aug 23 '18 at 1:11
  • $\begingroup$ That's how a warp drive works bruh. A gravity well is a warp in space time. $\endgroup$ – TCAT117 Aug 23 '18 at 1:13
  • $\begingroup$ There are some interesting considerations about attracting debris and energetic particles that encounter the artificial field. Suppose gravitons are like neutrinos in that they don't interact with EM fields, so they will be expelled in every direction and draw things towards the generator. This could be a bad thing! Alternatively, say you can focus your gravitons just towards the ship. A lot of those problems might be avoidable. $\endgroup$ – Geuis Aug 23 '18 at 1:16
  • $\begingroup$ Hah right, technically this would be a "warp drive" in the sense that mass emits gravitons (in this hypothetical situation) so all stars/planets etc are "warp drives". But with this idea, its not a Star Trek FTL drive. Its simply a gravity point source that can be turned on and off. While its on, it would bend space but not like in Alcubierre drive. $\endgroup$ – Geuis Aug 23 '18 at 1:20
  • $\begingroup$ Again, I refer to my statement earlier in my answer. Substitute FTL with the word magic. We're discussing something that is fundamentally impossible so its really whatever you want it to be. I simply detailed some known physics and the effects they have. $\endgroup$ – TCAT117 Aug 23 '18 at 1:25

Okay, just imagine the empire state building, and the tip of the antenna is the gravity well generator. The bottom of the ship is a giant thruster that pushes you forward with 1 g of force. Now everyone can stand around the office and talk and drink from the water coolers and stuff. Some floors would be apartments, others recreation or resteraunts or whatever you want. Just make sure in between each floor is a giant flipper that can revolve the floor so it's facing the opposite direction for when you start decelerating. Again, at 1 g so that you have basically normal gravity. And then whenever you decide to stop everyone needs to strap in and seal everything up so it doesn't float everywhere.

Also, everything is chrome.

Non relativistic gravity well ship:

Imagine a flying saucer. The gravity well generator can be rotated around this outside edge to create a 360° directional engine. Plus it's the perfect shape to shoot out of a railgun into space. Unfortunately the ship can only move on a two dimensional axis, so you'll need small thrusters to change the ships plane if you have to go somewhere that isn't aligned property.

Fortunately though, you can power these thrusters with hydrogen, because as you travel through spave, your gravity well will create locations with dense concentrations of matter than most of the empty void. Simply collect these as you go through to create fuel for jet thrusters. (Be advised, you aren't burning the hydrogen, just ejecting high pressure jets of it.)

Now the real problem is powering your ship in space, which I have to say depends on where you're going. If you stay close to our sun, or a different one, you could coat up in solar panels and rely mostly on that. If away from the sun you could do radioisotope thermalelectric generation, which is what powers satellites and probes. They don't produce tons of electricity, but you might have several or a really big one.

The thermoelectric generator could also work by aligning a spaceship so that one flat side faces the sun, and one side faces away. The temperature difference would be immense and you'd be able to have a rather large thermoelectric generator working.

You can also do something like a solar powered hydrolysis tank, and then a gas compressor, and finally a generator that uses hydrogen reacting with oxygen as fuel. I like this kind because it works as a battery that goes father distances then regular solar power.

  • $\begingroup$ Hey Clay. You wouldn't need thrusters plus the gravity generator. The generator is your source of propulsion, but it pulls you instead of pushing you. Also, I like chrome too but I'd add wood accent panelling. $\endgroup$ – Geuis Aug 23 '18 at 1:26
  • $\begingroup$ @Geuis The thrusters are only there to generate g force, since the gravity well won't accelerate you. $\endgroup$ – Clay Deitas Aug 23 '18 at 1:28
  • $\begingroup$ @Geuis Did not see the update, will change things accordingly. $\endgroup$ – Clay Deitas Aug 23 '18 at 1:33

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