Helical Engine (Real)

[TheSchwa1337]

Basically, I'm of the opinion that any feasible design should be allowed in rocket design. As, if the math is possible, I don't see why the ship wouldn't be possible. 
There are a few tidbits, that would make it seem like an end game item, and I, would tend to agree. Seeing as the "structure" for such a rocket would likely mirror the design for some type of an ion engine. Since that is likely what it would look like in real life, if a working model were ever to be made by kerbal/human scientist.   It would travel "theoretically" at relativistic speeds. 

Given the scope of KSP2, I believe this would be a relevant discussion for possible ship designs.
(Please feel free to throw out anything else on your mind when it comes to ship designs for this awesome game! Lets discuss!)
Explosions behind ships are cool, but so is pushing the envelope, to the very brink of the speed of light. 

Let the Kerbal Space Program be the first intelligent life form to reach near light speed!

Here is a relevant information, since this is how it works. 
The original paper on the feasibility.  
https://ntrs.nasa.gov/citations/20190029294
https://ntrs.nasa.gov/api/citations/20190029294/downloads/20190029294.pdf


 

[K^2]

This is fully equivalent to a perpetual motion. It's relatively easy to show that a closed system cannot generate thrust in principle. Unfortunately, being absolute crackpottery doesn't stop someone from submitting a paper and having it show up on a NASA website. Bottom line, this does not work, cannot work, and there is no need to even consider the details any more than if someone was suggesting pulling themselves along with a magnet. This is just as stupid and for all the same reasons. No matter how much somebody thinks they've found a way around the most fundamental conservation laws, they haven't.

There are only two ways to move through space. You either gain momentum or you warp the space. Former requires an exhaust and later requires negative energy in sufficient quantity to screen the contained mass. In either case, momentum is conserved.

[Draco T stand-up guy]

8 minutes ago, K^2 said:

Former requires an exhaust and later requires negative energy in sufficient quantity to screen the contained mass.

May not require negative energy for warp drive:

 

[OHara]

5 hours ago, TheSchwa1337 said:

Basically, I'm of the opinion that any feasible design should be allowed in rocket design. As, if the math is possible, I don't see why the ship wouldn't be possible.

The particular proposal that you linked, the Helical Engine, is missing the bit of math to account for He+ ions pushing sideways against their confinement in the section of helix that expands on the way up, contracts on the way down.
(It reminds me of the tiny mistake in KSP1 --- forgetting to account for the temporary thrust when the conceptual fuel pumps start and stop --- that allows an entertaining exploit (youtube link))

If you want, you could open a discussion on the Science and Spaceflight subforum about how this idea was supposed to work, and whether it is a sound idea.  KSP players have a high fraction of people working/studying in technology, where a big part of the job is sorting out the 10% good ideas from the 90% that just sound good at first.   

Everyone has had their own seemingly-good ideas based on some misconception, so it is a useful skill to learn to find and understand others' misconceptions, and clarify the concepts in a kind and clear and tactful way.

5 hours ago, TheSchwa1337 said:

Given the scope of KSP2, I believe this would be a relevant discussion for possible ship designs.

Several KSP forum members dislike the idea of KSP-2 engine designs that have been proposed in real life, but which the more careful people think will probably not work.  Speaking for myself, I dislike them because of the experience in clearing up real-life misconceptions; if people get too excited too early it makes the tactful explanation more difficult.  In several cases, the misconceptions have been used to fool people  into wasting money and effort (sometimes used innocently, by people who were also fooling themselves).    I don't want KSP to remind me of the unpleasant effects of misconceptions in real-world science.

The niche of the Helical Engine is a low-thrust, high-energy-input, engine that expends no mass.  I don't think the expended mass can be zero, but some extreme proposals for ion engines (link) get close to this niche by accelerating a little mass very fast.  Some of the designs are superficially similar to the Helical Engine proposal.   I think that KSP2 could happily pretend that Kerbal technology somehow builds such ion engines, to open up possibilities for a fun KSP2

Edited May 31, 2021 by OHara

[Starhelperdude]

2 hours ago, Draco T stand-up guy said:

May not require negative energy for warp drive:

 

though warp drives won't be in ksp2, as nate simphson said in a interview

[Guest]

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Edited June 20, 2021 by Guest

[K^2]

10 hours ago, Draco T stand-up guy said:

May not require negative energy for warp drive:

They do. Net mass of the ship under warp has to be zero. I know a lot of theoretical work is missing out on that requirement, but they're also working with bare bubbles with no source of curvature within it. At a minimum, you need amount of negative energy to cancel the ship's mass.

It's a somewhat interesting topic with a lot of math, but the caveat is you want a drive that acts locally. Sure, universe can expand at FTL rates, but because that expansion is inherently non-local. If you can lay out rail from here to destination and warp space all along in any way you want, you can avoid this restriction. But if you can draw an imaginary bubble around your ship and the warp field and say, "The warp effects only space within this bobble," then you can pull in some theorems from tensor calculus and the fact that stress energy is a conserved flow under GR and show that non-zero mass warp would cause problems.

Alcubierre Drive works precisely because a bare bubble has a zero mass. If you place a source of gravity within Alcubierre Drive, you actually have to adjust the metric and end up with mass of the bubble being exactly negative of the mass of the source. It's a wonderful example because the math for AD is comparatively simple and these results can be worked out explicitly. But we also know that it's a fundamental limitation.  Any fully contained device capable of going FTL has to have a net mass of zero. (Edit: Or if it moves from one location to another without something absorbing recoil, I should add, even if you don't go FTL. You can actually show that it's the same requirement for both these things AND time travel by using the fact that there are no absolute frames of reference in GR.)

Edited May 31, 2021 by K^2

[Draco T stand-up guy]

13 hours ago, K^2 said:

They do. Net mass of the ship under warp has to be zero. I know a lot of theoretical work is missing out on that requirement, but they're also working with bare bubbles with no source of curvature within it. At a minimum, you need amount of negative energy to cancel the ship's mass.

Maybe not:
 

Quote

 

Abstract:

The Alcubierre warp drive is an exotic solution in general relativity. It allows for superluminal travel at the cost of enormous amounts of matter with negative mass density. For this reason, the Alcubierre warp drive has been widely considered unphysical. In this study, we develop a model of a general warp drive spacetime in classical relativity that encloses all existing warp drive definitions and allows for new metrics without the most serious issues present in the Alcubierre solution. We present the first general model for subluminal positive-energy, spherically symmetric warp drives; construct superluminal warp-drive solutions which satisfy quantum inequalities; provide optimizations for the Alcubierre metric that decrease the negative energy requirements by two orders of magnitude; and introduce a warp drive spacetime in which space capacity and the rate of time can be chosen in a controlled manner. Conceptually, we demonstrate that any warp drive, including the Alcubierre drive, is a shell of regular or exotic material moving inertially with a certain velocity. Therefore, any warp drive requires propulsion. We show that a class of subluminal, spherically symmetric warp drive spacetimes, at least in principle, can be constructed based on the physical principles known to humanity today.

 

GR isn't the end of knowledge. Like Newtonian physics its just a step and is likely incomplete.

[Bej Kerman]

22 hours ago, Brikoleur said:

(No thanks to this sort of thing though. It's not just that it doesn't work, it's also that it would make the game less fun. To see for yourself, try building a craft with a docking port drive in KSP1. It's kind of fun the first time, but after that it's just dull and makes the rest of the game pointless, unless you just enjoy zipping all over the place in a flying saucer. This would be similarly unbalancing.)

In the previous paragraph, you said this would still be limiting though. Maneuvering about when your impulse only faces away from the general direction of Kerbol (or Kerbin) could be quite difficult, or at least more difficult than using a Kraken drive that has much more acceleration and can face any direction. Point being that Kraken drives and solar sails are apples and oranges.

[K^2]

11 hours ago, Draco T stand-up guy said:

Maybe not:

Have you read the paper? Do you understand the physics of the warp drive? This is the specific mistake in the text.

Quote

Such solutions are possible because the D_warp region may be set arbitrarily close to being flat, rendering the whole spacetime arbitrarily close to Minkowski spacetime.

You can't make the space in that region arbitrarily flat if you have a non-zero mass ship within the bubble without screening the curvature with non-positive-definite stress energy in the warp bubble. QED.

Keep in mind, this isn't a peer-reviewed paper, and if I can find problems in it that quickly, it wouldn't have survived a peer review process.

11 hours ago, Draco T stand-up guy said:

GR isn't the end of knowledge. Like Newtonian physics its just a step and is likely incomplete.

The underlying symmetries in Newtonian and General Relativity physics has not changed, and that underlying symmetry is what kills the concept.

And on a less fundamental note, your argument is essentially that the very principles on which we build the idea of warp drives could be flawed. Which, ok, maybe. But then you jump to conclusion that it might make that technology more plausible? I think not. If GR is incorrect, then we're just making up a fantasy drive that has no chance of ever doing anything. Sure, there might be other means of propulsion somewhere in physics unknown, but it might as well be unicorn farts at this point.

The sum of all of humanity's knowledge tells us in a dozen different ways that warp requires exotic energy. Is that possible? We don't know. The requirement that we balance out the energy perfectly to create a flat region of space-time beyond the bubble is rather precise, however. It has to be effectively flawless. Clasically, that's problematic. So the idea of practical warp drive lives or dies on quantum gravity. And this is, unfortunately, where our models hit a big fat divide by zero, almost literally, and we need a better approach to the theory before we could even properly model the quantum behavior of a warp field to see if it's going to be possible to make it into a stable configuration that "wants" to stay in tachyonic regime.

The other bit of good news is that while a flawless warp bubble is necessary to go FTL, for subluminal warp, you are allowed a margin of error. If the space-time beyond the bubble is merely nearly flat, then you are generating wake of gravity waves compensating for the non-zero accelerating mass. That means acceleration will sap energy, but potentially orders of magnitude less than it would have taken to accelerate without warp. That's not bad. Of course, you still need that negative energy in the bubble, because without it, the gravity waves you generate have to carry all of the compensating momentum, and that means you'd be better off, energy-wise, to just have a photon drive.

Finally, a subluminal warp doesn't have to have a static warp bubble. We don't know if a static configuration with negative energy density is possible at all, but dynamically unstable systems with regions of negative energy density are well known. There are even published works showing that oscillating warp field can reduce the amount of negative energy required. The net mass of the ship and bubble still has to be close to zero, which means the ship will have to emit an enormous amount of energy on departure and absorb it on arrival, which is way more energy than we know how to deal with, not to mention all of the engineering problems of maintaining bubble stability given that it will want to collapse to the ground state instantly absorbing the ship as such into a net vacuum with a small puff of radiation... We're basically at the stage where we're trying to figure out how to ride a steam rocket to the Moon with all of this. But you know, at least we're making progress. One thing we know with absolute certainty - if we manage to come up with practical warp drive as prescribed by general relativity, it will involve some form of exotic energy. Anything else is the violation of the very principles going into designing the thing.

[Guest]

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Edited June 20, 2021 by Guest

[TROPtastic]

On 5/31/2021 at 2:31 PM, K^2 said:

They do. Net mass of the ship under warp has to be zero. I know a lot of theoretical work is missing out on that requirement, but they're also working with bare bubbles with no source of curvature within it. At a minimum, you need amount of negative energy to cancel the ship's mass.

This is far outside my area of expertise, but a 2021 peer-reviewed paper claims that, for specially constructed arrangements of spacetime called solitons, the violations of the weak energy condition of general relativity of the Alcubierre drive (thus requiring negative energy) do not happen. There is obviously some debate about the claims, but so far allegations that the concept is unworkable seem to miss the unique aspects of this solution or seem to be non-rigorous.

Of course, even the author admits that there is a long way to go from "pre-existing spacetime bubbles using massive amounts of positive energy are theoretically possible" to "here is a practical warp drive design", but the math behind the paper suggests that it is not as "impossible" as previous concepts that required negative energy. I don't think KSP2 should include stock warp drives given that the engineering for this concept has a TRL of 0, but it's still interesting to follow advancements in theoretical math.

[K^2]

@TROPtastic Yeah, the problem isn't with a structure that can move through space-time at whatever velocity. I honestly never looked into that too deeply. The problem is with taking matter here and making it go over there. That requires either forming a warp bubble around an object, transporting it, and dissipating the warp bubble, or trying to hop onto a structure that's passing by.

I was discussing strictly the former method. We can do more comprehensive analysis when we start with ship being the only source of gravity prior to warp and after the warp and place very strict requirements on the whole procedure that way. The outcome of that analysis is that either the space-time around the warp bubble is flawlessly flat, requiring negative energy densities, or the accelerating bubble produces gravitational waves that require energies comparable to a photon drive. For FTL case, that energy requirement goes to infinity, so the cancellation has to be flawless, but for sub-light "close enough" could reduce energy requirements to sensible levels.

Now, if you have a structure that's already moving, we reduce the problem to hopping on. The issue, however, is that if it's an FTL soliton, then how do you even without already having a warp drive? That doesn't mean it's not an interesting concept. If these solutions are physical, there could be any number of FTL solitons bouncing around our universe. If we can learn to interact with them in any way, we can at least try encoding information, and having an FTL broadcast capability would already be huge. If you give me a few bits of classical data over an FTL channel, I can walk you through turning it into a proper interstellar high bandwidth network with this easy trick quantum physicists don't want you to know about a modified quantum teleportation algorithm using entangled photons as carrier.

Still doesn't help you move ships, unfortunately, unless you go full stargate on this concept. Which, maybe you do, but that's an entirely separate can of worms.