Explaining Fusion Engines in Realistic Sci-Fi

Spacedock delves into the intricacies of fusion engines as applied to sci-fi space travel.

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[Spacedock]

Get "Designing the Perfect Space Fighter - A Spacedock Reference Book" here!

[wild_lee_coyote]

Interesting fact: fusion has a declining return on power output the heavier the elements you use. Fission on the other hand has a diminishing return with the lighter the element you use. There is a point where both fission and fusion return less energy than what you put into them. That point is the element Iron. The element where nuclear power dies.

[MrQuantumInc]

If you can bend space and time for the sake of faster than light travel then you can probably produce fusion by simply condensing the space around the fusion fuel until it achieved the pressure of a star. If you can produce gravity artificially under the floors of your ship just for comfort and health of the crew, then you can focus that effect onto a piece of fusion fuel.

[IncoherentOrange]

Terra Invicta puts a lot of effort into implementing all sorts of propulsion mechanisms in for the player to develop and use on their ships - for good or bad. Yes, you can have an Orion-based design, lots of crappy ion engines, or eventually work your way up to actually good inertial confinement drives.

[Stukov]

Crossing my fingers for a video about a nuclear salt water engine. The probably most insane, but achievable, engine concept ever devised.

[oliverdemille]

I love the depiction of "Cosmic Rays" :)

[mattiasdevlin]

You missed the most obvious alternative of electric confinement fusion or Farnsworth–Hirsch fusor. This design works like an ideal fusion engine from the start (very little modification needed of the reactor) and can be fed with B-11 and hydrogen to produce a fairly clean fusion process with only helium/alpha particles as a side product. It could theoretically have insane specific impulses and pretty good thrust to weight ratios.

[AnythingMachine]

The Epstein drive is not absolutely impossible in the sense of contradicting physics to build a fusion drive that efficient, as you just need to ensure that the reaction is external and confined in a magnetic bottle behind the ship so that almost all the waste heat just radiates into space, then the rest can be handled by spraying dense hydrocarbon slush or water or something into the exhaust plume.

Though some commenters have questioned whether the various tech assumptions with regard to fusion gain and efficiency improvements are reasonable.

Basically if you buy,

* Exceptionally powerful magnetic confinement at multi-hundred meter ranges
* Either incredibly powerful fusion ignition lasers (very brief exawatt pulses) or incredibly high gain factors based on far future discoveries about the dynamics of fusion implosion

Then it works. Both of these are not what I'd consider handwaves since they're not outright breaking any physical laws - they're things we don't know how to do, can't demonstrate are impossible, but that we can predict the physical consequences of.

Of the two, the more reasonable is the magnetic confinement, because we need maybe only a 1 order of magnitude improvement in the parameters of the superconductors (critical field) rather than 6 or more orders of magnitude improvement in fusion gain factor.

Both are physical phenomena that we either don't know the governing laws for or are too computationally complex to model, so what the upper limit of fusion gain factor is for a particular implosion design, or what the highest critical field superconductor in existence is, we don't know.

But even if this is how the Epstein drive works, an Epstein is putting out about as much energy as an antimatter beam core drive only without using antimatter and so the exhaust beam should not look like a normal rocket engine like it does in the show, but rather like a ravening gigantic solid lance of death as with the venture star.

[lazyremnant]

I'm very late to the party, but I just wanna say, if you want to use high-thrust fusion engines in your setting while still making it sound realistic, you can limit it to Solar System only.
We don't really need more than a few hundred km/s of exhaust velocity even to Pluto; we don't have enough time to reach higher velocity before the flip-off point is reached.
Since fusion engines are capable of spewing its byproducts up to 1000 km/s, we can easily trade some excess velocity for higher thrust.

[srbrant]

For my novel, I’ve come up with spin-polarized fusion engines with antimagnetic nozzles to keep their magnetic bottles from interfering with each other, since they’re often bundled together. In addition, I was thinking of adding a little handwavium by using gravitic repulsion to squeeze reaction mass out at a faster speed, increasing efficiency.

[salamanda]

"Has advantages, such as not needing gigantic radiators"

I don't know that kinda sounds like a disadvantage to me XD

[The--Illusion]

Could you do a video on exotic sublight engines? Things like Star Trek's impulse engine are exotic due to their function being very different from other drives, either due to the engine itself or due to other mechanisms (like the impulse engine is plasma directed to the needed port instead of just dumped out the back)

[joshpord]

Suggestion topic: asteroid mining

Examples: EVE Online, The Expanse, Don’t Look Up

[antonberkbigler]

So, as part of an extremely expansive crossover AU I made a concept for a fusion reactor+engine that would have been made by Aperture Science. The key thing to remember with them is that although they are extremely smart, they also happen to be tremendously stupid and silly. So, the reactor part of it essentially used highly complex gravity fields to house an artificial star, with two exit points at the poles. Extremely energetic jets of fusion plasma would be emanated out of the artificial star and then piped into a series of pistons, literally just steam locomotive pistons in regards to design. Those pistons were hooked up to either solenoid or dynamo generators, but that’s whatever. This version of Aperture Science didn’t have anything strong enough to make turbine fans that could withstand fusion plasma, but they did have concepts for having twisted magnetic fields to create a sort of magnetic turbine fan in later iterations of this fusion reactor. The plasma would then be routed to a thruster mostly as just a way to utilize exhaust since they can’t just dump it Willy nilly like steam exhaust, but there is a sort of 'afterburner' system that would create a complex linear gravity field to fuse the plasma an additional level up the stellar fusion chain. Main reactor fuses hydrogen to helium, afterburner fuses the helium together.

[Tigershark_]

Spacedock is unironically one of my favorite youtube channels currently!
I was wondering: if you folks could make your dream air force (can use already existing aircraft or design your own), how would you make it?

Also, what would be your dream realistic fighter jet (invented from the ground up)

[tyrannicpuppy]

One thing I found myself super curious about by the end of The Expanse was what would it feel like to be inside the moving drum of the Nauvoo during the originally intended journey to it's new star system?

Because you get gravity along the length of the ship via the engines thrusting forwards, which presumably needs to keep happening through the entire trip for it to take even a remotely reasonable amount of time. And rotational gravity in the drum via the spinning of the drum.

So would you have two different sets of gravity pushing you against the outer edges of the drum and also feel like you were constantly being pulled in the direction of the engines at the end as well?

[kevinshepardson]

As a bonus, this also counts as a video on sci-fi weapons, per the Kzinti Lesson.

[richardrothkugel]

I'm working on a space game and I was using spaceship hulls that had about twice the mass of modern Navy warships (between 7000 and 14000 tonnes) on account of shields, plating and additional technology. I was planning using fusion reactors with ion thrusters as a baseline and found that constant thrust between 5000 and 30000 newton was the sweet spot for acceleration in my environments. Glad my calculations were on point.

[jlc]

I literally had this wait a second and process why is the spell jammer, (a giant magical, manta ray that swims in space in D&D )was an episode about fusion. Cosmic rays I go to bed now.

[montecorbit]

At 5:55
"....greater than a hummingbird's fart...."

That was pretty good, I had to stop and laugh at that!! Thank you....