Realistic fast Interstellar Propulsion Methods

[Erik1801]

This is my first time posting, so please excuse any mistakes.

I am grasping at straws here. I am working on a Hard-Sci Fi novel, plot, arcs, characters etc. are all worked out and i decided to take the deep dive in terms of Realism. For instance, there are no Fusion reactors. All that is important in terms of Setup is that we have Humans, and they want to go to a nearby Star system. Its ~4 Ly away and we would like for this transfer to not take 1000s of years.

The issue I am facing is that there seems to be no way to do this. I.e. achieve a high enough Velocity, fast enough, for the journey to not take 1000s of years. At least without breaking thermodynamics in a big fashion.

For example, I was told a Particle accelerator based propulsion system (using for example a Wakefield accelerator) could be a good method because the exhaust velocity is so high and it is pretty compact. In principle that is true, but when you go and do math, taking into account that the system will experience heating (We assume the Ship gets its power via a energy beam, microwaves or something. It doesn't carry the power generation equipment. The power is beamed to it). Even at a magical total system efficiency of 80% (So you pump in 100 Watt, 20 Watt is heat and you get to do work with 80), the real world acceleration might as well be nothing.

See this. It is possible that I didn't do the math correctly, but like Jesus.

As you can see, assuming a 400 GeV accelerator, a Radiator area of given, an Efficiency of 80% and a Ship mass of 100.000 tons (That number is based on some assumptions about Crew size, needed cargo capacity and some Ratios. For example that for each kg of Cargo you need ~0.25kg of Structural support), it takes 77000 Years to get to 0.127c.

I did similar math with Fusion (As in a Fusion reactor powered by the external beam), Anti-Matter, god dam light sails and even this really dumb concept, i think NWRE, which proposed to use a Fusion Engine to somehow cool an even better Engine.
My results were that while all of these would eventually get us to the target, all of them took like half a billion years (Hyperbolic). As a matter of fact, the particle accelerator performs the best. Which is like.... 77000 years D:

As it is so often the case, the issue is Heat. If we had a Radiator the size of Luxemburg we could get much better acceleration. Which ignores that a radiator the size of a nation presumably weighs more than 100k tons but also the practicality of carrying such a thing.

Ideally, i would like to have a solution which can get to 0.5c in ~24 Months. Which would mean a constant acceleration of 2.5m/s². But as far as I can tell, this is just straight up not possible as long as thermodynamics are of any concern. Of course this "works" if you bump the efficiency to something stupid like 0.99999999, but even then the accelerator would eat 80 times more energy than the World currently consumes. Which, I don't think is impossible in principle. I just seriously doubt you can concentrate that much energy into a 800 meter long accelerator.

And this is were I am stuck. People on Reddit keep talking about fast Interstellar transfer methods but all the ones I looked at just don't work as advertised. Even the all holy Anti-Matter based propulsion systems cant do this, because the ships would just be to heavy for any serious acceleration.
That being said, there is the option that i missed something very obvious somewhere along the way, hence why all the numbers look so terrible. I just have the detailed breakdown for the method for the Wakefield thingy, but guys... no propulsion method is bussin ngl.

So, to finish this off, my two core questions are;

1. Is there anything obviously wrong with my Math and or am I missing something which solves the thermal issues ?

2. Are there any methods of propulsion which could do the task ? I.e. 0.5c in 24 Months.

I hope this is informative enough to make answering it possible, if not like I am sorry xD Hopefully i can give good clarifications to comments should the need arise. Also excuse any typos or bad gramma, Ich bin deutsch und hab legasthenie.

 

[Filip Larsen]

Can I ask why you have settled on 1000 years as desired (max) travel time? Also, what is the reason the humans want to go there and is it a requirement that those who board the ship at Earth also gets to experience the destination system (which obviously makes it much harder to achieve)?

 

[Vanadium 50]

there seems to be no way to do this.

That is correct. If there were, we'd be sending probes to planets as science fair projects.

Efficiency of 80%

More like 0.1% is state of the art.

Your problem is simple. If you want to go at half the speed of light, you need to convert one quarter of your ship's mass to energy. We don't have a technology that can do that. If you allow lower efficiency, you need to carry more fuel, and more fuel to propel that fuel, and nor more fuel to propel that fuel, and now you have the rocket equation. And building a rocket to do this is impractical;.

What we want and what we can do are not the same

 

[Erik1801]

Can I ask why you have settled on 1000 years as desired (max) travel time? Also, what is the reason the humans want to go there and is it a requirement that those who board the ship at Earth also gets to experience the destination system (which obviously makes it much harder to achieve)?

So the 1000 year thing was hyperbolic. I should have included my desired timeline, which is ~7-8 years to get from Earth to the target. This is all still near future (around 2300). The reason why Humanity goes out there in the first place is because in a nearby system there is a source of Metallic Hydrogen. Essentially duo to geological quirks there is a planet which has Metallic Hydrogen deposits inside the Oceanic tectonic plates. Which in this universe is assumed to be what we irl hope it to be. So a high critical current Room temperature superconductor. Such a material would be just about the only thing i think could work as a motive to set up a large interstellar operation. But judging by the numbers, it isnt xD Regardless, the plot will still happen with it but i would just like to have something more plausible than "Ah yes, the magic engine".

TLDR; Humans want a RTS from an Exoplanet and they aint got no time to wait. This is just in time logistics chains !

 

[Erik1801]

That is correct. If there were, we'd be sending probes to planets as science fair projects.
More like 0.1% is state of the art.

Your problem is simple. If you want to go at half the speed of light, you need to convert one quarter of your ship's mass to energy. We don't have a technology that can do that. If you allow lower efficiency, you need to carry more fuel, and more fuel to propel that fuel, and nor more fuel to propel that fuel, and now you have the rocket equation. And building a rocket to do this is impractical;.

What we want and what we can do are not the same

;( I knew it was hard, but man.... its really hard to go interstellar.

Also... wdym 0.1% for the love of god i see my dreams getting incinerated ! 0.1%.... that's just straight up not bussin. But is that actually the efficiency Particle accelerators work at ? I was not able to find good numbers for Wakefield style accelerators. And machines like the LHC use superconductors, so i assumed it was fairly efficient ?

I was actually surprised how brutal the math is with these things. You can get decent acceleration for like 10 seconds or one measured in nm/s² for 1000s of years. But no matter how i change the numbers, make assumptions it never gets even close to what i would want. I guess in that sense it is hard sci-fi xD I feel like a real rocket engineer ! Because my dreams and hopes get burned...

May i ask, in your opinion, what would be the type of propulsion you would be the least "iffy" about ? Ultimatly non of this math is included in the Novel obviously. So i guess seeing as how it wont be possible to make it plausible on that level, the next best thing is to make it plausible on a word level.
For example, would you think it is more believable to use say Anti-Matter ?
From the numbers, my feeling is that using a particle accelerator is still the most semi-plausible way. But i dont know how other people would see that or if it is even true...

 

[Nik_2213]

IIRC, the BIS 'Daedalus' approach using pulsed fusion --Like 'Orion' but comparatively 'benign'-- would seem the logical contender. Starwisp is micro-scale, laser-boosted solar sails need a lot of compliant tech at home...
Big snag is such pulsed fusion looked practicable, but proved a cruel mirage: Almost half a century along, a rampant zoo of fusion failure modes are still slowly, expensively being beaten into submission...
IIRC --My autographed copy of 'Daedalus Final Report' is boxed away-- the un-crewed craft would need Deuterium 'mined' from eg Jupiter and much Tritium made for 'aneutronic' power.
That would be the 'lead' probe, effectively a 'sounding rocket' to demonstrate the tech with a fly-by of eg Barnard's Star. Of course, now we know there's an actual extra-solar planet or two in the Alpha Centauri / Proxima family that's the logical target.
Hardware proven, the Deuterium 'mines' and Tritium 'cookers' now fuelling many ships flitting about our solar system, a much, much bigger, crewed version becomes practicable, then buildable...
'Gotcha' is by that time, 'Teleparallel Gravity' may have been proven, realised in hardware. Still need those mega-tanks of Deuterium etc, but an entirely different propulsion paradigm...

 

[Vanadium 50]

You can estimate by looking at the electric bill to operate the accelerator compared to the energy output. But ultimately you are building a rocket so you're stuck with the rocket equation, which is not your friend.

Wakefields are even less efficient. Essentially, they couple two accelerators together, so your pay the price twice.

I decline to speculate on the last "iffy" option. If we had the technology, we'd have the technology. However, it is worth noting that the slower you go, the easier this is. A 15 year trip to Alpha Centauri is a lot easier than a 10 year trip and a 10 year trip is much easier than a 5 year trip.

 

[Erik1801]

IIRC, the BIS 'Daedalus' approach using pulsed fusion --Like 'Orion' but comparatively 'benign'-- would seem the logical contender. Starwisp is micro-scale, laser-boosted solar sails need a lot of compliant tech at home...
Big snag is such pulsed fusion looked practicable, but proved a cruel mirage: Almost half a century along, a rampant zoo of fusion failure modes are still slowly, expensively being beaten into submission...
IIRC --My autographed copy of 'Daedalus Final Report' is boxed away-- the un-crewed craft would need Deuterium 'mined' from eg Jupiter and much Tritium made for 'aneutronic' power.
That would be the 'lead' probe, effectively a 'sounding rocket' to demonstrate the tech with a fly-by of eg Barnard's Star. Of course, now we know there's an actual extra-solar planet or two in the Alpha Centauri / Proxima family that's the logical target.
Hardware proven, the Deuterium 'mines' and Tritium 'cookers' now fuelling many ships flitting about our solar system, a much, much bigger, crewed version becomes practicable, then buildable...
'Gotcha' is by that time, 'Teleparallel Gravity' may have been proven, realised in hardware. Still need those mega-tanks of Deuterium etc, but an entirely different propulsion paradigm...

As a part of the process i looked at something similar in concept, i think they called it a Fusion Highway. Basically you have a bunch of pallets layed out ahead of the ship. The ship then rams into those at every higher speeds and propels itself with pulsed fusion.

What you cite here sounds more reasonable. According to the first link on google, the og study proposed a travel time of 30 years for 5.9 Ly. Which is like... manageable. It is better than having to have an engine that is 1000s of times more powerful and efficient than possible. Though i am somewhat iffy on the numbers here.

From the Wiki it seems like Daedalus would use a pretty piss poor version of on board Fusion. I assumed external power being beamed to the Spacecraft and i didn't get anything near their performance for Fusion. And presumably my approach with beaming energy to the ship would be more effective ?

 

[Nik_2213]

"...beaming energy to the ship would be more effective ?"

Yes, but relies on the beam-system not having its plug pulled by adverse circumstance, be that politics, geology or fanatics...

 

[Erik1801]

"...beaming energy to the ship would be more effective ?"

Yes, but relies on the beam-system not having its plug pulled by adverse circumstance, be that politics, geology or fanatics...

Hm... ok ill look at my math for fusion again. Clearly something has gone wrong.

As for the power being cut, well... as my grandfather used to say, if they cut the power you will still break records as the fastest frozen corpses in history ! Always see the positive side of any situation !

 

[Vanadium 50]

Something else to think about. A rocket gains momentum p by tossing out mass with momentum -p out the nozzle. The energy it takes to do this is p²2/2m. So to minimize the energy you want to maximize the mass. So exotic propulsion like light or elementary particles all moves this in the wrong direction. You want m large, not small.

 

[Filip Larsen]

You want m large, not small.

By this you mean large ejected mass relative to the payload mass, giving a large delta-V from the rocket equation? If so, light is still the most fuel efficient propellant, i.e. giving the largest delta-V for same mass ratios (but has thos insane power requirements for high acceleration which I assume OP was referring to in first post).

 

[Rive]

I did similar math with Fusion

Hard sci-fi usually does not means no realilty-breaking at all: it means only limited amount of reality breaking, paired with reasonable math done where it's possible.

Any intent on going the Larry Niven way?

 

[Erik1801]

Hard sci-fi usually does not means no realilty-breaking at all: it means only limited amount of reality breaking, paired with reasonable math done where it's possible.

Any intent on going the Larry Niven way?

The ramjet has to be my favored type of spacecraft :D Its just so "us". "Ah yes, space is a vacuum, but what if we just travel so fast that isnt anymore ?"

Of course, this would be amazing. Which it is why it could never happen, no fun allowed in the real world ! I thought about using such a system but ultimately, especially after the comments here, i got my suspicious that while my math is obviously not perfect the general trend of "yeah no you cant travel this fast between stars" is correct.

In order to make it more believable, i split up the Human and cargo side of interstellar travel. Essentially there is a fast lane which consumes like 1000 times the energy to get Humans to the planet fast. And then there is the slow cargo lane that uses solar sails and takes 30-40 years to get to Earth.

That's probably a good balance between just laughably powerful ships but still the acknowledgment that this can only be done for Humans and anything of a time sensitive nature.

The basic line i drew is that the fast lane transports 200000 tons of Cargo each year using 20 ships, but has such a gigantic logistical and energy footprint that any expansion of this lane is just not practical anymore. Where as the slow lane transports 600000 tons of cargo each year at a energy cost so much smaller that it is not worth mentioning.

 

[Erik1801]

By this you mean large ejected mass relative to the payload mass, giving a large delta-V from the rocket equation? If so, light is still the most fuel efficient propellant, i.e. giving the largest delta-V for same mass ratios (but has thos insane power requirements for high acceleration which I assume OP was referring to in first post).

Here is the thing, if i raise the Particle mass yeah the ships get more acceleration. But the exhaust mass climbs fast to the point of several kg/s. Which is not going to happen within the mass limitations xD

 

[Filip Larsen]

In order to make it more believable, i split up the Human and cargo side of interstellar travel.

It certainly seems more feasible. If the destination system contains other resources, e.g. asteroids, it would make sense sending "light-weight" autonomous probes ahead that can locate and harvest local resources and start manufacturing heavier equipment to be ready for when the crew arrives. Assuming there is no rush to get there as such (other than perhaps the usual corporate incentive to beat any competition also aiming for mining the desired resource) it would make sense to establish an autonomous presence at the destination over time (e.g. 50 years) and only start the manned transports when enough of that has been established. Having established basic manufacturing capabilities also means you can now "send" new cargo to the system in 4 years simply by sending new designs to be manufactured.

However, the manned crew vehicle is still going to be a challenge. If the incentive to visit the system is to mine that highly desired resource and return it to Earth, then I would think it far more feasible to just stick with a fully autonomous mining operation, i.e. the corporate incentive would be to not send a human crew at all but just rely on the automation to eventually work. But I guess not having a crew vehicle will make a much different and adventure-less story.

 

[Erik1801]

It certainly seems more feasible. If the destination system contains other resources, e.g. asteroids, it would make sense sending "light-weight" autonomous probes ahead that can locate and harvest local resources and start manufacturing heavier equipment to be ready for when the crew arrives. Assuming there is no rush to get there as such (other than perhaps the usual corporate incentive to beat any competition also aiming for mining the desired resource) it would make sense to establish an autonomous presence at the destination over time (e.g. 50 years) and only start the manned transports when enough of that has been established. Having established basic manufacturing capabilities also means you can now "send" new cargo to the system in 4 years simply by sending new designs to be manufactured.

However, the manned crew vehicle is still going to be a challenge. If the incentive to visit the system is to mine that highly desired resource and return it to Earth, then I would think it far more feasible to just stick with a fully autonomous mining operation, i.e. the corporate incentive would be to not send a human crew at all but just rely on the automation to eventually work. But I guess not having a crew vehicle will make a much different and adventure-less story.

I would agree, you need a lot of exploration and autonomous missions ahead of time before sending the big boys. Or gals.
That being said, there is a rush to get there because, well this might not be strictly legal. In that, in world Humanity has agreed that this planet with the resource (Hela) belongs to the native life. Right until the moment someone noticed these weird magnetic fields in the oceans and was like "Is that a superconductor ?". The nanosecond this discovery was made, people asked "Yeah but what does "belong" really mean ?". One power block of the ongoing cold war on Earth found a clever way to avoid these legal and moral questions. You see, it is impossible to be subjected to International law if you never enter international jurisdiction. That's right, according to a lot of nations the Planet of Hela is not as a matter of fact in international waters like literally the entire rest of the observable universe but is actually a US territory. Obviously.
Is this legally dubious ? Yes. Is this immoral ? Yes. Do we care ? No. Will we allow other nations to mine ? They can certainly try !

On Humans. The way i see it automation, even really good one, is not worth it. Humans, in a sense, are automation. In that you make an upfront investment and get a tool, i.e. worker, how can change adapt and overcome. Ultimately you will have to have some guys over there regardless just for accountability, security and research reasons.
So i figure, they might as well make the core of the operation Human dependent.

That being said, a lot of stuff is automated. For example the ITV´s (So the fast spaceships) fly themselves and can deal with most issues / handle situations. Like refueling etc. The launch infrastructure to get the RTS into orbit is mostly automated and even the Off-Shore Drilling machines are automated. But it all happens with Human supervision. And well, often times it is easier to send a guy down and hit the thing with the wrench instead of having Boston Dynamics give it a shot.

 

[Vanadium 50]

Fundamentally, the issue us that the OP wants two incompatible things - "realistic" (with technology not much beyond today, e.g. he specifies "no fusion") and "fast interstellar travel".

Can't have it both ways.

Thee nearest star is about 100,000,000x as far as a person has ever traveled. This is comparable to a high jump vs. going to the moon. A pretty big gap to face.

 

[Algr]

Realistic fast Interstellar Propulsion Methods​

...don't exist.

Even generation ships seem very unlikely, IMHO, because of the social and political realities of keeping tiny communities stable for thousands of years. Look at Easter Island, or Biosphere 2 to see how that ends up. If you somehow transformed humanity into something that could survive the journey, they would not want to leave the ship. This goes double if they have to live underground for thousands of years after they arrive. (Due to no atmosphere or ozone.) They could have done that on post-nuclear-war Earth, so why go?

As I've said elsewhere, the only method with any chance of success would be clone ships. (IMHO again) These are DNA sample libraries, and human minds stored as data recordings. The ships are inert for thousands of years during the journey, and then the simplest life forms are cloned and revived first to terraform the destination. Progressively larger plants and animals would then be revived once possible, and humans regenerated last. This could take longer than the journey, but the humans would awake to find what they actually want: A viable new world to live one.

 

[gmax137]

This is why sci-fi always has warp drives or whatever. Apparently it is hard to write an interesting story where no action occurs over thousands of years.

As far as motive for going, I have a hard time believing any "resource" will have a positive ROI. The only motives that make sense to me are "the spirit of exploration," exotic sex with the inhabitants, or maybe exotic spices to make interesting food. Just look at what drove the sailing ships on multi-year voyages here on earth.

 

[Drakkith]

If you want to go to the nearest star, all you need to do is to throw mass out the back of your spacecraft (or light if you're really into raves and lases and not getting anywhere soon). We know how to do this. It can be done. But it cannot be done cheaply, it cannot be done quickly, and it cannot be done without stupendous amounts of fuel. The straightforward way is to simply build a really, REALLY big fuel tank (or a bunch of somewhat smaller fuel tanks that can be jettisoned when empty) and strap a bunch of engines onto it. Also a cockpit and living quarters and whatever else you need. Boom. Problem solved by application of brute force. Except for the 'fast' part.

The payments for your loan on your five-million metric ton spacecraft will be due monthly and your great-great-great grandchildren will probably still be paying it.

 

[Algr]

all you need to do is...

The three showstoppers for interplanetary journeys are:

1) Surviving the journey. This will take thousands, not hundreds, of years to go. Human societies have never survived that long without engaging in catastrophically destructive conflict, or other social psychosis.

2) What you will find on the new planet. There is zero chance of any extraterrestrial planet having an atmosphere breathable to humans. If oxygen exists, the lifeforms that made the oxygen will include pathogens that are profoundly unlike anything the human immune system has ever dealt with. It would probably be better to find a proto-habitable world, and terraform it with life from Earth. But that would take more thousands of years and is utterly uncertain to work. Meanwhile everyone is living where? In underground caves?

3) Convincing anyone to go. So if you go on this journey, you are committing yourself and your descendants to live in tight cave-like quarters or actual caves for probably tens of thousands of years. The risks of total extinction are enormous. But if we include actual Earth caves and the kind of technology needed for a generation ship, Earth could probably hold a hundred times its current population, with far greater safety and comfort than a generation ship. Antarctica is the garden of eden compared to what the colonists will face.

Even if nuclear war or total environmental collapse happens on Earth, conditions won't be so bad as even Mars, let alone some unknown extraterrestrial planet. Why go to another solar system when you can live in beautiful Antarctica?

 

[Rive]

there is the slow cargo lane

I can't really imagine any type of cargo which would make decades of waiting (after the establishment of a colony) faster (and: cheaper) than just producing it at the ends of the lane (any type of unobtainium is expected, but those should not be included in the first place).
Are you sure this would actually make the setup more believable?

 

[Erik1801]

I can't really imagine any type of cargo which would make decades of waiting (after the establishment of a colony) faster (and: cheaper) than just producing it at the ends of the lane (any type of unobtainium is expected, but those should not be included in the first place).
Are you sure this would actually make the setup more believable?

So, the way i have it set up rn is that this is not a Colony. Its a drilling operation. The idea is that duo to a chain of unlikely geological and astronomical events the planet of interest has metallic hydrogen in its crust. Mainly underneath the oceans because anything close to the surface has reacted away by now.

This is just about the only thing i can imagine being worth it. I am assuming that Metallic Hydrogen is indeed a Room temperature superconductor with a wide range of applications. So for instance, the critical current is high enough that it can be used for most if not just all Electronic applications.
Of course for this to work you need a lot of the stuff. 350 tons every year is not going to cut it. 600000 tons over the slow lane ? Maybe ? The main issue with making this number much bigger is that the Daily orbital lift capacity has to already be >1500 tons for this to work.

As for the slow lane being more believable. I think so, but i could be wrong of course. Supply side economics are not my strong suit, but in principle as soon as the system stands you get a steady supply of the stuff. The main issue is that the reaction time of the system is you know, decades.

 

[Erik1801]

This is why sci-fi always has warp drives or whatever. Apparently it is hard to write an interesting story where no action occurs over thousands of years.

As far as motive for going, I have a hard time believing any "resource" will have a positive ROI. The only motives that make sense to me are "the spirit of exploration," exotic sex with the inhabitants, or maybe exotic spices to make interesting food. Just look at what drove the sailing ships on multi-year voyages here on earth.

I think here we just fundamentally disagree. I don't think there is such a thing as "Spirit of exploration" with interstellar set up´s beyond sending a single probe. We see it with the Moon or Mars, both of which we could have either gone back to or got there by now. Yet we just don't really care because there is no incentive to do so.

I agree that resources are a tough sell. I was trying to make the resource in question (Metallic Hydrogen as a RTS) so useful that it would become practical to do. Even so, there is no shot this whole venture on its own makes any green numbers xD Which is fully acknowledged. The Company running this is semi nationalized and funded by over 44 Nations. There goal is not to make cash but to supply this resource to the member states.

I feel like this makes more economic sense because the impact of Room temperature superconductivity are so wide reaching and fundamental it should eventually pay off. At least once the system stands etc.
Now, that is just me and in a 100% realistic Scenario the planet could be entirely made of that stuff and it would never be practical to get it as we cant go there. And of course all of this also assumes it is easer to set up a Interstellar mining operation than to compress Hydrogen at 500 GPa. Which tbf, is quiet hard and unlikley to ever be scalable.

 

[Rive]

Metallic Hydrogen is indeed a Room temperature superconductor with a wide range of applications.

... sigh.
At this point with that extremely unstable (which can be made artificially even now) stuff mined from under an ocean you already have sufficient amount of handwavium at hand to make the whole 'fast and realistic interstellar propulsion' topic just a teeny bit absurd.

I would not push it so much. It does not worth to trade a smaller handwavium for multiple big ones. Just go on with whatever usual interstellar drive you see fit for your story, regardless the realism.

Remember: story rules.

 

[Erik1801]

... sigh.
At this point with that extremely unstable (which can be made artificially even now) stuff mined from under an ocean you already have sufficient amount of handwavium at hand to make the whole 'fast and realistic interstellar propulsion' topic just a teeny bit absurd.

I would not push it so much. It does not worth to trade a smaller handwavium for multiple big ones. Just go on with whatever usual interstellar drive you see fit for your story, regardless the realism.

Remember: story rules.

In some way it is ironic. I really tried to find something to justify all of this. But ultimatly i had to acknowledge the fact that the fast aspect is impossible as it stands. Thankfully the story itself dosnt really focus on those aspects. Still, would have been nice to have something more realistic but i guess you gotta take what you get

 

[Rive]

Thankfully the story itself dosnt really focus on those aspects.

It's a common trap trying to turn the story to a sightseeing tour in the personal universe of the writer.
But usually that'll only muddy things and divert the attention (both the author's and the reader's) from the story itself.

Hard sci-fi is hard due being hard on the really relevant things.

I recall the mesklinite series of Hall Clement revolving around the weather of multiple high gravity words (with different atmospheric constitutions), but mostly just waving about the way human crew got there...

 

[Erik1801]

It's a common trap trying to turn the story to a sightseeing tour in the personal universe of the writer.
But usually that'll only muddy things and divert the attention (both the author's and the reader's) from the story itself.

Hard sci-fi is hard due being hard on the really relevant things.

I recall the mesklinite series of Hall Clement revolving around the weather of multiple high gravity words (with different atmospheric constitutions), but mostly just waving about the way human crew got there...

I can attest as much xD My first proper novel attempt had this exact issue were i focused to much on the world. I am pretty confident this current attempt is avoiding it because i actually have strong themes, character arcs and clearly defined motivations, and am just now starting to consider the setting more broadly. So hopefully i am on the right track there.

I think a big part of the Hardness is to only talk about what does not need huge mental gymnastics to work. So there is value in knowing what doesn't work. For instance, after the discussions on this post i think it is a good move to intentionally avoid being to descriptive on the way the Thrusters for the Interstellar ships work. They just do, they provide thrust, you gotta refuel 10 times, and the ship is like just Radiators visually speaking. Just radiators everywhere you look. And that's as far as it goes.
On the other side of the coin, i can be more descriptive on what for example the exhaust looks like. Just a straight line, like a laser, going from one end of the Horizon to the other. Or rather disappearing / Fading out because the exhaust is just a relativistic jet at this point.

Virtually all of the story happens on the planet, so the biology of it is a lot more important. And i have a meeting with an actual biologist lined up to gain some more insight into the subject. Hell, one Character´s arc includes a Cell biology problem. So that will need a ton of research xD But then again, biology here is a solvable problem. Unlike the Thrusters xD

 

[Drakkith]

@Erik1801 Metallic hydrogen itself, outside of the core of high-mass planets, is already a pretty big break from reality. If nothing else I'd bring fusion power into your universe, as it is probably the most plausible power generation method to bring in.

 

[gmax137]

I'd bring fusion power into your universe, as it is probably the most plausible power generation method to bring in.

Well, that's what everyone thought, until 2093, when Huynh Bihn and Bart Mpemba independently discovered what we now know as the H-M drive. No, not that Mpemba.

That's all it takes for me, my disbelief is suspended...

 

[BWV]

The difficulty and cost of interstellar travel also make it economically stupid, so you have to have relatively cheap and easy interstellar travel to make you metallic hydrogen profitable to mine

And if its just mining, why send people? send billions of nano-ships that can be shot or propelled by local power sources, then assemble themselves in to a mining rig and some method for shooting the stuff back to our solar system?

 

[Drakkith]

@Erik1801 In any case, a story is, usually, about people and events, not about which propulsion technology those people are using. A story about a group of people sent to mine metallic hydrogen from another star system can be well loved if it is compelling and interesting even if the science isn't entirely realistic. Science and technology should serve as a framework for your story, showing you what is and isn't possible according to in-universe physical laws. Don't be afraid to change something to make your story more interesting, believable (as in make the story believable, not the science), or easier to write.

Just keep things consistent. A journey that takes 15 years and a million-ton vessel shouldn't suddenly be replaced by a journey of 5 years and a vessel of 5000 tons without a good explanation and reason in-universe. The more severe the jump, the more it taxes believability and the more extreme your explanations have to be to justify it. The jump in technology I just mentioned can be explained away pretty easily by saying "The application of intense research and copious amounts of money over thirty years gave us the Daedalus drive". But a sudden jump from decades-long journeys to FTL travel probably shouldn't be explained away as, "And then some kid from Boston developed an FTL drive."

Unless that's the 'style' of your story of course.

As is the case, anything is possible in fiction. People will accept very nearly anything if it fits the style and/or focus of the story. Remember, people mostly care about people and what those people do, not about the science letting them do it.

 

[gmax137]

. Remember, people mostly care about people and what those people do, not about the science letting them do it.

This^^^

 

[Filip Larsen]

Remember, people mostly care about people and what those people do, not about the science letting them do it.

True, but for a good sci-fi you kinda need a good mix of both. For example IIRC in Gentry Lee's continuation of the otherwise fascinating Rama story universe by Clarke, Lee ended up with a story that disappointing had almost nothing to do with Rama, the Ramanians or their technology. Using a spaceship in the story setup only to get a group of people "stuck with each other as if on an island" is in my opinion not enough to make it sci-fi.

 

[Drakkith]

True, but for a good sci-fi you kinda need a good mix of both.

I'd say you need to be consistent within your story and/or fictional universe. I haven't read the story you mentioned but it sounds as if Lee's choices were inconsistent with the tone, style, or other things that made the Rama universe well liked.

 

[Erik1801]

@Erik1801 In any case, a story is, usually, about people and events, not about which propulsion technology those people are using. A story about a group of people sent to mine metallic hydrogen from another star system can be well loved if it is compelling and interesting even if the science isn't entirely realistic. Science and technology should serve as a framework for your story, showing you what is and isn't possible according to in-universe physical laws. Don't be afraid to change something to make your story more interesting, believable (as in make the story believable, not the science), or easier to write.

Just keep things consistent. A journey that takes 15 years and a million-ton vessel shouldn't suddenly be replaced by a journey of 5 years and a vessel of 5000 tons without a good explanation and reason in-universe. The more severe the jump, the more it taxes believability and the more extreme your explanations have to be to justify it. The jump in technology I just mentioned can be explained away pretty easily by saying "The application of intense research and copious amounts of money over thirty years gave us the Daedalus drive". But a sudden jump from decades-long journeys to FTL travel probably shouldn't be explained away as, "And then some kid from Boston developed an FTL drive."

Unless that's the 'style' of your story of course.

As is the case, anything is possible in fiction. People will accept very nearly anything if it fits the style and/or focus of the story. Remember, people mostly care about people and what those people do, not about the science letting them do it.

Sorry for the long response time.

Ill reply to both comments you made here. The first was related to Metallic Hydrogen´s stability outside the core of gas giants. So, obviously, we dont know exactly whats up with Metallic Hydrogen besides that some theory suggests it might be a Superconductor and that it might be metastable at room temperature and pressure. I am willing enough to say it is for the sake of argument.
The big issue i faced was, well what incentive could there ever be to set up a operation on the scale i want ? Room Temperature superconductivity seems to be kind of the only one which works within the context of the story. Where we assume just some straight up magic Engines.

Onto this comment. I think you touched on something important there. The way i make stories is by starting with the theme, going to character motivations, deriving characters from there, then arcs and then the world around them.
For the theme, it is extremely helpful to have the whole interstellar drilling Op set up. It just plays well with it and the character metaphors. It would work on Earth, but that would also miss the mark thematically speaking. Regardless, i tend to focus way to much on these rather unimportant aspects late in the game because i just want to know what XYZ would be like. Be that a Thruster or Biology.

For consistency, i cant agree more. As mentioned in other places, the story really does not care about this particular aspect aside from some nice visuals. (At least to my understanding, such a Thruster would produce exhaust that looks like a straight line across the sky, slowly fading out duo to doppler beaming) In any case, it is made pretty clear that the transit is dangerous, each ships flight is planned a two decades in advance at least, it is super expensive and technologically speaking there isnt much room left to be faster.

On the last part, you see this gets me confused. I hear this from a lot of people and i do think characters are the A and O, but people are also really fast to complain about bad science. So, it seems like you still need to invest a lot in making the science supporting everything accurate

 

[Drakkith]

but people are also really fast to complain about bad science.

You need to know what you're writing about. You can't write about someone falling out of an airlock without a helmet on if you don't know anything about how people react when exposed to the vacuum of space. You can't write about a fighter pilot in world war two if you don't know anything about world war two aircraft. You can't write about a radio technician forced to repair a damaged VLF receiver on a submarine if you don't know anything about subs and radio equipment.

But you don't have to get everything perfect. The more minute the detail, the less people are going to notice. And you can often structure your writing to avoid all but the most broad information about the really technical stuff.

 

[Drakkith]

Forgive my ramblings, I started with the first paragraph below and just couldn't stop myself. I'm sure you know most of this already.

Also note that there is a difference between inventing new technology for your story and getting known technology and physics correct. Few are going to question your FTL technology unless it just doesn't make sense at all. A few more are going to question why your hull breach scene has a minutes-long hurricane-speed wind coming out of a breached compartment. Luckily, the average person has utterly no understanding of physics, so you can actually get away with quite a lot without most people noticing.

The problem with sci-fi is that you are commonly writing about situations which no one has actually had to deal with, but that we understand the basic physics of. When writing fantasy you don't have to worry about someone going, "Oh! That's not how spellcasting works in real life!" You don't have have undergrads who've taken basic magical beasts 101 and know that hydras only ever come with three heads, not five. But with sci-fi you absolutely have people who understand how fast air would escape from a hull breach and how long it would take to empty a given volume, or how radio communication would be affected by high-sublight speed travel, or how much fuel would be needed for a trip between planets using chemical rockets.

So you're always working on at least two sliding scales:
Realism vs fantasy (ftl, blasters, etc vs chemical/ion thrusters, guns using chemical propellants and bullets, etc).
Realism vs convenience (figuring out how a .30 cal bullet behaves when it impacts the flesh of an alien slug species without a brain vs "The slug monster dropped dead with a bullet in its main nerve cluster.")

The first is the 'hardness' of your setting. The harder the setting, the less stuff you can make up and, generally, the more technical you have to get in your writing. That last point is not an absolute rule, but because most people don't understand physics you often have to get into the details to explain why some situation is bad or how it leads into the next situation. For example, if your ship is traveling at high velocity into a star system, you probably have to explain that the blueshift of your radio signal has put the frequency too high for your buddy on-planet to detect with his equipment, instead of just saying that you won't be able to contact him until you slow down. This isn't sci-fi specific. All writers have to deal with this when writing about technical things or situations that people aren't familiar with. Sci-fi just tends to deal with a lot of this.

The 2nd scale is something all writers have to deal with to some extent. Hard sci-fi stories just tend to be less character driven and involve more technical stuff, making authors feel like they need to figure out every little detail of how things work. Which is sort of true. If your character can't contact someone on the radio, there should be a reason. But how much time do you want to spend figuring out how the environment on an alien planet affects radio transmission? Probably not a lot unless that's a really big plot point or it keeps coming up over and over again in your story.

The big issue i faced was, well what incentive could there ever be to set up a operation on the scale i want ? Room Temperature superconductivity seems to be kind of the only one which works within the context of the story. Where we assume just some straight up magic Engines.

Well, either you hand-wave this away, knowing that a few people will call you out on the existence and uses of metallic hydrogen, or you change things. Either option is fine. You're going to have to accept that not everything in your story is going to be 100% realistic. It's just up to you to decide which parts are and aren't.

A few ways to change/expand things comes to mind:

• There's a colony in-system that requires the material being mined. Perhaps highly concentrated metal ores, perhaps fuel, perhaps something else.
• The mined material is some exotic substance not found in our solar system and has unique and highly desirable properties. Unobtanium from the Avatar movies comes to mind.
• The material has been mostly used up in our solar system and this is the closest place to get it.
• The material is extremely rare, something like iridium, and the location being mined has a very high concentration of it.
• The mining operation is really a massive coverup for some clandestine operation.

None of these are perfect and each has their own 'flaws' in terms of realism and believability.

 

[Erik1801]

Forgive my ramblings, I started with the first paragraph below and just couldn't stop myself. I'm sure you know most of this already.

Also note that there is a difference between inventing new technology for your story and getting known technology and physics correct. Few are going to question your FTL technology unless it just doesn't make sense at all. A few more are going to question why your hull breach scene has a minutes-long hurricane-speed wind coming out of a breached compartment. Luckily, the average person has utterly no understanding of physics, so you can actually get away with quite a lot without most people noticing.

The problem with sci-fi is that you are commonly writing about situations which no one has actually had to deal with, but that we understand the basic physics of. When writing fantasy you don't have to worry about someone going, "Oh! That's not how spellcasting works in real life!" You don't have have undergrads who've taken basic magical beasts 101 and know that hydras only ever come with three heads, not five. But with sci-fi you absolutely have people who understand how fast air would escape from a hull breach and how long it would take to empty a given volume, or how radio communication would be affected by high-sublight speed travel, or how much fuel would be needed for a trip between planets using chemical rockets.

So you're always working on at least two sliding scales:
Realism vs fantasy (ftl, blasters, etc vs chemical/ion thrusters, guns using chemical propellants and bullets, etc).
Realism vs convenience (figuring out how a .30 cal bullet behaves when it impacts the flesh of an alien slug species without a brain vs "The slug monster dropped dead with a bullet in its main nerve cluster.")

The first is the 'hardness' of your setting. The harder the setting, the less stuff you can make up and, generally, the more technical you have to get in your writing. That last point is not an absolute rule, but because most people don't understand physics you often have to get into the details to explain why some situation is bad or how it leads into the next situation. For example, if your ship is traveling at high velocity into a star system, you probably have to explain that the blueshift of your radio signal has put the frequency too high for your buddy on-planet to detect with his equipment, instead of just saying that you won't be able to contact him until you slow down. This isn't sci-fi specific. All writers have to deal with this when writing about technical things or situations that people aren't familiar with. Sci-fi just tends to deal with a lot of this.

The 2nd scale is something all writers have to deal with to some extent. Hard sci-fi stories just tend to be less character driven and involve more technical stuff, making authors feel like they need to figure out every little detail of how things work. Which is sort of true. If your character can't contact someone on the radio, there should be a reason. But how much time do you want to spend figuring out how the environment on an alien planet affects radio transmission? Probably not a lot unless that's a really big plot point or it keeps coming up over and over again in your story.Well, either you hand-wave this away, knowing that a few people will call you out on the existence and uses of metallic hydrogen, or you change things. Either option is fine. You're going to have to accept that not everything in your story is going to be 100% realistic. It's just up to you to decide which parts are and aren't.

A few ways to change/expand things comes to mind:

• There's a colony in-system that requires the material being mined. Perhaps highly concentrated metal ores, perhaps fuel, perhaps something else.
• The mined material is some exotic substance not found in our solar system and has unique and highly desirable properties. Unobtanium from the Avatar movies comes to mind.
• The material has been mostly used up in our solar system and this is the closest place to get it.
• The material is extremely rare, something like iridium, and the location being mined has a very high concentration of it.
• The mining operation is really a massive coverup for some clandestine operation.

None of these are perfect and each has their own 'flaws' in terms of realism and believability.

No Biggy ! I like discussions so its cool :D

In my first novel (It is terrible don't ask, also Hard Sci fi but like bro what are themes ? That book certainly doesn't know) i went to the lengths of calculating all of these small things. Like how long it would take for Air to vent etc. Which, i mean ultimately didn't go anywhere but for different reasons.

My main goal here is to be as realistic as possible, even though it is a fundamentally character driven story. There are POV characters who get exposed to more technical detail, but like we spend most time with a character that isn't. To an extend this is the result of this new and cunning writing approach known as "Hey, maybe figure out the theme, character motives, arcs and so on before Worldbuilding and constraining yourself". Which simply results in more character driven plots.
Regardless, i am a staunch believer in "Visual Realism". As in, when something looks right it generally is right. Of course, this is not true for most of physics. A lot of it is counterintuitive. However, from a purely visual point of few i do think general readers are smart enough to understand why certain things happen. And if not, you only need a little bit of an explanation.

For instance, if we just accept for the moment that the ITV thrusters work as advertised, and we observe them from a planets surface, we would expect to see a straight laser like line in the sky going from one edge of the Horizon to the other. As it crosses over us, the line fades out. Of course it doesn't really fade out, rather this is a situation similar to a relativistic jet. As the exhaust moves away from us it becomes invisible duo to Redshift and Doppler Beaming.
While this might be an example that needs at least some other character explaining it, i do think there is a certain intuition here.

At this point, i am pretty set on just accepting the thrusters themselves are magic for all intend. And i just hope i can make everything around them very realistic. Such as the ITV´s being mostly radiators, how the exhaust looks, the general size of things and design decisions. Thankfully, other much more present aspects (The ITV´s are shown once in the beginning and later do like a backflip in the sky) don't need any of this magic to technically work. Its all proven / already existing tech. Ships, Planes, Off-Shore Rig´s and SSTO´s are a thing. (On the SSTO, god bless Metallic Hydrogen. It makes their math so much simpler. Even if they burn 30 Tons of Metallic Hydrogen to get 40 tons of it into orbit. But its not like the stuff is actually scarce on the planet).
And of course, the most preveniently featured aspect is the Biosphere. Which also has no need for any sort of magic.

I guess this entire post has just been my vein attempt at trying to get this one aspect realistic because i know non of the other major parts need this sort of "it works because i said so". Or rather, have good answers. Of course you can make the Interstellar ships 100% realistic. But then the journey takes 800 years instead of 7.

As for your suggestions, i figured Metallic Hydrogen (assuming it is a RTS) would fill the roles of points 2 & 4.
I probably just failed to give yall the context. Essentially there is this planet, Hela, which has Metallic Hydrogen in her crust. Similar to Natrual Gas fields on Earth, just less. I put some numbers down for exactly how much there is and the entire planet has between 2423 - 3093 Cubic kilometers of it. Which sounds like a lot but is a small fraction of the global Gas reserves and what has already been burned. On a planetary scale, this is not a lot. And this does factor in over 99% of it having decomposed back into Molecular Hydrogen duo to various geological reasons.
Regardless, while Metallic Hydrogen is not exactly uncommon it is basically impossible to get in the Solar System. Its near the core of the Gas Giants so like, bit hard to obtain.
Of course, this is another major leap in realism because, well i would like to see precisely how any of the metallic Hydrogen survived. Realistically speaking, non of it would have because the decomposing temperature is only a few 100 or 1000 Kelvin if i remember correctly, and the only way for it to get on the planet is if the planet was a Gas Giant core. Which currently is the lore, Hela is the remains of a Gas giant´s core. I don't really think a single cm³ of Metallic Hydrogen would have survived the planetary formation process. But then again, the story is really not about how it got here.

 

[Hornbein]

I think mining metallic hydrogen from the core of Jupiter would be enough of a challenge.

 

[Erik1801]

I think mining metallic hydrogen from the core of Jupiter would be enough of a challenge.

From what i understand, it is virtually impossible realistically speaking. The pressure down there is between 500 - 1500 GPa. That alone is somewhat of a problem seen as how we cant make anything of practical size that could survive these pressures. Note, the pressure at the Mariana trench is ~ 0.1 GPa. Even if you could make any sort of mining machine, how do you plan on getting it up ? Maybe super fancy balloons ?

All of that might work conceptually but i dont see any scale. If even if we give such an operation the same magic thruster tech we already assume, i dont see it. First you have to go through ~50km of clouds, then you have to go through idk a few 100km of Liquid Hydrogen, then Helium / Neon before finally reaching the Metallic Hydrogen. What would infrastructure for that even look like ? Cant build a space elevator since even carbon nanotubes are to weak for the tensile stresses. Active support ? Are we really suggesting building a several 1000km long Tower which is only held up by electricity ?
It just seems impossible to get down there, extract the good stuff, and bring it back. On the other hand, interstellar travel is at least something you can approach.

 

[Grelbr42]

Something else to think about. A rocket gains momentum p by tossing out mass with momentum -p out the nozzle. The energy it takes to do this is p²2/2m. So to minimize the energy you want to maximize the mass. So exotic propulsion like light or elementary particles all moves this in the wrong direction. You want m large, not small.

You should be thinking of the impulse you get per kg of fuel. That depends what efficiency you allow each type of system. And what rocket exhaust velocity you allow for the mass you chuck out the back.

If you allow perfect efficiency fusion, fuse 1 kg of Hydrogen to Helium, you get about 5.8E14 Joules. Send that 1 kg out the back with that kinetic energy and you get 3.4E7 kgm/s momentum from 1 kg of fuel.

If you allow perfect efficiency matter-anti-matter and start with 0.5 kg of each, you get mc^2 = 9E18 Joules. Send that backward as light and you get 3E8 kgm/s momentum. Not quite ten times as much per kg.

So which wins depends on what efficiency you allow each. Right now we can't do either one at all. So it's pretty much zero efficiency with existing tech. One might expect we are closer on the fusion thing. Making and storing many-kg sized allotments of anti-matter is grotesquely impossible right now. Releasing it in a controlled manner is kind of gnarly. And getting all the photons to go out the back is kind of baffling.

 

[sbrothy]

True, but for a good sci-fi you kinda need a good mix of both. For example IIRC in Gentry Lee's continuation of the otherwise fascinating Rama story universe by Clarke, Lee ended up with a story that disappointing had almost nothing to do with Rama, the Ramanians or their technology. Using a spaceship in the story setup only to get a group of people "stuck with each other as if on an island" is in my opinion not enough to make it sci-fi.

Gentry Lee was better at characterization though, but yeah.

 

[sbrothy]

This is my first time posting, so please excuse any mistakes.

I am grasping at straws here. I am working on a Hard-Sci Fi novel, plot, arcs, characters etc. are all worked out and i decided to take the deep dive in terms of Realism. For instance, there are no Fusion reactors. All that is important in terms of Setup is that we have Humans, and they want to go to a nearby Star system. Its ~4 Ly away and we would like for this transfer to not take 1000s of years.

The issue I am facing is that there seems to be no way to do this. I.e. achieve a high enough Velocity, fast enough, for the journey to not take 1000s of years. At least without breaking thermodynamics in a big fashion.

For example, I was told a Particle accelerator based propulsion system (using for example a Wakefield accelerator) could be a good method because the exhaust velocity is so high and it is pretty compact. In principle that is true, but when you go and do math, taking into account that the system will experience heating (We assume the Ship gets its power via a energy beam, microwaves or something. It doesn't carry the power generation equipment. The power is beamed to it). Even at a magical total system efficiency of 80% (So you pump in 100 Watt, 20 Watt is heat and you get to do work with 80), the real world acceleration might as well be nothing.

See this. It is possible that I didn't do the math correctly, but like Jesus.

As you can see, assuming a 400 GeV accelerator, a Radiator area of given, an Efficiency of 80% and a Ship mass of 100.000 tons (That number is based on some assumptions about Crew size, needed cargo capacity and some Ratios. For example that for each kg of Cargo you need ~0.25kg of Structural support), it takes 77000 Years to get to 0.127c.

I did similar math with Fusion (As in a Fusion reactor powered by the external beam), Anti-Matter, god dam light sails and even this really dumb concept, i think NWRE, which proposed to use a Fusion Engine to somehow cool an even better Engine.
My results were that while all of these would eventually get us to the target, all of them took like half a billion years (Hyperbolic). As a matter of fact, the particle accelerator performs the best. Which is like.... 77000 years D:

As it is so often the case, the issue is Heat. If we had a Radiator the size of Luxemburg we could get much better acceleration. Which ignores that a radiator the size of a nation presumably weighs more than 100k tons but also the practicality of carrying such a thing.

Ideally, i would like to have a solution which can get to 0.5c in ~24 Months. Which would mean a constant acceleration of 2.5m/s². But as far as I can tell, this is just straight up not possible as long as thermodynamics are of any concern. Of course this "works" if you bump the efficiency to something stupid like 0.99999999, but even then the accelerator would eat 80 times more energy than the World currently consumes. Which, I don't think is impossible in principle. I just seriously doubt you can concentrate that much energy into a 800 meter long accelerator.

And this is were I am stuck. People on Reddit keep talking about fast Interstellar transfer methods but all the ones I looked at just don't work as advertised. Even the all holy Anti-Matter based propulsion systems cant do this, because the ships would just be to heavy for any serious acceleration.
That being said, there is the option that i missed something very obvious somewhere along the way, hence why all the numbers look so terrible. I just have the detailed breakdown for the method for the Wakefield thingy, but guys... no propulsion method is bussin ngl.

So, to finish this off, my two core questions are;

1. Is there anything obviously wrong with my Math and or am I missing something which solves the thermal issues ?

2. Are there any methods of propulsion which could do the task ? I.e. 0.5c in 24 Months.

I hope this is informative enough to make answering it possible, if not like I am sorry xD Hopefully i can give good clarifications to comments should the need arise. Also excuse any typos or bad gramma, Ich bin deutsch und hab legasthenie.

I hope you've been by Atomic Rockets. If you make it hard enough you might get his "Rocket Cat Seal of Approval". :)

 

[sbrothy]

This is my first time posting, so please excuse any mistakes.

I am grasping at straws here. I am working on a Hard-Sci Fi novel, plot, arcs, characters etc. are all worked out and i decided to take the deep dive in terms of Realism. For instance, there are no Fusion reactors. All that is important in terms of Setup is that we have Humans, and they want to go to a nearby Star system. Its ~4 Ly away and we would like for this transfer to not take 1000s of years.

The issue I am facing is that there seems to be no way to do this. I.e. achieve a high enough Velocity, fast enough, for the journey to not take 1000s of years. At least without breaking thermodynamics in a big fashion.

For example, I was told a Particle accelerator based propulsion system (using for example a Wakefield accelerator) could be a good method because the exhaust velocity is so high and it is pretty compact. In principle that is true, but when you go and do math, taking into account that the system will experience heating (We assume the Ship gets its power via a energy beam, microwaves or something. It doesn't carry the power generation equipment. The power is beamed to it). Even at a magical total system efficiency of 80% (So you pump in 100 Watt, 20 Watt is heat and you get to do work with 80), the real world acceleration might as well be nothing.

See this. It is possible that I didn't do the math correctly, but like Jesus.

As you can see, assuming a 400 GeV accelerator, a Radiator area of given, an Efficiency of 80% and a Ship mass of 100.000 tons (That number is based on some assumptions about Crew size, needed cargo capacity and some Ratios. For example that for each kg of Cargo you need ~0.25kg of Structural support), it takes 77000 Years to get to 0.127c.

I did similar math with Fusion (As in a Fusion reactor powered by the external beam), Anti-Matter, god dam light sails and even this really dumb concept, i think NWRE, which proposed to use a Fusion Engine to somehow cool an even better Engine.
My results were that while all of these would eventually get us to the target, all of them took like half a billion years (Hyperbolic). As a matter of fact, the particle accelerator performs the best. Which is like.... 77000 years D:

As it is so often the case, the issue is Heat. If we had a Radiator the size of Luxemburg we could get much better acceleration. Which ignores that a radiator the size of a nation presumably weighs more than 100k tons but also the practicality of carrying such a thing.

Ideally, i would like to have a solution which can get to 0.5c in ~24 Months. Which would mean a constant acceleration of 2.5m/s². But as far as I can tell, this is just straight up not possible as long as thermodynamics are of any concern. Of course this "works" if you bump the efficiency to something stupid like 0.99999999, but even then the accelerator would eat 80 times more energy than the World currently consumes. Which, I don't think is impossible in principle. I just seriously doubt you can concentrate that much energy into a 800 meter long accelerator.

And this is were I am stuck. People on Reddit keep talking about fast Interstellar transfer methods but all the ones I looked at just don't work as advertised. Even the all holy Anti-Matter based propulsion systems cant do this, because the ships would just be to heavy for any serious acceleration.
That being said, there is the option that i missed something very obvious somewhere along the way, hence why all the numbers look so terrible. I just have the detailed breakdown for the method for the Wakefield thingy, but guys... no propulsion method is bussin ngl.

So, to finish this off, my two core questions are;

1. Is there anything obviously wrong with my Math and or am I missing something which solves the thermal issues ?

2. Are there any methods of propulsion which could do the task ? I.e. 0.5c in 24 Months.

I hope this is informative enough to make answering it possible, if not like I am sorry xD Hopefully i can give good clarifications to comments should the need arise. Also excuse any typos or bad gramma, Ich bin deutsch und hab legasthenie.

BTW, now that we are in SciFi-land you might want to look up "black hole" propulsion* or something similar. For instance in Schlock Mercenary - The Space Opera Webcomic (one of my favorite free online webcomics - it ran everyday for nigh on 20 years!), a specific type of white dwarf star (magnesium-oxygen-something....?) is used to power several worldships leaving the galaxy.

* There are even some serious "proposals" in the form of arxiv.org papers. I seem to remember that an artificial black hole 1 attometer in diameter would be optimal. I'll find som references when I get home (I'm on a weird public computer here), unless someone beats me to it that is....

EDIT: In the mean time : Wiki: Black Hole Starship.But yeah. This was about science fiction,right?

Regards.

 

[sbrothy]

BTW, now that we are in SciFi-land you might want to look up "black hole" propulsion* or something similar. For instance in Schlock Mercenary - The Space Opera Webcomic (one of my favorite free online webcomics - it ran everyday for nigh on 20 years!), a specific type of white dwarf star (magnesium-oxygen-something....?) is used to power several worldships leaving the galaxy.

* There are even some serious "proposals" in the form of arxiv.org papers. I seem to remember that an artificial black hole 1 attometer in diameter would be optimal. I'll find som references when I get home (I'm on a weird public computer here), unless someone beats me to it that is....

EDIT: In the mean time : Wiki: Black Hole Starship.But yeah. This was about science fiction,right?

Regards.

As promised:

From arxiv:

(0908.1803) Are Black Hole Starships Possible?
(1001.3887) Starships and Spinoza
(0910.1965) A Note on Relativistic RocketryEDIT: I think serious from "serious proposals" from my first answer should perhaps have been in double quotes too. It's getting a real workout here :)

I'm not sure how serious these papers are. For dreamers like me they're pretty fun though.Regards.

 

[Dr Wu]

Having read up on the threads in this post, the thought is not slow in forming that a ‘realistic’ high-speed interstellar journey dependant upon the use of any known onboard propulsion system is strictly for the birds.

Off-board systems, on the other hand, do at least offer a hope of evading the dreaded rocket equation. Laser propulsion is one such possibility. That this is currently the interstellar drive of choice out there in the real world — e.g. the Starshot Breakthrough Initiative — does at least offer a proof of concept, and one not to be sniffed at by SF writers. As a personal note, I did once contemplate penning a short story which posited locating an array of super-efficient solar panels on Mercury’s polar regions (here dubbed ‘The Black Forest’) to push a crewed spacecraft out to a nearby star system; but not before first sending a robotic return beamer etc to the aforesaid star. Laser attenuation was ‘solved’ by placing Fresnel lenses along the route. Impracticable, of course, but still doable in fictional terms, given the right sort of imaginative writing. . . lacking in this instance.

Otherwise, the only way round the problem, it seems, is to dump realistic drives for so-called unrealistic ones. The handwaving can be reduced, even banished altogether, were such ‘magical’ propulsion systems in the gift of an alien spacefaring species, not us dimwitted Earthling primates.

In the end, though, and to sum up what others have already pointed out, it comes down to whether the story is about the technology or the characters inhabiting it. If the latter, then use the technology to serve the story, not the other way round.



PS. Apologies about the 'shouty' font. This entry was pasted in from MS Word.

 

[Nik_2213]

If all else fails, you may hand-wave an 'off the wall' math-tweak. eg my Convention's FTL does not need anti-matter fuel or oodles of unobtanium because their nimble Alcubierre Drive variant deploys a 'Double Bubble'. The ship nestles within a 'Limaçon of Pascal'. Don't need 'deflector shields' either, except for in-system flight...

The other option is 'Red Mercury': Neither red nor Hg, but jokey 'code name' for a serendipitously discovered catalyst that allows production of stable 'Metallic Hydrogen' using heroic, but practicable processes...

"Yeah, well, it was like the trace of oxygen contamination that first catalysed ethylene's polymerisation, or the [REDACTED] impurities needed to reliably brew thermo-nukes' essential FOG_BANK..."

 

[Vanadium 50]

serendipitously discovered catalyst

Isn't that dilithium?