Writing an SF epic; need tech help.

I do, actually. Thing is, I need something that answers some particularly specific questions and without having to solve hopelessly complex equations (I'm really bad at math).

A lot of the equations needed to calculate things like mass, propulsion, delta-V. I handwave that stuff in my story by using an impulse drive not unlike in Star Trek. The thing is, how to make it plausible or at least believable.

More specifically, call it quantum something or nanomachines, since that's an acceptable form of magic in sci-fi.

Well the impulse drive is based around a single question in the context of my story: How can a ship have maximum Delta-V with minimum reaction mass? My idea is that they're magnetoplasmadynamic (that's a mouthful) engines powered by helium-4 reactors. I've read that helium-4 reactors can power both the ship and the engines.

As for radiators, they don't tend to glow orange or yellow-hot because of advances in cooling systems. They may be smaller as a result as well or be folded up during re-entry. Heat can be transmitted to power the engines, but I'm not sure how. In fact, the ships tend to resemble birds or fish because of how the radiators are designed!

There are Alcubierre Drives to act as FTL travel, although they are very advanced versions of the system that scarcely resemble NASA's proposal. They also generate quite a bit of heat, so expect wing-like radiators.

Another thing about the ships are that gravity generators are standard issue, so there are ships with decks that are arranged vertically or horizontally depending on how old or new the generators themselves are. Don't expect big windows and huge open ballrooms, however. Space is still at a premium, so a lot of things need to be travel-sized without turning the interior into a sardine can (Fallout 4: Vault-Tec Workshop has proven to be an excellent source of inspiration for this particular concept). And viewports are impractical weak spots, replaced by beta/alpha-wave free videoscreens. The "habitat sector" of the ship is tucked behind several other modules in the heart of the ship.

I've even considered making a catalog of items and systems for shipwrights and helionauts alike, a la SkyMall.

Like Star Trek, there are energy shields in addition to Whipple shields, but the reason they were invented is not just for combat, but for Kessler syndrome as well.

OK, I'm going to be bursting a lot of bubbles here, but I don't want you to get discouraged. Technical rigor in sci-fi can seem really daunting at first, but it's not so bad if you keep working at it. And to be honest, you can get pretty good results even by introducing one or two magical techs if you pick proper constraints for them.

Firstly your reaction drive, the fact of the matter is that you should read the Atomic Rocket intro to rocket engines (http://www.projectrho.com/public_html/rocket/engines.php). The math is all high school level, I can attest to doing calculations on the performance of the Rocinante with nothing more than a scientific calculator. Then you should read the section on Radiators.
These two things will give you the intuition you need to design realistic spacecraft.
I will warn you, that you will likely be disappointing by the results. The most realistic drive I could figure out for the Roci involved a hydrogen-boron fusion drive, a ridiculously reflective thermal reflector, and some wacky carbon fiber loom radiators - and it had nowhere near the performance listed in the books.

Now with your radiators... you're breaking thermodynamics depending on how exactly the radiators 'power the engines'. And better cooling technology... is not the issue, it's the that radiators are governed by some pretty restrictive physical laws in terms of how much they can dump.

Now, here are some options you might find interesting:
- Don't use Alcubierre drive for FTL, talk about the FTL drive as little as possible. The Alcubierre/Natario drive cannot in fact go FTL but it can be used as an excellent STL drive because it does not require reaction mass. This lets you sidestep the tyranny of the rocket equation. The more realistic way to do this is probably a displacement drive (http://www.orionsarm.com/eg-article/493f257196523) setup.
- Postulate one magic tech and abuse it. Figure out some sort of spooky action at a distance system that allows you to transfer force/momentum to physically objects. Don't explain how it works, because it's not possible as far as we know. Then you can use said force fields to create artificial gravity (aka paragravity) by just pushing everyone to the deck of the ship; you can use it to deploy hundred kilometer sheets of droplet radiators that will allow you to radiate to your heart's content even in combat (because the droplets will be moved around with force fields and won't be lost to space as you accelerate); it will allow you to create compact fusion reaction chambers for propulsion, power, and other fun applications; you can also use them as force fields (through in their case it's more of pushing projectiles and beams away and deploying mobile armor against lasers). This sort of momentum exchange also the structural stress on the hull to be evenly distributed through these force fields, which gives you more artistic license in terms of making ships look distinctive (no longer are you limited to making fuel tank skyscrapers).

One piece of information missing here is what kind of thrust you want your ships to have. Since one of your illustrations says that torchships are used by less advanced species, I doubt that it is below 1g. Atomic rockets define torchships as spaceships with engines that have both high trust and high specific impulse.


If you just want a ships that can go anywhere in a solar system without worrying of refueling, you are probably better off with stating that the same technology that gives you paragravity inside your ships can be used to construct some kind of gravitic impellers or something. Of course it’s handvawium, as Atomic Rockets would call it, but as I will demonstrate below, when you try to make a reaction drive that uses miniscule amounts of fuel and has high thrust you get into the realm of obscene power levels.


Because of that, I think that magnetoplasmodynamic thruster for your sublight propulsion is perhaps not the best choice. The thing is, it’s a relatively well developed technology and so its limitations are relatively well known. So making it the base for your absurdly powerful propulsion systems is like making a hypersonic plane driven by sails.
 The thing is, whatever you call your propulsion system, as long as it is a reaction drive, there is a fundamental lower limit on how much power it would require. Rocket equation does not depend on your propulsion principle. It is a fundamental limit.


So, let’s say you have a spacecraft with a wet mass of 1000 tons and 10% of it is fuel, i.e. 900 tons is the ship and 100 tons is fuel. I can’t see any propellant tanks on your second drawing, so I guess 100 tons is not what you consider miniscule, but it actually is. Let’s say that you want your craft to accelerate at 1g with full tank. Let’s say your ship can add 5% of the speed of light to it’s velocity by expending all the fuel, which is 15 000 km/s of delta V, which is a lot.

I will spare you all the calculations, like you asked. Your exhaust is moving at 47% of the speed of light, which makes it alone a relativistic weapon of mass destruction. Let’s say it is some kind of electric propulsion device. Then you need to supply at least 697 terrawats of power, which is almost 57 times more power that the whole human race consumed in 2012.


Now lets talk about waste heat. Let's say your 700 TW power plant runs at 85% efficiency, which is the theoretical maximum efficiency of direct conversion generators. Since your reactor uses the triple-alpha process you probably won’t be able to achieve that, since you need to harness high energy gamma rays produced by this reaction. Reactors in CDE usually don’t go about 22% efficiency. Let’s assume your engine is 95% efficient, which is also absurdly high. You will need to radiate 134 TW of waste heat. If you run your radiators at 500 K to keep them from glowing like you said, you will need 37900 square kilometers of radiators. That’s right, thirty eight thousand square kilometers.


You can also turn off your engine and use those 700 TW of power to power a laser or any other weapon. Think of what that will do to your setting. Actually, forget weapons. You can just accelerate this ship towards Earth and end all life on it. What does this do to your setting?


But let’s a bit more reasonable. Let’s assume we aim for 300 km/s of delta-v, closer to those primitive torch ships, and let’s assume we will run our radiators at 2500K, which is much more efficient. Then we will need only 14 terrawatt of electricity, which is still a ton, we will need to radiate 2.68 TW instead and at 2500K that will only take 1.21 square kilometers of radiators.

Here is the spreadsheet I made if you want to play with the numbers Attachment Deleted. Hope this helps.