Propellant Storage Figured Out, Reactor Controls Next
Hey Folks! I think I figured out how I'm going to handle propellants for the reactor/thruster, so I finished up adding that data to the game, and I'm starting on the reactor controls.
Yesterday, I wasn't sure how to handle storing propellants, since the fuel used in the reactor/thruster (He-3 and D) had such a low density, even as liquids instead of gases. I was calculating needing 40 of those 4 giant canisters you see in the image above. And while that would be realistic, it'd also be kind of a buzzkill.
However, one doesn't necessarily have to store these chemicals as pure liquids. As you'll notice on the tanks themselves, one of them is labeled "Liq. D2O." It turns out that if you store D2O (a.k.a. "heavy water"), you get more kg of deuterium per unit volume than if you store pure deuterium. Seems counterintuitive, but I can sort of see why.
You might think, "well, how are you going to get pure deuterium from heavy water? And what about all that oxygen you have left over?" Glad you asked!
One of the nifty things about water (H2O) is its electrochemistry. If you apply electricity to water, you can split it into hydrogen (H2) and oxygen (O2) gases. The reverse of this process is the basis for fuel cell tech. And one thing a fusion reactor has in spades is spare electricity. Once you get it running, you simply bleed off some energy to split the D2O into the needed D for the fusion. Plus, you get pure O2 as a byproduct for use elsewhere on the ship. Not bad!
So doing it this way, we get more space efficient storage, and some interesting trade-offs we can make with our reactor by exchanging power for thrust, as well as fuel for oxygen. (And in theory, you could also use the D2O as a substitute for water on ship systems. Even drinking, if you were desperate. It'd kill you after a few days of drinking it exclusively, but you could survive a little while on it. ;)
Okay, so that's a trick for D. What about He-3? That's actually our limiting factor. It's even less dense than D, and harder to come by. And He is notoriously difficult to bond with other elements. It likes being pure He gas.
Well here, I decided to take a bit of artistic license. Theoretically, you can pressurize He at very low temperatures and make it solid. We're talking 100s of GPa of pressure, but let's assume we have the tech for that 60 years from now with the advent of space economies and abundant fusion. So if you store He-3 as a solid, you increase storage efficiency by almost a factor of 2.
And the result? Well, those same four tanks above buy us ~3 days of constant 1g acceleration, which will almost get us anywhere in the inner System we want. And accounting for the mass ratio of D to He-3 (I'm assuming we need equal particle amounts of D and He-3 to maintain fusion, so 2kg of D for every 3kg He-3), we can tweak our storage to be 3 tanks of solid He-3 holding 5200kg each, and one tank of liquid D holding 8900kg. This gives us a more matched ratio and a burn time of ~5 days. Almost enough to go from the inner System to Jupiter! And if we're willing to skimp on thrust (i.e. <1g or "coast" part of the way), we can theoretically go much further, in exchange for a longer trip.
And that's where my next task comes in. Hooking up some controls to the course plotter to let the user specify maximum thrust, and to see things like how much burn time is left in the tanks. I'm pretty much already getting all the data I need from the ship's systems after some tweaks this afternoon, and now I need to figure out what this control panel looks like. Not a lot of reference imagery out there for me to use :)