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 :)


Marc13Bautista's picture

Science! I wonder what it would look like to see the ship explode...

Free Elusive Skill = Athletic x4 in ATN Enclave encounter

ra1's picture

Additional options:
- Disposable boosters and/or fuel tanks, which could be jettisoned after use to decrease ship mass
- Reusable "tug" ships which you could hire to give you an initial boost

dcfedor's picture

@Marc, probably not like what we're used to :)

The fusion reactor might be the most damaging. When active, it contains an ionized, high pressure, high temperature plasma composed of D, He-3, He, and protons. If that leaked into the ship, it'd vaporize anything it touched instantly. Heck, even if the reactor's shielding was only weakened, it'd probably fry anything on the ship via gamma radiation.

However, I think the nature of this reactor is actually pretty safe, since it can shut down quickly, and apart from the heat/pressure, there's nothing inherently dangerous about the plasma. (The gas-phase D might be flammable, but the He gas would starve it of oxygen.) And the open-nozzle nature of the reaction (used for thrust) means the plasma could safely vent into space.

I suspect it'd lance-out and vaporize a few areas of the ship a split second before the safety bypass shuts it down and exhausts the plasma. You'd have some holes to patch, some fires to extinguish, and anything/anyone unfortunate to be in the path of leaked gamma radiation is probably toast.

The D2O tank is essentially just water, so it'd leak/spray/flow like a cistern. If the ship was depressurized, the water might freeze into ice/snow as it does, which would be a spectacle.

Similarly, He-3 is basically as inert as you get. If anything, it'd suffocate any flame within it's bounds. The one thing about the He-3 tank is it's super-pressurized and cooled to keep the He-3 solid, so the tank might rupture or even burst if integrity was compromised. But again, it'd be like a high-pressure leak or wave of invisible fire-retardent :)

Definitely a weird combo of events if a ship is damaged!

@ra1, you could strap on some fuel tanks, for sure. I bet a lot of the long-haulers are going to look like that. Their single purpose is to straight-line from A to B with cargo over and over, so they can be these clunky cargo containers with fuel and engines attached.

I won't presume to tell the player how their ship should look/act, but I know I want my ship to be a little more multi-purpose and trope-y :) No disposable boosters for me!

Regarding the "tug" ships, this is actually something I'm thinking stations are going to need. Nobody's going to allow a pilot to fly a ship anywhere near a station for safety reasons. One screw up (or suicide bomber), and the entire station could be ruined. Never mind the fact that the exhaust of a torch ship is a weapon of mass destruction to anything within dozens of km of the wake.

So I'm thinking there will be some options:
- tug ships, as you suggest. Maybe not fusion torch-based, but chemical rockets.
- allow pilots monopropellant maneuver/RCS jets only within a certain radius of the station.
- tug "swarm" of drones that latch onto a ship and bring it in (or divert it if on collision course)
- park the ships off-station at some distance, and use dinghies, drones, and ferries to the station

But yeah, nobody lights-up their reactor/torch within 50km of population. Detecting the fusion pre-fire power surge is going to be all the station needs to justify spacing your ship :)

Dan Fedor - Founder, Blue Bottle Games

Respawn's picture

Tell me, when do weapons get implemented? :>


-Gone with the blastwave

dcfedor's picture

Probably much later. While I do intend for combat to be possible in this game, I didn't want it to be the focus.

If I can manage it, I'd like for combat to feel a bit like submarine warfare. Tiny blips on the ladar, heat signatures and EM spectrum analysis, torpedoes and countermeasures, and almost always a loss for both participants :)

Dan Fedor - Founder, Blue Bottle Games