Liquid Hydrogen Fuel + Engines

[3Davideo]

When I saw the Isp's for KSP's liquid fuel engines I noticed that they were quite a bit lower than I expected. Having read some on the IRL space race, I know the best chemical rocket fuel is liquid hydrogen (LH2) and liquid oxygen (LOX) which burns with an Isp somewhere between 420 and 450 seconds (examples: upper stages of Saturn V, Space Shuttle main tank). Space flight on Earth would be extremely difficult without this fuel combination; the Kerbals are doing ok probably only because Kerbin requires half the delta V to get into orbit that Earth does. So I was a little surprised to see the Kerbal engines with such low Isp, which I can only presume is some sort of hydrocarbon/LOX mixture (LiquidFuel sounds like kerosene).

So I propose that a new series of engines and fuel tanks be added that utilized liquid hydrogen as a fuel. LH2's chief advantage is the higher Isp, but its main disadvantage is that it is cryogenic: to keep it liquid, LH2 needs to be chilled below 14 K or so. As this requires more complicated rocketry, this would be an interesting technology to add to career mode's tech tree when it is added.

So how would this new fuel behave? LH2 can be burned with the existing Oxidizer resource in engines that have Isp's higher than the existing hydrocarbon engines. However, the LH2 tanks take ElectricCharge to run their refrigeration systems, proportional to how much LH2 is in the tank. If power stops, you start losing fuel. On the launchpad, this isn't a problem, since the launch clamps provide all the power you need, but this will pose problems if you want to store LH2 in orbit.

Ok, so so far it's just an alternative fuel with better performance but with storage problems. But there's other things you can do with hydrogen. One can combine hydrogen and oxygen in a fuel cell and get electricity and water, or combine water and electricity and get hydrogen and oxygen. So you could use hydrogen as a fuel tank for a generator, or if you had a source of water you can make more rocket fuel... in space! So the addition of LH2 as a resource can easily lead into implementing some sort of resource gathering system, if desired. And one can use hydrogen or water as realistic fuels for the nuclear engine, rather than the unrealistic liquidfuel.

So, in short, using liquid hydrogen as a rocket fuel can increase the performance of our rocket engines significantly, but requires refrigeration and more advanced technology as tradeoffs. Hydrogen and Oxygen can be exchanged for water and power (and vice versa), providing an "in" for in-situ resource utilization. And the nuclear engine will finally get a suitable fuel.

[leax256]

there is a mod that does this very think. also tweakables once fully added will be a bit like this.

[thox]

You've got some nice ideas in this post, and I guess you'll be pretty happy to hear that some of those are apparently already planned to be in the game at some point.

The devs dropped this flowchart some time ago, it displays how they want the resource system to be (even though I don't know if this is still up-to-date).

As you can see, once you've looked at it for a while (yeah, it took me a bit to figure out everything in the chart ;D ), fuel cells generating electricity and separators using electricity to make fuel and oxidizer are something the devs also want. I also assume (because there are no other kinds of rocket fuel) that the fuel in the diagram is LH2, otherwise fuel cells etc. wouldn't be possible. That would also mean that the current liquid fuel might already be LH2, so there will maybe not be a whole new system for that like you suggest, but that's just my thoughts, and who knows what we will finally get from the devs

EDIT: Resource chart is not up-to-date anymore (See replies below)

Edited September 27, 2013 by thox

[iNimrip]

Hi,

I am also into alternative fuels and have spent a long time researching, balancing existing and experimenting with new fuels including hydrogen. While it does have a high ISP and is very light weight, it doesn't like being compressed so u need to carry large bulky tanks around. I have tried cryogenic liquid hydrogen, slush hydrogen ( more dense ) and Nasa's experimental metallic gelled hydrogen propellant (uses Al gellent and at 10% results in significantly higher ISP and higher density.). The gelled propellants can be used on other liquid propellants including kerosine variants including KSPs RP-1

The Hydrogen fuel is only viable in KSP when there are much larger tanks I.e. The Saturn V. Lots of orange tanks on your small craft will ruin the look, mess with centre of gravity and handling and weight of tanks compared to using conventional tanks and fuel.

[iNimrip]

Sorry but I just forgot to mention that there are three main types of H2 gellents, Aluminium, CH4 methane and in the future, nano gellents.

[iNimrip]

Sorry but I just forgot to mention that there are three main types of H2 gellents, Aluminium, CH4 methane and in the future, nano gellents. I think ksp should allow an option for power uses for fuel slush physics and thus the effect of control and stability.

[3Davideo]

Well I'm glad that these ideas are being considered! The resource system definitely has quite a bit of potential and I'm happy the devs are looking to expand it.

[DaRocketCat]

Guys that ginourmous resource chart got scrapped. It will be replaced with something simpler.

Reason is that dev focus got shifted away from resources to developing career mode asap.

[amo28]

Link to Modular Fuel Tank Mod

[Scoundrel]

Sorry to say this, but there won't be different fuel types, as this is the Kerbal Universe which has slightly different physics than "our" universe. There may be tech nodes that say "improved fuel" or the like (pure speculation on my part) that alter some engine characteristics later on in the game, but that would likely be about as close as it gets to your suggestion.

As for the resource chart, HarvesteR stated back in April on a livestream that the resources chart is obsolete and that it has since been simplified, though we haven't gotten a glimpse at what changes were implemented, so who knows what is actually going to happen with it.

[iNimrip]

I have spent months crunching the numbers and doing mountains of research and I tried the modular fuel tank mod but the values were way off from all the info I had gathered, even some basic ones. Now anybody can be forgiven for getting the resource values out because how confusing they are and then it messed with my existing stuff. And using a different screws up rockets and u have to relearn how to build them. Note to 3Davideo, LH2 + LO2 is not the best/efficient rocket fuel. First place goes to theoretical metallic hydrogen and secondly if the hydrogen lithium fluorine tripropellent at 500+ISP. LH2 would behave similarly I assume as u can run it with the same engine as a rp1 LH2 LO2 tripropellent. The problem with using water to make rocket fuel ONBOARD is that it weighs 1ton per cubic metre and the conservation of energy rule means that u can only get out the net I putted energy, effectivley the engine becomes and electric powered engine and requires colossal Ammonts of power so it is not feasible for in the air but on the ground and on small scale ie drinking water it is ok idea. Maybe for the life support mod.