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[1.12.x] Cryogenic Engines: Liquid Hydrogen and Methane Rockets! (Jan 22, 2022)


Nertea

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1 hour ago, MechBFP said:

Why not make an upgrade in the tech tree that allow compressed fuels to be used later on? (Increase the volume allowed in a tank by 3 times or something like that)

Maybe even reduce the overall EC required to cool it slightly since it is all in one tank.

In general I have the same problem as other users right now, these engines simply aren’t worth it 90% of the time.  

The problem with having them as an upper stage is that I need to be able to generate enough electricity to prevent boil off, which either means nuke reactors or many heavy solar panels.

In GPP in particular, this is a major problem for the more distant planets as solar because useless, and nuke reactors need tons of expensive fuel to last long enough.  

The "Liquid Fuel" is not an analogue to compressed liquid hydrogen, or the LH2 is the Liquid Fuel uncompressed. The liquid fuel is an abstraction to some denser fuel, like Liquid Kerosene. Making cryogenic LH2 is a way to make it the most dense possible, with current technology. IRL LH2 is more efficient, but not always a good option for first stages.

Some people believe you could compress it even further and make metallic hydrogen, and use it as an ultra-powerful and efficient rocket fuel. But this still just theory.

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2 hours ago, MaximumThrust said:

Some people believe you could compress it even further and make metallic hydrogen, and use it as an ultra-powerful and efficient rocket fuel. But this still just theory.

That would be fine for me. If other mods have fusion engines, this could have this. :)
However, it doesn't sounds like this is going to happen since Nertea has more interesting things to work on, so might just have to mod it in myself, for myself.

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3 hours ago, Yuri kagarin56 said:

Can anyone explain to me like im three years old why I should use cryogenic rockets instead of regular ones?

They have less thrust and higher efficiency. You'll get a weaker engine that burn longer, that can be useful in many situations/designs. In my opinion, the vacuum ones fills up a great void the stock game have.

In the stock game I almost never used the vacuum engines. They have a thrust too low to put things in orbit with good payloads, and once you are in stable orbit, the nuclear engines are overkill. The vacuum engines in this mod are a mid-ground between the combustion and the nuclear ones. They can offer real advantages over the nuclear ones, making the design choices more dynamic and interesting.

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9 hours ago, MaximumThrust said:

They have less thrust and higher efficiency. You'll get a weaker engine that burn longer, that can be useful in many situations/designs. In my opinion, the vacuum ones fills up a great void the stock game have.

In the stock game I almost never used the vacuum engines. They have a thrust too low to put things in orbit with good payloads, and once you are in stable orbit, the nuclear engines are overkill. The vacuum engines in this mod are a mid-ground between the combustion and the nuclear ones. They can offer real advantages over the nuclear ones, making the design choices more dynamic and interesting.

So I get increased deltav for lower twr, but not to the extent of nuclear engines where it would take 5mins to perform a circularization burn?

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In a similar fashion to KA...

1.4.1 Update Status

  • Update paired with Kerbal Atomics
  • Fairly major set of fixes/revisions for ZBO tankage, about halfway through, need at least 3 weeks (considering other mods) to finish
  • Need to recompile/test DBS component
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Is there a way of preventing hydrogen boil-off when using stock tanks? As in, can I do something like add radiators to keep the hydrogen cool? I'm not bothered if it uses up EC/MegaJoules while doing so.

Edited by NoXion
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On 3/9/2018 at 7:42 PM, Yuri kagarin56 said:

So I get increased deltav for lower twr, but not to the extent of nuclear engines where it would take 5mins to perform a circularization burn?

Exactly. They are also lighter, smaller, cheaper. Goes well when you don't need too much Delta-V. But Kerbal Atomics, also from Nertea, make the "nukes fight back", introducing dual-mode nuclear engines, that can use oxidizer to increase the thrust (but reducing the ISP), making the choices even more interesting and dynamic.

In the other direction, Near Future Spacecraft introduces monopropellant engines. They are very light, with more TWR and lower ISP than the liquid fuel/cryo engines.

The mods from Nertea are like a "Kerbal Space Program 2" for me.

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On 2018-03-15 at 12:56 PM, NoXion said:

Is there a way of preventing hydrogen boil-off when using stock tanks? As in, can I do something like add radiators to keep the hydrogen cool? I'm not bothered if it uses up EC/MegaJoules while doing so.

If you right click on the tank in the VAB you should see a “Enable Cooling” button. 

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I'm thinking of doing a thing in the next update which will break stuff. Currently combustion ratios for the engines are a bit hydrogen heavy (15:1 cfg ratio). I would change that to 10:1, which has the advantage of making it a little closer to realism, mass-flow wise. However the interesting thing is that tank ratios might become more attractive to people who don't like large parts, as I will modify them something like so:

Old LH2/O Revised LH2/O Old LH2 New LH2
38,400/2,560 38,400/3,840 64,000 96,000

Basically artificially compressing the LH2. The fuel mass ratios will not change, so performance will be identical. However the total vehicle size will be ~ 30% smaller.

In addition, I would be slightly decreasing the power needed for boiloff, which would increase net performance a little. 

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3 hours ago, garwel said:

Can you really compress liquid hydrogen? I mean, it's a liquid after all.

This is not realistic. This is because KSP physics have issues dealing with the large size of vessels that use LH2 propulsion, especially if they are assembled in orbit. I've slowly come to the realization that I probably need to gamify this a little more than I have. Currently things are a little gamified, but not that much. 

As always, Real Fuels and RO are still things!

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7 hours ago, Nertea said:

I'm thinking of doing a thing in the next update which will break stuff. Currently combustion ratios for the engines are a bit hydrogen heavy (15:1 cfg ratio). I would change that to 10:1, which has the advantage of making it a little closer to realism, mass-flow wise. However the interesting thing is that tank ratios might become more attractive to people who don't like large parts, as I will modify them something like so:

Old LH2/O Revised LH2/O Old LH2 New LH2
38,400/2,560 38,400/3,840 64,000 96,000

Basically artificially compressing the LH2. The fuel mass ratios will not change, so performance will be identical. However the total vehicle size will be ~ 30% smaller.

In addition, I would be slightly decreasing the power needed for boiloff, which would increase net performance a little. 

Would it be possible to include some patch in the extras that allows the player to keep the old tank & engine configuration until they replace or recycle existing vessels?

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7 hours ago, Nertea said:

I'm thinking of doing a thing in the next update which will break stuff. Currently combustion ratios for the engines are a bit hydrogen heavy (15:1 cfg ratio). I would change that to 10:1, which has the advantage of making it a little closer to realism, mass-flow wise. However the interesting thing is that tank ratios might become more attractive to people who don't like large parts...

@Nertea, if you're re-balancing the tank ratios, I would also suggest a fresh look at the thrust levels of the cryo- and NTR- engines.  I've enjoyed the realism of LH2 causing design heartache on the volume front, made up for by the efficiency of the high Isp engines for orbital use, but I've always found it disconcerting to have to use outrageously large engines - compared to the tanks they go with - for getting into orbit, much less off the ground.  I personally haven't had problems with large vehicle assembly in orbit, but that may be a function of my recent use of KJR and/or weldable construction ports....  

In any case, my cryo upper stages always seemed to be chronically short on "oomf", and get killed by gravity losses, making them almost superfluous for low orbit heavy lift, unless I do a high-gee LFO first stage "loft" toward the target perigee, then sit through a long coast period.  I know not every engine can be an RS-25 or RS-68, but the really high efficiency upper stage analogues seem barely useful until you've pretty much already circularized to orbit.  I'm concerned the increased tank masses, for presumably the same standard part sizes, would exacerbate the relatively low TWR of craft using most of the cryo- and NTR engines.

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27 minutes ago, KSPrynk said:

@Nertea, if you're re-balancing the tank ratios, I would also suggest a fresh look at the thrust levels of the cryo- and NTR- engines.  I've enjoyed the realism of LH2 causing design heartache on the volume front, made up for by the efficiency of the high Isp engines for orbital use, but I've always found it disconcerting to have to use outrageously large engines - compared to the tanks they go with - for getting into orbit, much less off the ground.  I personally haven't had problems with large vehicle assembly in orbit, but that may be a function of my recent use of KJR and/or weldable construction ports....  

In any case, my cryo upper stages always seemed to be chronically short on "oomf", and get killed by gravity losses, making them almost superfluous for low orbit heavy lift, unless I do a high-gee LFO first stage "loft" toward the target perigee, then sit through a long coast period.  I know not every engine can be an RS-25 or RS-68, but the really high efficiency upper stage analogues seem barely useful until you've pretty much already circularized to orbit.  I'm concerned the increased tank masses, for presumably the same standard part sizes, would exacerbate the relatively low TWR of craft using most of the cryo- and NTR engines.

But do actual LH2 engines have enough trust for take off? The Arianne rockets use SRBs due the lack of thrust of the LH2 rockets. I've always assumed cryogenic engines would be for upper stages (were the tank volume becomes problematic due aerodynamics) or for use on low gravity worlds/orbit - and that seems somewhat realistic.

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6 hours ago, garwel said:

Cool, but I understand it discussed 7% densification, not 50%.

I think you missed the point. The discussion is about balancing a fictional representation of a resource, not adding a new one 50% more dense, while keeping the old LH2.

50 minutes ago, juanml82 said:

But do actual LH2 engines have enough trust for take off? The Arianne rockets use SRBs due the lack of thrust of the LH2 rockets. I've always assumed cryogenic engines would be for upper stages (were the tank volume becomes problematic due aerodynamics) or for use on low gravity worlds/orbit - and that seems somewhat realistic.

Yes. I think the most famous example is the Delta-IV heavy, which produces a pretty red flame. It also runs a incomplete combustion (with excess hydrogen), to improve exhaust velocity. It only misses some asparagus staging :D, I think the fuel lines are too late in the Human Tech Tree.

About the size of the tanks, I don't have any strong opinion (just hope I can implement it without much hassle or hyperediting, and it works in 1.3.1). I was curious to see how it looks like in real rockets, the first good visual representation I could think of is the might Saturn V.

77% of the total weight is in the first stage. The second stage have 16.6%. If you consider only the propellants weight, the fuel/ox in the first stage weights around 5 times more than the fuel/ox in the second. Interesting.

saturn-v-color-cut-away.jpg

Edited by MaximumThrust
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1 hour ago, MaximumThrust said:

Yes. I think the most famous example is the Delta-IV heavy, which produces a pretty red flame.

The reddish flame is actually due to the ablative nozzle extension - color comes from the ablator burning off.

1 hour ago, MaximumThrust said:

It also runs a incomplete combustion (with excess hydrogen)

Nearly all hydrolox engines do.  Full (stoichiometric) combustion would be an O/F ratio of 8, real hydrolox engines are usually in the 5.5-6.5 range.

But yes, as you say, there's no technical reason why a hydrolox engine can't be used for liftoff.  It's just that the higher Isp and lower TWR lend themselves more to being a long-burning sustainer with solid or kerolox boosters.

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I for one like the balance of having more efficient engines that have lower thrust and require greater volumes of fuel tankage; hopefully the new balance doesn't just make them flat-out better in all regards. Though I'm assuming the numbers will still be in the various .cfg files that can be tweaked with MM patches anyway?

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4 hours ago, juanml82 said:

Would it be possible to include some patch in the extras that allows the player to keep the old tank & engine configuration until they replace or recycle existing vessels?

It would be wise to retire all affected craft in advance of installing the update. What you're suggesting will merely only cause mental stress for Nertea and needlessly slow a process that needs to happen fast on the player's side. 

Players should know better by now and:

  • Exercise restraint when grabbing updates;
  • Pay more attention to the Backup folder within their save folders;
  • Keep a separate install of KSP for testing mod updates;
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8 hours ago, JadeOfMaar said:

It would be wise to retire all affected craft in advance of installing the update. What you're suggesting will merely only cause mental stress for Nertea and needlessly slow a process that needs to happen fast on the player's side. 

Not to mention that now may be the best time to do it than any other time in the near future, with a lot of the new stock parts requiring eventual craft rebuilding/retiring anyway.

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23 hours ago, Nertea said:

I'm thinking of doing a thing in the next update which will break stuff.

My only suggestion is to provide documentation and/or lead time to facilitate the updating of other mods that use the CryoEngines ratios/density. I know that BDB and SpaceY have some tanks/engines that use LH2(/O), and I think USI does too? And probably a number of others have one or two parts or patches that would be affected.

I don't know if there's a way to get a full list (maybe if I learned how to query CKAN to see what mods have CryoTanks as a dependency, I guess). But the CryoEngines paradigm gets used as a sort of de factor community standard, and I'm sure you'd prefer to cut down on the number of times that people ask why LH2O tanks have the "wrong" propellant ratios when used with engines from mod XYZ.

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(Reposted from NF thread)

I'm playing Career with KSP 1.3.1, with NFLV, CryoEngines, and CTT.  The CTT engine placement seems odd.  The Chelyabinsk and Tunguska, successive sizes of vacuum engine,  are both in Heavier Rocketry(160).  I seem to remember the Chelyabinsk being in Heavy Rocketry(90) in the past.  The Volcano and Odin, 2 sizes of sustainers, are both in Very Heavy Rocketry(550).  Why are different sizes of engine in the same node?  Unless this is a bug?

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8 hours ago, PocketBrotector said:

My only suggestion is to provide documentation and/or lead time to facilitate the updating of other mods that use the CryoEngines ratios/density. I know that BDB and SpaceY have some tanks/engines that use LH2(/O), and I think USI does too? And probably a number of others have one or two parts or patches that would be affected.

I don't know if there's a way to get a full list (maybe if I learned how to query CKAN to see what mods have CryoTanks as a dependency, I guess). But the CryoEngines paradigm gets used as a sort of de factor community standard, and I'm sure you'd prefer to cut down on the number of times that people ask why LH2O tanks have the "wrong" propellant ratios when used with engines from mod XYZ.

I was curious about this too.  Does every mod with a tank part have to "get on board" with the changes, or is Cryo Tanks simply applying a patch that calculates the appropriate LH2/O mass and mix ratio based on the starting LFO capacity?

Edited by KSPrynk
typo
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