Developer Insights #17 - Engines Archetypes

[TheTennesseeFireman]

2 hours ago, Pthigrivi said:

As to the general simplification of bipropelants I think it makes a lot of sense, and Methalox is great because it's right there in the middle. I understand what folks are saying about historical replicas but they never really functioned exactly right in KSP1 because of the scale of the planet and different performance stats. They were always at best 'look alikes' rather than 'perform-alikes'. And maybe down the road they could still add some Hydrolox engines since those resources will already be deeply embedded in the game. Easy as cake for modders in the meantime. 

Right. As fascinating and informative as the history of spaceflight is, this isn’t a game about that. This is a game about the present and future of spaceflight and the possibilities it unlocks. We’re not going to the Moon, we’re going to the the Mun. And that’s just the very tip of the iceberg of the journey this game wants us to take. For experienced players especially, the part of the game that exists before we reach today’s technology level (with our brand new Methalox engines) will be over in the blink of an eye. So if we’re going to standardize (and the thought process there has been well laid out), it makes vastly more sense to go with the fuel source that gives you simpler rocket designs, practical ISRU, and the most balanced stats.

[Drakenred65]

1 hour ago, Tangle said:

How do I opt out of that?

Sorry forgot to quote you

[Vl3d]

5 hours ago, samhuk said:

I find the discussion about what KSP2 should or shouldn't do, respectfully, a bit pointless, because of this. If KSP2 matches or exceeds KSP1's moddability, then it's likely you or somebody else will mod the game to your desired gameplay ... Now the base game does need to be at least somewhat balanced and logical ...

I feel like everyone should play stock KSP1 again before KSP2 EA releases because everyone is so used to mods that they forget what the purpose of the base game is.

It's my strong desire to not need to install ANY mod to have fun in KSP2. Except for some visual and QoL improvements I only really use 2 gameplay changing mods:

1. Unkerballed Start because it fixes the tech progression.

2. Simplex Kerbalism because it fixes the repetitive science system with mini-games, it creates incentives for differentiating between probe missions and more complex crewed missions, and it encourages learning and using engineering principles: prototyping, testing, including redundancy, iterative design and reuse.

And I should add that I feel like there's no mod that ever really improved the world building, adventure and discovery aspects of the game, despite some cool planet packs that have been created.

Other than these issues stock KSP is a wonderful (incomplete) game. The most important and hardest things to get right are the progression tempo of the game and adding incentives for exploration. The "lego" parts are just tools. Learning in the game should be fueled by the curiosity of exploring the stars! So be mindful about spending too much time on the ground, squabbling about fuel naming conventions.

Edited December 17, 2022 by Vl3d

[Drakenred65]

That’s what I’ve been doing and boy does it suck lol

[The Aziz]

6 hours ago, JoeSchmuckatelli said:

The only thing that kind of confuses me is why they decided to go 'methalox' and not just stick with LF+O.  That worked for KSP... So I'm guessing that having this slight level of specificity is because they will have parts (later) that carry liquid fuel but don't work with keralox engines. Kind of like a xenon tank or a monopropellant tank. 

With specified fuels like MH, hydrogen, xenon, helium, a vague "liquid fuel" wouldn't fit very well. Especially since there are few other liquid fuels among these. Why this can be named, but not that one? Liquid Fuel worked in KSP1 because it was universal, powered everything aside from RCS thrusters, Dawn and srbs.

[Bej Kerman]

6 hours ago, JoeSchmuckatelli said:

The only thing that kind of confuses me is why they decided to go 'methalox' and not just stick with LF+O

I don't particularly see how it'd make the game any more difficult - it's just a change of label to work with everything else. A resource called "Liquid Fuel" or "Oxidizer" won't look good next to "Metallic Hydrogen" and "Fusion Pellets"; it would make the game look a tad unfinished. Well, it would be a hangover from a game that had very little polish and only needed the one resource for all of its parts. The last thing KSP 2 should do is take pointers from KSP 1 beyond the core gameplay. "Methalox" does work with "Metallic Hydrogen" etc though, and for reasons stated by the devs, also makes the most sense compared to kerosene for example.

6 hours ago, Vl3d said:

Learning in the game should be fueled by the curiosity of exploring the stars! So be mindful about spending too much time on the ground, squabbling about fuel naming conventions.

Why not explore and discuss important naming conventions?

[intelliCom]

17 hours ago, JoeSchmuckatelli said:

may add back in Keralox

Implying that "Liquid Fuel" was Kerosene to begin with? It's always been ambiguous.
What I want to know is what OP meant by "brutish keralox". What are the differences between kerosene and methane as chemical rocket fuels? Besides of course the ease of ISRU with Methane.

Also, isn't methane a cryogenic fuel? Would we have to figure out how to manage cryogenic fuel storage? Does kerosene not have this cryogenics issue, hence why it might make more sense?

Edited December 18, 2022 by intelliCom
idiot cant spell, more news at 7

[Yellowburn10]

38 minutes ago, intelliCom said:

What I want to know is what OP meant by "brutish keralox". What are the differences between kerosene and methane with as chemical rocket fuels? Besides of course the ease of ISRU with Methane.

I interpreted it to mean that keralox is a fuel type that has produced several powerful engines over the years, while also being a very crude burning fuel compared to things like methalox or hydrolox. Now I'm no rocket scientist, so anyone feel free to correct me, but from what I understand in real life keralox rockets are relatively cheep and have comparatively simple designs, and it's fuel is very dense, meaning it's fuel tanks don't need to be as large. But it have can have issues with soot and are harder to work with more complex engine designs. Meanwhile methalox is cleaner burning and are more efficient, as well as not having as much limitations on rocket engine design.

 

50 minutes ago, intelliCom said:

Also, isn't methane a cryogenic fuel? Would we have to figure out how to manage cryogenic fuel storage? Does kerosene not have this cryogenics issue, hence why it might make more sense?

While methane does need cryogenic considerations, keep in mind that liquid oxygen does as well. In fact, both are chilled to around a similar temperature for fuel, so since lox needs to be cold anyways, everything we know about that could be applied to methane as well.

[Vl3d]

On 12/16/2022 at 4:38 PM, Vl3d said:

Q1: Somewhat related to engines - a quick question. Because we have a few preset diameters and length steps for fuel tanks - can the length be adjustable from the tank properties instead of each fuel tank with the same diameter being a separate part? Not asking for completely procedural tanks, just step-wise for length. It would de-clutter the part picker list. Same for solid fuel boosters..

Q2: Will there be fuel switching for engines, will we have engines that can use multiple fuel types?

@Nertea please allow me to quote some of my previous questions in the hope that maybe you can tell us something more. Also I would add:

Q3: Are there going to be difficulty settings introducing any limitations to engine run time, number of relight cycles, throttle control? Any chance of engine wear / damage / failure (not random)? Are there other ways to encourage using engine redundancy in the designs?

Q4: Are the engines going to change visually over the course of a mission? E.g. look dented if damaged or worn out after being used?

Q5: In gameplay videos I've seen that some engines have a very small delay when starting up (probably simulating turbo spool). I think this is great! Can you share any more details about it?

Q6: Sound is a very important part of an engine's "feel". Anything you can tell us about how the engines sound? Will we be able to hear the turbines at startup? Is sound dynamically changing depending on camera angle and atmospheric density? Will we hear the engines run in space?

Q7: Will the engines still gimbal when using rotational control inputs if they are turned off? (hope not)

Edited December 18, 2022 by Vl3d

[Turbo Ben]

I probably have over 1000 hours in KSP, so I'd like to add my opinion on fuels and tanks.

My main concern is with methane fueled jet engines. Other than a couple of experimental engines, this is just not a thing. To me, KSP is a fantastic education tool as well as a great game, and teaching wrong is bad form and a missed opportunity.

If onboarding new players is the concern, a bigger problem is only having sandbox mode in EA. I didn't have problems learning KSP 1 because I started in career mode and parts/principles were introduced slowly. How many players will be scared off in EA because they go to the VAB and are confronted with 100+ parts? In the scheme of things, having one extra fuel type adds very little complexity and for the gain in realism, I think it's a worthwhile tradeoff.

Solutions?

1. If onboarding is such a big concern, KSP 1's use of ambiguous "liquid fuel" was fine. The only reason to name the fuel is realism, but then methane jets contradict this.

2. If you need to name the fuel, kerosene would be a better option as it's used by both rocket and jet engines. Using methane to make ISRU production more realistic is all well and good, but it's at the sacrifice of the basics.

3. This is what I would like to see and satisfies the dev's criteria as far as I can make out. Early game, to aid onboarding, kerosene is used for both rockets and jets. Later on, once players are onboarded, Methane is unlocked for rocket engines only. Methane can be produced by ISRU, kerosene cannot.

Liquid fuel tanks:

I would like to see semi procedural liquid fuel tanks, where the length can be adjusted freely, and the diameter can be adjusted in steps. Having the length freely adjustable will allow fine tuning of fuel capacity so you're not carrying dry/wet mass that isn't needed and would also reduce part count. Larger/miniature diameters are unlocked as you progress. Make the top and bottom diameters independant to make interstage adapters . You then have a single "Liquid fuel tank" part that replaces every size and shape of tank/adapter, reducing the cluttered part list while giving the player more options.

Have the fuel switchable between kerolox and methalox and have a slider to adjust the fuel/oxidiser ratio. Have a button to lock/reset the ratio to standard. This way, the tank contents can be tuned from 100% fuel to 100% oxidiser or anywhere inbetween, and be returned to standard at the click of a button.

[Luriss]

15 minutes ago, Turbo Ben said:

3. This is what I would like to see and satisfies the dev's criteria as far as I can make out. Early game, to aid onboarding, kerosene is used for both rockets and jets. Later on, once players are onboarded, Methane is unlocked for rocket engines only. Methane can be produced by ISRU, kerosene cannot.

Playing off this idea I'd argue it'd be better to just have a different fuel type for each engine type rather than giving chemical rockets two fuel types later on; this way you retain some of the simplicity of the methalox only system while neatly playing into the one fuel per engine type trend with the nuclear and ion engines.

Nuclear = Hydrogen, Chemical = Methalox, Jet engines = Kerosene, Ion = Xenon, etc.

[Turbo Ben]

10 minutes ago, Luriss said:

Playing off this idea I'd argue it'd be better to just have a different fuel type for each engine type rather than giving chemical rockets two fuel types later on; this way you retain some of the simplicity of the methalox only system while neatly playing into the one fuel per engine type trend with the nuclear and ion engines.

Nuclear = Hydrogen, Chemical = Methalox, Jet engines = Kerosene, Ion = Xenon, etc.

You've reminded me, I did have a fourth option of having tanks specificly for jets (the same as ksp1) that just contain kerosine, and keeping the methalox tanks for rockets.

Two reasons I'd be against that. First, how would you build a spaceplane with both jets and rockets? You'd need seperate tanks for kerosene and methalox. It would be better to have all engines capable of running with kerosene.

Second, back to onboarding. This would add the extra fuel type early game, and would require either a new set of tanks or the need to switch fuel types. With my suggestion, you would just need to pick the liquid fuel tank (which would default be kerolox) and stick any rocket or jet engine on it and it would work. The small amount of extra complexity comes later once a player is already flying.

[JoeSchmuckatelli]

Methane can be used in a jet 

https://www.google.com/amp/s/energynews.us/2013/08/26/could-natural-gas-fuel-commercial-flights-of-the-future/

LNG “seems like it’s definitely feasible,” Bradley said in an interview Monday. “Its efficiency is greater [than conventional fuel], you’re able to clean up the greenhouse gas emissions, and you get a cleaner-burning fuel, as well,” with less sulfur and particulate content.

 

The major hurdles, Bradley said, relate to infrastructure and regulations. How could airports, already pressed for space, accommodate LNG storage tanks or on-site liquefaction facilities and pipelines?

[regex]

8 hours ago, Yellowburn10 said:

I interpreted it to mean that keralox is a fuel type that has produced several powerful engines over the years, while also being a very crude burning fuel compared to things like methalox or hydrolox. Now I'm no rocket scientist, so anyone feel free to correct me, but from what I understand in real life keralox rockets are relatively cheep and have comparatively simple designs, and it's fuel is very dense, meaning it's fuel tanks don't need to be as large. But it have can have issues with soot and are harder to work with more complex engine designs. Meanwhile methalox is cleaner burning and are more efficient, as well as not having as much limitations on rocket engine design.

Kerolox engines don't have to be simple, the RD-180 what the Atlas uses is a staged combustion engine. Some Soviet kerolox engines could still be considered "state of the art". Generally heavier, denser fuels are going to have greater thrust (but less isp because they can't muster higher exhaust velocities) than lighter ones, which is why a relatively small rocket like the Proton (using complex hypergolic molecules) can put ~23 tons on orbit (compare Proton to Delta-IV Heavy, which uses hydrolox).

Calling kerolox "brutish" is kind of amusing but understandable if your only reference is U.S. engines, which were lacking compared to their Soviet counterparts.

[Turbo Ben]

26 minutes ago, JoeSchmuckatelli said:

Methane can be used in a jet

I'm not saying it can't, in fact it already has in experimental engines. I'm saying it isn't.

[Yellowburn10]

42 minutes ago, regex said:

Kerolox engines don't have to be simple, the RD-180 what the Atlas uses is a staged combustion engine. Some Soviet kerolox engines could still be considered "state of the art". Generally heavier, denser fuels are going to have greater thrust (but less isp because they can't muster higher exhaust velocities) than lighter ones, which is why a relatively small rocket like the Proton (using complex hypergolic molecules) can put ~23 tons on orbit (compare Proton to Delta-IV Heavy, which uses hydrolox).

Calling kerolox "brutish" is kind of amusing but understandable if your only reference is U.S. engines, which were lacking compared to their Soviet counterparts.

To be fair, I never did say you couldn’t make more advanced engines with keralox, just that it was harder. The soviets worked their butts off to make their engines as good as they were, so I won’t knock them for that. It just took the US a lot longer and used other fuel types to make engines that were as state of the art. 

[Strawberry]

I dont see what nerfing interplanetary jets by making there fuel super exclusive adds considering they already have a pretty niche use case. Gameplay generally truimphs education (not to mention that most people know that jet engines run on oil), and having to micromanage fuel types when you want to make a ssto dual engine jet plane with a rocket engine attached to it just doesnt seem like good gameplay.

[Pthigrivi]

I hear what folks are saying but you can see what a can of worms this opens. Starting the game out with 3 different fuel types means 3 different kinds of engines, 3 different kinds of tanks, all in the first few minutes and hours of the game. KSP has a steep enough opening learning curve already, and we're trying to make the experience more accessible rather than less. Yes of course in the real world there are different fuels, engines can't be infinitely restarted, reaction wheels saturate, but these are all things that can pretty safely be simplified to make the game more playable. I think the reference to ISRU is particularly telling. Planes are definitely fun, but they aren't central to the game. If we're trying to choose between Methane or Kerosene as a the stand-in chemical fuel you want something that makes more sense for the deep progression into interplanetary colonization and eventually interstellar. While I'd love to see chemical rockets stay relevant deeper into the game depending on what resources were locally available its still just the first step in a much longer chain of technologies. There's no need to overcomplicate that, even if it leads to some things that don't exactly match up with the human history of aviation. So long as the science is there kids will have a lot to learn from it. 

[regex]

12 minutes ago, Yellowburn10 said:

To be fair, I never did say you couldn’t make more advanced engines with keralox, just that it was harder. The soviets worked their butts off to make their engines as good as they were, so I won’t knock them for that. It just took the US a lot longer and used other fuel types to make engines that were as state of the art. 

That wasn't criticism, I was expanding on what you had written. Also, IIRC, the US has never reached the same sophistication as the Soviets did with kerolox, they were hugely surprised by the NK-33 and -43, and likely the RD-180 as well.

And on the methane debate in this thread? I think it's kind of silly, personally. I'm glad they put a name to liquid fuel and I agree with the devs on all their reasons for choosing methane. KSP isn't recreating Earth's history and there's no reason Kerbals can't take a different technological path than we did. It's a real shame they're portrayed as bumbling idiots because they exhibit some excellent technical sophistication.

Are we getting a real name for monopropellant as well?

[The Aziz]

Last time I checked (back when fuel refineries were presented), it wasn't. It was assumed to be hydrazine, but name wasn't included. Probably, again, to avoid confusion among new players.

[Pthigrivi]

12 minutes ago, Laikanaut said:

Are you a developer?

No, just speaking as a fan of KSP and a member of the community I hope more players and especially young people are able to enjoy and progress and learn all the cool things I have about space travel. 

[regex]

1 hour ago, The Aziz said:

Last time I checked (back when fuel refineries were presented), it wasn't. It was assumed to be hydrazine, but name wasn't included. Probably, again, to avoid confusion among new players.

Why would "hydrazine" be more confusing to new players than "monopropellant"? Fuel gets used by engines, engines state what fuel they use under this new paradigm, which is awesome and simple.

[Pthigrivi]

22 minutes ago, Laikanaut said:

Ah, it just sounded like this as you said "we" and I suspect there are several accounts here being used by developers, without saying it openly.

Haha I wish. It does seem like fun, but no. Members of the dev team will comment from time to time but their names will appear in orange. 

[Book]

I see a lot of people saying using methane for airplanes doesn't make sense historically (because it entirely makes sense for the gameplay) but in a world where tech first developed rocket engines burning methane and then planes, it totally makes sense that plane engines would use methane, why reinvent the engine to get an inferior product?

Also we've got no proof that Kerbin has vast deposits of easily accessible dead plants from a time before dead plants could be recycled by the ecosystem. Just assuming kerosene is available isn't realistic, it's deciding Kerbin is Earth reskinned.

Finally and probably the most important : If Kerbals had the choice between dead plants and farts, they would totally go with the farts.

[X-Marshal]

Methane jets...?