Should Specific Impulse (ISP) be nerfed with improved aerodynamics?

[Northstar1989]

I am of the opinion that with improved aerodynamics (which if implemented correctly, should get rid of the stock "soup-o-sphere" and reduce the Delta-V to get to orbit to around 3.5 km/s for a streamlined rocekt design) the devs should also consider nerfing the default rocket fuel mixture to have lower ISP and density values- *possibly* to match real-world hypergolics (MMH/UDMH/Aerozine + N2O4).

Let it be said, I am a firm believer that the current stock fuel system is badly in need of overhaul anyways.

The fuels don't reflect any real world burn-ratio (Oxidizer is almost always required in MUCH greater quantities than LiquidFuel- even Kero/LOX burns in a roughly 2:1 volume ratio...) and their ISP is similar to Kero/LOX whereas their density is superior to even the much denser choice of hypergolics...

Why hypergolics? Because they have the highest density of any real-world fuel choice (and stock LF/O is already too dense- so this would require the smallest adjustment), their ISP is *inferior* to the current LF/O mixture (which is essential to nerfing the fuel mix so that getting to orbit still remains a challenge at only 3.5 km/s), and in real life they don't experience any boil-off (so it would put to rest any cries from realists that the fuels should have boil-off). By matching a real world fuel, the game would also have known values to work off (which, for hypergolics, already just *happen* to be well-balanced for KSP), and would even be able to re-name LF/O to real fuel names to make realists a bit happier...

I would emphasize that the fuels should also be re-named, because that would open the door to including other fuel mixtures down the line. Such as Kero/LOX (which have better ISP but lower density than hypergolics) and LH2/LOx (which have incredible ISP, but *very low* fuel-density). Which could be eventually (or immediately, if Squad wanted to be particularly proactive) implemented as alternative fuels that force players to trade-off reduced fuel-density for higher ISP, and could even simulate boil-off (hypergolics should be the "default" fuel, though, so new players don't have to deal with boil-off unless/until they ever feel ready...).

I know that everybody doesn't necessarily agree with me. Which is why I am trying to get people to discuss this- and this thread was started so as to facilitate such discussion. Please keep in mind that the main point is that ISP should be reduced, not that I think hypergolics would be the best fuel mixture to model the new (lower) ISP values off of. The bit about hypergolics is in some ways entirely separate from the need to nerf ISP when aerodynamics are improved- it just happens to be a convenient time to bring it up...

Regards,

Northstar

P.S. On second thought, maybe the devs should include Kero/LOX at the same time. Basically, go with 2 different directions on nerfing the fuels. Players could choose either to take a smaller hit to their fuel-density but lose ISP (by using hypergolics), or keep current ISP but lose even more fuel-density (Kero/LOX). It also feels rather weird having jet engines burn UDMH, so it might be better to have all the jet and RAPIER engines (RAPIER is for more advanced players anyways) use Kerosene, for a number of realism and balance reasons (stock jet engines are already EXTREMELY OP'd due to their not losing thrust with altitude and a quirk of how IntakeAir figures into ISP calculations- having them burn with a less dense fuel would do more to nerf them than reducing the ISP a small amount without fixing the IntakeAir issue...)

Edited December 20, 2014 by Northstar1989

[Carmoldu]

About the ISP nerfing, well, it will depend on what they really do to aerodynamics, we can't say they need to nerf it if we don't even know if adquiring an orbit will be easier. For the different fuels and all that stuff, while highly interesting, I don't think it's in scope (not everybody would enjoy it as you and I would, I think) and it sounds more like something for a mod (some already do it)...

[Bill Phil]

Yeah...

The 1st stage niche engines should be around 275 atmo to 310 vac. Then it would make sense at least, to me. But that's me. Plus we need 100kn engines...

Also, what about separate Oxodizer tanks? We already have fuel tanks... And we need 2.5 meter liquidfuel only tanks, it would make the LV-N a lot more difficult to use.

[Captain Sierra]

What if, instead we boosted the atmo height to almost 100km but with minimal density (rudimentary exosphere modeling)? Higher orbit needed = more dV to get to orbit.

[King Arthur]

As far as UDMH, that stuff is extremely toxic. Given how many rockets the Kerbals launch and seeming lack of any negative effects from them I have always entertained the idea that the LF/O the Kerbals use is in fact LH2/LOX and/or Kerosene/LOX depending on the engine.

With regards to ISP, I believe the lifter engines are fine as they are right now though our upper stage engines could possibly use a buff. The SSME (which the LV-T30/45 seem to base themselves off of, at least visually) have an ISP range of 366~452, so the 320~370 range that many of our lifter engines have isn't unreasonable. On the side of upper stage engines, the RL-10 has an ISP of up to 465 in vacuum, this means if anything our vacuum engines like the Poodle, LV-909, and KR-2L are underpowered being capped at 390 (380 in the case of KR-2L).

[Bill Phil]

Well, actually, if you ask me the LV-T # engines need to be nerfed. They don't seem like SSME to me... More like some of the early Rocketdyne engines... H-1 or something. I don't know exactly.

[NathanKell]

Yes. For example, they have an exhaust pipe. Not sure where youi're getting SSME from that. >.>

[MKI]

First off this game doesn't need a more complicated fuel system if it gives nothing back besides "more realism". This game was always fun because it was realistic on portraying space maneuvers and space flight. But details got more fuzzy when you get to other things, such as the fuel mixtures which are very unrealistic.

Now we can't say engines need nerfs if we don't know how the new aerodynamic system will act on them. So until we get more details dealing with the new system, we can't propose nerfs or buffs.

I personally do not believe this game should have different fuel mixtures. Things are already complicated as is in learning how to fly your ship in the game. You shouldn't have to be worrying about fuel mixtures and how they work. That sort of stuff can be left to mods for those who want it, not forced upon everyone just for realism.

PS comparing ISP values and fuel mixtures to real life isn't a good for this sorta game when there are glaring issues about total realism involved. Such as how Kerbin is pretty much an impossible planet.

[Empiro]

Yeah, I wouldn't mind seeing things tweaked a bit. It seems that every version buffs a bunch of engines, and almost none ever get nerfed. Maybe an across the board nerfing of ISP is on the horizon. Who knows.

You definitely feel it when you move from stock to FAR and back to stock. Things are far (heh) easier when you only need 3200 - 3500 m/s, and I've launched many designs that would never work in stock, even if FAR is supposed to be more challenging.

I'm not sure what's the best way to do it. Making Kerbin larger would also work, though that would also make launches take longer -- I kind of like how quickly you can get something up into space currently. IRL, burns take much longer, and that wouldn't be very fun.

[Northstar1989]

@MKI

First off this game doesn't need a more complicated fuel system if it gives nothing back besides "more realism". This game was always fun because it was realistic on portraying space maneuvers and space flight. But details got more fuzzy when you get to other things, such as the fuel mixtures which are very unrealistic.

Re-naming LF/O to MMH/N2O4 or Kerosene/LOX does NOT make the fuel system more complicated- nor does changing the burn ratio to be realistic in terms of relative amonnts of fuel vs. oxidizer needed. If ANYTHING, it makes the system SIMPLER, because then we have a real-world analog by which to understand what the rocket fuels actually represent.

Nerfing the ISP and/or fuel-density doesn't make it more complicated either (the TWR, on the other hand, is unrealistically low, and should be buffed to compensate a bit for the lower ISP and make the game more fun, if anything. I have no idea why you would want a 100 kN engine Bill Phil...)

Adding ADDITIONAL fuel mixture ALTERNATIVE such as LH2/LOX (which there is currently no good analog for) wouldn't make the game any harder or more complicated for average players either. Players who wished to do so could simply *ignore* the non-standard fuel mixtures...

Now we can't say engines need nerfs if we don't know how the new aerodynamic system will act on them. So until we get more details dealing with the new system, we can't propose nerfs or buffs.

It wouldn't be a real aerodynamics overhaul at all if they didn't change drag to be based on shape and size rather than mass. There is absolutely no question that it can't continue with a long, streamlined, full rocket and a short, empty lander falling at EXACTLY the same rate. That's the equivalent of dropping a bowling ball and a feather on Earth, and having them hit the ground at the same time.

If they change the drag model to be based on shape/mass, they will *in effect* be getting rid of the soup-o-sphere (which exists not as a matter of Kerbin's atmosphere actually being any denser than Earth's, but as a result of how drag is modeled) and reducing the Delta-V to get to orbit to around 3.5 km/s. Raising the atmosphere height is one option (although they would also need to increase the scale height to something closer to Earth's for this to be effective), but it's unlikely the devs will decide to do that- so something else in KSP's rocketry needs to be nerfed to compensate.

Reducing ISP or fuel-density to match one of the most likely real-world fuels (MMH/N2O4, which has much lower ISP; or Kerosene/LOX, which has much lower fuel-density) would be one way to accomplishing this.

I personally do not believe this game should have different fuel mixtures. Things are already complicated as is in learning how to fly your ship in the game. You shouldn't have to be worrying about fuel mixtures and how they work. That sort of stuff can be left to mods for those who want it, not forced upon everyone just for realism.

You're not listening. You're not paying attention. You're not actually looking at what's being suggested- you're only making assumptions about what you *THINK* a different fuel-system would mean.

One more time. There is nothing, I repeat NOTHING that is more complicated about MMH/N2O4 or Kersoene/LOX (without LOX boil-off being simulated) than with the current "LiquidFuel" and "Oxidizer" fuel-mixture. The ONLY difference is that the ISP or fuel-density (the amount of fuel that fits in a given sized tank) would be lower, and the name would be different- otherwise the fuels would behave EXACTLY the same, but with real-world names.

PS comparing ISP values and fuel mixtures to real life isn't a good for this sorta game when there are glaring issues about total realism involved. Such as how Kerbin is pretty much an impossible planet.

Every great journey is taken in small steps. Nobody is arguing for TOTAL realism, but the devs can and SHOULD work to increase realism wherever it detracts ABSOLUTELY NOTHING from game-play, and *especially* when in enhances the game experience: as in this case. The reason that the fuel-density or ISP should be nerfed to match, and the fuels re-named to a real fuel, once more, is NOT realism for the sake of realism- it's because the fuels should be nerfed at the same time as the aerodynamics change, for the sake of game balance, anyways.

Using a real-world set of ISP's, densities, and names in this case is simply a matter of convenience. The name-change helps queue players into the fact that something has changed (and ensure that they know to re-design their rockets, so they don't keep trying to use designs that no longer hold enough fuel), whereas the density and ISP for the real fuels are approximately what they should be aiming for, from a balance standpoint, anyways.

Regards,

Northstar

[Northstar1989]

Yeah, I wouldn't mind seeing things tweaked a bit. It seems that every version buffs a bunch of engines, and almost none ever get nerfed. Maybe an across the board nerfing of ISP is on the horizon. Who knows.

That's my hope. And, I think the devs should take the opportunity to simply re-name the fuels when they do so (LF/O --> MMH/N2O4 and LiquidFuel for jets --> Kerosene. The devs could also add Kerosene/LOX as an *alternative* fuel for rockets, as I think it actually throws newbies off more when they can burn jet fuel in rockets- I know it surprised me, even though it *can* be done with Kero/LOX rockets in real life...)

You definitely feel it when you move from stock to FAR and back to stock. Things are far (heh) easier when you only need 3200 - 3500 m/s, and I've launched many designs that would never work in stock, even if FAR is supposed to be more challenging.

I'm not sure what's the best way to do it. Making Kerbin larger would also work, though that would also make launches take longer -- I kind of like how quickly you can get something up into space currently. IRL, burns take much longer, and that wouldn't be very fun.

Yeah, I don't think making Kerbin larger is the way the devs would go. That would be a much more substantial increase to difficulty- although honestly, I would rather see Kerbin 2-3 times larger than it currently is anyways, as it breaks immersion when I can clearly see the curvature of Kerbin from just a few thousand meters above the surface (it's not even necessary to make it to orbit- you can see it from a plane).

By the way, rocket launches actually take less time with FAR installed (and hopefully would with the aerodynamics overhaul as well). The reduction in drag (with streamlined designs) from more accurate drag modeling means that rockets fly FASTER than they would in stock with the same amount of thrust, and thus end up taking less time to ascend to orbit (this is also part of the reason for the reduced Delta-V requirements to orbit with FAR: it's not just a matter of reduced atmospheric drag, reduced gravity-losses due to a faster ascent also play a MAJOR role...)

Regards,

Northstar

[NERVAfan]

as I think it actually throws newbies off more when they can burn jet fuel in rockets- I know it surprised me, even though it *can* be done with Kero/LOX rockets in real life...)

Can you, actually? I've read that jet fuel is too variable for rockets, though that book was talking about the situation in the 50s/60s when orbital rockets were first being figured out - maybe modern jet fuels are more uniform in composition?

Yeah, I don't think making Kerbin larger is the way the devs would go. That would be a much more substantial increase to difficulty- although honestly, I would rather see Kerbin 2-3 times larger than it currently is anyways, as it breaks immersion when I can clearly see the curvature of Kerbin from just a few thousand meters above the surface (it's not even necessary to make it to orbit- you can see it from a plane).

Theoretically, they could also increase the atmospheric pressure (and thus density) or gravity at Kerbin's surface... I doubt they would, though, since that would break the Earth-analogue nature of Kerbin.

[Joonatan1998]

I think the need for ISP reduction depends on what kind of improved model is added.

If the model has all the difficulty adding things from FAR, I think that engines shouldn't be nerfed.

[Pthigrivi]

Is there a real gameplay advantage to doing this besides satisfying the hyper-realists? Changing the fuel/oxidizer ratios and fuel densities and adding a whole new class of fuel creates a lot of work for the devs. Are we talking about a whole new class of tanks? New engines for each type of fuel? Or assigning some to one and some to the other? At the very least basically everything would have to be re-balanced.

I guess Im just not seeing the advantage for all the work involved. Maybe I'm missing something?

[PDCWolf]

Well, not sure why everybody is trying to run away from the topic, given the atmospheric work needed is pretty obvious (take the soup away for starters). If you take the soup away, then there's a lot less difficulty in reaching orbit. Both NEAR and Stock Drag Fix come in at about 3/3.5 km/s ratio so really, trying to avoid this discussion arguing we don't know what's going to happen to the atmosphere seems like a rather toxic behavior to me.

Personally, I would prefer making the planets/moons bigger to match their previous dV-to-orbit requirements, that way you kill 2 birds with a single stone: You get the accustomed dV to orbit requirements, and you also get planets that make a bit more sense that the ones we already have.

[Northstar1989]

Can you, actually? I've read that jet fuel is too variable for rockets, though that book was talking about the situation in the 50s/60s when orbital rockets were first being figured out - maybe modern jet fuels are more uniform in composition?

Technically, that book was right. You can't use standard jet fuel in a Kero/LOX rocket because the quality of the Kerosene is too low. But you CAN burn rocket-grade Kerosene (such as RP-1) in a jet engine- and it would be too complicated to add different grades of Kerosene to the stock game...

Theoretically, they could also increase the atmospheric pressure (and thus density) or gravity at Kerbin's surface... I doubt they would, though, since that would break the Earth-analogue nature of Kerbin.

I agree.

Merry Christmas and a Happy New Year!

-Northstar-

[Northstar1989]

Is there a real gameplay advantage to doing this besides satisfying the hyper-realists?

Yes. The Delta-V to orbit would become far too low for a balanced and satisfying game experience if the atmosphere were fixed without somehow nerfing rockets or their fuel accordingly. The most sensible nerf to me seems to be to reduce fuel ISP or density, since then players will end up building BIGGER rockets- and bigger is BETTER in KSP because it looks more awesome...

Changing the fuel/oxidizer ratios and fuel densities and adding a whole new class of fuel creates a lot of work for the devs. Are we talking about a whole new class of tanks? New engines for each type of fuel? Or assigning some to one and some to the other? At the very least basically everything would have to be re-balanced.

The whole point is to make these changes so as to alter the game balance to compensate for reduced Delta-V to orbit with more realistic aerodynamics. Nothing else would need to be changed besides the ISP of the engines that burn rocket fuel.

Ideally, the devs would also take this opportunity to fix the LF/O burn ratio and make a major overhaul to the tanks/fuels system by allowing players to select how much of each resource they want in a tank (allowing players to place more of their Oxidizer at the base of the rocket so Center of Mass shifts upwards during flight, for instance). Better yet, they would also re-name the fuel resources to real world names and change their ISP/density to match- as some real fuels have approximately the correct balance the devs should be aiming for...

Finally, the fuel tanks should be made tweakable as part of overhauling the fuels- this would allow players to change their distribution of fuel vs. oxidizer and even which fuel resources they carry (Hypergolcis vs. Kero/LOX, for instance) without new parts needing to be added. Several mods already have functional versions of this, including Real Fuels, Modular Fuel Tanks, and Firespitter.

I guess Im just not seeing the advantage for all the work involved. Maybe I'm missing something?

Maintaining a plausible look and feel for KSP. So players still have to build rockets that "look right" when KSP gets better aerodynamics. Also, it *DOES* satisfy the realists out there (such as myself)- and it's never a bad thing to improve the satisfaction of a portion of your player-base if it doesn't harm other players...

Merry Christmas and a Happy New Year!

-Northstar-

[Elthy]

I tried the ISP scaler once (with NEAR) and didnt like it:

Even shorter burn times, im dropping booster stages after just a few seconds.

Extreme acceleration changes in the low atmosphere since you loose much weight in a few seconds

Extreme acceleration very close to the ground, even worse than just with NEAR.

I think higher deltaV requirements are the way to go. A higher atmosphere doesnt help that much since it would have compensate over 1000m/s and would be way larger than Kerbin itself...

[ddenis]

I couldn't care less about:

- how fuel is named

- fuel's density

- particular number of fuel while the units in which it's measured isn't given

I would like to have:

- changed % of Payload to rocket mass so it would be needed to build bigger rocket in stock, but it would also require and changed parameters of building updates and etc. (I couldn't even get to orbit with 18t limit and halved isp) how it has to be done... there is many ways of doing it and I don't care which is used.

- ISP staying as it is now, because if it would be e.g. halved, then a "magic" difference would gone... 390 and 360 gives "bigger" difference is eyes of player than 195 and 180.

- updated ratios of full:empty tank masses to have empty tanks be lighter (more realistic)

- updated mass of engines to be more realistic (if I remember correctly, big mass of the engines were coded to give to rockets ability to fly in stock atmosphere)

And the question for me is how to combine: lighter engines with tanks and decreasing % of payload to orbit.

It's either the density of fuel or flying time to orbit.

And based on real rockets I would prefer time needed to get to 100 km with proper gravitation turn be around 10 minutes*, so the fuel density is the only value left as for me.

Edited December 28, 2014 by ddenis

[foamyesque]

I'd tend to support a restructuring of the tech tree to provide lower Isp/TWR engines first, better ones later. To some extent the current tree tries this, but it blows it by giving you early access to the LV-x engines and the RT-10.

I'm also hopeful at some point Squad'll fix the goofy Isp behaviour and make it scale thrust instead of fuel consumption, which changes the dynamics somewhat.

[Scoundrel]

I personally don't see the need to "nerf" Isp since Isp in KSP isn't Isp (though technically it is in the sense that it is a comparison of fuel consumption vs. thrust) as the esteemed poster above me has so rightly pointed out.

I think we need to see Isp properly implemented first before discussing whether or not Isp needs to be nerfed.

[Whirligig Girl]

No, just make the universe 2 times the scale. (or use Jumbo32). Or just don't remove the souposphere.

[Bill Phil]

I personally don't see the need to "nerf" Isp since Isp in KSP isn't Isp (though technically it is in the sense that it is a comparison of fuel consumption vs. thrust) as the esteemed poster above me has so rightly pointed out.

I think we need to see Isp properly implemented first before discussing whether or not Isp needs to be nerfed.

It's really improper scaling of fuel consumption, not incorrect ISP. The thrust should scale without scaling fuel consumption. But one way to scale thrust is to scale fuel consumption.

[Arugela]

First off this game doesn't need a more complicated fuel system if it gives nothing back besides "more realism". This game was always fun because it was realistic on portraying space maneuvers and space flight. But details got more fuzzy when you get to other things, such as the fuel mixtures which are very unrealistic.

Now we can't say engines need nerfs if we don't know how the new aerodynamic system will act on them. So until we get more details dealing with the new system, we can't propose nerfs or buffs.

I personally do not believe this game should have different fuel mixtures. Things are already complicated as is in learning how to fly your ship in the game. You shouldn't have to be worrying about fuel mixtures and how they work. That sort of stuff can be left to mods for those who want it, not forced upon everyone just for realism.

PS comparing ISP values and fuel mixtures to real life isn't a good for this sorta game when there are glaring issues about total realism involved. Such as how Kerbin is pretty much an impossible planet.

I would prefer the game were more challanging. Or a mode or difficutly option should be added with alot more realism for those who want the increased challenges. You can always have both options available. But the work has to be done to get it.

[Northstar1989]

I personally don't see the need to "nerf" Isp since Isp in KSP isn't Isp (though technically it is in the sense that it is a comparison of fuel consumption vs. thrust) as the esteemed poster above me has so rightly pointed out.

I think we need to see Isp properly implemented first before discussing whether or not Isp needs to be nerfed.

Devs announced Thrust/ISP relationship is going to be fixed in 1.0, so apparently they were listening to you.

NOW, can we start discussing a nerf to ISP or a switch to more realistic fuels (which would have effectively the same impact- of requiring larger rockets- since real fuels are either less like Hydrolox, or lower-ISP like hypergolics...)

Regards,

Northstar