GregroxMun

The Wolfhound and the Skiff's stats seem to be switched

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Posted (edited)

The facts:

  • The actual Service Propulsion System of the Apollo C/SM was a small low-efficiency hypergolic engine with 91 kN thrust and a specific impulse of 319 seconds.
  • The J-2 rocket engine on the Saturn V was a high efficiency rocket engine with 421 seconds Isp, and 486 kN of thrust.
  • The Wolfhound is the in-game SPS analogue. It has an Isp of 412 seconds and a thrust of 375 kN. 
  • The Skiff is the in-game J-2 analogue. It has an Isp of 330 seconds and a thrust of 300 kN--barely better than the LV-T30 Reliant. The in-game description describes it as having "high vacuum efficiency" and as being "powerful."

I do believe Squad have mixed up the stats for the Wolfhound and the Skiff.

But there is a deeper issue which is less obvious. In KSP, the densities of the LiquidFuel we use are comparable to the densities of Kerosene or Hydrazine. These are medium-to-low efficiency fuels and the engines in-game are pretty much balanced around that sort of fuel. Fuel density plays a huge role in rocket design. Bigger tanks are needed to store Hydrogen and Oxygen than Hydrazine and N2O4 in real life. The argument for or against having swappable fuels is not one I want to have right now, but what is important is that 412 or 421 seconds of specific impulse with KSP fuel density is far outside the realm of realism and game balance. 412s Isp with a high thrust to weight ratio results in an engine which may rival the nuclear thermal rocket LV-N "Nerv." Higher thrust, twice the propellant density (LV-Ns can only use LiquidFuel--and actually unless the LV-N is secretly an open cycle gas core NTR running on hydrazine it is a bit overpowered too)

At the very least a fix patch needs to swap the characteristics of the Skiff and the Wolfhound, that much is clear. But arguably even then the skiff should be buffed. EDIT: Also the "fixed" Wolfhound's TWR is far too high. The SPS is 91 kN for what should be a larger engine, versus 375 or 300 kN. :huh:

TLDR: The bug is that the Skiff and the Wolfhound are very obviously swapped with their Masses, Thrusts, and Specific Impulses. The design flaw: The Wolfhound (which should be the Skiff) is super overpowered because it uses low-density high efficiency with high-density fuel--essentially packing more delta-v into a given space. From a realism and a gameplay standpoint both.

Edited by GregroxMun
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Thanks for the reality check! I thought they seemed a bit too good compared to the old Terrier, Reliant et al. Especially the weight was very low for such powerful engines. Isn't the Skiff better than the Reliant in every single way? Lighter, stronger and better Isp? Thanks for making a much better argument than I ever could have.

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It's an interesting problem.

3 hours ago, GregroxMun said:

The facts:

  • The actual Service Propulsion System of the Apollo C/SM was a small low-efficiency hypergolic engine with 91 kN thrust and a specific impulse of 319 seconds.
  • The J-2 rocket engine on the Saturn V was a high efficiency rocket engine with 421 seconds Isp, and 486 kN of thrust.
  • The Wolfhound is the in-game SPS analogue. It has an Isp of 412 seconds and a thrust of 375 kN. 
  • The Skiff is the in-game J-2 analogue. It has an Isp of 330 seconds and a thrust of 300 kN--barely better than the LV-T30 Reliant. The in-game description describes it as having "high vacuum efficiency" and as being "powerful."

I do believe Squad have mixed up the stats for the Wolfhound and the Skiff. Good job guys.

But there is a deeper issue. In KSP, the densities of the LiquidFuel we use are comparable to the densities of Kerosene or Hydrazine. These are medium-to-low efficiency fuels and the engines in-game are pretty much balanced around that sort of fuel. Fuel density plays a huge role in rocket design. Bigger tanks are needed to store Hydrogen and Oxygen than Hydrazine and N2O4 in real life. The argument for or against having swappable fuels is not one I want to have right now, but what is important is that 412 or 421 seconds of specific impulse with KSP fuel density is far outside the realm of realism and game balance. 412s Isp with a high thrust to weight ratio results in an engine which may rival the nuclear thermal rocket LV-N "Nerv." Higher thrust, twice the propellant density (LV-Ns can only use LiquidFuel--and actually unless the LV-N is secretly an open cycle gas core NTR running on hydrazine it is a bit overpowered too)

At the very least a fix patch needs to swap the characteristics of the Skiff and the Wolfhound, that much is clear. But arguably even then the skiff should be buffed. EDIT: Also the "fixed" Wolfhound's TWR is far too high. The SPS is 91 kN for what should be a larger engine, versus 375 or 300 kN. In a word, no.

While not disagreeing with you on any points of fact (historical engines, etc.) ... it's not the same thing as saying that KSP should necessarily do one thing or another.

Because KSP isn't just a historical simulation, it's also a game.  And game balance matters, e.g. the balance among the various parts.  You raise a lot of cogent points above, talking about real-world historical rocket engines and real-world fuels and various real-world engineering solutions... but I don't see any mention at all made of game balance, e.g. "this engine should be more powerful than that one because <gameplay reason>."

Scientific/historical arguments, such as yours, are perfectly valid.  But so are gameplay/balance arguments.  Which one is "more important" will vary from one person to another, since different people have different priorities.  Some people are very passionate about realism and the history of the space program, and to someone like that, I could imagine that realism would be a lot more important than game balance.  On the other hand... some people are completely the other way around, and they couldn't care less about what real-world engine some KSP engine happens to look like.

Ideally, of course, an engine design in KSP would satisfy both requirements-- fit perfectly into the game balance against all the other parts in the game, and be historically accurate and so forth.  Unfortunately, the game is subject to a variety of constraints that make that difficult at best, impossible at worst.  Some examples:

  • As you point out, real-world engines use a variety of fuel types.  KSP engines use just one.  And it's the same stuff that's used for jet planes.  And for the LV-N.  So it's physically impossible to make complete historical sense in all cases, because the physical design of real-world engines reflect the different fuels they use.  There's no way to have them keep the same physical appearance, and use the same fuel, and have "realistic" relative stats to each other, and make visual sense in the game.
  • The old stock parts.  No matter what engines Making History adds... well, the Poodle and the Skipper and the Mainsail and so forth are still a part of the game.  So, from a gameplay balance perspective... the new parts have to fit in, at least somewhat reasonably.  And those stock parts don't look particularly like any historical engine, and weren't balanced with that in mind, and have been around so long that their stats are pretty much set in stone by now.  So the KSP designers are going to have to work around that.

Which basically boils down to "you can't have everything", and there are going to be places where a design decision has to be made between historical realism and gameplay, and doing better at one will mean doing worse at the other.  Which means somebody's going to be unhappy no matter what you do, since different people are going to want different things.

So the question of "what should KSP do" really becomes "what do most players want".  I would hazard a guess that passionate history buffs like yourself who are well-read enough to actually know what all the old engines were, and what fuels they used, and what their stats were, and so forth... are probably the minority of players.  I would guess that most players are probably more gameplay-oriented than historical-accuracy oriented.  So, that means design decisions are going to have to take that into account, and there are going to have to be places where historical accuracy's going to have to give a bit.

Or, put another way:  if you're going to try to convince folks that "the engine stats need to change"... it's going to be hard to persuade unless you make sure that there's also a solid gameplay story there, regardless of historical accuracy.

So, with that in mind... I'm not saying "you're wrong", but rather "I don't have enough data to have much of an opinion" because I'd need to see the numbers.  Specifically:

  • What stats do you propose for the Wolfhound?  Mass, vacuum thrust, Isp, position in tech tree.
  • What stats do you propose for the Skiff?  Mass, vacuum thrust, Isp, position in tech tree.

Since I'm overwhelmingly a "gameplay" person myself (as you might have guessed by now) :wink: ... whatever numbers you propose, I'm going to be looking at them through a "gameplay balance" lens.  Other than an insistence on balance, I'm fairly neutral, i.e. there are many potential sets of stats I could agree to, I think.   But give me a set of numbers that make sense to me from a gameplay perspective, and I can totally get on board.  :)

3 hours ago, dvader said:

Isn't the Skiff better than the Reliant in every single way?

No.  It's better in some ways, worse in others.

3 hours ago, dvader said:

Lighter, stronger and better Isp?

This is true.  But it's also a much larger engine (can't fit in any stack smaller than 1.875m)-- even in its narrowest configuration, it has over double the cross-sectional area of the Reliant.  Bigger size is a relative disadvantage.

For me, the real killer argument there, though, is that the Skiff is a full three tiers higher on the tech tree than the Reliant, which in my book means it's allowed to be objectively better, just as the HECS is better than the OKTO in every way.  The Reliant's a crude entry-level engine; the Skiff is a high-tech performer.

That's not the same thing as asserting that it is or isn't "overpowered" --- simply that it's not a slam dunk, and comes down to a judgment call based on how important one thinks the bigger size and tech tree placement are, relative to the other stats.  (For example, a player who always plays sandbox would be more likely to consider it overpowered, I suppose, since for them the "tech tree" isn't even a thing.)

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@Snark even without the historical argument, the Wolfhound is OP. It’s better than Poodle in every way. Something needs to be done.

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I have perhaps not made it obvious but my point is really a gameplay concern. 412s Isp with a dense fuel is wrong for realistic reasons, BUT those same reasons make it overpowered for gameplay reasons. In KSP we really need engines that are at least a little bit inferior to their real counterparts. This is because of the 1/10th scale stock system. This is done by using low efficiency engines of fairly high mass. With an engine using "realistic" hydrogen+oxygen specific impulse of over 400 seconds, such an engine performs incredibly better than real engines. This is not a realism problem. It is a gameplay problem. Engines should generally be worse than their real counterparts, or rockets either get short and stubby or far too powerful for their size. The engine not only performs better when attached to a rocket than it would in real life, it performs better than any other engine in the game.

In real life, Hydrogen/Oxygen rockets have a tradeoff from Kerosene/Oxygen or Hydrazine/N2O4. The hydrogen is big and bulky and thus you can not fit nearly as much of its mass into the same space as you could Kerosene or Hydrazine. But of course LH2 and LOx are a tremendously efficient fuel to make up for it. And the lightness of the fuel does have an upside--the thrust to weight ratio for the same amount of delta-v is higher.

1 minute ago, Snark said:

So, with that in mind... I'm not saying "you're wrong", but rather "I don't have enough data to have much of an opinion" because I'd need to see the numbers.  Specifically:

  • What stats do you propose for the Wolfhound?  Mass, vacuum thrust, Isp, position in tech tree.
  • What stats do you propose for the Skiff?  Mass, vacuum thrust, Isp, position in tech tree.

I propose two options for the question depending upon whether you think my argument about Isp is valid or not. I have no strong opinion on their relative position in the tech tree, though the Skiff should be sure to join the F-1alike Mastodon.

OPTION ONE: Balanced as it is now, but with the bug fixed

Skiff: Mass: 2.5 tons. Vacuum thrust: 375 kN. Specific Impulse: 280-412s.  Reasonably accurate to the J-2 Engine, but overpowered as LiquidFuel gains a huge amount of energy density.

Wolfhound: Mass: 0.8 ton. Vacuum thrust: 90 kN. Specific Impulse: 90-365s. High Isp to reflect its nozzle size, but still clearly a hydrazine or kerosene engine. Lower thrust. Still more powerful in Kerbal-scale than its real world counterpart is in real scale. Somewhere between Poodle and Terrier.

OPTION TWO: Rebalanced to account for KSP fuel density

Skiff: Mass: 2.5 tons. Vacuum thrust: 460 kN. Specific Impulse: 280-373s. Still the highest specific impulse engine aside from the Nerv and Dawn, but with an Isp within the realm of plausibility for the fuel densities in the game and not too overpowered from a game balance standpoint.

Wolfhound: Same as above.

I want to make this absolutely clear. It is not a balance issue that the Skiff and the Wolfhound have been swapped. As far as I can tell even their masses should be swapped for one another. So if you ignore the historical background and appearance of their models entirely, this is not a game balance problem. However, the way they are implemented now, trying to build the Saturn V with Skiffs on the rocket and a Wolfhound on the CSM will result in a rocket that behaves differently than it should. I firmly believe that it was a simple mistake on the part of the developers, and that this was not intentional. And further, though I have lingered on the point about fuel density and specific impulse more, simply because I feel it deserves explanation, the fact that the stats of the Skiff and the Wolfhound are switched is of far greater importance. I believe it is reasonable to be of the opinion that 412s is not ridiculously overpowered. But to be of the opinion that the Skiff and the Wolfhound are both fine as they are seems to be pointless and unreasonable.

I started this thread and its title before I discovered that Skiff and Wolfhound were swapped. After I submit this reply I will edit the post title from "Wolfhound is ridiculously overpowered and is swapped with the skiff" to "The Wolfhound and the Skiff's stats seem to be switched."

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21 minutes ago, sh1pman said:

@Snark even without the historical argument, the Wolfhound is OP. It’s better than Poodle in every way.

Well, it has a higher Isp, that's basically it.

It's got a higher thrust, yes, but also a higher mass-- but that just makes it bigger, not "better".

But yeah, the higher Isp gives it an edge.

 

24 minutes ago, GregroxMun said:

I propose two options for the question depending upon whether you think my argument about Isp is valid or not.

Well... I confess I'm having trouble following what your argument actually is, i.e. what exactly is it that you're proposing?  That "Isp should should be lower across the board for every engine in KSP"?  Or something else?  (I'm not criticizing your argument or anything, just want to be sure I understand what you're proposing.)

If you were to propose simply keeping the two sets of engine stats exactly as-is, and do a complete swap-- i.e. the equivalent of "give each engine the other one's model and name without changing anything else"-- then of course that would be a completely gameplay-balance-neutral change.  It would be  a purely cosmetic one, just swapping their roles.

However, the actual numbers you've proposed:

30 minutes ago, GregroxMun said:

OPTION ONE: Balanced as it is now, but with the bug fixed

Skiff: Mass: 2.5 tons. Vacuum thrust: 375 kN. Specific Impulse: 280-412s.  Reasonably accurate to the J-2 Engine, but overpowered as LiquidFuel gains a huge amount of energy density.

Wolfhound: Mass: 0.8 ton. Vacuum thrust: 90 kN. Specific Impulse: 90-365s. High Isp to reflect its nozzle size, but still clearly a hydrazine or kerosene engine. Lower thrust. Still more powerful in Kerbal-scale than its real world counterpart is in real scale. Somewhere between Poodle and Terrier.

This makes the Skiff feel incredibly overpowered and the Wolfhound incredibly underpowered, to me.

The problem with the Skiff is that it has a super-high vacuum Isp and a really good atmospheric Isp.  It's a good launch-off-the-pad engine and the engine you use to fly to Jool with.  There's no Achilles heel, nothing it's bad at-- it's too good all up and down the line.  The reason I'm okay with the game's current Wolfhound high Isp is that it's got absolutely abysmal atmospheric Isp, so that it's a specialist.  Picking this proposed set of stats would make the Skiff the go-to vacuum engine, as well as a decent heavy-lift engine.

Whereas the Wolfhound... I've got basically nowhere to use it.  For any large ship, the Skiff would be unambiguously better and I'd use that.  For smaller ships where 2.5 tons is just too much engine... well, then I'd more likely use a Terrier or Cheetah.  I'd basically never use the Wolfhound for anything ever.  It would be way too anemic to be useful.  The Terrier-- which is tiny, and available early in the tech tree-- has fully 60 kN thrust, and a pretty good Isp at 345.  It would just seem incredibly weird for this gargantuan, awkward engine to be barely better than the little Terrier.  Besides, we already have what amounts to a somewhat-bigger-Terrier in the game, which is the Cheetah.  So with this set of stats, there's essentially nowhere for me to use the Wolfhound where the Cheetah or Terrier wouldn't fit better.  Or perhaps a Poodle, depending on my thrust requirements (much higher TWR, Isp nearly as good).

36 minutes ago, GregroxMun said:

OPTION TWO: Rebalanced to account for KSP fuel density

Skiff: Mass: 2.5 tons. Vacuum thrust: 460 kN. Specific Impulse: 280-373s. Still the highest specific impulse engine aside from the Nerv and Dawn, but with an Isp within the realm of plausibility for the fuel densities in the game and not too overpowered from a game balance standpoint.

Wolfhound: Same as above.

Same issues with the Wolfhound as above.  Skiff is still overpowered, though not as badly so as above.

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36 minutes ago, Snark said:

This makes the Skiff feel incredibly overpowered and the Wolfhound incredibly underpowered, to me.

The skiff in my suggestion has pretty much same characteristics there as the Wolfhound does now. The Skiff shouldn't be a lifting engine. And neither should the Wolfhound. They are both based upon vacuum engines and the description of the Skiff refers to being used in vacuum--despite its Isp being mediocre for a vacuum engine.

 The wolfhound would still have a higher Isp, almost as good TWR as the Terrier, and you don't need a lot of thrust in space. Terrier has 0.5t and 60kN thrust. And the Wolfhound would still be good as a vacuum engine goes. But I would be willing to accept a higher TWR for the wolfhound. Not more than the Poodle though. Even just looking at the Wolfhound you can tell it should be a low thrust engine. Its bell is huge, sure, but the actual combustion chamber is pretty tiny.

40 minutes ago, Snark said:

Well... I confess I'm having trouble following what your argument actually is, i.e. what exactly is it that you're proposing?  That "Isp should should be lower across the board for every engine in KSP"?  Or something else?  (I'm not criticizing your argument or anything, just want to be sure I understand what you're proposing.)

Engine Isp and masses in KSP is fine already as it is. But they are generally worse than real rocket engines which use fuel of about the same density. The problem is that with the Skiff (or as it is now, the Wolfhound), the Isp and fuel energy density is better than the real world, which you do not want. Rocket parts need to have worse performance than real engines because the delta-v needed to do anything is roughly 1/3rd as much as you need in the real world. I don't see how my point isn't getting across.

42 minutes ago, Snark said:

If you were to propose simply keeping the two sets of engine stats exactly as-is, and do a complete swap-- i.e. the equivalent of "give each engine the other one's model and name without changing anything else"-- then of course that would be a completely gameplay-balance-neutral change.  It would be  a purely cosmetic one, just swapping their roles.

Yes. The cosmetics change is neccesary because Making History's parts are based upon real engines and currently they are the wrong way around. Literally it seems that what happened is that they were already switched by accident in development. The bare minimum for me is that they simply unswitch them.

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It is self-evidently true that @GregroxMun is right here. The SM engine only has to push a tiny stack, it makes no sense for it to be so powerful. It's gotta be an error.

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11 hours ago, GregroxMun said:

The Skiff shouldn't be a lifting engine. And neither should the Wolfhound.

I agree.  However, the reason I was calling your proposed Skiff stats "overpowered" is that with those stats, it would be a lifting engine:

13 hours ago, GregroxMun said:

Specific Impulse: 280-412s.

It's that ASL Isp of 280 that I was taking issue with.  The current Wolfhound has a really low atmospheric Isp, even lower than the Poodle's, so it is strictly a vacuum engine.  Your proposed revision would give the Skiff some stats that are like the current Wolfhound's... but also give it a pretty good atmospheric Isp, which would make it an uber-engine that can do anything.

Change that recommendation of 280 atmospheric Isp down to 70 or so, and then it's "pretty much the same characteristics" as the current Wolfhound, and I cheerfully withdraw my "overpowered" comment.

Basically, where I'm coming from is that the general balance tradeoff for stock KSP engines is this:  Really high vacuum Isp engines have crappy atmospheric Isp to make up for it.  So, any time I see an engine with a vacuum Isp that's in the Terrier/Poodle range or above, I think it needs to have abysmal performance in atmosphere.

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Posted (edited)

In my opinion, 412s would be too high for a J2 analogue in KSP. IRL, 421s isn't a high hydrolox vacuum isp, only a little better than the RS-68, which is a launch engine (although much newer).  Maybe just increase the thrust for the Skiff, it already has a better isp than the Skipper.

Since there is only one fuel/oxidizer mix in KSP, I think it makes sense for an orbital engine to have a higher isp than a second stage engine. But if the Wolfhound keeps the 412s (isn't this really high for any KSP engine?), it should have a relatively low TWR (I'm on mobile, so I don't have the engine masses in front of me).

One argument for higher than "realistic" thrust (but not OP TWR) for the Wolfhound is that it will probably be used for orbital insertion for an orbiter and lander combo. In KSP, with the small planets, insertion burns need to happen pretty quickly.

 

Edited by lurkoholic
Corrected J2 isp.

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412s is too high for a LFO engine in stock KSP. Since Isp directly scales the resulting dV in the rocket equation, and required dV in KSP is about 1/sqrt(10) "real life" dV requirements, an engine with those stats would be like a real world engine getting ~1,300 Isp.

I know KSP is meant to be easier, and I was fine with the line being drawn at 350s for the poodle, but increasing LFO Isp even more? I'm very skeptical (maybe I'll play at a higher rescale factor once kopernicus updates if I get this expansion)

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Posted (edited)

I also want to throw a proposal in the ring. IMO there are three factors that are important: First, gameplay and balance. KSP is a game first and foremost, and engines like the Vector (=SSME) have stayed true to that logic while still reflecting the real life engines role, it's amazing for space planes (with slight stretching and money balancing). It works well and is a well liked engine, so I think we can take that harsher balancing into account.

Additionally, the engine should fill their own role in KSP to flesh out the sortiment, and that role could still reflect the real lifes engines nature. The Vector was heavily nerfed in ISP compared to the SSME, but it's design makes it very attractive for space shuttles. So without further delay, that is what I'd argue:

 

Skiff: Mass: 3 tons. Vacuum thrust: 450 kN. Specific Impulse: 220-412s (more conservative: 240-370)

Quite the big change, isn't it? In real life, the Skiff is a high power upper stage engine, driving the Saturn 5 2nd and 3rd stage, after all! It is highly efficient thanks to LH2, but early tech, being both somewhat bulky and inefficient, notably optimized to still work the upper atmosphere! The model is also huge in KSP, indicating a powerful engine.

I think this change would make the engine fit a role that is not yet filled, a high power upper stage/orbital engine in 2.5m diameter (the poodle is not bad, but very weak for it's size), basically a more upper stage alternative to the Skipper. The high weight inefficiency can make up for the efficiency; we don't neccessarily need heavy tanks if we can just add a bit of weight to the engine itself. I also put a potential, more conservative ISP beside it, which might fit better.

Wolfhound: Mass: 2 ton. Vacuum thrust: 320 kN. Specific Impulse: 140-340s.

This engine is more straightforward, it is basically 'just' a purely orbital engine, but quite overpowered since it was thought to be a lander engine. The engine bell both indicates high power at relatively good efficiency, to me. I mean, that's basically what the SPS is, just scaled up to KSP-compatible thrust levels.

The thrust is 160kn per ton, which put it directly inbetween the extremly efficient but weak Poodle (142), and the slightly less efficient but surprisingly powerful Aerospike (180). This basically makes it a very versatile late upper stage/orbital engine, which is always good when a Poodle is just a bit too weak and you'd rather sacrifice a bit of efficiency for thrust (which I always feel with the Poodle). Also a bit heavier to make a better single stack upper/orbital stage engine.

 

In my opinion, this would both keep the engines as interesting alternatives to current engines, be reasonably enough balanced and also reflect the real life engines roles. What do you think?

edited a bit

Edited by Temeter
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3 hours ago, Snark said:

Change that recommendation of 280 atmospheric Isp down to 70 or so, and then it's "pretty much the same characteristics" as the current Wolfhound, and I cheerfully withdraw my "overpowered" comment.

Change 280 to 200. Also remember that TWR diminishes with Isp. So if you have an engine that is 400s in space but 300 on the ground, that is not as good as an engine of the same thrust rating that has an Isp of 300 on the ground and 350 in space. So 280 under 400 would pretty much cripple the Skiff in the air, 200 would cripple it further and be accurate to its basis. So 200 seconds would be my revision.

You can't have an extremely low surface Isp for a second stage engine because there's still some air when it starts and you don't want it to start with a horrible Isp and TWR even though you're 20 km up.

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47 minutes ago, GregroxMun said:

You can't have an extremely low surface Isp for a second stage engine because there's still some air when it starts

Sure you can.

Remember that air falls off really fast with altitude.  How high is your rocket when the second stage kicks in?  Depends a lot on your rocket design, of course, but in my own experience, I'm generally at least 6 km up, more likely 10 km or more.

And at 10 km, the air pressure is already down to a tiny fraction of ground level, and even so-called "vacuum" engines like the Terrier work great-- they get like 90% or more of their vacuum Isp, and that very quickly ramps up to 99% or better when they get over 20 km, which happens very very soon after 10 km.

So, having a really really low atmospheric Isp doesn't mean that it needs a pure vacuum-- just that it's not useful to launch off the pad.  At altitudes of 10 km or more, it'll work just fine.

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@Snark About the tech tree. It's just a bit odd when a new tech supersedes an old one without actually replacing it. If it is better than the Reliant in every way (except size), why not just upgrade the Reliants stats when the tech is researched? If it is bigger but lighter than the Reliant because it's built from new space age materials, why can't they make a new much lighter Reliant of the same materials? It just doesn't make much sense from a gaming perspective or an "internal realism" perspective.

As for the OKTO/HECS, I do think they should have made the electricity requirement much smaller for the OKTO than the HECS so it would still serve a purpose (not to mention that cube thing). Then it would still serve a niche purpose after the HECS is unlocked. It would be like running a rocket with an Arduino instead of a PC.

Also, new similar but non-replacing parts clutters up the parts list (which got much worse with the new all white and black parts).

 

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On 3/16/2018 at 4:32 PM, Snark said:

Sure you can.

Remember that air falls off really fast with altitude.  How high is your rocket when the second stage kicks in?  Depends a lot on your rocket design, of course, but in my own experience, I'm generally at least 6 km up, more likely 10 km or more.

And at 10 km, the air pressure is already down to a tiny fraction of ground level, and even so-called "vacuum" engines like the Terrier work great-- they get like 90% or more of their vacuum Isp, and that very quickly ramps up to 99% or better when they get over 20 km, which happens very very soon after 10 km.

So, having a really really low atmospheric Isp doesn't mean that it needs a pure vacuum-- just that it's not useful to launch off the pad.  At altitudes of 10 km or more, it'll work just fine.

This is true.

However, it seems absurdly obvious that the Wolfhound and the Skiff stats should be swapped 1-to-1. This must have been a mistake.

Consider:

screenshot5.png

The engine on the left is very clearly this:

Spoiler

SaturnV_3rd_J2_engine01.JPG

...and the engine on the right is very clearly this:

Spoiler

218727663_89f90783e2_b.jpg

However, when you look at stats:

Engine Mass (tonnes) Vacuum thrust (kN) Vacuum isp (s) TWR
CSM SPS 0.1 91 314 92
Wolfhound 2.5 375 412 15
Rocketdyne J-2 1.8  1,033 421 58
Skiff 1.0 300 330 30

You could literally just swap these stats. The SPS had twice the TWR of the J2, but the Skiff has twice the TWR of the Wolfhound. The J-2 had more total thrust than the SPS, but the Wolfhound has more total thrust than the Skiff. The isp lines up perfectly.

The stats are simply switched. There is no other possible explanation.

 

 

 

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Posted (edited)

I fully agree that if these two parts are meant to be replicas, then they seem to be switched.  

But... let's look at other parts in KSP that seem to be replicas, the Mammoth and Vector.  The Mammoth's stats are clearly for a first-stage lifter, 295s ASL and 315s vac, with colossal TWR and a very fine choice for a single-engine rocket to put a lot of payload in space by itself.  (The Vector then inherited the same stats when it showed up later.)  The real fully-cryogenic SSME/4xRS-25 for SLS has 363s ASL but 452s vac, and its contribution to launch thrust is 17% (Space Shuttle) or 19% (SLS).  Obviously it's a vacuum sustainer engine IRL that can't really move much by itself, and certainly not for the cost. 

The KSP stats are completely different because in some way they needed them to be completely different.  Perhaps it's the same for the MH parts, by some opaque game balance calculus.  Do I think that's really the case - no I do not, not in the least.  I don't think the devs actually care that much.  I personally believe that they are wary of chasing true replica stats, as the game has always been cartoonish and simplified, and getting any individual parts too close to replicas makes the rest look really strange by comparison.  I suspect when the next patch comes, they'll fix the small bugs, add a few small features (fingers crossed, window views in the new IVAs), and make some tiny tweaks to the Wolfhound and Skiff as a headfake towards "hey forum people, we hear you" but fundamentally leave them alone.

Edited by fourfa
typo

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My two cents:

Whatever Squad was actually tying to do, a faithful adaptation of the CSM engine would be terrible in KSP.  It was a simple, no-frills engine that ran on hypergolic propellant.   As I recall, the main advantages of the design were:

  • The simplicity made it (hopefully) reliable, particularly since it was designed to be restarted for multiple burns
  • The hypergolic fuel was stable, vacuum-tolerant, and could be stored in a small volume.  

But these considerations don't matter in stock KSP.  Engines don't fail, all engines can be restarted as often as fuel allows, and all LFO fuel is the same.  So an accurate interpretation of the CSM engine would be pretty bad, especially compared to a hydrogen-burning performance machine like the J-2.  

But, for balance purposes, they have to make the Wolfhound good at something, or no one will use it.*  Given that it's intended as an orbital engine, I think it makes sense for it to have better ISP, and worse TWR, than a sustainer engine like the Skiff.  If you did the reverse, people would use the Wolfhound as a lower-stage engine and the Skiff as an upper-stage engine, which just seems backward.  So in this case, you have to pick between being historically accurate as to how these engines worked, or historically accurate as to how they make sense to use.  They picked the latter, and I'm fine with that.  

All that said, some things just make no sense.  Why does the Wolfhound have more thrust than the Skiff?  This gets especially weird if you build a semi-accurate version of the Saturn V, with a single Skiff as the third stage.  The Wolfhound's ISP, and the Skiff's TWR, also both seem excessive compared to main game engines.  This poses problems for both realism (why such big differences if all the engines are using the same fuel?) and with gameplay balance.  

tl;dr: I am OK with the choice to make the Skiff a relatively low TWR, high ISP engine and the Wolfhound the opposite; but the actual numbers they picked still seem odd.

 

*I guess they don't have to; they made the Mastodon pretty bad at everything. 

 

 

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13 hours ago, Aegolius13 said:

*I guess they don't have to; they made the Mastodon pretty bad at everything. 

The Mastodon has one virtue and one use - the 'no shroud' version can be tightly clustered under the 5m tanks using the adapter provided.

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14 hours ago, Aegolius13 said:

Whatever Squad was actually tying to do, a faithful adaptation of the CSM engine would be terrible in KSP.  It was a simple, no-frills engine that ran on hypergolic propellant.   As I recall, the main advantages of the design were:

  • The simplicity made it (hopefully) reliable, particularly since it was designed to be restarted for multiple burns
  • The hypergolic fuel was stable, vacuum-tolerant, and could be stored in a small volume.  

But these considerations don't matter in stock KSP.  Engines don't fail, all engines can be restarted as often as fuel allows, and all LFO fuel is the same.  So an accurate interpretation of the CSM engine would be pretty bad, especially compared to a hydrogen-burning performance machine like the J-2.  

But, for balance purposes, they have to make the Wolfhound good at something, or no one will use it.*  Given that it's intended as an orbital engine, I think it makes sense for it to have better ISP, and worse TWR, than a sustainer engine like the Skiff.  If you did the reverse, people would use the Wolfhound as a lower-stage engine and the Skiff as an upper-stage engine, which just seems backward.  So in this case, you have to pick between being historically accurate as to how these engines worked, or historically accurate as to how they make sense to use.  They picked the latter, and I'm fine with that.

Well, the thing is that the stats are actually swapped.

The current Wolfhound is far heavier than the current Skiff. So that alone would suggest using the Skiff for the terminal stage and the Wolfhound for a lower stage. The low atmospheric isp of the Wolfhound won't be a problem unless it is actually used for the launch stage itself, which wasn't the case for the J-2 anyway.

They just need to switch the stats of the two engines.

1 hour ago, DerekL1963 said:

The Mastodon has one virtue and one use - the 'no shroud' version can be tightly clustered under the 5m tanks using the adapter provided.

They need a "no plate" version for every engine. Full stop.

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Posted (edited)

Interestingly, of all the filenames for the 8 new engines they added, only the Skiff and the Wolfhound share the RE prefix:

Gv5nP1p.png

Not evidence per se, but the case for them being switched by mistake gets a little easier to imagine.

 

Regarding the Wolfhound, Squad said this (my emphasis) when previewing it in the KSP Weekly:

Quote

This week we wrapped up our analogue to the Apollo Service Propulsion System (the AJ10-137), too.  While we’re still finalizing the statistics, it will be a vacuum engine in the same league as the Poodle. It will also have a mesh switching option, with a bare version suitable for clustering, as well as a 2.5 skirt version.  You can see a picture of it here.

 

So that was their intention, at least at that point in development.  However, as it stands now the Wolfhound's ISP vs the Poodle seems kinda "in the same league", certainly when compared to the Skiff.  

Poodle ISP:  asl-90, vac-350

Wolfhound ISP: asl-70, vac-412

So a little worse in atmosphere and a little better in space. Ok, alot better.  Asl-70, vac-370 is maybe a little more reasonable (-20/+20)? 412 is pretty high.

 

Skiff, meanwhile is clearly designed to be in the atmosphere:

Skiff ISP: asl-265, vac-330

 

I can't look at those numbers and say they engines are mistakenly switched. That looks like pretty much like they intended them to be.

Edited by klesh
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Gah, swapping correcting is going to be a mess. Hopefully a mod will allow nice save game conversion? Swapping the right one for the right thing?

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I recently bought MH after already playing KSP for several years.

I recently posted a showcase of a early-mid tech SSTO in "What did you do in KSP today" and "SSTOs! Post your pictures here~" topics.
In there I showcase a very efficient SSTO for hauling cargo with early tech parts.

The Wolfhound engine is one tech node further in the tree based of on the tech requirements of my spaceplane.
Making a design with said engine will make considerable further leap in Payload capacity to orbit.

For people not easily capable of building space planes it is a easy engine to enable them to build one on their own during much earlier career phases then your regular SSTO which are designs with at least whiplash engines typically. A blessing for some people who wanted a gap filler for spaceplane SSTO designs, overkill to others who are oriented towards gameplay balance and I join among that latter group.
The Wolfhound has a ISP of 360-380 in between 13-15 Km altitude, a typical altitude to enable rockets on a panther J404 based SSTO as they tend to flame out around there (actually that is dependent on specifics not further specified) And... EVEN MOAR ISP for the Wolfhound using a Whiplash based SSTO that goes even higher before flame out. Do the R.A.P.I.E.R.S. still have their function with their rocket mode if a better ISP engine like the Wolfhound is better combined with the Whiplash/Rapiers jet mode discarding the Rapier rocket mode altogether. If so, the Rapier rocket mode will never be a option anymore as you acquire the Wolfhound much earlier.

I'm not sure how this equates into actual gameplay, I have to build a test vessel but considering the stats certain gaps between engine combinations are filled that make certain engine modes obsolete in my view like the ones mentioned.
I don't know whether it makes the Rapiers rocket mode obsolete therefore and whether it does so completely in every spaceplane design, but this is a question that is on my mind and it should be tested, allow me to be the first to bring it up.

I'm also a little lost in what this engine is reminiscent of. The Apollo CSM engine is what it looks like. But it has a ISP of 412.....what?
What fuel mixture ends up with a ISP of 412 that is reminiscent of a CSM engine with a vaccuum optimized nozzle?
I'm not someone who argues that KSP need engine replicas out of real life, although MH is clearly based of such a idea. But if you go there by using models reminiscent of real life engines then why get fictional by adding non corresponding numbers to their statistics? As for the Wolfhound, why then the controversial ISP numbers thrown in?
For balancing purposes in the scale of distances that Kerbins solar system represents I'd expect lower ISP engines, not ones with greater numbers if anything, unless Squad intends to replicate Hydrolox resembling engines.

These by the way aren't Vacuum optimized engines in real life either. They have sufficient but poorer TWR at sea level and become more efficient as they climb.
In space Hydrogen leaks away so it can't really be a vacuum optimized engine if it is to resemble a Hydrogen engine.
Yet the Wolfhound hangs in between RP-1/LOX and Hydrolox fuel mixture ISP ranges. So what is it that it burns? Kerboloxillium? 

If the philosphy behind this engine is a exotic fictionalized fuel mixture as I jokingly put forth that is there to make the game easier, okido, I'm with that idea. If some people want that then who am I to judge? Personally though I'm against that philosophy also but at least in that case I can buy the argument. Nobody made the argument for the statistics choices of this engine yet, but I'm clearly signalling that someone in charge could tell me because I want to know and the reason behind these statistics seem mysterious to me. I will remain mysterious towards this until someone can clarify, which is obviously one of the developers in case they have an answer and might read.

Put the Wolfhound further up the tech tree please!

I'm gonna make a case for suggesting to move the Wolfhound engine further up the tech tree. It is a 90 science node after all and only requires R&D facility level 1 but has stats that should have it on the last science node.
Also, what looks like the CSM engine should act like a CSM engine IMHO if one were to ask yours truly, so I think a Isp of 315 is in order.
If it has to be better then current Terrier or Rhino then that is fine.
I'm not against a step up the ladder from our top tier LF/O efficient engines. But a area of 400+ is a bit silly if you ask me.

 

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Moving to Making History Discussion.

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Funnily enough, I was messing with something like you are talking about earlier...

NmyVG3R.png

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