Worried about KSP magic tech, unrealistic orbital mechanics, and lol-explosions

[chaos_forge]

2 hours ago, Brikoleur said:

Why is it so concerning that the devs don't actually understand the science? 

Because this is a highly science-based game. It is a game, yes, but it is also realistic. These properties are not in conflict. In fact, KSP is fun in part because it is realistic. KSP is fun because science is fun, and because realism is fun. If people didn't care about the real world when playing KSP, there wouldn't be dozens of recreations of historical rockets made by players, or players motivated to become real-life rocket scientists because of the game, or a huge fanbase of the game among scientists, etc etc etc.

Because part of the fun of KSP is its realism, I want the devs to be educated on the science. There are compromises made with realism, yes, and I wouldn't have it any other way. But the thing is, the devs can't properly navigate those compromises between realism and game design if they don't know the science. You have to learn the rules before you can break them, or else you won't be able to foresee and deal with the consequences of your actions.

[nejc]

Low pressure metallic hydrogen is not a small suspension of disbelief for someone who is scientifically knowledgeable (relevant meme below). It is more akin to ice remaining solid at low pressure above boiling point. This meddles with science of propulsion and not with engineering of propulsion which is what KSP is all about (at least for me). Moar boosters is an engineering thing that is the sentiment of KSP. In my opinion, speculative engineering yes, speculative science no.

There are actual engineering studies for fusion and even antimatter drives. It all operates on established scientific principles, whether or not engineering of that is actually possible. And we can produce small amounts of antimatter. Non of that is true for metallic hydrogen drives.

If there were no alternatives for this gateway tech, I would tolerate it better. But there are alternatives. Beefing up the nuclear thermal engines from project Timberwind represents a more scientifically accurate alternative for beyond NERVA tech. There is no alternative for too small planets without compromising game-play, so I tolerate that, but applaud the mod that fixes it.

Saying it's a game doesn't cut it for me (relevant meme for below). In more extreme example, we can't have flying pigs in zoo games as one of the main mechanics. But, we can have immortal zoo visitors, because the game might not be about them. So, I don't mind kerbals being immune to radiation or laying eggs or too small planets. It's about science of space flight. Not about science of biology or geophysics (at least for me).

Any of the following situations regarding metallic hydrogen drives would work for me:

• They are optional on the tech tree and can be substituted with alternatives like beefed up Timberwind.
• Going from chemical/thermal nuclear propulsion directly to nuclear pulse is possible, thus omitting gateway tech on the tech tree.
• Balance game-play in a way that modding away gateway tech does not compromise colonies etc.

All of this is my opinion, so I am merely casting a vote and hoping for not just variety of propulsion, but for a variety of game-play options as well.

[Guest]

1 hour ago, nejc said:

Low pressure metallic hydrogen is not a small suspension of disbelief for someone who is scientifically knowledgeable.

So is not being able to do a 20 years Jool mission strapped to a chair or any manned mission to the Eve surface.

Unless they use some sort of hard requirement system I seriously doubt that it would be mandatory to use all the technologies in the game, like everything else if you don't like it because it's not realistic or fun to use just don't use it.

 

Edited August 31, 2019 by Guest

[nejc]

59 minutes ago, Master39 said:

So is not being able to do a 20 years Jool mission strapped to a chair ...

I was clear above when I said, kerbal biology doesn't bother me because it's a physics game not biology game. My analogy was that you can have immortal zoo visitors in a zoo game because the game is not about them. But you can't have flying pigs in a zoo game. Immortal visitor = kerbal, flying pig = low pressure metallic hydrogen

59 minutes ago, Master39 said:

... or any manned mission to the Eve surface.

That is an engineering magic, not a change in scientific principles. As I specified, I am in favor of engineering magic, but no science magic. Engineering magic like moar boosters is the sentiment of KSP. Also, I specified that where there are no alternatives, science magic is more tolerable. There is no super spacesuit designs or concepts for long duration Venus/Eve mission. But, there is an alternative for low pressure metallic hydrogen drive. Just replace it with beefed up drive from project Timberwind.

59 minutes ago, Master39 said:

Unless they use some sort of hard requirement system I seriously doubt that it would be mandatory to use all the technologies in the game ...

Hopefully. That is what I meant by "variety of game-play options". My fear is that, since it is being labeled as gateway tech, it might be necessary for progression.

Edited August 31, 2019 by nejc

[Guest]

59 minutes ago, Master39 said:

So is not being able to do a 20 years Jool mission strapped to a chair or any manned mission to the Eve surface.

Actually, life support is confirmed to be in. So no more chairborne missions, your EVA supplies won't last that long. Any LS mod will fix that, as well. That particular problem is purely a matter of KSP completely ignoring an entire aspect of space travel, because the devs never got around to implementing something like that.

As for manned mission to Eve/Venus... it's doable with real engineering. There's also not much point in doing that, given the sheer difficulty of the task. Humans went to the bottom of the Mariana Trench once, mostly because there was, at the time, no other way of checking what's in there. Now that there is, and nobody goes in that deep. Space colonies, manned missions to pressure cooker worlds, Kuiper belt and other stars are merely mindbogglingly difficult... which is good, because the game is about overcoming those very problems (once you figure out the other difficult problems like, say, getting to the Moon with only punch card computers and basic chemical rockets). Metallic hydrogen propulsion is just plain impossible.

[Guest]

49 minutes ago, Dragon01 said:

Any LS mod will fix that, as well.

We're discussing about nitpicks that probably will be modded away or easily ignored in the first month after release, just like the lack of bases, life support or colonies in KSP1.

[Guest]

1 hour ago, Dragon01 said:

Actually, life support is confirmed to be in. So no more chairborne missions, your EVA supplies won't last that long. Any LS mod will fix that, as well. That particular problem is purely a matter of KSP completely ignoring an entire aspect of space travel, because the devs never got around to implementing something like that.

If it works like that, and it's not optional, then I (and many others) won't be playing the game any more.

Which is why I don't think it'll work like that.

[Guest]

6 minutes ago, Brikoleur said:

If it works like that, and it's not optional, then I (and many others) won't be playing the game any more.

Which is why I don't think it'll work like that.

From what I understand they were not so eager of confirming this and made a point of explaining it will not be anything like the mods we have now.

Probably just a system to make orbital and bases modules anything aside from passive, cosmetic crew containers, like having abitability and consumption requirements for the crew.

[Guest]

2 minutes ago, Master39 said:

Probably just a system to make orbital and bases modules anything aside from passive, cosmetic crew containers, like having abitability and consumption requirements for the crew.

If I had to take a guess, I'd expect that LS is involved with bases and interstellar vessels only, i.e. any mission you can do in KSP1 will work more or less the same way in KSP2. And in those cases I'd hope it's done in some relatively benign way, e.g. as a constraint to colony growth or interstellar vessel crew size.

[TBenz]

9 hours ago, KerikBalm said:

What are the largest ones then for KSP? Particularly with respect to the space flight (not counting Kerbal society and biology)... the small scale?

The reliability and restartability of engines?

These don't seem worse than an engine that runs on unobtanium.

I'd definitely rank "you only experience the gravitational pull of one celestial body at a time" higher on the suspension of disbelief list. Apparently gravity in the Kerbal universe is an inherently 2-body problem.

[Klapaucius]

On 8/26/2019 at 11:36 PM, Brikoleur said:

Then again learning by failing is also what KSP is all about, and explosions make failing much more fun.

I'm eagerly awaiting the first videos of learning the hard way with pulse engines.  See interview at 14:30.

 

 

[nubeees]

4 hours ago, Klapaucius said:

I'm eagerly awaiting the first videos of learning the hard way with pulse engines.  See interview at 14:30.

*snip

Twitch page showing as being removed, do you have an alternate source for the interview?

[Klapaucius]

2 minutes ago, nubeees said:

Twitch page showing as being removed, do you have an alternate source for the interview?

Try this?  Not sure what happened with the URL.

 

 

[nubeees]

That's working! Thanks!

[Snark]

On 8/30/2019 at 10:18 PM, chaos_forge said:

I also think it's worth pointing out that the KSP2 dev who's been doing interviews said in at least one of the interviews something along the lines of "oh, we read a paper saying metallic hydrogen exists, so we feel confident including it in the game." This, combined with other instances of devs failing to understand the science (such as not knowing that binary systems can't be modeled accurately by the SOI approximation), leads me to believe that their decision to include metallic hydrogen engines does not stem from a conscious choice to handwave the science in favor of gameplay, but rather from a misunderstanding of the science itself. And that is, ultimately, the most concerning aspect. I honestly would be much more okay with it if the devs understood the science and were choosing to ignore it than the current situation, in which it seems the devs do not actually understand the science.

So, I'm reading two assumptions into this statement (and into a lot of the other debate in this thread).  Those are:

1. That they're doing this because they don't understand or don't care or are lazy or something.
2. That they're making the wrong choice because their priorities are clearly "wrong" in some objective sense.

I believe that neither of those are the case.

Based on what I've seen, assumption #1 is simply flat-out wrong.  It's pretty clear to me that they understand perfectly well what they're doing, and are going after it diligently and carefully.  (I can totally see why #1 might look that way to folks, it's just that I've had the chance to visit Star Theory's studio and get a demo from the devs in person, and what I'm saying here is that based on the stuff I've seen, I believe it not to be the case.)

As for assumption #2... that's a subjective matter, of course, so there's no one "right answer".  Just, let's be careful not to conflate "someone who doesn't agree with me" with "someone who doesn't understand things as well as I do."  They have their priorities, and they have good reasons for those priorities.  They can't please everyone, so there are going to have to be compromises in places.  And whatever any individual player's priorities might be... it's perfectly reasonable for you to have those, but you're in no position to say that yours are "better" or more "right" than someone else's.

The following is going to be one of my Walls of Text™, which I understand not everyone wants to slog through, so I can summarize it thus:

• They really put a lot of effort into the little technical details of the stuff they're building, and the scientific underpinnings.  What you're seeing is the result of deliberate choices, often for gameplay reasons.  It's not due to ignorance or apathy.
• There are good gameplay reasons to want to have interstellar travel and other solar systems.  And given the difficulties of interstellar travel in real life, it's not surprising that something somewhere has gotta give to make things more accessible and fun for players.  That means they need some sort of MacGuffin, and personally I much prefer "some unrealistically high-Isp engine tech" to other choices they could have made, like wormholes or hyperspace or what-have-you.

 

Regarding "they don't understand science" or "they're lazy" or the like

From what I've seen, this is simply not the case.  There are plenty of space nerds there, and they care a lot about wanting to make things as "sciencey" as they can.  They take the trouble to go to places like NASA and consult with real-life space scientists.  (And those scientists appear to be happy to make time to talk to them, since the scientists tend to be big KSP fans.)

From chatting with them in person and seeing the stuff they were demoing to us at their studio, it's clear to me that Star Theory is really putting a lot of effort into this.  I mean, way above and beyond what went into KSP 1.  For example, celestial bodies:  they're trying hard to make all the celestial bodies have some sort of plausible "backstory", i.e. an astronomical / geological history that explains how they got this way.  Toy 1:10 scale solar system notwithstanding, they want it to make sense.

To pick just one example, let's take a single celestial body-- Minmus-- and compare what I might call the "KSP 1 attitude" with the "KSP 2 attitude".

• KSP 1:  "Ha ha it looks like it's made of mint ice cream."
• KSP 2:  "Okay, it's got all these flats.  Why?  How could that happen?  Well, it makes sense if they're frozen lakes, say of water.  But that would sublime over time!  How would you explain it not having long since been lost to space?  Well, okay, suppose that it's actually geologically very young.  Hey, perhaps Minmus is a captured comet and hasn't actually been around Kerbin all that long, in astronomical terms!"

And so on and so forth.  And then when they're doing the artwork for it, they incorporate that thinking:  the flats on KSP 2's Minmus actually look like ice.  Shiny, slightly-rippled-looking, clear ice.  They gave us a similar "backstory" for Pol:  how did it get to looking that way?

The engines are the same way.  They didn't just Google "futuristic propulsion", see "metallic hydrogen", get distracted by a shiny object, then arbitrarily throw together a bunch of greebles and ductwork to make something "futuristic looking".  They've put time and research into it.  They really, really want to know what would such an engine actually look like and behave?

Yes, you can argue about whether the basic premise (metastable metallic hydrogen at normal pressures) can even happen.  Maybe it can't.  But even if it can't... they can use it as a MacGuffin to start from, and take it from there.  And they've really spent time and effort talking to scientists and such to get a feel for "how would this thing actually look and work, if it were real".

They showed us their metallic-hydrogen model "up close", and pointed to the various bits of it and what the different parts do, and clearly they had put a lot of homework into it.  They weren't just making stuff up.

They also showed us the engine in action... and it had a funky, weird plume.  And they anticipated our reaction.  "Yeah, it looks weird.  But according to the people we talked to, that's actually how it would work, so that's what we modeled."  I gotta say, I have a lot of respect for that.  I mean, they could have just plunked down some fairly vanilla plume on the thing and be done with it... but they're actually making an effort to keep it as "real" as they can.  (And no, they weren't just trying to Hollywood it up.  The odd plume for that engine isn't particularly more "spectacular" than a normal plume, there's no eye-candy reason why they had to do it that way.  It's just... different, is all.)

So if you don't like their choice of using a "magical" propulsion system like metastable metallic hydrogen, that's fine-- of course everyone's entitled to their personal likes and dislikes (more about that in the next section, below).  But please don't just assume that the KSP 2 devs are being lazy or ignorant.  They're not.  They're making very deliberate and carefully researched design choices.  It's just that their choices may not be the same as yours, due to having different priorities.

 

Regarding design priorities, and what's "right" or "wrong"

Bear in mind that the developers of KSP 2 have to juggle a lot of different priorities, many of which may conflict with each other.  There's accuracy about rocket mechanics, then there's accuracy about underlying propulsion science, then there's playability, then there's avoiding-too-much-dissonance-from-KSP1, and so on and so forth.  No matter who you are (I'm speaking to the broader audience here, not specifically you, chaos_forge) and what your priorities are... other folks won't have all the same ones.

For example, I come from a science background and care a lot about scientific accuracy, myself.  I'd love it if they could avoid "magic" technologies.  However... I care about playability even more.  For example, they're going to introduce other solar systems as a feature, and I love that, because that means lots more worlds to explore and lots more design challenges to figure out.  But actual real-life interstellar travel is HARD, I mean ridiculously hard, to the point that if they stuck with easily-extrapolatable "real" science, they'd either have to just eliminate interstellar travel as a thing, or else it would have deleterious effects on gameplay.  There are excellent gameplay reasons for them to want to enable having multiple solar systems, and to make it so that accessing those solar systems doesn't require compromises that most players would be unwilling to make (such as taking excessively long to make the journey, or requiring excessively large ships, or other such things).

So if they want interstellar travel that's fun and playable and meshes reasonably with the more "interplanetary" mechanics of KSP... something's gotta give.  They need a MacGuffin if this is going to be playable.

They could have put in wormholes or hyperspace or something like that, i.e. some mechanism that basically teleports you from one solar system to another.  Instead, looks like they decided to go with good ol' Newtonian "accelerate towards the place you want to go, then decelerate to arrive", and then have made some engine designs that will allow that to happen.

So, for example, KSP has a toy-sized solar system that's at around 1:10 scale.  Squad did that to make it more playable and fun.  And that may be "unrealistic"... but at least the really important things (principles of orbital mechanics and the Tsiolkovsky rocket equation) are still captured.  Oberth effect is still Oberth effect, even when you're at 1:10 scale.  Tsiolkovsky is still Tsiolkovsky, even if the Isp or fuel tank mass ratio is different from IRL.  The actual numbers are unrealistic, but the principles (the equations behind everything, the physical laws) are modeled.  And the principles are the important thing.

KSP's a toy... but it's an educational toy.

So, I think interstellar propulsion technologies are much the same way.  If they're not going to use magical sci-fi hyperspace or wormholes or something... then to make interstellar travel playable and fun, they need something that can supply very high Isp at decent thrust levels.  Something has to fill that slot.  And as long as they continue to model the physical laws appropriately... I don't think the actual numbers are the really important thing.

It's sort of like ion drives.  KSP ion drives are at least a thousand times more powerful (in terms of thrust) than IRL ones... but they kinda had to do that, because if they actually modeled real ones, they'd take so long to work that players would lose patience and almost nobody would use them.  So they made a design choice to put in something that has high enough thrust to be playable... but still is much, much less TWR than most engines in exchange for a much higher Isp.  That way, it helps to educate players about the tradeoff, even if it's a "toy" one with numbers that are easier than IRL.  "This is the sort of thing you have to think about when you have a whole lot of dV but very tiny thrust".

Squad didn't make ion drives 1000x too powerful because they don't know how ion drives work.  They did it because they wanted something like ion drives, and needed to make compromises for playability.  And frankly, I think they made a pretty reasonable decision in that regard.

I think metallic hydrogen is in a similar boat.  They needed some futuristic propulsion technologies to bridge the gap for interstellar travel, and they wanted a variety of them, and they've chosen to put gameplay first.  So the metallic hydrogen is a handy way to do that, among other things that they haven't shown us yet.  Personally, as long as it's still governed by Isp and needing to make engineering decisions about tradeoffs, I'm fine with that.

 

For myself?  I like KSP as a tool for teaching "how does space travel basically work".  This XKCD strip pretty much sums up what's important to me about KSP (and incidentally, is the strip that finally got me past the tipping point and convinced me to try out the game in the first place):

For me personally... that's what KSP is about, right there.

I love that KSP conveys the tyranny of the rocket equation and the fact that dV is hard and why multi-stage rockets are a thing and the importance of TWR and aerodynamics and what a gravity curve is and how Isp works and Oberth effect and Hohmann transfer geometry and gravitational assists and the tradeoff between TWR-versus-Isp and angular momentum and suicide burns and ballistic coefficient and all the rest.

And the joy of exploration.

And it'll continue conveying those things, even if it puts the label "metallic hydrogen" on something, which is why I'm fine with that.

(And I don't mean to downplay the legitimate concerns of people who aren't fine with that.  Just... please don't assume that your way is the "right" way.  Other players have other needs.)

[nejc]

3 hours ago, Snark said:

(text right above)

I agree that we should use suspension of realism for fun and education, however just as we are of the opinion that we should not to use magical hyperspace drives, and instead use fusion drives, since they are a reasonable albeit less powerful alternative, why not substitute metallic hydrogen with pebble bed NTR?

Calculations for practical engine using metallic hydrogen give it an maximum Isp of 1120s. Pebble bed NTR from project Timberwind, a successor of NERVA, has a projected Isp of 1000s. They are in the same ball park, so no need to rely on potentially magic substances, when a realistic alternative is available. We could go on and say that maximum theoretical Isp for metallic hydrogen is acually 1700s, if we ignore cooling requirements, but that assumes another magic material that doesn't melt at 6000K. If we allow that, we can also beef up pebble bed NTRs, just like we allow beefed up reaction wheels.

(Someone please correct me if I have missed something.)

Also,  comparred to NTRs metallic hydrogen is in my opinion of lesser educational value. Showing people more powerful NTRs beyond NERVA is in my opinion of greater benefit due to all of nuclear fearmongering that is going on. If it weren't for that, maybe nuclear pulse drives would not be just paper rocket concepts right now. Unlike metallic hydrogen drives, we could build NTRs and Orion drives right now. 

Just my suggestion.

Edited September 1, 2019 by nejc

[dave1904]

On 8/31/2019 at 10:45 AM, Master39 said:

The fact that you can go in a 50+ years mission on a space chair is way worse to me.

The small scale is another one.

I understand point but the small text in the description of a family of engines is not at all a big problem, the engine's performance and balance and how it affect the gameplay could probably be.

so true. How can someone complain about metallic hydrogen in a game where you can fly to duna on a 1,5ton spaceship, Get into orbit with jet engines and even ion engines too. 

[dave1904]

On 8/31/2019 at 11:12 AM, chaos_forge said:

Because this is a highly science-based game. It is a game, yes, but it is also realistic. These properties are not in conflict. In fact, KSP is fun in part because it is realistic. KSP is fun because science is fun, and because realism is fun. If people didn't care about the real world when playing KSP, there wouldn't be dozens of recreations of historical rockets made by players, or players motivated to become real-life rocket scientists because of the game, or a huge fanbase of the game among scientists, etc etc etc.

Because part of the fun of KSP is its realism, I want the devs to be educated on the science. There are compromises made with realism, yes, and I wouldn't have it any other way. But the thing is, the devs can't properly navigate those compromises between realism and game design if they don't know the science. You have to learn the rules before you can break them, or else you won't be able to foresee and deal with the consequences of your actions.

For someone that takes realism and science so seriously I find it very odd that you can overlook the fact that the whole kerbal universe goes against the laws of physics in every way possible. Realism overhaul is as real as KSP can get and that mod changes every single part of the game. If the KSP devs did not know anything about science they wouldn't have came up with metallic hydrogen in the first place. Its far fetched I will give you that but imo so is everything else in KSP. Every player has their own view on where the line is drawn. I find stock ksp unplayable and far to easy. 

[Xurkitree]

1 hour ago, nejc said:

[snip]

I'm sure there are many advanced NERVA's as well. Just because devs say metallic hydrogen engines exist, doesn't mean any other sort of engines don't exist. We will get a bunch of NFT engines, before we cross over to metallic hydrogen, followed by true interstellar drives.

And i'm sure someone will go interstellar on ions alone.

[dave1904]

10 minutes ago, Xurkitree said:

I'm sure there are many advanced NERVA's as well. Just because devs say metallic hydrogen engines exist, doesn't mean any other sort of engines don't exist. We will get a bunch of NFT engines, before we cross over to metallic hydrogen, followed by true interstellar drives.

And i'm sure someone will go interstellar on ions alone.

You can go interstellar with a chemical rocket too. I cannot wait for the things people come up with. 

[Guest]

1 hour ago, dave1904 said:

so true. How can someone complain about metallic hydrogen in a game where you can fly to duna on a 1,5ton spaceship, Get into orbit with jet engines and even ion engines too. 

Because you can do this things in real life, with some finagling? Electric propulsion can be used for orbiting, you just need more power. Jet engines can't be used to make proper orbit in KSP, either, but they sure can get you close in both KSP and IRL. You could send a small spacecraft to Mars, too, if it's light enough (chairborne missions won't survive any kind of life support implementation). All those things are different from reality, but they are quantitative changes.

Metallic hydrogen is a qualitative shift. Something that doesn't exists IRL, yet it does in KSP. It's not really necessary, as it doesn't even provide better performance than an optimized NTR can (and for good reason - they're both thermally limited), while being based on dubious science.

[TBenz]

7 hours ago, nejc said:

I agree that we should use suspension of realism for fun and education, however just as we are of the opinion that we should not to use magical hyperspace drives, and instead use fusion drives, since they are a reasonable albeit less powerful alternative, why not substitute metallic hydrogen with pebble bed NTR?

Calculations for practical engine using metallic hydrogen give it an maximum Isp of 1120s. Pebble bed NTR from project Timberwind, a successor of NERVA, has a projected Isp of 1000s. They are in the same ball park, so no need to rely on potentially magic substances, when a realistic alternative is available. We could go on and say that maximum theoretical Isp for metallic hydrogen is acually 1700s, if we ignore cooling requirements, but that assumes another magic material that doesn't melt at 6000K. If we allow that, we can also beef up pebble bed NTRs, just like we allow beefed up reaction wheels.

(Someone please correct me if I have missed something.)

Also,  comparred to NTRs metallic hydrogen is in my opinion of lesser educational value. Showing people more powerful NTRs beyond NERVA is in my opinion of greater benefit due to all of nuclear fearmongering that is going on. If it weren't for that, maybe nuclear pulse drives would not be just paper rocket concepts right now. Unlike metallic hydrogen drives, we could build NTRs and Orion drives right now. 

Just my suggestion.

Engines aren't defined solely by their vacuum ISP. We need to consider atmospheric performance, thrust weight ratios, fuel availability, tank requirements. While I'm no expert on speculative rocket engines, I'd imagine that NTRs hold a different niche than a metallic hydrogen rocket, and the two aren't simply interchangeable. Also, I'd be very surprised if there weren't a variety of NTRs already planned for KSP 2. 

[Klapaucius]

10 hours ago, dave1904 said:

so true. How can someone complain about metallic hydrogen in a game where you can fly to duna on a 1,5ton spaceship, Get into orbit with jet engines and even ion engines too. 

Or use turbofans as underwater propulsion.... (Oh, and it also flies).

 

 

Edited September 2, 2019 by Klapaucius

[nejc]

6 hours ago, TBenz said:

Engines aren't defined solely by their vacuum ISP. We need to consider atmospheric performance, thrust weight ratios, fuel availability, tank requirements. While I'm no expert on speculative rocket engines, I'd imagine that NTRs hold a different niche than a metallic hydrogen rocket, and the two aren't simply interchangeable. Also, I'd be very surprised if there weren't a variety of NTRs already planned for KSP 2. 

I could't find any information on that. Just Isp. Given the fact that advanced NTRs were considered for first stages, and only cancelled for safety concerns, I assumed that performance could be sufficient. On top of that, If they can make planets 1/10 the size, and reaction wheels 10x the performance, then beefing up NTRs is nothing. It's just part of balancing. Also, I think we can safely assume that if development of nuclear rockets didn't stall for safety reasons, we would have even more advanced NTR designs. In my opinion, beefed up NTR is less magical than low pressure metallic hydrogen, even if both are.

I think we can make similar comparisons between Alcubierre vs Orion and metallic hydrogen vs. pebble bed NTR (beefed up). One is more powerful than the other, but relies on the potentially nonexistent substance - negative mass in one case, stable low pressure metallic hydrogen in the other. Which is why I view Metallic hydrogen rocket the same as Alcubierre drive - replaceable.

4 hours ago, Klapaucius said:

Or use turbofans as underwater propulsion.... (Oh, and it also flies).

The difference is that I can omit that. With metallic hydrogen being labeled as gateway tech, I might be forced to use it. If there are also other engine types as part of gateway tech, then I don't care if there is also metallic hydrogen. I can just ignore it then.

[Klapaucius]

6 minutes ago, nejc said:

The difference is that I can omit that. With metallic hydrogen being labeled as gateway tech, I might be forced to use it. If there are also other engine types as part of gateway tech, then I don't care if there is also metallic hydrogen. I can just ignore it then.

Fair point.