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

[Klapaucius]

19 hours ago, Snark said:

And the principles are the important thing.

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

 

 

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.

 

Great post all around.   Back in high-school physics class we solved problems with weights and frictionless pulleys. Why? Because when you are learning Newtonian Physics, getting every variable is not important and actually inhibits comprehension. 

 

Incidentally, have you ever picked up a Sci-Fi book where a ton of effort went into describing the realistic scenario but the plotting and characterization were flat and uninspired?  It is easy to lose the forest for the trees in a pursuit of perfect accuracy.

[magnemoe]

On 8/26/2019 at 2:12 PM, Psycho_zs said:

Considering support of thrusted timewarp, this would be a great scenario.

Looks like we don't even have to have craft in focus for burns, interstellar burns could be an year long. 
Note that this could be specific for interstellar burns. Not sure if we could just leave an probe with an ion engine. 

[Guest]

15 minutes ago, magnemoe said:

Note that this could be specific for interstellar burns. Not sure if we could just leave an probe with an ion engine. 

I doubt it'd be restricted to interstellar only, after all every interstellar burn starts out from orbit somewhere. If you have support for brachistochrone trajectories then I'd expect you have it everywhere.

In that case they could even rebalance the Dawn to be a bit more like its RL counterpart. In fact doing interplanetary missions in Dawn-powered craft would be a great way to practice the trajectory planning and general logistics of interstellar ones, but on a much more manageable scale.

[Guest]

1 hour ago, nejc said:

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.

DUMBO design promised rocket engine level TWR. As for atmospheric performance, that's just a matter of tuning the nozzle. There's nothing unrealistic about using NTRs for liftoff. High-performance nuclear engines would be far better than metallic hydrogen. If it's "cool new tech" factor they're after, they could use liquid core NTRs, they fit the "gateway tech" niche (performance isn't torchship-level, but they're a stepping stone to gas core NTRs), and they're a cool, yet realistic technology in their own right.

Also, it wasn't safety concerns, but money and politics (specifically, anti-nuclear panic) that stopped nuclear engine development. NTRs don't spew glowing radioactive death out of the nozzle (neither hydrogen nor methane are susceptible to neutron activation), and if you design them right, can survive a vehicle RUD and fall into the ocean intact. The biggest problem with using an NTR for liftoff is that unless you have an SSTO (which, to be fair, is a much more workable proposition if you go nuclear), you're throwing away an expensive nuclear reactor each launch, and even if you do have an SSTO, your liftoff engine won't be optimized for orbital operations, anyway. The advent of reusable lower stages might very well fix that.

[Superfluous J]

1 hour ago, nejc said:

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.

@resource[Liquid_Hydrogen]:LAST
{
	@name=Kerbolide
}

Suspension of disbelief reattained.

[magnemoe]

1 hour ago, Brikoleur said:

I doubt it'd be restricted to interstellar only, after all every interstellar burn starts out from orbit somewhere. If you have support for brachistochrone trajectories then I'd expect you have it everywhere.

In that case they could even rebalance the Dawn to be a bit more like its RL counterpart. In fact doing interplanetary missions in Dawn-powered craft would be a great way to practice the trajectory planning and general logistics of interstellar ones, but on a much more manageable scale.

Good point, however I expect the stars to be in fixed positions.

Yes they moves in real life but not so much it matter much for interstellar travel.
Yes they could make an sort of mini galaxy with an central black hole but that would give far to much star movement unless we are far away from it who makes its a bit stupid as we will get an limited number of stars like 20. 

No star movement would also make it easier to add new stars with dlc and mods as some players might be hundreds of year into the future. 

[Guest]

I don't see how it would make a difference if stars are fixed or move. A trajectory is a trajectory.

[Xd the great]

11 minutes ago, Brikoleur said:

I don't see how it would make a difference if stars are fixed or move. A trajectory is a trajectory.

Your transfer window would be seriously messed up.

Unless new star orbits Kerbol.

[Guest]

4 minutes ago, Xd the great said:

Your transfer window would be seriously messed up.

Unless new star orbits Kerbol.

Nah, even if the motion of stars was modelled in 1/10 scale it would be quite small over even several decades, i.e. it would make no major difference to the transfer -- you'd just have adjust it a tiny bit so you don't miss.

[Xd the great]

Just now, Brikoleur said:

Nah, even if the motion of stars was modelled in 1/10 scale it would be quite small over even several decades, i.e. it would make no major difference to the transfer -- you'd just have adjust it a tiny bit so you don't miss.

I feel like this new game needs a lotta timewrap.

And Scott Manley will do orbital mechanics for interstellar quest.

[Guest]

1 minute ago, Xd the great said:

I feel like this new game needs a lotta timewrap.

It most certainly does. But you still won't get transfer windows for interstellar flights, not unless you're planning a transfer that lasts on the order of 10 million years (in a 1/10 scale galaxy).

[dave1904]

9 hours ago, Klapaucius said:

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

 

 

I never knew that. How can you flie and dive with same craft? Sorry for the stupid question but for some reason I have never once went underwater in 2000 hours? Are there separate science defs or they simply splashed defs?

[Xurkitree]

10 minutes ago, dave1904 said:

I never knew that. How can you flie and dive with same craft? Sorry for the stupid question but for some reason I have never once went underwater in 2000 hours? Are there separate science defs or they simply splashed defs?

Apparently air is under water, so Jets work at full efficiency underwater. Rockets are uselss due to the high pressures.

[ModZero]

I really wish they just went with naming after function, it gives plenty of freedom in a setting where planets are made out of neutronium. So we'd have "liquid fuel," "cryo fuel," "oxidiser," "solid fuel," "monopropellant" and, last but not least, "fusion kibble."

I mean, people would still split hair over "what fusion kibble actually is," but it sets expectations better.

Edited September 2, 2019 by ModZero

[Klapaucius]

3 hours ago, dave1904 said:

I never knew that. How can you flie and dive with same craft? Sorry for the stupid question but for some reason I have never once went underwater in 2000 hours? Are there separate science defs or they simply splashed defs?

Dunno. My guess as to the reason, and this is only rather uninformed conjecture, is that water was a secondary consideration, and it was easier to allow existing engines to work in the medium than build a whole new set of propulsion.  As to the last part of your question,  I'm not a coder and have no idea how it works in the background.  Any others able to add some technical expertise to the discussion?

Kerbal water is weird anyway.  Like the fact that nearly everything except full ore tanks float, including metal debris.

Edited September 2, 2019 by Klapaucius

[magnemoe]

6 hours ago, Brikoleur said:

It most certainly does. But you still won't get transfer windows for interstellar flights, not unless you're planning a transfer that lasts on the order of 10 million years (in a 1/10 scale galaxy).

As I understand you can not only do full time warp during acceleration but you can also jump to other ships wile it accelerated and that surprised me a lot. 
Still interstelar ships will burn for months might up to an year. 
At this speeds you can ignore orbital mechanics, I don't expect the stars including Kerbol to move anyway. It would generate loads of issues like the obvious DLC with more star systems for some who might be hundreds of year into the game. 
As said before it would add a lots of hassle with very limited realism or benefits. 

[OHara]

There is more mention of new engines, and orbital mechanics in Rask-Rusk, in Scott Manley's interview of Nate Simpson here:  https://www.youtube.com/watch?v=n-xM_e5x6oc

Metallic hydrogen as rocket fuel does make the condensed-matter physicist in me cringe, so I'll just call it 'kerbolide' and get over it.  There is an atmospheric engine that dilutes the 'kerbolide' with water to reduce the chamber temperature;  and a vacuum engine that injects cesium, presumably for its low ionization energy so it makes a plasma, and a magnetic-field nozzle. I don't imagine anyone will force us to use them.

Rask and Rusk get "a custom solution" for orbital mechanics.  
That would be some solution to the 'restricted three-body problem', where the craft are light enough that we can neglect their effect on motion of the planets. 

I think the only solutions involve numerical integration.  This seems a small step from the restricted N-body problem of numerically integrating the trajectories of all craft, under the gravity of all the planets, leaving the planets themselves (unrealistically) on rails.  Then we would get the interesting gameplay part of the Principia mod, the complex motion of the craft, without the instability of the Jool system. I see the concerns about station-keeping of satellites, but when I look at examples, the orbital drift is usually negligible, and if I am close to a moon then finding a resonant orbit seems like it could be interesting (as it was around Duna in the Snarkiverse mod).

Constant acceleration of craft, during time warp and when we are flying other craft, sounds very nice.
That, and Kerbals' tolerance for long journeys in space without food, should enable interplanetary travel with believable fusion propulsion.   Accelerating at 1m/s² for 400 Kerbin days gets you to 3% c, so if the interstellar distances are scaled down to 10%, the trip is only few times as long as a trip to Eeloo in KSP1.

I hope my suspension of disbelief can follow roughly the same pattern as it did in KSP1, with immortal Kerbals flying under mostly-real physics on a compact planet where 2-g acceleration gets us to orbit in 3 minutes, and with many engineering details abstracted away.

Edited September 3, 2019 by OHara

[KerikBalm]

11 hours ago, OHara said:

Metallic hydrogen as rocket fuel does make the condensed-matter physicist in me cringe, so I'll just call it 'kerbolide' and get over it.  There is an atmospheric engine that dilutes the 'kerbolide' with water to reduce the chamber temperature;  and a vacuum engine that injects cesium, presumably for its low ionization energy so it makes a plasma, and a magnetic-field nozzle. I don't imagine anyone will force us to use them.

Magic tech.... magic teeeeccchhhhh..... Yea, I won't be using either variant.

Metallic hydrogen, or an allow with another metal as in this: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2764941/

Will not be metallic when it decomposes, which is what it does when it releases the energy. A little cesium mixed in isn't going to contain the hydrogen. Cs-H chemical bonds aren't going to help (not only that, but then the MW of the propellant is terrible and worse than water, so your Isp will be worse). If its a plasma, the H and Cs aren't bound, the Cs does nothing to help.

Now, alloying H with something can reduce the pressure needed to metalize the substance.... but that also results in less stored energy (since the energy storage is related to the pressure that was needed to metalize it). The Lithium alloying example linked above only allows the compound to be stable in the range over >100 GPa, so compared to a shuttle tank at about 250 kPa.

100,000,000 kPa vs 250 kPa... you need a tank holding 400,000x more pressure, if that is related proportionately to mass, then the engine is non-viable.

This cesium doping stuff makes no sense, and is just technobabble magic.

[Xd the great]

6 minutes ago, KerikBalm said:

Magic tech.... magic teeeeccchhhhh..... Yea, I won't be using either variant.

Metallic hydrogen, or an allow with another metal as in this: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2764941/

Will not be metallic when it decomposes, which is what it does when it releases the energy. A little cesium mixed in isn't going to contain the hydrogen. Cs-H chemical bonds aren't going to help (not only that, but then the MW of the propellant is terrible and worse than water, so your Isp will be worse). If its a plasma, the H and Cs aren't bound, the Cs does nothing to help.

Now, alloying H with something can reduce the pressure needed to metalize the substance.... but that also results in less stored energy (since the energy storage is related to the pressure that was needed to metalize it). The Lithium alloying example linked above only allows the compound to be stable in the range over >100 GPa, so compared to a shuttle tank at about 250 kPa.

100,000,000 kPa vs 250 kPa... you need a tank holding 400,000x more pressure, if that is related proportionately to mass, then the engine is non-viable.

This cesium doping stuff makes no sense, and is just technobabble magic.

What about Caesium being a MH binder, because quantumn physics, yet still gives MH an ISP of >1000 and a not-so-terrible think fuel tank?

Or magnetic confinement of MH? Just like fusion tech?

Edited September 3, 2019 by Xd the great

[Snark]

On 9/2/2019 at 7:40 AM, Xurkitree said:

Apparently air is under water, so Jets work at full efficiency underwater.

Though in KSP 1, at least, that's a configurable setting.  Not in-game, but air intakes have an actual disableUnderwater flag (in config files) that defaults to false.  It bugged me, so I made a little ModuleManager script to make intakes not work underwater (just switches all of them to set the flag to true).

No word yet, of course, on how KSP 2 will handle underwater stuff.  I'm a little bit torn about it, myself.  On the one hand, I'd love to have some water-exploration parts to play with... on the other hand, to me it's Kerbal Space Program, not Kerbal Submarine Program, and given how much stuff they've got on their plate, what matters most to me is that they totally nail the "it's about rockets" part without getting too distracted with other things.

Whatever they end up doing, though... they've made it very explicitly clear that the game is about designing and flying rockets, and that's the philosophy that's underpinning all their decisions, so I'm not inclined to worry too much. 

 

 

[KerikBalm]

4 hours ago, Xd the great said:

What about Caesium being a MH binder, because quantumn physics, yet still gives MH an ISP of >1000 and a not-so-terrible think fuel tank?

Or magnetic confinement of MH? Just like fusion tech?

The problem is that the exhaust itsn't metallic hydrogen, its molecular hydrogen. The energy for the engine comes from the phase change/release of pressure/binding energy.

In the reaction chamber, you have to deal with plain old hydrogen at >6000 C

*edit* which is 4000K too low to turn it into plasma, where magnetic confinement would work:

http://www.wag.caltech.edu/home/jsu/Thesis/node31.html

10,000 K

Edited September 3, 2019 by KerikBalm

[nejc]

16 hours ago, OHara said:

There is more mention of new engines, and orbital mechanics in Rask-Rusk, in Scott Manley's interview of Nate Simpson here:  https://www.youtube.com/watch?v=n-xM_e5x6oc

Metallic hydrogen as rocket fuel does make the condensed-matter physicist in me cringe, so I'll just call it 'kerbolide' and get over it.  There is an atmospheric engine that dilutes the 'kerbolide' with water to reduce the chamber temperature;  and a vacuum engine that injects cesium, presumably for its low ionization energy so it makes a plasma, and a magnetic-field nozzle. I don't imagine anyone will force us to use them.

Only metallic hydrogen was mentioned as gateway tech in the linked interview. We might be forced to us to use those engines, if we want to progress beyond a certain point. Quote from the interview:

Quote

One of the earlier engines that unlocks the interplanetary progression is metallic hydrogen engines.

I'm not sure what this means. Does it mean that only one of the engines that unlocks progression is metallic hydrogen? Or does it mean that one progression step is unlocked by metallic hydrogen engines specifically. If the latter, then we will be forced to use them.

16 hours ago, OHara said:

Rask and Rusk get "a custom solution" for orbital mechanics.  
That would be some solution to the 'restricted three-body problem', where the craft are light enough that we can neglect their effect on motion of the planets. 

I think the only solutions involve numerical integration.  This seems a small step from the restricted N-body problem of numerically integrating the trajectories of all craft, under the gravity of all the planets, leaving the planets themselves (unrealistically) on rails.  Then we would get the interesting gameplay part of the Principia mod, the complex motion of the craft, without the instability of the Jool system. I see the concerns about station-keeping of satellites, but when I look at examples, the orbital drift is usually negligible, and if I am close to a moon then finding a resonant orbit seems like it could be interesting (as it was around Duna in the Snarkiverse mod).

Didn't Scott suggest this in the interview? To keep the planets on rails, but make spacecraft under n-body influence? Then the developer said that they want to preserve a lot of the core game-play.

Edited September 3, 2019 by nejc

[dave1904]

On 9/1/2019 at 10:54 PM, Dragon01 said:

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.

To say metallic hydrogen doesn't exist is a bit of a stretch. Sure we will most likely never make a rocket fuel out of it but I am honestly very skeptical about many of the electric engines out there too. I mean they work extremely well but their power requirements are so beyond our current reactor technology that atleast in my opinion they just aren't realistic either. I get where you are coming from but as I said It just doesn't bother me that much. 

Anyway out of curiosity does anyone know what kind of engine the metallic hydrogen engine will be? I assumed a booster of some kind. Why have it as a vacuum engine if you have so many other better alternatives? 

4 minutes ago, nejc said:

I'm not sure what this means. Does it mean that only one of the engines that unlocks progression is metallic hydrogen? Or does it mean that one progression step is unlocked by metallic hydrogen engines specifically. If the latter, then we will be forced to use them.

I highly doubt you will be forced to use anything because KSP has never been about that. 

[KerikBalm]

@dave1904

They mentioned two forms. One will be metallic hydrogen and water (to stop it from melting itself, it should be higher thrust but lower Isp as a result), and for use in the atmosphere.

The second is technobabble "cesium doped" and uses a magnetic nozzle to confine the reaction, and apparently bad things happen if you use it in the atmosphere. Its presumably higher thrust, but lower Isp.

7 minutes ago, nejc said:

Only metallic hydrogen was mentioned as gateway tech in the linked interview. We might be forced to us to use those engines, if we want to progress beyond a certain point. Quote from the interview:

Quote

One of the earlier engines that unlocks the interplanetary progression is metallic hydrogen engines

I'm not sure what this means. Does it mean that only one of the engines that unlocks progression is metallic hydrogen? Or does it mean that one progression step is unlocked by metallic hydrogen engines specifically. If the latter, then we will be forced to use them.

Didn't Skott suggest this in the interview? To keep the planets on rails, but make spacecraft under n-body influence? Then the developer said that they want to preserve a lot of the core game-play.

I don't know what this means either, but it sounds dumb. We're perfectly capable of going interplanetary without magic engines, just using the old chemical reaction rockets - note metallic hydrogen engines wouldn't be a chemical reaction engine, but a phase change reaction, which technically isn't a chemical reaction, just like water melting isn't a chemical reaction

[Guest]

26 minutes ago, dave1904 said:

To say metallic hydrogen doesn't exist is a bit of a stretch. Sure we will most likely never make a rocket fuel out of it but I am honestly very skeptical about many of the electric engines out there too. I mean they work extremely well but their power requirements are so beyond our current reactor technology that atleast in my opinion they just aren't realistic either. I get where you are coming from but as I said It just doesn't bother me that much. 

Call it a thought shortcut. Metallic hydrogen as KSP devs implement it is not a thing. It may exist in laboratory, or in a gas giant's core. It's not a rocket fuel, and of no practical use due to pressures involved in keeping it in metallic state. The cesium thing is pure technobabble, and there's no place for that in KSP. Again, the problem is going against KSP's educational role. You can't use a game like this to tell people outright falsehoods, because aside from obvious things like Kerbals, everything else in the game is at least qualitatively correct.

Also, the electric engines aren't beyond our reactor technology. We have GW-level reactors in nuclear power plants, hardly any electric engine uses that much power. Submarines use compact reactors that still produce megawatts of power, which is sufficient to power VASIMRs, PITs, MPDs and what have you. What is a problem is: 1). Making a cooling system for one of those small enough (or, more Kerbally, a rocket big enough) for such a reactor to be launched into space. 2). Getting paperwork to actually send one of those into space.