On KSP2 and Special Relativity

[Spaceception]

1 minute ago, kerbiloid said:

3000 can be an overkill for Orion and Daedaulus, as well for KSPI-E engines.

What would look more reasonable to you? 300? 1000? Some other value?

[kerbiloid]

15 minutes ago, Spaceception said:

What would look more reasonable to you? 300? 1000? Some other value?

I don't know exactly how fast are the stock Daedalus and Orion, but I guess the lightspeed would be equal to this value.
So, accelerating at full throttle, they get closer and closer to c.
Say, they can be 0.1 real c = 30 000 km/s. If Kerbal c = 30 000, they will never reach it, but run at 29 900 km/s with relativistic effects of 0.99 c .

And any interplanetary ship at its 1000 km/s will be newtonian.

Upd.
Also too low lightspeed would mean slow signal movement causing lightspeed delay between, say, Kerbin and Mun.

Edited August 22, 2019 by kerbiloid

[LitaAlto]

35 minutes ago, Spaceception said:

In this case, something like Kerbal alarm clock, might be a much more important mod. Maybe important enough to become stock. Especially if you could make the game stop timewarp before any certain point so you don't miss things like that.

Integrating a notification/warning system like that would be very handy in general, and the deeper it is integrated into the stock game, the better. I'd definitely want a tab in either the flight view or map view that shows me upcoming events--not just maneuver nodes but arbitrarily set values like transfer windows or even RL events like, "Save the game and get some fresh air, you've been at it for six hours straight, yeesh!"

I know many players prefer to fly one mission at a time, but I figure that a sufficiently advanced space agency will have multiple missions going at a given time, with dedicated resources. Without KAC in KSP1, I'd lose my mind, not to mention, my contracts.

So yeah, fully agreed on that point. I'd say they should add that even if they make it relatively easy to fly from one star to another in a single gaming session, or throttle contracts to force you to complete only a few at a time at all stages of gameplay, or what-have-you.

*mutters under her breath* I still want speed caps, darn it.

[Cydonian Monk]

2 hours ago, LitaAlto said:

Do we even want an upper speed limit, as a community?

No. Because I'm an engineer, and I keep the scientist part of my brain that constantly spouts off about SR and the inviolate nature of the speed of light bound and gagged and locked in a box somewhere in the back of my brain.  

As a game mechanic I think it would be interesting to see relativistic effects modeled, but I'd rather have other things first. Like true N-body physics. 

[LitaAlto]

38 minutes ago, magnemoe said:

You might be able to  do asparagus staging with orion pulse nuclear drives , that would be kind of Kerbal. 
Hold my beer. 
You could do it with the big fusion powered craft to  1+8 to top it. 
Jeb is running away visibly scared 

I'm expecting Whackjob's Glorious Return to be a cluster of over 100 Daedalus engines taking off from Kerbin's surface. (It's "over 100" because he lost count, understandably.)

39 minutes ago, kerbiloid said:

In KSP orbits and planets are ~1/11 of their real size.
But their gravity acceleration is same.

Usually they say, the planets are dense.
I always insist that their density is normal, they are made of same rocks, but in the Kerbal Universe gravitational constant is increased.
(You don't know which part of GM is increased, so I believe that G).

...

39 minutes ago, kerbiloid said:

So, just decrease c, say, by an order of magnitude.
Then if Kerbal lightspeed = 30 000 km/s = 0.1 lightspeed IRL, then both Orion and Daedalus become relativistic starships.

*takes off sunglasses*

That's... absolutely brilliant. Doesn't that imply changes in the Chandrasekhar limit and changed effects on a number of other celestial objects which aren't currently planned to be included in stock KSP2?

7 minutes ago, Cydonian Monk said:

No. Because I'm an engineer, and I keep the scientist part of my brain that constantly spouts off about SR and the inviolate nature of the speed of light bound and gagged and locked in a box somewhere in the back of my brain.  

DON'T WORRY, SCIENTIST BRAIN, I'LL SAVE YOU!!!

*builds a rocket for a scientist rescue mission*
 

7 minutes ago, Cydonian Monk said:

As a game mechanic I think it would be interesting to see relativistic effects modeled, but I'd rather have other things first. Like true N-body physics. 

Would we be able to have a stable Kerbolar system and maintain current orbits and gravitational accelerations if KSP2 had N-body physics? We'd need a lot of planets to have harmonic resonances with one another, right?

[chaos_forge]

1 hour ago, LitaAlto said:

Although the overall mass if the ship, including fuel, may prevent sizable fractions of the speed of light

Yep, that's exactly the case. The rocket equation tells us that the delta-v of a rocket is equal to its exhaust velocity times the logarithm of the ratio of wet to dry mass. Since fuel tanks have mass, the mass ratio of a ship can only ever be at best equal to the mass ratio of the fuel tanks. So, given an engine with a certain ISP and fuel tanks with a certain mass ratio, there is a set maximum delta-v we can achieve. Asparagus staging can help somewhat, but you hit diminishing returns pretty quick.

[Cydonian Monk]

10 minutes ago, LitaAlto said:

Would we be able to have a stable Kerbolar system and maintain current orbits and gravitational accelerations if KSP2 had N-body physics? We'd need a lot of planets to have harmonic resonances with one another, right?

A bit off topic from SR, but it does "mostly" work now using Principia. The only majorly unstable system is Jool, but flipping the orbit of one of the small moons (Bop? Pol? I forget exactly which) resolves much of the near-term instability. Long term stability would require some other tweaks. No reason those small tweaks couldn't be made by the KSP2 devs at launch. (Or even recognizing the instability inherent in Tylo and ejecting it off into its own orbit?)

[LitaAlto]

1 minute ago, chaos_forge said:

Yep, that's exactly the case. The rocket equation tells us that the delta-v of a rocket is equal to its exhaust velocity times the logarithm of the ratio of wet to dry mass. Since fuel tanks have mass, the mass ratio of a ship can only ever be at best equal to the mass ratio of the fuel tanks. So, given an engine with a certain ISP and fuel tanks with a certain mass ratio, there is a set maximum delta-v we can achieve. Asparagus staging can help somewhat, but you hit diminishing returns pretty quick.

Yes, I'm aware of the rocket equation, which is why I phrased it like that.

I dunno, I admit that the whole argument from impracticality is still dissatisfying. But it's getting harder to put my thumb on what exactly about it is not satisfying. I still find myself wanting, if nothing else, the option to throttle vessel speeds to simulate relativistic effects on ships, just in case.

1 minute ago, Cydonian Monk said:

A bit off topic from SR, but it does "mostly" work now using Principia. The only majorly unstable system is Jool, but flipping the orbit of one of the small moons (Bop? Pol? I forget exactly which) resolves much of the near-term instability. Long term stability would require some other tweaks. No reason those small tweaks couldn't be made by the KSP2 devs at launch. (Or even recognizing the instability inherent in Tylo and ejecting it off into its own orbit?)

Flipping? How so? You mean moving out its orbit? I admit, Jool's SOI is pretty big, and the moons are very close in.

And wouldn't even minor instabilities amplify over time? Or does it amount to such ridiculous levels of deep time that no KSP player has, or *can*, experience it, even if they left the game open on top warp for decades?

[HebaruSan]

31 minutes ago, LitaAlto said:

Would we be able to have a stable Kerbolar system and maintain current orbits and gravitational accelerations if KSP2 had N-body physics? We'd need a lot of planets to have harmonic resonances with one another, right?

16 minutes ago, Cydonian Monk said:

A bit off topic from SR, but it does "mostly" work now using Principia. The only majorly unstable system is Jool, but flipping the orbit of one of the small moons (Bop? Pol? I forget exactly which) resolves much of the near-term instability.

Possibly even further off-topic, why do folks assume "N-body physics" means that celestial bodies can't be on rails? I get that that's how you'd do a scientific simulation of a solar system, but all we really need is for craft to be able to settle in or orbit Lagrange points. Get rid of SOIs and calculate gravitational forces on crafts based on all significant bodies, and we're most of the way there, aren't we?

[Cydonian Monk]

29 minutes ago, LitaAlto said:

Flipping? How so? You mean moving out its orbit? 

Literally going from prograde to retrograde, something like Phoebe. (Less possibility for protomolecular vomit zombies though.)

Quote

And wouldn't even minor instabilities amplify over time? Or does it amount to such ridiculous levels of deep time that no KSP player has, or *can*, experience it, even if they left the game open on top warp for decades?

The latter, yes. There may be other small tweaks made in the standard Principia planetary ephemera, but that's the major one I remember. Obviously having super-dense planetary matter alters how we expect this system to work. (Though at the same time we _could_ be able to observe time dilation through experimentation in Kerbin orbit at a small scale, similar to today's GPS, thanks to the super-density.)

I recall when running the Kerbol system through a few different N-body sims (before Principia), Tylo usually ejected one of the small Joolian moons first, within days. Eventually a few weeks later the rest of the Jool system breaks down resulting ultimately in Vall being ejected and then maybe Laythe. Tylo then leaves of its own accord. One of them ends up cometary, which is what destabilizes the lower system. (Some weak memory of mine is suggesting Scott Manley might have also made a video about this.)

 

6 minutes ago, HebaruSan said:

why do folks assume "N-body physics" means that celestial bodies can't be on rails?

Maybe we want to build ships so big that Gilly enters our ship's orbit? Obviously your suggestion might work, but I think in a forced inherently unstable system there will be cases in which the math breaks down and things that were previously in safe orbits end up being ejected at superrelativistic speeds. 

Edited August 22, 2019 by Cydonian Monk

[chaos_forge]

18 minutes ago, HebaruSan said:

Possibly even further off-topic, why do folks assume "N-body physics" means that celestial bodies can't be on rails? I get that that's how you'd do a scientific simulation of a solar system, but all we really need is for craft to be able to settle in or orbit Lagrange points. Get rid of SOIs and calculate gravitational forces on crafts based on all significant bodies, and we're most of the way there, aren't we?

At the risk of moving even further away from the topic, this post on the Principia github claims that putting celestial bodies on rails isn't as big of a performance increase as it would seem.

Edited August 22, 2019 by chaos_forge
updated link

[HebaruSan]

4 minutes ago, chaos_forge said:

At the risk of moving even further away from the topic, this post on the Principia github claims that putting celestial bodies on rails isn't as big of a performance increase as it would seem.

No one brought up performance (except you ). The question was stability.

[chaos_forge]

3 minutes ago, HebaruSan said:

No one brought up performance (except you ). The question was stability.

oh my bad, I confused this discussion with the one in the n-body thread

[LitaAlto]

18 minutes ago, HebaruSan said:

No one brought up performance (except you ). The question was stability.

 

13 minutes ago, chaos_forge said:

oh my bad, I confused this discussion with the one in the n-body thread

Yeah, no worries, but the discussion of this thread is about game physics, so while this is all kinda off-topic, it's still relevant. Especially if....
 

30 minutes ago, Cydonian Monk said:

...in a forced inherently unstable system there will be cases in which the math breaks down and things that were previously in safe orbits end up being ejected at superrelativistic speeds. 

...which would be REALLY INTERESTING if you had, say, a colony there at the time. Shades of Space: 1999 there, with a side of Einstein spinning in his grave.  

[Pthigrivi]

I tend to agree it might make things more complicated than necessary to model special relativity. Im sure they can just set engine power and interstellar distance such that getting above ~.3 c is unlikely.

[LitaAlto]

15 minutes ago, Pthigrivi said:

I tend to agree it might make things more complicated than necessary to model special relativity. Im sure they can just set engine power and interstellar distance such that getting above ~.3 c is unlikely.

Maybe so, but I'm pretty sure that some KSP player with a bad reputation for doing horrible things with the game will figure out something. For once, I'm *not* including me in those ranks... although I don't know if I'll be able to withstand the temptation forever.

Also, what do you think about Cydonian_Monk's comments about what n-body physics might do?

[Pthigrivi]

3 minutes ago, LitaAlto said:

Maybe so, but I'm pretty sure that some KSP player with a bad reputation for doing horrible things with the game will figure out something. For once, I'm *not* including me in those ranks... although I don't know if I'll be able to withstand the temptation forever.

Also, what do you think about Cydonian_Monk's comments about what n-body physics might do?

Oh I  mean Im still gonna see how fast I can get things to go haha. And yeah.. I do think orbiting lagrange points would be cool but it's probably better for performance to keep the bodies on rails... I might be wrong about that.

[Incarnation of Chaos]

Even if we had the most optimistic performance of Orion and Daedalus you're looking at 10% C for Orion and 40% C for Daedalus. Neither of these matter for us because kerbals don't age; so until we get >70% C we can safely ignore SR. 

Because of the scale of KSP I actually think even 10% of C will be less useful than people think; what use is getting where you want in days or minutes if it turns a lander into a kinetic impactor because you can't slow down fast enough.

[PTNLemay]

I feel it will kind of depend how they implement the interstellar aspect of the game. 

In the current game we are able to travel far enough and fast enough that eventually you leave the Kerbol sphere of influence, but I forget what happens after you do that.  I think that altitude and relative speed are all still measured according to Kerbol.  So if not that, what would the distances and speed be relative to?  A distant galactic center of some sort? 

If we assume the nearby solar system will be based on Alpha Centauri, and we continue using 10% the scale of the real world, then this new solar system would be around 0.44 lightyears away.  So... that's really not worth implementing any kind of speed limit.  Some flights in the Kerbol system can take several years anyway.  With the new super propulsion systems that trip could be done in a bit over 2 years while going at 0.2 C.

But... if they open the door for modders to make planet packs, and have available "slots" where new planets could go.  Or even slots for future official expansion packs (planet packs), and assuming some of these could be much more than 1 LY out.  Then... maybe we would want some form of SR. 

[Incarnation of Chaos]

2 hours ago, PTNLemay said:

I feel it will kind of depend how they implement the interstellar aspect of the game. 

In the current game we are able to travel far enough and fast enough that eventually you leave the Kerbol sphere of influence, but I forget what happens after you do that.  I think that altitude and relative speed are all still measured according to Kerbol.  So if not that, what would the distances and speed be relative to?  A distant galactic center of some sort? 

If we assume the nearby solar system will be based on Alpha Centauri, and we continue using 10% the scale of the real world, then this new solar system would be around 0.44 lightyears away.  So... that's really not worth implementing any kind of speed limit.  Some flights in the Kerbol system can take several years anyway.  With the new super propulsion systems that trip could be done in a bit over 2 years while going at 0.2 C.

But... if they open the door for modders to make planet packs, and have available "slots" where new planets could go.  Or even slots for future official expansion packs (planet packs), and assuming some of these could be much more than 1 LY out.  Then... maybe we would want some form of SR. 

The solutions tend to ship with the mods; if someone develops a crazy planet pack that has planets multiple parsecs out then I can almost guarantee that someone will make an SR implementation.

[kerbiloid]

7 hours ago, Cydonian Monk said:

Maybe we want to build ships so big that Gilly enters our ship's orbit?

Then we should be careful because we can build a ship which can collapse in a black hole and consume Kerbin.
Imho, leaving celestial bodies (except comets and asteroids) on rails is nice, while n-body for crafts makes sense for Lagrange points and orbit decay (in turn makes to periodically refuel an orbital station).

8 hours ago, LitaAlto said:

Doesn't that imply changes in the Chandrasekhar limit and changed effects on a number of other celestial objects

Yes, changed G and c result into Chabdrasekhar limit, into gravitational radius, and into typical mass of a celestial body (~1/1000 of their typical mass).
So, any celestial body in Kerbal Universe is much more lightweight and probably has a typical lifespan of millions years before a star burns out or planet gets geologically dead.

This in turn means that their biological evolution is shorter, and results in lesser amount of lifeforms (and we see this).
In turn this means that Kerbal planets don;t have a lot of coal, oil, and limestone. Though, periodically they can find local deposites.

[Lisias]

1 minute ago, kerbiloid said:

Then we should be careful because we can build a ship which can collapse in a black hole and consume Kerbin.

Obligatory mention:

 

[magnemoe]

One important point here is that maximum speed is kind of maximum acceleration * player boring level doing long burns. say 4g * 1 hour or 144 km/s, with 10 g this is 360 km/s
That is unlike they have added background burns. 

[Kerenatus]

I believe certain debatable phenomena are just compromises to gameplay experience like said above.

[rmaine]

23 hours ago, HebaruSan said:

I'd love to see a nod to SR, but I doubt that they'll want to get into time dilation.

And time raises further issues than "simple" dilation. Time being relative to the observer ends up implying that you can't even say whether two things happened at the same time or not. Also, the thing about light speed as a limit applies to information - not just physical objects. So if you wanted to do time "correctly" (or even some approximation to it), you would not be able to switch back and forth between focusing on your interstellar craft and the space center.