Lagrange Points in KSP - Not an "obvious solution" (Moderator Thread)

[Bej Kerman]

On 11/17/2023 at 8:45 PM, Kerbart said:

I always felt that this was a rather obvious solution to having them with patched conics

Cause these act nothing like lagrange points.

 

MODERATOR NOTE:

This discussion was split off from:

 

Edited Friday at 02:49 PM by Bej Kerman
Added link

[Kerbart]

1 hour ago, Bej Kerman said:

Cause these act nothing like lagrange points.

Since we're stuck with patched conics and spehere-of-influence based orbital mechanics, one has to improvise.  To have real  Lagrange points you'll need n-body physics. If you don't have that but you do want (semi-stable) fixed positions around planetary bodies, then you have to improvise.

There's a lot in KSP that doesn't act like anything in reality and we're still pretty happy with it.

[Iapetus7342]

On 11/7/2024 at 1:02 AM, Bej Kerman said:

Cause these act nothing like lagrange points.

It's better than nothing. Also this is the same system with comically-dense planets and a moon of a far-off gas giant that has liquid water on its surface so the lagrange points not lagranging is likely the least of your concerns

[Bej Kerman]

3 hours ago, Iapetus7342 said:

It's better than nothing.

Yes, for someone who doesn't mind their lagrange points acting like black holes. I've nothing against players who want that, but I do want to debunk the idea of this being an obvious solution that Squad somehow missed for so many years. Kepler's rules do a good enough job of estimating slingshot maneuvers and the like, but having black holes sitting at the L1-2 points is simply a bad approximation, one that Squad wasn't able to justify enough to actually implement.

3 hours ago, Iapetus7342 said:

Also this is the same system with comically-dense planets and a moon of a far-off gas giant that has liquid water on its surface so the lagrange points not lagranging is likely the least of your concerns

The KSP planets are  dense but it's nothing that breaks any laws of physics. There are things in real life with densities that compete with Kerbal, like white dwarves. Principia mostly agrees with the stock patched conics over how a vessel in a low orbit around Kerbin or Jool should behave. The planets being a bit dense isn't as bad realism-wise as having black holes sitting at each L1/2 point which have no effect on the planets - in which case, if Squad implemented that into stock, it would give newcomers a bad idea of how lagrange points behave.

Edited November 15 by Bej Kerman

[Kerbart]

9 hours ago, Iapetus7342 said:

It's better than nothing. Also this is the same system with comically-dense planets and a moon of a far-off gas giant that has liquid water on its surface so the lagrange points not lagranging is likely the least of your concerns

Don't forget the little-green-men aliens

[Kerbart]

6 hours ago, Bej Kerman said:

Yes, for someone who doesn't mind their lagrange points acting like black holes. [...] but having black holes sitting at the L1-2 points is simply a bad approximation, one that Squad wasn't able to justify enough to actually implement.

The KSP planets are  dense but it's nothing that breaks any laws of physics. There are things in real life with densities that compete with Kerbal, like white dwarves. [...]

You're a bit selective in what you find acceptable and not. If the concern is that newcomers would get terrible ideas of how things work in the real solar system then you can scrap ³/₄ of the game and the super density ("a bit dense" whahahaha) is a big, heavy part of that.  It's your choice to say "it's totally acceptable" but it's still a choice and not the obvious unbiased demarcation you make it out to be.

[Bej Kerman]

1 minute ago, Kerbart said:

If the concern is that newcomers would get terrible ideas of how things work in the real solar system then you can scrap ³/₄ of the game and the super density ("a bit dense" whahahaha) is a big, heavy part of that. 

You don't? It's not like high planetary densities break the laws of physics (in case you missed it in my original reply, you can get similarly dense things in real life), and patched conics were good enough for the Apollo program. It's dishonest to say that's the same as littering the system with literal black holes and labelling them "lagrange points". My point being people don't understand why this isn't the obvious, simple solution they make it out to be. Dense 1/10th planets and Kepler orbits give people a good enough idea of how rockets launch and travel through space - black holes don't give people a good idea of how lagrange points behave.

5 minutes ago, Kerbart said:

It's your choice to say "it's totally acceptable" but it's still a choice and not the obvious unbiased demarcation you make it out to be.

It's only me and Squad in agreement.

[LucalisIndustries]

suddenly this became a discussion ground about realism on a game that allows you to make an Single Stage To Jupiter, hahah.

[Kerbart]

On 11/15/2024 at 11:39 PM, Bej Kerman said:

You don't? It's not like high planetary densities break the laws of physics

It's only me and Squad in agreement.

Looking forward to that list of Pluto-sized dwarf-planets with a dense atmosphere. Why did NASA skip Osiris-Rex over Bennu instead of landing it there and drill for some core samples. All that traveling to scrape off some dust in a fly-by> Are they stupid? Don't they know it generates enough gravity to allow for serious drilling? It's made from neutronium, after all.

 

I'm glad you used the word "only," If I would make a list of "authorities on physics" and I'd be generous enough to include NDG on it, Squad would still not be on that list.

 

[Bej Kerman]

3 hours ago, Kerbart said:

Looking forward to that list of Pluto-sized dwarf-planets with a dense atmosphere

You think an ultra-dense planetary body is in the same bracket of unrealism as a system full of dozens of black holes that miraculously balance themselves at all the L1/2 points of all the moons and planets? Because it's not.  1/10th scale planets with kepler physics is good enough for introducing players to gravity and space travel, representing lagrange points as black holes was not 'good enough' for stock KSP. Reality doesn't validate the image you have of Squad's developers all sitting around a table thinking "how could we possibly represent lagrange points in a keplarian universe?" and failing to think of what this mod does. They certainly thought of it, and they certainly heard it a lot from players, but it's not the "rather obvious solution" you think it is. Black holes that you can use to swing 180 degrees in your orbit is clearly not the miraculous key to L-points in keplarian physics that Squad was looking for.

[Iapetus7342]

8 hours ago, Bej Kerman said:

You think an ultra-dense planetary body is in the same bracket of unrealism as a system full of dozens of black holes that miraculously balance themselves at all the L1/2 points of all the moons and planets? Because it's not.  1/10th scale planets with kepler physics is good enough for introducing players to gravity and space travel, representing lagrange points as black holes was not 'good enough' for stock KSP. Reality doesn't validate the image you have of Squad's developers all sitting around a table thinking "how could we possibly represent lagrange points in a keplarian universe?" and failing to think of what this mod does. They certainly thought of it, and they certainly heard it a lot from players, but it's not the "rather obvious solution" you think it is. Black holes that you can use to swing 180 degrees in your orbit is clearly not the miraculous key to L-points in keplarian physics that Squad was looking for.

There is a simple solution to this: Ignore the gosh diddily darn mod! If you don't like how langrange points work in this mod, might i suggest ignoring the mod or making your own?

[Bej Kerman]

9 minutes ago, Iapetus7342 said:

Ignore the gosh diddily darn mod!

I think you might be missing the point. People think this is an "obvious solution" and Squad are a bunch of thickos for not thinking about it, but they have  thought of it and it just isn't good enough for stock KSP, even compared to minifying the solar system so launches are quicker and distance-related errors aren't as bad. I don't actually care about using or complaining about the mod myself.

[Iapetus7342]

Just now, Bej Kerman said:

I don't actually care about using or complaining about the mod myself.

Cough cough

"You think an ultra-dense planetary body is in the same bracket of unrealism as a system full of dozens of black holes that miraculously balance themselves at all the L1/2 points of all the moons and planets? Because it's not.  1/10th scale planets with kepler physics is good enough for introducing players to gravity and space travel, representing lagrange points as black holes was not 'good enough' for stock KSP. Reality doesn't validate the image you have of Squad's developers all sitting around a table thinking "how could we possibly represent lagrange points in a keplarian universe?" and failing to think of what this mod does. They certainly thought of it, and they certainly heard it a lot from players, but it's not the "rather obvious solution" you think it is. Black holes that you can use to swing 180 degrees in your orbit is clearly not the miraculous key to L-points in keplarian physics that Squad was looking for. "

1. This is how lagrangian points have to work in Patched Conics.

2. You are also ignoring my advice to ignore the mod if you don't like it.

Either use Principia or make your own magical lagrange points that don't act like pocket black holes that orbit in-sync with the planets of your system of choice.

[Bej Kerman]

1 hour ago, Iapetus7342 said:

1. This is how lagrangian points have to work in Patched Conics.

And it's a "solution" that Squad has thought of and has been suggested, but deemed too inaccurate to implement. An approximation of lagrange points you can do gravity assists around is a crap approximation, and to say it fits in with the rest of the game is silly because 1/10th planets and kepler physics at least give people a good enough  idea of how spacecraft fly around in the real world. The planet Kerbin, 1/10th scale planets, and the gravitational maneuvers you can perform using stock Kepler physics have real world analogues, and you can teach players principles like gravity turns and gravitational slingshots with these - but there are no real world analogues for magic black holes that can remain fixed at L1/2 points without perturbing the system they're in. Not unless you bring the bar for "real world analogue" way down.

That's to say: it's not, as some people think, a case of Squad developers being too dense to bother with an obvious solution. Even with KSP's less realistic aspects considered, it's still a bad solution.

1 hour ago, Iapetus7342 said:

2. You are also ignoring my advice to ignore the mod if you don't like it.

Okay, so you haven't read the entire reply you quoted (75 words, only 13 of which ended up in your quote). I said in the reply the point of this discussion was to debunk the idea people have that "this is an obvious solution, I can't believe Squad was so dense they didn't think of this".   I couldn't care less about the mod itself, it was only the catalyst of the discussion.

[Entropian]

On 11/15/2024 at 1:49 PM, Bej Kerman said:

The planets being a bit dense

I highly suggest you take a course in, or read a book about planetary astrophysics in this context (e.g. Lane-Emden equation/polytropes, basic equations of state) and really get an idea of how unrealistic the planets are.  This seems like a minimization of a pretty serious aphysicality IMO.

13 hours ago, Bej Kerman said:

system full of dozens of black holes that miraculously balance themselves at all the L1/2 points of all the moons and planets?

You're trying to physically justify a low-order approximation to reality; an outcome like "black holes that miraculously balance themselves" is totally expected when one takes such a path.

[Lisias]

9 hours ago, Iapetus7342 said:

1. This is how lagrangian points have to work in Patched Conics.

2. You are also ignoring my advice to ignore the mod if you don't like it.

I know squat about how Kopernicus works but... it's possible to hot redefine a Celestial Body's gravity?

If yes, you can try to simulate the Lagrange by adjusting the "black hole" gravity according to the kinectic potential energy of the approaching vessel. Vessels coming too hot would trigger a no gravity state, while vessels approacing the point within a defined range of kinectic potential energy would trigger increasing levels of gravity. Let's call these... "Black Roles".

Obviously that this brings a whole new set of problems, like what to do when  a second craft is approaching. But it may be an acceptable solution if we manage to solve these new problems.

Edited Saturday at 01:22 AM by Lisias
Nope, kinect energy is not the solution. The potential one is.

[Iapetus7342]

6 hours ago, Bej Kerman said:

And it's a "solution" that Squad has thought of and has been suggested, but deemed too inaccurate to implement. An approximation of lagrange points you can do gravity assists around is a crap approximation, and to say it fits in with the rest of the game is silly because 1/10th planets and kepler physics at least give people a good enough  idea of how spacecraft fly around in the real world. The planet Kerbin, 1/10th scale planets, and the gravitational maneuvers you can perform using stock Kepler physics have real world analogues, and you can teach players principles like gravity turns and gravitational slingshots with these - but there are no real world analogues for magic black holes that can remain fixed at L1/2 points without perturbing the system they're in. Not unless you bring the bar for "real world analogue" way down.

That's to say: it's not, as some people think, a case of Squad developers being too dense to bother with an obvious solution. Even with KSP's less realistic aspects considered, it's still a bad solution.

Okay, so you haven't read the entire reply you quoted (75 words, only 13 of which ended up in your quote). I said in the reply the point of this discussion was to debunk the idea people have that "this is an obvious solution, I can't believe Squad was so dense they didn't think of this".   I couldn't care less about the mod itself, it was only the catalyst of the discussion.

Very well then, let the nuclear fallout decend

[magnemoe]

On 11/15/2024 at 10:49 PM, Bej Kerman said:

Yes, for someone who doesn't mind their lagrange points acting like black holes. I've nothing against players who want that, but I do want to debunk the idea of this being an obvious solution that Squad somehow missed for so many years. Kepler's rules do a good enough job of estimating slingshot maneuvers and the like, but having black holes sitting at the L1-2 points is simply a bad approximation, one that Squad wasn't able to justify enough to actually implement.

You have singularities in KSP, you just has to clip trough the surface of an airless body and fall to its center. In KSP 2 it just require time warp while landed on legs or wheels. 
They are unreliable as planc time in KSP is 50 ms and your status is landed so you can not save. 

Having some in the open is fun but again way more unrealistic than dense planets and can be used for fun and profit.  
Now you could probably fix it mixing positive an negative gravity generating an shallow bowl for L4 and 5, an spike or better a smaller bowls for the others as you don't have automatic station keeping in KSP. 
But at this point its probably better to handle the 3 body problem
 

[Bej Kerman]

13 hours ago, Entropian said:

I highly suggest you take a course in, or read a book about planetary astrophysics in this context (e.g. Lane-Emden equation/polytropes, basic equations of state) and really get an idea of how unrealistic the planets are.  This seems like a minimization of a pretty serious aphysicality IMO. 

Yes, obviously. It's still good enough you can show it to someone who has only ever been exposed to Star Trek and Star Wars and say "this will give you a better idea of how rockets work in real life". You can demonstrate things like gravitational assists, the Oberth effect, aerobraking, gravity turns, dV, etc. with KSP, then they'll have a rough understanding when you start showing them real-life space missions. The ways KSP differs from reality only serve to make understanding the concepts it shows easier to understand.  The question I have for you is what real-life concept that black hole-like lagrange points are meant to approximate, because anything you can do absurd gravitational assists around don't approximate lagrange points.

7 hours ago, magnemoe said:

You have singularities in KSP, you just has to clip trough the surface of an airless body and fall to its center. In KSP 2 it just require time warp while landed on legs or wheels. 

Yes. Planets are singularities, because why would Squad model planetary interiors when it's not a state you're meant to achieve in intended gameplay?

7 hours ago, magnemoe said:

Having some in the open is fun but again way more unrealistic than dense planets and can be used for fun and profit.  
Now you could probably fix it mixing positive an negative gravity generating an shallow bowl for L4 and 5, an spike or better a smaller bowls for the others as you don't have automatic station keeping in KSP. 
But at this point its probably better to handle the 3 body problem

Okay, yeah. I agree here. Squad didn't do Kepler lagrange points because all the ways you'd need to fix patched conics to avoid odd things like your vessel entering an L1/2 point and being spat out of the system would just lead you back to doing N-body gravity on the vessel.

 

 

 

 

9 hours ago, Iapetus7342 said:

Very well then, let the nuclear fallout decend

Uh, okay.

[magnemoe]

7 hours ago, Bej Kerman said:

Yes, obviously. It's still good enough you can show it to someone who has only ever been exposed to Star Trek and Star Wars and say "this will give you a better idea of how rockets work in real life". You can demonstrate things like gravitational assists, the Oberth effect, aerobraking, gravity turns, dV, etc. with KSP, then they'll have a rough understanding when you start showing them real-life space missions. The ways KSP differs from reality only serve to make understanding the concepts it shows easier to understand.  The question I have for you is what real-life concept that black hole-like lagrange points are meant to approximate, because anything you can do absurd gravitational assists around don't approximate lagrange points.

Yes. Planets are singularities, because why would Squad model planetary interiors when it's not a state you're meant to achieve in intended gameplay?

Okay, yeah. I agree here. Squad didn't do Kepler lagrange points because all the ways you'd need to fix patched conics to avoid odd things like your vessel entering an L1/2 point and being spat out of the system would just lead you back to doing N-body gravity on the vessel.

For the above point, I agree and why N-body would be bad outside of performance. 
I send an probe to Duna it worked fine, now my manned mission is pulled outward bug report. Reason was that Jool is now right outside your trajectory not on the other side of the sun as it was for the probe.