DAL59

Here's how to have lagrange points while keeping patched conics- and it will improve the game alot

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Make lagrange points blue spheres that can be targeted.  When a craft enters a point, and is moving slowly, a button appears to lock onto the point and be frozen inside it.    

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i'm not sure i quite understand what you're getting at, but having lagrange points would be awesome.

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Lagrange points as stable orbit locations only makes sense if there is some mechanism making all other orbits decay or become unstable, having one without the other is kind of pointless.

Currently all orbits are stable, and by introducing decay or instability you would detract from the entry level fun and friendly nature of KSP :)

Having said that, it would be nice to have some educational DLC covering the finer details of real orbits (legrange points, procession, solar pressure, lumpy gravity, atmosphere decay, etc..)

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2 hours ago, DAL59 said:

Make lagrange points blue spheres that can be targeted.  When a craft enters a point, and is moving slowly, a button appears to lock onto the point and be frozen inside it.    

Absolutely awesome idea! One might simply target, rendezvous and kill relative velocity to said LaGrange the same as any other rendezvous! However, I can see there may be some trouble making that intuitive to the player with no actual object there. New players, or players who are only just learning about orbital mechanics who might do their own research and find conflicting results, like Blasty alludes to here:

 

1 hour ago, Blasty McBlastblast said:

Lagrange points as stable orbit locations only makes sense if there is some mechanism making all other orbits decay or become unstable, having one without the other is kind of pointless.

After all, its a shared instability in gravitational forces which creates every celestial body, system and expanse in the cosmos and makes them so difficult to replicate in a lab...

Also, I can't imagine how much trouble that programming language is/isn't, so I'll leave that argument to the pros. I have some idea, however, about just how heavy the game would be on my poor lil laptop with so many extra calculations that must take place at any given time. I did give a certain mod -sorry, I forget the name. I think "Prince" for some reason- a shot, which was supposed to give realistic orbital calculations in real time. My system couldn't hack it and sometimes others were losing whole moons and planets to the inherent instability in the Kerbol system (especially around Jool :confused: ) if the orbits aren't "on rails."

 

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2 hours ago, Dark Lion said:

I did give a certain mod -sorry, I forget the name. I think "Prince" for some reason- a shot,

It's called Principa:

Which is named after the famous texts written by Isaac Newton, which are the basis for Newtonian Physics.

Edited by Gargamel
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Not quite what the OP had in mind, but the devs could also add some tiny pseudo SOIs at the Lagrange points.   They could be considered part of their parent's bodies SOI for most purposes, (sort of like the how launchpad and crawler way are "mini-biomes").

Edited by AVaughan
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5 minutes ago, AVaughan said:

Not quite what the OP had in mind, but the devs could also add some tiny pseudo SOIs at the Lagrange points.   They could be considered part of their parent's bodies SOI for most purposes, (sort of like the how launchpad and crawler way are "mini-biomes").

I wonder if this could be done as a mod?  

I know I'd love to drop a couple ComSats in L4 and L5. 

 

The problem with an object to rendezvous with, is that if you send up a couple craft there, there's a good chance they'll go bumping into one another.    If the LP is a tiny SOI, like radius 500km, there's enough space there to have multiple craft orbiting an infinitely small barycenter withouot running into each other.    The insanely slow orbital speeds would be similar to station keeping operations that would be needed at Lagrange points.   Not a lot, just a little puff here or there.    And short of physically running into the point source, the extremely weak SOI's would have little effect on ships that accidentally fell into it.    Might be a tad difficult to reach though....   threading the needle let's say. 

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28 minutes ago, AVaughan said:

Not quite what the OP had in mind, but the devs could also add some tiny pseudo SOIs at the Lagrange points.

That idea actually comes up every couple of months. But what I've read is that this won't work very well because the engine will shake your stuff to pieces or behave pretty awfully if you ever com close or even hit the center of that mini SOI.

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45 minutes ago, Harry Rhodan said:

That idea actually comes up every couple of months. But what I've read is that this won't work very well because the engine will shake your stuff to pieces or behave pretty awfully if you ever com close or even hit the center of that mini SOI.

My idea for this would be to have 2 SOIs, one with a point-source planet of the right mass to give the main SOI, and one tiny SOI with a 0-mass object that overwrites the point source. So, if you ever DO get on or near that point, you'll just be somewhere with 0 gravity.

However, I have no idea how KSP would treat a 0-mass object with an SOI, no idea how it would handle an SOI covering the center of another SOI, and no idea how well it would even work in practice if mathematically it DID function okay.

Also, I have no idea how to do it in Kopernicus :D

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Honestly, it's genuinely easier to install Principia than to fool with "pseudo-SOI" and "0-mass object that overwrites the point source."  And because Principia arrives at libration points the same way the real world does (via their balance of gravitation from multiple bodies) it will correctly fail to provide them, for instance, in the case of Ike and Duna (you need a ratio of at least ~80:1 between the masses of the two main bodies, and Ike is much too heavy).

Now, Principia does also make the rest of the game a bit harder -- just setting up a transfer to the Mun is more complicated than with patched conics -- but it also lets you do things like go places with lots of patience and not much delta-V, like the orbit that was used to save the Clementine mission -- a transfer from an eccentric LEO to Lunar orbit using only a few hundred m/s of vehicle thrusters after the kick motor that was supposed to send the craft to the moon failed.  Also, as far as I can tell, Principia doesn't add much load on your computer; apparently accurate calculation isn't much if any more work than putting planets (or anything you're not looking at) "on rails" and calculating patched conics for active objects.  This is, after all, what computers are good at -- calculation.

Edited by Zeiss Ikon
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2 hours ago, Zeiss Ikon said:

Honestly, it's genuinely easier to install Principia (...)

I always get a bit suspicious when it’s announced how easy it is to implement something that radically alters the game. Many objections against an n-body engine have been brought up in the past.

The problem might indeed not be calculation, although the argument “that is what computers are good at” is not particularly convincing. Breaking cryptographic codes is merely calculation, computers are good at it and yet it turns out to be incredibly hard to do it quickly. I’m not convinced that calculation, providing the same level of stability to all players as patched conics does right now is that easy to implement. I doubt anyone thinks NASA lacks smart people, yet they resort to patched conics for there initial calculations because it’s so much faster than n-body calculations.

However, ditching patched conics has some side effects. Orbits aren’t stable, planet transfers are harder, Jool’s moons get ejected over time, those kind of things. Some may be mitigated, others are not. In short, the game will change drastically, a large part has to be rewritten (at the expense of many other things that cannot get done) and what for? “Because it would be cool to have Lagrange points.

And that is why the suggestions to use some kind of artifical patched-conics solution comes up. Because it offers the ability to have them without changing the way the game works right now, which means that if the suggestion works there’s actually a chance it would get implemented.

Edited by Kerbart
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3 hours ago, Zeiss Ikon said:

Honestly, it's genuinely easier to install Principia than to fool with "pseudo-SOI" and "0-mass object that overwrites the point source."  And because Principia arrives at libration points the same way the real world does (via their balance of gravitation from multiple bodies) it will correctly fail to provide them, for instance, in the case of Ike and Duna (you need a ratio of at least ~80:1 between the masses of the two main bodies, and Ike is much too heavy).

But then you have decay and n body.  

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Lagrange points truly exist only for a very specific problem, namely 2 massive bodies in perfectly circular orbits around their mutual center of mass plus the third low-mass body.

So, where exactly should LP be placed if orbit is eccentric? At what velocity should they move (if we want to be able to match velocities with them)?

And, well, there is an even easier way to have Lagrange-points-like behavior in patched conics - have the SOIs large enough to include objects that have the same orbital periods around a smaller body as the smaller body has around the larger body. In some way, that would be more realistic than the OP's suggestion: the Lagrange points won't be stable and low-energy transfers between L1 and L2 are possible.

Another thing is that Lagrange points are in reality very spacious. Herschel space telescope, according to Wikipedia, "entered a Lissajous orbit of 800,000 km average radius around the second Lagrangian point (L2) of the Earth-Sun system, 1.5 million kilometres from the Earth". That is not quite what I'd call a "tiny pseudoSOI".

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11 hours ago, Zeiss Ikon said:

Honestly, it's genuinely easier to install Principia than to fool with "pseudo-SOI" and "0-mass object that overwrites the point source." 

Honestly, I've done it and I didn't find it easier or more enjoyable.

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1 hour ago, 5thHorseman said:

Honestly, I've done it and I didn't find it easier or more enjoyable.

Done which -- fought with real-world physics under Principia (which I'd believe) or implemented pseudo-SOI libration points under the stock physics model?

 

10 hours ago, DAL59 said:

But then you have decay and n body.  

As far as I'm aware, Principia doesn't mess with atmospheres, hence shouldn't introduce orbital decay.  Classical decay is caused by atmosphere being significantly non-zero far, far beyond common LEO altitude.  There's enough drag at the 400 km height of ISS to require the station to be reboosted every couple years; Mir require reboosting more often than that, because it was in a lower orbit.  It also doesn't (at this time, confirmed by the devs) model tidal bulges, so can't cover long-term effects like Earth pushing the Moon a little further out every century, or Mars pulling Phobos down a little on a slightly faster time frame.

And of course you have n-body effects with Principia -- that's what Principia does.  It's the n-body effects that create libration points, chaotic orbits, co-orbits (like some of Saturn's shepherd moons, or that 100 m rock that's been co-orbiting with Earth for the past couple centuries), and so forth.

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7 minutes ago, Zeiss Ikon said:

Done which -- fought with real-world physics under Principia (which I'd believe) or implemented pseudo-SOI libration points under the stock physics model?

Fought with the UI and lack of tools in Principia. I can handle the physics. I can't handle the lack of tools.

I won't play KSP without a decent interface.

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Okay.  I haven't gotten far enough from Earth's surface in my RSS/RO/RP-1/Principia saves for it to matter what physics model I'm using (barely matters where the Earth is flat or round, never mind whether it's round or oblate; I'm not trying to achieve pinpoint artillery accuracy).  Highest apogee to date is a little over 900 km, flight time not much over ten minutes.  There's no n-body effect that will be detectable on that scale, and the maneuver nodes (or lack thereof) won't matter at least until I have an orbiter with some spare dV.

When I set this up, I installed Principia thinking that if I'm going to play in the real solar system, I should play with real physics.  I expect it'll be a while before I have to think about the problems you're talking about.

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ConsoleKSP players input for this....

Without adding any math to the machine, simply ask a grad student to calculate the appropriate placement of the Lagrange points, then, without confusing my PS4 with equations and variables, simply allocate a few locations (defined in blue if you want)  where stability in relation to the parent body occurs.

;-)

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L3; L4 and L5 already happen to be stable with patched conics.

I find it a bit strange to ask for L1 and L2 without asking for N-body dynamics. L1 and L2 are not even stable, and their main point is cheap transfer.

IRL, L1 and L2 are used only because of N-body dynamics, either because it makes flight cheaper, or because they are the only nearby parking place relative to Earth and the Sun (or to a pair of bodies). By comparison, in patched conics, you can park in any 1:1 resonant orbit, including close ones. You can have all the advantages of L1 and L2 by parking in the same orbit as the lighter body, right after and right before it.

Patched conics do not lack Lagrange points, patched conics has an infinity of stable Lagrange points, where N-body dynamics only has 5 of them, 3 of them being unstable, and the 2 it has exclusively are not especially worth of notice outside of N-body dynamics.

Edited by Kesa
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Can anyone explain what a lagrange point is, because all I keep picturing is Billy Gibbons of ZZ Top floating out in space.  :D

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1 hour ago, djr5899 said:

Can anyone explain what a lagrange point is, because all I keep picturing is Billy Gibbons of ZZ Top floating out in space.  :D

If you're asking what a real-world Lagrange point is it might be easier to just Google it than ask another forum user to type up something that's already explained at length on wikipedia and other places   :/

 

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14 hours ago, djr5899 said:

Can anyone explain what a lagrange point is, because all I keep picturing is Billy Gibbons of ZZ Top floating out in space.  :D

https://en.wikipedia.org/wiki/Lagrangian_point

These are equilibrium points in the three-body_problem.

As you may or may not know, spacecraft, planets and moon in Kerbin are only ever influenced by one massive body at a time. A trajectory around a body is called a conic which stands conic_section and as you change of sphere of influence, you get patched_conics.

If you want to have a probe which does not move relative to the Mun (which is in equilibirum in the Kerbin-Mun referential, which is centered at Kerbin and rotate with the Mun), it's easy : match the orbit of the Mun while staying outside of it's SOI (eg a little bit ahead, diametrally opposed...).

 

If they could be influenced by two, or more bodies at a time, for our example Kerin and the Mun, everything would be much less stable, and only 5 points in space allow you to stand still relative to the Mun. These are the Lagrangian points. It happens that only 3 of these points are equilibrium under patched conics.

 

Some people are asking for the two missing ones, without realising asking for them without removing the infinity available under patched conics is asking for folklore in a very unelegant way. Some other people ask for something already present under patched conics.

(arguably, L4 and L5 points are stable equilibrium, while under patched conic, 1:1 resonant orbit including L4 and L5 are neutral equilibrium, arguably instable on the very long run if the orbital period is disturbed, but in practice, they can remain stable for centuries before needing adjustement of less than 1m/s, unlike the 3 unstable Lagragian point which require frequent monitoring for spacecraft wanting to stay there).

Edited by Kesa
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On 6/17/2018 at 3:09 AM, Zeiss Ikon said:

As far as I'm aware, Principia doesn't mess with atmospheres, hence shouldn't introduce orbital decay.

Under patched conics, there are an infinity of points of equilibrium in the rotating Kerbin Mun referential : match the Mun Orbit while staying out of its SOI. Under 3-body dynamics, there are only 5 such points.

Matching Mun orbit while remaining out of its SOI does result in an unstable decaying orbit under 3-body, unless done at L4 and L5.

Atmospheric drag is the most common cause of decay, but not the only one, and under N-body dynamics, gravity is a cause of decay.

 

IMO, it feels nonsensical to add 2 stability points from a model supposed to be more unstable, a bit like asking to be able to aerobrake between 70km and 250km but without experiencing atmospheric drag induced decay at these altitudes (all that while aerobraking at 50-70km already provide anything you need).

Edited by Kesa
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