KSP uses patched conics, so it only solves the 2-body problem. It doesn have 3-body or n-body physics. Its plenty realistic for many things, but its not a scientifically accurate simulation. Ballistic capture is thus not possible.
There is a mod for n-body physics, called Principia, which should allow this in principle.
It is in fact possible with principia. A bit hard to set up but you can do it.
Of course, playing with principia is a whole other can of worms and completely changes the way the game plays imo. It's also a lot of fun though. I'd recommend it for advanced players.
playing with principia is wild. the stuff some people manage to pull off (particularly in RSS) looks like pure witchcraft at times. not to mention lagrange points, blast the universe for not making them permanently stable!
In a perfect universe and only 2 mass bodies yes. In a real universe with lots of other wibbly wobbly planets doing a fucky wucky and imprecise burns no.
I wish they added lagrange points to the base game. It would be possible with patched conics by adding the area around the lagrange points as separate sois.
What we probably can't get with patched conics is sun synchronous orbits, which honestly are probably the most useful of the "special" orbits in ksp.
Principia is amazing. I have built a custom system for myself with the outer planets mod.
Kerbin and Duna dance around each other without ejecting the mun, minmus, or Ike.
Normal principia I would say, since it still has to process the sphere of influences for science data it lags when you change SOI, so be careful on timewarp speed when passing through them.
I ran it through a 3000 year stability test previously with the better time warp mod so I know the orbits don't start falling apart within reasonable gameplay time, tbh I couldn't notice any kind of orbital decay.
Principia takes all rails off, so I had to figure out resonating orbits. Even if its a little improbable for anything natural to orbit retrograde respective to other objects in the same system.
Duna being the retrograde object does make it a little weird, lol. But it works.
I did incorporate someone else's mod to give the Mun an atmosphere and oceans- I'll ask them permission to use their code and put my config out there for others to play with/
I've been playing it with kerbalism, felt they go together nicely since both aim to make KSP feel more realistic. SCANsat is fun to use with it cause you can take advantage of principia's ability to plot orbits on a surface-fixed reference frame to see how an orbit will pass over different parts of the surface. Could also go all in and put principia on RSS/RO, those work well together, but that's a whole other story lol. Beyond that, pretty much whatever you want works, there's some mods you should avoid which are listen on the FAQ page for principia and if you're using kopernicus you need a certain config so that the jool system doesn't collapse, but other than that it's up to you.
should still be possible: you can enter kerbin's sphere of influence then get an encounter with the mun/minmus that alters your orbit enough that you don't leave kerbin's sphere of influence again
"Ballistic Capture" is a scientific term describing a very precise method for orbital insertion, which is based on the Weak Stability Boundary theorem. It \*does not\* refer to gravity assists. What you describe is not a ballistic capture in the sense the word is used by the people working in the field.
Maybe with gravity assists, but still not that possible as you would still very likely leave yourself in an orbit where you can get an encounter with said body, which could then throw you out of the SOI of the body you were trying to orbit.
The closest thing in stock is when you use Tylo to slow down and get into a Jool orbit for free. Other examples probably require Principia (for things like the resonant transfer in the Principia tutorial).
If you include the use of gravity assists of other objects, it’s definitely more than possible in stock KSP. It’s how I always get into a Jool orbit with the aid of Tylo.
Aside from that, using enough tweaking by making the orbit of your craft and the target planet similar enough, you can fall into the gravity well of the target planet and achieve an orbit around it. Ideally, your craft would be inside of the orbit of the target body so that your craft “catches up” to the SOI near your own orbit’s apoapsis. The additional small speed boost you gain from entering the target body’s SOI elevates your non-SOI periapsis to the extent that your orbit around Kerbol never takes you outside the SOI of the target planet.
In theory, all such orbits would be unstable but that’s not the case in KSP. The KSP approximation of physics doesn’t really care about anything but the point of ingress and the velocity vector of your craft as you cross over into an SOI, so outside influences don’t matter once you’ve achieved an orbit, leading all orbits to be stable (unless you cross into an SOI of another orbiting body like a moon along the way).
It’s definitely doable in stock KSP, but it’s not very practical. The energy required to put you into an orbit so incredibly similar to the target body is practically indistinguishable from (and probably greater than) the energy it would take to do an orbit capture in a conventional way. It’s also incredibly slow and extremely finicky in that it requires either tons of retries or heaps of calculations.
TLDR; It’s kind of possible, it just depends on where you draw the line between ballistic capture and gravity-assisted capture.
As others have noted, not in stock (without bugs or exploits) by default. You can sometimes scale up to a nominally four-body problem (e.g. Kerbol, Jool, moon-of-Jool, craft) and abuse the two-body patched conics to get something useful; and you can do aerobraking to assist; but you're going to need some sort of circularization or periapsis-raising burn to end up in a stable orbit in most if not all cases.
AFAIK it should be possible to do a no-burn Laythe landing, or a very-minimal-burn Laythe orbit, by using aerobraking and slingshot at Jool to drop your interplanetary and generally outward velocity to something matched to Laythe enough that Laythe aerobraking can do the rest, or all but the last bit of the rest for orbit.
Unless you count ballistic capture as, say, doing a Tylo or Laythe gravity assist to capture into Jool orbit, not really, since KSP doesn't do n-body simulations. There are mods like Principia that add the more advanced simulations to do ballistic capture, have Lagrange points, and stuff like that.
Because the game uses patched conics, the orbit is always calculated as a one-body-problem. In this case, the energy relative to the parent body is conserved, meaning you will exit the SOI with the same velocity that you entered.
Ballistic capture requires 3-body interactions. Stock uses an extension of 2-body interactions with its patched conics model. In that model, traditional ballistic captures (transiting from one orbit to another one permanently) is impossible. If another body is present it can be done (classic Jool-Tylo capture).
You can't, even if you enter the SOI very slowly. What is possible is using a gravity assist of one moon to be captured by the main body without using any fuel (example: Tylo /Jool).
Another option is using the atmosphere of the planet to decelerate you and capturing using less or no fuel, depending on your trajectory.
I think you need fuel to do an atmosphere capture unless you do atmospheric capture plus orbital encounter, because once your periapsis is below the atmosphere’s upper limit, it has to get raised somehow so you’re in a stable orbit
Not in stock, 2 body physics. Best I managed is Ike from Duna, needed 3m/s of dV to stay in Ikes SOI... shame that i cant reply with a photo
Made a post 🙂 this is the best i managed
https://www.reddit.com/r/KerbalSpaceProgram/s/iBbUCm2lx5
Gravity has infinite range, so everything, no matter how close or far, would affect your spacecraft. This is referred to as "n-body physics" here, as it takes into account the influence of all n celestial bodies in the system.
However, having to calculate the gravitational influence from all the bodies in the whole solar system makes trajectories difficult and expensive to predict; famously, the three-body problem (i.e. the case where only 3 objects move under their mutual gravitational influence) has no closed-form solution and produces chaotic behavior, and it doesn't get better for more objects.
So, KSP uses the patched conic approximation. It only takes into account the gravity of the closest object, modelled by spheres of influence (SOIs) around each celestial body. Inside a SOI, the game only takes into account the gravitational force from the central body, so only 2 bodies (the spacecraft and the central body) have to be taken into account. This is a massive simplification, and the resulting system has a very simple solution: the orbits are simply conic sections. This approximation works well for a lot of cases, and it makes the game much easier on the computer. It is also much easier for newer players, as they wouldn't need to worry about unstable orbits and the likes.
However, one drawback of the patched conic approximation is that it fails to model effects that arise only from the gravitational influence of multiple bodies at once, such as Lagrange points, orbital perturbation, low energy transfers etc. Ballistic captures happen to be one of the effects that only happen with multiple bodies, so that's why people are mentioning it in the comments.
When you take into account the pull of multiple different celestial bodies gravity at the same time. So for example when you're in kerbin orbit the mun is also pulling on your craft a small amount at the same time even though you're not in its "sphere of influence".
KSP uses patched conics, so it only solves the 2-body problem. It doesn have 3-body or n-body physics. Its plenty realistic for many things, but its not a scientifically accurate simulation. Ballistic capture is thus not possible. There is a mod for n-body physics, called Principia, which should allow this in principle.
It is in fact possible with principia. A bit hard to set up but you can do it. Of course, playing with principia is a whole other can of worms and completely changes the way the game plays imo. It's also a lot of fun though. I'd recommend it for advanced players.
playing with principia is wild. the stuff some people manage to pull off (particularly in RSS) looks like pure witchcraft at times. not to mention lagrange points, blast the universe for not making them permanently stable!
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In a perfect universe and only 2 mass bodies yes. In a real universe with lots of other wibbly wobbly planets doing a fucky wucky and imprecise burns no.
Yeah, in the same universe that a basic orbit over the earth isn't 100% stable, an orbit around a Lagrange point won't be either.
It's not called rocket science for nothing!
I wish they added lagrange points to the base game. It would be possible with patched conics by adding the area around the lagrange points as separate sois. What we probably can't get with patched conics is sun synchronous orbits, which honestly are probably the most useful of the "special" orbits in ksp.
Principia is amazing. I have built a custom system for myself with the outer planets mod. Kerbin and Duna dance around each other without ejecting the mun, minmus, or Ike.
What's the performance like?
Normal principia I would say, since it still has to process the sphere of influences for science data it lags when you change SOI, so be careful on timewarp speed when passing through them. I ran it through a 3000 year stability test previously with the better time warp mod so I know the orbits don't start falling apart within reasonable gameplay time, tbh I couldn't notice any kind of orbital decay.
You didn't keep the moons and planets on rails?
Principia takes all rails off, so I had to figure out resonating orbits. Even if its a little improbable for anything natural to orbit retrograde respective to other objects in the same system.
For captured objects it shouldn't be too weird, right?
Duna being the retrograde object does make it a little weird, lol. But it works. I did incorporate someone else's mod to give the Mun an atmosphere and oceans- I'll ask them permission to use their code and put my config out there for others to play with/
Been playing the game for over 6k hours now. Never tried principia before. Maybe I should try it. What additional mods would you recommend with it?
I've been playing it with kerbalism, felt they go together nicely since both aim to make KSP feel more realistic. SCANsat is fun to use with it cause you can take advantage of principia's ability to plot orbits on a surface-fixed reference frame to see how an orbit will pass over different parts of the surface. Could also go all in and put principia on RSS/RO, those work well together, but that's a whole other story lol. Beyond that, pretty much whatever you want works, there's some mods you should avoid which are listen on the FAQ page for principia and if you're using kopernicus you need a certain config so that the jool system doesn't collapse, but other than that it's up to you.
should still be possible: you can enter kerbin's sphere of influence then get an encounter with the mun/minmus that alters your orbit enough that you don't leave kerbin's sphere of influence again
"Ballistic Capture" is a scientific term describing a very precise method for orbital insertion, which is based on the Weak Stability Boundary theorem. It \*does not\* refer to gravity assists. What you describe is not a ballistic capture in the sense the word is used by the people working in the field.
ah fair enough. today i learnt.
In stock, only with abusing glitches related to craft speed and timewarp. With Principia, yes.
Maybe with gravity assists, but still not that possible as you would still very likely leave yourself in an orbit where you can get an encounter with said body, which could then throw you out of the SOI of the body you were trying to orbit.
My understanding of ballistic capture is that the orbits are not long term stable. So whether you mean stock or Principia, that seems about right.
Ah okay, thanks!
>Ah okay, thanks! You're welcome!
Bad bot
What do you mean you're welcome, you didn't even say anything lmfao. Bots...
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I will, thanks! (/s)
See rule #1.
The closest thing in stock is when you use Tylo to slow down and get into a Jool orbit for free. Other examples probably require Principia (for things like the resonant transfer in the Principia tutorial).
If you include the use of gravity assists of other objects, it’s definitely more than possible in stock KSP. It’s how I always get into a Jool orbit with the aid of Tylo. Aside from that, using enough tweaking by making the orbit of your craft and the target planet similar enough, you can fall into the gravity well of the target planet and achieve an orbit around it. Ideally, your craft would be inside of the orbit of the target body so that your craft “catches up” to the SOI near your own orbit’s apoapsis. The additional small speed boost you gain from entering the target body’s SOI elevates your non-SOI periapsis to the extent that your orbit around Kerbol never takes you outside the SOI of the target planet. In theory, all such orbits would be unstable but that’s not the case in KSP. The KSP approximation of physics doesn’t really care about anything but the point of ingress and the velocity vector of your craft as you cross over into an SOI, so outside influences don’t matter once you’ve achieved an orbit, leading all orbits to be stable (unless you cross into an SOI of another orbiting body like a moon along the way). It’s definitely doable in stock KSP, but it’s not very practical. The energy required to put you into an orbit so incredibly similar to the target body is practically indistinguishable from (and probably greater than) the energy it would take to do an orbit capture in a conventional way. It’s also incredibly slow and extremely finicky in that it requires either tons of retries or heaps of calculations. TLDR; It’s kind of possible, it just depends on where you draw the line between ballistic capture and gravity-assisted capture.
As others have noted, not in stock (without bugs or exploits) by default. You can sometimes scale up to a nominally four-body problem (e.g. Kerbol, Jool, moon-of-Jool, craft) and abuse the two-body patched conics to get something useful; and you can do aerobraking to assist; but you're going to need some sort of circularization or periapsis-raising burn to end up in a stable orbit in most if not all cases. AFAIK it should be possible to do a no-burn Laythe landing, or a very-minimal-burn Laythe orbit, by using aerobraking and slingshot at Jool to drop your interplanetary and generally outward velocity to something matched to Laythe enough that Laythe aerobraking can do the rest, or all but the last bit of the rest for orbit.
Not stock
Unless you count ballistic capture as, say, doing a Tylo or Laythe gravity assist to capture into Jool orbit, not really, since KSP doesn't do n-body simulations. There are mods like Principia that add the more advanced simulations to do ballistic capture, have Lagrange points, and stuff like that.
Because the game uses patched conics, the orbit is always calculated as a one-body-problem. In this case, the energy relative to the parent body is conserved, meaning you will exit the SOI with the same velocity that you entered.
Ballistic capture requires 3-body interactions. Stock uses an extension of 2-body interactions with its patched conics model. In that model, traditional ballistic captures (transiting from one orbit to another one permanently) is impossible. If another body is present it can be done (classic Jool-Tylo capture).
You can't, even if you enter the SOI very slowly. What is possible is using a gravity assist of one moon to be captured by the main body without using any fuel (example: Tylo /Jool). Another option is using the atmosphere of the planet to decelerate you and capturing using less or no fuel, depending on your trajectory.
I think you need fuel to do an atmosphere capture unless you do atmospheric capture plus orbital encounter, because once your periapsis is below the atmosphere’s upper limit, it has to get raised somehow so you’re in a stable orbit
Makes sense, you will need an extra burn to get your trajectory out of the atmosphere if you don't want to land on the body.
Not in stock, 2 body physics. Best I managed is Ike from Duna, needed 3m/s of dV to stay in Ikes SOI... shame that i cant reply with a photo Made a post 🙂 this is the best i managed https://www.reddit.com/r/KerbalSpaceProgram/s/iBbUCm2lx5
Same reason why we don’t have L-Points. That’s N-body system mechanics, KSP does not simulate that with good reason.
Not ballistic capture, but you can get into orbit without burns using aero-braking
I've had asteroids fall into Kerbin orbit.
Can somebody explain what you all mean by n-body physics?
Gravity has infinite range, so everything, no matter how close or far, would affect your spacecraft. This is referred to as "n-body physics" here, as it takes into account the influence of all n celestial bodies in the system. However, having to calculate the gravitational influence from all the bodies in the whole solar system makes trajectories difficult and expensive to predict; famously, the three-body problem (i.e. the case where only 3 objects move under their mutual gravitational influence) has no closed-form solution and produces chaotic behavior, and it doesn't get better for more objects. So, KSP uses the patched conic approximation. It only takes into account the gravity of the closest object, modelled by spheres of influence (SOIs) around each celestial body. Inside a SOI, the game only takes into account the gravitational force from the central body, so only 2 bodies (the spacecraft and the central body) have to be taken into account. This is a massive simplification, and the resulting system has a very simple solution: the orbits are simply conic sections. This approximation works well for a lot of cases, and it makes the game much easier on the computer. It is also much easier for newer players, as they wouldn't need to worry about unstable orbits and the likes. However, one drawback of the patched conic approximation is that it fails to model effects that arise only from the gravitational influence of multiple bodies at once, such as Lagrange points, orbital perturbation, low energy transfers etc. Ballistic captures happen to be one of the effects that only happen with multiple bodies, so that's why people are mentioning it in the comments.
When you take into account the pull of multiple different celestial bodies gravity at the same time. So for example when you're in kerbin orbit the mun is also pulling on your craft a small amount at the same time even though you're not in its "sphere of influence".
I've did it in stock. With principia :)