Are the Orbits of Planets in KSP Stable?

Though KSP is a quite realistic physics simulator when it comes to games, there are things in the game that might indicate that the orbits shouldn't be as stable as they let on. KSP assumes each body to be in a two-body system, this ignores the influence of other celestial bodies, which is not entirely accurate. So this video investigates whether it is justified to make this simplification.
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📝 Sources & Information 📝
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Extra info
en.wikipedia.o...
Explanation of the code used (made by others)
• Let's Build a Solar Sy...
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🎵 Music 🎵
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Kevin MacLeod - Backed Vibes
License: CC BY 3.0 (goo.gl/BlcHZR)

[@curious_ksp_ksa]

Small mistake: the first boost that Vall gets is from Laythe (at least, it looks like that is the case)

[@jansenart0]

Between that and the audio, I wouldn't mind a reupload... (also a call to an easter egg where rings form around Jool would be amazing)

[@curious_ksp_ksa]

@@jansenart0 Depending on the initial conditions Vall either crashes or gets ejected. So technically, yes, it probably crashed, but in this simulation the objects are point masses and thus behaved such. In the end it doesn't matter too much, the conclusion stays the same: Vall's orbit is not stable. When it comes to audio: it sounds perfectly fine on my end, but some people with no headphones or speakers have told me it wasn't as great, so I will be making videos more headphone-less user friendly in the future. I find no need to reupload for now, maybe some mention of some clarification.

[@gavros9636]

At the point where Vall get's slingshotted out I think that was because Vall actually collided with Tylo and the program didn't simulate the collision, as that's what is often seen from time warping into a Jool collision which tends to send parts flying out of the Kerbol system at 3x light speed.

[@TiagoNugentComposer]

fun fact: in KSP 1 there's a mod called Principia which changes the gravity system so the planets can influence each other. They had to change the orbits of Jool's moons so that the same thing you found wouldn't happen.

[@bobbybobby325]

does it let you change the orbit? or asteroids?

[@gmyra]

I thought it just did N body calculations with your crafts and not the planets themselves

[@kedrednael]

@@gmyra It also does it with the planets, Scott Manley has a video about it

[@Bruce_Games]

What's the point the orbits are all stable?

[@Maker0824]

@@Bruce_Games did you see how on Duna both bodies were rotating around a common point? it's stable, but not like it is in normal ksp

[@simracingmax1775]

I'd recommend looking at a universe sandbox version of the kerbolar system. A lot of interesting things occur, such as kerbin and eve losing it's moons. Furthermore, all the inclinations and arguments of periapsis are already set up.

[@attilavs2]

Where did you find it ?

[@simracingmax1775]

@@attilavs2 the steam community simulations I believe

[@attilavs2]

@@simracingmax1775 As simple as that, thx !

[@curious_ksp_ksa]

Sadly I do not own universe sandbox already, so I didn't want to buy a game for just one or two videos when I have a way to run simulations for free. Good suggestion though, so maybe when this channel grows, I will use it (more).

[@theairacobra]

val collides with laythe and the other 2 muns get removed from the joolian system

[@zuthalsoraniz6764]

The reason why Jool and Eeloo are fine is probably because they are in a 2:3 orbital resonance, similar to the IRL situation of Neptune and Pluto.

[@zotzot5]

fun fact: in an older version of the mod principia that did not change jool's moons orbits, val would be slingshot out of the kerbolar system, and brick the save, they fixed this by tweaking the orbits. Edit: the -> they (thanks, xyler dawson!)

[@KrisiCrossi]

you forgot creator if you dont mind me telling you since it just says the fixed

[@zotzot5]

@@KrisiCrossi oops, I forgot a y

[@hylobateslar4151]

With the distance between Tylo and Vall in those encounters, it seems like they actually would have collided, and the simulation perhaps doesn't account for that.

[@curious_ksp_ksa]

Could be yes, this simulation does not indicate that, but I have increased the little spheres representing the moons, to make them more visible. And it also depends on initial conditions whether it crashes or is ejected. The conclusion remains the same: Vall's orbit is not stable.

[@joshuahudson2170]

@@curious_ksp_ksa A better simulation was ran long ago. Two moons are ejected from the Jool system with no collisions.

[@Bellezzasolo]

When I ran it in Principia a couple of years ago, I got a collision: kzbin.info/www/bejne/epTTfGOChLJ-gM0

[@thundersheild926]

​@@joshuahudson2170 I wouldn't necessarily say better. These simulations are extremely temperamental to initial conditions, and even slight variations can result in extremely different outcomes. There have been many simulations of the Jool system, and all of them have resulted in the system being unstable, which is the main takeaway from them all.

[@Admiral45-10]

Fun fact: Kerbol is smaller and less bright than EBLM J0555-57Ab, the smallest found object classified as a star, yet the game tries to portray it as yellow dwarf star (like our Sun). It's also barely more massive than Eve, which is more massive than Jool. But it's also important to mention, that the game itself is based on tremendous approximations and Newtonian mechanics - it lacks the artificial objects' gravity and overall relativistic physics. Also, considering KSP 2 uses welding as a method of attaching wings to aircrafts, I don't think anything will really change in this matter.

[@eekee6034]

Fun fact: Kerbin is so dense, it can't be made of normal matter. Everything is scaled down 10 times so perhaps it's best to assume the laws of physics are different, though I don't know if consistent laws could be found for the system. :) There's one thing that I've heard works out well: if the Jool system is scaled up to normal proportions and densities, Laythe is tidally heated to exactly the temperature the game gives it.

[@jansenart0]

2:50 That was an impact, not a slingshot. Jool should have some mega-impressive rings.

[@bboi1489]

The fact that it took this long for an in-depth science video of the kerbolar system is baffling. Definitely earned this sub

[@minmus5]

It looks like Vall crashes into Tylo. If Vall was closer to Laythe Valls orbit mite, be staple.

[@achi335]

why did gilly even end up orbiting eve? also how kerbin get its second moon? this might be a very simple question to answer, but i couldnt think of any reasonable answer.

[@bboi1489]

There's a theory that Minmus is a captured comet, but a lot of stuff doesn't add up.

[@NOT_A_ROBOT]

@@bboi1489 comet* edit: it was fixed

[@Cl0ud897]

Here, I didn't read it all the way, but I hope it helps! en.wikipedia.org/wiki/Asteroid_capture

[@bboi1489]

@@NOT_A_ROBOT by far the weirdest autocorect thing I've ever gotten.

[@kahlzun]

Stable orbit capture requires three+ bodies if only gravity is involved. Minmus actually makes some sense, though you would expect its orbit to approach the muns soi more. Gilly is a mystery.

[@Cl0ud897]

Actually the Joolean system was supposed to be in a 1:2:4 orbital resonance (which is very stable), just like Io, Europa and Ganymede around Jupiter. The orbital periods do match up, but the phases are in sync, instead of having some delay, so it messes up everything. Here's a wiki page about that: en.wikipedia.org/wiki/Orbital_resonance

[@sammyjpeg8322]

And then vall existed

[@alexolas1246]

Very surprised you didn’t bring up the Principia mod. The Jool system’s instability has been known for years, and that mod applies some minor changes to Jool’s moons to make them stable: Namely, raising the orbits of Vall & Tylo, and making Bop orbit retrograde.

[@ryuk5673]

He’s still pretty new to KSP

[@haztepolvo5809]

I tried to simulate all systems in ksp in universe sandbox given all the data the game gives, it was so cool watching laythe collide with vall

[@Boop__Doop]

Kerbol system: kinda Jool system: no

[@tranchedecake3897]

maybe the kerbol system is stable because devs have calculated orbital resonnances before setting up their orbits, and just for jool they've just wanted to have close moons

[@bottlekruiser]

the Val slingshot at 2:54 looks a lot like numeric instability to me

[@curious_ksp_ksa]

could be, the method is not super accurate

[@strycker9682]

video idea:why is jool green?

[@p_pattedd5477]

Mesh Texture Diffuse

[@jerry3790]

The main problem with the Jool system is the postition of the planets in their orbits, as opposed to the orbits themselves

[@jerryq1837]

This video is interesting. I know that Principia flings pol, bop and vall out of the SOI of Jool, so those are very unstable, but I never knew about the stability of other bodies. Nice video!

[@Gopnik_B57_2]

here's an idea: how long would you survive on each planet and moon in ksp without a spacesuit?

[@warpey5632]

All bodies without atmospheres are less than 5 minutes except for Moho which may or may not accelerate your death by roasting you alive. Duna and Eve's lack of oxygen in their atmospheres will also make death no more than 5 minutes away. Eve's atmospheric pressure might instantaneously crush you. Jool's atmospheric pressure will defenitely instantaneously crush you. Laythe and Kerbin are perfectly habitable with breathable atmospheres and survivable temperatures.

[@theendlessvoid7124]

Moho:

[@Graknorke]

almost all of them would be either instant death from temperature, or about three minutes from vacuum

[@Memezuii]

@@Graknorke or precisely 30 seconds if you know you know

[@quoniam426]

Minmus/Mun is also unstable, look at what the JNSQ modteam did to compensate it...

[@emberthecatgirl8796]

2:38 I’m pretty sure that the gravity assist came from Laythe, Tylo only pulled Vall up a tiny bit for it’s orbit to come close to the orbit of Laythe.

[@katsikopoulos8184]

the jool system is too cool to care about physics

[@MinerBat]

what about the kerbin-mun-minmus system? that is the only other planet with multiple moons so it might have some interesting results. also, with moon-planet simulations you should probably include the star too as its effect is significant enough to change the outcome

[@curious_ksp_ksa]

Yeah, I wanted to look at Kerbin and Eve, but that would take more time. I wanted to upload today at very latest. I want to upload at least once a week.

[@bboi1489]

​@@curious_ksp_ksa next video maybe?

[@TlalocTemporal]

I really want to see a full system simulation in a proper orbit integrator now.

[@MinerBat]

@@TlalocTemporal look up the channel Matt Roesle

[@jansenart0]

Great topic, but the audio mix is almost inaudible. Give yourself +30db gain.

[@chubbycatbrian3918]

I’ve always wondered why jool is green

[@curious_ksp_ksa]

A lot of people have been asking about this, guess I'll have to get to work haha

[@chubbycatbrian3918]

@@curious_ksp_ksa gotta say these videos are amazing. I’ve just watched all your videos in one sitting and learned so much so quickly. Thank you!

[@curious_ksp_ksa]

@@chubbycatbrian3918 No, thank YOU! I am really happy that I can provide you with content that you enjoy!

[@krio1267]

​@@chubbycatbrian3918 might be its composition

[@cmdrgraves3308]

Just subbed :) those equations at the beginning will never make sense but I love these types of vids

[@thejuicecart246]

I like how in the joolian system laythe and jools orbital paths make a cats eye

[@a_coloradan8689]

I checked as well with the inclination and AoP. Minmuses orbit would get pulled away from kerbin and become its own planet along with jools moons going crazy. Gilly also started acting weird but not crazy

[@vesnabernjak-ord8674]

Fun fact: eeloo’s orbit in KSP is similar to plutos orbit in real life, eeloo and pluto have a irregular but stable orbit.

[@Kerman_von_Braun]

Got a viddy idea for you: How many Jool gravity assists would you need to do to knock Jool out of Kerball orbit

[@ccoeltrains]

Congrats on 1K subs!

[@wrath908]

So where did you get the software and code to run an n-body simulation? I've been looking for something like that for a while now due to a project I'm working on.

[@curious_ksp_ksa]

Spyder is a piece of software that lets you code in the Python language. I really like python because it is a good language to simulate anything and to sort, visualize data and such. If you don't know the language it might take some time to learn but in the end I found it relatively intuitive. It is the only language I know. Edit: the youtube video in the description explains the code I used

[@40_gjb19]

I’ve been wondering what the far future of the Kerbol System could look like overtime, like what changes would happen, maybe like After Kerbin events or something like that

[@MartinMizner]

I made my own 2D KSP game with realistic gravity and atmospheric friction and also had to modify Jool's moons. Gilly had super tiny hill sphere that ended just 10 kilometers above its surface in closest to Eve. Keeping Spaceship stable around Duna or Jool was very difficult.

[@bermchasin]

very cool! I made a code a long time ago that would calculate how long it would take for the kerbol system to align in any particular way, specifically so that I could do a 'grand tour' mission of the planets.

[@VSaranara]

Fun fact the principia mod remakes the joolian system since the orbits would be unstable

[@mrbyzantine0528]

I would love to see more of this, however many videos it takes to explore it all!

[@jansenart0]

A good video topic might be how the devs based the Joolian system on the Jovian system (the Galilean moons) and fudged the surface gravity and radiuses but kept other numbers. (i've hated the Joolian system for almost a decade.)

[@curious_ksp_ksa]

Why do you hate the Joolian system?

[@jansenart0]

@@curious_ksp_ksa It's complicated, but its on-rails nature is part of it. I don't wanna get into it.

[@shitposter3249]

Imagine making a whole video about this without even doing a quick search and seeing this topic has already been covered; see Principia.

[@titan-1802]

*who cares, we still doing it anyways*

[@petersmythe6462]

How many orbits did you simulate the whole system for? Often something that is stable for 1000 orbits might not be after a billion orbits.

[@GoldballIndustries]

I mean yeah, if you just look at Tylo its basically kerbin but with no atmosphere or water, its GOING to influence orbits.

[@ExcaliburAero]

Can you try the Juno system from Juno: New Origins?

[@memerightsactivist7972]

How are you getting these absolutely stunning images of the planets? That frame with Jool and its moons 2:30 was beautiful!

[@curious_ksp_ksa]

I just launched the game, took screenshots and cropped them out of the environment as backgroundless pngs :D

[@wildrosomak3395]

It's from KSP 2

[@ahmed4363]

yeah im pretty sure thats ksp2

[@KrisiCrossi]

@@ahmed4363 its not ksp 2 its still just ksp 1 with some visual mods

[@vesnabernjak-ord8674]

@@KrisiCrossiit is KSP 2.

[@HowToDota]

Try principia mod, it emulates real physics orbits for vessels and celestial bodies

[@scottwilliams846]

This may or may not be why the developers have said that N Body physics would be impossible for this game.

[@entropic-decay]

I'm fairly sure the boost Vall got from Laythe there would actually have been a collision. Bad news for any lifeforms that might've been developing in Laythe's waters.

[@ethanwolman6383]

i'm not the only one that noticed that Vall actually HITS tylo, should that be accounted for?

[@mr.cat_cz5184]

0:18 Can I ask you what script did you use to simulate the orbits? I'm trying to figure out a stable orbits for terrestrial moons.

[@thespacedinos4037]

nice, new vid vall is just weird also first

[@curious_ksp_ksa]

I give hereby confirmation that you are indeed first.

[@Iandothing]

I absolutely love your scientific breakdowns of kerbal space program! These videos always teach me something new :)

[@Ethan-fj2cn]

I feel like I just found gold!

[@aceathor]

10 years earlier we were saying that in KSP 2 there will no longer be a sphere of influence like in KSP 1. But like the real overlapping spheres of influence. But no, and I'm very disappointed... ^^ They even accentuate this system by creating a virtual sphere around the planets. 1 meter before there is no gravity, and 1 meter after there is gravity... Sorry if bad English, I'm French

[@VorynDagoth]

Wait until he finds out about universe sandbox

[@susangoaway]

0:47 And that's how you do that in orbital mechanics as well. Including the spheres of influence. It's a simplification, though for long-term predictions, it is too inaccurate. 2:55 Correction: So close even, that they crash together. 3:24 There are pulls from the entire system, especially Kerbol to consider. Isolating a system like that is where this sphere of influence may fail a bit. Not to forget that the furthest body may disrupt the jool moon system with how close it gets. Our own Moon is also on a very unstable orbit around Earth. Well, unstable if you are the size of microns.

[@curious_ksp_ksa]

Of course, simplifications were made. Even though I did not include Kerbol for the Jool system, it still proves the point. Indeed the Tylo and Vall actually crash into eachother but in this model they are point masses. One question that I have: what do you mean when refering to bodies the size of microns?

[@susangoaway]

@@curious_ksp_ksa In the sense of the dimensions of the perturbations that our Moon experiences from the gravitational pull from other celestial bodies. Microns being a short for micrometers.

[@curious_ksp_ksa]

In that sense. I wouldn't call that unstable myself though, hence my confusion. I do know what microns are, I am not from the states haha.

[@awsumguy-bh9pz]

Can you do a video predicting how the kerbol system formed and changed 👍🏼

[@ProjectPhysX]

Which integration scheme did you use? Ideal should be Velocity Verlet!

[@curious_ksp_ksa]

Link to the video explaining the code is in the description. I did not make the script myself, as that would take to much time. I just made it do what I wanted.

[@capapofa]

Contrats on 1k

[@K-SHABAB]

Imagine perfect rss mod for ksp 2 with perfect principia omg

[@carterschuller1583]

Hey, I'm curious if you're using a different equation like ksp's equation for grav force. But if you're "calculating" or using the equation for grave force it's essential to make sure GMm is over r^2 not r^3 as obviously this drastically changes the gravitational force value you would get. Correct me if there's a misconception in the equation you were using!

[@curious_ksp_ksa]

The equations I wrote down are the vectors of the forces. the vector behind every component contains "r", so r divided by r^3 is technically r^-2. This is indeed confusing and another way to have done it is by taking the unit vector r and not just r vector. Edit: if this is still confusing, then feel free to ask more in the upcoming live stream I am doing

[@carterschuller1583]

@@curious_ksp_ksa super cool! Thanks for clearing up my misconception.

[@dnkmmr69420]

What about kerbin with the mun and mimus?

[@Arlington0588]

0:21 Eve is missing

[@spagiololi2011]

what was the name of the software did you use for the orbit simulations?

[@curious_ksp_ksa]

It is written in the Python language and I use Spyder (software) to write and run the code

[@StormyCanuck]

Please keep making these videos, they are very entertaining! (also second lol)

[@Stratenblitz]

why did you remove the pictures of you during explanations? (exept the end)

[@curious_ksp_ksa]

I don't really know tbh haha

[@Stratenblitz]

@@curious_ksp_ksa it was unique tbh

[@curious_ksp_ksa]

@@Stratenblitz i'll keep that in mind :)

[@Stratenblitz]

@@curious_ksp_ksa 👍

[@draedon6865]

can you take into account vall and tylo colliding early on?

[@curious_ksp_ksa]

that really depends on the initial conditions that you put in. Like their position when you begin the simulation. I started them at periapsis.

[@Cl0ud897]

@@curious_ksp_ksa But... their orbits are perfectly circular!

[@curious_ksp_ksa]

@@Cl0ud897 if the moons start in different positions, then the CoM of the system will also be different. So, this would affect the wat they orbit. That would be my reasoning

[@Cl0ud897]

@@curious_ksp_ksa I know, you just said "I started them at periapsis" when the orbits were circular, I found it funny

[@curious_ksp_ksa]

@@Cl0ud897 ooooo hahaha how stupid of me lol. Yeah i not really stand still when faced with that fact. Yeah it was defined in a way on the wiki, so i just did that haha

[@austinfaust3374]

What was the program you used to simulate the planets in python called?

[@glauberglousger6643]

A Simplerockets 2... ahem, Juno: New Origins system analysis would also be cool, it’s far less complicated but well, maybe?

[@tiny_desk_engineer]

What temperature is on every body in KSP?

[@tadeuszthetree9786]

Calling it now this dude is going to be big

[@AuTo69420]

If I may make a suggestion, record yourself at a much higher volume I have the amplifier, youtube and computer all maxxed out on volume and can't hear you

[@curious_ksp_ksa]

Might be due to the fact you arent using headphones maybe? It sounds fine on my side, but I'll make it more headphone-less friendly next time

[@AuTo69420]

@@curious_ksp_ksa I'm using 1600 watts of speakers

[@AuTo69420]

@@curious_ksp_ksa but yeah thank you. It can get really hectic when one video is super quiet and the next is super loud

[@GoldenRuben1]

Nice video! Are you a dutchie?

[@curious_ksp_ksa]

Jazeker, mede-kaaskoppen kunnen elkaar altijd terug vinden, welke taal dan ook lol

[@GoldenRuben1]

@@curious_ksp_ksa haha grappig, je kan veel beter engels uitspreken dan dat ik kan xd

[@curious_ksp_ksa]

@@GoldenRuben1 dankje haha

[@Def1qnt]

what was the code name and where can I find it?

[@Xelaria]

I see you took a bit of my advice!, also I feel as though you may ran out of things to talk about in ksp. So I could recommend looking at physics in other games as well.

[@curious_ksp_ksa]

Yep, still things to improve, but step by step it gets better. Edit: and when it comes to views, it is going quite well

[@SKILLERZX1]

Pls try juno system

[@FlyToSpace1000]

Acctually In The Game Laythe Is The Victim Of Val

[@SkyHigh_xx]

why did you call the Sun "Kerbal"

[@filippomunari8147]

vall says cya suckers and just left

[@jopjop9400]

but what if i wanna deorbit a planet

[@realdragon]

I just thought KSP system was based on Solar system which is stable

[@hunterwolf8539]

Just shove it in universe sandbox mimicking all orbital parameters and such.

[@kerball417]

The mimus flats or mimus in general

[@supermaxrocks2]

What’s the name of the simulator?

[@JohannAlbrecht]

awesome video

[@EXMUTRKS]

I wanna 3 Body Problem in KSP

[@pman8312]

There I somthing I have somehow made kerbin orbit Joel 😅

[@ArkaSaurusRex218]

Bascially a computerized three body problem

[@siyacer]

interesting

[@bradenwolf2179]

ALL HAIL RETROBOP!!!

[@smarty265]

no way

[@GizmoMagui]

i have trust issues watching the numbers. and just focus on the line haha

[@maxwiseman5537]

Pretty sure mun and minimus aren't stable

[@curious_ksp_ksa]

I didn't have time to check them as well, so next video!

[@theairacobra]

i recommend you talk a little bit louder, its a bit hard to hear you

[@curious_ksp_ksa]

When I listen to it, it sounds fine to me. Might it be the case that you are listening on a phone with no headphones or ear buds? Just curious

[@capapofa]

Yo

[@theairacobra]

@@curious_ksp_ksa i had my youtube volume maxed and my computer's volume as usual

[@curious_ksp_ksa]

@@theairacobra strange, I will up it a bit next time

[@highlandsprings5752]

WTF is a stable orbit.

[@curious_ksp_ksa]

one that remains the same, one that isn't being perturbed that much by other bodies.

[@highlandsprings5752]

@@curious_ksp_ksa I don't think they exist in nature lol

[@curious_ksp_ksa]

@@highlandsprings5752 not in the strictest sense of the word no, but they do in the practical sense

[@titanicbigship]

@@highlandsprings5752uh the moon?

[@highlandsprings5752]

@@titanicbigship 3.1415926535 8979323846 2643383279 5028841971 6939937510 5820974944 5923078164 0628620899 8628034825 3421170679. This incredibly large number says no : (

[@The_Cameraman_From_WW2_Space]

142nd!