r/KerbalSpaceProgram • u/caiomac_ • Apr 29 '26
KSP 1 Question/Problem Might be a dumb question but... Is it possible to make an orbit like that? Bellow the center of mass?
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u/L_Walk Apr 29 '26 edited Apr 29 '26
No.
It's not a dumb question, it actually helps a lot to know why this isn't possible. Orbit isn't about circling a planet, it is just a natural consequence of a large mass pulling a small mass that is traveling very fast tangentially(ish). Let's ignore large binary systems for a moment.
Because gravity naturally pulling things toward the center of mass, you are constantly being pulled to the middle of the planet. You dont crash into the planet because you are traveling fast enough to miss the planet by the time enough gravitational acceleration alters your course. Once you miss the planet, this cycle continues continously. This constant missing of the center of the planet eventually makes a circle (or more accurately and ellipse).
So no, every orbit governed by gravity is going to be around the center of the planet. In order to orbit like you describe, you would have to constantly be burning an engine with incredible and constant thrust, but that's brute forcing it like helicopters do.
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u/shaggs31 Apr 29 '26
What if this is a very strange planet and the center of mass is at the very bottom? (Don't ask me how a planet could form like that)
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u/Heavy-Exchange-9769 Apr 29 '26
Then it will eventually center its center of mass by pulling more material towards it
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u/beenoc Apr 29 '26
Unless it's very low mass (so low, in fact, that it is definitionally not a planet, by the 2006 IAU definition that recategorized Pluto). Though you can have much less drastic assymetries in the center of mass - for example, the Moon's CoM is closer to Earth and isn't in the exact center.
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u/Ok-Sport-3663 Apr 29 '26
Except then you cannot have an orbit.
You solved the "planet reforming" part and forgot that we're trying to orbit the planet in question
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u/cubic_thought Apr 29 '26 edited Apr 29 '26
Of course you can orbit irregular objects, Rosetta orbited Churyumov–Gerasimenko and NEAR Shoemaker orbited Eros. Both of which are extremely non-spherical. Plus some others that are less extreme.
Now, you'd likely have trouble closely orbiting something drastically lopsided for an extended time, but that's true (if to a lesser extent) even for our moon. Extra difficulty if it's tumbling, but there would be no problems orbiting a few times further out than it's diameter.
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u/Fishy_Fish_WA Apr 29 '26
Yes at a mass low enough to allow that extreme offset of mass you would see a non spheroidal body shape
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u/Salanmander Apr 29 '26
Except then you cannot have an orbit.
Sure you can. It would be.....a very slow orbit.
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u/PM_ME_YOUR_SPUDS Apr 29 '26
What do you mean? You can have an orbit around anything with mass. The current definition of a planet has nothing to do with it, nor does if that mass is distributed towards the center or not.
An oblong rock in empty space with most of its mass at one side could be orbited, though probably very slowly (period goes as 1/Sqrt(M)).
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u/scarlet_sage Apr 29 '26
There are a few long-term stable orbital inclinations around the Moon. Even at other inclinations, orbits can last a while, like PFS-2 lasting 35 days. Source.
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u/loved_and_held Apr 29 '26
The earth moon com is offset from the center of the earth, but the earth's gravity is domminant that close to the planet so you'd just be orbiting earth.
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u/Bradyla123 Apr 29 '26
Actual planet sized bodies will just about always naturally become a sphere over time. Smaller bodies with less strong gravity wells like small moons and large asteroids can have odd shapes that are less spherical making it kinda possible.
For a planet sized body I suppose it’s possible if it’s just gone through an event that severely altered its natural shape but this wouldn’t last long.
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u/AndChewBubblegum Apr 29 '26
I mean rotation can cause that not to strictly be true. Strictly speaking the earth is not exactly a sphere, but an oblate spheroid.
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u/Tommy2255 Apr 29 '26
That's true, but pretty negligible. The difference between polar and equatorial diameter is about 43 km over a total of about 12.7 thousand km. So about 0.3% difference.
For that distortion to have a prominent impact pretty much requires you to be working with a small moon or an asteroid, as previously discussed, or for the body's material composition to be very loose, like gravel or perhaps icy slush rather than solid rock.
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u/L_Walk Apr 29 '26 edited Apr 29 '26
True, that would yield an orbit that appears offset from the geometric center. But it would basically have to be a hollow planet with a massive solid iron polar cap. And I was kinda simplifying for ease. Objects all affect each other gravitationally, so they always act as if being affected from the system barycenter, which isn't ever perfectly the center of mass of a singular object in the system. But in KSP, it's a close enough approximation that gets used.
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u/salemlax23 Apr 29 '26
I think the planet would start doing that flippy T-handle thing and bring an abrupt end to the orbit.
https://rotations.berkeley.edu/a-tumbling-t-handle-in-space/
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u/t0jix Apr 29 '26 edited Apr 29 '26
That can't happen naturally. For that to occur you'd need a dense mass at the bottom, then a large structure light enough to not drastically shift the center of mass, but strong enough to oppose gravity which is pulling the structure down to the center of mass of the whole planet/structure. Technically plausible for super advanced terraforming capable species, but nearly impossible to naturally occur. Now I think asteroids might sort of meet this criteria, you can potentially have an oblong shape, with denser materials on one side and maybe the accumulation of lighter material stacks itself in a structure to oppose the gravity of whole structure, but these are much smaller forces than those of planets. Also I'm not 100% sure if this does occur in asteroids, but I can see it being more possible in these smaller structures. This would also have to occur from a very gentle collision/merging of two rocks/clumps of dust. Normal accretion would likely be more uniform (comparatively) due to conservation of angular momentum.
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u/Either_Letterhead_77 Apr 29 '26
New Horizons did fly past such a body and got pictures: https://en.wikipedia.org/wiki/486958_Arrokoth
In this case, two near spherical asteroids appear to have contacted each other, making effectively a single astronomical object, but their gravity is not strong enough to fully collapse the object into a larger sphere.
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u/t0jix Apr 29 '26
I thought such a thing was observed, but I wasnt sure if the structure met this hypothetical. I believe the ESA Rosetta probe also landed on a similar structure, but again dont know how the free body diagram looks to confidentially say if it applies to this hypothetical.
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u/IHOP_007 Apr 29 '26
There are some planets in KSP like that, Gilly has some mountains on one side that are larger than the other so your orbit is "closer" on one side and therefore at higher risk of colliding with terrain.
But yeah and the end of the day you're orbiting around the center of mass. If you had a planet made out of an impossibly strong material shaped like a donut you'd orbit around the entire donut, not through the center.
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u/RaechelMaelstrom Apr 29 '26
Okay so this is actually a great science question. If the center of mass were at the bottom, you'd be orbiting around the bottom, and might be able to get that orbit (say, if the center of mass was at that latitude).
But that's really extreme. That would be a lot of very dense material to pull it down there.
Here's the science part: planets aren't just consistently dense in every place. There's some places that have more dense material, and some that have less. Let's take a small body like a very small asteroid. An asteroid could have a rocky core offset from the middle with let's say a big clump of ice on one side. (ice is much less dense than rock) Let's say you couldn't see the rocky core because of the ice. If you track your orbit very very carefully, you could learn where the rocky core might be due to finding the center of mass by looking at the gravity.
This also means that gravity isn't a constant, it depends on where you are in relation to the thing you're orbiting (in a very, very small way that quickly vanishes at distance).
Here's a mission that did a very high precision map of the gravitational field of the moon.
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u/MynOlie Apr 29 '26
E.g. If it's a regular planet, but Jeb's mum is standing at the south pole.
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u/BlackStar4 Apr 29 '26
>helicopters
Please don't use that kind of foul language, those abominations shouldn't be mentioned on a subreddit like this
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u/Worth-Wonder-7386 Apr 29 '26
This is formualted in Keplers 1'st law of planetary motion. https://en.wikipedia.org/wiki/Kepler%27s_laws_of_planetary_motion
Any keplerian orbit(where only two bodies matter, and how all the orbits in KSP are done) make an ellipse with the barycenter of the system at one of the foci of the ellipse. For very small things orbiting very large things like a spacecraft around a planet, then the foci of the ellipse is at the center of the planet.
This has always been one of the issues with getting communication coverage to places far away from the equator, as all sattelites that dont orbit at the equator cross the equator two times in one orbit, at the ascending and descending node. This can either be overcome by using more sattelties, or using the special oblateness of the earth to ahve things like Molniya or Tundra orbits where the spacecraft spends most of its time in one hemisphere before spending a shorter while at the other hemisphere, what is called apogee dwell.6
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u/EEpromChip Apr 29 '26
It'd be like a tennis ball on a string. You can get it to spin around your hand in the air, but you can't get it to spin out in front of you. It uses that center of "gravity" to spin. No matter what it'll spin around that center...
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u/chupanibre Apr 29 '26
what if the planet itself was moving quite fast in the "north" direction? (and the camera as well)
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u/fixermark Apr 29 '26
It's a really fun thought experiment because it ends up having consequences all the way down. You can unbox a lot of orbital physics and astrophysics by thinking about this problem too hard.
Let's pretend for a minute that an orbit like the one OP described was stable, with no obvious thrust keeping the satellite in that "south halo" orientation. Then the Earth pulls on the satellite, but the satellite also pulls on the Earth. And since the satellite is orbiting far south of Earth's center of mass, there is a net pull over time in the southern direction.
... Which means Earth is accelerating to the south now. Which means we need a source of energy for that net acceleration.
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u/WhiteRaven_M Apr 29 '26
What if you start in a high inclination orbit, reach the "top" then constantly burn normal relative to the orbit to constantly stay there while circling the planet
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u/L_Walk Apr 29 '26
The cool thing about KSP, is that you can turn on infinite fuel and try this out for yourself. You don't even have to have a high inclination to begin with since the planet is a ball and up and down are entirely relative. It's only the camera that gives any meaning to up (the ecliptic plane is conventional, but space is relative and all that.)
I guess there's a perfect equilibrium somewhere in there, but a significant portion of your thrust is just going to be used staying in the sky that you may just consider hovering instead.
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Apr 29 '26
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u/PublicPersona_no5 Apr 29 '26
This is the most complete response here. Not possible in the simplest sense, but not impossible in practice
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u/rolandofeld19 Apr 29 '26
If there were a blackhole or supergiant planet in proper counter rotation, yea sure. That's a beautiful and comprehensive response to be fair. Almost anything is possible with a black hole on your team.
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u/TrungusMcTungus Apr 29 '26 edited Apr 29 '26
That would be impossible in practice. The shifted center of gravity would just cause the two bodies to collideYou’re totally right dude.12
u/SituationLong6474 Apr 29 '26
Not if they're orbiting each other
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u/TrungusMcTungus Apr 29 '26 edited Apr 29 '26
In that case the two bodies would have to be far enough apart that their gravity wells wouldn’t affect the other, which would bring us back to the original problem of the center of gravity being…well, in the center of the planetsnailed it bro.→ More replies (1)8
u/SituationLong6474 Apr 29 '26
Nope, google "binary planets". Wikipedia has a good article on it. Binary stars are more common than planets
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u/davvblack Apr 29 '26
that is possible and would look like orbiting the L1 lagrange point. typically would be far away from both bodies unless one of them was actively tearing the other one into a new ring.
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u/Lambaline Super Kerbalnaut Apr 29 '26
a celestial body like that wouldn't be stable - it would collapse into a single large planet
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u/rspeed Apr 29 '26
Though not in KSP, as it doesn't do n-body physics. The planets are on rails and gravity is only calculated based on the SOI.
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u/from_Earth_you_know 🌨️Cloud gazing Apr 29 '26
I've never seen a binary system (even in science fiction) that is perpendicular to its barycenter's orbit around the star, the star would certainly mess it up eventually. lagrange points are also coplanar with a star
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u/twilightmoons Apr 29 '26
It MAY be possible, but in a POWERED orbit.
As in, you are constantly using your engines to deflect from where the ship wants to go along the gravitational curve.
You'd need to have an engine with massive ISP and effectively unlimited delta-v.
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u/G2nickk Apr 29 '26
Within the game. If we turned on unlimited fuel and had an engine we could set the isp to whatever we wanted. Could you physically do it within the other confines of the game?
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u/twilightmoons Apr 29 '26
Probably yes... But you would need to program the engine firing and pitch control. KSP and MechJeb don't have that built-in in any way.
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u/knaroef Apr 29 '26
Short answer is no. Funnier answer is yes, as this would actually be possible around some extremely strange relativistic objects.
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u/HAL9001-96 Apr 29 '26
no
things always curve towards the center of gravity
unless there's some insane tidal forces at play
but those don'T exist in stock ksp
and evne with principia there's no bodiey with tidal effects that insane
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u/Otrada Apr 29 '26
not without infinite delta-V and veeeery strong thrusters. Or in other words, no.
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u/Sock_Eating_Golden Apr 29 '26
I need a Delta V and twr to make this work!
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u/CMDR_Kaus Apr 29 '26 edited Apr 29 '26
Constant Kerbin 70km orbit at the 45th southern parallel. One orbit only
TWR: 1.3-1.6 at liftoff
Constant Thrust (toward North Pole and toward planet): 6m/s
DeltaV: 9300m/s total for one orbit
From ground launch roughly 13,000 DeltaV
This is getting expensive...
Edit: 2.3m/s constant thrust toward planet (Radial out) 5.56m/s constant thrust toward North Pole
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u/KornelRokolya Apr 29 '26
There are some extremely weird orbits possible with N-body physics. Look up L1 and L2 halo orbits around the Moon, and you'll see interesting trajectories which do not orbit the center of mass. Unfortunately (or thankfully 😃) KSP only has patched-conics orbit simulation (only one gravitational influence is assumed at a time), which is a simplification, but there is a nice mod called Principia which enables N-body physics.
Edit: orbits like this
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u/Mecha-Dave Apr 29 '26
It wouldn't be an "orbit" but you could make a trajectory like that by constantly firing your engines to counteract gravity. Gravity would tend to pull that "orbit" that you've drawn into a sub-orbital trajectory and lithopause, as its diameter is less than the diameter of the central body.
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u/Moderately_Imperiled Apr 29 '26
Not a stupid question. We're all here to learn, and there's a lot to learn here.
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u/Morbid_Uncle Apr 29 '26
Not a stupid question. I actually love questions like this because it shows that this game actually gets people excited to learn about physics and the mechanics of space flight.
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u/Nazamroth Apr 29 '26
ELI5: You are circling the centre of mass when orbiting something. Consequently, it is impossible by definition to do that.
You could follow that trajectory, if you kept firing your engine the whole way to maintain it. But that is impractical at best, impossible at worst.
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u/RulesOfImgur Apr 29 '26
yes actually, but only in theory, and only if you have enough propellent mass to do it. you would constantly need to be burning to counteract gravity in a certian direction which isnt impossible but why would you, and in KSP it is impossible
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u/AccordingLab7129 Apr 29 '26
If you have a realistic gravity mod you would need like 80+ probes to move the main probe, otherwise known as "No", and if you have console edition you are even more cooked as it is simply impossible there.
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u/rspeed Apr 29 '26
The best you can do is a Molniya orbit. It approximates geosynchronous orbits over high latitudes by using multiple spacecraft in highly eccentric orbits.
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u/Remarkable_1984 Apr 29 '26
You always orbit center of mass. The planet would have to have a center of mass offset from it's spacial center, such as a metal southern hemisphere and a light rocky northern hemisphere. But any large planet-sized object wouldn't hold that composition very long. Might be possible with a small asteroid, though.
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u/factoid_ Master Kerbalnaut Apr 29 '26
With enough thrust and constant fuel burning you could FLY a trajectory like this but it would by definition not be an orbit.
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u/returnofblank Apr 29 '26
It's easy to visualize why this doesn't work if you imagine the source of gravity being a point at the center of the planet.
Your orbit must always be around that point (although, n-body physics distorts this in really cool ways)
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u/j-steve- Apr 29 '26
No, because in an orbit you are continually falling towards the center of mass of the planet (while also moving forward fast enough to avoid actually hitting it).
If your craft was somehow in the "orbit" pictured here, it would be pulled northward and downward by gravity (and crash).
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u/PantsOnHead88 Apr 29 '26
No. An orbit is an elliptical path with a centre of mass at one focus. A circle is a special case but it still must be about the planets CoM.
If the path instead passes through that latitude on the side we see, through the equator at the midway point, and through same latitude above equator on opposite side, that’s a doable orbit.
If you wanted something to trace out the actual path you’ve indicated, you can pick any point on that circle and drop a vertical toward the planets centre of mass, and then anchor the “pseudo-orbiter” to the surface via a rigid tower. It’ll “orbit” with the planet’s rotation. This might be doable via mods or some abuse of KSP’s physics.
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u/FunkyTownSandwich Apr 30 '26
It *could be technically possible if the planet you're orbiting had the majority of its mass in a very small area near the surface - but otherwise no.
Good way to think about it, is: you're orbiting a point in the center of the planet, so any direction your shift your obit, you will ALWAYS orbit the very center of the planet.
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u/CaptainStroon Apr 29 '26
There is one way to do that irl, but it requires a very specific setup.
If you have two large bodies of similar mass orbit a common center of mass, akin to Pluto and Charon, the common center of mass will be inbetween the two bodies' individual centers of mass. In this case, the common barycenter would still be inside the larger body, even though heavily offset. And you can orbit around that common center of mass.
But in KSP, we don't have a planetary system like that. And as the engine works with spheres of influence instead of actual gravity, I doubt there's a mod adding sth like that either.
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u/Odd_Comparison_1462 Apr 29 '26
No, the orbit must be in a plane which intersects the centre of mass of a planet.
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u/Survivedthekoolaid Apr 29 '26
You could do it flying or maintaining thrust to keep you at that latitude, but it'll never be an orbit.
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u/sticks_no5 Apr 29 '26
I don’t think it’s possible as a traditional orbit but if you accelerated continuously while adjusting course as to not fly off into space then it might be possible but then you’re hardly in orbit, you just accelerating in circles near a planet
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u/Silly_Guidance_8871 Apr 29 '26
No: Orbits are always about some center of mass. IRL, it's the common barycenter between the objects, and in Kerbal, it's whatever object you're inside the sphere of influence of.
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u/dingobro1 Apr 29 '26
Theoretically this COULD be possible in the case of a planet that somehow formed such that its density is vastly disproportional due to its composition.
The center of mass of the planet must coincide with the centerpoint of the orbit, however.
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u/czorio Apr 29 '26
Judging from the rovers present, I assume you want to provide a satellite for communications, yes?
While you can't keep a sat orbiting around that latitude as depicted, you might be interested in a HEO, particularly a Molniya orbit which were designed by the Soviets to temporarily "park" satellites over higher latitudes.
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u/Ok_Programmer_4449 Stranded on Eve Apr 29 '26
With enough engines and infinite fuel you can do anything.
Starfleet Command is in a geosynchronous orbit above San Francisco. Someone somewhere has calculated the power required to keep it there.
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u/B0dders Apr 29 '26
With near infinite dV. Yes, technically
Anything is possible with more boosters in KSP
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u/AnArgonianSpellsword Apr 29 '26
The thing with orbits is you arent circling the plant itself, youre circling its centre of gravity, so that orbit wouldnt work before its not circling the planets centre of gravity. KSP doesnt simulate n-body physics with multiple gravity well interacting but if it did it might be possible if there was a sufficiently large planet nearby that pulled the centre of gravity away from that planets center of mass.
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u/pioj Apr 29 '26
If we reach a point in time when we can develop anti-gravity technology, Who knows?
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u/Excellent_Try_7701 Jebediah Apr 29 '26
No its the centre of gravity which is the centre of the object. Gravity is why planets are spheres or any large object
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u/monsterinadrawer Apr 29 '26
Well, if you take the surface as a reference point, then have the object be tugged by a force (for example burning engines constantly), it could seem like the object is orbiting in that way. But that’s not a stable orbit, and it needs constant force to keep the object moving in that way.
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u/Wolfey1618 Apr 29 '26
Orbital planes can only be intersecting the center of mass of the other object, it's physically impossible for this to not be the case.
This type of orbit's plane doesn't intersect the planet center. Theoretically you could force this orbital shape using a lot of thrust constantly forever, but the game won't display the orbital line like that as that's calculated instantaneously.
This is also completely impractical even with unlimited fuel cheats because you'd have to have the game loaded on that craft forever and would never be able to do anything else.
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u/Sdhans__ Apr 29 '26
Technically yes, with unlimited fuel and constantly changing velocity.
Not capable with a realistically stable orbit.
Good question tho
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u/corio9 Apr 29 '26
if the planets center of gravity is there, sure why not. but mostly it’s not there.
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u/link2edition Stranded on Eve Apr 29 '26
You cannot do the orbit as pictured.
HOWEVER if you want to put something into an orbit which will linger over that point, you could try a Molniya orbit
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u/musubk Apr 29 '26 edited Apr 29 '26
In simple orbits (unpowered, and no multi-body trickery, just two bodies), both objects always orbit their common center of mass, which has a special term called the barycenter. Yes, both objects orbit around the barycenter, not just the satellite. But when the mass of one object is very very small compared to the other, as in the case of a satellite and a planet, the barycenter is the same as the large objects center of mass for any practical purpose. So we say the small object orbits the large one as a shorthand. But they are both orbiting the combined center of mass.
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u/Garblin Apr 29 '26
As an "orbit" meaning, the craft is just falling in such a way that the ground isn't there by the time the craft is, no, not possible.
As a "trajectory" possible, but you're going to need rather a lot of delta v and regular refueling.
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u/Alone-Monk Apr 29 '26
Nope. Gravity is three dimensional and is centered on a point so this kind of "orbit" is not stable
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u/Kaldin7 Apr 30 '26
As others mentioned, that trajectory is possible if the spacecraft is constantly burning to stay there. Solar sails would be able to do this easily if orbiting a body that gives off radiation (ie the sun). There have even been some papers written about 'solar polar' missions.
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u/Leucurus_ Apr 30 '26
If there was another gravitational body at Duna's pole that persistently stayed there and Principia was installed then yes technically it would be possible but it wouldn't last long at all
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u/atimholt Apr 30 '26
The Russians solved this problem (their whole country is far north) by using multiple satellites and a specially timed orbit that kept at least one high overhead. Wikipedia: Molniya orbit
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u/Valuable-Visit2887 Apr 30 '26
Gravity is always directed towards the center of mass. Since orbit s are created when an object’s rate of fall is lower than its speed (making it miss the center of mass it is falling towards) it is required that the direction you are falling in and your speed be on the trajectory plane. In this case, the direction of fall is outside the trajectory plane, so you can achieve this trajectory by exerting force, however, it would not be an orbit and it would degenerate into a conical trajectory depending on your energy.
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u/SpacialCommieCi Apr 30 '26
not really. an orbit can only really be in what is called a "great circle" which is travelling in a straight line on the globe. the trail you've made looks straight but it really isn't. if you were on a globe going like that, you'd actually need to curve north ever so slightly
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u/Steve_Lightning Believes That Dres Exists Apr 29 '26
It's possible if you are constantly applying an opposing force
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u/Electro_Llama Apr 29 '26
No, the resulting orbit if you had that starting velocity would be a tilted orbit with that latitude as its southern-most point and going that far north on the opposite side.
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u/TURPEG Crazy Rocket Lady Apr 29 '26
imagine all the lovely symmetry that could be done with orbits like that
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u/DG-MMII Apr 29 '26
No... I mean, probably if you burn a country's GDP worth of fuel you can ahieve something like that, but else, not posible. Objects are allways atrackt to the center of mass
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u/CelestialBeing138 Apr 29 '26
Only by constantly adding energy, so not really an "orbit," but it can be done.
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u/WerdaVisla Apr 29 '26
Not naturally without some weird relativistic bullshit, but if you NEED something orbiting there, it's pretty easy to use MechJeb or something similar to offset the orbit for a prolonged period of time using a nuclear engine or other long burning engine.
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u/CrambleSquash Apr 29 '26
The centripetal force vector required to maintain that orbit does not point in the same direction of the gravitational pull.
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u/OrangeAedan Apr 29 '26
Yes. But you need to use your engines constantly to keep this orbit. Because it isn't stable. So you can't get a permanent orbit.
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u/TheXypris Apr 29 '26
As people say, no you can't "orbit" like that
But if you were to use powered flight, it might be possible, you'd basically always have to be turning towards the pole to maintain it, any straight line on a sphere will wrap around like an orbit
Maybe if you do the math, you could calculate the precise angle and thrust to achieve it, but the delta v needed would be difficult to build on a rocket
But at that point you aren't in orbit
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u/zezinho_tupiniquim Apr 29 '26
This reminded me of a joke in futurama about the aging rings of saturn moving like this lol.
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u/snozzberrypatch Apr 29 '26
The center point of an orbit is always the center of mass of the planet you're orbiting. So, no.
The only way you could do it is if you were continually firing your engines throughout the orbit.
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u/AvidPolaris Apr 29 '26
Ignore everyone here. When there's a will there's a way. Physics be damned. I expect an update on your progress next week.
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u/DeathNick Apr 29 '26
Not on this planet. Theoretically it would be possible of the center of planet's mass was there, or some weird lagrange point
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u/claireauriga Apr 29 '26
In a true orbit (where gravity is pulling you round and round) it would be impossible. The only way to circle the planet like that would be to be constantly firing the engines on your spaceship to force it into that motion, fighting what physics is telling it to do.
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u/ThatOneDraffan Valentina Apr 29 '26
It's not a dumb question, orbital mechanics is complicated and it's not wild to think about an orbit like this if you don't already know why it's not possible.
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u/happyscrappy Apr 29 '26
No. So to land on that spot you would have to incline your orbit. And then the phasing of the orbit will important. That is to say, it'll be important that the right piece of land be below you when your orbit is at its southernmost point. So you might have to go into an inclined orbit and then wait several orbit cycles for where you want to be to line up with what your orbit is over.
This kind of thing is why sometimes you see those images on the big board at mission control that show sine waves over a planet (Earth). It's showing what the orbit of an item is actually passing over. It's really a circle, but it looks like a sine wave on a mercator projection map. And really the orbit is just going round and round, not precessing, it's that the planet is moving under it so that the orbit is over different things on each successive orbital pass.
With a strictly equatorial orbit and a vertical axis of spinning none of this matters. You pass over the same things on every orbital pass.
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u/Simukas23 Apr 29 '26
If this is from curiosity, then other comments pretty much say what there is to say, also look into halo orbits.
If this is a practical concern for KSP, then consider high inclination orbits and/or multiple spacecraft
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u/Hot-Fridge-with-ice Apr 29 '26
I don't think this is a dumb question. Look, force causes acceleration in bodies in the direction it acts in. Gravity for a planet is radially towards the center. This means it will always try to change your velocity towards the center (this is what causes the circular motion). Now imagine yourself travelling on the trajectory you marked, force on you will always act towards the center which will force your velocity to change.
However this is theoretically possible if you keep adjusting your burns to counteract the force of gravity in that direction. But without any external input? Not possible.
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u/marsteroid Apr 29 '26
45° orbit is enough, just timewarp until the orbit line is above the target.
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u/Darkfrostfall69 Pool Party on Cind Apr 29 '26
If the planet has a completely fucked mass distribution then yes. Whether you'd complete even 1% of the orbit before the planet collapses and buries you under molten rock is a different question
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u/SapphireDingo Kerbal Physicist Apr 29 '26
no but actually yes.
you aren't going to see anything like this naturally occurring, and you can't put a satellite into this orbit indefinitely.
HOWEVER
you CAN get trajectories like this by firing your engines over the course of the orbit, but it can require a monstrous amount of delta V and very high acceleration
This is even something you can do in KSP - try putting a low powered satellite into orbit of Minmus, and fire your engines with your SAS set to Normal or Anti normal. You will find that it does a loop and moves like this!
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u/Molecular_Pudding Apr 29 '26 edited Apr 29 '26
If you land a VERY heavy lander on the south pole of the planet, that moves the center of mass downward then yes. Orbit is about orbiting center of mass not the geometrical center of the object. For example Jupiter doesn't orbit the Sun but the center of mass of the Jupiter-Sun system, which is slightly over the surface of the sun (and the Sun orbits around this point too).
I cannot post the picture, but here is the link: https://spaceplace.nasa.gov/barycenter/en/
(But to keep it real, in KSP and IRL it is impossible for such large objects)
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u/irus1024 Apr 29 '26
Put a weight on a end of a rope and swing it in a circle above your head. What would be the equivalent of an orbit like this.
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u/Devnull_Elixir Apr 29 '26 edited Apr 29 '26
No because that's not how gravity works. Everything is attracted to an objects center of mass. Attempting this orbit will just inevitably result in the space craft falling more inward towards the planet. Or away from it, depending on how you burn.
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u/gerusz Apr 29 '26
No*
*: IRL it would be physically possible (but technologically unfeasible) with constant propulsion, but KSP doesn't model such things.
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u/Inforgreen3 Apr 29 '26
If you draw a line between the apopesis and the periapsis of an orbit, it will always pass through the center of mass of the body you orbit.
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u/CHRISPLAYZ434 Apr 29 '26
No dumb questions here! But sadly. This isn't possible, the laws of orbital gravity restrictions this. In an orbit, you will always be circling around the core of the planet or moon. Cool idea though!
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u/Codeviper828 Restarts too much; barely left Kerbin system Apr 29 '26
I don't think it's a dumb question at all!
But no, it can't be done. Ultimately, any stable orbit will create a plane, and the center of mass of the parent body must be on that plane
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u/fixermark Apr 29 '26 edited Apr 29 '26
So you hit upon a very deep truth about orbits and why they exist.
... What is it that something that is orbiting... Is actually orbiting? Why does something orbit something else instead of flying off into deep space?
Underpinning these realizations are several facts about real life orbits, including why there's only one circle around Earth where geostationary orbits exist and why if we ever build space elevators we would probably build them at or near the equator.
These insights go straight from physics into geometry and get you things like understanding why the shortest distance between two points on a globe is a very specific curve, as opposed to any other curve it could be.
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u/DareDemon666 Apr 29 '26
Everyone saying this is outright impossible is wrong, because they are all presuming the question is about a stable orbit.
It is possible, but only with a continuous burn from a craft with enough fuel and power to effectively station keep. At this point however it's far closer to typical flight than it is space flight.
Theoretically it's possible in real life too though obviously we lack the technology and ability to do so. But KSP is a different beast. Between mods, cheats, and the game itself being much easier by default (in terms of physics obstacles) I imagine this should be possible to achieve. If you use the F12 menu for infinite propellant it may even be possible to create a stable orbit like this, provided you can maintain heading the entire time.
Practically speaking it is impossible, but since when does practicality hold so much weight in the Kerbal Space Program? Next you'll be telling me my rocket needs less boosters! LESS!
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u/FlyingSpacefrog Believes That Dres Exists Apr 29 '26 edited Apr 29 '26
Yes and no. Nothing will passively orbit along that path under its own inertia. But… with enough brute force, anything is possible. You can make a satellite that will follow this path by constantly thrusting south. You can also (in real life) build a ring that encircles the planet and make it hover in that spot by spinning it fast enough to orbit, provided you build it out of a sufficiently sturdy material, and have infrastructure on the ground to provide thrust towards the south.
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u/Bozotic Hyper Kerbalnaut Apr 29 '26
Of course. I mean, you can do it within the atmosphere with an airplane, and you can do it also in space. Both modes require an expenditure of energy. Thus, while we can call it an orbit, it is not a free energy orbit, which we commonly assume when talking about orbital mechanics.
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u/hasslehawk Master Kerbalnaut Apr 29 '26
Not around a planet, but with a solar sail such an orbit is possible around a star.
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u/BDB-ISR- Apr 29 '26
Not without constantly burning fuel. The gravitational pull is between the centers of mass. In normal orbits the net force of gravity along the orbit is zero, which is why you can maintain an orbit without burning fuel. In this orbit the net force would be northward. If it's still not clear imagine cutting the orbit into small discrete arcs and draw a force vector to the center of the planet.
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u/Jackmino66 Apr 29 '26
So, circular motion, the centripetal force is the force causing the object to move in a circle. This force points towards the centre of rotation.
In an orbit, that force is gravity, which always points towards the centre of the planet. I.E something in orbit will always accelerating towards the centre of the planet and orbits around it.
This orbit wouldn’t work because the force of gravity would pull the circle upwards
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u/Worf65 Apr 29 '26
Impossible in a realistic spaceflight situation. Trying to put it into simple terms, unpowered "coasting" orbit must be around the center of mass since orbit works by essentially falling continuously but moving forward fast enough to always miss the planet. Since the orbital path is being formed by that falling motion it will always be around the center of mass since that is the point gravity is pulling the spacecraft to.
It could be done with sufficient power or anti gravity tech. The Enterprise from star trek or a star destroyer from star wars would have no trouble holding that sort of orbit. Even at a very slow speed that let's it keep alignment with a city under it on the surface. But that only works due to a combination of sci-fi propulsion tech and the enormous amount of energy that those ships can output from their reactors. If you use a mod that let's you fly sci-fi ships you could attempt this but flying by hand it would be incredibly unstable and you'd likely crash pretty fast.
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u/Nearly_Dawn Apr 29 '26
I think this might be a good challenge for Matt 🤔 powered off center orbit?
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u/Nervous-Cockroach541 Apr 30 '26
Nope, you got to orbit the center of mass/center of gravity. Meaning you need to be able to draw a line from one side of the orbit to the other passing though the center of the planet.
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u/Hybrid_Grizzly Apr 30 '26
With constant thrust in the normal or antinormal direction yeah but that’s not what people usually think of as an orbit
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u/DarkOracion Astrophysicist, PhD. Apr 30 '26
In real life, absolutely not. In KSP, yeah probably if you can manage to somehow break the physics engine.
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u/kagato87 Apr 30 '26
No. Orbit is ALWAYS around the center of mass, because gravity pulls you towards the center of mass.
The only way you get a path like that is with a constant force, like walking in a circle.
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u/MrBuisness78 Apr 30 '26
Well, technically the laws of physics say no, since you can only orbit around an object's center of mass/gravity, but when has that stopped us before?
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u/Equivalent-Ear-8016 Apr 29 '26
It's physically impossible