SOI map for KSP?

[WhiteWeasel]

I would like to see a map that shows the influence radius or "hill spheres" of the planets & moons so we know where we could park our ships without having them accidently encountering any planets or moons.

Edited June 17, 2013 by WhiteWeasel

[Tw1]

I haven't seen one around, but it shouldn't be too hard to put together. The figures from the wiki are probably accurate.

[Vuktars]

I have all the data from that wiki . Every planet and moon has a detail description there. Including sphere of influence and synchronous orbits.

But I like maps and lists like WhiteWeasel too. So I collect data and ... link

Red marked Sync-Orbits are not applicable, because they are outside of the sphere of influence.

But keep in mind that the SOI in KSP is different (one-body). Inside of it, there is no influence from the parent sun/planet. Outside of it , no influence of the moon like it would be in reality. No Lagrange points f.ex.

[Brofessional]

Pretty sure this is still accurate. It doesn't list data on the moons though.

[Tank Buddy]

There is an image for the SOIs of the Joolian moons; I recon that is the only location you would really need that info. Otherwise you just need to look at the size of the SOI in the wiki.

Edited August 1, 2015 by Tank Buddy

[Geschosskopf]

On the subject of SOIs.... I get the distinct impression that they're not actually spherical. In fact, seems to me there's a noticeable Doppler Effect that makes SOI's more teardrop-shaped, shorter in front and longer behind the planet/moon along its direction of motion. But the game's left hand doesn't know what it's right hand is doing, so you see everything displayed as if the SOI was spherical. But then suddenly you get a surprise encounter when passing close behind the body because some part of the game has been making the SOI really is elongated. And when the display part of the game realizes this, it often summons the Hell Kraken because of the internal conflict, instead of showing you in the body's SOI, which it thinks really isn't there.

That's my theory anyway. I dunno. I do know, however, that satellites positioned at a fake Lagrange point behind a body tend to get thrown all over space, and that interplanetary ships passing close behind Mun on the way out of Kerbin tend to get eaten by the Hell Kraken a lot. Maybe this is because the planets move continuously but their SOIs move in periodic steps. so the SOIs really are spherical but not always centered on the body. Or maybe I'm just nuts.

[Vuktars]

Nice maps. It seems that I have to keep my arrival orbit around Jool, for my future Laythe mission, small. So that I won't crash into an other moon.

@Geschoßkopf: I can't remember trying to place a craft near the SOI border, so I have no experience. But to KSP, an object 1m inside the sphere is orbiting the 'moon' and 1 m outside it is orbiting the planet. A rough edge. So I can image that placing crafts ON that border on the fake L1 and L2 point you mention, that tiny rounding miscalculations building up to kick your craft somewhere.

[Kobymaru]

On the subject of SOIs.... I get the distinct impression that they're not actually spherical. In fact, seems to me there's a noticeable Doppler Effect that makes SOI's more teardrop-shaped, shorter in front and longer behind the planet/moon along its direction of motion. But the game's left hand doesn't know what it's right hand is doing, so you see everything displayed as if the SOI was spherical. But then suddenly you get a surprise encounter when passing close behind the body because some part of the game has been making the SOI really is elongated. And when the display part of the game realizes this, it often summons the Hell Kraken because of the internal conflict, instead of showing you in the body's SOI, which it thinks really isn't there.

That's my theory anyway. I dunno. I do know, however, that satellites positioned at a fake Lagrange point behind a body tend to get thrown all over space, and that interplanetary ships passing close behind Mun on the way out of Kerbin tend to get eaten by the Hell Kraken a lot. Maybe this is because the planets move continuously but their SOIs move in periodic steps. so the SOIs really are spherical but not always centered on the body. Or maybe I'm just nuts.

That's what it is! I swear to god I placed a leading communication satellite in perfectly Mun-synchronous Orbit right outside the Mun SOI. Next time I check back there, satellite is in eccentric orbit. ...?

Then, when I fixed the orbit and while I was resynchronizing, the "orbit line" shows no encounter, so I just timewarp. Suddenly BAM !!surprise encounter and I'm out again. There's something seriously weird about how KSP does SOI transitions.

Can we make this a little science project, where the SOI actually end and begin?

[GoSlash27]

On the subject of SOIs.... I get the distinct impression that they're not actually spherical. In fact, seems to me there's a noticeable Doppler Effect that makes SOI's more teardrop-shaped, shorter in front and longer behind the planet/moon along its direction of motion. But the game's left hand doesn't know what it's right hand is doing, so you see everything displayed as if the SOI was spherical. But then suddenly you get a surprise encounter when passing close behind the body because some part of the game has been making the SOI really is elongated. And when the display part of the game realizes this, it often summons the Hell Kraken because of the internal conflict, instead of showing you in the body's SOI, which it thinks really isn't there.

That's my theory anyway. I dunno. I do know, however, that satellites positioned at a fake Lagrange point behind a body tend to get thrown all over space, and that interplanetary ships passing close behind Mun on the way out of Kerbin tend to get eaten by the Hell Kraken a lot. Maybe this is because the planets move continuously but their SOIs move in periodic steps. so the SOIs really are spherical but not always centered on the body. Or maybe I'm just nuts.

This would make sense, since the gravity of the parent body is stronger on the downhill side. This is reflected in the math to determine the SoI.

The change in SOI occurs where the moon's gravity is stronger than the planet.

Best,

-Slashy

[Gargamel]

This would make sense, since the gravity of the parent body is stronger on the downhill side. This is reflected in the math to determine the SoI.

Best,

-Slashy

The way I'm reading that is that you're implying there is a doppler like effect on gravity?

[GoSlash27]

The way I'm reading that is that you're implying there is a doppler like effect on gravity?

gargamel,

Not "doppler like" per se. Just that the formula would predict an oblate spheroid boundary rather than a sphere.

The gravitational attraction of the smaller body is uniformly spherical, but in the region of the smaller body, the attraction to the larger body is higher closer in than farther away.

This, coupled with the fact that the larger body tends to pull you into an encounter with the smaller body when you're on the far side, but pulls you away when on the near side means that the SoI boundary would tend to be egg-shaped rather than spherical.

Best,

-Slashy

Edited August 2, 2015 by GoSlash27

[FancyMouse]

It is a sphere. It's just not centered at the planet, but a little further, depending on their mass ratio. Doing some careful computation can reveal that. In particular, if the two planet has the same mass, then the "sphere" degenerates to a plane (with infinite radius) placing in the middle of them.

[Pecan]

...Just that the formula would predict an oblate spheroid boundary rather than a sphere....

Exactly like the tides on Earth, for instance ;-0

(Trouble is, Geschosskopf said in the pro/retro direction, not radial)

[GoSlash27]

Exactly like the tides on Earth, for instance ;-0

(Trouble is, Geschosskopf said in the pro/retro direction, not radial)

Oh... I see what you mean!

Yeah, the math (as I understand it) wouldn't predict that. I really can't comment on that since I've never experienced it myself.

Best,

-Slashy

[FancyMouse]

Ok some more math. Let me define my question first - I'm finding the geometry where the gravity from two bodies have the same scalar value. I call it my SoI. Suppose if we have two celestial bodies with mass m1, m2 with distance d, and m1<m2, and we look at my SoI radius around m1. Let ratio lambda = m2/m1 - 1 (which is positive by assumption), then SoI sphere center is away from m1 (outside m1 in the direction from m2 to m1) for d/lambda, and my SoI radius is d*sqrt(lambda^-1 + lambda^-2).

It degenerates correctly - when lambda->0 (m1=m2), radius->infinity (becomes a plane), and radius - center_offset->d/2 (middle of the two bodies).

Now, this doesn't seem to match game's stats - for Mun my computation is showing 221km of center offset with 1645km of SoI radius (wrt that center) - different from game's 2430km

So at least in game, SoI boundary doesn't mean equal gravity (and verified by hyperedit testing). So now I don't know what to say further...