How can I put a space station in a locked orbit around kerbin with the Mun?

[grievous056]

I would like to set up a space station that will be at about half way between kerbin and the mun, and that while orbiting kerbin will always remain lined up with the mun. Does anybody know if this is possible and if so, how?

[maltesh]

It's not possible.

Any object in orbit around Kerbin with a period equal to that of the Mun has to have a semi-major axis the same as that of the mun. In the KSP physics simulation (and in general, in reality, with a few significant exceptions) any object whose orbit is entirely inside the Mun's orbit will have a period shorter than that of the Mun, and will drift (or race) out of the line of Kerbin-Mun alignment.

[Ydoow]

What maltesh said, but with a little less jargon for those with a lesser vocabulary:

Gravity becomes weaker the farther away from the planet you are, so your craft requires less speed - less centrifugal force - to counteract gravity.

Obviously, the slower you are going, and the larger your orbit (having a larger altitude) means you have a slower orbital period (time to complete 1 orbit).

The inverse is true also, being closer means you have to go faster, and have a shorter orbital period.

With a few exceptions that aren't modeled in KSP, every altitude will require a different orbital speed, and therefore a different orbital period.

--The only way to make a space station stay synchronous with the Mun is to have it at the same altitude as the Mun

[Cykyrios]

... Or have your ship tethered all the way to the Mun - not exactly feasible . Of course, in real life, you could try orbiting at the Lagrange point, where the gravity pull from the two bodies is equal.

KSP physics don't allow for this, though, so what you want to do is not possible.

[AncientAstronaut]

Actually... It's possible. But EXTREMELY HARD. Put a rocket on your rocket that is pointing anti-radially (towards the planet) and thrusting while you orbit. Essentially adding MORE gravity and forcing you to have to move faster to continue orbiting at that altitude. It would be so ridiculously difficult and require so much serious math that you're unlikely to want to even try. Also, you wouldn't want to go faster, you'd want to go slower. Making it even harder.

Just take the idea that it's not possible as easier.

[Cykyrios]

If you somehow find a way to get unlimited fuel (and I'm not talking about cfg edits or the dev tools), your powered orbit isn't going to last long. But yeah, it would theoretically be possible to compensate gravity with some thrust.

[Carl]

Yeah not possibble sadly, though you may be able to setup a free return trajectory between kerbin and the mun and thus get it to sort of track the whole way, but i have no idea how you'd actually go about setting anything up in one of those. Maths heavy for sure.

[hubbazoot]

About the best 'alternative' I could think of would be to put something in synchronous orbit, which would be 2900 km from the Mun, which is a problem since its sphere of influence is 2.4km.

I think you could, in theory, get a figure 8 orbit between the Mun and Kerbin at least once, but I don't think you'd be able to get it to repeat itself in a really viable manner.

If you want something near the Mun that would remain relatively stationary, you could put a satellite up in orbit at the height of the Mun and either have it 'chase' the Mun or have the Mun chase it.

[rkman]

Actually... It's possible. But EXTREMELY HARD. Put a rocket on your rocket that is pointing anti-radially (towards the planet) and thrusting while you orbit.

It's possible but by definition not an orbit.

orbit

1. (Astronomy) Astronomy the curved path, usually elliptical, followed by a planet, satellite, comet, etc., in its motion around another celestial body under the influence of gravitation

http://www.thefreedictionary.com/orbit

[Meteora]

I doubt its possible. Though its possible to have a vessel orbit as far as to Mun's orbit and back to Kerbin, just not following the moon.

Don't ask me how I did it, it was a fluke. I still haven't been able to land on Mun because I derped my landing and ended up with this orbit.

[pebble_garden]

You might try parking a station on the Mun's orbit, in a different location.

For example, if the Mun is at 12 o'clock, try placing the station at 10 or 2 o'clock in the same orbit, moving the same speed and direction.

In the real world there are a few points of gravitational stability (relatively speaking) called Lagrangian Points (http://en.wikipedia.org/wiki/Lagrangian_point). Specifically, the L4 and L5 points might be useful for you.

I'm pretty sure KSP doesn't model this phenomenon, but if it thinks you are in Kerbin's Sphere of Influence - not the Mun's - I can't think of a reason the parking orbit wouldn't be stable.

[maltesh]

Another option is the quasi-satellite orbit; In a 1:1 orbital resonance with another satellite, but sufficiently elliptical and/or out of phase so that it never enters comes under the influence of the other satellite. It's so named because, from the rotating frame of reference in the viewpoint of the other satellite, the quasi-satellite appears to trace out a weird, retrograde oblong orbit around the satellite.

I was experimenting to see how little of an eccentricity I could get with synchronized quasi-satellites on the Mun and Minmus' orbits, without ever entering either body's SOI, while maintaining a synchronicity that put the Mun/Minmus directly below the quasi-sat at Apopasis, and directly above the quasi-sat at periapsis.

As I recall, I was able to place a stable Mun-Synchronized quasisat with the above restrictions with an eccentricity as low as 0.25, For Minmus-syncrhonicity, I was able to go down to 0.075, and for Kerbin, managed 0.01.

Though, as implied upthread, this doesn't satisfly the OP's specific request either.

[Yourself]

... Or have your ship tethered all the way to the Mun - not exactly feasible . Of course, in real life, you could try orbiting at the Lagrange point, where the gravity pull from the two bodies is equal.

KSP physics don't allow for this, though, so what you want to do is not possible.

To be specific, the Lagrange points are not where the gravitational pull from both bodies is equal. At the L1 point (the point between Kerbin and the Mun), Kerbin's gravitational pull is actually slightly stronger. It has to be stronger in order to provide the necessary centripetal force to keep the spacecraft moving in a circle. Lagrange points are simply those points where a low-mass object can be placed such that it will remain in that spot relative to the other two co-orbiting bodies (although some of these points are unstable, so if you're not exactly on top of them you'll gradually move away from them).

[Bluejayek]

As hubbazoot mentioned, the only way to do this would be a munosychronous orbit. Since the Mun is tidally locked, this would stay in the same spot relative to both the Mun and kerbin at all times.

Unfortunately, the SOI is 2400km, and munar synchronous orbit is at 2900km, so this is not possible.