Get into Kerbomunar-Synchronous orbit

[Guest]

In other words, I'm trying to get a satellite to orbit at the same speed as the Mun, but not orbiting the Mun.

Any altitudes and speeds required to perform this?

Examples: If the satellite were in front of the Mun, it would be seen as if it were, well, staying in front of the Mun.

Edited June 12, 2013 by spink00
moar information

[UNSC]

I don't know how stable it would be, eventually you will get an encounter (and likely a collision with) the mun. But wouldn't it be the same altitude as the mun in a circular orbit?

Disregard the above, I didn't quite understand what you were saying...

Yeah, like the guy below me said, you can only have one gravity well acting upon you at a time.

Edited June 12, 2013 by UNSC

[tntristan12]

Not possible in KSP. The only place that can is at a Lagrange point, and those don't exist. For many explanations about why that is, search Lagrange points in the forum. The closest you can get is to put a spacecraft in orbit around Kerbin at 11,000km, but even that isn't perfect as with even the slightest deviation in SMA your positiion relative to the Mun will drift.

[stupid_chris]

In other words, I'm trying to get a satellite to orbit at the same speed as the Mun, but not orbiting the Mun.

Any altitudes and speeds required to perform this?

Examples: If the satellite were in front of the Mun, it would be seen as if it were, well, staying in front of the Mun.

You can't do that in KSP. In real life you could by using the L1 Larange point, but they don't exist in KSP and probably won't ever exist either. To have the same orbital period as the Mun, you need to have the same semi major axis, and there is two solutions to that: either having the exact same orbit as the moon, meaning on the same orbital height as her, or you would have a highly eccentric orbit that would allow you to get close encounters to the Mun below her orbit without getting in her SOI twice per orbit. But there's sadly no way you will get in a locked orbit with the moon at a different orbital altitude.

[kahlzun]

You can land on the Mun.

You're not orbiting it, and you're travelling at the same speed.

Alternatively, if you have a satellite orbiting Kerbin at the same SMA as the Mun, just in a different quadrant (ie: 90 degrees from the Mun) then it will maintain a fixed position relative to the body.

[Nibb31]

This is not possible. Orbital altitude and speed are linked, so an object orbiting at an orbit below the Mun will always be going faster than the Mun. A higher object will always be going slower.

In real-life, we have Lagrange points. EML1 (Earth Moon Lagrange 1) is located between the Moon and Earth, where the gravity of both bodies cancel out, making a somewhat stable orbit possible. EML2 is similar, but on the opposite side of the Moon. However, KSP doesn't do Lagrange points because n-body gravity calculation on rails is too computer intensive for a personal computer.

[Temstar]

In KSP, if you orbit Kerbin on the exact same orbit as the Mun then every point on Mun's orbit outside of Mun's SOI is a Lagrangian point, since unlike in real life Mun's gravity cannot affect you unless you're inside the Mun SOI.

[Nibb31]

If you could orbit the Mun on a geostationary orbit, you could simulate the EML1 and 2 points. However, the wiki indicates that the Mun's stationary orbit is beyond its SOI, therefore it's not possible either.

[stibbons]

The entry for Mun in the KSP wiki gives its orbital characteristics. It's in a completely circular orbit at 12000 km with 0 degrees inclination. As others have said, you only have one gravity well acting on you at a time, so you just have to put yourself in the same orbit.

Get yourself in LKO, then set up a maneuver node to push your Ap to 12000km. If that puts on you on a Mun intercept, then move your maneuver node until it doesn't. Then just circularise out there and you're done.

[Crush]

Theoretically, it is possible.

You just have to get into an orbit which lies exactly on that of the Mun, but outside the mun's SOI. This works especially because KSP doesn't model multiple gravity sources. Otherwise there would only be two points on a moon orbit which would be stable (Langrange 4 and 5), but because the mun gravity only affects you when inside the mun SOI, the whole mun orbit outside the SOI is stable.

But practically you won't be able to do that accurately enough, so your craft will slowly drift into the mun SOI and crash into it, unless you do regular correction burns.

Edited June 12, 2013 by Crush

[Mr Shifty]

But practically you won't be able to do that accurately enough, so your craft will slowly drift into the mun SOI and crash into it, unless you do regular correction burns.

MechJeb gives you the semi-major axis to 0.01Mm of precision. So the maximum error in your sma, carefully adjusted is 5km. For circular orbits, the velocity of the orbit is proportional to the inverse square root of the radius. So, using an orbit 5km less than the Muns, you get a relative speed of about 0.113m/s. If you start 4000 meters from the Mun, you will process into its SOI in about 160 days.

If not sure if other tools give you more precise SMAs. (Engineer Redux.) Another digit of precision would increase that time by about 3-fold. If you could get it to the meter, it would give you about 50 (Earth) years of breathing space.

[tomf]

If you wanted to fake a munar synchronous orbit you would need to be at an altitude of 2.9e6 meters away from the surface of the mun, 500 km outside its sphere of influence. That would give you about 50 days before you drifted into the soi.

[Mr Shifty]

MechJeb gives you the semi-major axis to 0.01Mm of precision. So the maximum error in your sma, carefully adjusted is 5km. For circular orbits, the velocity of the orbit is proportional to the inverse square root of the radius. So, using an orbit 5km less than the Muns, you get a relative speed of about 0.113m/s. If you start 4000 meters from the Mun, you will process into its SOI in about 160 days.

If not sure if other tools give you more precise SMAs. (Engineer Redux.) Another digit of precision would increase that time by about 3-fold. If you could get it to the meter, it would give you about 50 (Earth) years of breathing space.

Actually, I think MechJeb gives you the period to the second. If you can match periods to within a second (probably possible with RCS; I know you can do it for geosync Kerbin orbits), you can get your breathing space (from an initial 4000km stand-off) to a minimum of about 75 Earth years.

[PapaGuido]

Is it possible to have an orbit at the same distance from Kerbin as the Mun... In effect you could basically trail the Mun?

[kahlzun]

Is it possible to have an orbit at the same distance from Kerbin as the Mun... In effect you could basically trail the Mun?

easily, yes. Do a Munshot, and miss.

Then circularise. Easy.

[zanzibar196]

I say, the solution is simple... Use the moon and orbit that...

[OdinYggd]

Treat the mun as an object in a formation.

If your satellite exactly matches the Mun's orbit, but is a few degrees ahead of it or behind it, the mun won't capture it for a long time. Eventually though enough position error will accumulate that it will be captured by the mun, and either flung back at Kerbin or out into the sun.

I've put remotetech relays in position this way a few times, relaying from Kerbin to an array around the mun itself.

[th3shameless]

this is possible, simply time your burns right so you're ahead or behind the mun then circulize. i actually am going to try this