Mun Orbit

[Deaf3279]

I has been look around for what lowest mun stable orbit I can put? Last thing I wanted put station into deorbit path. I'm work on build station server as refuel before return home or going mun

[ComradeGoat]

I don't generally orbit lower than 9K, but 5 should be safe ish. Docking with a station in very low orbit can be annoying, BTW: the effect of being in a slightly different orbit causes drift quickly, and even at close differences. It's really not very much Delta V to get to a decently high Münar orbit.

[Deaf3279]

Thanks.... I think I'll go for 20k Safe than sorry.

[Guest]

Theoretically, you can put something into a stable 3.5km orbit since the highest point on the Mun is 3.4km. From the standpoint of usability, however, I wouldn't put a station any lower than 10km.

[ComradeGoat]

Theoretically, you can put something into a stable 3.5km orbit since the highest point on the Mun is 3.4km. From the standpoint of usability, however, I wouldn't put a station any lower than 10km.

Yeah. I think my Münar station is at about 150k. I tried lower, and it's laaaaaaaaaaaggggggggy and annoying.

[Guest]

I put a little bare-bones probe (no RCS or other engines) in a 3.5k "stable" orbit, only to find it was losing 1 metre of altitude every 5 seconds. Needless to say it was a short expedition.

[Daze]

I put a little bare-bones probe (no RCS or other engines) in a 3.5k "stable" orbit, only to find it was losing 1 metre of altitude every 5 seconds. Needless to say it was a short expedition.

So it's pratically like in reality? I like it.

[Deaf3279]

Core Station has deployed. From game, it look great but picture ehhh.. Oh well

[Guest]

Core Station has deployed. From game, it look great but picture ehhh.. Oh well

To quote Pink Floyd, "I'll see you on the dark side of the Mun..."

[Francesco]

I put a little bare-bones probe (no RCS or other engines) in a 3.5k "stable" orbit, only to find it was losing 1 metre of altitude every 5 seconds. Needless to say it was a short expedition.

really? why does this happen?

[Guest]

Every orbit drifts. This one happened to be drifting downward at the time, and bad things can happen when you're skimming the bottom of a gravity well with a margin for error of approximately 100 metres.

[Francesco]

well every orbit drifts, in real life;

in KSP, I was only aware of this phenomenon as due to the use of time warp, and sometimes randomly happening as you maneuver your ship.

so you're saying this also happens while playing in real time, by actually doing nothing?

[Tw1]

Real life orbits are even more complex, as bodies have in even surfaces. Areas with higher mass have a stronger pull. Imagine orbiting while gravity was changing slightly, up, and down, as you went along.

This effect is most obvious on the Moon. It was first observed when Apollo astronauts launched a satalite from their ship. Its altitude varied, and eventually the orbit decayed.

Moon orbits must be calculated so that the probe orbits over areas of even density, or so areas where it is pulled closer to the Moon are balanced with areas where it drifts out.

I'm glad we don't need to worry about that in KSP.

Drift to do with the fact that planets move but orbits are inertial, isn't it?

[Guest]

Yes, just and in reality, orbits in KSP drift. The one thing they don't do that real-life orbits do is decay. The physics model used in the game is simplified, so that any orbit is essential "on rails". But as far as drift is concerned, you can easily observe this. Place three satellites in geosynchronous orbit, equidistant from one another. Let the simulation run. Real time or warp, it doesn't matter outside of the fact that warp will magnify the effects thanks to it skipping big chunks of mathematical samples. The orbits will remain stable (+/- some small percentage), but their distances from one another will not.

A spacecraft's orbit around a planet or moon will vary minutely in distance from the orbited body. You can see this readily by using a controlling factor such as MechJeb (oh, hush up). Launch a craft into orbit around Kerbin to an altitude of, say, 100km. It will not stay precisely at 100km. There will be a variance of +/- some small percentage over the course of the orbit. But again, unlike real life, the orbit will never decay on its own.

[CalculusWarrior]

Yeah, even if you use HyperEdit to put a satellite into a pretty damn near circular orbit, you will still have it jitter up and down by +/- 20m.

[JimJones]

I have had this happen twice to me so far. I tested it with my second ship. I got it in an orbit around the mun with a Ap of 127,800 and Pe 123,690 and it is nearly exactly on the equator or both lines touch the Muns orbital path(not sure if that's consider the Muns equator). Both markers were twitching and changing it seemed like by about 12 meters every 5 minutes. I let the game run over night to see what would happen and this morning the Ap is 192,300 and the Pe is 47,980. I have a very similar ship in orbit around Kerbin and it has been sitting in nearly the exact orbit for quite awhile, almost a week.

The ship isnt spinning rapidly or shaking.

Anyone know why this is? I'd like to get a Mun Station going in a stable orbit.

Here is a picture of the ship and you can see last night orbit path on there as well(http://www.skddayz.com/photos/picture.php?/22/category/2). -

[hobbsyoyo]

I have had this happen twice to me so far. I tested it with my second ship. I got it in an orbit around the mun with a Ap of 127,800 and Pe 123,690 and it is nearly exactly on the equator or both lines touch the Muns orbital path(not sure if that's consider the Muns equator). Both markers were twitching and changing it seemed like by about 12 meters every 5 minutes. I let the game run over night to see what would happen and this morning the Ap is 192,300 and the Pe is 47,980. I have a very similar ship in orbit around Kerbin and it has been sitting in nearly the exact orbit for quite awhile, almost a week.

The ship isnt spinning rapidly or shaking.

Anyone know why this is? I'd like to get a Mun Station going in a stable orbit.

Here is a picture of the ship and you can see last night orbit path on there as well(http://www.skddayz.com/photos/picture.php?/22/category/2). -

Did you leave SAS and RCS on overnight?

[paleorob]

I remember reading about the effects of floating point calculations on orbits and someone mentioned that circular (or nearly so) orbits in KSP are actually less stable than elliptical orbits. Forget the exact reasoning behind it though.

[SpaceSphereOfDeath]

Theoretically, you can put something into a stable 3.5km orbit since the highest point on the Mun is 3.4km. From the standpoint of usability, however, I wouldn't put a station any lower than 10km.

Nope, not on the new mun, the highest point now is above 8km

Wiki pages: http://wiki.kerbalspaceprogram.com/wiki/File:Mun_heights.svg

http://wiki.kerbalspaceprogram.com/wiki/Mun

[JimJones]

Did you leave SAS and RCS on overnight?

I left just SAS on, but not RCS. Would SAS alone cause an issue? I did try it with no SAS and the numbers still fluctuate, but I didn't leave it for an extended period of time.

[FITorion]

It depends on your orbits inclination. There are some tall peaks near the Muns poles ...

I find that 10Km is safe for all inclinations and 7Km is safe for an equatorial orbit.

[FITorion]

I left just SAS on, but not RCS. Would SAS alone cause an issue? I did try it with no SAS and the numbers still fluctuate, but I didn't leave it for an extended period of time.

Yes SAS with cause that.

Also it only happens when you are focused on the vessel. If you had watched from the tracking station... or time warped from another ship the orbit of the ship around the Mun would never change. Because when the ship is not the focus then no physics is being done on it. The game keeps it on it's path forever ... (excepting paths which hit a planet) You don't have to worry about debris while a ship is "on rails" like this either. The ship has no physical form and will pass right through any other ship or piece of ship. So long as neither is the focus that is.

[JimJones]

Yes SAS with cause that.

Also it only happens when you are focused on the vessel. If you had watched from the tracking station... or time warped from another ship the orbit of the ship around the Mun would never change. Because when the ship is not the focus then no physics is being done on it. The game keeps it on it's path forever ... (excepting paths which hit a planet) You don't have to worry about debris while a ship is "on rails" like this either. The ship has no physical form and will pass right through any other ship or piece of ship. So long as neither is the focus that is.

Ah, it feels like cheating, but I guess that works. Thanks for info.