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need help with ejecting from mun orbit


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I cannot create a successful return orbit. I think I'm folloeing the instructions, but here's what I end up with

 

what is the purple orbital line and how should it relate to the golden escape track? I assume the purple track is the new orbit as planned, but how do you merge that with the ship's orbit? Also with this setup I can't lower kerbin periapsis then about 2.000.000 m. Basically I'm rather confused.

I'm trying to insert a screenshot but it isn't showing up.

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19 hours ago, alfrank said:

what is the purple orbital line and how should it relate to the golden escape track? I assume the purple track is the new orbit as planned, but how do you merge that with the ship's orbit? Also with this setup I can't lower kerbin periapsis then about 2.000.000 m. Basically I'm rather confused.

 

I'm trying to insert a screenshot but it isn't showing up.

the golden line is your trajectory inside mun's sphere of influence. the purple line is your trajectory in kerbin's orbit. so if you execute the maneuver you will go on the golden track, up until the circle - that's where you will escape mun's gravity and be back in kerbin's gravity (in case you don't know, the game considers the gravity of one celestial body at the time, for simplicity of calculations). after you escape mun and end up on the purple track, you will stay in that orbit - until eventually you'll cross mun again, but that's a different issue.

 

your maneuver is not working because it's poorly made. why do you have a 222 m/s radial component? there are times when you make radial maneuvers, but it's very rare. most of the times you'll only pull a few m/s radial as course correction. try a 280 m/s prograde maneuver in that same spot, and you should return to kerbin. if it does not work, try to move the node a bit.

 

mun is in a high orbit around kerbin, and while you are orbiting mun you are also in such a high orbit. to return to kerbin you want to lower periapsis into the atmosphere, so you can start aerobraking. and to do so, you need to burn retrograde.

and it's exactly what you do. except that your frame of reference is mun, not kerbin, and you will get an additional deviation by mun's gravity, and so there are some changes to take that into account. basically, you want to exit behind mun - that will mean you're slower than mun, so your orbit will get lower. what you are apparently trying to do with your maneuver instead is to aim straight at kerbin - of course it does not work, because you are also rotating around kerbin at the same time.

 

in fact, if you read the full instructions shown in your screenshot, the advice is better worded. it says

drag the prograde handle until you have an escape trajectory. now move the node and watch as kerbin's periapsis changes.

if you can't get less than 2000 km, then increase the burn - more prograde, not radial - and move the node again.

 

incidentallly,, if you miss your mun return and end up in kerbin orbit, it's not a big deal; you can just make a new periapsis lowering maneuver one in kerbin's orbit. it's going to be less efficient, though

 

Edited by king of nowhere
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Ah, there we go.

before executing the ejection burn, what mode should the navbal be set to - maneuver, stability assist or prograde

 

 

 

 

 

 

before executing the ejection burn, what mode should the navbal be set to - maneuver, stability assist or prograde

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There's rarely a need to burn anything other than prograde or retrograde. In this case, wait for the right moment and burn prograde. The maneuver indicator should be in the same spot if you've plotted the maneuver correctly anyway. 

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