Can't reach a round kerbin orbit

[Luc1fer]

Just that, i can get easily into kerbin orbit, but all my orbits seem egg-like, not round, how do you acomplish a round orbit?

 

[Val]

Moved from KSP Discussion.

[Superfluous J]

To raise your Periapsis, burn prograde at your Apoapsis. Actually, do it a few seconds before you get there. In map mode, you can click your Apoapsis to see how far away it is in time. Turn to keep pointing prograde, or "hold prograde" if your pilot/probe core is good enough. Make sure if your Apoapsis starts getting ahead of you, you stop burning until you reach it again. Try not to ever pass it, it makes it (slightly) more difficult.

Same for lowering your Apoapsis, only at periapsis and burning retrograde.

You can also burn (not too much) before your Apoapsis/Periapsis, and turn a bit radial in or out to keep your *apsis marker from going away from you, forward or back. However, that's a bit more advanced. Get comfortable with the first part before trying anything else.

And remember, as with anything in this game orbital maneuvers are a skill you hone over time. You're not expected to get it on the first try, or even the 10th try. But when you do get it, you'll have it for life.

Edited February 23, 2018 by 5thHorseman

[Vanamonde]

It takes A LOT of engine burning to get up to orbital speed, but once you've attained that, even quite small burns will turn the orbit into an ellipse rather than a circle. It's really just a matter of watching the curve of your path in map mode and turning the engine off slightly sooner than you have been.  But don't sweat it either way. There's nothing special about a circular orbit except that it looks tidier. 

[Starman4308]

A few theoretical points to keep in mind:

First, in an elliptical orbit, you always return to where you last made a maneuver at.

 

Second, the biggest effects of burning in the six primary directions:

Prograde: Increases orbital altitude 180 degrees away from you.

Retrograde: Decreases orbital altitude 180 degrees away from you.

Normal/anti-normal: Changes your inclination, or how tilted the orbit is with respect to the equator.

Radial out: Increases orbital altitude 90 degrees ahead, decreases orbital altitude 90 degrees behind you. Much less efficient than prograde/retrograde burns.

Radial in: Decreases orbital altitude 90 degrees ahead, increases orbital altitude 90 degrees behind you. Much less efficient than prograde/retrograde burns.

 

Third: eccentricity is the measure of how egg-shaped vs. circular your orbit is.

e=0: Perfectly circular orbit, which is generally treated as a special-case of elliptical orbits.

0<e<1: Elliptical orbit, with higher eccentricity orbits being less circular.

e=1: Parabolic orbit. In this orbit, you have exactly enough orbital energy to escape the gravity of what you're orbiting*, and will go off to infinity, approaching infinite distance and 0 velocity.

e > 1: Hyperbolic orbit. You have more than enough orbital energy to escape the gravity of what you're orbiting, approaching infinite distance and a finite velocity.

 

*This analysis assumes that whatever you're orbiting is the only celestial body in existence. In the real world, the gravitational influence of other bodies will always make this an approximation. In KSP, because celestial bodies other than the Sun have a finite-size sphere of influence, you can actually escape from an elliptical orbit if apoapsis is higher than the SOI edge.

[Scarecrow]

Maybe the origin of your problem is burning for too long while you are still on your way to orbit, which is pushing your Apoapsis further out than you need/desire.  While still burning for orbit, keep an eye on your Apoapsis (HUD from mods like Kerbal Engineer, or just normal map mode) and as soon as your Apo reaches the height that you want your orbit to be, cut your engines.  Coast up to Apo, and about 20 seconds before you get there, burn prograde to bring your Periapsis up to the same height, and then cut your engines again.  Job done.