How do you move the Periapsis

[Tyler Frazier]

Ive been playing for a bit now and love playing KSP so far but i can not figure out how to move the periapsis. I can move into orbit fine now i have done it multiple times but I accepted a mission called "Position satellite in a polar orbit of Kerbin". I can move the Apoapsis fine but can not figure out how to move the periapsis. Also recently i found out i cant use batteries for the power which wont allow me to do the mission for about an hour because i need to unlock my first solar panel.

Orbit Specifics

Apoapsis-4,031,524 meters

Periapsis-2,643,811 meters

Inclination-90 degrees

Longitude of ascending node-63.7

Argument of periapsis-131 degrees

It does give me the orbital path i need in the map so really all i need to do is match the orbital path. I can move the Apoapsis to 4,031524 meters easily, but aligning myself to the correct orbit is a challenge, that doesn't matter though because i cant get the periapsis out to 2,643,811 at all. Also is I seem to be unable to move the satellite around without the engines burning, I assume this has something to do with the unmanned probe as I have never ran into that issue before and i do have well over enough electricity and i can see it using electricity when im trying to position it but it doesn't move without the engines burning.

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I figured it out after hours of trying, the forums are a great way to learn something when stuck and im shocked at how easy it is. all i needed to do was create a second node after my first, which will push my periapsis to a farther distance.

[cicatrix]

At the point opposite to the desired periapsis just burn retrograde. Initial point of burn, of course, should be higher than the desired periapsis height.

If your orbit is eccentric you can also burn radially to move your LAN thus changing your periapsis longitude too.

As for the power - batteries get depleted over time and once they're empty you would have an uncontrollable craft. You need solar panels to charge them up.

Edited January 3, 2015 by cicatrix

[vexx32]

Moving apoapsis or periapsis is identical; simply burn either prograde or retrograde in order to alter the path of your orbit. The Ap/Pe positions on your orbit will change depending on where on your orbit you burn. If you, for example, burn prograde at a point on your orbit, that point will quickly become your Periapsis, since the opposite site has been heightened and become the Apoapsis; in other words, they are always at exactly opposite points on the orbit. Similarly, burning retrograde will cause the apoapsis to shift towards your position, since every other point of the orbit is shrinking while you burn retrograde.

For these contracts, where the Ap/Pe have to be in fairly specific locations, I've found it best to first get into a stable orbit around 100km or so, then look at your target orbit. Either burn at the position on your current orbit that matches the apoapsis or periapsis of the target orbit (preferably slightly before, to ensure you get the position fairly close). If you have maneuver nodes unlocked, they'll help out with your planning.

One thing you need to remember is that for the most part you don't have to be perfectly accurate; most of the contracts will permit a reasonable deviation from the target orbit in all parameters.

[gmiddlemass]

As cicatrix says above, to alter your periapsis you need to burn at apoapsis... Burning prograde will raise it, retrograde will lower it.

[Tyler Frazier]

thank you, I watched this video in the tutorial forums http://www.dailymotion.com/video/x1948ip_maneuver-nodes-hd-a-ksp-0-19-0-tutorial_videogames and found that I needed to create a second node which makes sense. Not sure how to switch this to answered.

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I have everything needed unlocked, i did originally explain this in more detail but the moderator who approved the most must have thought my explanation was trivial which it probably was to the question at hand.

[Tyler Frazier]

Nvm, my side of the things was not showing my the info i wrote till now, it was just showing the header to the question. sorry new to the forums haha

[RainDreamer]

Here is how:

http://forum.kerbalspaceprogram.com/threads/85063-How-to-change-Unanswered-to-Answered

You should try out the tutorials that the game has, it will give you a basic idea of orbital mechanics and maneuvers.

[sal_vager]

if you have your Periapsis correct but it's in the wrong place you can burn radial (directly away from the planet) or anti-radial (directly towards the planet) when at Apoapsis to move your Periapsis to where you need it, and you don't even need nodes

[DelayedReaction]

I've found launching to the required Pe altitude and circularizing there, allows me to see how far deviated I am from where I need to be, I will correct the inclination etc there, and then work out where I need to be burning in order to raise the Ap to the required altitude works well enough for me.

[Anquietas314]

if you have your Periapsis correct but it's in the wrong place you can burn radial (directly away from the planet) or anti-radial (directly towards the planet) when at Apoapsis to move your Periapsis to where you need it, and you don't even need nodes

You're actually best to do it where the orbits intersect, assuming that's not at apoapsis. If you do a radial burn at Ap you inevitably raise your apoapsis and usually lower your periapsis, regardless of whether you burn radial or anti-radial, unless of course the burn's so slow that it exactly matches your vertical acceleration at apoapsis, but that's horribly inefficient for rotating the orbit.