At which orbit point should I burn to get to another orbit in the most efficient way?

[pinkdragon]

Ok, so I want to get a transfer from one orbit to another in the most efficient way. How can I calculate the optimal point? Hypothetically, is there some quantity or physics equation that would indicate the best point in my current orbit at which to burn?

[Taki117]

Depends on where you are trying to go. If you are just Changing your -apsis then you want to burn at the opposite -apsis. (To change apoapsis burn at periapsis and vice versa). To actually go interplanetary you will need something like Alexmoon's calculator for determining launch windows. It also works for Moons and other things orbiting things.

Edited February 27, 2014 by Taki117
Added link

[KerikBalm]

To get to another celestial body, you want to be orbiting the current body as low as possible (Oberth effect).

Use maneuver nodes to fine tune it.

*assuming a prograde orbit* Generally, to get to the mun or minmus, you'll want to start burning when kerbin is nearly between you and either moon.

When going to a planet farther out, you want to burn about when the angle between you, kerbin, and the sun is nearly 90, so that your escape trajectory is rather flat when Kerbin is between you and the sun.

Start from there, and then use the maneuver nodes to find the optimum - remember to set a target, that helps you figure it out

To get to another planet, there are many calculators out there, but I find this list most convenient:

http://www.eiden.fi/ksp/

Ie, to get to Duna from Kerbin:

http://www.eiden.fi/ksp/phaseangle-Kerbin-Duna.txt

Leave on days 59 or 291 for the first year (58, 292, etc also work, but the closer to those days, the better)

[Kasuha]

Ok, so I want to get a transfer from one orbit to another in the most efficient way. How can I calculate the optimal point? Hypothetically, is there some quantity or physics equation that would indicate the best point in my current orbit at which to burn?

There are various approaches and what to do depends on what is the relation between your initial and desired orbits. There are Hohmann transfers, bielliptic transfers, inclination changes, bielliptic inclination changes, and radial burns. Sometimes you can combine them to save even more dv and sometimes the combination may be rather tricky.

[Starstrider42]

A good rule of thumb in orbital maneuvering is that burns in the plane of your orbit almost always have the biggest effect on the opposite side of the planet, while burns out of the plane (i.e., inclination changes) have their biggest effect one quarter of the way around. That one rule covers most of the basic maneuvers you would want to do.

For transfer orbits specifically, I suggest reading the Wiki: http://wiki.kerbalspaceprogram.com/wiki/Tutorial:_Advanced_Orbiting. The Hohmann and Bi-Elliptical transfers are both quite handy, though the latter requires a bit of planning (i.e., setting multiple maneuver nodes, and considering the total delta-V of all of them).

[Kryxal]

These days I LOVE the bielliptic inclination change when orbiting a new body ... capture into a long elliptical orbit, change inclination at apoapsis, then bring your apoapsis down ... it takes extra time, but it's so much more efficient if you can't insert into the orbit you want.

[EtherDragon]

Ok, so I want to get a transfer from one orbit to another in the most efficient way. How can I calculate the optimal point? Hypothetically, is there some quantity or physics equation that would indicate the best point in my current orbit at which to burn?

Are you asking about transferring to another planet, e.g. from Kerbin to Duna, or to a the Mun or other minor body?