Matching planes with Moho, Dres and Eeloo

[johnnyhandsome]

Is is better to do this while in Kerbin orbit or after escaping from Kerbin? I've tried both ways and missed (not enough fuel in the end), was wondering. I think it's better to do before leaving Kerbin orbit, as you can expend the fuel to match orbit and then refuel and head out with a full tank.

[ZingidyZongxxx]

It would be better to match planes before leaving Kerbin, but this is usually impossible as your descending or ascending node would have to match up perfectly with where Kerbin is in its orbit around the sun.

[DMagic]

You also have to keep in mind that you will need a highly inclined orbit around Kerbin to match the inclination of another planet.

I have done this many times going to Moho, and it requires about a 20^o inclination around Kerbin to match the 7^o inclination of Moho around the sun. So the only efficient way to do this is to launch into the right inclination, or change your inclination from a very high Kerbin orbit (further away than the Mun).

[Francesco]

DMagic, I had thought about that as well in the past, but I couldn't figure out the right way to do it:

sometimes, after leaving Kerbin's SOI, my ship even had an inclination that went in the opposite direction I was seeking. ugh.

what's your method?

[DMagic]

When launching into the correct inclination I first have to wait for Kerbin and Moho to be at a node (I think I use the descending node, because that lets you meet Moho near its periapsis). Just target Moho so that its orbit shows up in green, then try to look straight through Kerbin to the sun. You can use the Mun's orbit to do this, line everything up so that the Mun passes directly in front and directly behind Kerbin. Then just wait until you are about to cross Moho's orbit, the green circle representing its orbit will start to collapse to a single green line near a node.

Then you have to launch at the right time. When the KSC is directly opposite from the sun (so it is midnight KSC time) is when I launch into a 20^o orbit, but you could also launch into the opposite orbit at noon and have the same effect. This means that when I burn for Moho, on the side of Kerbin facing the sun, I'll be heading down on the map and should come out of Kerbin's SOI within 1^o or so of Moho's orbit.

The important part is timing your launch correctly and figuring out whether you need a positive or a negative inclination. Launching near midnight or noon should put you in the right orbit (actually a little before midnight or noon would probably be best). You just have to figure out which node you are at with respect to Moho. It's a little counter intuitive since you are burning retrograde with respect to Kerbin's orbit around the sun, but it makes sense if you think about it a bit.

Edit: This might help a bit. Moho's orbit is in green. This is just before the ascending node, so the green circle is collapsing into a straight green line going up from left to right. The white line through the middle is the Mun's orbit, I'm using that to line up my view.

Edited June 22, 2013 by DMagic

[Francesco]

hmmm thanks, I will have to try this.

brotip: to know a planet's inclination relative to Kerbin at any time, put a probe in a heliocentric Kerbin-like orbit