So I'm planning a flight to Eve. Is it better to launch directly to a retrograde orbit, or launch to a prograde orbit, then do a plane change to get retrograde?

2. The former. If you're going to head for the inner planets, it's better to go with an orbit with an inclination of 180º, ascending directly to it (I use inclination because prograde/retrograde still leaves some room for ambiguity; the direction you are travelling in is always referred to as "prograde" for the purpose of navigation, but the orbit itself is called "retrograde" if the inclination is between 90º and -90º. Bah.). Make sure you plan for a much more difficult launch; it takes a quite of extra delta v, because you'll have to cancel-out the current rotation around an inclination of 0º (imparted by the rotation of Kerbin) and then expend the usual amount to get into a stable orbit.

Plane changes are generally very costly in terms of delta-v, and are best avoided (in some cases, it may be even less expensive to slingshot yourself around some nearby object to help with a plane change).

3. ... is a retrograde orbit?

4. Originally Posted by spl1nt
Let me just google that for you.

5. A orbit going in the opposite direction of the planets rotation.

6. Why do people keep saying you have to be in a retrograde orbit to head to an inner planet? YOU DO NOT. You only have to make your injection burn retrograde in respect to Kerbin's orbit around the sun, which you can do just as easily in an easterly prograde as in a westerly retrograde orbit.

All you are accomplishing by launching on any heading other than 090 or by other ways of getting into a retrograde orbit is wasting an awful lot of fuel.

Please stop telling people "this is how it's done." That is not how it's done. Example: the real-world Venus probes did it... they all injected from easterly, prograde orbits.

7. Yes, but the IRL venus probes could use n-body physics, not patched conics. Can you get to Eve launching into a prograde orbit using less delta V than launching retrograde?

8. Exactly what RoboRay said. There is no benefit to launching at 270 degrees.

9. OK. It's better to launch prograde, then burn prograde on the daylight side of the orbit... So is kosmo-not's post wrong? Or is Olex's webpage wrong? I want details and formulae, not just "it's better!" How specifically do I determine when to burn?

10. Originally Posted by spl1nt