180 Orbital inclination and getting to other planets

[Seeker89]

I've been playing with mechjeb's ascent guidance and been setting my inclination to 180. What i have noticed is that it takes about the same dv to get to the body I want.

The question I have is would I have a better chance getting there?

Thanks in advance

Seeker

[nhnifong]

The dv savings of taking off to the east is about 200 m/s I think. That's a nice savings if you do everything perfectly, but it can still be dwarfed by leaving at the wrong time, or having to do an orbital inclination change.

[Beowolf]

There was a discussion about this several months back. The conclusion was it doesn't help. Consider the picture looking down at Kerbin from solar-system-north: To go to the outer planets, you want to leave orbit in the same direction Kerbin's orbiting the sun. For the inner planets, you leave orbit at the opposite point, when you're moving opposite to the direction Kerbin orbits. Whatever your orbital direction, there are always two opposite points in the orbit where you can depart inward or outward.

So all you're doing launching into a retrograde orbit is giving up the free velocity you have from Kerbin's rotational speed.

[Superfluous J]

The only (and minor) help is that you don't have to pack extra batteries to do your burn on the night side when going to outer planets.

Batteries weigh far less than the fuel it will cost to go 200 extra m/s (and is it 200, or 400? I thought you get a 200m/s boost, which means you have to cancel that boost and then get 200 more to get back to what you had going east).

IOW, go East, unless you don't care about fuel, dV, or that kind of stuff. Which is perfectly fine, but as you're asking the question I (and the rest of us) assume you care.

[KerbMav]

I've been playing with mechjeb's ascent guidance and been setting my inclination to 180. What i have noticed is that it takes about the same dv to get to the body I want.

The question I have is would I have a better chance getting there?

Did you circularize first and then set out to the other planet?

Because the dV saving from going east has then gone into your orbit.

Departing from an orbit costs the same regardless of a "left" or "right" orbit.

[SRV Ron]

Did you circularize first and then set out to the other planet?

Because the dV saving from going east has then gone into your orbit.

Departing from an orbit costs the same regardless of a "left" or "right" orbit.

And, there is a savings in delta V when you make the escape burn from orbit regardless if you head prograde or retrograde from Kerban then straight up launch at dawn or dusk.

[numerobis]

Kerbin rotates at 174.5 m/s, so you save 174.5 going east compared to going polar, and you lose 174.5 going west. Sum is 349 m/s. That's not counting the extra drag from going ~350 m/s faster in surface speed, or the extra gravity drag from it taking longer to get up to speed.

There's very little reason to leave at 180 inclination.

Once you're in orbit, it's true, it doesn't matter except for day/night cycles.

[phuzz]

Not to mention, if you don't add the batteries then you can almost guarantee that you'll have to do a darkside burn once you get to your destination.

[Kasuha]

Retrograde or prograde Kerbin orbit has no effect on your travel to other planets, you just lose some dv getting to that orbit.

There might be some advantages for starting from an inclined or polar orbit, though, particularly if you match the inclination you'll need for ejection. But even that can be usually fixed by rising your orbit's apoapsis and changing the inclination there, then finishing the burn back at periapsis. It's just harder to plan as you need to plan your ejection one quite lengthy orbit ahead.