Which method is more economical when launching an interplanetary vehicle?

[Cesrate]

A. Launch into LEO, prograde burn, use Moon's gravity assist to escape from Earth's SOI.

B. Launch vertically until reaching escape velocity of Earth (may also use Moon's gravity assist).

[Nibb31]

I think that the Moon doesn't have sufficient gravity to make a gravity-assist manoeuver worthwhile. You would probably use more propellant to get to the Moon than you would save.

[magnemoe]

Launch to orbit first, you might save some dV by doing an direct launch however the liftoff is the most critical phase and is often delayed so you want to keep the craft in orbit for some time before the burn, this also gives time to check things out and do stuff like unfolding solar planes and antennas.

You do not use an moon slingshot as you can launch in any angle anyway. Has you ever used Mun this way in KSP, here you can use it then returning from Minmus.

[LongbowEOD]

I think the truth is somewhere between your two options. Launch, do a gravity turn, but don't stop at LEO, just keep burning until Earth escape velocity on whatever vector you want. As for gravity assists, I believe it's a matter of timing, waiting for them to be lined up just perfectly so that your slingshot maneuver saves you more fuel than you use getting into position for the slingshot.

ETA: While many real spacecraft have used multiple gravity assists on their journeys, I wasn't able to find any that used a lunar slingshot. So maybe it isn't that feasible.

[Rune]

I'd say with the Mun's low gravity, you can get more out of Oberth by making your burn as close to Kerbin as you can than what a Mun gravity assist can give you. However, if you time things so you can use both to the full extent, then of course that will be more efficient. It will take quite a bit of precision and timing, though.

Rune. So if you fly manual, don't bother.

[SunJumper]

I think the truth is somewhere between your two options. Launch, do a gravity turn, but don't stop at LEO, just keep burning until Earth escape velocity on whatever vector you want. As for gravity assists, I believe it's a matter of timing, waiting for them to be lined up just perfectly so that your slingshot maneuver saves you more fuel than you use getting into position for the slingshot.

ETA: While many real spacecraft have used multiple gravity assists on their journeys, I wasn't able to find any that used a lunar slingshot. So maybe it isn't that feasible.

Some sort of have. Their destination was the moon, but it was a flyby, and some of those crafts were slingshotted entirely into solar orbit.

[LongbowEOD]

Some sort of have. Their destination was the moon, but it was a flyby, and some of those crafts were slingshotted entirely into solar orbit.

So not as much "lunar slingshot" as "encounter without capture." I guess for me, "slingshot" implies getting to somewhere else. Still, effective way of gaining a few hundred m/s delta-v to get to heliocentric orbit.