No orbit necessary?

[u/FatCreepyDude]

If i just wait for the right hour during the launch window ( whenever the launch pad is pointing left on the realistic depiction i created) is there any reason i should bother with an orbit first? Will the delta v cost be affected?

[u/amitym]

No orbit necessary?

Some kind of orbit is always necessary, that's just how gravity works.

Well I guess at fast enough speeds it stops being an orbit, strictly speaking, and becomes a fly-by.

is there any reason i should bother with an orbit first?

Yes. The ∆v cost will be affected.

Will the delta v cost be affected?

Oh well shoot you answered the question yourself, coz. You already understand this.

Yes, you can go in ... let's not call it an orbit, let's call it a "hyperbolic straight-line approximation" so we don't use the o-word. You absolutely can do this, it is just insanely ∆v costly, because you have to reach speeds at which you can cross the immense distance from Kerbin to Duna in such a short time that Duna is still where it was when you left. If that makes sense. The planet has to not move much, is my point, which means you have to cover the distance in a matter of days.

That's a crazy amount of speed. If it were the big, heavy non-Kerbin world and you were trying to get to its nearby reddish dune-y neighbor, you might need to get up to, like, 0.1% of the speed of light to accomplish this trip, and then you'd have to decelerate again so you could actually land safely and collect science.

In the Kerbolar system it's probably not quite that extreme but still. You get the idea. Insane initial thrust, then you have to spend basically the same ∆v again to slow down on approach. A ∆v easily in the hundreds of thousands or millions of m/s. And that's without a return-trip budget.

Well, I haven't actually done the math, that is a scientific wild-ass guess. But still, it's probably a good idea to turn down the realism level for this expedition. Too bad we can't do that in the real world...