Cartz

^^ This guy gets it... The second we paid for this title, we freed ourselves from the chains of traditional alpha/beta development expectations. I hope you can see how paying for the KSP Alpha to fund further development work is different from being a part of a free, early access beta where devs may actually even be paying for the servers you're playing on for free. If we, as customers, are gracious enough to provide details of a flaw in a piece of software we've paid for, and provide a list of mods that we're using and their versions to go with it, then the devs should be falling all over themselves with gratuity to us and giving their best effort to determine if the flaw is in their software, that of the mod, or the interface between the two. All we should be expected to do is provide a .sfs file, a list of installed mods, and details of the error. The developers, whom we have paid, should handle the rest.

It's EXACTLY the same thing, just, the vomit comet does not have enough horizontal velocity to miss the ground. Orbit is literally a free fall with enough sideways motion to constantly miss the earth. The comet can do the freefall bit, just not the missing the earth bit. To the OP, who just posted a follow-up, its an interesting point that I hadn't considered before. But I'd have to assume that yes, as you approach orbital velocities that your inertia would being to alter your perception of gravity. Seeing as the null hypothesis would postulate a 'normal' gravitational experience until orbital velocity was achieved, at which time weightlessness is experienced instantaneously, one has to assume there is some sort of gradual introduction to weightlessness. I have no idea what that curve looks like, and I have even no desire to math it out.

I have to agree with Teirusu, you really do want to ensure that you have an engine active for the final seconds of your descent to Duna. What I will say though, is that drogue chutes are much more useful on Duna than normal chutes. They fully deploy higher, and one or two of those will bleed off all of your non-vertical movement rather quickly. If you switch to surface targetting and lightly burn a low thrust engine directly at your retrograde with a few of those chutes open, you will have a very uneventful and easy descent. I find it far easier to land on Duna then on the Mun. As for a vessel to complete the round trip, as long as you're not looking to bring several tonnes of equipment to the surface of Duna, or do sightseeing on Ike then a single rocket can service the trip with ease. If you're paranoid about your ability to spend your delta-v efficiently then send up a small refueling ship to LKO. The most important two things, IMO, is 1. to ensure that your ship has a docking port. With a docking port any delta v miscalculations can be remedied. 2. use a seperate descent stage, don't land your entire vessel on Duna. Although this can be done on Mun missions without much thought, an efficient and safe trip to Duna should make use of a lander while the interplanetary stage stays in orbit.

Check to see if your staging order is correct, are you decoupling the engine before, or on the same stage, as when you light it?

As someone said burning towards the retrograde vector (the green plane with the x through it) until that vector points straight vertical will kill all of your lateral momentum over the surface of the world you're landing on. For extremely delicate landings I would recommend, once you get close to vertical, to just burn vertical and use your rcs to translate out the last bit of momentum. Also for landing rovers, it might be advisable to land on legs which you then fold up to set the rover down with. You might even consider decoupling the rover and dropping it to the surface from underneath your lander. Either way, learning the prograde/retrograde vectors on the navball, and what they imply about your momentum, is absolutely essential to any fine motion work you aim to achieve.

A little trick I learned to simplify landing is to do your descents to atmosphereless worlds in two stages. First, burn retrograde (backwards) at your apoapsis to lower your periapsis to only a few km above the surface of the planet/moon. Then, burn retrograde at your periapsis, but actively follow your retrograde vector as it moves towards the vertical as you slow down. When the retrograde vector is pointing straight up, you've stopped moving laterally and can just decend the last few hundred/thousand m to the surface in a very controlled manner. Two reasons I do it like this: First, it limits the area in which you will end up landing significantly, making precision landings a bit easier. (this is relevant if you're about to send a rescue mission) Second, when you're burning retrograde at your periapsis, your vertical velocity is nil so your orbital velocity is your lateral velocity so you have a very good idea of how much burn is required to halt that motion. Another thing I like to do is just at touchdown, assuming my spacecraft is facing directly vertical, is to flare the engines quickly to nearly halt my decent 3-5m from the surface, then cut power completely with x. Then as my craft is hitting the ground, use RCS translate down to halt any potential bounces or rattling around.