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I’m currently designing a Tylo mission. Let's assume I have myself a Tylo intercept straight from Kerbin with a nice and low Pe. My logic indicates that if I try to land directly from my interplanetary trajectory, since I’m going so fast, it will be more expensive than if I use gravity assists to first capture around Jool and lower my Jool orbit as much as possible. Is my logic sound? Is there any gravity assist trickery that can make my Tylo landing cheaper?

Hi all, I'm attempting my first ever Jool mission. Not one for half measures, it's going to be a Jool 5. I've got a very large spaceplane with about 1100dV remaining as it plunges to its doom in the Jool system, and .38 TWR. It has IRSU and if we can get into Laythe's atmosphere in one piece, i am very confident of being able to land the thing (even dead stick) , get mining, and complete the mission. The problem is that whilst i think i've got a fair understanding of stock aerodynamics and can fly decently, I'm terrible at orbital mechanics. Was very pleased with myself using only 2200 or so to get an encounter with Jool from LKO, normally i use 2 or 3 times the estimates. Now the capture burn would be another 2k dV if doing it propulsively, and you're looking at the same again or even more to get into Laythe. Now I hear that all the smart kids actually do it by using gravity assists. This is where i'm struggling - On the Kerbin-Jool transfer burn we hit an AP of 77 billion then arced back down to this encounter with Jool. We swung around the back of Jool itself, and as luck would have it, can pass just in front of Tylo to get a massive gravity braking assist. Do i need to tune this to be a bit less aggressive? As you can see, it's going to have us plunge to our doom on Jool. Miraculously (some would think it intentional) we get another encounter with Laythe, on our way down to oblivion. But we're going 5300m/s plus at this point, and Laythe's atmosphere goes from thick enough for jet flight at 40km to zero at 50, so setting PE high enough to not blow up the ship means you're only in the atmosphere for a second or two. No appreciable braking possible. As for the gravity assist, it can substantially affect our trajectory, but only after we've smashed to bits on jool.

Imagine if there was a planet with such high gravity and no atmosphere, it was begging to be used for gravity assists... But, there is a catch; it is nowhere near a flat planet, in fact, it's quite the opposite. 40 kilometer-high mountains, a ludicrously short day, combined with its low-orbiting moon (about the half the size, but twice the annoyingness as Ike) make exploiting its precious gravity a gamble. Yet, it's tantalizingly close orbit to Kerbin makes it such an irresistible option. Will you take this chance to reap the rewards? Requiring just a little more fuel to get to than Minmus, this planet can be a valuable resource to your missions. Just make sure not to crash... With a diameter close to that of Vall, but having a mass so high that it has a density roughly 1½ times that of Kerbin; its gravity will be much higher than that of Kerbin and potentially Eve.

Proof, if any were needed, that I'm ok with planes, even spaceplanes, but really don't know what I'm doing in a rocket. Early in a career game, I reckon I can get a good science boost by using a gravity assist to get out to the Jool system ahead of time. Unfortunately I don't quite have the skills of this guy - So, according to the wiki - I need to launch my probe and lower it's PE within the orbit of Eve to get an encounter. Then pass behind it to pick up a gravity assist, catch another one somehow from Kerbin on my way out to the newly raised AP, and then bounce between Kerbin and Eve till I raise my AP up to Jool territory. Profit. Now, when doing a "gain speed" assist the goal seems to be to pass behind the planet as close as possible. The closer behind , the bigger the assist. Except that if i get too close to Eve it bends my flight path too much, slinging me radially or anti radially with respect to the sun (Kerbol) and the extra energy is wasted. In fact I've had it throw me straight back on a reciprocal course, drastically lowering AP. Is this bad planning or just a limit on how much you can gain from a single pass? In that diagram from the wiki, the spacecraft is coming in at quite a steep trajectory WRT to the planet. This allows the flight path to be "bent" greatly, but actually have it work in your favour putting you on a prograde trajectory WRT to orbiting around the sun. The problem is, to get this steeper angle when passing Eve, I'd have to lower my PE well below Eve's orbit. Which is very expensive in Delta V terms, more so than just going Jool direct?