Kerbin Encounter Help

[wrappy]

So I have done a few runs outside the of kerbin's gravity sphere, and every time I do so I am able to re enter kerbin's gravity well pretty easily but burning prograde till I get close, then doing a correction burn to get closer. This time though something weird is happening, I am trying to exit from eve and at first it looks normal, where the encounter node things are getting closer. https://imgur.com/YJf1vvi

But then I add just a teeny bit more thrust and my closest encounter suddenly switches to the other side https://imgur.com/fkNdtCa

This wouldn't be a problem, when I burn more it switches back to the other side but doesn't get any closer, then it keeps switching back and fourth over and over again until they both just disappear, I am able to get a little closer using normal and anti-normal burns but nothing close enough to correct into an encounter! Please help!

Oh also in case it is relevant I am not currently in a good encounter window, I am trying to do it with just the help of eve.

[Anth]

Sometimes KSP is wrong when it comes to its encounter arrows.

I just recommend playing around with it and do some quicksaves/quickloads until you figure out.

Sorry I cant be more help than that.

[FleshJeb]

@wrappy Fine-tuning with Radial In/Out can help with timing issues. Due to physics (this is my short answer), orbits are less sensitive to those inputs, so you can get more precision out of them. As a bonus, the extra dV cost is negligible (blame Pythagoras).

[AHHans]

Hello @wrappy, welcome to the Forums.

KSP tries to display the closest encounter with the target (-body), which can be a few orbits down the line. This leads to the encounter flipping around a lot when you don't already have a good encounter. In your case it looks like it flips to an earlier encounter (when you are still on your way to the AP), so what you can do is put a "dummy" maneuver node (with 0 m/s dV)  at around the AP, then it will only show you encounters after that.

Another issue: you are not leaving at a transfer window, so if you want to optimize for low dV then you should wait till you are at one. Otherwise you can also fine-tune your transfer by changing the time of your burn (along the orbit around Eve), i.e. change the direction with which you leave Eve's SOI.

[king of nowhere]

your way of getting encounters is... not efficient.

first, as ahhans pointed out, you should wait a transfer window. getting an encounter under your current conditions is possible, but very expensive; I don't know if it is feasible with your current fuel budget.

Second, you are not taking into account orbital inclination. that will create a lot of problems. Your orbit being inclined means that even when you're overlapping kerbin's position, you'll be over or under it. the simplest (though not always most efficient) way to fix inclination is to wait until you are on top of a node (marked as AN and DN, for ascending node and descending node) and then make a burn in the appropriate normal direction until you remove orbital inclination.

if your orbital inclination is not fixed, you will have a hard time getting an encounter, because the game will only find encounters close to the nodes - because away from the nodes, there is no way you can ever meet the planet.

finally, from the magnitude of your manuever, it seems you are in an elliptic orbit around eve - which is good, it's the most efficient way to get in the system and leave for a small cost. unfortunately, it also makes things harder as far as trasnfer windows are concerned.

An alternative, very robust method to force an encounter in those conditions (again, though, not particularly efficient) is to touch kerbin's orbit with your trajectory (be careful of plane nodes!), and then make a new manuever there, to change your orbital time so that you can catch kerbin on the next orbit. this always works.

I suspect your previous target was duna, which has no orbital inclination compared to kerbin and is generally much more forgiving

 

[wrappy]

Thank you all for the responses but I managed to get back to Kerbin with just about 500 delta V's, I knew that this was inefficient and that I should wait for a transfer window but I'm lazy. Honestly I still don't actually know what happened, I ended up just getting as close as I could from that node with the plan to do a correction at the sun's periapsis, but then when I got there the closest encounter just disappeared , luckily I seemed to be in a good spot at that point because I was able to get an encounter pretty easily from there. Thank you all for the help and I will try the dummy node trick! Also I know that while it's better to wait for a encounter window I had heard from a youtuber named Matt Lowne that you can do it pretty efficiently by just doing a burn in low Eve orbit (I was around 110 km about eve), and that seemed to work fine in the end!

[Anth]

The closest encounter just disappeared? Sounds like a bug that I came across, though mine were longer distances like Jool or Eeloo

[Reactordrone]

Drop a second manoeuvre node at the descending node to correct the inclination, then fine tune the first manoeuvre node.

[paul_c]

I use https://alexmoon.github.io/ksp/#/Eve/18000/Kerbin/100/false/optimalPlaneChange/false/37/227 to work out the transfer window. Simply read off the UT (universal time?), then enter this in the "earliest departure", then it will give you the best time/date to do your burn to leave Eve and return to Kerbin. A big elliptical (or inclined in Eve) orbit isn't such an issue, since so long as you're roughly within a few days at the transfer window, the burn won't cost too much dV. You don't need to-the-second precision here. Similarly, if you're inclined, it will take a bit more dV but its not really worth* aligning to 0deg inclination just for the sake of the transfer burn.

The "set as target" then use the indications to see the closest approach distance is handy, especially if the two bodies are inclined (such as Eve and Kerbin) because it doesn't require you to be precise enough to have the encounter within the Kerbin SOI. But its clear from your screenshot that you're miles away in your encounter. I suspect you're on the edge of what KSP actually say is/isn't an encounter (it doesn't give you it if its so far away) so I think if you get the basic position much closer, it will also be more stable when you make (small) corrections to optimise the encounter to get you home.

For interplanetary stuff, its not massively time critical (unlike, say a Mun encounter where you want to burn at a precise point around the orbit of Kerbin) so you can afford the time to use the manoeuvre planning tool to tweak it so its good, then time warp there and do the relevant burn.

Makes sense to do the prograde/retrograde as near to the Ap or Pe (or while still in Eve SOI) and the normal/antinormal as near to or at the AN/DN.