Going to fast to get into another planet's SOI reasonably

[gooseapple5]

I have been having trouble getting into another planet/moons SOI, it seems that half of the time the speed that i am travelling is the normal amount, and sometimes it is WAY too much, sometimes as much as 5 km/s. The one that i was going too fast at was anything but the Mun and Minmus.

[Palaceviking]

2 hours ago, gooseapple5 said:

I have been having trouble getting into another planet/moons SOI, it seems that half of the time the speed that i am travelling is the normal amount, and sometimes it is WAY too much, sometimes as much as 5 km/s. The one that i was going too fast at was anything but the Mun and Minmus.

Dres perchance?

[DD_bwest]

the only planet i ever have trouble with would be moho,  and thats largely cause i like to use ion thrusters that close to the sun.

 

but from the sound of things. my guess the reason your relative velocity  is so high is because of your intercept trajectory. are you meeting your destination  a good deal away from  your AP/pe?  are you having to raise your ap much higher than the orbit of your destination in order to get the encounter?

 

edit.: think about it the same way you would for rendezvous and docking,  if your meetig point is tofar from the ap/pe and if your inclinations are off, it adds to the relative velocity you need to cancel out to match speeds.  

Edited October 21, 2017 by DD_bwest

[Snark]

On 10/21/2017 at 1:28 PM, gooseapple5 said:

I have been having trouble getting into another planet/moons SOI, it seems that half of the time the speed that i am travelling is the normal amount, and sometimes it is WAY too much, sometimes as much as 5 km/s. The one that i was going too fast at was anything but the Mun and Minmus.

It's a navigation thing.  Make sure that you have a reasonable transfer orbit when you're going to another planet.  Here's an easy way to tell whether you've got a good one:  In the map view, look at your intercept, i.e. the way that your ship's orbit meets the target planet's.

In the ideal case (i.e. where you arrive at the planet not going too fast), your orbit should be as close to parallel to the target's orbit as possible at the point of intersection.  In other words, you want it to be tangent, so that your ellipse and the target's ellipse just sort of "kiss" at one spot.

The bad case is when they cross, i.e. if your orbit and the target's look like an X where one crosses the other.  That's bad, because it means that you're moving in a very different direction than the target planet is, which means a huge relative velocity at the point of intersection.

The way that you make your transfer have the happy case rather than the bad case is to launch with a good transfer window, i.e. get your timing right so that your origin and destination planets have the correct relative position.  There are various tools that can help you with that; my personal favorite is http://ksp.olex.biz because of its very simple graphical interface, but there are others out there, as well.

Sorry if the above advice is kind of vague and general, but that's about the best one can do if you don't provide more specifics.    If you'd like better advice, please give us an example.  For example:  give us a screenshot of a mission where you had difficulty.  Specifically, your screenshot should be from your map view, showing the path of your orbit from planet A to planet B.  If we can see that, then we can tell you specifically what the problem is and what you should do differently.