Inclined transfer windows

[Plusck]

1 hour ago, Nich said:

So I did have an additional question.  I got the intercept pretty easily but getting my PE down to 95 km was quite challenging.  I know that time is quite important however I would think that 1/2 hour or even a day would not make much or any difference as the time scale is so small compared to the rotation.  I am very good at tweaking rendezvous (I have actually collided with a couple stations because I was not paying attention) Has anyone seen a tutorial on how to push things around with a ballistic intercept?  Burn angle, Radial, normal and prograde all seamed to have a lot of cross coupling.

I haven't seen a tutorial, and yes there is a lot of cross coupling which is a pain to deal with. This is one of the reasons why I absolutely support any development to KSP that would simplify the node-adjusting process (like having the node appear in a small box next to the navball while you focus on another planet).

So in the meantime, I try to think logically about what changing each node will do. Not that that really helps because each situation is different and I think (but would welcome any correction) that the different variables (are you heading inwards or outwards? are you meeting the target SOI perfectly head-on or are you looping further out or in before the encounter? are you making your corrections at the quarter-orbit mark or closer to the target?) make it excessively complicated to try to give any hard-and-fast rules.

 

I originally thought I'd be able to give more definite answers. So I started writing the following post. As you can see, it was getting ridiculous with all the ifs and buts and provisos:

Assuming these are all very minor adjustments, and assuming you're making them about a quarter of an orbit prior to the encounter, I think that the following is true:

• in any event, not only prograde (obviously) but also normal and antinormal will always increase your orbital velocity slightly;

1. For the following points, your original intercept has to be very good (i.e. you're not looping past the target before catching it on the way back in (or out, if heading in-system) rather than meeting it head-on:
   1. if heading outwards (e.g. from Kerbin to Duna or Jool), and bearing in mind that in this case, the target's SOI will be approaching from behind you as you reach solar Ap.:

• radial out will also speed you up slightly and radial in slow you down;
• in the meantime, radial out and radial in will both have you intercept the SOI further inwards from the sun, if your original encounter was nearly perfect, but at different times (earlier if radial out, later if radial in). Any deviation from a perfect encounter will alter this "rule"...;
• speeding up will get you there sooner (if done a quarter orbit before the encounter), and cause an intercept that is further sunwards and/or retrograde on the SOI's edge;
• if your trajectory has you going past the target orbit before the encounter, the opposite is true (but at what point does it become neutral and swap over? not sure about that...);
• um
• this is starting to get far too complex to be worth posting...

[Geschosskopf]

8 hours ago, Nich said:

So I did have an additional question.  I got the intercept pretty easily but getting my PE down to 95 km was quite challenging.  I know that time is quite important however I would think that 1/2 hour or even a day would not make much or any difference as the time scale is so small compared to the rotation.  I am very good at tweaking rendezvous (I have actually collided with a couple stations because I was not paying attention) Has anyone seen a tutorial on how to push things around with a ballistic intercept?  Burn angle, Radial, normal and prograde all seamed to have a lot of cross coupling.

Really, at interplanetary distances, you're NEVER going to have the perfect trajectory with a Pe at the target exactly where you want it, and it's a complete waste of time to try for one.  This is because of the inherent floating point errors that accumulate at such distances and over the course of so many calculations while you're en route.  Plus, you have to cross at least 2 SOI boundaries en route, each of which totally reorients the coordinate system and introduces even more floating point error.  IOW, either you can't get what you want to start with or, if you somehow manage that, it won't stay how you want it over the course of the trip.

So, leave when you've got something that's close enough for government work and resign yourself that you'll have to do at least 1 tweak burn somewhere along the line to finetune your Pe at the the target.  Perfection at any distance beyond Kerbin's SOI is pretty much an impossibility in KSP.

[Nich]

hhmmm...  Since I have been using the 5x time warp (1 arrow) on SOI boundaries I have not needed more then a 5 dv correction if any.  I have also found that slamming on 10,000x warp from stationary will screw up ships interplanetary even your controlling a ship at the launch pad.  I have had better experience stepping up time warp using the ">" key so it gets double precision and goes on rails before working my way up to 10,000x

[Plusck]

5 minutes ago, Nich said:

hhmmm...  Since I have been using the 5x time warp (1 arrow) on SOI boundaries I have not needed more then a 5 dv correction if any.  I have also found that slamming on 10,000x warp from stationary will screw up ships interplanetary even your controlling a ship at the launch pad.  I have had better experience stepping up time warp using the ">" key so it gets double precision and goes on rails before working my way up to 10,000x

I warp at the 4th arrow (or at the third, if I can be bothered...) and it's fine for me too. It's only at the sixth arrow that I've noticed any real problem, so I feel four is safe and three very safe.

[Nich]

Ya I normally use the 3rd or 4th if the ship has plenty of dv just laying around or I have to make a correction burn anyways.