The perfect gravity assist is almost perfectly wrong (conic draw mode problems)

[allmhuran]

Behold, my encounter with Eve using draw mode 0. It looks like an almost perfect gravity assist. My approach is almost directly solar-retrograde towards Eve, swings around really close and exits almost directly solar prograde. This is pretty close to the ideal gravity slingshot trajectory.

But wait! Look at my resulting orbit (the red dashed line). It's half way to Moho. What's going on?

What's going on is a problem with conic draw mode zero. Mode zero lets me focus in on eve and actually see the intercept to fine tune it, which you can't do with *any* of the other modes. However, it shows the path I will take when Eve circles around to the intercept position! And the intercept position is almost 180 degrees around from where Eve is now (You can see it on the other side of Eve's orbit in the picture). So you have to flip the encounter trajectory around too, which means this is an almost perfect anti-assist!

This is a pretty big problem with draw mode zero. But with any other draw mode there's no way to zoom in on the encounter to see what is actually happening!

So... anyone know a solution to this problem? I believe there are 5 draw modes in the game.... but I also believe none of them are actually useful. (Mode 3 is probably fine if you're just going to the Mun...)

What would be really nice would be a picture-in-picture box that popped up when you had an encounter, and which you could drag around, showing a tight focus around any intercepts that are happening. Or at least, it would be nice if mode 0 showed your trajectory from the SOI of the target (as it does now) but drew the trajectory in the timeframe of the encounter.

Edited October 26, 2013 by allmhuran

[Sirine]

No solution for me, just some reference for you.

http://forum.kerbalspaceprogram.com/threads/11322-Different-Conic-drawing-modes

[Nemoricus]

Your problem is that it's patched conic mode 0. It shows orbits relative to the current positions of the planets. However, the effect of a gravity assist depends on the planet's position at the time of your exit. I think mode 2 might be the best for planning a gravity assist, but I'm not sure.

[Kasuha]

Mode 0 is in my opinion best for any purpose. You just must not forget the big picture because of small details. It's not enough to look at Eve and perfect your slingshot there.

My approach is: get the maneuver to a slingshot. Any slingshot. Then click on the periapsis to have it highlighted all the time and zoom out. From now on watch your Eve periapsis to not drop too low, but instead of nudging trajectory around Eve, nudge the resulting trajectory after escaping from Eve. Because that's what you need to bring you where you want to be. The slingshot gives you unbelievable freedom in setting up that orbit for a price of tenths of m/s.

If the maneuver is too sensitive and you have problems doing that with the maneuver node, execute that maneuver and fine tune the real trajectory with RCS. It's no problem to switch the trajectory to the other side of Eve with just RCS if you're half an orbit away.

Oh and one more small detail: make sure to cross SOIs at lowest possible time warp (x5 is the best, better even than x1). Crossing SOI at high time warp may destroy your carefully prepared maneuver completely.

Edited October 26, 2013 by Kasuha

[Superfluous J]

I've found that by selecting Kerbol (or sometimes Moho) I can get my mode-3 approach on the screen and zoomed in enough to see what's going on. Takes some zooming and panning but you can get it. I'm not sure what you mean that mode 3 is only good for Mun/Minmus encounters. I use it exclusively for everything and never have any problems that aren't surmountable.

I agree though that we should be able to select anything along our path (that periapsis tag, or the ghost of Eve you'd see in other drawing modes), or be able to translate the camera to any arbitrary location in the map. That would be ideal.

[allmhuran]

I know it shows the trajectory at the current position. That's what allows you to zoom in on it. That part is good.

The problem is that the plot of your trajectory through that SOI is not rotated to account for the orbit of the planet around the sun. If the mode 0 patch looks like solar retrogtade, but the planet is currently 180 degrees away from where you will intercept it, the trajectory is actually solar prograde (because the direction of the target will have changed 180 degrees). If it's showing your trajectory relative to the current position of the target, it should ALSO show it relative to the current DIRECTION of the target.

Edit, In case that's still not clear: In my image, it looks like I will enter the SOI from the inside of the Eve's orbit (lower solar altitude) and exit on the outside (higher solar orbit). But that's not what's going to happen. I will enter from the outside of Eve's orbit and leave on the inside.

I'll have a look at mode 2, don't think I've ever used it.

Edited October 26, 2013 by allmhuran