What does it mean: Patched conic

[ibanix]

So I've seen the term 'patched conics' thrown around. The wiki isn't very help. I understand it has something to do with how KSP computes trajectories. Can someone enlighten me on what the term means, and what I need to know about how it applies to real situations in KSP?

Thanks!

Edited July 6, 2015 by ibanix

[jarmund]

It basically means that the elpse representing your orbit will account for escape velocities and therefore other bodies as well. Without patched conics you will only have a grey elipse describing your orbit. With it, on the other hand, you can see an estimate of how you will move through several encounters.

[Sharpy]

First, conic curve is a line you obtain by intersecting a cone with a plane - depending on angle of the plane and the cone, this can be a circle, an ellipse, or a parabola, which are all shapes of possible orbits or fly-bys. Now, the "Patched" part means they are glued together as the ship exits SOI of one body and enters another - that's KSP's simplification vs real life where the other body still acts upon the ship, meaning the real orbits aren't pure ellipses or parabolas, but modelling n-body gravity would be far too much, so KSP uses the concept of "Sphere of Influence" meaning if you're in Minmus orbit, Kerbin doesn't act upon you at all. So, patching (pasting end-to-end) the conic curves across multiple SOIs creates a "patched conic".

A side result of this simplification is that KSP has no Lagrangian Points.

[nightingale]

Behold the great wiki.

In short, patched conics is how KSP models gravity calculations - by splitting up each body into a sphere of influence and making an N-body problem into a much simple two-body problem.

You may also hear talk about the "conic patch limit", which is a setting that says how many sphere of influence changes KSP will display/calculate your trajectory for.

In-game you'll see that upgrading the tracking station unlocks "patched conics", which is nonsense if you read the wiki article I linked to. What it's really unlocking is a conic patch limit greater than 1 (ie. showing what happens when you change SOIs).

EDIT: I guess it's not complete non-sense reading Sharpy's post above - although it's still modelling things using patched conics, it's not "patching" any conic sections together (ie not showing accross SOI changes)... so the tracking station unlocking "patched conics" actually does make sense.

Edited July 6, 2015 by nightingale

[ibanix]

Thank you!