Docking Tutorial and how it can be improved

[Kordy]

Hello.

I'm not quite new to KSP, but since the release I've had friends asking me about particular things about orbital mechanics, and the question "how does docking work?" is one of the big ones. I was told the docking tutorial wasn't that good and they had problems matching orbits. So I delved in to see how and why they were failing.

So far so good, we have two ships on different elliptic orbits. Our rescue ship is low, so it goes faster compared to our stranded ship.

So what's our first order of business?

Uh oh. The descending node is way, way too far. Let's, for a second, assume we do go with what the tutorial suggests.

Okay, that done, now the tutorial asks us to place a maneuver node for intersection.

But that's not really good. We're too far in our orbit compared to our target, and doing an intersection with a single maneuver is only possible roughly 10-12 orbits later. You can see here how the intersection moves away as we continue along our orbit.

My proposed change is to make the first burn on Ascending Node instead. It ends up like this:

That gives us plent of time and dV left to get a favorable intersection, like this:

A bit of RCS and maneuvering after, docking complete!

However, the problems of the tutorial doesn't end here. Let's say you managed to delete the maneuver node with say, 1-5 m/s dV left. Your intersection will still be further away than what the game requires - 5km. But even if you do manage to get your intersection under 5km after that point, the tutorial still thinks you skipped a step and will not progress.

Also, if we DO get the stranded kerbals down to kerbin, the staging is set to discard the hab first

I'd love to be able to point my friends to a tutorial that gives them a better understanding.

[Scarecrow88]

I agree that the optimal burn to align the orbits is at the ascending node, but by following the tutorial and doing it at the descending node just means that when you do your intersect burn, the rescue ship orbit needs to go higher than the stranded ship. Your closest intersection then becomes the point where the rescue ship crosses from being higher than the stranded ship, to being lower.

Having said all that, I ran in to the same problem subsequently, in that the tutorial wouldn't progress beyond telling me to perform the intersect burn. I'm not sure if it thought I had missed a step, or if I didn't perform the burn quite to it's liking, but as a novice if I had got this far with the tutorial I would have been stuck.

I didn't proceed with the tutorial beyond the actual docking, so can't comment on the staging and how you get everything back to the surface.

[Kordy]

I agree that the optimal burn to align the orbits is at the ascending node, but by following the tutorial and doing it at the descending node just means that when you do your intersect burn, the rescue ship orbit needs to go higher than the stranded ship. Your closest intersection then becomes the point where the rescue ship crosses from being higher than the stranded ship, to being lower.

Yeah, but that is inefficient as all hell.

If I burned at DN, I got a 265ms burn to a higher orbit, and when I finally approached my target at around 10km, the relative speed difference was 500 m/s. If I burned at AN instead, my first burn was 285 m/s, but the relative speed difference at 10km to target was 200 m/s.

Maybe it should be split into two? Docking 101 where you get to use the oberth effect and easy inclinations, and Docking 102 where you have a really eccentric orbit where you have to burn more fuel to get there, I dunno.

[Bandock]

Playing around with that tutorial, I find it interesting that if you plan to rescue the stranded Kerbals they're likely to die anyhow if you ever decouple. :|

[DarkGravity]

The default view should be focused on the planet when you are adjusting your orbit. When you are approaching the stranded craft, the tutorial should tell you to switch the view to focus on your ship, and you shouldn't have to hit the Tab key 14 times to focus on your ship.

[Reactordrone]

Playing around with that tutorial, I find it interesting that if you plan to rescue the stranded Kerbals they're likely to die anyhow if you ever decouple. :|

Yeah, for some reason decoupling the ships summons the kraken. I even tried EVAing Jeb over to the stranded ship after the rescue ship spontaneously disassembled itself but as soon as he tried to manoeuvre it that ship also disassembled itself and flew off into space at high speed