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I have finally figure out how to align inclination and rotate my orbit so that my Kerbal and the stranded one are chasing each other around Kerbin.

So the last part before approach is to get closer. I have read a few tutorials and this excellent answer How do I rendezvous and dock with a ship in orbit?, but I still cannot grok this last bit.

Lets say I am leading. I need to do a series of prograde, retrograde burns only I think, but I can't figure out how to time them or or whether I should be doing target or orbit pro/retro-grade burns.

I am thinking that a prograde orbit burn at apsis should increase my orbital path, which means I am going slower, which gives the other guy a chance to catch up, then a retrograde orbit burn to drop in nearby. But then one of the tutorials talks about doing a target prograde burn and in general I am just guessing and end up with an orbital path intersecting the planet (and perhaps this is how it should look part way though the maneuver for all I know).

The inclination and rotational adjustments are easy with the manuever controls to assist, but I can quite grasp this one - perhaps I can use the manuever controls to assist with this also?

He has been up there for four days. He is getting hungry.

  • Did you see the second video I posted with that answer? I intentionally perform the last part less than optimally for explanations sake. – MBraedley Dec 13 '13 at 12:19
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    Hah, that cleared it up @MBraedley - I got within 35m but had run out of battery and no solar panels - and haven't got rcs in career mode yet. I waved through the window. – Paul Dec 15 '13 at 13:32
  • @Paul: Way too late I suspect - but if you got to within 35m you can switch to the hungry Kerbal. Then switch on his jetpack rcs and let him cover the last few meters on his own, grab the command module and board. I think I've managed to switch to a lone kerbal from around a 1km and got him to the rescue ship. – Grhm Apr 17 '15 at 12:05
  • I'm assuming the kerbal to be rescued is adrift on EVA - not in a ship... – Grhm Apr 17 '15 at 12:06
  • @Grhm He was in a ship, but it was without fuel. I got there in the end and walked him over. It was one of those moments in KSP. – Paul Apr 17 '15 at 12:08
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Here is the whole procedure you need to do, right from the beginning. I'm writing all this just to avoid any confusion between your initial intersects, and fine tuning your approach.

First thing here is to make sure your inclinations are as close as possible to eachother.

If you are leading the ship/object you want to dock to, burn prograde to increase your AP/PE. Your goal here is to make your orbit larger than the other ship's orbit. However, ensure that at some point, the 2 orbits intersect each other, and not at sharp angles. Try to make them as close to parallel as possible where they meet.

If you are trailing the ship, burn retrograde in order to make your orbit smaller. Again ensuring the orbits intersect at some point.

Don't go crazy with the difference in the two orbits, time and experimentation will give you more experience on getting this right. You can also re-adjust your orbits now and then by burning either prograde or retrograde at the point where the 2 orbits intersect, and seeing how it affects your intercepts.

To give you an idea how this works; a ship with a smaller orbit will make one orbit faster than a ship with a larger orbit. So a smaller orbit is "faster". So yes you were correct in your statement.

Then it's just a matter of time warping until you intersect. Make sure to right-click on the other ship/object in the map view and set it as the target. This will then show you orange and red arrows that indicate where, when, and how close you will intercept your target.

When you see the intercept arrows, you can stop the time warp and try adding a maneuver node at different spots in your orbit to try different things that may make your intercept closer. Check your distance by hovering your mouse over the orange or red arrow, make a small adjustment to the node and check to see the difference. Again, more experimenting.

Once you are within 0-10 km's (under 10 is my personal preference but it depends on your ship's abilities), you then want to click on the speedometer above the navball until it says "target" and a speed under it. This is your speed relative to your target, so if it shows 0 (zero), then you are moving at the exact same speed as your target.

Now you will point directly towards your target (purple on navball) and do a burn to get closer and raise that target speed. At this point you will see your distance from the target dropping. Now, you're moving towards your target, but your orbits are different so you will likely not hit it directly unless you were really close to begin with.

Turn your ship now to point at the yellow retrograde. Since you are in "target mode", the retrograde is adjusted in reference to your target and its orbit.

As you start getting close, you may find that you are passing beside it. This is normal. Still pointing at the yellow retrograde, you want to now burn and get your speed back down to zero. Then, point back to your target (purple) and repeat this until you are within 1KM (1000 meters) or less. Be aware that you don't want to get too close to your target when burning with a rocket because rockets can push your target away from you or send it into a spin.

Once you're within 1KM and you've brought your speed down to zero, you can now switch to using RCS only for the rest of the approach. RCS thrusters will not affect the other ship like rockets do so you don't have to worry about using them when you're close to it.

The most important part of all of this is to have patience and don't rush. If you pick up to much speed when trying to get closer, you could screw it up by overshooting your target. And it's normal to have to do several slower approaches to get closer and closer. The more you do this, the better you'll get at it.

Good luck!

  • Thanks XToro, that is a great answer. Right now I am trailing, 300km. The intercept point is at apo, but the peri is at 69km. In order for me to go lower, I am going to scrape the atmosphere. Does this mean my option is to go higher, and wait for a go around? – Paul Dec 13 '13 at 12:10
  • @Paul: If you're trailing by 300km, it's going to take a long time to catch up by setting your periapsis low. What I would do in your circumstance is do a burn at your current apoapsis in the prograde direction until the encounter markers show that you'll be leading by about 5km or less on the next orbit. That extra 5km is to give you time to slow down, as you'll be travelling significantly faster at that point. From there, it's a much simpler final approach. – MBraedley Dec 13 '13 at 12:26
  • @Paul Yes. This can sometimes happen where you need to take the longer way around to get to your target. So in this case, match your peri to your target's orbit and raise your apo. You won't be catching up to it, instead you'll slow and let it go all the way around and catch up to you. It takes longer but sometimes it's the only option. Or, you could make peri and apo 70-71km to speed past it, then raise your apo and peri again to let it catch up. Either way will work. – Dorian Dec 13 '13 at 12:26
  • @XToro Yes, thanks I was thinking of it the wrong way, and burning at apo. Of course it makes sense to adjust at the low point where you have loads of room at the other side. Well I got within 10km which is a first, then got confused when the purple/yellow didn't react how I thought they would, and then ran out of fuel! – Paul Dec 13 '13 at 13:11
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    Xtoro's link is giving me a 403 error, so here is a link to the wiki (which you have likely found already) which shows the symbols. Don't confuse these symbols with the prograde/normal/radial symbols you have on the orbital map! – Cocoa Nibs Jackson Dec 21 '13 at 17:33

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