How to "Catch up" in a orbital rendezvous?

[Imaus]

A less then ingenious idea, which was to have my two part mun lander have a command capsule and a lander separate has lead to a difficult situation. I have never done a rendezvous before. Now after many edits markers, I have reached an almost perfect orbit overlap with the command pod, but they are separated by a huge margin and I have no clue how to get them closer.

http://imgur.com/pqfibga 10/10 MS paint diagram.

Learning to rendezvous would have gone much better in a controlled situation, but not all of us are that lucky. Any help would cause 3 less deaths in the space program!

[Taki117]

There are two ways of doing this, neither are very fast. The first is to lower your orbit inside your targets orbit and then wait for the close approach markers to get close together. The second, is to do the same thing, but make your orbit larger and let your target "catch up" to you.

[FenrirWolf]

There are two ways of doing this, neither are very fast. The first is to lower your orbit inside your targets orbit and then wait for the close approach markers to get close together. The second, is to do the same thing, but make your orbit larger and let your target "catch up" to you.

This. The general principle to remember is that orbits closer to the planet are faster. So if you want ship A to catch up with ship B, make sure that ship A's orbit is lower than B's on average.

[Lheim]

So, the basic useful fact is that higher orbits move slower, and lower orbits move faster.

If you bring a portion of your orbit down lower than the target's orbit, you will .. orbit by orbit, creep up closer behind it. How much depends on how much lower you go - or you could go higher, and going slower gradually let the target 'lap' you.

It's a matter of going around a few orbits and keep trying the maneuver nodes at the point where your orbits overlap to see if you can adjust the timing with prograde or retrograde thrusts so that the next orbit around you come close to each other.

[NoClass]

It's a matter of going around a few orbits and keep trying the maneuver nodes at the point where your orbits overlap to see if you can adjust the timing with prograde or retrograde thrusts so that the next orbit around you come close to each other.

If you have the delta V, you can put a maneuver node on the next intercept point and just extend until the predicted intercepts are close together. This, of course, assumes that your orbital angles are the same.

[ColdWarrior000]

Make the orbit smaller with one intersect point.

[lodestar]

Reaching a nearly perfect orbit overlap when you are far apart isn't very useful, but if your orbits are already nearly exactly equal, you can figure out your distance and phase angle. Once you know that, you can change your orbital period such that after n orbital revolutions you'll be very close. If you are in front of the lander you want to rendezvous with, you have to increase your orbital period so the lander will catch up with you. If you are behind, you have to decrease it so you'll move faster and catch up with it. You can do it in small steps and wait, but what's the point of playing Kerbal Space Program if you're not putting your knowledge of orbital mechanics to good use? All you need to know is how to calculate your orbital period from your orbit, and the other way around, how to calculate your orbit from your orbital period, and you can do it in a single pass.

As an example, let's say you you are in a 40km circular orbit around the Mun, you're in front of the lander, and your angle of separation is 77°.

1. With that orbit, you have an orbital period of 2894 seconds. Divide that by 360 and you have around 8 seconds/degree.

2. If your angle of separation is 77°, you need to increase your orbital period by 77*8=616 seconds, or to 3510 seconds.

3. To have an orbital period of 3510 seconds around the Mun you need a Semi Major of 272.92km. With a 40km periapsis that means you need to raise your apoapsis to 105.84.

4. So, raise your apoapsis to 105.84, and after one revolution, you should be very close to the lander.

5. When you are closest to your lander, target it, point to the target velocity prograde marker and match velocities by burning until the relative velocity is near 0m/s.

6. To rendezvous, point to the target prograde marker and burn until you get a few m/s relative velocity.

7. When you are at the closest approach, point to the velocity retrograde marker and match velocity again.

8. If you are within 100m or less, you can fire up RCS and dock. If not, go back to 6 and repeat until you are close enough.

Edited July 23, 2014 by lodestar

[Imaus]

These really helped, I manged to get sorta close and moved my people to the other ship, no docking yet but in due time it will happen.