Intercept Altitude....

[RizzoTheRat]

If I wanted to launch to intercept a craft in an 80km equatorial orbit I would launch to 80km but ahead of the target, then push my Ap out further to slow down and get an intercept on the next orbit.

If I wanted to launch to intercept a craft in a 200km equatorial orbit I'd launch to 75-80km but behind the target, and push my AP out to 200km at the right time to get an intercept half an orbit later

Is there either an optimal altitude at which one approach becomes more efficient than the other, or is there a better way entirely?

 

[Vanamonde]

Why not skip a step and time the launch to arrive at the target? It takes some practice but is definitely possible. For a while I was doing a lot of assembling things in orbit and got pretty good at eyeballing a launch-to-intercept. 

[18Watt]

4 hours ago, RizzoTheRat said:

Is there either an optimal altitude at which one approach becomes more efficient than the other, or is there a better way entirely?

The methods you described work well for me.  As long as your correction orbits are not ridiculously large or small, it really makes little if any difference.

If you are truly worried about efficiency, the real problem is the decision to intercept after one more orbit.   If you are patient, and can wait multiple orbits, you can save fuel.  Much more fuel than you’d get by worrying about wether it’s better to approach from behind or ahead.

Or, as @Vanamonde said, just launch directly to intercept!  

[RizzoTheRat]

12 hours ago, Vanamonde said:

Why not skip a step and time the launch to arrive at the target? It takes some practice but is definitely possible. For a while I was doing a lot of assembling things in orbit and got pretty good at eyeballing a launch-to-intercept. 

I've never managed to get close enough trying that to not end up burning a fair bit of fuel fixing it, wheras can reliable get within a couple of km by orbiting first, which only needs a tiny bit of fuel to correct. 

Updating my kOS scripts so trying to define some specific parameters for it. 

8 hours ago, 18Watt said:

The methods you described work well for me.  As long as your correction orbits are not ridiculously large or small, it really makes little if any difference.

If you are truly worried about efficiency, the real problem is the decision to intercept after one more orbit.   If you are patient, and can wait multiple orbits, you can save fuel.  Much more fuel than you’d get by worrying about wether it’s better to approach from behind or ahead.

Or, as @Vanamonde said, just launch directly to intercept!  

The idea is to get the timing right so it only takes one orbit,  but agree fur any further apart several orbits is more efficient.   Not that worried about efficiency though I don't think there's a massive difference between them, but need to define some specific criteria for my kOS scripts

[18Watt]

Just as a personal preference I usually aim to be just ahead of my target reaching orbit, and then burn for a larger, slower orbit to rendezvous.  In terms of efficiency I do not think it matters at all, just what’s easiest for me.

And I do agree that launching to direct intercept is almost always less efficient for me- I’m just not that good.  It is fun to do that sometimes, but if I’m saving every drop of fuel I don’t attempt a direct intercept. 

[king of nowhere]

16 hours ago, RizzoTheRat said:

If I wanted to launch to intercept a craft in an 80km equatorial orbit I would launch to 80km but ahead of the target, then push my Ap out further to slow down and get an intercept on the next orbit.

If I wanted to launch to intercept a craft in a 200km equatorial orbit I'd launch to 75-80km but behind the target, and push my AP out to 200km at the right time to get an intercept half an orbit later

Is there either an optimal altitude at which one approach becomes more efficient than the other, or is there a better way entirely?

 

actually, it is always more efficient to intercept from a lower trajectory. the reason is that it takes fuel to raise your apoapsis, and then fuel to lower it. so for an 80 km equatorial orbit the right orbit to intercept efficeintly is a 75 km orbit