Docking while changing orbits?

[Sisyphus]

Howdy - I have a question that stumping me.

I think this is a similar calculation to planetary insertions, just on a smaller scale

I have my tug at a 200km orbit around Kerbin. It has 400dV left.

I have my fuel drop orbit at a 77 km orbit around kerbin.

Both are on aligned orbits, and I'm trying to work out when to make the orbital change - but I cant make the closest intersect anything less than a 100+km...

I think i will have to wait for a few orbits before everything aligns - but how do I work out how much time to wait?

Edited January 12, 2014 by Sisyphus

[shand]

Personally use the manoeuvre nodes. plot it out so you have a closest intersect - then move the node around the orbit. works especialyl well for intercepting a circular orbit from a circular orbit - the more ecliptical the orbit the more fiddly it is...

Keep moving the node and you'll see the effect on the the intercept.

otherwise get some paper out and do the maths! or i beleive a few mods can do the maths for you (mechjeb and engineer redux come to mind)

hope that helps!

[Sisyphus]

yeah.. moving the manuver node around never seems to result in an intercept

[SuperBigD60]

You're right, it is just like interplanetary transfer windows...

With those orbits, if you're going from the lower orbit to the higher one, I bet you want to wait until you're roughly 20 degrees or so behind the tug.

Once you get close you can jimmy around with the maneuver node and find an intercept.

[kujuman]

Assuming near circular orbits...

1) Burn to have the tug lower its Pe to 77km, it doesn't really matter where, but I like to have the Pe be on the dayside, as this is where the rendezvous will occur

(I like to burn so that my Pe is just inside the orbit of my target, the goal is that if the paths intersect, the closest approach measurements seem more accurate)

2) Wait. Keep an eye on the closest approach markers every orbit. You should notice eventually the "target" marker will move from being behind your vessel at closest approach to moving in front of it. As soon as this happens, burn retrograde until the markers line up; you will have your rendezvous on the next orbit.

To know if this is going to work correctly, the closest approaches should be at or near your Pe.

I hope this is clear enough. It's not as fast as other methods, but it will work. Good luck

If you just want a fast intercept and have plenty of fuel, you can also try burning radial in and radial out with the maneuver node to fine tune closest approaches, but it does waste fuel.

[SuperBigD60]

Assuming near circular orbits...

1) Burn to have the tug lower its Pe to 77km, it doesn't really matter where, but I like to have the Pe be on the dayside, as this is where the rendezvous will occur

(I like to burn so that my Pe is just inside the orbit of my target, the goal is that if the paths intersect, the closest approach measurements seem more accurate)

2) Wait. Keep an eye on the closest approach markers every orbit. You should notice eventually the "target" marker will move from being behind your vessel at closest approach to moving in front of it. As soon as this happens, burn retrograde until the markers line up; you will have your rendezvous on the next orbit.

To know if this is going to work correctly, the closest approaches should be at or near your Pe.

I hope this is clear enough. It's not as fast as other methods, but it will work. Good luck

If you just want a fast intercept and have plenty of fuel, you can also try burning radial in and radial out with the maneuver node to fine tune closest approaches, but it does waste fuel.

Yeah, this is easier

[Sisyphus]

thanks.

Tug picked up its fuel and the Munar lander - and brought them back to the Mün Worked perfectly!

[Sisyphus]

Great, how do I set this thread as answered.