Rendezvous with Jeb: An elliptical orbit rendezvous

[Whirligig Girl]

Here's the story

Jeb is on EVA in an elliptical orbit, with around 43% fuel, Pe is around 90 km, Ap is around 10,000 km, and I need to rendezvous with him using only tier 2.5 technology, how? I need help.

EDIT: Jeb only has 34% fuel left.

Edited November 2, 2013 by GregroxMun

[Taki117]

Have two command pods and pack lots of delta-V. Plan a rendezvous when Jeb gets close to the planet, then match his velocity and approach slowly. Since he has quiet a bit of fuel left switch to him to make the final approach.

[Whirligig Girl]

I was wrong, he only has 34%, is that still enough?

[andrewas]

Should be if you match orbits closely enough.

[Leatherneck]

Should be if you match orbits closely enough.

Yeah, if you do most of the work with the rescue ship, Jeb shouldn't have to use too much to close the gap. It is possible, as I had to do something similar once with an ailing space craft that was unable to maneuver at all.

[Kasuha]

Jeb's remaining jetpack fuel is irrelevant as long as he has at least something. You can get within a few meters with very simple tech.

Best for the task is a small ship with a retrograde engine so you can brake without turning around. Set up switching of the two engines on command keys such as 1 to activate prograde and shutdown retrograde, 2 to activate retrograde and shutdown prograde.

1/ Get in orbit. It may be circular or elliptical but it's good if it is smaller than the target elliptical orbit (i.e. completely inside it). Another option (if the target orbit is too small) is to make target orbit completely inside yours in the first step.

2/ Select Jeb as target.

3/ Match orbital planes in DN/AN node

4/ Enlarge/reduce your orbit so it just touches the destination orbit in one point. The red marker should show up. It's good if the touching point is in PA or AP of your orbit and it's even better if the AN/DN node is there, too. But these are not necessary.

5/ Put a maneuver to the touch point just behind the red marker and add prograde (to enlarge your orbit) until the two arrows match. If the target orbit is inside yours, do that with retrograde. Do not get on the other side of the target orbit, i.e. the resulting orbit should be between your current orbit and Jeb's orbit.

5a/ if you don't succeed (i.e. the two arrows don't match even if you match the two orbits), wait one orbit and try again

5b/ if you get a match, execute that maneuver. It's good to delete the maneuver during the burn and watch what the two arrows are really doing, you can get much better match that way. If you overshoot you can switch to your retrograde engine and brake a little.

6/ after you left the touch area, put another maneuver to the point where the two arrows are. Use whatever is needed to make your orbit visually overlap the target orbit as well as possible. Theoretically just a prograde/retrograde burn should suffice but it's possible you may need to add some radial component.

7/ Start executing that maneuver early - do not wait for half the burn time, instead start at exactly the time estimated as burn length. Do not finish that burn! It only gives you a good position and direction for braking for the final rendezvous. But you need to finish the rest using navball and normal view. Make sure your navball is in target mode. The task is not to execute that maneuver exactly but to zero relative speed with the target and at the same time minimize the distance between you and the target.

8/ When you brake to zero relative velocity, turn towards the target and get some velocity towards it. Do not overshoot, good practice is to have about 1-5% speed relative to distance (i.e. 50 m/s when distance is 1 km, 5 m/s when the distance is 100 m). Use your retrograde engine to brake for corrections.

When you get really close, make sure you don't push Jeb away with your retrograde burn.

This way you can get to within hand's reach from the ladder to Jeb with no problems.

Edited November 2, 2013 by Kasuha