Rescue! Elliptical Orbit Rendezvous - Please Help

[gordon_freeman]

So I have a Kerbal who has been stuck on his own circling the solar system in a large elliptical orbit for nearly 20 years. He is in a huge elliptical orbit that goes from just inside Jool orbit at apopapsis to inside of Kerbin orbit at periapsis. He ended up stranded without gas, and after all these years I've decided to try and go rescue him. No luck. I get decent ships with ample delta-v out there but I just cannot seem to line things up correctly. The rendezvous technique I typically use is to null relative velocity, point at target and accelerate, then repeat until I'm close enough to use RCS. At these distances, that just won't work, I need to fine tune this, I need to do the math I think.

Does anyone know a good calculator or process for approaching this problem? I'm sick of eyeballing it, I want to get this Kerbal home so he can take a shower!

[Gromaz]

The easiest way I can think of would be to achieve the same orbit as the thing your are trying to dock to, very similar to dock to something orbiting Kerbin.

Use RCS when you are about 50m from the object and at a releative velocity of 0.0m/s (+/- 0.1m/s) as usual.

It's difficult to say something more specific without seeing the orbit of the rogue object, can you post a solar system picture with the orbit perhaps?

Naturally it would seem that it would be best to catch the rogue while close to Kerbin but I think that is much harder.

[Awaras]

1. Set the stranded ship as the target.

2. Achieve a circular orbit at the same height as the PE of the elliptical orbit.

3. Match inclination.

4. Place a maneuver node at the PE of the elliptical orbit. Raise/lower the AP until you achieve intercept with target vessel at the PE point.

5. Execute the maneuver node.

6. Rendezvous as usual.

Unless you get very lucky, it will probably take you 1-3 full orbits to do all this, so it could take a long time... :/

Edited May 16, 2013 by Awaras

[Merinsan]

I've done this once before, and it was a pain, when my Eeloo mission ran out of fuel returning.

The biggest problem I had was the physics went a bit weird when I time accelerated and the ships jumped (ie I was within 1km then time accelerated and it jumped to 5km).

Once I got within 200 meters the problem stopped.

To start with I used the standard rendezvous method you described, but I could only get a closest approach of about 300km. I then waited till that point and switched to target mode to cancel relative velocity, which took quite a while.

By the time I was close enough, I had ran out of RCS (the ship itself was not well balanced for RCS) but I managed to dock with engines alone.

Good luck.

[gordon_freeman]

Thanks for all the replies. It really is a pain. The orbit this Kerbal was stuck in was a huge ellipse

I took the suggestion from Awaras to match periapsis, and it took forever, and suddenly I noticed that my first rescue attempt, a ship that had been shadowing this Kerbal in a nearly identicle orbit had finally drifted fairly close (within a few million kms) So I used that. Here's a shot of the rendezvous. The lone kerbal (Desperately in need of a shower) is dead centre in the image, rescue ship to the left)