A guide to performing low orbit rendezvous

This document explains how to use the reference frame fixing a target vessel to perform a rendezvous with a vessel in low orbit around Kerbin.

The first thing to do is to establish the reference frame. You select a target vessel in map view by checking Select target vessel... in the main Principia window and clicking on the vessel. Then you set the speed display of the navball to target mode. You can use the panel to pick the reference celestial, Kerbin in our case.

Before doing the final rendezvous procedure your orbit must have a relatively low inclination relative to the target and be at roughly the same distance from Kerbin. Then, you must warp until you are close to an ascending or descending node (indicated by the markers AN and DN).

When you are near a node, you must kill the velocity normal to the orbital plane. This is best done by planning the manœuvre in the Kerbin-Centred Inertial (KCI) frame, burning along the binormal (either + or -) so that the ellipse doesn't change shape.

Once you have matched the orbital plane of the target, change the orbit size to catch up with the target vessel at a suitable speed. Every orbit spent catching up will look like a loop, over a series of loops your predicted trajectory should get closer to the target. The markers showing the closest approaches help you evaluate this. Eventually you must tune as precisely as possible the closest approach a few orbits away.

Once you reach a good closest approach (a few kilometers) you must kill most of the relative velocity. You must tune your approach so as to stay close to the target for many orbits. Iterate to make the closest approach closer and closer to the target.

This will bring you within a few hundred meters of the target. After that it's business as usual for the final docking.