On-orbit servicing missions induce challenges for the rendezvous and docking system since a typical target satellite is not specially prepared for such a mission, can be partly damaged or even freely tumbling with lost attitude control. In contrast to manned spaceflight or formation flying missions, new sensors and algorithms have to be designed for relative navigation. Dependent on the distance to the target, optical sensors such as mono and stereo cameras as well as 3D sensors like laser scanners can be employed as rendezvous sensors. Navigation methods for far and close range and different verification methods are discussed.