Crossing a wide open area can be achieved on the basis of a simple reactive "avoid obstacles" loop, whereas traversing a rough and dangerous area requires slowest speeds, finer terrain modeling and finer motion execution control for instance. The rover must therefore be able to choose among a set of various navigation modes (see the introduction on rovers nagivation and [Lacroix 1994, Chatila 1997]). The definition and the number of these modes depend on the rover mechanical structure and on the kind of terrains he might encounter during its missions.

As a consequence, we have developped a bunch of different algorithms:

• Potential fields

• Circle arcs generation

• Nearest diagram method

• On rough terrains: a local planner based on a 3D digital elevation map and a rover placement function.

All these algorithms are integrated within a modular, evolutive architecture [Lacroix 2002], and controlled according to the context thanks to navigation strategies.