Moving across ground you can't fully trust
Wheeled locomotion sounds simple until the ground itself becomes an unreliable partner. Planetary surfaces are often covered in loose regolith, fine, dusty, granular material that behaves less like solid ground and more like dry sand, capable of shifting, compacting unevenly, or swallowing a wheel that sinks in further than expected. Rover wheels have to be designed specifically for this kind of terrain, often using rigid metal construction with aggressive treads to maximize traction and resist punctures, since a wheel damaged by a sharp rock cannot simply be swapped out later. Rocks, slopes, sand traps, and terrain that looks stable from orbital imagery but isn't up close all pose real hazards, and the rover has to detect and evaluate them largely on its own given the autonomy constraints from the previous lesson.
This produces a mobility strategy that looks almost absurdly cautious by terrestrial robotics standards, and deliberately so. Rovers typically move at a pace that would seem glacial for any Earth-bound vehicle, frequently pausing to reassess the terrain ahead, build a local map, and re-plan before continuing. Path planning tends to favor routes that are demonstrably safe over routes that are merely efficient, willing to take a longer path around a hazard rather than a shorter one through uncertain ground. This conservatism is a direct consequence of the reality established in the first lesson of this course: a single mobility failure, a wheel stuck in sand, a puncture, a rover tipped on a slope, can end a mission permanently, since there is no recovery vehicle and no tow truck.