Robotic Space Rovers Keep Getting Stuck — Engineers Have Figured Out Why

When a multimillion-dollar extraterrestrial vehicle gets stuck in soft sand or gravel — as did the Mars rover Spirit in 2009 — Earth-based engineers take over like a virtual tow truck, issuing a series of commands that move its wheels or reverse its course in a delicate, time-consuming effort to free it and continue its exploratory mission. While Spirit remained permanently stuck, in the future, better terrain testing right here on terra firma could help avert these celestial crises.