Last February, the Mars rover Perseverance—the most advanced robot ever to explore another world—landed on Mars. The helicopter hitched a ride to Mars aboard the rover, and went on to perform the first powered controlled flight of an aircraft on another planet. As the rover reached an altitude of two miles above Mars, rocky boulders and steep cliffs suddenly appeared in high-def. As the rover descended, he was relieved to see that the navigation systems appeared to be working. Space and the deep ocean both lack the constellations of sensors that make such navigation technology possible.