At least 18 according to the Jet Propulsion Laboratory at NASA based on the article for pi day — Oh, the Places We Go: 18 Ways NASA Uses Pi. Number 12 on the list: Keeping rover wheels turning:
Rover wheels have distinct designs on them that leave patterns on the ground as they turn. These patterns serve as visual markers that help operators while driving the Mars rovers remotely from Earth. Pi is used to calculate how far the rover should travel with each wheel rotation. By measuring the distance from one wheel mark to another, rover drivers can determine if the wheels are slipping or if they’ve driven the expected distance.
Each of the 18 on the list has an associated project with a printable poster. The Celebrate Pi Day with NASA page has resources for educators, students, and pi day enthusiasts.