NASA has delayed the first flight of its Ingenuity Mars helicopter after a crucial test-spin of the drone’s rotor blades abruptly stopped.

This was the last major test to make sure the helicopter would be ready for its first flight, which was originally scheduled for early Monday. Now NASA has delayed the historic liftoff — which would mark the first powered, controlled flight on another planet — to Wednesday.

For the test on Friday, Ingenuity was supposed to spin its blades at full speed while on the ground. The two pairs of blades should have spun in opposite directions at more than 2500 rotations per minute — about eight times faster than an Earth helicopter. On flight day, they’ll need that speed to lift the 4-pound drone into the thin Martian atmosphere. That air has just 1% the density of Earth’s atmosphere, making Ingenuity’s task the equivalent of flying three times higher than the peak of Mount Everest.