On September 18th, NASA’s Ingenuity helicopter was supposed to take to the Martian sky for the 14th time and perform a brief hover flight that would have demonstrated its capability of flying with a higher rotor speed. However, during its pre-flight checkout, things didn’t go well for the chopper.
To adjust for the decreasing atmospheric density caused by seasonal changes on Mars, Ingenuity has been getting ready to fly with a higher rotor speed. Step one was to do a high-speed spin test at 2,800 rpm on the ground. If all went accordingly, step two was to perform a short flight at an altitude of 16 feet (5 meters) with a 2,700 rpm rotor speed.
On September 15th, Ingenuity’s motors spun the rotors up to 2,800 rpm, successfully completing its high-speed spin test. This gave the rotorcraft the green light to execute Flight 14. After that, however, NASA canceled the little helicopter’s short journey. So what exactly happened?
Well, according to the space agency, during Ingenuity’s automatic pre-flight checkout, the chopper detected an anomaly in two of the small flight-control servo motors. While servo motors are considerably smaller than those that spin the rotors, they are crucial to stable, controlled flight.
This self-test that Ingenuity performed ahead of its flight verified the six servos through a sequence of steps that checks if they reach their designated positions after each step. The data collected by NASA shows that two of the upper rotor swashplate servos started to oscillate with an amplitude of roughly 1 degree about their assigned positions.
Currently, NASA is investigating the anomaly’s cause and has proposed two theories that might explain what happened. One is that the moving parts in the servo motors are beginning to show signs of wear. And that wouldn’t be a surprise, considering that Ingenuity has performed 13 challenging flights in the thin atmosphere of Mars by now.
Another possibility might be that the high-speed spin test left the top rotor in a position that loads the servo motors in an oscillation-inducing manner. Whatever might be the case, NASA is confident that the rotorcraft will be back on the Martian sky.