Though Ingenuity successfully completed a preflight high speed test of its rotors on September 15th, when it came time to do its fourteenth flight two days later, intended as a short airborne test of that high speed, the helicopter’s computer sensed an issue prior to take-off and scrubbed the flight.
The goal of the high speed test and short flight were to see if Ingenuity could fly during the winter months when the atmosphere of Mars is thinner, thus requiring a higher rotor speed. Initially it was not expected the helicopter would still be operational at this point, so this is another example of it pushing its expected capabilities. The scrub however might be signalling the end date for Ingenuity, related to servo motors that help control the helicpoter:
Ingenuity performs an automated check on the servos before every flight. This self-test drives the six servos through a sequence of steps over their range of motion and verifies that they reach their commanded positions after each step. We affectionately refer to the Ingenuity servo self-test as the “servo wiggle.”
The data from the anomalous pre-flight servo wiggle shows that two of the upper rotor swashplate servos – servos 1 and 2 – began to oscillate with an amplitude of approximately 1 degree about their commanded positions just after the second step of the sequence. Ingenuity’s software detected this oscillation and promptly canceled the self-test and flight.
Our team is still looking into the anomaly. To gather more data, we had Ingenuity execute additional servo wiggle tests during the past week, with one wiggle test on Sept. 21, 2021 (Sol 209) and one on Sept. 23, 2021 (Sol 211). Both of the wiggle tests ran successfully, so the issue isn’t entirely repeatable.
One theory for what’s happening is that moving parts in the servo gearboxes and swashplate linkages are beginning to show some wear now that Ingenuity has flown well over twice as many flights as originally planned (13 completed versus five planned). Wear in these moving parts would cause increased clearances and increased looseness, and could explain servo oscillation. Another theory is that the high-speed spin test left the upper rotor at a position that loads servos 1 and 2 in a unique, oscillation-inducing way that we haven’t encountered before.
Because communications with Mars are now paused for two weeks because the Sun is in the way, the engineering team is holding off further tests until communications resume.