The Lil' Helo That Could... Will Again
In an update to the Mars Helicopter Blog, NASA broke news of Flight 14's postponement.
Engineers want more time to address small issues in the aircraft as it sits more than 212 million nautical miles away. Serving beyond its initial assignment, the probe must compensate for seasonal decreases in atmospheric density by boosting output. A series of ground and vibration tests have been optimistic in addressing the changes, but an anomaly in two of the flight-control servomotors prevented a brief Sept. 18 test flight.
Rotary-wing pilots might shudder to imagine a similar situation, stranded millions of miles from home, testing extended operation with the needle pegged beyond the red line, long after their TBO has passed, without a single wrenching hand in sight. This situation is nothing new for a NASA project, as many continue to serve long after their expected service life thanks to inherent design and build quality. Previous Mars Rovers were sent in 2003 for a planned mission of 3 months, but soldiered on for years afterward. Contact was finally lost in 2018, when a Martian dust storm blanketed portions of the region.
The tiny, four pound Mars Helicopter Ingenuity marked a new phase in space exploration when it left the rocky surface for the arid red skies. Initially expected to provide a proof-of-concept tech demo before going offline, an extended operation phase has flown almost 200% longer than expected, completing 11 flights. In one blog update, Teddy Tzanetos, Team Lead on Ingenuity, posted a picture of a red-colored pilot's logbook filled with flights and said "Before our campaign began, we were hoping for at least one, maybe up to three or four successful flights" Originally, he notes, Ingenuity was simply intended to take off and hover over flat terrain to test the parameters for powered drone flight on Mars. Now, multiple flights across perilous, rocky topography have pushed the limits of the navigation system as it provides multi-angle photos and 3-dimensional imagery of the surface.
Now, as the air density changes six months after landing, the crew must battle unexpected conditions. In this case, the previous power setting of 2,500 rpm is insufficient to maintain lift, which could now produce a thrust margin as low as 8%, a fraction of the 30% enjoyed on previous flights. Increasing to 2,800 rpm could make the sorely needed difference in thrust, if testing proves the setting safe.
The change requires a suite of checks and tests before extended flight, as potential vibrational resonances could cause a cascade of issues in sensors and flight control systems. Unlike terrestrial rotorcraft, the flyweight martian has little to rely on in case of damage.
Conjectures about the cause of the grounding anomaly are possible wear between moving parts, changing tolerances that now read as servo oscillation to the sensors. Another is the theory that the last high-speed spin test left the upper rotor at a position that loads the errant servos in an unusual way that causes the oscillation. The team remains optimistic that their tools will solve the issue within a few weeks, a perfect time for a pause as Mars will lie behind the Sun until Mid-October. Future Ingenuity updates are expected then.
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