Mars helicopter went silent for six sols, imperilled Perseverance rover
Ingenuity's still setting records, but waking it up and chatting are getting harder
NASA has revealed a six-day stretch during which it could not contact its Ingenuity Mars helicopter.
In a lengthy post, chief engineer Travis Brown explained that after the copter's 49th flight, radio contact was lost for six sols – just short of six days and six hours of terrestrial time.
Initially, NASA's Mars boffins weren't unduly concerned. The Perseverance Rover had moved behind a rocky outcrop that created a "communication shadow." Brown wrote that since Sol 685 the helicopter "had unfortunately been drifting in and out of night-time survival mode" which made daily contact with the craft difficult. So a day or two without contact wasn't worrying.
But once Perseverance moved to another location and Ingenuity still could not be found, Brown wrote "the situation began to generate some unease."
"Poor telecom performance was seen as a plausible explanation, but there were reasons to doubt it," he wrote. "In more than 700 sols operating the helicopter on Mars, not once had we ever experienced a total radio blackout. Even in the worst communications environments, we had always seen some indication of activity."
But the signal received on that day, sol 761, was just a simple ACK (acknowledgement). The next day, the copter again acknowledged a command, but did little else.
Mission staff determined that the ridge separating Ingenuity and Perseverance was a challenge for the copter's radio. It didn't help that Perseverance's helicopter base station (HBS) antenna is mounted low on the vehicle's right and is subject to occlusion effects.
While NASA folk figured that out, Perseverance moved towards its next goal – but that created new problems.
"It is extremely important for Ingenuity to stay ahead of Perseverance while moving through the narrow channels of the Jezero delta," Brown wrote, as the rotorcraft's job is to scout ahead for the wheeled rover. And NASA operates a no-fly zone around Perseverance.
With the rover on the move, and the helicopter stopped, it became imperative to get Ingenuity moving.
"Relying on the helicopter's onboard pre-flight checks to ensure vehicle safety and banking on solid communications from the rover's imminent proximity, the team uplinked the flight plan," Brown wrote.
Ingenuity did more than just ACK that upload. It ingested and executed it, resulting in its 50th flight and an altitude record of 18 meters.
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"It would be an understatement to say that the helicopter team was relieved to see the successful flight telemetry in the Sol 763 downlink the following morning," Brown wrote.
But he added that anxious days lie ahead.
"It now appears that the dust covering our solar panel will ensure that Ingenuity will likely remain in this transitional power state for some time," he wrote. "This means that, much to the chagrin of her team, we are not yet done playing this high-stakes game of hide and seek with the playful little helicopter."
Ingenuity last flew on April 22, when it made a 188-meter hop at an altitude of 12 meters. The craft was designed to fly just five times, so has already vastly exceeded expectations. ®