from
https://www.theregister.com/2023/05/30/ingenuity_mars_helicopter_offline/

Mars helicopter went silent for six sols, imperilled Perseverance rover

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Ingenuity's still setting records, but waking it up and chatting are
getting harder
iconSimon Sharwood
Tue 30 May 2023 // 00:29 UTC
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. ®

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