Declining power supply could end NASA’s InSight Mars mission next year

One of InSight’s solar arrays, on the left, is covered in dust in this picture taken in May. Credit: NASA/JPL-Caltech

Without a fortuitous whirlwind to clear dust off its solar panels, NASA’s InSight lander could end its mission on Mars within a year due to dropping power levels, the project’s chief scientist said last week.

“We have a two-year extended mission which should take us to the end of calendar year 2022 if we can stay alive that long on Mars,” said Bruce Banerdt, InSight’s principal investigator.

InSight landed on Mars in November 2018 on a mission to measure seismic activity and study the Red Planet’s deep interior. Despite some snags with one of its two primary instruments, InSight has met all of its top-level mission objectives, Banerdt said in a June 21 meeting of the Mars Exploration Program Analysis Group.

InSight’s two-year primary mission ended at the end of 2020, and NASA approved a two-year extension to continue the mission’s measurements.

Banerdt said the spacecraft is “experiencing some pretty severe solar energy issues” after dust accumulated on the solar arrays. The solar power crunch is “limiting our ability to take science measurements and is likely to eventually cause the end of the mission,” he said.

Mission planners knew dust build-up on the lander’s solar panels could limit the mission’s longevity, but officials hoped wind gusts or dust devils might periodically clear off the fan-shaped arrays. So far, that hasn’t happened.

“This was all anticipated before we launched,” Banerdt said. “We were designed to be able to finish our prime mission with plenty of margin. We had hoped to get some dust cleaning, but that hasn’t happened.”

Banerdt said the InSight lander’s two fan-shaped solar arrays are currently operating at just 20% efficiency.

“The dust accumulation on the solar arrays has been considerable,” he said.

Mars is approaching aphelion July 12, the point in its orbit where it is farthest from the sun. That’s when InSight’s solar arrays will receive minimum energy from the sun, and temperatures at the spacecraft’s landing site will be near their lowest.

“That’s going to be extremely challenging in order to operate through that, especially with the instruments,” Banerdt said.

Ground teams at JPL have managed to keep InSight’s seismometer operating as the lander’s power levels have declined. For a time, scientists expected that the lander’s entire science payload would have to be shut off for six months.

At best, that would have resulted in a big data gap in InSight’s science results. At worst, officials worried InSight would have been unable to survive the treacherous period around aphelion.

Now managers are hopeful the lander will make it through the next few months. And there’s a chance the seismometer could remain operational.

“Most of the other sensors have either been turned off or are being operated sporadically,” Banerdt said. “This is resulting in an unfortunate hole in the meteorological data and the magnetic field data that we have been maintaining over the last Martian year.

“We’ve been rationing the on time of the instruments to accommodate the energy decrease, and we may have to actually power off the entire payload for some period around aphelion,” he said.

“We think we can probably get through the straits of aphelion here, but we’re not sure.”

InSight’s ground team devised a novel method of helping clear some of the dust off the craft’s solar arrays. Using the scoop at the end of the lander’s robotic arm, controllers gathered sand from the Martian surface and sprinkled the grains just upwind of the solar arrays.

The wind blew the sand grains across the top of the solar arrays, knocking off some of the dust. The first try at this new technique resulted in a gain of about 30 watt-hours of energy per sol, or Martian day.

That news was “extremely, extremely welcome” to the InSight team, Banerdt said.

InSight’s team has tried the same technique several more times, each giving a “marginal” boost to the lander’s power output, he said.

“We believe we’re understanding better how to do this operation,” Banerdt said. “We may be able to try it again before energy decreases to the point where we can’t use our robotic arm. But at least that buys us a little bit of headroom that we didn’t have before.”

Before attempting to sprinkle sand over the solar arrays, engineers sent commands to activate the spacecraft’s solar panel deployment motors to shake the dust off, but that didn’t succeed.

As Mars begins traveling closer to the sun, more solar energy should allow InSight to begin generating more electricity. But the improvement may only be temporary until dust storm season begins next year.

“Some time during the middle of next calendar year, around March/April of 2022, the energy starts to decrease pretty rapidly again because of the confluence of increased dust accumulation, because of a dustier atmosphere, and the Mars orbital geometry,” Banerdt said. “So unless we get a fairly significant increase in our solar array output, we’re likely to end our mission some time around that time next year.”

Artist’s concept of the InSight lander on Mars. Credit: NASA/JPL-Caltech

InSight’s French seismometer instrument has recorded 630 seismic events to date, according to Banerdt. Scientists confirmed InSight made the first-ever detection of a “marsquake” in early 2019.

Banerdt said five of those seismic events are “gold standard events” with clear seismic phases and polarization data to help locate the source of the tremors.

Another 106 have clearly observed seismic signals and phases, but no polarization. Virtually all of those have been confirmed as genuine tectonic quakes, Banerdt said.

He said many of the other seismic signals are also likely real marsquakes, but haven’t been confirmed.

The five quakes with confirmed locations all occurred in the Cerberus Fossae region, home to trenches that scientists previously hypothesized could be created from faults where segments of the Martian surface are being pulled apart. InSight’s findings confirm the region is seismically active.

InSight’s other main instrument is the German-developed Heat Flow and Physical Properties Package, or HP3.

A major element of the HP3 instrument is a self-hammering 16-inch (40-centimeter) probe that was supposed to dig into the Martian soil to measure the thermal gradient in the uppermost layers of the crust. The metallic probe, with a trailing umbilical tether, needed to reach a depth of at least 10 feet (3 meters) to provide the expected science data.

Instead, the mole only reached about a foot, or 30 centimeters, below the surface before its progress stalled. Ground teams tried nearly two years to get the mole into the Martian crust, including attempts using the scoop on InSight’s robotic arm to help push the probe into the ground.

But the tries turned up empty, and mission managers gave up on the mole in January.

Banerdt said the instrument is returning some partial data on the thermal conductivity of the top layer of Martian soil.

Despite the instrument woes and the declining power generation, which was expected, Banerdt said InSight has been a success. The mission was the first to detect marsquakes, yielding insights into the Martian interior that will help scientists chart Martian evolution and compare the planet’s evolution with that of Earth.

Some of the mission’s findings are still awaiting publication in scientific journals.

“This is finally the payoff of 25 to 30 years of efforts by many of us in the geophysical community and on the InSight team,” Banerdt said. “I think we’ve broken a lot of our theoretical models of Mars’s formation and evolution.”

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