WASHINGTON — NASA has officially ended the mission of the InSight Mars lander after power levels on the spacecraft dropped to the point where it could no longer communicate with Earth.
NASA announced Dec. 21 that InSight had missed two consecutive communications sessions, the threshold the agency set in November for declaring the mission over. The lack of communications, engineers concluded, came after the spacecraft’s batteries were drained, a condition called “dead bus.”
InSight missed its first planned communications session Dec. 18 after communicating with Earth as expected three days earlier, the agency said Dec. 19. NASA did not disclose when the second missed communications session was scheduled. The agency will continue to listen for any transmissions from the lander for some time, but said in a statement it is unlikely to hear from it again.
Project leaders had been closely monitoring power levels on the spacecraft since last year as dust accumulated on the spacecraft’s solar arrays, diminishing the power they can generate. Those arrays produced 5,000 watt-hours of power at the beginning of the mission but had dropped to just 700 watt-hours in June 2021. As of Dec. 12, power levels had dropped to 285 watt-hours.
Engineers made several attempts to try and remove the accumulated dust, including using the lander’s robotic arm to scoop up regolith and dump it near the arrays, allowing some wind-borne particles to bounce off the arrays and, in the process, remove dust. That process, called saltation, did boost power levels slightly on the arrays but was not a long-term solution.
InSight, selected in 2012 as part of NASA’s Discovery line of planetary science missions, landed on Mars in November 2018 and far exceeded its prime mission of one Martian year, or 687 Earth days. The spacecraft carried two major instruments: a seismometer and a heat flow probe, designed to help scientists understand the interior structure of the planet.
The seismometer worked well, recording more than 1,300 “marsquakes” during the mission. However, the heat flow probe, designed to burrow into the surface to a depth of up to five meters, got stuck just below the surface as it could not gain traction with soil despite extensive efforts to hammer or push it the probe deeper.
“The heat flux experiment actually did return science. It did not get the heat flow measurements that we wanted to get, but it did get a lot of other really great science,” Bruce Banerdt, principal investigator for InSight at the Jet Propulsion Laboratory, said in a Dec. 12 talk about the mission during American Geophysical Union (AGU) Fall Meeting. That included measuring the mechanical properties and thermal conductivity of the soil.
In addition to those two main instruments, InSight carried several other payloads, including engineering sensors, a camera and a suite of meteorological instruments that provided what Banerdt called “an unprecedently complete set of meteorological data,” such as pressure and wind speeds, for more than one Martian year.
“InSight has more than lived up to its name,” Laurie Leshin, director of JPL, said in a statement. “As a scientist who’s spent a career studying Mars, it’s been a thrill to see what the lander has achieved, thanks to an entire team of people across the globe who helped make this mission a success.”
InSight continued collecting seismic data up until the end of the mission, although limited power meant that the seismometer could only operate for eight hours at a time, after which it would rest for three days to recharge batteries. That hastened the mission’s demise, Banerdt said in his AGU talk. “We made the decision that collecting data on Mars is the reason why we’re here, so even though we could extend the life of the mission, it doesn’t make any sense if you’re not getting any data.”
In that talk, he acknowledged the mission was in its final weeks as its power levels dropped. He said that his entry into a “dead pool” predicting the end of the mission was Jan. 30, “which was later than most people on the project, but we’ll see what happens.”
NASA spent $813.8 million on InSight through the end of its prime mission in late 2020, including the spacecraft, launch and operations. France and Germany, which contributed the seismometer and heat flow probe, spent about $180 million.
“InSight really isn’t a very pretentious mission. It’s kind of a laid-back mission. It’s kind of an underdog mission,” Banerdt said in his AGU talk. “I spent about 20 years trying to convince people that this was a mission worth doing, and I think InSight has proved it was definitely worth doing.”