Exploring Mars is hazardous work. Robotic missions that are sent there have to contend with extreme temperatures, dust storms, intermittent sunlight, and rough terrain. In recent years, two robotic missions were lost due to dust alone, and all that roving around has done a number on the Curiosity rover’s treads. It’s understandable why mission teams are pleasantly surprised when their missions make it through a rough patch. This was the case with the Ingenuity team when they discovered that the rotorcraft, which has been exploring Mars alongside Perseverance, survived the night and is back in working order.
Testing how robotic helicopters fair in the Martian environment is one of the objectives of Ingenuity, which is the first mission of its kind on Mars. On May 3rd, 2022, the mission team learned that Ingenuity had lost power after trying to keep itself warm during the cold Martian night. Luckily, there was enough sunlight the following morning for the little rotorcraft to power up its batteries again and resume normal operations. This was a welcome relief, given that the Opportunity rover and InSight lander were both lost to the extreme cold and dust that characterize a Martian winter.
Like Earth, Mars’ tilted axis means it experiences seasonal change throughout the year. But since a year last about twice as long on Mars (687 Earth days), the seasons are similarly twice as long. The Jezero Crater, where Perseverance and Ingenuity are exploring, is located in the Northern Lowlands of Mars, which is currently in the midst of winter and will be for another eight months. According to data collected by the Perseverance rover, temperatures in the Jezero crater reach a high of -16 °C (3.2 °F) during the day and a low of -81 °C (-113.8 °F).
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During a typical night, Ingenuity‘s heaters keep the robot’s internal components at a temperature of -15 °C (5 °F), a serious drain on its batteries. However, the helicopter was designed for a short flight-test campaign meant to last for just a few months during the Martian spring of 2021. But since the mission has remained in operation for 657 days after its first flight (April 19th, 2021), it has had to endure the biting cold of Martian winter. As a result, the team was forced to implement a new operational paradigm where its systems experienced a complete shutdown every night and were reset the next morning.
This process is performed by the “Lazarus circuit,” which (as the name suggests) brings the rover back to life after being effectively dead for the night. This requires that the helicopter generate enough electrical batters to activate its heaters, thaw out the frozen battery, and charge it sufficiently before bringing the avionics back online. Travis Brown, Ingenuity‘s Chief Engineer at NASA’s JPL, explained in a NASA press release:
“The overnight brownout, while not fatal, does reset the onboard clock, causing Ingenuity to lose all sense of time and forget to wake up as scheduled. Instead, the computer wakes up and attempts to talk to the rover 2 hours and 15 minutes after the initial power-on. The exact timing of this entire process is based on a complicated combination of fluctuating factors such as battery charge, wind, dust, and temperature.
“As each morning’s wakeup was different, the team had to use the helicopter base station on the rover to search for Ingenuity’s signal using a search window covering the predicted wakeup time. Only when a communications link was established could Ingenuity’s clock be synchronized to allow a scheduled activity later in the day.”
This process became increasingly challenging as the winter nights grew colder, the days grew shorter, and the onset of winter brought with it Mars’ infamous “dust storm season.” The first component to fail was the inclinometer, which failed soon after the start of winter operations. This sensor measures the direction and pull of gravity before spin-up and takeoff to determine how the rotorcraft is oriented. Eventually, the mission team decided to ground the helicopter for two consecutive months. As the dust storms abated and the days grew longer, the team managed to resume operations with a series of short flights.
This made it difficult for the solar-powered helicopter to keep up with Perseverance, which relies on a multi-mission radioisotope thermoelectric generator (MMRTP). Unfortunately, Ingenuity was hit by several more dust storms, causing the layer of dust on its solar panels to grow thicker and making the odds of surviving each night fainter. The mission team planned to conduct a new flight on December 24th that would shake off the dust it had accumulated, but another storm dashed these hopes. In January, Ingenuity managed to make three short day flights and kept shutting down completely at night.
But on January 24th, 2023, after eight long months of winter, Ingenuity managed to stay warm (a relative term) throughout the night. According to the downlinked data reviewed by the mission team, Ingenuity also managed to bank power in its batteries early in the mornings and reached end-of-sol charge rates of more than 90%. This suggests that Ingenuity could be ready to resume regular flights, catch up to the Perseverance rover – currently a few hundred meters away – and provide valuable advanced imaging. At the same time, the mission team is cautiously optimistic about what the future holds. Said Brown:
“We’ve known since before our first flight on Mars that the rover sets an aggressive pace. Staying with or getting ahead of Perseverance has been a challenge in the past, and will it only grow more difficult as we enter the rugged, unfamiliar terrain of the delta. We expect that Ingenuity’s flight paths and landing zones will be full of hazards, and that radio performance between helicopter and rover may drop in and around the large geographic features that dominate this area. We know that any significant setback in flight distance or frequency may quickly put us out of communications range as the rover drives forward, never to return.
But of course, challenges are an everyday issue with the Ingenuity mission, and her team is prepared to keep pushing the boundaries of its performance and survivability. The purpose of the experimental mission is to test the capabilities of small rotorcraft in the Martian atmosphere, which always entails a significant margin of risk. Said Brown:
“It goes without saying that there are no guarantees when it comes to flying on Mars, but as long as our helicopter continues to endure each Martian night, and talk to us each Martian morning, we’re going to keep pushing further, faster, and higher. We’re going to stretch our legs, shake off the Martian dust, and fly like we’ve never flown before.
Further Reading: NASA