WASHINGTON — NASA’s Ingenuity Mars helicopter crashed early this year when its navigation system was confused by the featureless terrain it was flying over, project engineers concluded.
Leaders of the Ingenuity Mars helicopter project at the Jet Propulsion Laboratory briefed the results of what they have dubbed the “first aircraft accident investigation on another world” at the annual meeting of the American Geophysical Union here Dec. 11, explaining what they believe happened on Ingenuity’s 72nd and final flight in January.
“The root cause of this was degraded navigation due to visually bland terrain, possibly in combination with high local slopes,” said Håvard Grip, chief pilot for the first half of Ingenuity’s mission at JPL.
The helicopter used a downward-facing camera to track features on the surface, an approach that worked well for most of the mission when the helicopter was flying over terrain with plenty of rocks and other features. However, by the time of the crash, Ingenuity had reached a region of sand ripples that provided few features its navigation system could lock on to.
On Flight 70, the navigation system was “starting to struggle,” said Travis Brown, chief engineer and team lead for Ingenuity, but was still within the experience on past flights. “By Flight 71, however, that vision navigation trouble eventually triggered an emergency landing.”
On Flight 71, Ingenuity touched down with a horizontal velocity of about 2.5 meters per second, five times what it was designed for, but the helicopter did not appear to be damaged. “We can see signs that the helicopter bounced and plowed through the surface,” Grip said.
He said something similar appeared to happen on Flight 72, a “pop-up” flight to allow controllers to get their bearings after the emergency landing on the previous flight. “We see signs that the helicopter bounced, plowed through the sand and threw sand away from the landing gear. From that, we can infer that, in Flight 72 as well, we had a hard landing with high lateral velocities.”
Shortly after that final flight, project officials speculated that the rotors contacted the surface during the hard landing, causing them to break. They no longer believe that was the case.
Grip said the blades were instead damaged by bending loads upon landing. All four blades suffered similar damage, breaking off about one-third of the way from the tip. “It suggests that they were all subjected to similar loads and they broke at a weak structural point along the blade,” he said, a conclusion supported by structural analysis of the blades.
That analysis was based on limited telemetry and images from Ingenuity. “We don’t have enough information to disentangle some of the details about the sequence of events right around landing,” he said, noting that fatigue over time or unobserved damage from the previous flight could have played a role, causing rotor blades to break just before landing instead of after touchdown.
The investigation led to several recommendations, such as improving navigation systems to handle terrain with few features and more robust handling of telemetry in the event on anomalies.
Those recommendations and other experience from Ingenuity will support potential future Mars helicopters. At the briefing, Teddy Tzanetos, Ingenuity project manager, discussed one concept called Mars Chopper. While Ingenuity weighed less than two kilograms, Mars Chopper would be far larger, with six sets of rotors.
It could carry five kilograms of payload and fly three kilometers per Martian day, traversing terrain far faster than rovers. “In about a week, you could cover the distance that Perseverance has driven,” he said. “It’s really a gamechanger when it comes to exploration and discovery.”
Officials emphasized that Mars Chopper is a concept with no firm plans to develop it for a future Mars mission. “It is a concept, intended to put out there a possibility for something that could be — and, obviously, we hope, would be — implementable in the future,” Grip said.
Ingenuity, despite the hard landing, lives on. “Ingenuity, aside from the rotor system, is still alive and well,” Tzanetos said. “Even after the hard landing on Flight 72, avionics, battery, sensors have all been functional.” The helicopter is now serving as a weather station, collecting data daily. It could continue in that role for up to 20 years based on the amount of flash memory available.
The helicopter remains in occasional contact with Perseverance, which relays data to Earth, even as the rover has moved more than three kilometers away. “That’s actually farther than we ever through we could get radio comms,” Brown said.
He added, though, that the rover is about to go over a terrain feature that will take it out of line-of-sight with Ingenuity, cutting off those communications. “It’s a good bet that, within the next month, we’ll lose contact forever,” he said, “or until we come back in 20 years with astronauts.”