A mid-air error led NASA's Mars helicopter to tilt wildly back and forth in its latest flight - but it landed safely

• NASA's Ingenuity helicopter encountered a navigation glitch in its most dangerous Mars flight yet.
• The drone tilted back and forth during the last 200 feet of its flight but managed to land safely.
• Ingenuity still showed off new technical skills as part of a fresh mission to test its limits.

NASA's Ingenuity helicopter suffered a glitch during its most recent flight, which caused it to tilt back and forth as it flew over uncharted Martian terrain.

On Saturday, the little drone spun its rotor blades and lifted itself into the thin Martian air for the sixth time. Its goal was to fly more than 700 feet in just 140 seconds to reach a new landing spot - the rotorcraft's riskiest voyage yet.

Ingenuity navigates via a camera on its belly, which transmits images to its flight computer. But about 54 seconds into the flight, a small glitch occured in the transition of navigation images to the helicopter's computer. The chopper lost just one image, but that meant that each following photo was delivered with the wrong timestamp.

That made the helicopter roll and pitch, leaning more than 20 degrees from one side to the other. Despite the wild ride, however, Ingenuity touched down safely within about 16 feet (5 meters) of its target spot.

"While we did not intentionally plan such a stressful flight, NASA now has flight data probing the outer reaches of the helicopter's performance envelope," Håvard Grip, Ingenuity's chief pilot, wrote in a blog update on Thursday.

An ambitious 6th flight

Engineers didn't expect Ingenuity to live long enough for six flights, must less to land safely after a mid-air software error.

The 4-pound drone's recent assignment was its most ambitious yet: Fly 492 feet (150 meters) southwest, then readjust to move 49 feet (15 meters) south, then switch directions and fly another 164 feet (50 meters) northeast. There, it was set to land in an unsurveyed, obscure spot called "Field C."

The excursion required more precise maneuvering and navigation than any of Ingenuity's previous flights.

The first leg of the journey went as planned, but once Ingenuity's system started receiving incorrect information about its location, the drone's navigation algorithm began trying to correct its flight path. To fly sideways, the helicopter tilts itself just 15 degrees. So the unexpected 20-degree tilting caused by the correction attempts led Ingenuity to oscillate back and forth along its flight path.

"In a very real sense, Ingenuity muscled through the situation," Grip wrote.

However, a little extra power fueled Ingenuity through its side-to-side tilting. And its safe landing was possible, in part, because it's designed to stop using navigation images during descent and landing.

The data from Ingenuity's brush with disaster will help NASA understand how the glitch happened and how to better design future Mars helicopters.

"All data will be carefully analyzed in the time ahead, expanding our reservoir of knowledge about flying helicopters on Mars," Grip said.

Ingenuity's mission may not be over yet

Ingenuity's daring one-way trips to new areas are part of a secondary mission: After it exceeded NASA's expectations, the team behind the helicopter sent it to scout Martian terrain and test operations that the agency might want to conduct with future space helicopters. That includes exploring rough areas that rovers can't access, observing interesting features of Mars from the air, and snapping photos for elevation maps.

This was the first flight of that extended mission, and also Ingenuity's first foray into totally new territory. Its first four flights landed in the same spot where they lifted off, and its fifth flight set it down in a new airfield that it had previously flown over, photographed, and mapped.

NASA extended Ingenuity's mission by 30 days on April 30, so the mission isn't guaranteed to continue next month. Still, the drone could keep flying longer as long as it stays alive and doesn't interfere with the science work of the Perseverance rover, which carried Ingenuity to Mars.

"We're in a kind of see-how-it-goes phase," Lori Glaze, director of NASA's Planetary Science Division, said last month.

If Ingenuity does fly again, it will probably require a software adjustment to prevent a repeat of Saturday's navigation error.

Perseverance, meanwhile, has begun its main mission on the red planet: hunting for fossils of ancient alien microbes. For now, that work is taking place near Ingenuity, since the helicopter must communicate with NASA through the rover.

NASA's initial plan called for Perseverance to travel farther from its landing spot in the Jezero Crater than it has by now. But then the rover photographed some promising rocks that convinced NASA scientists to further investigate the immediate region.

"These rocks are likely to be mudstones, very fine grained, once mud on the bottom of the lake," Perseverance scientist Ken Farley said in a briefing last month. "These are very important for our investigation, because this is the kind of environment that we expect to be the most habitable by organisms that might have existed on Mars billions of years ago."