By Stephen Clark
NASA’s Ingenuity helicopter safely landed after wobbling, suffering power spikes, and enduring velocity fluctuations on its sixth flight at Mars.
The helicopter took off on 22 May on its sixth automated flight and completed the first leg of a planned 215-metre (705-foot) excursion without a hitch. But Ingenuity started tilting back and forth in an oscillating pattern, encountering roll and pitch excursions of more than 20 degrees, registering large control inputs, and suffered spikes in power consumption, according to Håvard Grip, the helicopter’s chief pilot at NASA’s Jet Propulsion Laboratory in California.
Ingenuity overcame the glitch, which engineers traced to part of the helicopter’s navigation system. The helicopter limped through the rest of its flight and safely landed about 5 meters (16 feet) from its planned touchdown location, NASA said.
The 49-centimetre (1.6-foot-tall) rotorcraft, delivered to Mars in February by NASA’s Perseverance rover, accomplished the first flight in the atmosphere of another planet 19 April. Since then, Ingenuity has flown four more times, reaching higher altitudes, traveling at higher speeds, and covering longer distances with each takeoff.
NASA said a glitch in helicopter’s navigation system caused Ingenuity to start swaying about 54 seconds into a planned 140-second flight last week.
The helicopter navigates using an inertial measurement unit, which measures the craft’s accelerations and rotational rates. The data helps Ingenuity determine where it is, how fast it is moving, and its orientation in flight. But the measurement unit is prone to errors over time.
Ingenuity uses a down-facing navigation camera to track its flight path relative to features like rocks and sand ripples on the Martian surface. The camera takes pictures 30 times per second, and each picture comes with a timestamp for the helicopter’s navigation system to compare series of images to estimate the rotorcraft’s motion.
“Approximately 54 seconds into the flight, a glitch occurred in the pipeline of images being delivered by the navigation camera,” Grip wrote in a post on NASA’s website. “This glitch caused a single image to be lost, but more importantly, it resulted in all later navigation images being delivered with inaccurate timestamps.
“From this point on, each time the navigation algorithm performed a correction based on a navigation image, it was operating on the basis of incorrect information about when the image was taken,” Grip wrote. “The resulting inconsistencies significantly degraded the information used to fly the helicopter, leading to estimates being constantly ‘corrected’ to account for phantom errors. Large oscillations ensued.”
The video below, released by NASA, shows the final 29 seconds of the May 22 flight. The helicopter is designed to ignore navigation camera images during landing, and instead performs a straight-down descent back to the surface of Mars.
The helicopter’s performance had been perfect until the sixth flight last week. Grip, who led development of Ingenuity’s flight control system, wrote that the problem on the sixth flight gives engineers valuable data about the helicopter’s design limits.
“Flight Six ended with Ingenuity safely on the ground because a number of subsystems — the rotor system, the actuators, and the power system — responded to increased demands to keep the helicopter flying,” Grip wrote. “In a very real sense, Ingenuity muscled through the situation, and while the flight uncovered a timing vulnerability that will now have to be addressed, it also confirmed the robustness of the system in multiple ways.”
Driven by 1.2-metre (4-foot) counter-rotating rotor blades, Ingenuity continued its flight despite the navigation error. The goal of the 22 May flight was to demonstrate the helicopter’s aerial imaging capabilities, while remaining airborne for a longer time and moving at higher speeds than previous flights.
The top speed for the May 22 flight was targeted for 4 metres per second (9 mph) as the helicopter traveled to new base of operations, or “airfield,” at a location not previously scouted by Ingenuity or the Perseverance rover.
Perseverance did not image the helicopter during the 22 May flight, which was Ingenuity’s first excursion of an extended mission phase intended to demonstrate the rotorcraft’s utility in aerial reconnaissance and exploration. The helicopter’s first five flights were focused on demonstrating the craft’s design and proving a rotorcraft could safely take off and land on another world.
The Martian atmosphere is less than one percent the density of Earth’s at sea level, and Ingenuity’s rovers have to spin at some 2,500 rpm to generate lift in the thin air.
NASA added the $85 million Mars helicopter technology experiment to the $2.7 billion Perseverance rover mission, which has a primary goal of identifying, collecting, and sealing Martian rock samples for return to Earth by future spacecraft. With the first phase of the Ingenuity helicopter’s tech demo complete, Perseverance is now preparing for its own science mission.
The rover continues to serve as a communications relay station between Ingenuity and ground teams on Earth.
This most recent Ingenuity flight began with an ascent to an altitude of 10 metres (33 feet) before heading southwest for about 150 metres (492 feet). The next movement was to translate 15 metres (49 feet) to the south while a side-facing colour camera took pictures toward the western horizon. The helicopter was then supposed to fly another 50 metres (164 feet) to the northeast and land at its new airfield, a region shown by orbital imagery to be relatively flat and free of large surface hazards.
In the end, the helicopter ended up just 4.8 metres (16 feet) from its intended location, despite the navigation glitch, NASA said.
“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,” Grip wrote. “That data will be carefully analysed in the time ahead, expanding our reservoir of knowledge about flying helicopters on Mars.”
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Follow Stephen Clark on Twitter: @StephenClark1.
June 1, 2021 at 02:34AM
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