NASA’s Ingenuity helicopter completes a sixth flight despite some ‘unexpected motion’

NASA‘s Ingenuity Mars helicopter has survived its sixth flight on the Red Planet, but not everyone went to plan, with some ‘unexpected motion’ in the final few feet.

This motion was from an ‘image processing issue’ but the 4lb copter ‘muscled through’ the final 213ft of its 703ft flight over the Martian surface, NASA JPL tweeted.

The flight happened last week, on May 22, but NASA said it would be taking more time to review each flight before releasing data after the fifth flight was over, so information on it surviving the ‘wobble’ weren’t released until Thursday. 

Despite the issue the helicopter, currently in a new phase where it is helping Perseverance scout for locations, ‘landed safely and is ready to fly again.’ 

The latest trip was designed to expand the flight envelope and demonstrate aerial-imaging capabilities by taking stereo images of a region of interest to the west.

Ingenuity climbed 33ft, moved 492ft southwest at 9 mph, travelled 49ft south while capturing images towards the west, before going another 164ft to its landing site. 

Despite encountering an anomaly in flight, the helicopter landed within 16ft of the intended landing location and did so due to ‘stability margins’ within flight control.

The NASA team are now planning a seventh flight for the 18 inch tall drone, that will happen after they’ve fixed the ‘timing vulnerability’ that led to the in-air ‘wobble’. 

Ingenuity arrived on Mars on February 18 strapped to the belly of the Perseverance rover, which acted as a data relay and photographer when flights first started.

The small robotic flying drone made its first flight on April 19, 2021, making history as the first powered controlled flight on another planet. 

Since then it has completed sixth successful flights, the first five as part of a ‘technical demonstration’ to prove something could fly on Mars, then this sixth flight was part of an extended mission support role, helping Perseverance. 

Telemetry from the sixth shows that the first 490ft leg of the flight went off without a hitch, but it was towards the end of that leg the first issue was detected.

Just over 50 seconds into the flight a glitch occurred in a pipeline of images used by the navigation system to predict the helicopters location, velocity and altitude.

This caused one single image out of hundreds to be lost, resulting in the navigation system operating from inaccurate information that caused the mid-flight wobble.  

NASA can’t see this issues happening in real time due to the delay in sending data to and from the Red Planet – currently 207 million miles away from the Earth.

Scouring through the flight data after it was sent back to mission control – three hours after the helicopter landed – Ingenuity began adjusting its velocity and titling back and forth in an oscillating pattern. 

‘This behaviour persisted throughout the rest of the flight,’ wrote HÃ¥vard Grip, Ingenuity Mars Helicopter Chief Pilot.

‘Prior to landing safely, onboard sensors indicated the rotorcraft encountered roll and pitch excursions of more than 20 degrees, large control inputs, and spikes in power consumption.’ 

While airborne, Ingenuity keeps track of its motion using an onboard inertial measurement unit (IMU) – that tracks acceleration and rotation rates. 

By integrating this information over time, it is possible to estimate where it is, how fast it is moving, and how it is oriented in space. 

The onboard control system reacts to the estimated motions by adjusting control inputs rapidly – at a rate of 500 times per second.

If the navigation system relied on the IMU alone, it would not be very accurate in the long run, according to NASA JPL, who added that errors would quickly accumulate, and the helicopter would eventually lose its way. 

To solve this the navigation camera sends data back into the system to correct the IMU estimates on a regular basis.

‘For the majority of time airborne, the downward-looking navcams takes 30 pictures a second of the Martian surface and immediately feeds them into the helicopter’s navigation system,’ NASA explained.

As the image comes in the navigation system examines the timestamp to determine when it was taken and the algorithm makes predictions about what the camera should have bee seeing based on previous sets of predictions.

This includes surface features from images taken moments before and where those features actually appear in the new image.

This shift in surface features – however tiny – allows the artificial intelligence system to predict the actual location and estimate the position of the helicopter.

One single image was lost abut 54 seconds in, meaning all future images had the wrong timestamp, meaning the AI was working from inaccurate information.

‘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 said. 

‘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.’ 

Despite encountering this anomaly, Ingenuity was able to maintain flight and land safely on the surface within approximately 16 feet of the intended landing location.

One reason it was able to do so is the considerable effort that has gone into ensuring that the helicopter’s flight control system has ample “stability margin’. 

‘We designed Ingenuity to tolerate significant errors without becoming unstable, including errors in timing,’ said Grip.

They didn’t need the ‘stability margin’ in the earlier flights as it wasn’t being pushed outside the realms of what the team expected for ‘normal operations’.

But during flight six Ingenuity was pushed to travel faster, harder and further than in the previous five, causing the margin of error to ‘come to the rescue’.

NASA also stops using navigation cameras in the final phase of a flight – during the descent and landing – in order to ensure smooth and continuous estimates.

‘That design decision also paid off during Flight Six,’ said Grip, adding that ‘Ingenuity ignored the camera images in the final moments of flight, stopped oscillating, levelled its attitude, and touched down at the speed as designed.’

Despite the issues the flight was a success, according to NASA, with rotor system, actuators and power systems responding well to increased demands. 

‘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,’ said Grip.