When NASA’s Perseverance rover landed in Jezero Crater on February 18, 2021, it brought an interesting little companion that has been causing a stir lately! We are of course talking about the Ingenuity Mars Helicopter, an experimental flight system that is supposed to show whether air systems can work on Mars. Since its maiden flight on April 19, the helicopter has pushed the boundaries of flight on Mars, flying farther and faster each time.
In fact, the helicopter broke several records during its first five flights, reaching a maximum distance of 266 m (873 ft) in 117 seconds. Unfortunately, Ingenuity’s sixth and final flight didn’t go so well. Due to a navigation timing error, the helicopter lost its trajectory, but was only able to land safely a few meters from its target.
This is the first time Ingenuity has suffered a malfunction since it first ascended to the skies of Mars over six weeks ago. Fortunately, the fail-safe systems prevented accidents and the mission leaders were able to pinpoint the source of the problem. The difficulties began towards the end of the first leg of the sixth test flight of the helicopter, which took place on Saturday, May 22nd, or day 91 of the Perseverance mission (Sol 91).
Long range photo of Ingenuity taken with Perseverance’s SuperCam instrument. Photo credit: NASA / JPL-Caltech / LANL / CNES / IRAP / Kevin M. Gill
According to chief pilot Håvard Grip, who recently wrote about the bug on the mission’s status update page, this flight should shift the flight range even further and demonstrate the helicopter’s aerial photography capabilities before descending at 4 m / s (14.4 km / h; 9 mph) Fly 150 m (492 ft) horizontally southwest.
Once there, it should move west an additional 15 m during the acquisition, then fly an additional 50 m (164 ft) northeast before landing – a total of 215 m (705 ft) round trip.
“The telemetry of flight six shows that the first 150-meter stretch of the flight went smoothly. But towards the end of this section, something happened: Ingenuity began to adjust its speed and lean back and forth in an oscillating pattern. This behavior persisted for the rest of the flight. Before the safe landing, on-board sensors indicated that the rotorcraft was experiencing roll and pitch deflections of more than 20 degrees, large control inputs and peaks in power consumption. “
The problem appears to have been the result of a “bug” in the image pipeline sent from the navigation camera to the navigation system, throwing the timing sequence off track and confusing the vehicle with its location. The navigation camera is one of two used by Ingenuity and is responsible for tracking surface features used by the helicopter’s flight computer to keep the helicopter within its predetermined flight path.
As Ingenuity travels greater distances, more images are needed to track its trajectory and ensure it stays on course. According to chief pilot Havard Grip, this “error” occurred in the pipeline of the images sent by the navigation camera approximately 54 seconds after the flight:
“This bug resulted in a single image being lost, but more importantly, all subsequent navigation images were delivered with inaccurate timestamps. From that point on, every time it made a correction based on a navigation image, the navigation algorithm worked on incorrect information about the time of the shot. The resulting inconsistencies significantly deteriorated the information used to fly the helicopter, resulting in estimates being continually “corrected” to account for phantom errors. Great vibrations followed. “
Fortunately, NASA’s Jet Propulsion Laboratory engineers who built Ingenuity were sure they were adding a large “margin of stability” to the design of the helicopter’s flight control system (so that it can tolerate significant errors without becoming unstable). This kicked in during the flight and allowed Grip and the mission team to safely lower the helicopter just 5 meters (16 feet) from its intended landing site.
In addition, the mission team has a process in place to stop using the navigation camera images during the final phase of the descent and landing. This ensures a smooth and continuous estimation of the movement of the helicopter during this particularly critical phase of flight testing. This practice paid off here as it ensured that by the end of the sixth flight, Ingenuity ignored images with timing errors and could stop oscillating and leveling before touchdown.
Ingenuity’s image was captured by Perseverance’s Mastcam-Z instrument on May 23, 2021 – the day after its sixth flight. Photo credit: NASA / JPL-Caltech / ASU / MSSS
While the flight failed, Grip emphasized that it was demonstrating the effectiveness of the Ingenuity skill and the subsystems that came into play. This included the rotor system, the actuators and the propulsion system of the helicopter, which responded to the increased power requirement caused by the breakdown and kept the helicopter in the air. It was precisely these fail safes that enabled a margin of success in what could otherwise have been a catastrophe.
“Ingenuity literally struggled through the situation, and while the flight uncovered a timing vulnerability that needs to be addressed, it also confirmed the robustness of the system in several ways,” said Grip. “Although we didn’t intentionally plan such a stressful flight, NASA now has flight data that examines the outer reaches of the helicopter’s power range. This data will be carefully analyzed in the coming period and our knowledge base about flying helicopters on Mars will be expanded. “
Two months after the Perseverance rover landed on Mars, Ingenuity became the first aircraft to perform a powered flight on another planet. Originally, the technology demonstrator was only supposed to carry out five test flights over 30 mission days (sols). NASA has been so impressed by the success to date that it has decided to extend its mission by at least a month.
The data collected will feed into future missions to Mars and other non-airless bodies (such as Titan), where aircraft will be able to do science and offer a unique perspective on alien environments. In short, this “little helicopter that could” was nothing if it didn’t have the right name!
Further reading: Phys.org, NASA