US space agency NASA is laying claim to the first ever aircraft accident investigation conducted on another planet.
NASA says engineers from the agency’s Jet Propulsion Laboratory (JPL) are collaborating with uncrewed aircraft manufacturer AeroVironment on a “detailed assessment” of the final flight made by the Ingenuity Mars Helicopter on 18 January 2024. Damage sustained during that flight led NASA to retire Ingenuity permanently.
That sortie was Ingenuity’s 72nd flight on Mars, with the small craft greatly surpassing its original goal of completing five technology demonstration flights over 30 days.
Designed by JPL and AeroVironment, the autonomous solar-powered Ingenuity became the first aircraft to conduct extraterrestrial powered controlled flight. Arriving on Mars in 2021 aboard the Perseverance rover, Ingenuity was able to achieve lift in the thin Martian atmosphere via a unique coaxial rotor system.
The rotor design featured two counter-rotating, hinge-less, dual-bladed rotors, each with a diameter of 1.2m (4ft).
Over its unexpected three years of operations on Mars, Ingenuity accumulated more than 2h of flight time and logged distances more than 30 times beyond its original parameters, according to NASA.
Each sortie was short by terrestrial standards, typically lasting less than 1min and often covering just a few dozen metres. Ingenuity’s longest flight was 704m.
The pioneering rotorcraft’s career came to an end when Ingenuity suffered catastrophic rotor damage while returning from its 72nd mission. An initial summary of the crash investigation released by NASA on 11 December finds navigational error was to blame.
“The investigation concludes that the inability of Ingenuity’s navigation system to provide accurate data during the flight likely caused a chain of events that ended the mission,” the agency says.
Ingenuity’s 72nd mission is described as a “brief vertical hop” to assess to rotorcraft’s flight systems and collect photographic imagery of the surrounding area. Flight data indicates the craft reached a height of 40ft, where it hovered and then initiated descent after 19s of flight.
The helicopter touched down 32s after lift off and promptly lost contact with its handlers on Earth. After communication links were re-established, imagery taken by Ingenuity’s onboard navigation camera revealed “severe” rotor damage had occurred during flight 72.
This was ascertained through visual examination of shadows cast by the rotor blades on to the Martian surface. A subsequent photo captured by the Perseverance rover shows Ingenuity resting near the apex of a Martian sand ripple, with one of the helicopter’s rotor blades lying on the surface some 15m away.
“When running an accident investigation from 100 million miles away, you don’t have any black boxes or eyewitnesses,” says Ingenuity’s first pilot, Havard Grip of the Jet Propulsion Lab.
While Grip says there are multiple scenarios that could be consistent with the data NASA has received, the navigation error is the most likely.
“Lack of surface texture gave the navigation system too little information to work with,” he says.
Ingenuity’s visual navigation system was designed to track visible features on the Martian surface using a downward-looking camera over “well-textured (pebbly) but flat terrain”, NASA notes.
While the agency says that design was “more than sufficient” for the terrain where Ingenuity’s first five flights took place, by the time the small helicopter had reached hop 72 it was in a region of Mars marked by “steep, relatively featureless sand ripples”, NASA says.
The signal transmission delay between Mars and Earth precluded real time remote control of rotorcraft by a human pilot. Instead, Ingenuity had to be flown by an autonomous flight system capable of operating without human control inputs.
Around 20s into its last flight, the Ingenuity navigation system “couldn’t find enough surface features to track”, according to NASA, resulting in unsafe horizontal velocities during touchdown. NASA believes this condition led to a hard impact on the slope of a Martian sand ripple, causing Ingenuity to pitch and roll.
“The rapid attitude change resulted in loads on the fast-rotating rotor blades beyond their design limits, snapping all four of them off at their weakest point — about a third of the way from the tip,” NASA concludes.
Excessive vibration generated by the damaged rotors ripped the remainder of one blade from its housing and created excessive power demand that produced the temporary loss of communication with Ingenuity.
Although the rotorcraft is no longer flightworthy, its other systems remain functional. NASA says Ingenuity still beams weather and avionics test data to the Perseverance rover once per week.
“The avionics data is already proving useful to engineers working on future designs of aircraft and other vehicles for the Red Planet,” the agency notes.
Ingenuity’s unexpected longevity on Mars is also helping inform the design of future extraterrestrial aircraft. Because of budgetary constraints, mission project manager Teddy Tzanetos notes Ingenuity was the first craft in deep space designed to fly using commercial off-the-shelf mobile phone processors.
“We’re now approaching four years of continuous operations, suggesting that not everything needs to be bigger, heavier, and radiation-hardened to work in the harsh Martian environment,” Tzanetos says.
A successor concept called the Mars Chopper is already being researched by the Ingenuity team. NASA says that next-generation craft would be approximately 20 times heavier than Ingenuity, with a payload of several kilograms and a daily range of up to 3km.
An animation of the Mars Chopper released by NASA depicts a six-rotor design, with the multi-bladed rotor assemblies arranged in a hexagon formation around central control unit.
