When a tiny helicopter nicknamed Ginny took off from the surface of Mars, it was only expected to survive for 30 days.
Its mere lift-off – the first attempt to fly a powered aircraft on another planet – was swiftly hailed as a second “Wright brothers moment” by excited observers on Earth.
More than two years later, Nasa’s Ingenuity is still going strong, flitting across the planet’s rocky wilderness in what its engineers have described as a “miracle”.
Scientists now believe the unexpected success could prove pivotal to a growing ambition held by the likes of Elon Musk for humans to colonise Mars.
“We’ll have fleets of drones flying around the first astronauts,” Teddy Tzanetos, team lead on the Ingenuity programme, told The Telegraph.
He said Ingenuity has shown that Mars explorers could one day pilot helicopters across the planet – at least “from a purely physics standpoint”.
“You’re trying to set up base camp on Mars and you need tools delivered, like ‘oh, I left my wrench at camp’. You could send one Ingenuity drone to pick it up, things like that,” he said.
At 19in tall and weighing just a few pounds, its simple design was meant to keep costs down. It was built for five flights but has now completed more than 10 times that number since it landed on Mars in February 2021 on board the Perseverance rover mission.
None of its team at the Jet Propulsion Laboratory (JPL) in southern California is quite sure how it has managed to keep taking to the air, or for how long it can keep going.
Nor, for that matter, are any of the onlookers in the wider scientific community.
Ian Crawford, a planetary science professor at Birkbeck, University of London, is “astonished” at how resilient the diminutive craft has proved.
“I think it’s fundamentally changed the paradigm for exploring the surface of Mars,” he said.
Mars’s atmosphere is 1 per cent of the density of Earth’s, meaning Ingenuity’s carbon fibre rotors need to spin five times as fast to stay airborne.
Helicopters need an atmosphere to fly, which rules out the Moon, while gas giants such as Jupiter that are essentially made of atmosphere are too violent to navigate. But other worlds are ripe for discovery.
Data from the Ingenuity flights is being passed on to the team preparing to launch a rotorcraft on Titan, Saturn’s largest moon, as part of a mission to land in the mid-2030s.
But before any of that, the craft’s success has reshaped Nasa’s next mission to Mars, which will collect samples near the Jezero Crater to be sent to Earth for analysis.
The space agency is now sending two vehicles modelled on Ingenuity – their blades will be marginally longer – to gather the samples. There is even a chance that the two generations of helicopters will cross paths.
The thin atmosphere on Mars means flying is “almost impossible”, according to JPL engineers.
This meant they faced an uneasy three-hour wait to see if it could raise itself off the ground after landing attached to the belly of the Perseverance rover in February 2021.
It did, briefly hovering 10ft above Mars’s dusty red surface. Back in California, project manager Mimi Aung ripped up the emergency plans in case the flight failed.
Since then, Ingenuity has completed dozens of flights, travelling up to about half a mile at a time, while braving temperatures as low as -125C.
That is not to say it was all plain sailing. The rotorcraft was never built to survive the bitter nights of the Martian winter. It froze in May last year, its team staring helplessly 150 million miles away as it disappeared from their screens.
Steeling themselves for the worst, they tried to predict when it would thaw out so they could re-establish contact. For two days, the little helicopter was on its own.
Finally, after an agonising game of hide and seek, a stream of data from Ingenuity began to filter back.
“We’re told to not anthropomorphise the robots, but I imagine it’s like if you lost your puppy in the park,” said Mr Tzanetos.
“You’re just out screaming for your dog and then eventually you just hear a bark in the distance and you think: ‘Oh, thank God.’ And then surprise – ‘holy s—t, she’s a lot tougher than we thought’.”
It survived an emergency landing on its 53rd flight late last month, when images from its measurement camera failed to match data from its inertial measurement unit. The code was tweaked and it has returned to the skies twice more.
Nevertheless, Mr Tzanetos is aware its time is ticking down, and that whenever Ingenuity loses contact with JPL they may never recover it.
“I’ve been telling myself that every day could be our last, every sol [solar day] could be the last, every downlink could be our last,” he said.
Ingenuity’s solar panel has lost around 30 per cent of its output, probably thanks to a light coating of Martian dust.
Having proved an aircraft can fly in Mars’s unbreathable atmosphere, the JPL scientists believe we are on the cusp of revolutionary changes in the exploration of space.
“Where I think they will come into their own is they will make accessing parts of the surface of Mars possible that would be very difficult or impossible to access with a rover,” said Prof Crawford.
“Anywhere that needed a rover to go through very bouldery terrain … an aerial vehicle can fly over these obstacles and just land and make measurements in some inaccessible place.”