By David Millward,

US Correspondent

Nasa has been playing a hi-tech game of hide and seek with a mini-helicopter it dropped on the surface of Mars just over two years ago that has surpassed all expectations.

Scientists have been baffled by the longevity of the aircraft, which was expected to carry out about five flights and then stop working about two years ago.

Six days later the rotorcraft, weighing 1.8 kilograms (4 pounds) which cost Nasa approximately $85 million (£68.2m) to develop, has now completed more than 50 flights taking invaluable images of the Mars surface.

The helicopter is controlled via radio signals relayed from Perseverance, the SUV-size rover studying Martian soil. Ingenuity was designed to roam the skies ahead of the rover as a scout, collecting additional data.

After 28 flights, the Ingenuity entered its “low power” state, with scientists doubtful that it would be able to power its heater to protect vital components and omit a signal on a planet where the temperature can drop to -125C (-195F).

But scientists began using data on Martian sunrises to calculate when the helicopter would thaw out so they could find it after its programmed flights. Scientists have had to calculate Ingenuity’s morning “wake-up time” when it would emit a signal, wrote Travis Brown, the project’s chief engineer, said.

The team was able to work out when it would be back online.

“We still need to play some of these games every once in a while, depending on how cold it is or windy it is overnight,” Mr Tzanetos explained. “But the team’s gotten very good at that.”

The fact that the craft, a drone with spindly legs, had lasted that long was something of a surprise to scientists.

“It’s absolutely ridiculous,” Ingenuity team leader Teddy Tzanetos told The Washington Post. Originally it was only supposed to perform five flights, but somehow it kept going. 

“At that point, we’re on borrowed time,” Mr Tzanetos added. “None of the mechanisms were designed to survive longer than that.”

How long Ingenuity lasts is anybody’s guess. But two replacements are being sent to the red planet.

“Well, I hope that our children or our grandchildren can build off this, Here we are, Ingenuity’s still flying, and we’re designing the second generation.”

The Ingenuity carried out the first powered flight by an aircraft on another planet in April 2021, in what Nasa billed a “Wright brothers moment”.

The unexpected success of the Ingenuity helicopter has pushed Nasa to consider further developing helicopter technology for space exploration.