How did Nasa engineers build a helicopter to fly on Mars?

Nasa's Ingenuity helicopter lifted off from the surface of Mars on Monday as part of a pioneering mission to prove that flights on other planets were possible.

The small drone-like rotorcraft reached an altitude of three metres, staying aloft for 39.1 seconds before landing back on the planet's surface in a landmark moment in space exploration.

The unique challenge required a vehicle built specifically for the job.

With its extremely thin atmosphere, low gravity and vast distance from Earth, Mars presented several challenges to Earth-bound engineers.

To overcome them, the team of scientists and engineers at  Nasa’s Jet Propulsion Laboratory in the US used cutting-edge materials and technology.

In order to even make it to the red planet, Ingenuity's weight had to be kept to a strict minimum.

The Martian atmosphere is less than one per cent as dense as that on Earth, requiring much larger blades to create the lift needed for flight.

Each of the helicopter’s 1.2 metre rotor blades weighs just 35 grams – about the same as six dirham coins.

To achieve this weight, the blades were made from foam coated with a thin skin of carbon fibre, the same light, but strong, material used extensively in the construction of Formula 1 cars and spacecraft.

Engineers were uncompromising in saving weight. The entire helicopter weighs 1.8 kilograms – about the same as a small laptop.

As a result of the thin atmosphere, flying on the surface of Mars is roughly equivalent to attempting to fly at an altitude of 100,000 feet on Earth.

The highest a helicopter has ever flown on Earth is about 40,000 feet, a little higher than the cruising altitude of a jet aircraft.

To generate enough lift to get airborne on Mars, Ingenuity's rotor blades have to spin at incredibly high speeds, averaging around 2,500rpm during flight, or more than 40 rotations a second.

By contrast, a normal helicopter’s rotors spin at around 500rpm.

Ingenuity's twin blades work together to increase lift, with their contra-rotating arrangement improving efficiency and creating stability.

But not all of Ingenuity's parts were bespoke to the project. JPL's engineers also made extensive use of off-the-shelf components to enable the technology demonstrator to fly autonomously.

Ingenuity's brain – the CPU that allows it to navigate, recharge its batteries and stay warm during the freezing Martian nights – is the same Qualcomm Snapdragon 801 that was commonly found in Android smartphones in 2015, running a version of the Linux operating system.

Although outclassed by many more modern smartphone processors, Ingenuity's CPU is much more powerful than the one on board the Perseverance rover, which is said to have roughly the same amount of computing power as the original 1998 Apple iMac.

Several other components on board Ingenuity were also sourced from commercial suppliers, including cameras, a laser altimeter and other sensors for measuring the helicopter's position.

Recreating the conditions on Mars during testing on Earth was another key challenge engineers had to overcome.

The helicopter designed for Mars is so specialised that it would not function properly under normal conditions on Earth, so JPL engineers used a giant vacuum chamber to simulate the low pressures of the red planet during test flights.

An array of computer fans was installed in the chamber to simulate winds.

To recreate the low gravity of Mars – which is only a third as strong as what we experience on Earth – engineers turned to a decidedly low-tech solution.

A length of fishing line was attached to the prototype, which was pulled upwards to partially offset its weight and simulate low gravity.

Ingenuity will play no part in Perseverance's science mission. Its only payload is a small piece of canvas from the Wright brothers' aircraft, which first flew on Earth in 1903.

As a technology demonstrator, Ingenuity's only purpose is to fly.

Nasa is planning several more flights over the coming weeks.

The US space agency hopes the mission will lay the groundwork for the future use of helicopters and drones in space exploration.