Taking inspiration from albatross flight, a team of University of Arizona aerospace experts and a NASA planetary scientist have designed a motorless sailplane that they hope can be used to study the atmosphere and geology on Mars.
At present, eight active spacecraft, including three operated by NASA, orbit Mars, gathering imagery of the planet’s surface at a resolution of about 30 centimetres per pixel. Three rovers traverse the ground, mapping small areas of the planet with greater precision. But what lies in the hundreds of kilometres between the rovers and the orbiters – including atmospheric climate processes and geological features such as volcanoes and canyons – is often of most interest to planetary scientists.
‘You have this really important, critical piece in this planetary boundary layer, like in the first few kilometres above the ground,’ said Alexandre Kling, a research scientist in NASA’s Mars Climate Modeling Center. ‘This is where all the exchanges between the surface and atmosphere happen. This is where the dust is picked up and sent into the atmosphere, where trace gases are mixed, where the modulation of large-scale winds by mountain-valley flows happen. And we just don’t have very much data about it.’
Kling has partnered with a team of University of Arizona engineers to design a vehicle capable of soaring over the Martian surface for days at a time, using only wind energy for propulsion. Equipped with flight, temperature and gas sensors, as well as cameras, the sailplanes would weigh only five kilograms each.
Flight on Mars is challenging due to the planet’s thin atmosphere, and this isn’t the first team to try to address this challenge. Most notably, NASA’s Ingenuity is a 1.8-kilogram helicopter that landed in the Jezero Crater on Mars in 2021. With miniaturised flight technology and a rotor-system span of about 1.2 metres, it’s the first device to test powered, controlled flight on another planet. But the solar-powered vehicle can fly for only three minutes at a time and reaches heights of just 12 metres.
‘These other technologies have all been very limited by energy,’ said Adrien Bouskela, an aerospace engineering doctoral student. ‘What we’re proposing is just using the energy in situ. It’s kind of a leap forward in those methods of extending missions. Because the main question is: How can you fly for free? How can you use the wind that’s there, the thermal dynamics that are there, to avoid using solar panels and relying on batteries that need to be recharged?’
Lightweight, low-cost, wind-powered sailplanes may be the answer. The planes, which have a wingspan of about 3.4 metres, will use several different flight methods, including simple static soaring when sufficient vertical winds are present. But they can also use a technique called dynamic soaring, which, like an albatross on a long journey, takes advantage of how horizontal wind speed often increases with altitude – a phenomenon particularly common on Mars.
By flying at a slight upward angle into slow-moving, low-altitude wind, the planes rise. When they reach the faster, high-altitude wind, they turn 180° and let the high-speed wind power them forward at a slight downward angle. When they start to run out of energy from the high-speed wind, they repeat the process, weaving their way forward. With this nimble manoeuvring, the sailplanes can continually harvest energy from the atmosphere, flying for hours or even days at a time.‘It’s almost something you have to see it to believe,’ said Jekan Thanga, a UArizona associate professor of aerospace and mechanical engineering.
Current rovers have mostly captured images of Mars’s flat, sandy plains – the only areas where the rovers can safely land. But the sailplanes would be able to explore new areas by taking advantage of how wind patterns shift around geological formations such as canyons and volcanoes. ‘With this platform, you could just fly around and access those really interesting, really cool places,’ Kling said.
The team has proposed sending the sailplanes to Mars as a secondary payload on a larger mission. The sailplanes would be packaged in CubeSats. Once the CubeSats are launched and the planes released, the planes could potentially unfold, like origami, or inflate, like high-tech pool floaties, and rigidise at their full size. After landing on the Martian surface, the planes would continue to relay information about the atmosphere back to the spacecraft, essentially becoming weather stations.
‘If we run out of flight energy, or if our inertial sensors suddenly fail for whatever reason, we expect to then keep doing science,’ Bouskela said. ‘From the planetary-science perspective, the mission continues.’
The team has carried out extensive mathematical modelling for the sailplanes’ flight patterns based on Mars climate data. This summer, the engineers will test experimental planes at about 5,000 metres above sea level, where the Earth’s atmosphere is thinner and flight conditions are more akin to those on Mars.
The team’s proposal has been published in Aerospace.