Gentle touch

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UAV landing technology based on Mars rover design uses parachute and airbag designed to better protect delicate instrumentation. Siobhan Wagner reports

Italian aerospace and defence safety systems specialist

Aero Sekur

has developed a UAV landing system it claims will better protect delicate onboard technology, such as optronics and sensor arrays.

The technology — combining a parachute and airbag shock attenuation system — is based on the design that will accompany the robotic rover due to be landed on Mars as part of ESA's ExoMars 2013 mission.

Weighing about 200kg, the rover will be released from an orbiter and dropped on to the surface of Mars using Aero Sekur's parachute and airbag landing system. It will be a key test for ESA to show its ability to land large payloads on the planet.

'We took the basic concept and the technology we were applying for space missions and applied it to Earth-based UAVs,' said Mark Butler, chief executive of Aero Sekur.

The system goes into action when a UAV finishes its mission or if an emergency occurs onboard. first, a parachute is deployed, which allows the craft to fall gently to Earth. It then uses an onboard laser altimeter to measure its distance from the ground. This is done by measuring the time that a pulse of light takes to leave the UAV, reflect off the ground and return to the UAV's collecting mirror.

'At a pre-specified height the system actuates and the airbags are very rapidly inflated with a gassing system,' said Butler. 'Typically you look for an inflation time of 1.5-2 seconds.'

As the system hits the ground, its built-in valves allow the airbag to deflate slowly and absorb the shock.

'It's the same sort of principle as an airbag in a car,' said Butler. 'When you have a crash, the bag deploys very rapidly and absorbs your impact by having a controlled deflation.'

The R&D team at Aero Sekur has spent the last three years simulating its parachute deployment and airbag inflation systems through LS-DYNA computer simulation software.

'Although the physics was fairly well understood there is always a degree of iteration in the design process — typically in terms of timing the release valves and the actual speed you allow them to deflate the system to absorb the shock,' said Butler.

Computer modelling is particularly important for the team's work on the landing system for the Mars rover. 'Obviously it's much more difficult when you are working on a landing system for Mars because it's harder to experimentally simulate the atmospheric conditions, so the use of modelling to actually refine a system has been quite important,' he said.

Butler said Aero Sekur believes it has developed a system that can quickly operate under hazardous conditions, both on Earth and Mars and cope with a wide variety of landing areas.

'We've built a system that can actually sense if it has landed on a rock and adjust the way it deflates itself to keep the load safe and level,' he said.

Most other commercial UAV landing systems, claimed Butler, rely on a simple parachute, but as technology on UAVs advances further, better recovery systems are needed.

'Most of the time using just a parachute will return the airframe relatively undamaged, but optronics and sensor arrays are far more sensitive and expensive and therefore require a different level of protection,' he said.

The system will be displayed at this month's Farnborough International Airshow.