October 2020

40 n PRECISION ENGINEERING AND MOTION CONTROL October 2020 www.drivesncontrols.com Nasa goes brushless for new Mars mission O 31 July this year, Nasa’s latest mission to Mars blasted off from Cape Canaveral, carrying the fifth rover vehicle to head for the red planet. The main mission of the Perseverance rover, due to touch down on 18 February, 2021, is to collect soil samples that will eventually be brought back to Earth for analysis. The rover will also carry a drone helicopter, called Ingenuity, that will make the first flights on the planet, and take images. The main aim of the 1.8kg solar-powered aircraft is to test the concept for future drones. Perseverance will gather more than 30 soil samples, seal them in containers and deposit them on the surface of Mars, ready for a future mission to bring them back them to Earth to be analysed. For the $2.4bn Perseverance mission, Nasa specified miniature brushless DC motors for the first time on a Mars rover. Several of these motors are installed in the 2.1m-long robotic arm that will transfer samples between test stations on board the rover. Other motors will be used to seal and deposit the sample containers. Six 10mm-diameter brushed motors are also being used on board the helicopter to control the tilt of its rotor blades, and thus its direction of flight. The drives needed to be light, dynamic and energy-efficient because every gramme counts on the drone. Flying on Mars will not be easy. The atmosphere is extremely thin – comparable to the conditions 30km above the Earth. The $80m drone helicopter, with two 1.2m-long contra-rotating blades spinning at 2,400 rpm, has already flown in a test environment at Nasa’s Jet Propulsion Laboratory (JPL). Whether it will work on Mars remains to be seen. The Swiss miniature motor specialist maxon motor supplied several motors for the mission, both for the rover and the helicopter. Maxon has considerable experience of developing drives to operate on Mars and more than 100 of its motors have already travelled to the planet. As with most previous Mars missions, the drives are modified versions of standard maxon products: nine EC 32 flat drives; and one EC 20 combined with a GP 22 UP planetary gearhead. Working with JPL, maxon developed the drives over several years. “We've learned a lot from this exciting project,” says Robin Phillips, head of maxon’s SpaceLab. “Customers from other industries. such as the medical sector, where requirements are often similar, also benefit from this know-how.” Space missions place heavy stresses on drive systems including: vibrations during the launch; vacuum conditions during the inter-planetary journey; heavy impacts on landing; and harsh conditions on the surface of Mars, where temperatures can fluctuate between –125 and +20°C, and dust penetrates everywhere. n Nasa’s latest Mars rover vehicle and a companion drone are due to reach the red planet in February. For the first time, Nasa has specified miniature brushless DC motors for various duties on board the rover. An artist’s impression of the Mars Perseverance rover due to reach the red planet in February. Image: Nasa/JPL-Caltech