Mars is already hard on aircraft, and NASA just pushed that problem a little further.
Rotor blades for the agency’s next-generation Mars helicopters broke the sound barrier during March tests at NASA’s Jet Propulsion Laboratory in Southern California, according to data from a test campaign inside a chamber that simulates conditions on the Red Planet.
The data indicate the fastest-moving part of the blades, the tips, can be accelerated beyond Mach 1 without breaking apart. Engineers gathered data from 137 test runs, which NASA says will help them design aircraft capable of carrying heavier payloads, including science instruments.
“NASA had a great run with the Ingenuity Mars Helicopter, but we are asking these next-generation aircraft to do even more at the Red Planet,” said Al Chen, Mars Exploration Program manager at JPL. “That’s not an easy ask. While everything about Mars is hard, flying there is just about the hardest thing you can do. That’s because its atmosphere is so incredibly thin that it is hard to generate lift, and yet Mars has significant gravity.”
Ingenuity performed the first powered, controlled flight on another planet on April 19, 2021, just over five years ago. It was a technology demonstration and did not carry science instruments.
NASA said its recently announced SkyFall project and other possible future Mars aircraft will be able to carry payloads, including science instruments and sensors, to collect data in support of future human and robotic missions.
On Mars, maximizing thrust means pushing blade tips toward the speed of sound to generate significant lift because the atmosphere is only 1 percent as dense as Earth’s. NASA said that while small-diameter rotors on Earth can also spin at thousands of revolutions per minute, they have more air molecules to push and do not need to get as close to the sonic edge.
The Ingenuity team never let the rotational speed of its composite-skinned foam rotors go above 2,700 rpm during the helicopter’s 72 flights on Mars. NASA said that was done to avoid the unpredictable physics around the sound barrier and to prevent a gust of wind from pushing the rotor tips over the sonic edge.
“If Chuck Yeager were here, he’d tell you things can get squirrely around Mach 1,” said JPL’s Jaakko Karras, the rotor test lead. “With that in mind, we planned Ingenuity’s flights to keep the rotor blade tips at Mach 0.7 with no wind so that if we encountered a Martian headwind while in flight, the rotor tips wouldn’t go supersonic. But we want more performance from our next-gen Mars aircraft. We needed to know that our rotors could go faster safely.”
NASA said Mach 1 at sea level on Earth is about 1,223 kph, while the speed of sound on Mars is roughly 869 kph because of the planet’s thin, cold, carbon-dioxide-rich atmosphere.
For the tests, rotors developed and manufactured by AeroVironment in Simi Valley, California, were mounted inside JPL’s 25-Foot Space Simulator. The team evacuated the air, replaced it with enough carbon dioxide to match the Martian atmosphere, and blasted the rotor with wind while it spun faster and faster.
Engineers lined part of the chamber with sheet metal in case the blades broke apart during the supersonic test. From a nearby control room, the team watched data displays and a view inside the chamber as the rotor speed climbed to 3,750 rpm. At that rate, the blade tips were traveling at Mach 0.98.
The engineers then activated a fan inside the chamber to hit the rotors with headwinds, increasing wind velocity after each run. NASA said the team pushed rotor tip speeds to Mach 1.08, boosting the Mars vehicle’s lift capability by 30 percent.
NASA said that gain would allow future missions to support heavier scientific payloads, including advanced sensors and larger batteries for longer flights.
The team also tested the two-bladed SkyFall rotor. NASA said it is slightly longer than the three-bladed version, so it needed only 3,570 rpm to reach the same near-supersonic tip speed before headwinds were introduced.
“The successful testing of these rotors was a major step toward proving the feasibility of flight in more demanding environments, which is key for next-gen vehicles,” said Shannah Withrow-Maser, an aerodynamicist from NASA’s Ames Research Center in Silicon Valley and member of the test team. “We thought we’d be lucky to hit Mach 1.05, and we reached Mach 1.08 on our last runs. We’re still digging into the data, and there may be even more thrust on the table. These next-gen helicopters are going to be amazing.”
NASA said the SkyFall mission design team has already incorporated the findings into its performance specifications. SkyFall is designed to carry three next-generation Mars helicopters to the planet in December 2028.
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