Podcast: Creating Ingenuity

By Cat Hofacker|February 17, 2021

The Mars Helicopter’s chief engineer on the project’s early days and what’s to come

This story has been updated.

NASA’s Perseverance rover touched down on Mars on Feb. 18, concluding its seven-month journey to the red planet. But before the rover can begin its task of analyzing and caching samples of Martian rocks and soil, it has to dispatch the little hitchhiker in its belly, the Ingenuity Mars Helicopter.

For decades, scientists have dreamed of flying aircraft over Mars to explore the rockier terrain that rovers and landers can’t traverse. Now, they could get their first chance to prove that that’s possible.

“Anything that has to fly on Mars has to be extremely light,” said Bob Balaram of the Jet Propulsion Laboratory in California. The atmosphere near the surface is just 1% as dense as Earth’s, so flying there is like flying “at about 100,000 feet here on Earth.”

Balaram is the chief engineer for Ingenuity, a battery-powered drone that on Earth weighed about as much as a chicken, but a chicken with two gangly rotor blades that, at 1.2 meters, look impossibly long for its body. Spinning those blades in opposite directions at a rate of 2,400 revolutions per minute, several times faster than a helicopter on Earth, should generate enough lift to soar a few meters above the Martian surface.

It’ll be an ambitious demonstration of the concept, and one that might not be happening were it not for Balaram. In the 1990s, he attended a robotics conference that featured a talk on miniature helicopters.

“I realized that, hey, flying something small here in the thick atmosphere of Earth is equal to flying something that’s large diameter in the thin atmosphere of Mars,” he said. “The flight regimes come out to be the same. Why don’t we consider helicopters for Mars exploration?

So he wrote up a research proposal detailing how a Martian helicopter might be built. But agency-wide budget cuts at NASA eliminated any chance of further studying that idea, so he shelved it. Fast forward to 2013: then-JPL director Charles Elachi attended a talk on commercial drones where he heard about how technology breakthroughs including lighter, more powerful processors were leading to more inexpensive drones capable of conducting more intricate flight paths. “Could NASA send such a craft to Mars?” Elachi asked the robotics division at JPL. Engineers unearthed Balaram’s old proposal, and it became the starting point for designing the Ingenuity helicopter.

“What I had looked at in the ’90s was more fundamental work, in the sense of, what should the blades look like? How big should they be? What kind of power would they need and so forth?” Balaram said. “Whereas what we ended up having to navigate in the last seven years was one, how do you build an aircraft that will really fly on Mars? And then more importantly, how do you make this aircraft also a spacecraft?”

Along with having the right mass and dimensions to fly in the thin Martian air, Ingenuity also had to withstand conditions including the radiation of deep space and the drastic temperature fluctuations on Mars.

Most importantly, the helicopter had to be ready to launch in 2020 with the Perseverance rover. Because Ingenuity is an experimental craft, JPL chose off-the-shelf parts for some components, including the lithium-ion batteries that would power the helicopter and cellphone-like processors for storing flight software.

“What’s been possible in the last five or 10 years is with all these new technologies, we were in a position to sort of exploit them and build these things light enough so that we can build this extremely lightweight aircraft that is able to fly in that very thin atmosphere,” Balaram said. “I think that’s the main enabler that allowed something like this to happen now.”

They’ll soon see if those years of designing, building and testing Ingenuity pay off. In the aftermath of the Perseverance rover’s landing, mission controllers will spend a few weeks checking out the rover’s hardware and instruments. Then, they’ll find a flat stretch of terrain and command Perseverance to release the aeroshell covering the helicopter. A collection of springs and motors will lower Ingenuity to the surface. Once they’ve verified the helicopter is in good condition, Balaram and his team have a 30-day window for the flights.

The plan is to conduct five flights lasting up to 90 seconds, during which Ingenuity would ascend to an altitude of between 3 meters and 4.5 meters. NASA needs to make sure Ingenuity has the right combination of mass, dimensions and RPM to fly on Mars. The JPL team thinks it has a good design, based on findings from flights in a test chamber where they replicated the thin Martian air. But they couldn’t exactly replicate Martian gravity, which is a third of Earth’s. The only way to know for sure is to fly on Mars.

“It really comes down to getting enough data to prove model validation. That’s what this sort of tech demo is all about,” Balaram said. “So, if we get back good data and if our models stand up well against what actually happens on Mars, then that’ll make my day.”

That data would also help shape the design for next-generation Mars helicopters, larger craft that could fly farther and longer. He says one day we might even consider helicopters just as essential for planetary exploration as rovers and orbiters.

“There’s a whole spectrum of possibilities, everything from little assistants to full-fledged science craft, up to the 30-kilogram class,” he said. Whether the funding would be available for those future aircraft is less certain, but “I think it could change the way Mars exploration gets done.”