Roving Mars, by air and land

The first helicopter ever to fly on another planet will soon attempt its first trip above the surface of Mars. Carried under the belly of the Perseverance rover, the helicopter, a drone-like device named "Ingenuity," will test the feasibility of Mars flight. This is a difficult challenge compared with flight on Earth, because the Martian atmosphere is only 1% as dense as Earth’s at the surface.

Ingenuity will be a technology demonstration for the Mars 2020 mission, but one day such rotorcraft could provide reconnaissance for rovers to help guide their routes, says Rob Sullivan, a research scientist at the Cornell Center for Astrophysics & Planetary Science and a member of the Mars 2020 science team. Currently, pictures taken from orbit help determine a rover’s route. Those images are impressively good – as high as 25 centimeters per pixel – but still not as good as images obtained from the rover.

Beginning April 2021, the window opens for the first flight of NASA’s Ingenuity Mars Helicopter. It will be history’s first attempt at powered, controlled flight on another planet. JPL/NASA

“Inevitably the rover encounters things at ground scale that are totally unexpected, which can change the mission team’s mind about what’s important,” says Sullivan. “There's a resolution gap between what we can see from orbit, and the much higher resolution views we can get from the rover itself but which are necessarily limited in range by the height of the rover mast they're mounted to.  A low-flying rotorcraft could fill the gap between the rover and the orbiter and also help extrapolate rover results more broadly to either side of the rover's traverse than the rover itself can see.”

Identifying a safe place where Ingenuity could conduct its flight tests was Perseverance’s first task. The helicopter needs a relatively flat surface of mostly soil with no large rocks. Martian soil usually includes rock fragments of various sizes, mixed with sand, silt and dust-sized grains, according to Sullivan.

Martian soil characteristics are important to rovers as well as rotorcrafts. Back in 2010, Sullivan and a team of students spent months doing soil tests with different materials and a rover wheel to understand how soil properties affect rover wheel performance, on behalf of the Mars Exploration Rover mission.

“Knowing something about the physical properties of the Martian soil you'll be driving on can be a confidence builder when planning a typical day's rover drive on Mars,” says Sullivan. “Mars can be a hazardous place. Depending on soil properties, certain soil and slope combinations can cause problems and mission delays that cost time that we can't get back at the end of the mission. We need to be efficient getting from place to place, every time." 

The Mars 2020 mission also includes a soils working team, on which Sullivan serves.

Understanding Mars’ landscape also requires understanding aeolian (wind-related) processes, says Sullivan, which has been his focus with Mars 2020. Because Mars has been extremely dry for most of its history, aeolian processes have contributed much more significantly to shaping the Martian landscape than on Earth. Erosion of surface rocks by wind-blown sand grains has shaped entire landscapes, and the tiny grains performing this work can also accumulate into sedimentary rocks that preserve a long record of Martian history.

“Some of the things that wind uses as its tools to shape landscapes, like sand and silt, also contribute directly to the soil that we have to drive over, so you can see how it's all kind of related,” Sullivan says.

Sullivan came to Cornell in 1997 and has worked on every rover mission to Mars, including the Spirit and Opportunity rovers, for which Steve Squyres ’78, Ph.D. ’81, the James A. Weeks Professor of Physical Sciences Emeritus, was the principle investigator. Sullivan also worked on the Mars Pathfinder, which delivered the first successful Martian rover to the red planet. Like Ingenuity that rover, named Sojourner, was also a technology demonstration. In addition to Mars, Sullivan has also explored Jupiter and the asteroid belt as part of the Galileo mission.

“I'm extremely lucky to get to do what I do. It's very humbling,” says Sullivan. “My colleagues are truly inspiring, are such impressive persons that I deeply admire. I've learned a lot from how clearly they think and how articulate they are in sharing what they know and how they do their jobs.”

Among spaceflight missions to other planets, rover missions can be especially dynamic to conduct, because rover missions change with each new stop, notes Sullivan. By comparison, "orbital missions rely on a certain amount of predictability for their success: one should know many days or weeks in advance what parts of a planet an orbiter will be flying over, allowing orbiter observations to be carefully planned well ahead of time. But rovers don't allow that. You drive across the surface and depending on what you discovered today, you might be compelled to drive in a different direction tomorrow.”

On any spaceflight mission, tight teamwork is essential and is what makes the work so enjoyable, says Sullivan. For previous rover missions, the whole science team would live and work together for the first several weeks in order for everyone to learn their roles, perfect their coordination and fine-tune their efficiency as a team. But because of the pandemic, the Mars 2020 mission has had to operate almost entirely virtually from the start.

“It's a huge team effort, with hundreds of team members coordinating to keep the rover constantly busy with the highest-priority tasks it can do, and for the most part none of us have seen each other face-to-face for over a year, and in some cases, never,” says Sullivan. “That's sort of the miracle of this mission: numerous delicate, critical and complicated tasks have to be coordinated and carried out by remote individuals, for a rover that's many times even more remote.”

Perseverance’s main goal is to collect samples that will later be picked up by a follow-on mission and returned to Earth. The samples will help scientists determine if life ever evolved, or began to evolve, on the Red Planet.

A geologist by training, Sullivan says that to identify such early life, very old rocks are needed, on the order of 3 billion years or older. Earth’s active surface tends to erase rocks that old, but the Martian surface preserves more of such ancient rocks.

The rover’s landing site, Jezero Crater, was once filled with water deeply enough, and long enough, for a river delta to have formed within it. “Sediments were being deposited fairly rapidly, at least on a geological timescale, so it's a good place to look for ancient organics or other signs of emerging biology that might have been trapped in those ancient delta sediments, and that we could sample and bring back to Earth for analysis,” says Sullivan.

Bringing Mars samples back to Earth, rather than analyzing them in place with just a few small instruments that a rover can carry, will be a powerful investment in the future, Sullivan says. “Like the Lunar samples Apollo brought back, we’ll have these Mars samples forever, allowing scientists of the future to apply superior apparatus than currently available in their analyses of these samples.”

Some of those future scientists may well get their start at Cornell, working with planetary explorers like Sullivan and others currently at Cornell, roving Mars as part of a giant remote team.

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		small helicopter flying over a barren, orange landscape