Want to fly a rotorcraft on another planet? Here’s what it takes.
MONDAY, APRIL 12, 2021 (pbs.org)
NASA has delayed the first flight of its Ingenuity Mars helicopter, announcing that it expects to set a new date next week.
The helicopter, which arrived on the red planet tucked inside the Perseverance rover in February, was initially set to fly on Sunday, securing its position as the first rotorcraft to lift off on another world. Late on Friday night, however, a high-speed test of Ingenuity’s rotors ended early: As the helicopter’s command sequence tried to transition the flight computer from “preflight” to “flight” mode, engineers were alerted to a potential problem. The team has decided to update Ingenuity’s flight control software before attempting a maiden flight.
During this first flight, the Ingenuity Mars helicopter will lift off, hover 10 feet above the Martian surface, take pictures, and touch back down—all in a period of about 40 seconds. Meanwhile, some 200 feet away, the Perseverance rover will snap pictures and videos of its companion’s brief voyage.
This first flight will be a modest beginning of a much more ambitious task: In the next 30 days, the Ingenuity team at NASA’s Jet Propulsion Laboratory will attempt a total of five flights, each longer and more technical than the last.
“Each world only gets one first flight,” Ingenuity Project Manager MiMi Aung said during a press conference on Friday. It’s a “historic moment that has analogues in 1903,” NASA’s Associate Administrator for Science Thomas Zurbuchen added, referring to the year the Wright brothers became the first in the world to fly a motor-operated airplane—after two failed liftoffs.
“History tells us that Orville and Wilbur took this setback like true engineers,” confirming that their fundamental understanding of flight was correct and going back and making subtle changes, Aung said during Friday’s press conference. Aung believes she and her team have become similarly well-versed in the unique challenges of flying a hovercraft on another planet and are aware that despite years of preparation, something could go wrong when it’s time for the first attempt. “I want to be conservative,” Aung said on Friday, adding the Ingenuity team had yet to celebrate the Mars helicopter’s achievements.
Perhaps the greatest challenge the team will face is the Martian atmosphere. Made up of mostly carbon dioxide, Mars’ atmosphere is a mere 1% as thick as our own planet’s, which is primarily nitrogen. Its thinness makes it the equivalent of flying at three times the height of Mount Everest, Ingenuity chamber test engineer Amelia Quon said on Friday.
Rotorcrafts, including helicopters, fly by generating lift. As their blades spin, they push the air and this lifts the craft up, Aung explains. In a thin atmosphere, she says, there are fewer molecules to push, “so you need to spin much faster to get lift,” she says. While the blades of most Earthly helicopters operate at around 450 to 500 revolutions per minute, Ingenuity’s will move at 2,400 rpm.
Ingenuity’s rotors “are not something off the shelf; they’re really fine-tuned to maximize lift in a really thin atmosphere,” Aung said. Weighing in at about 35 grams, the rotors have a foam core for lightweightedness and are covered in carbon fiber, laid out in a grid, for optimal stiffness and strength.
Like its blades, the body of the Mars helicopter is also lightweight, at less than four pounds. “We couldn’t make this happen” with technology that existed 10 or 15 years ago, Aung said.
Mars’ strong winds also pose a challenge. If gusts become too strong before Ingenuity is scheduled to fly, there’s no way of automatically postponing or canceling the flight through Perseverance, Ingenuity Operations Lead Tim Canham explained during Friday’s press conference. This is because the Perseverance rover’s weather-determining system has no connection to Ingenuity. And Ingenuity has no way to right itself; if it fails to land right-side-up during any of its flights, its mission on Mars would end.
But there’s good news: Martian weather is easy to predict. “Weather on Mars tends to stay the same over a period of sols,” Canham explains. (At 24 hours, 39 minutes, and 35 seconds, a Martian sol is slightly longer than a day on Earth.) The Ingenuity team initially chose 12:30 p.m. Martian time Sunday, the equivalent of 11:00 p.m. EDT, for a potential first liftoff because the team calculated that’s when Ingenuity would have the most charged battery and Mars would have the calmest skies.
The team started testing in 2014 whether Ingenuity could successfully fly on another planet. We “made Mars on Earth,” Quon said, referring to NASA’s Jet Propulsion Laboratory’s 25-foot space simulator thermal vacuum chamber, which Voyager 1 and 2 were tested in before making their way into space and out of our solar system.
First, the team used a flight model to illustrate that lift is possible—picture a couple of hops and a crash landing—in a Martian-like environment. Then, in 2018, the team had the model spin up three feet in the air and turn. In 2019, NASA scientists took data from previous tests and applied them to testing the actual Ingenuity Mars helicopter.
If all goes well, during its first sol after taking to the sky, Ingenuity will transmit its black-and-white photos and flight summary data to Perseverance, which will transmit the data to scientists on Earth. In the following days, scientists expect to receive color imagery and more complex data from the flight.
Canham is also eager to hear the sound of Ingenuity’s liftoff: Perseverance is equipped with a microphone specifically designed to survive on Mars—and capture the snaps, crackles and pops of its sizzling stones. It’s possible for the microphone to capture Ingenuity’s liftoff, but given its somewhat significant distance (more than 200 feet) from the helicopter, there are no guarantees. It’s “very touch and go on whether we’ll get anything,” Canham said on Friday. “But who knows.”
What’s more certain is that Perseverance will capture its own photos of Ingenuity’s first flight.
Before, during, and after Ingenuity’s 40-second airtime, Perseverance will snap six to seven photos a second using its onboard Mastcam-Z cameras, one with zoomed-in perspective and the other a zoomed-out perspective. (You can view images as they come in on NASA’s website here.)
The Ingenuity team expects its second flight to happen four days after its initial flight. And if that one goes well—the goal being to have the helicopter fly up to 15 feet—the team will move to an every-three-day flight cadence.
“We want to have fun” with the fourth and fifth flights, Aung said, suggesting that the team may venture at least 150 feet out and back from the helicopter’s takeoff site, possibly into never-before-seen territory. “This is all about the future. This is all about being a pathfinder,” she said, explaining that Ingenuity can inform how future space helicopters, which will be bigger and heavier, should function.
Like NASA’s first Mars rover—the modest 23-pound microwave-sized Sojourner, which touched down on the red planet in 1997—Ingenuity is a “tech demonstration,” explained Zurbuchen, NASA’s Associate Administrator for Science. Similar to Sojourner’s brief mission on Mars, Zurbuchen believes, decades from now, we’ll look back on Ingenuity’s month of flight with awe and fondness.
“Ingenuity’s month will be an aggressive demonstration of what it can possibly do,” he said. And, teammate Elsa Jensen added, “Big Sister”—Perseverance—“will be watching.”