“For some years,” wrote Wilbur Wright in 1900, “I have been afflicted with the belief that flight is possible to man. My disease has increased in severity and I feel that it will soon cost me an increased amount of money if not my life.”
That may be the most poetic thing Wilbur or his brother Orville ever said. But what the Wright brothers did three years later had a natural poetry to it: They flew. They borrowed the magic of birds. And so a sort of magic has been conferred on them. We remember them more eloquently than they probably lived.
An American spacecraft is now on its way to Mars, expected to arrive Feb. 18. There’s magic to that, too. If ever there was life on that now-frigid world, NASA’s Perseverance rover is designed to find signs of it.
But it’s complicated to explain. It requires discussion of organic chemistry, Martian geology, and a lot of engineering. You have to know why stromatolites are important, and what a spectrometer does. Perseverance is looking for past life, but if it tripped across something living today (it won’t, not at least at its planned landing site; Mars is frozen and bombarded by cosmic radiation), its instruments wouldn’t be able to tell. The plan is for the rover to drill into the Martian surface, take rock and soil samples, and save them, probably for years, in super-sterilized containers that would be returned to Earth by a future mission that is as yet only partly designed, and not yet approved or funded. The samples might not get back here until the early 2030s, if they ever do. The rover does not lend itself to a simple summation.
Which is why it’s nice that Perseverance is carrying with it an almost entirely separate, second vehicle. It’s a tiny robotic helicopter, nicknamed Ingenuity—essentially, a drone, designed to fly on Mars. The first flying machine ever sent to another world.
“This is really a Wright brothers moment, but on another planet,” says MiMi Aung, the Ingenuity project manager at NASA’s Jet Propulsion Laboratory in California. She and her colleagues repeat that mantra at every opportunity.
The four-pound drone, built for about $80 million, probably won’t outshine the 2,200-pound rover, with its budget somewhere north of $2.46 billion and its ambitious goals. But the drone’s mission is refreshingly simple. It has been sent to fly—probably no more than 20-30 feet high and 1,000 feet horizontally, and for no more than 90 seconds at a time. That’s all. But if it works, it could, for a moment, steal the imagination.
Bob Balaram is chief engineer for the helicopter project. “I think about what the little Sojourner rover proved,” he says. Sojourner was NASA’s first Martian rover, back in 1997. “The reason it went there was you wanted to drive on Mars. We wanted to drive, and now we want to fly.”
Balaram wrote NASA’s first proposal for a Mars helicopter in the late 1990s and says the idea “sat on a shelf” for 15 years until a JPL manager went to a conference on drones and a colleague remembered Balaram’s paper. Balaram and a team worked on prototypes and finally got a go-ahead to piggyback on the Perseverance rover in 2018. Piggyback is probably the wrong word: The little drone was actually bolted to the rover’s bottom for the trip to Mars.
It does seem like a simple idea, but if there’s anything the engineers learned as they designed and built Ingenuity, it’s that it’s awfully complicated to fly on Mars. The rules of aeronautics are the same, but everything feels different.
For starters, the Martian atmosphere, mostly carbon dioxide, is about a hundredth as thick as the air at ground level on Earth. Nighttime temperatures regularly drop to 130 degrees below zero Fahrenheit—great for killing Ingenuity’s six lithium-ion batteries. So the helicopter had to be very sturdy, and very light. The fuselage, containing a microprocessor, radio, heater, accelerometer, altimeter, and two cameras, is about the size of a box of tissues. There is a small solar panel on top. It turned out power would mostly be needed not to fly but to keep the drone’s electronics warm inside. Mission planners briefly considered insulating them with aerogel, an ultralight foam used on previous Mars probes that’s sometimes been called “solid smoke,” but they decided it was too heavy.
And there was more. If you have watched an earthly helicopter revving up, you probably noticed that the rotor blades tend to be a bit floppy—which is good if you want them to bend but not break in our nice, thick atmosphere, but probably fatal if you’re trying to maintain control in the wispy air of Mars. The Ingenuity team solved the problem with two stiffened carbon-fiber rotors, one on top of the other, each about four feet long, spinning in opposite directions at about 2,400 rotations per minute. (A typical helicopter on Earth does less than 500 rpm.) If the drone went any slower it would never get airborne; any faster and the tips of the blades might flirt with supersonic speed, causing shock waves that would make control all but impossible.
“Imagine a breeze on Earth,” says Teddy Tzanetos, the flight test conductor lead. “Now imagine having 1 percent of that to bite into or grab onto for lift and control.” It turned out that gusts of Martian wind were one of the few things the engineers didn’t have to worry about; the air is simply too thin to push the drone around with any force.
The plan is that after the rover has landed, been checked out, and found an appropriately flat spot, it will gently drop the helicopter upright to the ground. That should happen about 60 Martian days, or sols, after landing. (A sol is about 24 hours and 39 minutes long.) The rover would then move about 100 yards away, cameras at the ready, and watch the drone try to fly.
Ingenuity is slated for a maximum of five flights over a period of 30 sols, but if it flies just once, says Tzanetos, “we’ll all go out and celebrate.”
NASA says that if Ingenuity succeeds, it may lead to future flying machines that can go scouting ahead of rovers or astronauts, or explore cliffs or volcanoes that are too steep to be reached by wheeled vehicles or on foot. Balaram suggests a drone might be the way to look at the icecaps at the Martian poles.
So coolness alone is not enough to get a mission approved, but it helps. Even if you are dealing in complex concepts, even if there is a lot of detail essential to understanding the project, it helps to have thematic simplicity.
The Wright brothers themselves, engineers to the core, had a difficult time explaining their own accomplishment, even though they knew what they had managed at Kitty Hawk. They flew four times on the morning of Dec. 17, 1903, and probably would have tried some more if their flyer had not been mangled by a gust of wind while they were having lunch. Their telegram that afternoon to their father had the color of a lab report:
Success four flights thursday morning all against twenty one mile wind started from Level with engine power alone average speed through air thirty one miles longest 57 seconds inform Press home Christmas.
NASA, which has often been stuck with a muddled mission in the years since Neil Armstrong walked on the moon, has taken the Wrights’ lesson to heart. It has become expert at communicating what it’s up to. Searching for biosignatures of past microbial life in the Martian soil? That’s important but complicated. Flying on another world? That only takes ingenuity.
“NASA management, some in Congress were interested, I think, by some aspects of the excitement of exploration,” Balaram says. “But at JPL I think it was more a case of thinking, if this works, this is a new way of exploring Mars, and that’s what we’re in the business of.”