We’ve seen NASA’s Mars helicopter Ingenuity sitting on the Red Planet’s surface. We’ve seen it fly and hover. We’ve even seen it kick up dust and travel horizontally in a demonstration of its usefulness. The only thing we haven’t done is hear what the helicopter sounds like on Mars. Now, thanks to NASA’s Perseverance rover and the robot’s conveniently-placed Mastcam microphone, we have the opportunity to hear the aircraft for the first time.
In a new blog post by NASA’s Jet Propulsion Laboratory, we get to see the helicopter’s fourth flight in action. The trip was the most daring of its flight attempts when it launched, taking the helicopter on a long horizontal flight path before returning to its designated takeoff/landing location. What makes this video different is that we finally have audio to go along with it, and we can thank Perseverance and NASA scientists for making it possible.
The tricky thing about listening in to Ingenuity is the distance between the Perseverance rover and the helicopter. The tiny chopper is electrically powered and doesn’t make a lot of noise when it flies. The rover, meanwhile, is parked over 250 feet away, and with Mars’ notorious winds, the rover’s handlers weren’t even sure if they were going to be able to pick up the sound of the helicopter at all.
Even during flight, when the helicopter’s blades spin at 2,537 rpm, the sound is greatly muffled by the thin Martian atmosphere. It is further obscured by Martian wind gusts during the initial moments of the flight. Listen closely, though, and the helicopter’s hum can be heard faintly above the sound of those winds.
The result is a video with accompanying audio that includes the subtle hum of the aircraft’s rapidly spinning rotors. The audio had to be tweaked significantly in order to bring out the sound of the helicopter, as it was virtually undetectable to the human ear in its original form.
Scientists made the audio, which is recorded in mono, easier to hear by isolating the 84 hertz helicopter blade sound, reducing the frequencies below 80 hertz and above 90 hertz, and increasing the volume of the remaining signal. Some frequencies were clipped to bring out the helicopter’s hum, which is loudest when the helicopter passes through the field of view of the camera.
“This is a very good surprise,” David Mimoun, a member of the Perseverance mission team, said in a statement. “We had carried out tests and simulations that told us the microphone would barely pick up the sounds of the helicopter, as the Mars atmosphere damps the sound propagation strongly. We have been lucky to register the helicopter at such a distance. This recording will be a gold mine for our understanding of the Martian atmosphere.”
The Ingenuity chopper has since completed its fifth flight as well, taking it to a new location where the team will continue to test its capabilities.