On April 6, NASA's Perseverance rover took a historic photo with the Ingenuity helicopter on the surface of Mars. Now, the Jet Propulsion Laboratory at the California Institute of Technology has revealed some of the process behind Perseverance's out-of-this-world selfie.
For humans, taking a selfie just means holding out a camera at arm's length, pointing and hitting the button. But for a robot on another planet, that selfie is a multi-step affair.
The Perseverance selfie is actually 62 separate images, taken one at a time by the rover's WATSON camera. That camera is "designed primarily for getting close-up detail shots of rock textures, not wide-angle images," JPL said.
To put the smaller images together in one larger image, a robotic arm twisted and maneuvered the WATSON camera around, to get a comprehensive look at the rover, the Ingenuity helicopter, and their Martian surroundings — all based on commands input by NASA scientists.
The robotic arm the WATSON camera rests on "acts like a selfie stick," JPL said, and with so many images combined to create one end product, the arm stays "just out of frame" in the end.
Planning, testing and implementing that process involved a core team of "about a dozen people," according to JPL. That team included engineers running tests at JPL, rover drivers and camera operations engineers who "developed the camera sequence, processed the images, and stitched them together."
Plotting the many commands involved took roughly a week, according to a statement from JPL.
That week also ran on "Mars time," following the schedule of a planet with a day about 37 minutes longer than one on Earth. The team would often stay up through the middle of the night and catch up on sleep in the middle of the day, experiencing interplanetary jetlag to get the Perseverance selfie together.
“The thing that took the most attention was getting Ingenuity into the right place in the selfie,” said Mike Ravine, Advanced Projects Manager at Malin Space Science Systems in San Diego. “Given how small it is, I thought we did a pretty good job.”
After each individual image made its way back to Earth, transmitted from Mars, MSSS image processing engineers put the photos together. After cleaning out "blemishes caused by dust that settled on the camera’s light detector," the engineers "assemble the individual image frames into a mosaic and smooth out their seams using software," so they all look like one larger photo.
While historic in its own right, Perseverance's photo is not the first selfie taken by a rover from another planet. That achievement belongs to the Curiosity rover, which took a black-and-white image of itself from the surface of Mars on Oct. 31, 2012.
“When we took that first selfie, we didn’t realize these would become so iconic and routine,” said Vandi Verma, Perseverance’s chief engineer for robotic operations at JPL, in a statement from the lab.
Verma helped create that first Curiosity selfie as a driver for the Opportunity and Curiosity rovers, in addition to her more recent work on the Perseverance selfie.
According to JPL, because the "selfie stick" turret on Perseverance is 30 inches long, much larger than Curiosity's 22-inch turret, the Perseverance photo was more difficult to take. JPL had to create a special software to avoid collisions between the robotic arm and the rover itself, which are just "centimeters" away from each other during the selfie process.
The command sequence the software executes gets the arm "as close as we could get to the rover’s body without touching it," Verma said.
The Perseverance selfie is also, uniquely, accompanied by sound, as the rover is the first spacecraft to bring microphones to Mars.
The rover carries an entry, descent and landing microphone, as well as a microphone attached to its SuperCam instrument. Part of their purpose is to help scientists discover any problems that may have arisen on Mars.
"It’s like your car: Even if you’re not a mechanic, sometimes you hear a problem before you realize something’s wrong,” Verma said.
But a side effect of the microphones is a robotic whirring noise that accompanies Perseverance's selfie, which Verma said can sound "musical, like a flute" as the pitch changes.
The end result is an extraordinary photo of two spacecraft, on their mission to analyze the geology and past climate of another world.