When a $2.5 billion piece of NASA hardware is hurtling at twice the speed of sound toward a planet’s surface, its parachute had better open and survive.
Thanks, in part, to NASA engineer and USC Adjunct Professor Anita Sengupta, the parachute performed flawlessly and the much-anticipated Mars Science Laboratory Curiosity made a successful and spectacular touchdown.
Sengupta, who graduated from USC with a master’s degree in 2000 and a PhD in aerospace engineering in 2005, developed the supersonic parachute that slowed the spacecraft’s blistering descent onto Mars. The parachute deployed seven miles above the surface of the planet while Curiosity was careening toward the ground at 900 miles per hour at Mach 2. At 70 feet in diameter, it was the largest parachute opening at the highest speed ever on Mars.
Sengupta teaches spacecraft design in the Department of Astronautical Engineering at the USC Viterbi School of Engineering. She’s also an expert in Entry, Descent and Landing (EDL) at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena.
Her career at JPL began with the design of ion engines, a type of spacecraft propulsion system that generates thrust by accelerating a plasma, but she switched to EDL to broaden her knowledge and join the team that would land Curiosity on Mars.
“As an aerospace engineer, the more areas of expertise you have, the better able you are to work on a variety of mission types,” Sengupta said.
Tests done in the 1960s and ’70s in support of the Viking Lander mission have showed that, at speeds greater than 1.5 times the speed of sound on Mars, parachutes tend to inflate and collapse over and over, reducing their ability to effectively slow down falling payloads and in some cases resulting in the failure of the parachute.
“It kind of looks like crazy jellyfish. But with Mars EDL you only get one parachute so it has to work and survive,” Sengupta said.
No one bothered to figure out why, until now when, due to the size of Curiosity, a 2,000-pound behemoth rover encapsulated inside a 15.5-ft. diameter entry capsule, it became necessary to design a massive parachute to survive at in excess of two times the speed on sound on Mars.
Sengupta and her colleagues discovered that the turbulent wake from the falling entry capsule would modify the bow shock and pressure distribution in front of the parachute, causing the collapsing or deflating cycle that had been observed.
“We discovered fascinating new physics and solved the mystery that had been around for decades,” she said.
Armed with this knowledge, the team was able to design a parachute that was similar to ones used in the past but strong enough to survive flight through the Martian atmosphere.
Through careful ground testing in a vacuum chamber to simulate the Martian environment, Sengupta also analyzed how the engine plumes from the sky crane that lowered Curiosity to the ground would affect the terrain around the rover.
“We basically got to play in a giant sandbox for two weeks,” as Sengupta put it, and the team was able to ensure that the sky crane’s engines wouldn’t bury the rover in dust and dirt upon landing.
Though the landing — parachute, sky crane and all — was a huge success, Sengupta’s work is far from over. Up next she’s designing a quantum physics experiment that could launch to the International Space Station as early as 2015, and then a spacecraft to explore the habitability of Europa, one of Jupiter’s moons that is covered in ice, possibly with an ocean beneath the surface.
Meanwhile, she’ll be back in a USC classroom in the fall — preparing the next generation of engineers and scientists to push humanity ever further into space.
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