Twelve years ago NASA landed its six-wheeled science lab using a daring new technology that lowers the rover using a robotic jetpack.
The sky crane, developed due to Curiosity’s size and weight, enabled precise landings in scientifically valuable locations. Initially questioned, this innovative system has proven indispensable for missions and can be adapted for use on other celestial bodies.
NASA’s Curiosity rover mission is celebrating its 12th anniversary on the Red Planet, where the six-wheeled scientist continues to make great discoveries as it slowly moves along the base of a Martian mountain. It has just successfully landed on Mars is an accomplishment, but the Curiosity mission went a few steps further on August 5, 2012, and deployed a bold new technique: the skycrane maneuver.
Pioneering work for sky crane technology
A descending robotic jetpack carried Curiosity to its landing zone and lowered it to the surface using nylon ropes, then cut the ropes and flew off to make a controlled crash landing safely out of the rover’s reach.
Of course, all of this was out of sight of the Curiosity engineering team, who sat in the mission control center at NASA’s Jet Propulsion Laboratory in Southern California and waited seven agonizing minutes (see video below) before erupting in cries of joy when they got the signal that the rover had successfully landed.
The skycrane maneuver was born out of necessity: Curiosity was too big and heavy to land like its predecessors – wrapped in airbags that bounced across the Martian surface. The technique also allowed for greater precision, resulting in a smaller landing ellipse (see image below).
When Perseverance, NASA’s newest Mars rover, landed in February 2021, Skycrane technology was even more precise: By adding what’s known as terrain-relative navigation, the SUV-sized rover was able to land safely on the bottom of an ancient lake riddled with rocks and craters.
Development of a Mars landing
JPL has been involved in NASA’s Mars landings since 1976. At that time, the laboratory worked together with the agency’s Langley Research Center in Hampton, Virginia, on the two stationary Viking landers, which touched down with expensive, throttled landing engines.
For the landing of the Mars Pathfinder mission in 1997, the Jet Propulsion Laboratory (JPL) proposed something new: While the lander dangled from a parachute, giant airbags would inflate around it. Then, three braking rockets halfway between the airbags and the parachute would bring the spacecraft to a stop above the surface, and the airbag-encased spacecraft would fall about 20 meters to Mars, bouncing several times—sometimes as high as 15 meters—before coming to rest.
It worked so well that NASA used the same technique in 2004 to land the Spirit and Opportunity rovers. At the time, however, there were few places on Mars where engineers were sure the spacecraft wouldn’t hit a terrain feature that could puncture the airbags or send the pack rolling uncontrollably down a slope.
“We barely found three locations on Mars that we could safely consider,” said Al Chen of JPL, who played a key role in the entry, descent and landing teams of Curiosity and Perseverance.
It also became clear that airbags simply weren’t feasible for a rover as large and heavy as Curiosity. If NASA wanted to land larger spacecraft in more scientifically exciting locations, better technology was needed.
Rover on a rope
In the early 2000s, engineers began toying with the concept of a “smart” landing system. New types of radar had become available that provided real-time velocity measurements – information that could help spacecraft guide their descent. A new type of thruster could be used to steer the spacecraft toward specific locations or even provide some lift to steer it away from danger. The sky crane maneuver began to take shape.
JPL Fellow Rob Manning worked on the original concept in February 2000 and remembers the reaction people got when they saw that the jetpack was mounted above the rover rather than below it.
“That confused people,” he said. “They assumed that the propulsion would always be underneath you, like you see in old science fiction stories when a rocket lands on a planet.”
Watch NASA’s Perseverance rover land on Mars in 2021 using the same skycrane maneuver that Curiosity used in 2012. Image credit: NASA/JPL-Caltech
Manning and his colleagues wanted to put as much distance between the ground and these thrusters as possible. A lander’s thrusters would not only kick up debris, but also dig holes that a rover would be unable to get out of. And while previous missions used a lander that housed the rovers and had a ramp extended so they could roll down, placing the thrusters above the rover meant its wheels could touch down directly on the surface, effectively acting as a landing gear and saving the extra weight of carrying a landing platform.
But engineers weren’t sure how to suspend a large rover from ropes without it swinging uncontrollably. When they looked at how the problem was solved for giant transport helicopters on Earth (called sky cranes), they realized that Curiosity’s jetpack would have to be able to sense and control the swinging.
“With all this new technology, we have a real chance of getting to the right place on the surface,” Chen said.
Best of all, the concept could also be used for larger spacecraft – not just on Mars, but elsewhere in the solar system. “If you wanted to have a payload transport service in the future, you could easily use this architecture to get to the surface of the moon or elsewhere without ever touching the ground,” Manning said.
NASA’s Curiosity Rover
NASA’s Curiosity rover, officially called the Mars Science Laboratory (MSL), has been exploring the Martian surface since its successful landing on August 6, 2012. Curiosity is equipped with a suite of scientific instruments designed to analyze rocks, soil and atmosphere. Its primary mission is to study the planet’s climate and geology and determine whether Mars could have ever supported microbial life. The rover’s key achievements include the discovery of ancient water currents, complex organic molecules and fluctuating methane levels in the Martian atmosphere, indicating a more habitable past for the planet. Its ongoing journey through Gale Crater continues to provide valuable data on Mars’ environmental history and natural processes.
