Stunt doubleNASA built Mars-bound C

Stunt double

NASA built Mars-bound Curiosity along with an identical twin. That second rover amounted to a stunt double. It underwent tests in the laboratory that might have risked Curiosity’s safety.

Curiosity was the first Mars rover that would parachute down through the atmosphere, landing only on its wheels. Savannah McCoy, an engineer at JPL, helped test the stunt double to ensure that Curiosity could complete the maneuver. If the vehicle landed too hard, it could destroy the wheels — maybe even the chassis, or frame. That would not be a good start for a vehicle that might be asked to travel 100,000 kilometers (62,000 miles) over the next several years.

The spacecraft initially zoomed toward the Red Planet at about 12,875 kilometers per hour (or 8,000 miles per hour), according to JPL’s Tomas Martin-Mur. He led the team responsible for navigating Curiosity. As the spacecraft got closer to Mars, the planet’s gravity tugged on the craft, accelerating its speed to about 21,000 kilometers per hour.

But as soon as it reached the thin Martian atmosphere, the spacecraft had to brake quickly, precisely — and carefully. The atmosphere helped, by offering some resistance, known as “drag.” The outside of the spacecraft heated intensely as it zoomed through this atmosphere.

Several minutes later the craft had cooled somewhat. Here, at about 11,000 kilometers (some 6,800 miles) above the Martian surface, a mammoth parachute sprung open to further slow Curiosity’s descent. At an altitude of about 1 mile, the parachute was cut free and the spacecraft ejected the rover.

But the valuable vehicle didn’t crash. The rover dangled by ropelike tethers below a final stage of the spacecraft, known as a sky crane. Powerful engines, called thrusters, on the landing craft turned on at precisely timed intervals. These further braked Curiosity’s fall to a gentle pace. Immediately after landing, the sky crane flew away, to set down well clear of the rover.

A half-day before touchdown, Steltzner noted with relief that Mars’ atmosphere had decided to cooperate with Curiosity’s arrival by delivering “perfect” weather for landing. The spacecraft was arriving in a transitional season on the planet, a time “between the cold and clear season on Mars and the warm and dusty season,” he said. During this in-between period, many storms develop.

Such storms had begun developing in the weeks before Curiosity’s descent, Steltzner says. That could have made maneuvering to the landing site difficult. One storm raged just east of the rover landing site but didn’t get in Curiosity’s way. And luckily, once the rover touches down onto the Martian surface, “dust doesn’t really matter,” the researcher explains.

President Obama has asked NASA to plan for sending humans to Mars in the mid-2030s. This week’s successful landing “marks a significant step toward achieving this goal," NASA director Bolden says.