Curiosity readies for dramatic entrance
Mars rover to touch down August 5
By Nadia Drake
Web edition : Tuesday, July 31st, 2012

Editor’s note: This is the first of two articles previewing the Mars Curiosity rover’s upcoming Mars landing. This installment describes the vehicle’s landing on the Red Planet, scheduled for Sunday evening, August 5, Pacific Daylight Time; the next will cover the rover’s science mission. Science News astronomy writer Nadia Drake will be covering the landing live from NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

An enormous robot is about to hit the red dirt of Mars — not too hard, NASA hopes — in search of life-friendly environments, or remnants of them. The Curiosity rover’s off-road adventures will begin only if it survives a daring seven-minute, 125-kilometer plunge through the planet’s carbon dioxide atmosphere.

Scientists on Earth expect to observe the touchdown at 10:30 p.m. Pacific Daylight Time on August 5.

Curiosity, which is the size of a small car, is the newest and largest addition to NASA’s family of robotic planet explorers. Its target on Mars is Gale Crater, 154 kilometers wide and home to a massive peak that scientists call Mount Sharp.

After a nearly nine-month journey, the spacecraft carrying Curiosity will enter Mars’ thin atmosphere going approximately 21,250 kilometers per hour. Seven minutes later, just before the rover sets wheels on the fourth rock from the sun, it had better be going approximately zero.

“The Curiosity landing is the hardest NASA robotic mission ever attempted,” says John Grunsfeld, associate administrator for NASA’s Science Mission Directorate. “This is risky business.”

Rather than being cushioned by interplanetary airbags — as the Spirit and Opportunity rovers were in 2004 — Curiosity’s touchdown involves a “sky crane” maneuver that seems ripped from a James Bond film.

That concept includes a parachute deployment 11 kilometers above the planet, once the atmosphere has slowed the spacecraft to a relatively pokey 1,400 kilometers per hour. At 1.6 kilometers above the surface, while falling at nearly 300 kilometers per hour, the parachute is designed to separate from the rover, leaving the craft folded up like a giant bionic insect underneath what’s called the descent vehicle.

Then the descent vehicle should fire its retro-rockets, slowing the plunge even more and setting the stage for the sky crane maneuver to begin. At 20 meters above the planet’s surface — and now dropping at just 2.7 kilometers per hour — the rover will descend from the mother ship on nylon cables and the still-tethered pair will move slowly toward the surface.

“Is it crazy? Well, not so much,” says NASA’s Doug McCuistion. “Once you understand it, it’s not a crazy concept. It works.”

After the rover has stretched its legs and is safely on the ground, it will sever the umbilical cords, allowing the descent vehicle to fly off and ditch itself in the dust about half a kilometer from the landing site.

During the spacecraft’s entry, descent and landing, NASA’s Mars Odyssey orbiter will act as an interplanetary Internet router, relaying information from the rover to scientists on Earth in near real time. (It takes almost 14 minutes for radio signals to travel between the two planets.)

And there will be video: The one-ton, six-wheeled, nuclear-powered rover will film the descent with a camera on its belly. Scientists hope to release the video soon after landing. “That’s just going to be an awesome video, landing on the surface of Mars,” says project scientist John Grotzinger of Caltech. “We’re going to go swinging out like an amusement park ride, and maybe see the flank of Mount Sharp, and then come back down again and see the ground, and the other side — maybe the crater rim.”

After spending a bit of time making sure that all systems are go, the rover will make tracks, driven by scientists wielding computer commands from nearly 250 million kilometers away. “I’m really envious of the rover drivers,” Grotzinger says. “I always wanted to be a rover driver.”

If the spacecraft comes down safely, team members will begin working in shifts on Mars time, synchronizing their days and nights to match the Martian day, which is roughly 40 minutes longer than an Earth day. It’s like being perpetually jet-lagged. “Every day, you come in to work 40 minutes later,” says Ryan Anderson, a planetary scientist at the U.S. Geological Survey Astrogeology Science Center in Flagstaff, Ariz. “If you started in the morning, several weeks later, you’re starting in the middle of the night.”

For at least 90 days, Curiosity will trundle along during the Martian day while scientists on Earth work the Red Planet’s night shift. “We wake up when the rover is going to sleep and work through the Mars night so that by morning, we can send the rover new commands for the next day,” Anderson says.

Of course, all that assumes Curiosity will land safely. If it doesn’t? “We don’t talk about that much,” Anderson says.


Curiosity, NASA’s newest Mars rover, will search for signs of life-friendly environments on Mars — if it survives the journey to the Martian surface on August 5. The journey’s final step is a maneuver that engineers call the sky crane (illustrated), in which a hovering spacecraft lowers the rover to the reddish soil. Credit: NASA; JPL-Caltech