An engineering feat for the ages!

Strange but True: Curiosity’s Sky Crane

July 30, 2012:  On August 5th at 10:31 p.m. Pacific Time, NASA will gently deposit their new, 2000-pound Curiosity rover on the surface of Mars, wheels-first and ready to roll. Quite a feat – because it will come screaming through the Martian atmosphere at 13,000 mph.

Curiosity, aka the Mars Science Laboratory, will be the largest mission ever to land on another planet. It’s big because it has a big mystery to solve: was Mars ever or is it still capable of harboring life?

During its grand entrance, the lander must slow to 1 1/2 mph to touch down safely. That kind of braking action for a one-ton payload demands the nail-bitingly precise unfolding of an intricately choreographed sequence of events. Key players: a red-hot heat shield, a huge parachute, 76 explosive bolts — and a Sky Crane.

The now-famous “Seven Minutes of Terror” video dramatically documents Curiosity’s descent to the surface of Mars. Play it

“The whole ballgame transpires within 7 minutes, from atmospheric entry to touch-down,” says Jet Propulsion Laboratory’s Steve Sell, Deputy Operations Lead for Entry, Descent, and Landing. “The onboard computer calls the shots. And if any one maneuver fails, it’s game over.”

Here’s the game plan.

“Atmospheric friction slows the capsule containing Sky Crane — an eight-rocket jetpack attached to the rover — from 13000 to 1000 mph. [Mars' atmosphere is too thin to slow it more.] The friction burnishes the capsule’s heat shield to a glowing 3800 degrees Fahrenheit (2100 degrees Celsius). Then a 60-foot diameter parachute deploys and inflates above the capsule on 160-foot lines. What’s left of the heat shield jettisons, giving Curiosity its first look at its new home below.”

This is the largest, strongest parachute ever flown to another world. It has to be a super-chute to handle the 65000 pounds of force produced when the rover snaps to attention below it.

The Sky Crane in action. Larger image

“After the payload slows to about 200 mph, explosive bolts free the chute and Sky Crane free-falls for a second. Then its retrorockets fire.”

The rockets slow the descent to 1 ½ mph and power a sideways parry to avoid the faster falling chute. As Sky Crane descends to 60 feet above Mars’ surface, the rover inches down from underneath it on three nylon ropes like a spider spinning strands of its web. With Curiosity dangling 20 feet below, Sky Crane continues its downward progress until the rover is resting on the surface. Explosive bolts cut Curiosity’s last physical attachments to the outside world, and Sky Crane flies away to death-plunge into the red sands, its incredible job done.

It might sound frighteningly complicated, “but what appears to be a complex system actually simplifies the landing greatly,” explains Sell.

Previous missions such as Vikings I and II and the Mars Phoenix Lander used retrorockets to lower spacecraft all the way to the surface atop a legged lander. Others have used airbags. Neither method is feasible for Curiosity.

“With a payload this size, the rockets could kick up enough dust to compromise the rover and its instruments,” explains Sell. “And the rockets could excavate craters Curiosity would have to avoid as it drives away. Add to that the risk of a big, heavy vehicle driving down off the lander via an exit ramp to reach the surface.”

Pathfinder, Spirit, and Opportunity used airbags to eliminate these concerns. But Curiosity is too large for airbags.

“Bags big enough to soften its landing would be too heavy or too costly to launch. Besides, you’d have to drop the payload so slowly for the bags to survive the load, you may as well place the rover right on its wheels.”

Three generations of Mars rovers. Curiosity (pictured right) is more massive than its predecessors, which is why NASA had to develop an innovative landing system.

Sky Crane, says Sell, makes sense for Curiosity. But it still keeps him up at night.

“I leave myself voicemails in the middle of the night about things to check in the morning. We’ve run thousands of tests and simulations, thinking of ways to ‘break’ the system so we can build in comfortable performance margins. We’re still testing. There’s always one more test we can run. We’re always afraid we missed something.”

In the control room at JPL the night of August 5th, it will be too late. It takes 14 minutes for signals to travel from Mars to Earth. When the team receives the signal ‘I am entering the atmosphere,’ Curiosity will be alive or dead on the surface.

Says Sell: “I’m already holding my breath.”

 

NASA Lands Car-Size Rover Beside Martian Mountain

August 6, 2012: NASA’s most advanced Mars rover Curiosity has landed on the Red Planet. The one-ton rover, hanging by ropes from a rocket backpack, touched down onto Mars Sunday to end a 36-week flight and begin a two-year investigation.

The Mars Science Laboratory (MSL) spacecraft that carried Curiosity succeeded in every step of the most complex landing ever attempted on Mars, including the final severing of the bridle cords and flyaway maneuver of the rocket backpack.

Curiosity landed at 10:32 p.m. Aug. 5, PDT, (1:32 a.m. EDT Aug. 6) near the foot of a mountain three miles tall and 96 miles in diameter inside Gale Crater. During a nearly two-year prime mission, the rover will investigate whether the region ever offered conditions favorable for microbial life.

One of Curiosity’s first images (inset) shows the rover’s shadow. The picture was taken through a wide-angle lens on rover’s rear Hazard-Avoidance camera. It’s only one-quarter of full resolution. As planned, the rover’s early engineering images are lower resolution. Larger color images are expected later in the week when the rover’s mast, carrying high-resolution cameras, is deployed. More images

“The Seven Minutes of Terror has turned into the Seven Minutes of Triumph,” said NASA Associate Administrator for Science John Grunsfeld. “My immense joy in the success of this mission is matched only by overwhelming pride I feel for the women and men of the mission’s team.”

Curiosity returned its first view of Mars, a wide-angle scene of rocky ground near the front of the rover. More images are anticipated in the next several days as the mission blends observations of the landing site with activities to configure the rover for work and check the performance of its instruments and mechanisms.

“Today, the wheels of Curiosity have begun to blaze the trail for human footprints on Mars,” declared NASA Administrator Charles Bolden. “Curiosity, the most sophisticated rover ever built, is now on the surface of the Red Planet, where it will seek to answer age-old questions about whether life ever existed on Mars — or if the planet can sustain life in the future,”

Confirmation of Curiosity’s successful landing came in communications relayed by NASA’s Mars Odyssey orbiter and received by the Canberra, Australia, antenna station of NASA’s Deep Space Network.

Curiosity carries 10 science instruments with a total mass 15 times as large as the science payloads on the Mars rovers Spirit and Opportunity. Some of the tools are the first of their kind on Mars, such as a laser-firing instrument for checking elemental composition of rocks from a distance. The rover will use a drill and scoop at the end of its robotic arm to gather soil and powdered samples of rock interiors, then sieve and parcel out these samples into analytical laboratory instruments inside the rover.

To handle this science toolkit, Curiosity is twice as long and five times as heavy as Spirit or Opportunity. The Gale Crater landing site places the rover within driving distance of layers of the crater’s interior mountain. Observations from orbit have identified clay and sulfate minerals in the lower layers, indicating a wet history.

“This is an amazing achievement, made possible by a team of scientists and engineers from around the world and led by the extraordinary men and women of NASA and our Jet Propulsion Laboratory,” added Bolden. ” President Obama has laid out a bold vision for sending humans to Mars in the mid-2030′s, and today’s landing marks a significant step toward achieving this goal.”

This entry was posted on Monday, August 6th, 2012 at 6:23 am and is filed under Science, Space Exploration, Special Report, Technology. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.