Curiosity's perilous landing? 'Cleaner than any of our tests'

Local scientist directly involved with the Curiosity Program which successfully landed a rover on Mars

At 10:24 p.m. PDT Sunday night, the Curiosity rover splashed into the Martian atmosphere at more than 13,000 mph. Then, for a moment, it appeared that NASA's nickname for Curiosity's daring landing sequence ? "seven minutes of terror" ? was coming true.

Inside mission control, an alarm flashed on engineers' computer screens warning that Curiosity was coming in at the wrong angle, a potentially fatal development that engineers could not correct because the landing was entirely automated. Then, a passing satellite indicated that it was ready to relay messages from Curiosity. But for 30 seconds, a lifetime in this context, no data arrived. When the data started flowing in, the spacecraft appeared to be moving more slowly than engineers had planned.

And then, just as quickly, it all disappeared. The craft was not moving slowly, but deliberately. It was simply taking its time to find a comfortable spot inside a 3-billion-year-old meteor crater. The data flow from the passing satellite began streaming across engineers' computer screens. Curiosity's "wrong" angle turned out to be statistical noise ? "just a puff of air," said Al Chen, a Jet Propulsion Laboratory engineer and a member of the mission's landing team.

Photos: Mars rover mission

Curiosity's landing, it turned out, was as close to perfect as an eight-month journey through space can produce. In interviews with The Times, engineers said initial reviews of Curiosity's final minutes in flight revealed a startling fact: the landing ran into fewer problems than any of the hundreds of simulations they had run over the last two years.

"It was cleaner than any of our tests," Chen said, shaking his head with amazement. "It was a blast."

The tension reached a boiling point at 9:49 p.m., when Curiosity began executing a series of "irreversible" maneuvers, including the first of 79 pyrotechnic explosions that readied the craft for landing.

Interactive: Curiosity: Liftoff to landing

At 10:08, another critical moment: Because the Earth had "set" below the Martian horizon, Curiosity had no direct contact with scientists back home. It needed a relay throw ? a "bent pipe" maneuver, in space-science parlance, in which a passing satellite would gather Curiosity's data and send it back home.

But the only satellite available wasNASA'sOdyssey, which was 10 years old and missing a key part. No one knew whether the satellite would cooperate. And then, it did. "They're going be there for us!" an engineer shouted across mission control, which erupted in applause.

At 10:13, mission control began receiving "heartbeat tones" from Curiosity, indicating that it was alive and emitting information about its journey.

At 10:24, the "seven minutes of terror" began. The spacecraft was already on the ground ? but because of the vast distance between Earth and Mars, scientists wouldn't know whether it was alive or dead for seven minutes.

Two minutes later, an engineer reported that the Odyssey satellite might be failing after all. The satellite was trying, but no data were coming through. "We have a connection. But we do not actually? " Before the engineer could finish the sentence, a strong stream of telemetry began scrolling across mission control's screens.

From that point on, hope rose with every maneuver. Some engineers clasped their hands tightly, as if trying to squeeze out the last of the danger. By now, many were sweating. "I was feeling ? everything all at once," said engineer Ray Baker.

Each successful step was met with a moment of applause.

At 10:29, Curiosity's parachute ? the largest supersonic chute ever used in space ? deployed, sharply reducing the spacecraft's speed.

Twenty-four seconds later, Curiosity released its heat shield. This was critical; the heat shield had been acting like a lens cap on a camera, blocking Curiosity's radar from seeing the ground to pinpoint its landing. With the radar on, scientists would now know in seconds whether the spacecraft was where it "thought" it was based on a course calculation that had begun with a relatively rudimentary alignment of the sun and stars.

Miguel San Martin, the chief engineer of Curiosity's guidance and control, glanced at his screen to see the results, and was dumbfounded. In its final seconds, Curiosity would require a correction of less than 10 feet, startling accuracy after a journey of 352 million miles. Curiosity also "knew" its velocity to within three feet per second.

At 10:31, the zany "sky crane" deployed, lowering Curiosity toward the surface beneath the now-hovering spacecraft.

At 10:32, Curiosity's wheels neared the ground.

Steve Sell, another member of the entry, descent and landing team, knew the craft was close. But it still had one critical task: firing a series of small explosions to sweep blades across the tethers that still connected it to the sky crane. It had to happen at precisely the right moment ? too early, and the craft could tumble to the ground; too late, and the sky crane could begin to drift and drag the rover by the tethers over the surface of Mars.

Ten seconds later, the charges fired, Sell said, slicing the ropes to cut Curiosity free.

The sky crane was now in the form of a jellyfish, with long, free-flowing tethers that looked like tentacles hanging below the domed "shell" that had spat out the rover seconds earlier. The crane's engines throttled up, casting it several hundred yards to the north, where it crash-landed, on purpose, to get it out of the way.

The rover was now alone, in silence, and safe. Mission control exploded with cheers and applause.

"We train ourselves for years to think the worst all the time," San Martin said. "You're in the shower thinking about what could possibly give you a bad day. That's what you do, and then you can never turn that off."

In the end, San Martin said with a wry smile, "we did well."

scott.gold@latimes.com

Source: http://feeds.latimes.com/~r/latimes/news/science/~3/uxmvd6Hcd4I/la-sci-mars-seven-minutes-20120807,0,4024227.story

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