NASA's Curiosity rover lands on Mars
BY WILLIAM HARWOOD
STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION
Posted: August 6, 2012
PASADENA, Calif.--In an unparalleled technological triumph, a one-ton nuclear-powered rover the size of a small car was lowered to the surface of Mars on the end of a 25-foot-long bridle suspended from the belly of a rocket-powered flying crane late Sunday to kick off an unprecedented $2.5 billion mission.
"Touchdown confirmed. We're safe on Mars!" said mission control commentator Allen Chen as the flight control team erupted in cheers and applause.
"It's just absolutely incredible, it doesn't get any better than this," said NASA Administrator Charles Bolden. "I was a basket case in there, I was really on pins and needles.
"It's a huge day for the nation, it's a huge day for all of our partners and it's a huge day for the American people," he said. "Everybody in the morning should be sticking their chests out, saying 'that's my rover on Mars.' Because it belongs to all of us."
The target landing zone was Gale Crater near the base of a three-mile-high mound of layered rock that represents hundreds of thousands to tens of millions of years of martian history, a frozen record of the planet's changing environment and evolution.
While the rover's exact position was not immediately known, there were no obvious problems during the dramatic entry, descent and landing and Curiosity presumably made it down inside a predicted footprint measuring four miles wide and 12 miles long -- a pinpoint landing compared to previous missions.
The seven-minute descent to the surface provided high drama as flight controllers monitored telemetry from the spacecrat, relayed through NASA's aging Mars Odyssey spacecraft. As each major milestone ticked off, engineers clapped and cheered.
"We have acquired the ground with the radar," Chen reported. "Heat shield has separated, we have found the ground. We're standing by to prime the engines in preparation for powered flight. Six-point-nine kilometers and descending..."
A few minutes later, the rover and its descent stage fell away from the vehicle's braking parachute and eight rocket engines ignited to stabilize the craft and slow the fall to touchdown velocity.
"We are in powered flight," Chen reported. "We're at an altitude of one kilometer and descending about 70 meters per second... 500 meters in altitude... standing by for sky crane. We found a nice flat place, we're coming in ready for sky crane. Down to 10 meters per second, 40 meters altitude."
A few moments later, just above the surface, the rocket-powered sky crane lowered Curiosity to the surface on the end of a 25-foot-long bridle, a landing technique never before attempted and one that added tension to an already anxious atmosphere.
While engineers did not expect pictures right away, blurry low-resolution thumbnails from the rover's rear hazard avoidance cameras were transmitted within minutes of touchdown showing a wheel on the surface of Mars.
"Odysesey data is still strong," Chen reported. "Odyseey is nice and high in the sky. At this time we're standing by for images..."
"We've got thumbnails," someone said.
"We are wheels down on Mars!" Chen reported.
"Oh my God," someone said in the background.
But before the rover's geological fieldwork can begin, engineers will devote several weeks to carefully checking out Curiosity's complex systems and testing its state-of-the-art instruments and cameras.
Curiosity's landing represented the most challenging robotic descent to the surface of another world ever attempted, a tightly choreographed sequence of autonomously executed events with little margin for error.
NASA managers went out of their way to brace reporters for the possibility of failure.
"No matter what happens, I just want the team to know I am really proud and privileged to have worked with these guys and gals," Doug McCuistion, director of Mars exploration at NASA Headquarters, said earlier Sunday. "They're amazing. They've done everything humanly possible to make this happen."
Adam Steltzner, the leader of the EDL team at the Jet Propulsion Laboratory in Pasadena, Calif., said earlier Sunday he was "rationally confident, emotionally terrified."
"This team ... has worked really hard for the better part of a decade, and the fruits of that labor get put to the test tonight," he said. "It's a little anxiety provoking. But I will say I slept better last night than I have slept in a couple of years, because she's kind of on her own now. When I look back on the hard work that we've done, I believe the team has done everything that we can to deserve success tonight."
And that's exactly what they got. While precise numbers were not expected until the telemetry could be analyzed, the entry, descent and landing appeared to follow the script as planned, which is reflected in the following description.
The Mars Science Laboratory spacecraft consisted of an interplanetary cruise stage, providing power and communications during the long-flight out from Earth, and the Curiosity rover, cocooned inside a heat shield and aeroshell to protect it from the extreme temperatures of atmospheric entry.
After covering 352 million miles since launch from Cape Canaveral, Fla., last November, the cruise stage separated from the lander around 10 p.m. But because of the distance between Earth and Mars -- 154 million miles -- it took radio signals confirming critical events 13.8 minutes to reach the flight control team at JPL. That translated into 10:14 p.m. "Earth-received time."
One minute later, thrusters fired to stop the entry vehicle's 2-rpm rotation and the spacecraft re-oriented itself heat shield forward and slammed into the discernible atmosphere at 10:24 p.m. at an altitude of about 78 miles and a velocity of 13,200 mph. At that point, it was about 390 miles -- seven minutes -- from touchdown in Gale Crater.
To control its lift, which allowed Curiosity's flight computer to make a pinpoint landing, two 165-pound tungsten weights were ejected just before entry to change the spacecraft's center of mass. During hypersonic flight, thruster firings controlled the orientation of the vehicle's "lift vector" to compensate for actual atmospheric conditions as it precisely controlled its path toward Gale Crater.
About one minute and 15 seconds after entry, the spacecraft's heat shield was expected to experience peak temperatures of up to 3,800 degrees Fahrenheit as atmospheric friction provided 90 percent of the spacecraft's deceleration. Ten seconds after peak heating, that deceleration was expected to peak at 10 to 15 times the force of Earth's gravity at sea level.
Plummeting toward Mars, the rover's flight computer continued steering the spacecraft, firing thrusters to make subtle changes in the flight path as required by atmospheric density and other variables.
The guided entry phase of flight was programmed to an end about four minutes after entry began. Six 55-pound weights then had to be ejected to move the center of mass back to the central axis of the spacecraft to help ensure stability when its braking parachute deployed.
Seconds later, at an altitude of about seven miles and a velocity of some 900 miles per hour, the huge chute unfurled and inflated to a diameter of 70 feet, delivering a 65,000-pound jolt to the still-supersonic spacecraft.
The heat shield was expected to be jettisoned about 24 seconds later, at an altitude of about five miles and a descent rate of 280 mph, exposing the rover's undercarriage to view.
A sophisticated radar altimeter then began measuring altitude and velocity, feeding those data to the rover's flight computer while a high-definition camera began recording video of the remaining few minutes of the descent.
An instant later, eight hydrazine-burning rocket engines, two at each corner of the descent stage, ignited to stabilize and quickly slow the craft's vertical velocity to less than 2 mph.
About 16 seconds before touchdown, at an altitude of just under 70 feet, Curiosity was lowered on the end of a 25-foot-long bridle made up of three cables. As the support and data cables unreeled, the rover's six motorized wheels presumably snapped into position for touchdown.
Finally, seven minutes after the entry began and descending at a gentle 1.7 mph, Curiosity's wheels touched the surface of Mars. Radio confirmation of landing came in at 10:32 p.m., about 3 p.m. local time on Mars.
Curiosity's flight computer, sensing "weight on wheels," then sent commands to fire small explosive devices that severed the cables connecting the rover to the still-firing propulsion system. Its work complete, the descent stage flew away to a crash landing a safe distance away.
"We have three different signals we would use to confirm touchdown and we need all three of those things to look right before we say so," Steltzner said earlier Sunday. "One of those is a message from the spacecraft that says 'I touched down, and this is the velocity I touched down at and where I think I am.'
"The rover has an inertial measurement unit, a gyro and an accelerometer set, and we look at that stream to say the rover's not moving at all, that signal says 'I think I'm on the ground and I'm not moving.' And the third is, we wait a safe period of time and confirm we're getting continuous UHF (radio) transmission. And frankly, that's there to make sure the descent stage hasn't fallen back down on top of the rover. When all three of those signals are positive, we declare touchdown confirmation."
And that's exactly what Chen reported at 10:32 p.m.
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