PASADENA, Calif.--In an unparalleled technological triumph, a one-ton nuclear-powered rover the size of a smallwas 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.
With flight controllers at NASA's Jet Propulsion Laboratory anxiously watching telemetry flowing in from Mars, 154 million miles away and 13.8 minutes after the fact, the Mars Science Laboratory rover -- Curiosity -- radioed confirmation of touchdown at 10:32 p.m. PDT (GMT-7; 1:32 a.m. EDT Monday).
"Touchdown confirmed. We're safe on Mars!" said mission control commentator Allen Chen as the flight control team erupted in boisterous 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 the floor of Gale Crater near the base of a 3-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 spacecraft, relayed through NASA's aging Mars Odyssey orbiter. As each major milestone ticked off, engineers clapped and cheered, increasingly optimistic as the spacecraft passed one hurdle after another.
"Vehicle reports entry interface," Chen said as the descent vehicle plunged into the discernible atmosphere at a blistering 13,200 mph. "At this time it will begin pressurizing the propulsion system to increase the thrust of the system. It'll use that for all the maneuvering in the atmosphere we're about to do... We are standing by for guidance start and the start of guided entry."
A few moments later: "We are beginning to feel the atmosphere as we go in here," Chen said. "The vehicle has just reported via tones that it has started guided entry. At this time, the vehicle is beginning to steer its way to the target... It's starting its first bank reversal."
As the spacecraft guided itself through two banking roll reversals to bleed off velocity as it zeroed in on the target landing zone, Chen noted "we have seen peak deceleration. We've passed through peak heating and peak deceleration. It is reporting we are seeing Gs on the order of 11 to 12 Earth Gs."
Guided entry then ended as expected and the spacecraft's huge parachute deployed and inflated as it fell toward Mars at 1.7 times the speed of sound, quickly decelerating as required.
"Stand by for parachute deploy... Parachute deploy!" Chen reported as the flight control team applauded. "Thrusters have been re-enabled, we will control attitude on chute, we are decelerating. About 10 kilometers (10.2 miles) and descending, we are at 150 meters per second (335 mph)..."
"We are nine kilometers (5.6 miles) and descending... We have acquired the ground with the radar (applause). Heat shield has separated, we have found the ground. We're standing by to prime the MLE engines in preparation for powered flight. We're down to 90 meters per second (201 mph) at an altitude of 6.9 kilometers (4.3 miles) and descending."
Right on schedule
As Curiosity fell, Earth dropped below the martian horizon, cutting off simple tones sent back by the spacecraft to mark major events. But the Mars Odyssey orbiter continued beaming back an uninterrupted flow of telemetry, giving flight engineers a ringside seat.
"We're down to 86 meters per second (192 mph) at an altitude of four kilometers (2.5 miles) and descending," Chen said. "We have lost tones from Earth at this time, this is expected. We're continuing on Odyssey telemetry... Standing by for backshell separation..."
Right on schedule, less than a mile above the surface, Curiosity and its "sky crane" backpack fell away from the parachute and backshell and an instant later, eight rocket engines, two on each corner ignited to stabilize the craft and slow it to a sedate 1.7 mph.
"We are in powered flight," Chen reported, prompting more applause. "We're at an altitude of one kilometer (0.6 miles) and descending about 70 meters per second (157 mph)... Down to 50 meters per second (112 mph), 500 meters (1,640 feet) 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 (22 mph), 40 meters altitude (131 feet)...
"Sky crane has started (applause)... Descending at about point 75 meters per second (1.7 mph) as expected... Expecting bridle cut shortly."
As Curiosity's wheels settled to the surface, the flight computer sent commands to cut the cables connecting it to the sky crane descent stage, which then flew away to a crash landing as planned.
Finally, after checking telemetry and confirming its status, Chen reported "touchdown confirmed. We're safe on Mars!"
Amid jubilant applause and cheers, he added: "Time to see where Curiosity will take us!"
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.
"Odyssey data is still strong," Chen reported. "Odyssey 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 else said in the background.
Exploring the crater floor and climbing Mount Sharp over the next two years, Curiosity will look for signs of past or present habitability and search for carbon compounds, the building blocks of life as it is known on Earth.
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.
"I can guarantee you in the days, months and years from now you'll be hearing an incredible science story," said Project Scientist John Grotzinger. "The money, two-and-a-half billion dollars, we don't put it in the rover and send it to mars, we spend it on Earth.
"This whole enterprise, if you divide by every woman, man and child in this country, comes out to be the cost of a movie (about $7). I speak on behalf of all my colleagues in science, that's a movie I want to see!"
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.
But it all worked and the cheers that rocked the halls of the mission operations center signaled the pride -- and relief -- felt by the flight control team, engineers and scientists who labored for nearly a decade to design, build, launch and land the Mars Science Laboratory.
"Today, right now, the wheels of Curiosity have begun to blaze the trail for human footprints on Mars," Bolden said at a post-landing news conference. "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 there on Mars or if the planet can sustain life in the future. This an amazing achievement."
John Holdren, President Obama's science adviser, said the landing was a "technological tour de force."
"It's an enormous step forward in planetary exploration, nobody has ever done anything like this," he said. "This lander is vastly bigger, vastly more capable, much more complicated to bring in, many new technologies had to work in perfect succession and perfect synchronization for this to happen.
"This is by far the most capable device, set of instruments, we've put up there for determining whether Mars every could have supported life. ... We stand to learn a tremendous amount from this Curiosity Mars Science Laboratory. It's going to do incredible things."
While precise numbers were not expected until the telemetry could be analyzed, the entry, descent and landing appeared to follow the EDL team's script without any major problems.
"It looked extremely clean," said Adam Seltzner, the lead engineer on the entry, descent and landing team. "Our navigation error was on the low side of our expectation. ... Our powered flight appears to have been excellent. We landed with 140 kilograms of fuel reserves out of a total of 400 kilos we carried in.
"It looked good, in short, good and clean," he said.
The timing of events in the following description were predicted and may be slightly different from the actual values, which depended on atmospheric conditions and other factors. But given the successful touchdown, the spacecraft lived up to the team's sky-high expectations.
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.
The guided entry
The Mars Science Laboratory was the first spacecraft to attempt a so-called guided entry on another planet.
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 experienced 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.
Six minutes after entry, now one mile up and falling toward the surface at roughly 180 mph, the rover and its rocket pack were cut away from the parachute and backshell, falling like a rock through the thin martian atmosphere.
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.
Update 2:15 a.m. PT:Added details, quotes, and photos following news conference.