MSN / By Alan Boyle

PASADENA, Calif. — After eight years of planning and eight months of interplanetary travel, NASA's Mars Science Laboratory is expected to pull off a touchdown of Super Bowl proportions without any further human assistance.

The $2.5 billion probe is right on target for its designated landing zone in 96-mile-wide (154-kilometer-wide) Gale Crater — so much on target that mission managers decided to pass up their last scheduled opportunity to upload fresh data on the spacecraft's position, said mission team member John Essmiller.

That means that if everything proceeds as expected, scientists and engineers here at NASA's Jet Propulsion Laboratory will merely be watching along with everyone else from now until they're due to receive word of Mars Science Laboratory's landing at 10:31 p.m. PT Sunday (1:31 a.m. ET Monday).

"We're all along for the ride," said Adam Steltzner, the JPL engineer in charge of the spacecraft's landing sequence.

Studying the chemistry of life
The Mars Science Laboratory mission is aimed at putting the 1-ton, car-sized Curiosity rover on the surface inside Gale Crater. Scientists say a 3-mile-high (5-kilometer-high) mountain inside the crater could preserve billions of years' worth of geological history, shedding light on the planet's transition from its warmer, wetter past to its current cold, dry climate.

Curiosity is the biggest and most capable robotic laboratory ever sent to another celestial body: Its 10 scientific instruments are designed to study the chemistry of Mars' rocks, soil and atmosphere and determine whether the Red Planet had the right stuff to be habitable in ancient times. Some scientists think Curiosity could even detect the signs of present-day life, although NASA doesn't go that far.

A successful landing would open the way for at least two years of exploration, potentially reinvigorating America's space program. Failure could kick off a years-long cycle of soul-searching.

"Tonight is it: the Super Bowl of planetary exploration," said Doug McCuistion, director of the Mars Exploration Program at NASA Headquarters. "One-yard line, one play left. ... We score and win, or we don't score and we don't win."

But even if the play ends up in a loss, McCuistion vowed that the space agency would go ahead with future missions to Mars. "We'll pick ourselves up, dust ourselves off and do it again," he told reporters.

Risky descent
The final phase of the Mars Science Laboratory's journey relies on technologies that have never been tried before in outer space — which is why it's called the "seven minutes of terror."

Seven minutes before landing, Mars Science Laboratory will throw off its cruise stage and begin its plunge through the planet's atmosphere at a speed of 13,200 mph (5,900 meters per second). It'll jettison two solid-tungsten weights, shifting the spacecraft's balance to become more like a wing. Small thrusters will fire to put the craft through a series of "S" turns to adjust the trajectory.

All this has to be done autonomously, due to the 14-minute light-travel time between Mars and Earth. If something goes wrong, controllers back on Earth won't know until it's over.

The heat shield will have to weather temperatures ranging up to 3,800 degrees Fahrenheit (2,100 degrees Celsius). At an altitude of about 7 miles (11 kilometers), the spacecraft will deploy its parachute, even while it's traveling at supersonic speeds.

First the heat shield drops away. A couple of minutes later, the parachute and the back shell fly off. What's left is the rover and its rocket-powered "sky crane."

The sky crane handles the final phase of the slowdown by firing eight retro rockets. It will descend to a height of 65 feet (20 meters) and lower the rover to the surface on the end of three cables. When the rover hits the ground, the cables will be cut loose, and the sky crane will blast itself away from the landing site.

Steltzner admits that the plan looks crazy, but insists that it's actually the "least crazy" alternative for delivering a 1-ton rover to Mars. All that weight is too heavy for the airbag-cushioned system that was used for previous Mars rovers, and too unstable to put on a lander with legs, he said.

Steltzner said he and his team were "rationally confident" and "emotionally terrified" in the final hours before landing. Steltzner himself, a former rock musician with an Elvis haircut, sounded as if he was leaning toward the rationally confident side of the spectrum as he discussed the Curiosity rover, which he consistently refers to as a "she."

"I slept better last night than I slept in a couple of years — because she's on her own now," Steltzner said.

Steltzner may be better-rested that some of the others who worked on the landing plan. Mark Sirangelo, who heads Sierra Nevada Corp.'s space systems division, noted that his company had a hand in building the sky crane. So what will he be doing while the descent is under way? "I'm going to be in a room with my eyes closed," Sirangelo said, only half-jokingly.

How we'll hear
When Curiosity touches down, it will be out of Earth's direct line of sight, so three orbiting probes — NASA's Mars Odyssey and Mars Reconnaissance Orbiter, as well as the European Space Agency's Mars Express — will be monitoring the data being sent out by the spacecraft. However, only Odyssey is capable of relaying the data back immediately, using what's called a "bent pipe" communication mode.

Telemetry will be sent back from Mars orbit to be picked up by an Australian radio telescope that's part of NASA's Deep Space Network, and relayed to the Jet Propulsion Laboratory. In full view of TV cameras, scientists, engineers and VIPs at JPL will be tracking what happened at Mars 14 minutes before.

Among the VIPs due to be in attendance are Black Eyed Peas musician Will.I.Am; actors Nichelle Nichols (Lt. Uhura on the original "Star Trek"), Wil Wheaton (Wesley Crusher on "Star Trek: Next Generation"), June Lockhart (from "Lost in Space" and "Lassie"); "Jeopardy" host Alex Trebek and "Through the Wormhole" host Morgan Freeman. NASA Administrator Charles Bolden and White House science adviser John Holdren were also scheduled to show up.

If the engineers receives blips of data at 10:31 p.m. PT, indicating that Curiosity has survived the seven minutes of terror, the news will be telegraphed by a wave of smiles, back-slaps and high-fives. A few minutes afterward, Odyssey may even relay the first thumbnail pictures taken by the rover. But if no signals are received, that will kick off an hours-long wait-and-see exercise.

A couple of hours after landing time, Odyssey could beam back data and pictures from Curiosity. Later on, Mars Reconnaissance Orbiter will have an opportunity to transmit the data as well, perhaps including a snapshot of Curiosity taken while it was in mid-descent.

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