NASA's Mars explorer Curiosity, the most capable robotic rover ever built for taking the measure of a planet, is nestled snugly in its protective fairing atop an Atlas V rocket, awaiting a 10:02 launch this morning from the Kennedy Space Center in Florida.
Not since the twin Viking landers touched down on the Martian surface in 1976 has an advanced robotic chemistry lab been dispatched to the planet – a sibling of Earth that has captured the human imagination for millenniums.
Unlike Vikings 1 and 2, Curiosity will not hunt for direct evidence of life on Mars. Instead, scientists fielding the Mini Cooper-sized rover with its seven foot "neck" will analyze the layered terrain in Gale Crater to read in its rocks the history of the environment there.
The crater's rocks show evidence of water in their distant past. And the formations appear to record a progression from wet, to occasionally wet, to dry conditions. Now researchers are hunting for clues about the broader chemical and atmospheric processes affecting the planet during these changes, conditions that could have encouraged or inhibited the possible emergence of life on Mars.
Any life that exists on Mars "will be a function of its environment," says Pamela Conrad, an astrobiologist at the Goddard Space Flight Center in Greenbelt, Md., and a deputy principal investigator for one of the soil-analysis instruments Curiosity carries.
"We can't say with any definitive knowledge that we could recognize life somewhere else in the solar system, or beyond the solar system, without being able to unbolt all the assumptions and all the experience we have" looking at life on Earth, Dr. Conrad says.
For Mars, Curiosity represents the tool that will suggest to astrobiologists how loose bolts have to be.
But first, Curiosity has to get there.
It's a 354-million-mile trip that begins with this morning's lift-off. Once Curiosity reaches space, the craft's Centaur upper stage will ignite and place the craft in a temporary parking orbit around Earth. Roughly 20 minutes later, the upper stage will ignite once more to send Curiosity on its way to Mars.
During the trip, scientists and engineers will make sure the 10 science instruments aboard the rover are working properly, make any course corrections that might be needed to keep Curiosity on the interplanetary not-so-straight but narrow, and plan the early stages of their exploration of Gale Crater.
Over the course of Curiosity's 98-week primary mission, the rover is expected to cover about 12 miles. But mission managers say they expect it to rack up far more than that if the mission receives extensions, according to Peter Theisinger, project manager for the Mars Science Laboratory at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The Mars Exploration Rovers Spirit and Opportunity, which reached Mars in January 2004, were required to cover about 0.6 of a mile during their 90-sol primary mission. Each sol, or solar day on Mars, lasts about 24 hours and 40 minutes. Both of those smaller rovers lasted well beyond their 90-sol minimum. Spirit finally fell silent in 2010. Opportunity is still active and has covered some 21 miles during its explorations.
If liftoffs and reentries represent the tensest moments in spaceflight, when Curiosity arrives the mission team will endure another nail-biter – on a never-flown-before approach to setting the rover down on Martial soil.
The Viking landers used rocket motors to slow their final descent onto Mars. Mars Pathfinder in 1997 and the Mars Exploration Rovers Spirit and Opportunity were encased in air bags that inflated just before touchdown. Once the rovers bounced to a stop, the bags deflated and the vehicles drove off their landing platforms.
Curiosity, however, tips the scales at just under 1 ton. It was deemed far too large and heavy for an air-bag-and-platform combination.
Instead, Curiosity will be lowered the last 200 feet on a tethered harness, played out from a module that sports eight rocket motors.
This re-entry-and-descent module's motors are designed to ignite when it and its cargo are about a mile above the surface. When the duo reaches the final 200 feet, the module is designed to lower Curiosity at about 2-1/2 feet per second. If all goes well, Curiosity lands on its six wheels, the module cuts the harness lines, then rockets off to crash-land in some other part of the crater.
The approach raises eyebrows, Mr. Theisinger acknowledges.
"A lot of people look at that and say: What were you thinking?" he acknowledges. But "we've done everything we could think of to do" to test the system's components.
He and other NASA officials acknowledge the risk.
"Mars is the Bermuda Triangle of the solar system," quips Colleen Hartmann, assistant associate administrator at NASA headquarters in Washington.
Collectively, the US, Russians, Japanese, and Europeans are batting .329 on Mars missions. The US has enjoyed the highest success rate. Since the mid-1960s, the US has succeeded in 11 out of 16 Mars missions, which include fly-bys, orbiters, landers, and rovers.
Still, "this is the most interesting science we could possibly do," Dr. Hartman says, science whose data will inform future NASA robotic and human missions to the red planet, as well as answer scientists' questions about habitability.
The novel approach for depositing Curiosity on Mars flows directly from the ambitiousness of the $2.5 billion mission and the size and mass of the lander required to perform the science experiments, she says.
"Is this really a good bet that it will work?" she asks. After iterations of design, testing, engineering reviews, and risk analyses, the answer was yes, she says.