All is set for one of the most ambitious space missions ever devised. 25 November 2011
Nasa is about to launch its latest Mars rover, nicknamed Curiosity, from Cape Canaveral, Florida.
At nearly a tonne, the six-wheeled vehicle dwarfs all previous robots sent to the surface of the planet.
The machine carries a suite of sophisticated instruments and tools, including a hammer drill and a laser, to find out whether Mars is, or ever has been, suitable for life.
The US space agency will get its first opportunity to launch the robot - also known as the Mars Science Laboratory (MSL) - at 10:02 local time (15:02 GMT) on Saturday.
Weather conditions look good on the Space Coast and engineers report no technical issues after replacing a suspect battery in Curiosity's Atlas 5 launch rocket earlier in the week.
Lift-off is just the start for what Nasa hopes will be a multi-year campaign at the Red Planet.
The rover is equipped with a plutonium battery and so should have ample power to keep rolling for more than a decade. It is likely the mechanisms on MSL will wear out long before its energy supply.
"MSL is an incredibly important flagship mission for this agency… as important as Hubble," observed Doug McCuistion, Nasa's Mars exploration programme director.
The organisation has certainly invested a huge amount of money in the project (costed at $2.5bn/£1.6bn), and has had to bear a barrage of criticism for delays and budget overruns.
But Nasa believes the memory of past woes will quickly fade when this exciting mission reaches the surface of Mars in eight-and-a-half-months' time. That is how long the robot will take to cover the 570-million-km cruise distance to the Red Planet after Saturday's launch.
MSL is being aimed at a deep equatorial depression called Gale Crater, which contains a central mountain that rises some 5km above the plain below.
The crater was chosen as the landing site because satellite imagery had suggested it may well be one of the best places on Mars to look for evidence that ancient environments could have supported microbial activity. This included pictures of sediments at the base of the peak that were clearly laid down in the presence of abundant water.
MSL will use its suite of 10 instruments to study the local rock, soil and atmosphere.
"We feel confident that within two years we can achieve a level in the mound that's probably 350m to 400m up," said project scientist John Grotzinger.
"After that, the warranty expires. But pending the interest of science to keep on going, we think the slopes are gentle enough that if you took an appropriately circuitous route you could make it to the top of the mound."
First, though, MSL-Curiosity has to land safely, and the history of Mars exploration is wretched. Of the 40 or so ventures launched since 1960, only about a third have delivered any real level of success.
The US rovers Spirit and Opportunity, which landed in 2004, and the Pathfinder-Sojourner robot, which landed in 1997, all used the very effective technique of wrapping the vehicles in airbags to cushion their impact on the surface.
But Curiosity is too heavy to employ the same system and so will be using a rocket-powered "skycrane" to slow the final moments of descent and to position the rover softly on the crater floor.
It is a novel approach and, should it prove successful, will point the way to ever more massive objects being landed on Mars - a capability that will be important if manned missions are ever to be sent to the Red Planet.
Although predominantly a US venture, MSL-Curiosity has important contributions from Russia, Canada, Spain and France. Europe in particular will be watching Curiosity closely because the rover design will form the template for its proposed joint mission with America in 2018.
That rover - known in Europe as ExoMars - would be the first step in a multi-mission objective to bring Martian rocks back to Earth.
ExoMars would seek out signs of life on, and just below, the surface, and also cache rocks for collection by later spacecraft.