NASA spills last details of Mars space truck trip
Skycrane landing, mountain climbing, nail biting
NASA Mars Science Laboratory is buttoned up into its fairing atop its Atlas booster, ready for liftoff on November 25 with touchdown scheduled for August of next year – a reentry and landing that will have NASA space boffins biting their nails.
"Any entry, descent, and landing on Mars is a place where you take pause and bite your nails a little bit," said MSL project manager Pete Theisinger at a NASA press conference on Thursday. "It's not a risk-free environment."
The main nail-biting aspect of the landing will be that it will not be done using the air-bag cushioning scheme perfected in previous Mars missions – the Pathfinder  mission with its Sojourner rover, and the the Mars Exploration Rovers  Spirit and Opportunity of 2003.
NASA's Phoenix  lander used a no-airbag landing system, but it was far less complex – and risky – than the MSL, in that it had no rover to deliver.
The MSL rover, Curiosity , is far larger than previous Mars rovers, and will be delivered to its landing site in the Gale Crater  by a thrust-based lander from which it will be lowered and placed on the Martian surface by what NASA refers to as a "skycrane".
Curiosity is about twice as long and five times as heavy as previos rovers, weighing in at about 900 kilograms (2,000 lbs.) and standing about six feet tall. Like its predecessors, it has six wheels – but unlike previous rovers, should one wheel's motor fail, it will be able to be set to freewheel, and thus not need to be dragged along as was the failed wheel on Spirit, which was stuck for three years.
Creating an airbag landing system for Curiosity was not an option. "When the agency decided the objectives for this mission and the suite of instruments that would be required to perform the science, and we saw that we had to develop a very large rover," said Theisinger, "it was very clear that that was beyond the scale of airbags to be able to land successfully."
And so NASA decided to go with a propulsive lander. "If you think about it," Theisinger continued, "there's only two ways to land a rover propulsively on the planet: that's to put the rover on top of the propulsion system or put the rover under the propulsive system."
If the rover sat on top of the propulsion system, there's an obvious problem: how to get a 900 kilogram rover off the top of the system and down to the surface. "That was a daunting, daunting thing to do," Theisinger said.
Curiosity will be lowered to the Martian surface using a skycrane attached to a propulsion system (click to enlarge) 
He also noted that the MSL already has built-in landing gear: Curiosity's six wheels. "So the challenge is simply – and I shouldn't say simply – is to put it there softly enough," he said.
Hence the skycrane. "We went to a lot of non-NASA control specialists – the people who actually fly helicopter skycranes, we got them in the game – to talk about not only was this an achievable design system, but whether or not we could put together a test program that would verify it adequately enough."
Mars ≠ Earth
Although he expressed great confidence in the skycrane system, Theisinger admitted that some uncertainties remain. "You can't do the test in an end-to-end sense," he said, "because you can't land on Mars on the Earth."
Should Curiosity land successfully, there will be plenty for it to do. As explained by MSL Deputy Project Scientist Ashwin Vasavada, "What really dominates the design of this rover is the fact that it has the ability to sample rocks and soils on Mars for the first time."
That sampling will be done, he explained, using a drill on the end of Curiosity's six-foot robotic arm. The rover can survey its surroundings and pick tasty samples to, well, sample, both with HD cameras and with a laser that can determine the chemical composition of terrain within twenty feet.
Curiosity also has its own weather station, the ability to sound below itself to determine if there are any minerals below that contain water, and a detector for natural high-energy radation. "This kind of radiation is critical to measure for the day when we do send humans to Mars," Vasavada said.
Curiosity's two labs will be fed both samples and data from sensors and a rock-probing drill (click to enlarge) 
On the tip of the arm is what Vasavada described as "the meat and potatoes" of the MSL: a "whole bunch of sensors", including a magnifying-glass camera, a sensitive chemical detector, and the aforementioned drill.
The drill will dig into the rock and deliver samples to Curiosity's two internal labs for analysis, "which we've never done before on Mars, and that's really where the science will come from." One of those labs will measure the mineral content of the rocks, and the other, as Vasavada explained, "looks element by element, which chemical elements are there, and looks for any organic material that might be present."
As might be guessed, MSL's landing site has been carefully chosen: Gale Crater and the three-mile-high mountain in its center. "That mountain inside the crater is what caught the eye of the scientists that have been studying Mars for the last decade, and resulted in it being chosen for this mission."
Gale Crater is about 160 kilometers miles wide, and the landing area is 20 kilometers in diameter – which may sound like it offers a high margin for error, but it's by far the tightest landing zone of any previous Mars mission: previous targets were in the 100-kilometer range.
The great opportunity provided by the mountain – which Curiosity will drive towards at its safe-and-sane speed of one-tenth of a mile per hour – is that it has a layered composition, with both ancient and newer rock open for examination.
The entire history of Mars in one mountain
"Probably the entire early history of Mars is here for us," Vasavada said. The goal is to sample and lower levels, then drive up the mountain.
One tremendous advantage that Curiosity has over earlier rovers – in addition to its size and more-sophisticated instrumentation – is its cooperative relationship with the Mars Reconnaisance Orbiter , which is able to do 30-centimeter photography of the surface, both guiding Curiosity to interesting sampling sites and determining promising routes for it to follow to and up the mountain.
Curiosity will traverse the Gale crater, then climb its three-mile-high central mountain (click to enlarge) 
Curiosity's mission is scheduled to last two years, but all of its equipment, Theisinger said, has been tested to "three times its normal life," and there are no life-limiting consumables onboard – its nuclear power source will last for many years – and he says that the rover is both less susceptible to dust and better able to handle winter than the Mars Exploration Rovers.
With all its capabilities, Curiosity is not on a mission to determine if there's life on Mars, but rather to examine if the conditions are conducive to life, and to gather information that will support efforts to eventually land humans on the Red Planet.
"It's important to know that this mission has the purpose of setting us up for the day when we'll go to Mars and do the life-detection experiments," Vasavada said. "It turns out that those are pretty hard to do, and you actually need to know a lot about Mars to understand where to go to do those experiments."
MSL will provide information about habitable environments, but its follow-on missions – such as the joint NASA–European Space Agency ExoMars rover planned for 2018 – will explore those environments after they have been identified.
NASA's Martian exploits each build upon data collected by previous probes, orbiters, and rovers (click to enlarge) 
Although that NASA-ESA collaboration may be hobbled by budget constraints, NASA's Mars Project Director Doug McCuistion said that MSL and Curiosity are fully funded.
"MSL is an incredibility important flagship mission for this agency," he said. "It's as important to this agency – personal opinion, a little biased, maybe – as Hubble. The funding for MSL is stable."
Even if budget-cutters should try to pull the plug, McCuistion said, the money for MSL has already been set aside. "If there are funding reductions in the 2012 budget once it gets passed by Congress – and in the current budget uncertainties, who knows. But if there are, the MSL operations funding is safe." ®
Tuesday's NASA event came one day after Russia's Phobos-Grunt Mars expedition came a cropper. When asked if NASA were helping the Russian space agency jumpstart their balky probe, McCuistion said, diplomatically: "We have offered assistance, and if they need it, we will provide [it] to the best of our ability with our space communications network."