Planetary scientists sometimes joke that we know more about Mars than we do about the moon. NASA first landed a spacecraft on the surface of the fourth planet during the U.S. Bicentennial, five years before the first space shuttle ever lifted off. And we’ve learned plenty in the intervening 35 years: Viking 1 and 2 analyzed Mars rocks, Spirit and Opportunity found evidence of ancient water, and Phoenix saw the Martian snow. Yet the biggest question — whether Mars could ever be home to life — still eludes us.
NASA’s newest rover, Curiosity, sets off this week in search of answers. It’s the most complex interplanetary explorer ever, earning a PopSci 2011 Best of What's New award. If everything goes to plan — from Saturday’s thundering Atlas V launch to the rover’s self-piloted atmospheric entry and hovercraft airdrop — it just might become the type of once-in-a-generation explorer that raises even more questions than it answers.
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The Mars Science Laboratory mission is much more than the wheeled, sedan-sized, beefy-armed rover Curiosity. Its hovercraft sky crane and guided landing system is a major feat in itself, enabling NASA to land the rover with the utmost precision. With 11 tools designed for zapping, baking and X-raying rocks, it is the most advanced robotic geologist ever built. It will look for the chemical ingredients for life — oxygen, nitrogen, carbon, and/or hydrogen — the first Mars rover capable of doing so.
“We will be able to do chemistry better than any other spacecraft. We will know, element by element, what is there, and we’ll see chemical isotopes as well,” said Ashwin Vasavada, MSL deputy project scientist at NASA’s Jet Propulsion Laboratory, where the rover was built. “We will not only know what elements are there, but what minerals they formed into, and that tells you the exact temperature, the amount of water around, and the environmental conditions in which those minerals formed.”
When MSL was being planned, shortly after Spirit and Opportunity started driving around, NASA engineers said they wanted two things: A much more precise landing, the better to pinpoint rocks to study, and a rover that could drill into those rocks and sample their insides. The guided landing will place Curiosity within a 12-mile by 15-mile ellipse — it may sound pretty imprecise compared to Earth-based airdrop tech, but remember that this is 45 million miles away on another planet. (Spirit and Opportunity landed in a 90-mile ellipse.)
But that's just the beginning. Here’s a peek at some of the key new technologies that will enable MSL’s journey of discovery.
Barring any problems, Saturday’s launch from Cape Canaveral will set Curiosity on a course for Mars arrival in August of next year. When it approaches the Red Planet, its aeroshell, shaped like a chicken pot pie, will shed its hydrazine-powered cruise stage and tip its heat shield toward the planet. Thrusters on the backshell will correct the bulky 15-foot-diameter saucer and guide its descent, aiming it precisely for a flat surface in Gale Crater.
When atmospheric friction has slowed it sufficiently, a 165-foot-long, 51-foot-diameter parachute will unfurl — the largest one ever on another planet, designed to withstand Mach 2.2 speeds — and the heat shield will jettison, enabling a radar system to start tracking surface distance. At this point, Curiosity is pointed wheels-down toward the surface of Mars. And there are no airbags.
“It is too big and heavy to put in airbags, and the engineers here realized that if you’re not using airbags, the other alternative is to land it on some kind of platform,” Vasavada said. “But when you’re building this very sturdy rover with its own wheels and suspension, it can take the load of landing on Mars on its own wheels. That turned out to be the best way to land it.”
Down plummets Curiosity, wheels first, and the chute is jettisoned once the rover is a few hundred feet off the ground. Then eight retro-rockets on the hovercraft fire, further slowing the spacecraft’s descent. Three tethers and a communications umbilical cord unfurl, and slowly set the rover on the ground. Once the lines go slack, the rover cuts them off and the hovercraft flies away to crash in a safe place. This will all be captured in 5 frames-per-second high-definition video.
And it all happens autonomously, by the way. The speed of light delay between Earth and Mars makes it impossible to control the rover in real time, so if an unexpected gust or Martian dust devil comes along, the rover will have to handle that by itself.
The guided landing will be a boon for geologists, Vasavada said.
“It meant we could get much closer in, and snuggle up the landing next to features that would be too dangerous to land on, which always turn out to be the more interesting geologic things. Most of the things we want to study on Mars are not flat, boring things,” he said.
Once Curiosity checks out healthy, it will snap several 3-D HD panoramic photos of its surroundings, and pinpoint some interesting things to look at. When scientists on Earth have some targets, the ChemCam instrument will get to work.
MSL’s science missions will unfold with the regimented precision of any good working laboratory. In careful sequence, 11 instruments will peer at a Mars rock, zap holes into it, drill the holes, collect the drill dust, sift and sieve it, bake it and X-ray it, characterizing everything there is to know about that rock and its history. The bulk of the work begins with ChemCam, MSL’s laser and camera.
From a distance of nearly 25 feet, the laser zaps material from the surface of a rock, dusting it off and ablating weatherized surfaces, creating a plasma that can be analyzed using the instrument’s telescope. For just five nanoseconds, the laser directs the energy of a million light bulbs into the area the size of a pinhead, said Roger Wiens, the instrument’s principal investigator, based at Los Alamos National Laboratory.
“ChemCam is supposed to be a workhorse for the rover in identifying unique samples for the other instruments to spend more time on,” he said. “The ability to reach out and touch the rock from almost 25 feet away is a real advantage.”
One ChemCam sample would entail taking a closeup picture of a rock, then a wide-angle shot, and then firing up to 75 laser pulses. It can analyze one sample every six minutes, using just two watt-hours of power.
Because ChemCam will help the rest of the roving laboratory find its targets, Wiens expects it to be called into action almost every day throughout the rover’s two-year (in Earth years) primary mission. Luckily for ChemCam’s science team, the instrument is a collaboration with the French space agency, so international partners will share half the burden.
After ChemCam’s hands-free analysis, MSL scientists might decide to drive the rover to an interesting rock and start getting dirty.
Among MSL’s many firsts is its shrunken X-ray machine, a real feat of engineering that has already enabled a suite of new Earth spinoffs. The CheMin instrument, short for “Chemistry and Mineralogy,” brings a standard method of elemental identification to the surface of another world for the first time. X-ray diffraction identifies minerals by examining the diffraction patterns of X-rays that pass through the spaces in between atoms, said David Blake, CheMin’s principal investigator, from NASA’s Ames Research Center.
“If you’re ever driving by a field of trees that are planted regularly, you can look down the rows, and every once in a while you can see a path right through them. There are various patterns in a crystal that are like that, where light goes through, and these are patterns where diffraction occurs,” he said. “All crystalline materials have slightly different diffraction patterns, so diffraction tells you, without any kind of quibbling, what is the exact material you are looking at.”To take this type of measurement, you would spread out sifted rock samples and ideally bounce them around, sending them flying past the X-ray source. But moving parts are generally a nonstarter on a spacecraft. To get around this, Blake and his team had to design a piezoelectric device that jiggles the sand grains. The design is partly inspired on a bunch of small buzzers Blake and colleagues bought from Radio Shack several years ago. When CheMin is in operation, it moves at a frequency rate roughly that of a double-high C note — it'll sound like a soprano singer.
Blake has been working on a miniaturized X-ray diffraction machine for more than 20 years, he said. It's the best way to identify a mineral, which is the best way to learn the environment in which a rock formed, and if there were any constituents that might have been handy for prebiotic compounds or even life, Blake said.
MSL’s other instruments will all be looking for this, too.
Alongside the CheMin array, the Sample Analysis at Mars (SAM) instrument will heat up the drilled sample and gassify its contents, examining the vapor with a gas chromatograph and two types of spectrometers. As a sample is heated, different materials become volatile and are emitted as gas — like water, to start. The contents of these vapors can be detected to determine a material’s composition. This will be one of the key ways in which MSL will look for signs of life. Finding any such evidence would be paradigm-shattering, to say the least, so MSL is equipped with a self-test kit, Vasavada said. It’s a ceramic sample-blank that contains an engineered organic compound — not life, but a fluorinated organic compound that would not occur in real life on Earth. If there’s ever any controversy about SAM’s organic material analysis, the sample blank will help verify its analytical integrity.
If all this sounds repetitive, that’s because it is — and that’s part of the point, according to Vasavada.
“There are several different ways of looking at a rock, and no single technique is unambiguous,” he said. “When we have confirmation two or three ways that a rock has that mineral in there, or that element, then we can piece that story together, by integrating the results from all these different instruments.”
MSL's primary goal is a one-Mars-year, two-Earth-year primary investigative mission, but this could be extended and likely will, should Curiosity fare as well as its forebears. The Spirit and Opportunity rovers, designed to perform for three months, outlasted their warranty by nearly eight years (and counting, for Opportunity). Engineers hope Curiosity will roll across the Red Planet for a decade.
“This isn’t a mission where you land, get as much information as you can, and everything else is gravy,” Vasavada said. “This is a mission that is planned to unfold over the course of a couple of years.”
So Curiosity will have plenty of time to answer deep questions — and potentially open brand-new profound ones too.
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