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Thursday, May 23, 2013
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Earth's latest foray into the final frontier should paint a much clearer picture than before.
If you want to meet a nuclear-powered, laser-toting monster truck of science, head to the Gale Crater on Mars to get a glimpse. Let us tell you a little more about the $2.5 billion Curiosity rover.
Years of testing, development and building-in fault tolerances culminated at 10:02 a.m. EST on Nov. 26, 2011, when the Mars Science Laboratory (MSL) launched from Cape Canaveral Air Force Station aboard an Atlas V rocket. It landed successfully on Mars at 1:32 a.m. EDT, Aug. 6, 2012.
Before loading Curiosity into its shell, engineers subjected the rover to a rigorous series of tests simulating both internal faults and external problems, punishments that included centrifuges, drop tests, pull tests, drive tests, load tests, stress tests and tests of shorting circuits.
Meanwhile, Nasa had to decide where the new rover would explore, how it would get there and how the space agency could land it safely - easier said than done. Earth and Mars revolve around the sun at different rates - 686.98 Earth days for Mars versus 365.26 for Earth - which means their relative distance varies enormously. Reaching Mars on as little fuel as possible meant launching when the red planet passes closest to us. This was no minor consideration: Mars swings out more than seven times as far from Earth at its farthest extreme (401.3 million kilometres) than at its nearest approach (55.7 million kilometres).
Like a quarterback throwing a pass, the launch system aimed not for where Mars was, but for where it would be when the craft arrived. Nasa threw that pass, and the rover-football reached its round and red receiver more than 250 days later, and touched down on Sunday, Aug. 6, 2012 (Eastern Daylight Time).
Nasa did not "throw" MSL from Earth's surface, however; the agency launched it from planetary orbit. Here's how: Once the lifting vehicle reached space from Cape Canaveral, its nose cone, or fairing, opened like a clamshell and fell away, along with the rocket's first stage, which cut off and plummeted to the Atlantic Ocean. The second stage, a Centaur engine, then kicked in, placing the craft into a parking orbit. Once everything was properly lined up, the rocket kicked off a second burn, propelling the craft toward Mars. About 44 minutes after launch, MSL separated from its rocket and began communicating with Earth. As it continued on its way, it made occasional planned course corrections. Once it hit the Martian atmosphere, the fun really began.
Within Mars, rising higher than Mount Rainier towers above Seattle, stands a sediment mountain five kilometres high. Composed of layers of minerals and soils - including clays and sulfates, which point to a watery history - these layers will provide an invaluable map of Martian geological history.
Past water would have flowed toward and collected in Gale Crater's lowlands, making it a likely repository for the remains of streams, pools and lakes, and therefore an ideal place to find evidence of Mars's past habitability.
When the spacecraft carrying Curiosity swung into the Martian atmosphere 125 kilometres above the ground, it steered and braked through a series of S-curves like those used by the space shuttles. During the minutes before touchdown, at around 11 kilometres up, the craft popped a parachute to slow its 1,448 kph descent. It then ejected its heat shield from the bottom of the cone, creating an exit for Curiosity.
The rover, with its upper stage clamped to its back like a turtle shell, fell clear of the cone. A few moments later, the upper stage's rim-mounted retro rockets blasted to life, stabilising the pair into a hovering position about 20 metres above the surface; from here, the upper stage acted as a sky crane, lowering Curiosity like a spider on silk. Once the rover was safely on the ground, its tether was cut, and Curiosity set off on its journey.
Shortly before touchdown, the Mars Descent Imager took high-definition colour video of the landing zone. This footage aided with landing and provided a bird's-eye-view of the exploration area for researchers and mission specialists back home. Another array of instruments, the Mars Science Laboratory Entry, Descent and Landing Instrument Suite, will measure atmospheric conditions and spacecraft performance. Nasa will use this data when planning and designing future missions.
The novel landing system was more complicated, but also more precisely controlled, than any before, enabling mission planners to bull's-eye the long-desired target of Gale Crater. Landing within Curiosity's 20-kilometre target area within the crater would have been impossible for Spirit and Opportunity, which needed five times as much area when bouncing down in their space-age bubble wrap. This success opened up a slew of desirable sites, including steep-walled craters previously off-limits due to their tricky terrain.
Curiosity will also lay the groundwork for future missions, just as previous Mars jaunts made the new rover's expedition possible. Such missions could include scooping up rocks and flying them back home, or carrying out more far-reaching surface surveys, seeking evidence of Martian microbial life and its key chemical ingredients. Now that we've landed safe and sound, let's take a look at what kind of equipment comes standard with the Mars Science Laboratory package.
Whether packing for a two-week vacation or provisioning for a scientific expedition in a hostile desert millions of miles away, the basic problem remains the same: What to bring, what to bring...
Curiosity is utterly on its own. When there's no repair crew on call, no spare parts in the trunk and every signal from Earth takes around 14 minutes to reach you, self-reliance is all you have.
Curiosity isn't on Mars to sightsee, however. It's tasked with collecting rock and soil samples and placing them into onboard instruments for analysis. With this in mind, the rover comes equipped with a 2.1-metre camera mast and a 2.1-metre, three-jointed robotic arm sporting more attachments than an industrial vacuum cleaner. This Sample Acquisition/Sample Preparation and Handling System will scoop, dust, drill, powder, collect, sort, sieve and deliver samples to a variety of analytical assets:
- A miniaturised gas chromatograph and mass spectrometre will separate and analyse chemical compounds in samples.
- A tunable laser spectrometre will look for organic (carbon-containing) compounds and determine the ratio of key isotopes - both vital to unlocking Mars's atmospheric and aquatic past.
- CheMin, an X-ray diffraction and fluorescence instrument, will measure the bulk composition of samples and detect their constituent minerals.
- Located on the rover arm, the Mars Hand Lens Imager will photograph rocks, soil - and, if present, ice - in extreme close-up. This uber-camera can spot details thinner than a human hair or focus on objects more than an arm's length away.
- The Alpha Particle X-ray Spectrometre for Mars Science Laboratory, also located on the arm, will figure out the relative amounts of various elements present in Martian rocks and soils.
Curiosity's neck, or mast, is also decked out in instrumentation:
- The Mars Science Laboratory Mast Camera (MSLMC), attached at human-eye height, will help the rover navigate and record its surroundings in high-resolution stereo and colour stills or high-definition video. The MSLMC can view materials collected or treated by the arm.
- Stereo hazard-avoidance cameras located further down the mast will aid the rover's navigation.
- Another mast-mounted instrument, ChemCam, will vaporise thin layers of material up to nine metres away using laser pulses, then analyse them with its spectrometre. Its telescope can capture images of the beam's target area.
Beyond these sample-analysis instruments, the rover also packs scientific gadgets that will examine local conditions, which could prove relevant for future human missions or understanding the planet's capacity for supporting life:
- The Radiation Assessment Detector will monitor surface radiation levels.
- The Rover Environmental Monitoring Station will take readings of atmospheric pressure, temperature, humidity and wind, as well as levels of ultraviolet radiation.
- The Dynamic Albedo of Neutrons instrument can detect hydrogen - a potential indicator of ice or water trapped in minerals - up to 3 feet (1 metre) beneath the surface.
That's an impressive array of luxury appointments, but it won't do Nasa much good unless Curiosity's got it under the hood. Let's take a peek at what powers this puppy.
The "monster truck of science" isn't a nitro-burning, fire-breathing funny car, or a plain old internal-combustion gas-guzzler. Nor does it sport the solar panels that generated juice for its forerunners. No, on this mission, Nasa went nuclear.
Curiosity pulls power from plutonium-oxide. As the radioisotope decays, it gives off heat, which the rover converts to electricity using thermocouples. This Multi‐Mission Radioisotope Thermoelectric Generator (MMRTG) will keep the rover's battery topped off with 110 watts of electrical power.
The system packs more power than the solar approach and has no moving parts to break, but can this generator outperform good old gallium-arsenide panels? After all, Spirit operated until the spring of 2010, and diehard Opportunity is still spinning its odometre, having racked up 34 kilometres at 100 metres, per day. These exceptional vehicles far exceeded their 90-day mission mandates, partly because of free, renewable, solar power.
Well, don't nuke the nuke just yet. The radioisotope system's 14-year life expectancy could outlast the rover itself, and will never fall victim to the whims of Martian weather, dust or winter. Besides, the extra power is worth the tradeoff: Curiosity will cover more ground than its predecessors, travelling at roughly twice their speed. In the single Martian year (about 687 Earth days) of its initial mission, it will rack up 19 kilometres inside Gale Crater, carrying a scientific payload 10-15 times more massive than Spirit or Opportunity. Power will remain available all along, as will excess heat that Curiosity will use to keep its vital instruments warm.
Helping Curiosity put that horsepower to effective use is Nasa's old-and-improved rover rocker-bogie chassis, an assembly of jointed titanium tubes attached to six aluminium wheels so thin they flex like rubber. All four corner wheels can rotate through 90 degrees, which enables the rover to turn in place. Engineers beefed up Curiosity's suspension somewhat to suit its new role as landing gear, and to accommodate a heftier vehicle that must cross more rugged terrain.
Shortly after landing, that chassis will cart the rover to its first destination: a rocky outcrop nicknamed "the fence." Nasa targeted this crag because previous Mars observations revealed that it contains aqueous deposits - minerals formed in water. From there, Curiosity will venture into canyons, rocky mountainsides and hill country reminiscent of Sedona, Arizona's red rocks, which also formed in a watery environment. By then, its first Martian year will have come and gone.
From there, the rover will delve into rockier and more rugged terrain. Exploring this area will require several years, but, once across, the rover's cameras will be treated to a panorama of the path Curiosity has travelled.
All along the way, the Mars Science Laboratory will investigate whether conditions exist, or have ever existed, that could support microbial life on Mars, and whether clues to such life remain preserved in Mars's rocks and soil.
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