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NASA going to Jupiter with green energy

The robotic explorer Juno is set to become the most distant probe ever powered by the sun.

深圳桑拿网

Juno is equipped with three tractor-trailer-size solar panels for its 3.22 billion km journey into the outer solar system. It will be launched on Friday morning (0134 AEST Saturday) aboard an unmanned Atlas V rocket – barely two weeks after NASA’s final space shuttle flight.

The shuttle’s demise is giving extra oomph to the $US1.1 billion ($A1 billion) voyage to the largest and probably oldest planet in the solar system. It’s the first of three high-profile astronomy missions coming up for NASA in the next four months.

Jupiter – a planet several NASA spacecraft have studied before – is so vast it could hold everything else in the solar system, minus the sun. Scientists hope to learn more about planetary origins through Juno’s exploration of the giant gas-filled planet, a body far different from rocky Earth and Mars.

NASA’s long-range blueprint would have astronauts reach an asteroid by 2025 and Earth’s next-door neighbour Mars a decade later, although there’s still uncertainty surrounding the rockets needed for the job. A Juno success would be a good sign for future solar-powered missions of all types.

Jupiter may be just two planets over, but it’s far enough away to be considered the outer solar system.

It will take Juno five years to reach its target, five times farther from the sun than Earth. No spacecraft has ever ventured so far, powered by solar wings. Europe’s solar-powered, comet-chasing Rosetta probe made it as far as the asteroid belt between the orbits of Mars and Jupiter.

Each of Juno’s three wings is 8.84 metres long and 2.74 metres wide, necessary given that Jupiter receives 25 times less sunlight than Earth. The panels – folded for launch – emanate from the spacecraft much like the blades of a windmill.

At Jupiter, about 800 million km from the sun, Juno’s panels will provide 400 watts of power. In orbit around Earth, these panels would generate 35 times as much power.

NASA’s six-wheeled, Jeep-size Mars rover named Curiosity, due to launch in late November, will be powered by more than 10 pounds of plutonium.

NASA’s Grail mission – twin spacecraft to be launched next month to Earth’s moon – employs solar panels.

Eight robotic craft already have flown to or near Jupiter and its many moons, as far back as the 1970s: NASA’s Voyagers and Pioneers, Galileo, Ulysses, Cassini and, most recently in 2007, the Pluto-bound New Horizons.

Juno – named after the cloud-piercing wife of Jupiter, the Roman god – will go into an oval-shaped orbit around Jupiter’s poles in July 2016, after travelling 2.8 billion km.

The craft will fly within 5000 km of the dense cloud tops, closer than any previous spacecraft. Any closer, and Juno would feel the tug of the planet’s atmosphere, which in turn would alter the spacecraft’s orbiting path and hamper its gravity experiment.

The spinning spacecraft will circle the planet for at least a year, beaming back data that should help explain the composition of its mysterious insides. Each orbit will last 11 days, for a total of 33 orbits covering 560 million km.

Nine instruments are on board, including JunoCam, a wide-angle colour camera, which will beam back images.

Scientists believe Jupiter was formed from most of the leftovers of the sun’s creation. That’s why it’s so intriguing; by identifying the planet’s contents, besides hydrogen and helium, astronomers can better explain how the solar system came to be.

“We want to know that ingredient list” for Jupiter, said Southwest Research Institute astrophysicist Scott Bolton, Juno’s principal investigator. “What we’re really after is discovering the recipe for making planets.”

For these answers, Juno will study Jupiter’s gravity and magnetic fields, and turbulent, cloud-socked atmosphere, which can spawn 300 mph wind and hurricanes double the size of Earth. The experiments will investigate the abundance of water, and oxygen, in Jupiter’s atmosphere and help determine whether the planet’s core is solid or gaseous.

Once its work is done in 2017, Juno will make a kamikaze dive into Jupiter. NASA doesn’t want the spacecraft hanging around and crashing into Europa or other moons, possibly contaminating them for future generations of explorers.

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