- Associated Press - Monday, August 1, 2011

CAPE CANAVERAL, Fla. — NASA’s upcoming mission to Jupiter can’t get much greener than this: a solar-powered, windmill-shaped spacecraft.

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

Juno is equipped with three tractor-trailer-size solar panels for its 2 billion-mile journey into the outer solar system. It will be launched Friday morning 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 $1.1 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.

**FILE** In this photo from May 27, 2011, made available by NASA, technicians at Astrotech's payload processing facility in Titusville, Fla., stow solar array #2 against the body of NASA's Juno spacecraft. (Associated Press/NASA)
**FILE** In this photo from May 27, 2011, made available by NASA, ... more >

“Look at it this way — it is a new era,” said Jim Green, NASA’s director of planetary science. “Humans plan to go beyond low-Earth orbit. When we do that, it’s not like ‘Star Trek.’ It’s not ‘go where no man has gone before.’”

Plunging deeper into space will require robotic scouts first, he said.

Southwest Research Institute astrophysicist Scott Bolton, Juno’s principal investigator, said it’s also important for people to realize “NASA’s not going out of business.”

“If we’re going to learn who we are and where we came from, and how the Earth works, we’ve got to keep doing these science missions, not just Juno,” Bolton said.

NASA’s long-range blueprint would have astronauts reach an asteroid by 2025 and Earth’s next-door neighbor 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 29 feet long and 9 feet wide, necessary given that Jupiter receives 25 percent less sunlight than Earth. The panels — folded for launch — emanate from the spacecraft much like the blades of a windmill.

At Jupiter, nearly 500 million miles 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.

The choice of solar was a practical one, Bolton said. No plutonium-powered generators were available to him and his San Antonio-based team nearly a decade ago, so they opted for solar panels rather than develop a new nuclear source. They wanted to avoid ballooning costs and possible delays connected with developing new technologies.

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