Juno's so-called radiation vault weighs about 200 kilograms (500 pounds), has walls that measure about a square meter (nearly 9 square feet) in area, are about 1 centimeter (a third of an inch) in thickness, and weigh 18 kilograms (40 pounds). About the size of an SUV's trunk - the vault encloses Juno's command and data handling box, power and data distribution unit and about 20 other electronic assemblies, according to NASA.
"For the 15 months Juno orbits Jupiter, the spacecraft will have to withstand the equivalent of more than 100 million dental X-rays," said Bill McAlpine, Juno's radiation control manager, based at NASA's Jet Propulsion Laboratory in Pasadena, Calif., in a release.
Juno's handlers are taking it on a path that takes the spacecraft around Jupiter's poles, spending as little time as possible in those radiation belt areas. Engineers also used designs for electronics already approved for the Martian radiation environment, which is harsher than Earth's, though not as harsh as Jupiter's. Parts of the electronics were made from tantalum, or tungsten, another radiation-resistant metal. Some assemblies also have their own mini-vaults for protection, NASA stated.
Packing Juno's innards next to each other allows them to shield their neighbors. In addition, engineers wrapped copper and stainless steel braids like chain mail around wires connecting the electronics to other parts of the spacecraft, NASA stated.
Juno is basically an armored tank going to Jupiter," said Scott Bolton, Juno's principal investigator, based at Southwest Research Institute in San Antonio. "Without its protective shield, or radiation vault, Juno's brain would get fried on the very first pass near Jupiter."
Expected to launch August 2011, NASA has outlined a number of key challenges for Juno:
- Juno will determine the global structure and motions of the planet's atmosphere below its colorful cloud tops for the first time, mapping variations in the atmosphere's composition, temperature, clouds and patterns of movement down to unprecedented depths, NASA said.
- Deep in Jupiter's atmosphere, under great pressure, hydrogen gas is squeezed into a fluid known as metallic hydrogen. At these great depths, the hydrogen acts like an electrically conducting metal which is believed to be the source of the planet's intense magnetic field. This powerful magnetic environment creates the brightest auroras in our solar system, as charged particles precipitate down into the planet's atmosphere. Juno will directly sample the charged particles and magnetic fields near Jupiter's poles for the first time, while simultaneously observing the auroras in ultraviolet light produced by the extraordinary amounts of energy crashing into the polar regions, NASA said.
NASA's Juno mission is the second spacecraft designed under NASA's New Frontiers Program. The first was the Pluto New Horizons mission. Launched into space in January 2006 and has been hurtling toward Pluto at about 50,000 mph. Even at that rate the 1,054lb satellite will get it close to the dwarf planet sometime around July 2015.
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