Juno Armored Up to Go to Jupiter

Feature July 12, 2010

Juno Armored Up to Go to Jupiter

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2010-230&cid=release_2010-230

NASA's Juno spacecraft will be forging ahead into a treacherous environment at Jupiter
with more radiation than any other place NASA has ever sent a spacecraft, except the
sun. In a specially filtered cleanroom in Denver, where Juno is being assembled, engineers
recently added a unique protective shield around its sensitive electronics. New pictures of
the assembly were released today.

"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."

An invisible force field filled with high-energy particles coming off from Jupiter and its
moons surrounds the largest planet in our solar system. This magnetic force field, similar
to a less powerful one around Earth, shields Jupiter from charged particles flying off the
sun. The electrons, protons and ions around Jupiter are energized by the planet's super-
fast rotation, sped up to nearly the speed of light.

Jupiter's radiation belts are shaped like a huge doughnut around the planet's equatorial
region and extend out past the moon Europa, about 650,000 kilometers (400,000 miles)
out from the top of Jupiter's clouds.

"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 the
same way human beings need to protect their organs during an X-ray exam, we have to
protect Juno's brain and heart."

The strategy? Give Juno a kind of six-sided lead apron on steroids.

With guidance from JPL and the principal investigator, engineers at Lockheed Martin
Space Systems designed and built a special radiation vault made of titanium for a
centralized electronics hub. While other materials exist that make good radiation blockers,
engineers chose titanium because lead is too soft to withstand the vibrations of launch,
and some other materials were too difficult to work with.

Each titanium wall measures nearly a square meter (nearly 9 square feet) in area, about 1
centimeter (a third of an inch) in thickness, and 18 kilograms (40 pounds) in mass. This
titanium box -- about the size of an SUV's trunk – encloses Juno's command and data
handling box (the spacecraft's brain), power and data distribution unit (its heart) and
about 20 other electronic assemblies. The whole vault weighs about 200 kilograms (500
pounds).

The vault is not designed to completely prevent every Jovian electron, ion or proton from
hitting the system, but it will dramatically slow down the aging effect radiation has on
electronics for the duration of the mission.

"The centralized radiation vault is the first of its kind," Bolton said. "We basically
designed it from the ground up."

When NASA's Galileo spacecraft visited Jupiter from 1995 to 2003, its electronics were
shielded by special components designed to be resistant to radiation. Galileo also didn't
need to survive the harshest radiation regions, where Juno will operate.

But Juno isn't relying solely on the radiation vault. Scientists designed a path that takes
Juno around Jupiter's poles, spending as little time as possible in the sizzling radiation
belts around Jupiter's equator. 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.

Packing the assemblies 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.

JPL tested pieces of the vault in a radiation environment similar to Jupiter's to make sure
the design will be able to handle the stress of space flight and the Jupiter environment,
McAlpine said. In a special lead-lined testing tub there, they battered pieces of the
spacecraft with gamma rays from radioactive cobalt pellets and analyzed the results for
Juno's expedition.

The vault was lifted onto Juno's propulsion module on May 19 at Lockheed Martin's
high-bay cleanroom. It will undergo further testing once the whole spacecraft is put
together. The assembly and testing process, which also includes installing solar panels for
the first-ever solar-powered mission to Jupiter, is expected to last through next spring.
Juno is expected to launch in August 2011.

"The Juno assembly is proceeding well," said Tim Gasparrini, Lockheed Martin program
manager. "We have a number of the flight and test unit spacecraft avionics components
installed into the radiation vault for system testing and we have also just installed the first
instrument, the microwave radiometer."

JPL manages the Juno mission for the principal investigator, Scott Bolton, of Southwest
Research Institute at San Antonio, Texas. Lockheed Martin Space Systems, Denver,
Colo., is building the spacecraft. The Italian Space Agency in Rome is contributing an
infrared spectrometer instrument and a portion of the radio science experiment.

More information about Juno is online at http://www.nasa.gov/juno .

#2010-230

-end-

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook@jpl.nasa.gov

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