Juno image of Jupiter
Jupiter and its volcanic moon Io show up in the last image taken by the JunoCam instrument on NASA’s Juno spacecraft before all the instruments were powered down in preparation for orbital insertion. The June 29 picture was taken from a distance of 3.3 million miles from Jupiter. (Credit: NASA / JPL-Caltech / SwRI / MSSS)

NASA’s farthest-out solar-powered probe, the Juno spacecraft, successfully entered orbit around Jupiter tonight after a five-year, 1.8 billion-mile cruise through interplanetary space – and many hours’ worth of high tension back on Earth.

Mission managers at NASA’s Jet Propulsion Laboratory in California had to program Juno’s computer in advance to execute a 35-minute rocket engine firing that put the probe in the correct orbit. If anything went wrong, Juno could have zoomed right past Jupiter, and flight controllers couldn’t have done anything about it.

It took 48 minutes for signals to travel from the spacecraft to Earth at the speed of light, which meant no one on Earth knew that the engine burn had even started until 13 minutes after it was over. Mission managers said the engine burn was just 1 second off what was planned.

Team members at JPL cheered and hugged each other when they heard that the burn was successful.

“Juno, welcome to Jupiter,” mission control commentator Jennifer Delavan said..

“We just did the hardest thing NASA has ever done!” the $1.1 billion mission’s principal investigator, Scott Bolton of the Southwest Research Institute, told his teammates.

Even Google celebrated Juno’s success with the “Google Doodle” on its home page:

Google Doodle

Miscalculation wasn’t the only risk during orbital insertion. There was also a chance that flecks of debris from Jupiter’s faint rings could have damaged Juno on the way in. To minimize the damage from debris and from Jupiter’s punishing radiation environment, the spacecraft is “built like an armored tank,” Bolton said before the maneuver.

Juno, which was launched from Cape Canaveral Air Force Station in Florida in 2011, is equipped with a trio of 30-foot-long solar panels to generate the electrical power needed to keep the probe and its nine scientific instruments running for a 20-month mission in orbit.

In the past, probes that have gone out to Jupiter or farther have gotten their energy from plutonium-powered generators. Juno is the first spacecraft in the outer solar system to take advantage of advances in solar power generation.

The last time NASA had a probe in orbit around Jupiter was in 2003, when the Galileo spacecraft wrapped up a 14-year space mission to the planet and its moons. Galileo sent back stunning pictures of Jupiter and its colorful bands of clouds.

“It’s a gorgeous planet,” Bolton said. “What Juno’s about is looking beneath that surface. We’ve got to go down and look at what’s inside, see how it’s built, how deep do these features go, learn about its real secrets.”

Juno’s prime objectives are to map its magnetic and gravitational field, and to determine its interior composition. How abundant are water, ammonia and other chemicals deep within the clouds? Does the planet’s center consist of ultra-pressurized liquid hydrogen, or does it have a solid, rocky core? The answers to such questions could help scientists get a better fix on the origins of the solar system.

The magnetic and gravitational mapping will require Juno to zoom as close as 3,000 miles to Jupiter’s cloud tops. That’s much nearer than Galileo ever came, and the probe’s JunoCam instrument could take some spectacular close-up shots. But there’s a price to pay: Even though Juno has titanium shielding, Jupiter’s intense radiation flux is expected to degrade the probe’s electronics over time.

Scientists expect to wrap up Juno’s science mission by 2018 and then send it on a final plunge into Jupiter’s clouds. That will head off any possibility of contaminating the giant planet’s potentially habitable moons with spacecraft debris.

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