NASA Probe Arrives at Jupiter After 5-Year Trek

NASA's robotic Juno probe began circling the solar system's largest planettonight (July 4), ending a nearly five-year journey through deep space and becoming the first spacecraft to enter Jupiter orbit since NASA's Galileo mission did so in 1995.

The milestone came late tonight, as Juno fired its main engine in a crucial 35-minute burn that slowed the probe down enough to be captured by Jupiter's powerful gravity. That burn started at 11:18 p.m. EDT (0318 GMT Tuesday) and ended on schedule at 11:53 p.m.

In the hours leading up to the engine burn, that same gravity had accelerated Juno to an estimated 165,000 mph (265,000 km/h) relative to Earth — faster than any human-made object has ever traveled, mission team members have said.

Tonight's orbit-insertion burn, which Juno performed on autopilot, was a make-or-break maneuver: If anything had gone seriously wrong, Juno would have gone sailing right past Jupiter, and the science goals of the $1.1 billion mission — which including mapping the planet's gravitational and magnetic fields and characterizing its composition and interior structure — would have gone unaccomplished.

So the jubilation that erupted at Juno mission control here at NASA's Jet Propulsion Laboratory (JPL) — shouts of joy, high-fiving and hugging among team members — made a lot of sense.

"Welcome to Jupiter!" a mission commentator announced just after the burn ended, eliciting a second round of cheers and then, a few moments later, a standing ovation.

"It feels great — this is phenomenal!" Geoff Yoder, acting Associate Administrator for NASA's Science Mission Directorate, said when the celebration died down.

Record-setting journey

Juno launched in August 2011 and took a circuitous route through the solar system, looping back to make a speed-boosting flyby of Earth in October 2013.

Juno notched more than just the all-time speed record during its long trek. This past January, the probe became the farthest-flung solar-powered spacecraft in history, zooming past the record of 492 million miles (792 million kilometers) from the sun, which had been held by the European Space Agency's comet-chasing Rosetta mission.

Jupiter lies five times farther from the sun than Earth does, and as a result receives 25 times less sunlight than our home planet gets. To harness that meager supply, Juno sports a total of 18,698 individual solar cells, which are spread among three 29.5-foot-long (9 meters) panels.

With these panels extended, Juno is about the size of a basketball court.
Gathering enough energy to operate is far from the only challenge Juno faces at Jupiter. For example, the area around the giant planet is the most intense radiation environment in the solar system, mission team members have said.
Jupiter's magnetic field, which is 20,000 times stronger than that of Earth, accelerates huge swarms of electrons to nearly the speed of light.

"Once these electrons hit a spacecraft, they immediately begin to ricochet and release energy, creating secondary photons and particles, which then ricochet," Heidi Becker, leader of Juno’s radiation-monitoring team, said during a news conference on June 16. "It's like a spray of radiation bullets." 

Juno's flight computer and other sensitive electronics are encased by a 400-lb. (180 kilograms) titanium vault to protect them against this barrage. The spacecraft's scientific instruments also wear what Becker called "bulletproof vests," as does the star-tracking camera Juno uses for navigation.

Such precautions are necessary when dealing with the king of planets, which is so big that all of the other bodies in the solar system except the sun — all the planets, dwarf planets, comets and asteroids — could fit inside it.

"Jupiter is a planet on steroids," Juno principal investigator Scott Bolton, of the Southwest Research Institute in San Antonio, said during the same news conference. "Everything about it is extreme."