NASA's Juno Mission Risks Daring Plunge to Reach Jupiter

As many travelers would probably prefer, NASA’s Juno spacecraft will sleep through the most dangerous part of its journey to the planet Jupiter.

That happens on July 4, when Juno will rendezvous with Jupiter and attempt to slip into its gravitational grasp. Launched in August 2011 (after a slight delay caused by an errant boat near Cape Canaveral), solar-powered Juno has flown more than 1.7 billion miles (2.8 billion kilometers) on its way to solve the mysteries of the giant planet’s interior and evolution.

Now, a few days out, the spacecraft has already entered Jupiter’s intense magnetic field—a behemoth structure more than 3 million miles (4.8 million kilometers) wide, on average. The only instrument that’s awake right now is a star tracker, which helps keep the craft on course.

The spacecraft’s cameras and other science instruments are powered down, and as Juno nears its target, that star tracker will also blink off, leaving the spacecraft flying blind.

Paradoxically, it’s the only way to keep Juno safe.

To pull into orbit, Juno must fly a Jovian gauntlet that will expose it to belts of radiation unlike anything any spacecraft has ever encountered.

“The trickiest thing about that is we have no idea what we’re going to face, because nobody’s been there before,” says the mission’s lead radiation monitor, Heidi Becker of NASA’s Jet Propulsion Laboratory in California.

“When you sail into terra incognita, that is always going to make you sit on the edge of your seat, because you don’t really know for sure what you’re facing.”

Jupiter’s magnetic field is so strong that it catapults surrounding electrons to light speed, creating a deadly hailstorm of charged particles more than capable of annihilating sensitive electronics.

As a result, Juno is heavily armored, outfitted with a 400-pound (180-kilogram) titanium shield around its computers and smaller shields protecting its instruments. To minimize the risk of any damage happening early in the mission, Juno’s team decided to shut down the instruments during the delicate process of getting the probe into orbit.

“We won’t be seeing the radiation, because all of the instruments that can tell us about it are already off,” Becker says.

Assuming the orbital insertion goes to plan, the craft will fly 33 science orbits around Jupiter over the next 20 months. During this time, it will dip in and out of the belts, exposing its instruments to the equivalent of a hundred million dental X-rays and almost certainly causing damage and degradation.

For now, the most crucial maneuver is a 35-minute engine burn beginning at 11:18 p.m. ET on July 4. That burn will slow the speeding craft enough for it to be captured by Jupiter’s gravity.

To end up in orbit, this burn needs to happen precisely on time, for the right amount of time. Otherwise, Juno will sail right past the planet and the mission will be moot.

Then, the spacecraft needs to turn its giant solar array back toward the sun so it can charge its batteries.

“You can get into orbit, but you need power,” Becker says.

The only way the team will know if all has gone well will be dozens of tones sent back to Earth announcing the completion of each step in the orbit insertion. Traveling at the speed of light, these tones will take 48 minutes to arrive.

That means when the tone announcing the beginning of the engine burn arrives at mission control, the burn will have already been completed—and Juno will either be in orbit, or it won’t.

“We’ll be listening to the music,” says Becker. “I think I’ll personally feel pretty good around 9 p.m. [Pacific time] Monday.”

When Juno’s instruments turn back on over the next week, it will be the first spacecraft to see Jupiter’s poles as it orbits the giant world, skimming its cloud tops and collecting data about what lies beneath the planet’s colorful, iconic bands and shrinking Great Red Spot.

Among the questions Juno could answer is what type of material is churning deep inside Jupiter and generating that immense, deadly magnetic field, which is capable of producing magnificent auroras. According to some theories, that material could be a strange, exotic form of molten hydrogen. The science team also hopes to find out how much water is tucked into Jupiter’s interior.

“That is crucial to understanding the weather and storms we see,” says Amy Simon of NASA’s Goddard Space Flight Center in Maryland. “This also ties to how and where Jupiter formed, which is interesting in terms of understanding all the exoplanets we have now found.”

After all, of the thousands of planets discovered so far beyond our solar system, many are around the size of Jupiter or larger, including worlds called hot Jupiters that, unlike any of our gas giants, are in sweltering orbits very close to their host stars.

At the end of its mission, Juno will plunge through the Jovian clouds. Its dramatic demise means the craft won’t accidentally contaminate any of the planet’s moons with hitchhiking Earthly life-forms—specifically Europa, an intriguing icy moon that will be the target of NASA’s next mission to the outer planets, slated to launch in the 2020s.

Follow Nadia Drake on Twitter.

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