How NASA's New Spacecraft Will Fly Closer To Jupiter Than Any Probe Before It
Juno's journey is to one of the most treacherous places in the solar system.
BY REBECCA BOYLE | Jul 6, 2016 | Technology
To the naked eye, Jupiter is a placid beacon, the brightest thing in the sky besides Venus and the moon. Seen through a telescope, it's a brightly banded world surrounded by a coterie of moons, some of which have water and just might harbour life. But up close, the biggest planet is just the worst. Jupiter is a true baddie, a hellacious place, a giant that can dismember the very atoms of those who venture too near. It is the most treacherous environment in the solar system other than the sun.
"Jupiter is a planet on steroids," says Scott Bolton, lead scientist for the Juno spacecraft. "Everything about it is extreme.”
"Everything is in a bulletproof vest, but some of the bullets will still get in."
Juno is NASA's next great planetary spacecraft, built to fly closer to Jupiter than any probe has ever gone before. It is scheduled to arrive next week, at 9PM Eastern on Monday, July 4, which will mark the end of a five-year trip. (Juno took the scenic route, leaving home in 2011 and swinging back by Earth in 2013 for a gravity assist.) As Juno makes the treacherous approach that marks the end of its journey, the craft will shut off its instruments and blindly launch itself into a polar orbit that gets closer and closer to the great planet. When it opens its eyes on the other side, Juno will try to learn how Jupiter formed and what that tells us about the origin of our entire solar system.
The planet will not give up its secrets without a fight, though. So NASA made Juno the most heavily armoured spacecraft ever built.
Jupiter's deadly radiation storms come from its powerful magnetic field, which in turn comes from the way Jupiter was built. Like the sun, Jupiter is mostly made of hydrogen and helium gas; it sucked up most of what was left over from the sun's birth 4.5 billion years ago. At the incredible pressures found deep within Jupiter, hydrogen gets squeezed into a fluid, and this fluid acts like a conductive metal. That action generates a dynamo that drives a magnetic field around the planet.
The magnetic field, 20,000 times more powerful than Earth's, captures an enormous number of electrons and ions—some particles come from Jupiter's volcanic moon Io, and some come from the solar wind. The particles are flung around "like a spray of radiation bullets," says Heidi Becker, an engineer at the Jet Propulsion Laboratory. In other words, NASA's spacecraft is flying into a hellscape.
"Jupiter is a planet on steroids."
Juno has a custom radiation vault that will protect its heart and brain from Jupiter's lightning bolts of radiation. Its instruments have shielding designed to ward off those loose electrons that Jupiter's magnetic fields fling at speeds that approach the speed of light. Juno is swaddled in shiny thermal blankets that insulate it and protect it from tiny particles; they also allow electricity to flow around Juno rather than building up a dangerous charge. And just in case the shielding isn't enough, Juno has two copies of the controls for every essential instrument.
Four star trackers help Juno navigate, and each is capped with an 18-pound radiation shield. But this won't be enough to prevent electrons from snowing over the cameras' view. Unlike its spacecraft brethren, Juno only looks at the brightest stars, eschewing the dim ones that normally help distant explorers find their way in favour of those that'll be easier to see once the navigation system starts wearing down.
Despite all these precautions, Jupiter's radiation will kill Juno. The spacecraft will receive 80 percent of its radiation dose in the second half of its mission, and this will do lasting damage. Stray electrons will collide with its computers, corrupting its memory. Each electron collision will produce a shower of secondary particles, which will also collide with Juno and create more showers of even smaller particles, and so on. Eventually, this constant bombardment will cause memory failure, computer errors and potential hardware problems that could not only jeopardise scientific research, but also cause Juno to spiral out of control. To prevent it from crashing on Jupiter's moon Europa, which has liquid oceans under its frozen surface, scientists will instead send Juno plunging into the giant planet in February 2018 , says Becker.
"Everything is in a bulletproof vest, but some of the bullets will still get in. That is what limits Juno's lifetime," she says. "We are just not able to keep everything out."
Becker has been working on Juno since 2004 and designed the radiation vault, which is made of titanium and weighs about 400 pounds when empty. Its walls are about a third of an inch thick, with a little extra padding next to the main computer and power distribution centre. For added protection, Juno's electronics are nested like matryoshka dolls, one inside another. Without the vault, the spacecraft's instruments would be blasted with radiation roughly equivalent to 100 million dental X-rays over the next year. The vault cuts that down by a factor of about 800, but Juno still receives a hefty radiation dose.
While working on the vault design, Becker had to do some unusual tests to make sure it would all work. "There are no environments on Earth where you could flip a switch and it would give you Jupiter radiation," she says. "We would go to cancer hospitals where they give you high-energy radiation, or places that would test the integrity of a submarine hull.”
She also had to make some careful estimates about just what Juno would face. Because Jupiter is so horrible, Juno is going where no other spacecraft has before. The Galileo probe, which visited Jupiter in the 1990s, stayed farther out; the Pioneer and Voyager probes did only brief flybys. So nobody knows what the radiation environment will look like. "I'm excited to see what it actually is," Becker says.
The Juno team had to overbuild the spacecraft to save it from Jupiter's wrath. But at the same time, it also has to do science, which means exposing some parts of Juno to the elements. As the spacecraft spins (about twice a minute for stability), its instruments can take turns pointing at Jupiter, Bolton says. "There is not a lot of fancy pointing in this. It's all built into the design."
The spin-stabilised spacecraft is about the size of a basketball court and its three solar arrays form a big Y around a hexagonal body at the centre. Jupiter orbits five times farther from the sun than Earth does, so sunlight there is 25 times dimmer. The solar panels had to be designed to soak up as much sun as possible without becoming too brittle in the frigid cold of space. Ultimately, Jupiter will destroy them, too.
"Jupiter was the first planet to form, so it gives you the very first step in that recipe."
Scientists hope Juno will answer some key questions about the magnetic fields of Jupiter, which could help them understand how the gas giant formed. In turn, understanding the big planet's formation would provide better starting point for the solar system's origin story, and understanding how planets form around other stars in the cosmos.
"What we really want is the recipe. How do you make these planets?" says Bolton. "Jupiter was the first planet to form, so it gives you the very first step in that recipe. What happened after the sun formed that allowed the planets to form? That is not only the history of our solar system, but of us here at Earth.”
That's not all Juno will do. The craft will look for hints of water in Jupiter's clouds, and its magnetometer will map the planet's gravitational field, information that could tell scientists whether Jupiter has a solid core. Three cameras will take pictures in three wavelengths of light, including spectacular close-ups better than any Jupiter photo we've ever seen. Other instruments will study Jupiter's powerful auroras and atmosphere and investigate the roots of the Great Red Spot, a storm that has raged for 400 years.
"Jupiter is the most extreme planet we have, and we're going right next to it. We've got to do the extreme. It's got to do the extreme," Bolton says. "We put together an armoured tank going to Jupiter. We're shielded and ready, but there is definitely risk.”
From: Popular Mechanics.