The day has come. As fireworks mark the Fourth of July, scientists and engineers at the Jet Propulsion Laboratory hope to celebrate a milestone of their own: NASA’s Juno spacecraft entering orbit around Jupiter.
NASA’s Juno is within hours of reaching Jovian orbit, said Scott Bolton, Juno’s principal investigator at the Southwest Research Institute. The spacecraft passed Callisto, one of the four Galilean moons, Sunday around 11 a.m., followed by Ganymede (the largest of the four) in Monday’s early hours. It zipped by watery Europa around 10:30 a.m. and was set to pass volcanic Io a little after 2 p.m.
“It’s hard to believe after 15 years we’re finally arriving,” Bolton said at a Monday morning press briefing at JPL in La Cañada Flintridge.
Launched in 2011, NASA’s Juno mission has traveled for nearly five years and close to 1.8 billion miles in order to solve some of the deepest secrets of this imposing gas giant.
Jupiter, like the sun, is made mostly out of hydrogen and helium, with a few trace elements thrown in for good measure. (Jupiter has a larger share of those trace elements than the sun.) It was also the first planet to coalesce out of the gas and dust that surrounded our young star, and holds more than twice the mass of all the other planets. If there’s a recipe for our solar system, it’s held within Jupiter.
“I think there’s no question we will probably discover new moons of Jupiter,” Bolton said.
However, Jupiter gives visiting spacecraft a brutal welcome. Juno will face space missiles of all sizes, from piercing dust particles to giant rocks; the planet’s powerful magnetic fields trap high-energy electrons that could quickly fry a lesser spacecraft. All in all, over the 37 orbits during the 20-month mission, Juno will receive the equivalent of more than 100 million dental X-rays.
The spacecraft will begin its final maneuvers to enter orbit around 8:18 p.m., a burn sequence that takes about 35 minutes. The problem is, it takes light 48 minutes to get back to Earth from Jupiter — which means that the engineers in the JPL control room will not be able to give Juno any real-time guidance. The spacecraft will have to make the drop solo — and it will be executing the maneuver while blind, because its star-tracker cameras will be off.
As it completes the steps in the burn sequence, Juno will send back a series of tones to tell the researchers that the maneuver is going smoothly.
Rick Nybakken, Juno’s project manager at JPL, said he would breathe easier when Juno sends back the telltale tone that it has finished the burn and entered orbit.
“When we receive the last tone that tells us the burn is successful, it’ll be music to my ears,” he said at the briefing.
But Bolton said he’d finally relax after the spacecraft had come from behind the planet and back into the sunlight, where it could recharge from the distant sun’s faint rays. During that dark period, Juno will have to rely on its limited supply of battery power — and make it back to the light before that power runs out.
“We’ve got to get the blood flowing through Juno’s veins again,” Bolton said. “And that’s the key. So maybe I’m most scared of not getting back [in] the sun.”
MORE IN SCIENCE: