Juno at Jupiter
An illustration of NASA's Juno spacecraft in orbit around Jupiter. Credit: NASA/JPL-Caltech

Updated at 1:50 a.m. Eastern.

WASHINGTON — NASA’s Juno spacecraft, on a mission to study Jupiter’s interior and its magnetic field, successfully entered orbit around the planet late July 4 after completing a critical maneuver.

Juno fired its main engine as planned at 11:18 p.m. Eastern time July 4, slowing down the spacecraft as it made a close approach to Jupiter. The engine shut down 35 minutes later, within one second of its planned duration, placing the spacecraft into a 53-day orbit around the planet.

“We have the tone for burn cutoff on delta-v,” mission control at NASA’s Jet Propulsion Laboratory announced to cheers as they received telemetry from the spacecraft that the engine had shut down at the end of its burn. “Welcome to Jupiter.”

“NASA did it again,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute, at a press conference shortly after orbit insertion. “Now the fun begins with science.”

Guy Beutelschies, director of interplanetary missions at Lockheed Martin Space Systems, which built Juno for NASA, said at the press conference that the spacecraft appeared to be functioning well, based on the limited telemetry it returned during and after the orbit insertion maneuver. “It did everything that it needed to do,” he said. “We’re very pleased with its performance.”

Juno arrived at Jupiter nearly five years after its launch on an Atlas 5. Mission leaders considered the do-or-die orbit insertion, the one chance they had to put the spacecraft into orbit, the riskiest part of the mission next to the launch itself.

At a JPL press conference early July 4, project officials said they were nervous about the maneuver, but confident that it would work despite the hazardous environment around Jupiter. “We’re doing everything humanly possible. I’m confident it’s going to work,” said Bolton. “But I’ll be happy when it’s over and we’re in orbit.”

A key challenge for the mission is dealing with Jupiter’s intense radiation environment, created by charged particles accelerated by the planet’s strong magnetic field to nearly the speed of light. Juno, in its approach to Jupiter, passed closer to the planet than any other with the exception of those that deliberately entered its atmosphere.

“Juno is going to go into the scariest part of the scariest place that we know about,” said Heidi Becker, radiation monitoring investigation lead for the mission at JPL, at the pre-encounter briefing. “It’s part of Jupiter’s radiation environment where nobody has ever been.”

Becker and other project officials said that, despite the powerful radiation environment, they were confident the spacecraft’s key instruments and other subsystems were sufficiently shielded to survive both the initial encounter and subsequent close approaches, as Juno enters into a 14-day science orbit where the spacecraft will remain through the end of its mission in early 2018.

Bolton, at the pre-encounter briefing, raised another risk he acknowledged was not widely discussed earlier. Juno would pass through the vicinity of Jupiter’s tenuous ring. The extent of the ring is not well known, he said, and thus there was a small chance a dust particle from the ring could collide with the spacecraft, traveling through the region with its engine nozzle facing forward.

“If any dust is in our way and hits that nozzle, it will knock a hole right through the coating that protects the nozzle and allows the engine to burn uninterrupted,” he said.

The successful orbit insertion is not the final maneuver Juno must make. A second engine burn, lasting about 22 minutes, is planned for October that will place the spacecraft into its final science orbit.

Scientists hope Juno’s instruments shed light on the formation of both Jupiter and the solar system in general. Among the goals of the mission are to measure the water content of Jupiter’s atmosphere and determine how large of a core, if any, the planet has.

Another goal, Bolton said, is to understand the dynamics of the Great Red Spot, the Earth-sized storm in Jupiter’s atmosphere that has existed for at least several hundred years. “We don’t actually understand very much about the Great Red Spot,” he said at the pre-encounter briefing. Juno, he said, will be able to probe how deep the storm extends. “It’s one of the most exciting things that Juno will return.”

Juno, with a total mission cost of $1.1 billion, is the second of NASA’s New Frontiers series of medium-sized planetary science missions. The first, New Horizons, flew past Pluto in July 2015, and NASA approved plans July 1 for the spacecraft to make a flyby of a distant Kuiper Belt object in January 2019. The third New Frontiers mission, an asteroid sample return spacecraft called OSIRIS-REx, is scheduled for launch in September.

NASA plans to release the announcement of opportunity for the fourth New Frontiers mission in January 2017. NASA is considering several potential destinations for that mission, from a lunar sample return mission to a Venus lander to spacecraft that would visit the “ocean worlds” of Enceladus or Titan, two moons of Saturn.

Jeff Foust writes about space policy, commercial space, and related topics for SpaceNews. He earned a Ph.D. in planetary sciences from the Massachusetts Institute of Technology and a bachelor’s degree with honors in geophysics and planetary science...