NASA’s Juno probe enters near-perfect orbit around Jupiter

Jubilation, relief and exhaustion. That’s the mood at NASA’s Jet Propulsion Laboratories in California, the heart of the Juno mission, which pulled into orbit around Jupiter last night.

I was at JPL yesterday, the most dangerous day for NASA’s Juno spacecraft since its launch in 2011. The long communication time between the probe and Earth made human intervention impossible, so mission engineers had nothing to do but wait to hear whether it had succeeded.

When confirmation comes, the room erupts into shouts of jubilance, hollers and cheers more common to a sports stadium than a scientific event. Juno has made the fastest approach ever attempted by a spacecraft going into orbit, at more than 200,000 kilometres per hour relative to Earth. After five years and 869 million kilometres, the spacecraft has slipped into a near-perfect orbit around Jupiter.

“We conquered Jupiter!” says mission lead Scott Bolton during his post-insertion briefing, to an explosion of wild applause.

This moment has been a long time coming. Juno started its critical capture burn at 2018 Pacific Standard Time on 4 July. As the thrusters fired for 35 minutes, the spacecraft stayed in communication with the Deep Space Network stations in Goldstone, California, and Canberra, Australia. That “heartbeat” tone provided telemetry, telling mission engineers that Juno was healthy and functioning properly.

When Bolton first saw the telemetry, he was overwhelmed. “All that went through my head is ‘Wow. It’s perfect.’” He wasn’t exaggerating: Juno’s orbit is so close to ideal, it’s just one second away from the projected calculations. The entire room reverberates with excitement, giddy giggles spreading quickly as high-strung nerves melt into happy exhaustion and relief.

When Juno’s project manager Rich Nybakken gets his turn to speak, he dramatically holds up a stack of paper. “We had a contingency communication plan,” Nybakken starts. “You know what?” He pauses mischievously, giving the room a grin, then shreds the paper. The applause and cheering are mixed with laughter and impertinent catcalls.

This was a mission-critical event. If Juno’s engines hadn’t fired, the spacecraft would have been lost to deep space. If they fired too long, Juno’s new orbit would have crashed it into Jupiter. Just as critically, the probe needed to turn and point towards the sun to switch back on to solar panel before its batteries ran dry.

But despite all the things that could have gone wrong, Juno hit every milestone perfectly.

In the weeks before approach, Juno captured the majestic dance of Jupiter and its four largest moons: Io, Europa, Ganymede and Calisto (see video). The probe’s scientific instruments were switched off during orbital insertion, but now Juno will complete the current 53.5 day capture orbit, then turn its instruments back on and loop around again.

It will burn its main engine again on 14 October, tightening up into a 14-day orbit for main science operations. Over the next year and a half, the spacecraft will investigate some of the biggest mysteries about Jupiter, mapping the planet’s gravity and magnetic fields, looking for evidence of a solid core, and tracking its auroras.