Juno Will Stay in Current Orbit Around Jupiter

NASA has announced that its Juno mission will remain in a wide-ranging path around Jupiter.

Jupiter's south pole

Stormy times over Jupiter's southern pole. This image was captured by JunoCam on February 2, 2017, from a range of 62,800 miles (101,000 kilometers).
NASA / JPL-Caltech / SwRI / MSSS / John Landino

NASA has decided to leave the Juno spacecraft in its current 53-day orbit around Jupiter for the remainder of the mission. The decision follows the discovery of a possible engine malfunction in October 2016. Maintaining a wide-ranging orbit will allow the spacecraft's instruments to safely complete the mission's science objectives, while avoiding the risk of another engine malfunction stranding the spacecraft in an unplanned orbit.

“Juno is healthy, its science instruments are fully operational, and the data and images we've received are nothing short of amazing,” says Thomas Zurbuchen (NASA-Science Directorate) in a recent press release. “The decision to forego the burn is the right thing to do — preserving a valuable asset so that Juno can continue its exciting journey of discovery.”

Launched on August 5, 2011, atop an Atlas 5 rocket from Cape Canaveral Air Force Station, Juno entered its initial and current orbit on July 4, 2016. The plan was to make two wide initial capture orbits around Jupiter, burning the main engine on October 19, 2016, to enter a series of 34 shorter, 14-day science orbits.

NASA/JPL

The original plan for NASA's Juno spacecraft, with two initial capture orbits versus the final phase of science orbits.
NASA / JPL

However, the unexpected occurred last October: Juno went into safe mode following what was to be the final firing of the spacecraft's main engine. Telemetry later indicated that a pair of helium check valves in the main engine took several minutes to open, longer than on previous firings.

Saving Juno

Engineers analyzed the situation and decided that the best bet was for the spacecraft to stay put, rather than risk another firing of the main engine. Juno will still be able to accomplish its main mission objectives, including probing the magnetosphere, radiation belts, and the gas giant's deep interior. It will now focus on documenting the far reaches of the planet's magnetic field as well. Also, the quality of the data gathered on each pass will remain the same, as the closest passage on the current orbit is identical to those on the hoped-for science orbits. The only difference now is the span of time between passes.

Juno's current orbit takes it from a perijove (closest approach) of just 2,600 miles (4,100 kilometers) over the Jovian cloud tops, to far out past the orbit of Callisto with an apojove of 5 million miles (8.1 million kilometers) distant.

Juno has completed four orbits of Jupiter thus far, giving us some amazing never-before-seen views of the planet's polar regions, and we're expecting to see some of the first science papers using this data in the coming months. Citizen scientists are also making good use of images provided by JunoCam, presenting us with some compelling views.

Juno approaches Jupiter

Jupiter as seen by Juno's JunoCam on first approach last August.
NASA / JPL-Caltech / SwRI / MSSS

The next perijove pass is set for March 27, 2017.

There's another silver lining to the engine anomaly, as Juno may get a brief reprieve before its grand finale. The original plan called for the mission to terminate by entry into Jupiter's atmosphere about a year from now, in February 2018. Juno receives a large amount of radiation on each successive pass, degrading the instruments and spacecraft controls. Engineers planned for a controlled entry in order to protect Jovian moons, such as Europa, from contamination. Orbital precession also carries Juno deeper into Jupiter's radiation belts on each successive pass. Now, NASA plans to operate the mission through July 2018, for a total of 12 orbits, before proposing for a mission extension.

The extended orbit might just be good news after all, as Juno gets a longer rest period between successive doses of instrument damaging radiation. In the end, Juno's loss of an operable main engine might just be science's gain.

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