JPL Engineers Restore NASA’s Juno Spacecraft After Safe Mode Events at Jupiter

NASA’s Juno spacecraft has resumed normal operations after unexpectedly entering safe mode twice during its 71st close approach to Jupiter, according to mission officials at the Jet Propulsion Laboratory in Pasadena.

The solar-powered spacecraft, which has been orbiting Jupiter since July 2016, entered safe mode on April 4 at 5:17 a.m. EDT—approximately one hour before reaching its closest point to Jupiter, known as perijove. A second safe mode event occurred 45 minutes after the spacecraft passed its perijove point.

According to NASA’s update on April 9, “The mission operations team has reestablished high-rate data transmission with Juno, and the spacecraft is currently conducting flight software diagnostics. The team will work in the ensuing days to transmit the engineering and science data collected before and after the safe-mode events to Earth.”

Safe mode is a protective measure spacecraft are designed to enter when they detect anomalies in their systems. During both incidents, Juno performed exactly as intended by rebooting its computer, powering down nonessential functions, and orienting its antenna toward Earth to maintain communication capabilities. As part of this safety protocol, Juno’s science instruments were automatically powered down for the remainder of the flyby.

Radiation challenges

Preliminary data analysis by Jet Propulsion Laboratory engineers suggests the safe mode events occurred as Juno passed through Jupiter’s intense radiation belts, widely considered some of the most hostile environments in the solar system.

Jupiter’s radiation environment presents significant challenges for the spacecraft. According to the mission documentation, “Of all the planets in our solar system, Jupiter is home to the most hostile environment, with the radiation belts closest to the planet being the most intense.”

To protect sensitive electronics from high-energy particles, Jet Propulsion Laboratory engineers designed Juno with a titanium radiation vault. This protective feature has been crucial to the spacecraft’s longevity in Jupiter’s harsh environment.

The April incidents mark the third and fourth times Juno has unexpectedly entered safe mode since arriving at Jupiter nearly nine years ago. Previous occurrences happened in 2016 during its second orbit and in 2022 during its 39th orbit. In December 2022, the spacecraft also experienced a memory anomaly following its 47th close flyby, likely caused by a radiation spike. In all cases, Jet Propulsion Laboratory’s operations team successfully recovered the spacecraft to full capability.

Mission adaptations

Juno was launched on Aug. 5, 2011, and completed its five-year, 1,740-million-mile journey to Jupiter on July 4, 2016. The mission was originally designed for shorter, 14-day science orbits, but concerns about the spacecraft’s main engine led NASA to maintain Juno in its initial 53-day orbit.

“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,” said Thomas Zurbuchen, then at NASA’s Science Directorate, when the orbital adjustment was canceled.

This adaptive approach has proven successful, with Jet Propulsion Laboratory engineers and mission planners transforming Juno from a Jupiter-focused mission into a full Jovian system explorer that now studies not only the gas giant but also its rings and moons.

Looking ahead

Juno’s next perijove will occur on May 7, 2025, and will include a flyby of the volcanic Jovian moon Io at a distance of about 55,300 miles (89,000 kilometers). This upcoming encounter is particularly significant following Juno’s observations from Dec. 27, 2024, including “the detection of what scientists called ‘the most intense volcanic eruption ever recorded on Io'” during that flyby.

The Juno mission is managed by NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, for principal investigator Scott Bolton of the Southwest Research Institute in San Antonio. The mission is part of NASA’s New Frontiers Program, which is managed at NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington.

Several institutions contributed to the mission: the Italian Space Agency funded the Jovian InfraRed Auroral Mapper instrument, Lockheed Martin Space in Denver built and operates the spacecraft, and various other institutions across the United States provided several of Juno’s scientific instruments.

The current mission extension is scheduled to continue through September 2025, adding to Juno’s substantial scientific legacy while navigating one of the solar system’s most challenging environments.