JunoCam, a visible-light color camera designed primarily for public engagement, has also contributed key scientific data throughout Juno's mission. Positioned outside the spacecraft's radiation-shielded vault, the camera is highly exposed to Jupiter's intense radiation belts-considered the most extreme of any planetary environment in the solar system.
Although engineers anticipated JunoCam might endure through eight orbits, it continued to perform reliably for 34 orbits during the prime mission. Trouble emerged by the 47th orbit, and by orbit 56, nearly all images were compromised due to suspected radiation damage.
The mission team hypothesized that the camera's voltage regulator had sustained damage. With no physical repair possible, engineers turned to an annealing technique: heating the camera to 77oF (25oC) using its internal heater in hopes of mitigating silicon defects at the microscopic level.
"We commanded JunoCam's one heater to raise the camera's temperature to 77 degrees Fahrenheit (25 degrees Celsius) - much warmer than typical for JunoCam - and waited with bated breath to see the results," said Jacob Schaffner of Malin Space Science Systems, the firm that developed and operates JunoCam.
The initial round of annealing worked, producing sharp images for several orbits. However, by orbit 55, the degradation resumed. With a key flyby of Io fast approaching, the team gambled on more extreme annealing.
"After orbit 55, our images were full of streaks and noise," said Michael Ravine, JunoCam instrument lead at Malin. "We tried different schemes for processing the images to improve the quality, but nothing worked. With the close encounter of Io bearing down on us in a few weeks, it was Hail Mary time: The only thing left we hadn't tried was to crank JunoCam's heater all the way up and see if more extreme annealing would save us."
Initially, the intensified heating showed little improvement. But as Juno neared Io in late December, the imagery began improving rapidly. On Dec. 30, 2023, during a pass just 930 miles from the volcanic moon, JunoCam captured near-original-quality images. The photos revealed rugged blocks blanketed in sulfur dioxide frost and previously unseen volcanic formations with extensive lava flows.
Juno has now completed 74 orbits around Jupiter. Although image noise returned during the latest orbit, the team continues refining the annealing approach, aiming to extend JunoCam's useful life. Variants of the thermal repair method are now being tested on other Juno instruments and systems.
"Juno is teaching us how to create and maintain spacecraft tolerant to radiation, providing key insights that will benefit not only Juno, but satellites in orbit around Earth," said Scott Bolton, Juno's principal investigator at the Southwest Research Institute. "I expect the lessons learned from Juno will be applicable to both defense and commercial satellites as well as other NASA missions."
NASA's Jet Propulsion Laboratory manages the Juno mission, part of the agency's New Frontiers Program, with contributions from the Italian Space Agency and other partners. The spacecraft was built and is operated by Lockheed Martin Space.
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