Can a camera as far away as almost 600 million kilometers be repaired with no more than a burst of heat and an act of engineering wishful thinking? That was the question NASA engineers were confronted with when JunoCam, the favorite imager on the Juno spacecraft, started malfunctioning far inside Jupiter’s brutal radiation belts.
JunoCam’s existence was always a tightrope walk. Built to withstand only eight passes through the most hostile planetary radiation environments in our solar system, the camera performed far better than expected, well in excess of 45 orbits, before succumbing to its first symptom of distress. The cause: radiation-induced damage, an ever-present threat in the Jovian environment, where the planet’s magnetic field is 20,000 times stronger than Earth’s and constitutes a giant particle accelerator, showering spacecraft with high-energy electrons and ions. The optical element of JunoCam, situated outside the radiation vault’s titanium-walled shielding of the spacecraft, was at most risk, weathering conditions tolerated by few instruments for days JunoCam is a color, visible-light camera whose camera lens lies outside of a titanium-shelled radiation vault.
When image quality dipped to zero on Juno’s 47th orbit, the NASA Jet Propulsion Laboratory engineers guessed a malfunctioning voltage regulator, a vital component for the camera’s power supply. With the spacecraft 595 million kilometers from Earth, hardware replacement was impossible. The astronauts resorted to a measure of desperation: annealing, a process in which a material most typically silicon is heated to a precise temperature so that radiation-damaged atoms may reorganize or heal. As JunoCam engineer Jacob Schaffner explained, “We knew annealing can sometimes alter a material like silicon at a microscopic level but didn’t know if this would fix the damage.” The team instructed JunoCam’s heater to heat the camera up to 77°F, well beyond its operating range, and waited nervously.
The bet paid off at least temporarily. The images from the camera snapped back into sharp focus, and for a few orbits, JunoCam again provided clear images of Jupiter’s storm clouds. But the relief was temporary. As Juno descended deeper into Jupiter’s radiation belts, the camera images again began degrading, with noise streaks and artifacts. Michael Ravine, JunoCam’s instrument lead, described the desperation: “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.”
The second, more intense annealing was scheduled just before a key flyby of Jupiter’s volcanic moon Io late in 2023. The result was unpredictable initially, but when Juno flew close to Io, the pictures were breathtaking. The camera took high-resolution views of Io’s north polar region, with unseen volcanic ground and mountain blocks topped with sulfur dioxide frost. The success of this remote repair not only saved a valuable science opportunity but also established the value of annealing as an in-situ field tool for hardware repair. A few days after annealing, JunoCam started delivering good images for the subsequent couple of orbits.
The technical success highlights the unique challenge of doing business in Jupiter’s radiation regime. In contrast to Earth’s Van Allen belts, Jupiter’s radiation belts are gigantic and incredibly dense with high-energy particles, the majority of which result from volcanism on Io. single event upsets temporary errors within electronic circuits and cumulative total ionizing dose (TID) effects, slowly degrading semiconductor performance by trapping charge and inducing atomic-scale defects can be caused by such particles. high-energy protons and electrons ionize the electrons in atoms, leaving a surplus of charge carriers. By radiation-hardened design, i.e., heavy shielding and increased oxide, Jupiter’s belt energy still outpaces current technology MOSFETs Earth-based applications are not typically hardened against the extreme radiation near Jupiter.
Annealing has been employed for decades in the production of semiconductors and even used in medical dosimetry to repair irradiated devices but using it as a spacecraft electronics remote repair tool is new. By intentionally overheating the silicon electronics of the camera, NASA engineers took advantage of the material’s self-healing tendency at the atomic level at least long enough to reverse TID damage. The process is not entirely risk-free; too much heat can be damaging in itself to delicate components, and the process has to be controlled to a high level millions of kilometers away.
The reach of JunoCam’s recovery goes beyond a single mission. As Juno lead scientist Scott Bolton explained, “Juno is teaching us how to create and maintain spacecraft tolerant to radiation, providing insights that will benefit satellites in orbit around Earth”. I expect the lessons learned from Juno will be applicable to both defense and commercial satellites as well as other NASA missions. I believe what we learn with Juno will extend to defense and commercial satellites and other NASA missions. The Juno team has then gone on to try using annealing with other instruments and subsystems as a means to creating an expanded suite of autonomous or remote fixes in deep space the Juno team has used derivations of this process of annealing on a number of Juno instruments and engineering subsystems.
Even with these advances, the battle against radiation continues. JunoCam brought back high-grade imagery by orbit 74, though more recent orbits are now experiencing signs of degradation again. NASA has not yet made up its mind whether another annealing attempt is to be done or if the phenomenal mission of the camera is done. For the next generations of Jupiter and beyond wanderers, JunoCam’s tales of determination, inventiveness, and the power of heat will inspire the generations to come of spacecraft built to survive where no repair crew can ever go.
