Launching another camera isn’t exactly an option, considering the total costs of the Juno spacecraft and mission sit at $1.13 billion, and it’s not like there’s a camera repair shop on Jupiter. That was the statement of one NASA engineer summarizing the bleak situation facing the mission controllers when JunoCam, the visible-light camera on the Juno spacecraft, began to fail millions of miles deep within Jupiter’s hostile radiation belts. But what ensued was not merely a story of distant troubleshooting, but an exhibition of the technical prowess and creative problem-solving that define space travel in the modern era.
The crisis center came many years after Juno had completed its first 34-orbit mission. As the spacecraft persisted on its long journey, JunoCam’s images hitherto crisp and helpful to science and education were deteriorating. By pass 47, unmistakable evidence of radiation damage had crept in: grainy texture, lines cutting across frames, and dirty photos. By pass 56, nearly all photos were being ruined, threatening the shutdown of one of the mission’s most iconic instruments. The engineers had a titanic challenge: locate the bad component and design a repair, 370 million miles away.
Diagnosis initially yielded a decisive finding. Despite initial suspicion, the image sensor itself was not damaged by Jupiter’s pounding but for partly being held within a titanium-lined “radiation vault.” The issue actually lay within a damaged voltage regulator in JunoCam power supply a component of smooth operation but notoriously vulnerable to the relentless battering of high-energy particles. As JunoCam Instrument Lead Michael Ravine put it, “Clues pointed to a damaged voltage regulator that is vital to JunoCam’s power supply.” The distinction was crucial: sensor damage well might have been irreparable, but power electronics issues offered a glimmer of infinitesimally tiny hope.
Radiation-hardened electronics are de rigueur in deep space, but even hardened parts have very long odds near Jupiter. The development of these types of systems calls for genuine process care from manufacturing, wafer recipes, through exhaustive testing. As IR HiRel’s Eric Toulouse puts it, The only way to provide components that are bulletproof with the highest level of radiation hardening is by optimizing each and every step of the process, starting with the wafer recipe itself. Even with such precautions, however, Jupiter’s sheer intensity of radiation 100 million X-rays worth can eventually outmatch even the most sophisticated equipment.
With the diagnosis in hand, NASA engineers turned to a highly improbable cure: annealing. The process, used in materials science, heats an element to some temperature, holds it for a period of time, and allows it to cool. It was hoped that annealing would heal microscopic defects in the voltage regulator’s silicon and restore it to operation. “We knew annealing can sometimes alter a material like silicon at a microscopic level but didn’t know if this would fix the damage,” Malin Space Science Systems’ JunoCam engineer Jacob Schaffner said. The engineers commanded JunoCam’s heater to warm up to 25°C (77°F), significantly above its normal operating point. Outcomes were stunning: picture quality improved radically on subsequent orbits. The victory was short-lived, though.
As Juno continued to press deeper into Jupiter’s radiation field, image degradation again became a problem. With a close flyby of Io, the most volcanically active of Jupiter’s moons and the closest moon of the solar system to its parent planet, hanging on the horizon, the team attempted a more aggressive annealing cycle. The heater was this time at maximum, with the warm temperature sustained for one week. The gamble paid off. When Juno drew near Io, the camera delivered photos “almost as good as the day the first images were taken” by the spacecraft, allowing researchers to capture images never before seen in its observation of Io’s volcanic terrain. The engineering achievement did not end there. The success of the annealing process has prompted NASA engineers to apply similar procedures to other instruments on the Juno spacecraft, which could extend their lifetimes in one of the solar system’s most extreme environments. This test sets a new benchmark for spaceflight repair: on-orbit thermal annealing as an effective way of avoiding radiation damage, especially for voltage regulators and other sensitive electronics.
This technique is essentially a subset of the overall spacecraft thermal management field. Using passive techniques like multi-layer insulation, thermal coatings, and radiators or active techniques like heaters and thermoelectric coolers, precise thermal control for day-to-day processes and impeccable maintenance is needed. The JunoCam case shows that with a combination of thermal design and radiation protection, life-saving outcomes can be achieved even for equipment millions of miles away from home.
As Juno begins its odyssey, well beyond its 74th orbit Jupiter, the lessons learned through this record thermal operation are to be felt for years to come in spacecraft operations and design. JunoCam’s is not just a story of survival, but of innovation on the cusp of what is possible.
