Juno’s mission to Jupiter faced a host of challenges and obstacles. The gas giant is a long way from the Sun, limiting the available solar energy. The distance also makes communication with the spacecraft problematic. Add to that the complex environment, with Jupiter’s massive gravitational pull and the orbital complexity of its four Galilean moons creating a constantly shifting field of gravitational interactions.
But the biggest obstacle is likely Jupiter’s intense radiation.
Jupiter has extremely powerful magnetic fields, and those fields trap charged particles that create a damaging environment for spacecraft and their delicate electronics. Juno has a titanium vault in which it holds its most precious electronics, but unfortunately, there wasn’t room for everything inside the vault. Since JunoCam isn’t one of the mission’s primary science instruments, it didn’t make the cut. JunoCam is an optical imager included with the spacecraft primarily for the benefit of regular people who want to see what the spacecraft sees, although it has made scientific contributions, too.
Juno’s titanium radiation vault being lowered onto the spacecraft in 2010. There was no room in the vault for JunoCam. Image Credit: By NASA – http://photojournal.jpl.nasa.gov/jpeg/PIA13715.jpg, Public Domain.
After dozens of orbits and almost 10 years spent orbiting Jupiter, JunoCam is feeling the effects of radiation exposure.
Juno follows a wide, polar orbit that allows it to image Jupiter’s entire surface as the planet orbits under the spacecraft. The orbit takes the spacecraft plunging through Jupiter’s radiation belts then escaping to transmit its data and observe from a greater distance. So during each of its orbits, it spends a brief time in the perilous radiation.
Malin Space Science Systems built JunoCam and they were confident it could survive Juno’s first eight orbits. But after that, the instrument’s fate was uncertain. Juno’s prime mission lasted for 34 orbits, and JunoCam worked perfectly during that time. But eventually, things changed.
During its 47th orbit, the camera showed signs of radiation damage. By orbit 56, almost all of JunoCam’s images were corrupted. The images were grainy and polluted with horizontal streaks.
JunoCam captured this image of Jupiter on Nov. 22, 2023. It shows a circumpolar cyclone on Jupiter’s north pole, but the image is grainy and corrupted with horizontal lines. Image Credit: NASA/JPL-Caltech/SwRI/MSSS
Digital cameras are built around CCDs, Charge-Coupled Devices. They detect photons and convert them into electrical charges, so it’s easy to see how an intense radiation field would negatively affect them. Unwanted radiation introduces unwanted electrical signals that show up as streaks, bright spots, and noise, and over time can damage the silicon-crystal structure of CCDs.
As JunoCam showed evidence of radiation damage, there weren’t many options to try to extend the camera’s life from 600 million kilometers away. But there were clues as to what was actually being damaged. After assessing the situation, mission personnel figured out that is was a voltage regulator in the camera’s power supply that was malfunctioning.
JunoCam is mounted on the outside of the Juno spacecraft, where it lacks the radiation protection the spacecraft’s titanium vault provides for other instruments. Image Credit: C. J. Hansen et al. 2014.
With few options at hand, the team turned to heat.
Annealing is a common heat-treatment process in metal working, where a material is heated above its recrystallization temperature and then recooled. It makes metal more workable. JunoCam has a heater that keeps the camera at optimal operating temperatures in the cold space environment. Engineers decided that using the heater to anneal the camera was their best option, even though they weren’t sure if it would work.
“We knew annealing can sometimes alter a material like silicon at a microscopic level but didn’t know if this would fix the damage,” said JunoCam imaging engineer Jacob Schaffner of Malin Space Science Systems. “We commanded JunoCam’s one heater to raise the camera’s temperature to 77 degrees Fahrenheit — much warmer than typical for JunoCam — and waited with bated breath to see the results.”
The swashbuckling approach worked. JunoCam’s imaging was restored, and for the next few orbits, it delivered the crystal clear images we’re all used to enjoying.
But Juno was designed to get progressively closer to Jupiter on later orbits, and that meant an increased exposure to radiation. Imaging problems surfaced again, and the spacecraft was on course for a close approach to Jupiter’s volcanic moon Io. That was an imaging and science opportunity that nobody wanted to miss.
“After orbit 55, our images were full of streaks and noise,” said JunoCam instrument lead Michael Ravine of Malin Space Science Systems. “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.”
At first, test images showed very little improvement, and the camera’s degraded performance in the face of the upcoming Io flyby was cause for anxiety. It would be a missed opportunity with no other opportunity to image Io so closely anytime in the near future.
Then, with the Io approach only days away, the images improved. On December 30th, 2023, Juno came within 1500 km (930 miles) of Io. JunoCam delivered crisp, clear images of Io’s north polar region.
JunoCam captured this crisp image of Io’s north polar region on December 30th, 2023. It shows mountain blocks rising nearly 10km above the terrain, lava flows, and a surface coloured by volcanic eruptions. Image Credit: Image data: NASA/JPL-Caltech/SwRI/MSSS. Image processing by Gerald Eichst
Juno has now completed 74 orbits of Jupiter, twice as many as the 37 outlined in its prime mission. But now, JunoCam’s image problems are reappearing. The Juno team is experimenting with more annealing, hoping to be successful again.
This has turned into a valuable and unique learning opportunity for Juno mission personnel. The Juno team has used the annealing process on some of the spacecraft’s other instruments, as part of a broader strategy to keep the spacecraft functioning in Jupiter’s intense radiation environment. In the future, instruments may be designed specifically to be annealed when the need arises.
“Juno is teaching us how to create and maintain spacecraft tolerant to radiation, providing insights that will benefit satellites in orbit around Earth,” said Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio. “I expect the lessons learned from Juno will be applicable to both defense and commercial satellites as well as other NASA missions.”