NASA’s Juno spacecraft, which launched in 2011 to investigate Jupiter’s origin and evolution, travels through the solar system’s most intense planetary radiation fields. When the spacecraft’s JunoCam—a color, visible-light camera—began to suffer the consequences in December 2023, the mission team back on Earth had to think of a remote fix before they lost their chance to photograph the Jovian moon, Io.
A relatively simple process was ultimately what enabled the long-distance save: heating the instrument before slowly cooling it down (I trust they tried turning it off and on again). The experience has provided insightful lessons on spacecraft radiation tolerance for mission scientists beyond the Juno team, according to a Jet Propulsion Laboratory statement published yesterday.
Scientists estimated that JunoCam, whose optical unit is located outside of a protective radiation vault, could resist radiation for the spacecraft’s first eight orbits around Jupiter. It wasn’t until Juno’s 47th orbit, however, that the scientists began to observe radiation damage.
The team identified evidence suggesting that the radiation had damaged the voltage regulator, which is crucial to JunoCam’s power supply. From hundreds of millions of miles away, their options were limited. As such, they decided to try a lesser-known process called annealing, which consists of heating a material for a given amount of time to reduce its defects before slowly cooling it down.
“We knew annealing can sometimes alter a material like silicon at a microscopic level but didn’t know if this would fix the damage,” Jacob Schaffner, a JunoCam imaging engineer from Malin Space Science Systems, said in the statement. “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.”
While their approach successfully enabled JunoCam to capture clear photographs for several orbits, the spacecraft continued to barrel into Jupiter’s radiation fields, and the damage was soon apparent again.
“After orbit 55, our images were full of streaks and noise,” explained JunoCam instrument lead Michael Ravine, also from 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, the more extreme annealing didn’t seem to produce any improvements, but as the Io approach got nearer, and with just days to go, the images suddenly improved significantly. On December 30, 2023, JunoCam successfully captured detailed photographs of Io’s north polar region, including previously undocumented volcanoes. Scientists presented the accomplishment at the Institute of Electrical and Electronics Engineers Nuclear & Space Radiation Effects Conference in Nashville on July 16.
Despite the fact that the image corruption returned during its recent 74th orbit, “Juno is teaching us how to create and maintain spacecraft tolerant to radiation, providing insights that will benefit satellites in orbit around Earth,” explained Scott Bolton, Juno’s principal investigator from 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.”