Recently discovered flaws in electronic circuits onboard NASA’s Europa Clipper spacecraft could threaten the longevity or even the launch of the $5 billion mission to explore Jupiter’s icy moon and the ocean inside it. While the packaged up probe continues to be prepared for an October flight from Florida’s Kennedy Space Center, a “tiger team” of engineers convened by the space agency is reviewing the issue, with a report expected later this month.
The problem stems from a batch of circuit elements, called metal-oxide-semiconductor field-effect transistors, or MOSFETS, that do not meet the radiation-hardness standards set for the mission. The transistors serve as amplifiers or switches, turning power off and on to parts of the spacecraft. But like all electronics, they can be damaged by high-energy radiation particles. And Clipper, as it flies past Europa some 50 times during its planned life, will repeatedly face Jupiter’s radiation environment, one of the harshest ever navigated by a NASA mission.
Engineers at NASA’s Jet Propulsion Laboratory (JPL), which leads the development of Clipper, discovered the problem in May after talking with colleagues about a classified satellite at a conference. They told the JPL staff that a batch of radiation-hard MOSFETs developed by Infineon Technologies, a leading commercial supplier, was falling far below desired performance levels.
Those concerns were passed along to NASA officials, who 2 days ago briefed scientists on the agency’s independent planetary science panel. “We’re seeing some MOSFETs fail at lower radiation levels,” said Shannon Fitzpatrick, associate director of planetary science flight programs, speaking on 9 July to NASA’s Planetary Science Advisory Committee (PSAC). “There is a risk these MOSFET transistors may not meet the radiation tolerance we require.” NASA declined to answer specific questions about the issue by deadline, but released a blog post on the problem today.
Radiation exposure has long been a central problem of exploring Jupiter and its moons. Jupiter’s magnetic field is 20,000 times stronger than Earth’s, and it spins rapidly, creating a torrent of bombarding charged particles. The Europa mission, which will search the moon for evidence of habitable conditions in its subsurface ocean, was originally designed as an orbiter. But JPL shifted to a mission design of dozens of flybys that would minimize the time spent in the harshest radiation environment and mitigate the chances of damage—a strategy used by Juno, another NASA mission that is currently orbiting the gas giant.
Some years ago, Infineon changed its manufacturing process for its radiation-hard MOSFETs, which it designs to meet U.S. military specifications—the same radiation-resistance standards used by the Clipper team. After this change, the company’s classified customers found that several lots of the transistors failed at lower than expected radiation levels, Fitzpatrick said. The company has already corrected the mistake, but Infineon did not report the flaw to NASA because the company did not know what the transistors would be used for, Fitzpatrick said. “They did not realize it was going to affect us.” Infineon did not respond to a request for comment.
“This is concerning,” said Deborah Woods, a planetary scientist at the Massachusetts Institute of Technology’s Lincoln Laboratory, at the PSAC meeting. “It’s fortunate that you happened to talk to people at the conference and learn of this issue. It’s troubling that this was the only way this was uncovered.”
The transistors cannot simply be replaced. Clipper’s aluminum-zinc electronics vault, meant to provide a measure of radiation resistance, was sealed in October 2023. Barring an indication that the faulty MOSFETs will cause catastrophic failure, the agency will likely seek to continue with the launch—although backup windows are available the next 2 years.
NASA engineers, working closely with Infineon, are now studying how many of the defective transistors are onboard Clipper, where in the hardware they are deployed, and which ones would most threaten the mission if they failed. They are also looking at possible ways to mitigate the problem, such as turning off certain switches for parts of the spacecraft’s lifetime, or naturally healing the vulnerable transistors, potentially by raising temperatures, a process called annealing.
The full extent of the problem, and the risk it poses to the mission, will not be known for several weeks, while testing continues at JPL, the Johns Hopkins University Applied Physics Laboratory, and NASA’s Goddard Space Flight Center. But at its most simple, the problem is easy to understand, Fitzpatrick said at the meeting. “A switch would not work when we need it to work.”
More: https://www.science.org/content/article/vulnerable-transistors-threaten-upend-europa-clipper-mission
