We have found the ATSAMD51 microcontroller used on PyCubed Mainboards (v00 - v05) exhibiting a surprisingly high sensitivity to 50MeV protons. Our KickSat-2 and VR3X missions had zero issues with the ATSAMD51 and the part does have some radiation literature. But after troubleshooting unexplained reboots on our recent PY4 mission, we decided to test it ourselves.
More details:
It's quite possible the ATSAMD51 has undergone some manufacturing changes in the nearly 10 years since it was selected for PyCubed that introduced new avenues for rad susceptibility (atmel acquired by microchip, chip shortage shaking up fab availability, etc). Additionally, much of our personal flight heritage with the part has been during different periods of the solar cycle and not subject to the high bursts of proton fluxes currently observed in the 2024 solar maximum.
In our testing, all of our test articles (all use ATSAMD51 with date codes within the past two years) will consistently experience latch-up of one or more peripherals when exposed to 50MeV protons to a fluence of 5E8 p/cm2 or less. We saw this manifest as many things such as halted serial communication (SPI/I2C/UART) but continued external watchdog PWM, or latch-up of certain GPIO power domains (groups of pins) while continued operation of others. Suffice to say when we release a v06 PyCubed mainboard design, it will not utilize the ATSAMD51 microcontroller.
It is worth mentioning that, with the culprit ATSAMD51 masked from the beam, the remainder of the PyCubed bus operated without issue under accelerated exposure until we ran out of time on the beam (equivalent to multiple years on orbit).
NOTE: We are posting this summary to notify the community as quickly as possible. These are just preliminary findings, interpret it however you wish.