Hardware

The ESA had been using a series of SPARCv8 cores designed specifically for aerospace applications (with all the associated fault-tolerance, formal verification, and radiation hardening), the LEON series, since the early 1990s. That was back when SPARCv8 was new (it was introduced in the late 1980s). The LEON series has since dropped SPARCv8 (like maybe five years ago), and adopted RISC-V instead (because SPARC is dead, and its ecosystem is dead), so it doesn't seem to me that NASA is doing anything particularly radical in adopting RISC-V.