SpaceX's workhouse Falcon 9 rocket is powered by liquid oxygen, rocket-grade kerosene, and Linux
Like supercomputers, Internet of Things (IoT) devices, and many mission-critical devices, the Falcon 9 flies with Linux. The Falcon 9's onboard operating system is a stripped-down Linux running on three ordinary dual-core x86 processors. The flight software itself runs separately on each processor and is written in C/C++.
More details at From Earth to orbit with Linux and SpaceX | ZDNet
SpaceX's workhouse Falcon 9 rocket, which flew NASA astronauts Bob Behnken and Doug Hurley to the International Space Station, is powered by liquid oxygen, rocket-grade kerosene, and Linux.