Hi @tog!
Welcome
For the kind of reference frame rotation used in those applications, I highly suggest using the package https://github.com/JuliaSpace/ReferenceFrameRotations.jl
I use it in SatelliteToolbox.jl and in the AOCS simulator built at INPE as reported here: Julia and the satellite Amazonia-1
You have all the tools to convert between Euler angles, Euler angle and axis, DCM, and Quaternions (modified Rodrigues parameters are coming!). We also have functions to compute the time derivative of Quaternions and DCM to propagate the attitude.