Thank you for all your replies!!! Following your advises, I tried to perform a reentry with SAS locked in retrograde mode and it went well, Jebediah survived... Then I tried again a "free" reentry and I found, for example, that my vessel is unstable at Mach 5.75 @ 31 km of altitude, so I used FAR tools (I did the computation inside the SPH). Here the results: Then, I used the FAR tools also with the well-known stable vessel, i.e. Pod + Heat shield and, surprisingly, they have similar results!!!!! What do you think?