Thanks for your responses.
This fixed my issue. I don't know how I manage to add some trim to my probe.
I create this probe to be in orbit of neidon, a planet of the mod "outer planets mod" far away from kerbol. On my screen we can see the two last stages of my ship, the nerv (empty but didn't decouple yet) and a argon thruster (near future technologies mod).
I though the nerv was a good engine because of the high ISP in vacum. This is a bad idea ? And for the RCS, I use them to turn my ship for manoeuvre node. I can do these only with reaction whell even with the nerv (200h on KSP, never used reaction whell )?
Thanks