The active damping aspect is treated of the spacecraft control laboratory experiment (SCOLE). A continuum model, rather than a finite element model, is used. First, a group of rather weak sufficient conditions for strong stabilizability is presented. Structural passive damping is no longer required to be positive definite and, in fact, can even be zero, while strong stabilizability can still be achieved by active damping. Then, the mode excitation problem is studied for both linear and (saturating) nonlinear active damping. The popular notions of ‘characteristic equation’ and ‘root locus’ in feedback control are extended to our distributed parameter system, which is a feature of this work. The root locus provides an insight into the nature of active damping