Disturbances attenuation, typically up to 200 Hz, onboard satellites is a key issue for advanced optical space systems with stringent spatial and temporal resolution requirements. Under ESA contract, Matra Marconi Space has conducted an ambitious proof-of-concept programme aiming at designing and demonstrating through prototypes and test innovative active vibration damping systems. In particular, a centralized anti-phase control (APC) system operating on distributed sensors and actuators to compensate stationary harmonic disturbances has been breadboarded and tested. The APC algorithm involves three major functions: (i) extraction of the harmonics signal by synchronous demodulation, (ii) identification of the complex gains between sensors and actuators using a recursive least squares algorithm, and (iii) anti-phase computation. The control algorithm has been implemented on a real-time test bench based on a fast DSP computer. The experiment has been performed on an engineering model of a representative space platform, namely MARCOTS. The measured performances, i.e. harmonic rejection at the controlled frequencies, range from 20 to 40 dB and are consistent with predictions from numerical simulations. Finally, a major advantage of the APC algorithm is intrinsic robustness to actuator failures, without performance impact for a single failure and 10 dB degradation for a double failure.