The STIX (Spectrometer/Telescope for Imaging X-rays) instrument on the ESA Solar Orbiter satellite is designed to study the Sunrays emissions. The wide energy range of incident X-ray fluxes, expected during the solar flares, requires the incorporation of a moveable X-ray attenuator covering and uncovering the instrument detectors depending on X-ray fluxes intensity. In the frame of the STIX Detector Module Prime Contract with ESA, Almatech has designed an attenuator mechanism provided with 2 end-strokes and 1 neutralmid- stroke stable positions. In particular, the two stable end-stroke positions avoid the use of a dedicated launchlock device to reduce complexity, lower the total mass while increasing the system reliability, all in the same time. Flexures as well as end-position switches are used as accelerator/decelerator devices in the mechanism. A cam-shaped switch trigger design allows the optimization of their dynamic contributions in the system. This article first presents the design of the STIX Attenuator Mechanism and then focuses on presenting the optimization of its dynamic response that plays a major role in the limitation of exported force, micro vibrations and torque to the spacecraft on one hand, as well as on the required actuation power on the other hand.