Each of the four ITER Electron Cyclotron Heating Upper Launcher (ECHUL) features eight transmission lines (TLs) that are used to inject 170-GHz microwave power into the plasma at a level of up to 1.31 MW (at the TL diamond window) per line. The millimeter waves are guided through a quasi-optical section consisting of three fixed mirror sets (M1, M2, and M3) and one front steering mirror set (M4), with a steering range of & x005B;& x2212;7, & x002B;7 & x005D;& x00B0;. The M4 mirror assembly (upper and lower) will each reflect nearly four Gaussian beams at the correct location in the plasma for suppression of the/1 NTMs. EPFL-SPC has developed a novel steering mirror assembly (SMA) actuator system, which is based on four pressure-controlled, helium-filled bellows working against six helicoidally machined, preloaded, compressive springs, that rotate around two frictionless flexure pivots. This article will outline the design and thermal & x2013;mechanical analysis of such bellows, springs, housing (stator), and the remote-handling compatible support frame.