L-3 Integrated Optical Systems (IOS) Division has been selected by the National Solar Observatory (NSO) to design and
produce the Top End Optical Assembly (TEOA) for the 4-meter Advanced Technology Solar Telescope (ATST) to
operate at Haleakalā, Maui. ATST will perform to a very high optical performance level in a difficult thermal
environment. The TEOA, containing the 0.65-meter silicon carbide secondary mirror and support, mirror thermal
management system, mirror positioning and fast tip-tilt system, field stop with thermally managed heat dump, thermally
managed Lyot stop, safety interlock and control system, and support frame, operates in the "hot spot" at the prime focus
of the ATST and so presents special challenges. In this paper, we describe progress in the L-3 technical approach to
meeting these challenges, including silicon carbide off-axis mirror design, fabrication, and high accuracy figuring and
polishing all within L-3; mirror support design; the design for stray light control; subsystems for opto-mechanical
positioning and high accuracy absolute mirror orientation sensing; Lyot stop design; and thermal management of all
design elements to remain close to ambient temperature despite the imposed solar irradiance load.
Friction is a well-known performance limitation for gimbaled EO director systems. While much research study has been directed to bearing friction, the well-known friction models in literature, being represented in time, position, and rate domain, are not amenable to most LOS jitter analysis. Furthermore the type of mission profiles to which large gimbals are subjected have received limited attention in this field of research, so the selection of an appropriate friction model is not obvious. This paper fits popular friction models to experimental data, and studies the models in frequency domain.