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.
Current trends in astronomical research necessitate a large number of small to medium sized telescopes be commissioned
to support and augment the science goals of larger ground-based observatories and space observatories. The science
mission requirements for these telescopes vary widely, yet the critical design requirements for the telescopes are largely
consistent across many missions. This paper clarifies the critical functional and performance parameters of a gimbaled
telescope system as dictated by three significant classes of telescope missions: laser transmission, wide area surveys and
pointed surveys. Within these classifications several specific example science missions are considered from which
specific telescope functional requirements are derived. Detailed telescope performance requirements are then evaluated
from a systems engineering perspective, highlighting typical performance that may be expected from a modern
telescope. Additional commentary is provided on the probable feasibility of upgrading older facilities in contrast to
commissioning new telescopes systems.
Based on the predictions of the NSF / NOAO sponsored ReSTAR report, it is assumed that the demand for highobservation-
volume pointed surveys will increase rapidly within the next ten years. A case is made for the high science
value of high gimbal slew rates on the basis of effective throughput in pointed survey applications.