  The utilization of a 6.5m monolithic primary mirror in a compact three-mirror
anastigmat (TMA) telescope design offers unprecedented capabilities to
accommodate various next generation science instruments. This design enables
the rapid and efficient development of a large aperture telescope without
segmented mirrors while maintaining a compact overall form factor. With its
exceptional photon collection area and diffraction-limited resolving power, the
TMA design is ideally suited for both the ground and space active/adaptive
optics concepts, which require the capture of natural guide stars within the
field of view for wavefront measurement to correct for misalignments and shape
deformation caused by thermal gradients. The wide field of view requirement is
based on a statistical analysis of bright natural guide stars available during
observation. The primary mirror clear aperture, compactness requirement, and
detector pixel sizes led to the choice of TMA over simpler two-mirror solutions
like Ritchey-Chretien (RC) telescopes, and the TMA design offers superior
diffraction-limited performance across the entire field of view. The standard
conic surfaces applied to all three mirrors (M1, M2, and M3) simplify the
optical fabrication, testing, and alignment process. Additionally, the TMA
design is more tolerant than RC telescopes. Stray light control is critical for
UV science instrumentation, and the field stop and Lyot stop are conveniently
located in the TMA design for this purpose.
