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Telescope Systems

Relescope

Rendering of the telescope in which the primary, secondary and tertiary mirrors are shown.

Optics

The telescope optical design is a folded Ritchey-Chrétien. Both the primary and secondary mirrors are hyperboloidal, and together they form a well-corrected focus. The tertiary mirror is used to fold and steer the light path so that the science beam can be delivered to any of eight instruments that will be mounted on the two main Nasmyth platfoms. The image is formed 20 meters from the center of the tertiary mirror. The focal ratio of the telescope is f/15.

Adaptive Optics

The first light Adaptive Optics (AO) architecture for the TMT has been defined to provide near-diffraction-limited wavefront quality and high sky coverage in the near infra-red (IR) for the first TMT science instruments IRIS  and IRMS. NFIRAOS is an order 60 x 60 laser guide star (LGS) multi-conjugate AO (MCAO) system, which provides uniform, diffraction-limited performance in the J, H, and K bands over 34 x 34 arc sec fields with 50 per cent sky coverage at the galactic pole, as required to support the TMT science cases.  

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Controls

TMT is a complex system-of-systems. As a result, the telescope controls are responsible for over 30,000 input/output channels and nearly 12,000 controlled degrees of freedom. This includes controlling the pointing and tracking of the mount, the position, tilt and active optics shape control of the primary, secondary and tertiary mirrors, the alignment and phasing system, the wavefront sensors built into the instruments, and coordinating the motions of the enclosure.

Telescope Structure

The role of the telescope structure is to carry the telescope optics and instruments, the telescope utilites, laser guide star system and other subsystems. The telescope structure consists of all moving parts of the telescope except the science instruments and telescope optics. This include the azimuth journal, azimuth platforms, elevation structure and telescope drives.

Rendering of the telescope structure design.

Rendering of the front view of the telescope structure showing the NFIRAOS instrument on the left, and WFOS instrument on the right. For perspective the telescope is ~55m or 180 feet wide and ~50m or 160 feet tall. The segment handling platform is to the rear and the mirror cleaning arms can be seen at the front and rear edges of the primary mirror. Image credit to Mitsubishi Electric Corporation and National Astronomical Observatory of Japan