GMTNIRS (Giant Magellan Telescope Near-Infrared Spectrograph): Structural-Mechanical Design

A near-infrared spectrograph (NIRS) has been designed and proposed for utilization as a first-light instrument on the Giant Magellan Telescope (GMT). GMTNIRS includes modular JHK, LM spectrograph units mounted to two sides of a cryogenic optical bench. The optical bench and surrounding, protective radiation (thermal) shield are containerized within a rigid cryostat vessel, which mounts to the GMT instrument platform. A support structure on the secondary side of the optical bench provides multi-dimensional stiffness to the optical bench, to prevent excessive displacements of the optical components during tracking of the telescope. Extensive mechanical simulation and optimization was utilized to arrive at synergistic designs of the optical bench, support structure, cryostat, and thermal isolation system. Additionally, detailed steady-state and transient thermal analyses were conducted to optimize and verify the mechanical designs to maximize thermal efficiency and to size cryogenic coolers and conductors. This paper explains the mechanical and thermal design points stemming from optical component placement and mounting and structural and thermal characteristics needed to achieve instrument science requirements. The thermal and mechanical simulations will be described and the data will be summarized. Sufficient details of the analyses and data will be provided to validate the design decisions.