Lessons learned from the design, fabrication, integration, and test of a cryogenic, IR spectrometer for ground-based astronomy

摘要

The Infrared Multi-Object Spectrograph (IRMOS) is an instrument for the Kitt Peak National Observatory (KPNO) Mayall (3.8m) and 2.1m telescopes. IRMOS is a low- to mid-resolving power (R = λ/Δλ = 300―3000), near-IR (0.8―2.5 μm) spectrometer that produces simultaneous spectra of ～100 objects in its field of view using a real-time programmable, multi-aperture slit mask. The instrument operating temperature is ～85K to allow for infrared (IR) detector operation and for improved K-band performance. The optical bench and mirrors are machined from aluminum 6061-T651 and then further treated, theoretically allowing for less ambient to cryo change in the optical alignment. IRMOS utilizes four powered mirrors, three flat mirrors, two rotary mechanisms, one linear mechanism, a commercial micro electro-mechanical systems (MEMS) micro-mirror array device and a 1024x1024, HgCdTe detector. The final design of the instrument and all of its components evolved through several iterations and a series of requirement/feasibility trades. During the design process, we found the heritage of past instruments with similar operating conditions to be invaluable in understanding our challenge, maximizing performance, and minimizing cost. The decision-making process of our design, as well as some of the major technical achievements, are described from a systems point of view in order to provide a list of "lessons learned" for future cryogenic instrument design and construction.