ULTIMATE-Subaru GLAO Star Simulator: a Cassegrain mounted wave front sensor calibration source

The Ultimate-GLAO project for the Subaru Telescope requires a set of calibration sources and alignment fiducials for the cassegrain mounted, natural and laser guide star wave-front sensors. The availability of a replica Cassegrain structure (called the Cassegrain Simulator) at the National Astronomical Observatory of Japan (NAOJ) base in Hilo, usually used to check interface compatibility with Cassegrain mounted instruments, led naturally to the concept of an”on telescope” calibration source. The calibration system consists of a set of modular light sources which simulate the optical behaviour of the telescope, for actual sources at various altitudes (to cover laser and natural guide star sources). The Cassegrain Simulator allows motion in elevation, allowing gravity flexure of the wave front sensors to be calibrated also. A key advantage of this approach to the wave front sensor system alignment and calibration is the substantial reduction of engineering time on the telescope during the Ultimate-GLAO system assembly, integration and test (AIT) activities. Alignment and calibration activities performed at the NAOJ base are also far more efficient than those performed at the summit. This paper will discuss the concept and planned implementation of the so called”Star Simulator” and present analysis to justify the design.