Updates to the optical alignment and test plan for the James Webb Space Telescope integrated science instrument module

Abstract

NASA's James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40K). The JWST Observatory architecture includes the Optical Telescope Element (OTE) and the Integrated Science Instrument Module (ISIM) element that contains four science instruments (SI) including a Guider. The SIs and Guider are mounted to a composite metering structure with outer dimensions of ~2.2x2.2x1.7m. The SI and Guider units are integrated to the ISIM structure and optically tested at NASA Goddard Space Flight Center as an instrument suite using a telescope simulator (Optical telescope element SIMulator; OSIM). OSIM is a high-fidelity, cryogenic JWST telescope simulator that features a ~1.5m diameter powered mirror. The SIs are aligned to the structure's coordinate system under ambient, clean room conditions using optomechanical metrology. OSIM is aligned to the ISIM mechanical coordinate system at the cryogenic operating temperature via internal mechanisms and feedback from alignment sensors in six degrees of freedom. SI performance, including focus, pupil shear, pupil roll, boresight, wavefront error, and image quality, is evaluated at the operating temperature using OSIM. This work updates the assembly and ambient and cryogenic optical alignment, test and verification plan for ISIM.

Liquid deformable mirror for advanced sub-optical system testing

“…A wavefront w m produced by the FDM is given by a linear combination of the individual response functions of the actuators in the matrix form: , m = w Ha (1) where H is called the influence matrix and a is a vector made of the control signals (currents) of the actuators. Each column of the control matrix H represents the response function of a single actuator shifted to its corresponding location on the hexagonal grid, while each row of H corresponds to a single wavefront data sample.…”

“…The most common example is JWST. In a recent updates, R. Ohl from NASA [1] described in detail how complex an optical system can be. Because each individual science instrument (SI) is attached to a common support structure, the science instruments must be verified in terms of performance and alignment requirements.…”

Cryogenic testing of detector alignment of the Fine Guidance Sensor for the James Webb Space Telescope

“…Mechanical GSE is used to simulate the mechanical interface to the ISIM 4 . A precision representation of the ISIM interface (a fixture called the ambient science instrument mechanical interface fixture or ASMIF 5,6 ) is used during the assembly, integration and alignment at ambient to provide the required relationship between the FGS and the OTE. A cryogenic test fixture is then used to replicate the ISIM interface at operating temperatures.…”

Cryogenic metrology for the James Webb Space Telescope Integrated Science Instrument Module alignment target fixtures using laser radar through a chamber window

“…The GSE alignment target plates consist of large (~1m), metal and composite structures containing a host of optical and mechanical metrology targets that are used by various ambient and cryogenic metrology systems during ISIM and OSIM alignment and test [3,4]. The purpose of these fixtures is to align the telescope-like output of OSIM to the flight coordinate system of ISIM.…”