F. David Robinson

The Optical Telescope Element Simulator for the James Webb Space Telescope

The James Webb Space Telescope Observatory will consist of three flight elements: (1) the Optical Telescope Element (OTE), (2) the Integrated Science Instrument Module Element (ISIM), and (3) the Spacecraft Element. The ISIM element consists of a composite bench structure that uses kinematic mounts to interface to each of the optical benches of the three science instruments and the guider. The ISIM is also kinematically mounted to the telescope primary mirror structure. An enclosure surrounds the ISIM structure, isolates the ISIM region thermally from the other thermal regions of the Observatory, and serves as a radiator for the science instruments and guider. Cryogenic optical testing of the ISIM Structure and the Science Instruments will be conducted at Goddard Space Flight Center using an optical telescope simulator that is being developed by a team from Ball Aerospace and Goddard Space Flight Center, and other local contractors. This simulator will be used to verify the performance of the ISIM element before delivery to the Northup Grumman team for integration with the OTE. In this paper, we describe the O OTE Sim TE Simulator (OSIM) and provide a brief overview of the optical test program. ulator

Cryogenic Optical Position Encoders for Mechanisms in the JWST Optical Telescope Element Simulator (OSIM)

The JWST Optical Telescope Element Simulator (OSIM) is a configurable, cryogenic, optical stimulus for high fidelity ground characterization and calibration of JWST’s flight instruments. OSIM and its associated Beam Image Analyzer (BIA) contain several ultra-precise, cryogenic mechanisms that enable OSIM to project point sources into the instruments according to the same optical prescription as the flight telescope will image stars – correct in focal surface position and chief ray angle. OSIM’s and BIA’s fifteen axes of mechanisms navigate according to redundant, cryogenic, absolute, optical encoders – 32 in all operating at or below 100 K. OSIM’s encoder subsystem, the engineering challenges met in its development, and the encoders’ sub-micron and sub-arcsecond performance are discussed.

Cryogenic system for interferometry of high-precision optics at 20 K: design and performance

This report describes the facility and experimental methods at the Goddard Space Flight Center Optics Branch for the measurement of the surface figure of cryogenically-cooled spherical mirrors using standard phase-shifting interferometry, with a standard uncertainty below 2nm rms. Two developmental silicon carbide mirrors were tested: both were spheres with radius of curvature of 600 mm, and clear apertures of 150 mm. The mirrors were cooled within a cryostat, and the surface figure error measured through a fused-silica window. The GSFC team developed methods to measure the change in surface figure with temperature (the cryo-change) with a combined standard uncertainty below 1 nm rms. This paper will present the measurement facility, methods, and uncertainty analysis.

H2RG detector characterization for RIMAS and instrument efficiencies

The Rapid infrared IMAger-Spectrometer (RIMAS) is a near-infrared (NIR) imager and spectrometer that will quickly follow up gamma-ray burst afterglows on the 4.3-meter Discovery Channel Telescope (DCT). RIMAS has two optical arms which allows simultaneous coverage over two bandpasses (YJ and HK) in either imaging or spectroscopy mode. RIMAS utilizes two Teledyne HgCdTe H2RG detectors controlled by Astronomical Research Cameras, Inc. (ARC/Leach) drivers. We report the laboratory characterization of RIMASs detectors: conversion gain, read noise, linearity, saturation, dynamic range, and dark current. We also present RIMASs instrument efficiency from atmospheric transmission models and optics data (both telescope and instrument) in all three observing modes.