Manufacturing and integration status of the JWST OSIM optical simulator

Abstract

OSIM is a full field, cryogenic, optical simulator of the James Webb Space Telescope (JWST) Optical Telescope Element (OTE). It provides simulated point source/star images for optical performance testing of the JWST Integrated Science Instrument Module (ISIM). OSIM is currently being assembled at the Goddard Space Flight Center (GSFC). In this paper, we describe the capabilities, design, manufacturing and integration status, and uses of the OSIM during the optical test program of ISIM and the Science Instruments. Where applicable, the ISIM tests are also described.

The integration and test program of the James Webb Space Telescope

“…The fully integrated ISIM is located in the He-cooled upper portion of the test chamber, achieving its 35-40K operating temperature within a Surrogate Thermal Management System that emulates the thermal interface temperatures the ISIM will see when mounted in the JWST observatory. The science instruments are fed an optical beam from the Optical Telescope Element Simulator (OSIM) 11 , which operates at 100K in the lower LN2-cooled portion of the test chamber and accurately replicates the optical beam that will ultimately delivered to the ISIM by the JWST OTE in the critical parameters of wavefront quality, image position, f/#, chief ray angle, and pupil position. The 100K operating temperature for OSIM was chosen to be just cold enough to support optical testing of the mid-infrared instrument MIRI in its shortest wavelength band (5.6 μm -the longer MIRI wavelength bands would be saturated by a 100K input), while not placing undue cryogenic demands on the various optical elements, light sources, and mechanisms that make up the OSIM.…”

Ray-tracing for coordinate knowledge in the JWST Integrated Science Instrument Module

“…OSIM is a finite-conjugate, optical relay which enables simultaneous, CV stimulus of all ISIM science instruments with accurate exit pupil and image coordinates [4,5]. Its basic optical design is similar to a Schmidt telescope with the corrector plate omitted.…”

Pupil alignment considerations for large deployable space telescopes

“…At that point the relative position between the OSIM PAR and the science instrument PAR is encoded in the beam. The light then travels back out of the instrument towards the OSIM, passes through the OSIM beamsplitter and then is collected by a detector in the OSIM's pupil imaging module (PIM) 8 ( Figure 7 shows an image of the PIM hardware being prepared for cryogenic performance verification). The collected image is then analyzed to determine the relative location and rotation of the science instrument PAR with respect to the OSIM PAR.…”

“…Due to the optical test architecture developed for the JWST program, the most thorough investigation of the telescope's pupil alignment will occur during the ISIM Element's cryogenic thermal vacuum test campaign using an OTE surrogate called the OSIM (OTE Simulator) 8,9 . During the observatory-level testing, currently planned to occur in the large (27 m high and 17 m diameter internal volume) thermal vacuum chamber, Chamber A, at the Johnson Space Center (JSC) 10 , pupil characteristics will only be checked at three points in the telescope's field of view.…”