Wolfgang Holota

Ultra-precisely manufactured mirror assemblies with well-defined reference structures

Aspherical surfaces for imaging or spectroscopy are a centerpiece of high-performance optics. Due to the high alignment sensitivity of aspheric surfaces, reference elements and interfaces with a tight geometrical relation to the mirror are as important as the high quality of the optical surface itself. The developed manufacturing method, which accounts for the shape and also for the position of the mirror surfaces, allows controlling and precisely correcting not only the form, but also the alignment of reference marks, interfaces or even other mirrors in the sub-assembly using diamond turning. For Korsch or TMA telescopes it is also possible to diamond turn whole sub-assemblies containing two or more mirrors with a relative position error as low as the machine precision. Reference elements allow the correction of the shape and position of mirrors as well as the position of interfaces for system integration. The presented method opens up a novel manufacturing strategy to enhance the relative positioning accuracy of optic assemblies by one order of magnitude.

NIRSpec: near-infrared spectrograph for the JWST

The James Webb Space Telescope (JWST) is a passively cooled, 6.5m aperture class telescope, optimized for diffraction-limited performance in the near-infrared wavelength region (1 - 5 μm). JWST will be capable of high-resolution imaging and spectroscopy and will carry a scientific payload consisting of three scientific instruments. One of the instruments - NIRSpec - is a near-infrared, multi-object, dispersive spectrograph, which will be provided by ESA. EADS Astrium and its subcontractors have been involved in all ESA instrument studies for JWST. The actual NIRSpec design has evolved during three years of studying of different spectrometer design and performance options. Basic feature of the current design is the all ceramic material concept for the instrument structure and mirror optics; both were successfully tested on component level. This paper presents our NIRSpec design concept and its predicted performance.

The James Webb Space Telescope science instrument suite: an overview of optical designs

The James Webb Space Telescope (JWST) Observatory, the follow-on mission to the Hubble Space Telescope and to the Spitzer Space Facility, will yield astounding breakthroughs in the realms of infrared space science. The science instrument suite for this Observatory will consist of a Near-Infrared Camera, a Near-Infrared Spectrograph, a Mid-Infrared Instrument with imager, coronagraph and integral field spectroscopy modes, and a Fine Guider System Instrument with both a Guider module and a Tunable Filter Module. In this paper we present an overview of the optical designs of the telescope and instruments.

Large aperture freeform VIS telescope with smart alignment approach

The development of smart alignment and integration strategies for imaging mirror systems to be used within astronomical instrumentation are especially important with regard to the increasing impact of non-rotationally symmetric optics. In the present work, well-known assembly approaches preferentially applied in the course of infrared instrumentation are transferred to visible applications and are verified during the integration of an anamorphic imaging telescope breadboard. The four mirror imaging system is based on a modular concept using mechanically fixed arrangements of each two freeform surfaces, generated by servo assisted diamond machining and corrected using Magnetorheological Finishing as a figuring and smoothing step. Surface testing include optical CGH interferometry as well as tactile profilometry and is conducted with respect to diamond milled fiducials at the mirror bodies. A strict compliance of surface referencing during all significant fabrication steps allow for an easy integration and direct measurement of the systems wave aberration after initial assembly. The achievable imaging performance, as well as influences of the tight tolerance budget and mid-spatial frequency errors, are discussed and experimentally evaluated.

Optical design of the near-infrared spectrograph NIRSpec

The near-infrared spectrograph (NIRSpec) is part of the James Webb Space Telescope (JWST) science mission: NIRSpec is a spectrograph that works in the near infrared spectral region (0.6micron - 5.0micron) and allows the observation of spectral features of the incident star light with different spectral resolution (R=100, R=1000, R=3000). It is designed for spectroscopy of more than 100 objects simultaneously. The optical design of the NIRSpec instrument is characterized by a straight optical system layout: It constitutes of a set of optical modules of similar optical design type with high performance and low module tolerances. The NIRSpec instrument development is a cooperation of the European Space Agency and EADS Astrium Germany GmbH as prime contractor for instrument development, design, and manufacturing.

Opto-mechanical design of the near-infrared spectrograph NIRSpec

The NIRSpec instrument on the James Webb Space Telescope (JWST) is a multi-object spectrograph capable of measuring the near infrared spectrum of at least 100 objects simultaneously at various spectral resolutions. It operates under cryogenic conditions (T~ 35 K). NIRSpec is part of the JWST science instruments suite. Its main purpose is to provide low (R=100), medium (R=1000) and high resolution (R=2700) spectroscopic observations over the wavelength range 0.6 μm - 5.0 μm in support of the four JWST science programs. The NIRSpec instrument is being developed by the European Space Agency with EADS Astrium Germany GmbH as the prime contractor.

The European optical contribution to the James Webb Space Telescope

Abstract The James Webb Space Telescope (JWST) is frequently referred to as the follow-on mission to the Hubble Space Telescope (HST). The ‘Webb’ will be the biggest space telescope ever built and is expected to enable astounding new science. The observatory comprises a 6.5-m-diameter telescope with a segmented primary mirror and four high-performance optical science instruments. The JWST has mostly been optimized to work in the near- (0.6–5.0 μm) and mid-infrared (5.0–29 μm) wavelength regions. The project is a strong international partnership led by the National Aeronautics and Space Administration (NASA) with contributions from the European Space Agency (ESA) and the Canadian Space Agency (CSA). The observatory is currently scheduled for launch in early 2021 from Kourou, French Guyana, by an ESA-provided Ariane 5 rocket. This paper will focus on the European optical contribution to the mission, which mainly consists of two highly advanced optical science instruments: The multi-object near-infrared spectrograph (NIRSpec) and the mid-infrared instrument (MIRI). The opto-mechanical design considerations and the realization of both instruments will be described, and we will conclude with a short JWST project status report and future outlook.