Maurice te Plate

Overview of the near-infrared spectrograph (NIRSpec) instrument on-board the James Webb Space Telescope (JWST)

The James Webb Space Telescope (JWST) mission is a collaborative project between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA). JWST is considered the successor to the Hubble Space Telescope (HST) and although its design and science objectives are quite different, JWST is expected to yield equivalently astonishing breakthroughs in infrared space science. Due to be launched in 2013 from the French Guiana, the JWST observatory will be placed in an orbit around the anti- Sun Earth-Sun Lagrangian point, L2, by an Ariane 5 launcher, provided by ESA. The payload on board the JWST observatory consists of four main scientific instruments: a near-infrared camera (NIRCam), a combined mid-infrared camera/spectrograph (MIRI), a near-infrared tunable filter (TFI) and a nearinfrared spectrograph (NIRSpec). The instrument suite is completed by a Fine Guidance Sensor (FGS). Besides the provision of the Ariane 5 launcher, ESA, with EADS Astrium GmbH (D) as Prime Contractor, is fully responsible for the funding and the furnishing of NIRSpec and, at the same time, for approximately half of MIRI costs through special contributions from the ESA member states. NIRSpec is a multi-object, spectrograph capable of measuring the spectra of about 100 objects simultaneously at low (R=100), medium (R=1000), and high (R=2700) resolutions over the wavelength range between 0.6 micron and 5.0 micron. In this article we provide a general overview of its main design features and performances.

The JWST near-infrared spectrograph NIRSpec: status

The Near-Infrared Spectrograph NIRSpec is one of the four instruments of the James Webb Space Telescope (JWST). NIRSpec will cover the 0.6-5.0 micron range and will be capable of obtaining spectra of more than 100 objects simultaneously in its multi-object spectroscopy (MOS) mode. It also features a set of slits and an aperture for high contrast spectroscopy of individual sources, as well as an integral-field unit (IFU) for 3D spectroscopy. We will first show how these capabilities are linked to the four main JWST scientific themes. We will then give an overview of the NIRpec modes and spectral configurations with an emphasis on the layout of the field of view and of the spectra. Last, we will provide an update on the status of the instrument.

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.

LISA pathfinder optical interferometry

The LISA Technology Package (LTP) aboard of LISA pathfinder mission is dedicated to demonstrate and verify key technologies for LISA, in particular drag free control, ultra-precise laser interferometry and gravitational sensor. Two inertial sensor, the optical interferometry in between combined with the dimensional stable Glass ceramic Zerodur structure are setting up the LTP. The validation of drag free operation of the spacecraft is planned by measuring laser interferometrically the relative displacement and tilt between two test masses (and the optical bench) with a noise levels of 10pm/√Hz and 10 nrad/√Hz between 3mHz and 30mHz. This performance and additionally overall environmental tests was currently verified on EM level. The OB structure is able to support two inertial sensors (≈17kg each) and to withstand 25 g design loads as well as 0...40°C temperature range. Optical functionality was verified successfully after environmental tests. The engineering model development and manufacturing of the optical bench and interferometry hardware and their verification tests will be presented.

Optical wavefront characterization using phase retrieval for the NIRSpec demonstration model for the James Webb Space Telescope

Phase retrieval results are presented for the James Webb Space Telescope (JWST) Near InfraRed Spectrograph (NIRSpec) demonstration model (DM). NIRSpec is one of five science instruments (SIs) comprising the Integrated Science Instrument Module (ISIM); the NIRSpec is being built for the European Space Agency by a consortium led by EADS Astrium GmbH. During this initial DM test campaign, focal-sweep images were collected over the science field of view (FOV) for determining best focus at both ambient and cryogenic (cryo) temperature environments, and these images were then used as input to the Hybrid Diversity Algorithm (HDA) for phase retrieval, using Variable Sampling Mapping (VSM). Wavefront estimates from phase retrieval, an error budget, and diagnostics used to assess phase retrieval stability and convergence are discussed. The ambient phase retrieval results were compared against wavefront measurements taken with a Shack-Hartmann wavefront sensor.

Cryogenic pupil alignment test architecture for the James Webb Space Telescope integrated science instrument module

The James Webb Space Telescope (JWST) is a space-based, infrared observatory designed to study the early stages of galaxy formation in the Universe. It is currently scheduled to be launched in 2013 and will go into orbit about the second Lagrange point of the Sun-Earth system and passively cooled to 30-50 K to enable astronomical observations from 0.6 to 28 μm. The JWST observatory consists of three primary elements: the spacecraft, the optical telescope element (OTE) and the integrated science instrument module (ISIM). The ISIM Element primarily consists of a mechanical metering structure, three science instruments and a fine guidance sensor with significant scientific capability. One of the critical opto-mechanical alignments for mission success is the co-registration of the OTE exit pupil with the entrance pupils of the ISIM instruments. To verify that the ISIM Element will be properly aligned with the nominal OTE exit pupil when the two elements come together, we have developed a cryogenic pupil measurement test architecture to measure three of the most critical pupil degrees-of-freedom during optical testing of the ISIM Element. The pupil measurement scheme makes use of: specularly reflective pupil alignment references located inside of the JWST instruments; ground support equipment that contains a pupil imaging module; an OTE simulator; and pupil viewing channels in two of the JWST flight instruments. Current modeling and analysis activities indicate this measurement approach will be able to verify pupil shear to an accuracy of 0.5-1%.

The integral field unit for the James Webb space telescope's near-infrared spectrograph.

The European Space Agency (ESA) is providing the Near Infrared Spectrograph (NIRSpec) developed by EADS Astrium GmbH to fly on the James Webb Space Telescope (JWST). NIRSpec covers the 0.6-5.0 µm domain. It will be primarily operated as a multi-object spectrograph, using a MEMS micro-shutter array (MSA) provided by NASA to select multiple objects from the field of view at an intermediate image plane formed by the NIRSpec fore-optics. The MSA apertures form multiple entrance slits of the spectrometer section.

The accuracy of the NIRSpec grating wheel position sensors

We present a detailed analysis of measurements collected during the first ground-based cryogenic calibration campaign of NIRSpec, the Near-Infrared Spectrograph for the James Webb Space Telescope (JWST). In this paper we concentrate on the performances of the NIRSpec grating wheel, showing that the magneto-resistive position sensors installed on the wheel provide very accurate information on the position of the wheel itself, thereby enabling an efficient acquisition of the science targets and a very accurate extraction and calibration of their spectra.

The Near Infrared Spectrograph (NIRSpec) on-ground calibration campaign

The Near Infrared Spectrograph (NIRSpec) is one of four science instruments aboard the James Webb Space Telescope (JWST) scheduled for launch in 2018. NIRSpec is sensitive in the wavelength range from ~0.6 to 5.0 micron and will be capable of obtaining spectra from more than a 100 objects simultaneously by means of a programmable micro shutter array. It will also provide an integral eld unit for 3D spectroscopy and xed slits for high contrast spectroscopy of individual sources and planet transit observations. We present results obtained during the rst cryogenic instrument testing in early 2011, demonstrating the excellent optical performance of the instrument. We also describe the planning of NIRSpecs forthcoming second calibration campaign scheduled for early 2013.

Calibrating the position of images and spectra in the NIRSpec instrument for the James Webb Space Telescope

The Near Infrared Spectrograph (NIRSpec) is one of four science instruments on board the James Webb Space Telescope (JWST). NIRSpec offers multi-object, fixed slit, and integral field spectroscopy. There are eight optical elements mounted on the grating wheel assembly (GWA), six gratings, a double-pass prism, and a mirror. The precise knowledge of the position and tilt of these elements is critical for target acquisition and an accurate extraction and calibration of science data. We present the concept of calibrating the position/tilt sensors during the NIRSpec flight model ground calibration campaign, the performance of the sensors and first results concerning the GWA repeatability.