ESA Science & Technology - Publications Archive
The Cooler Subsystem for the Mid InfRared Instrument (MIRI) of the James Webb Space Telescope (JWST) features a 6 Kelvin Joule-Thomson (JT) cooler pre-cooled by a three-stage Pulse Tube (PT) cryocooler to provide 65 mW of cooling at the instrument. MIRI's 6 Kelvin cooling load, directly behind the primary mirror of JWST, is remote from the location of the compressors and pre-cooler. This distance, and the parasitic heat load on the refrigerant lines spanning it, is accommodated by the design. The effort during 2006 and the first part of 2007 has focused on the demonstration of a MIRI Cooler prototype in the relevant environment, required to achieve Technology Readiness Level 6 (TRL 6) as defined by NASA. The tests that have been used to successfully demonstrate TRL 6: launch vibration and cooler performance in the relevant thermal-vacuum environment, will be discussed.
We have developed microshutter array systems at NASA Goddard Space Flight Center for use as multi-object aperture arrays for a Near-Infrared Spectrometer (NIRSpec) instrument. The instrument will be carried on the James Webb Space Telescope (JWST), the next generation of space telescope, after the Hubble Space Telescope retires. The microshutter arrays (MSAs) are designed for the selective transmission of light from objected galaxies in space with high efficiency and high contrast. Arrays are close-packed silicon nitride membranes with a pixel size close to 100x200 micron. Individual shutters are patterned with a torsion flexure permitting shutters to open 90 degrees with minimized stress concentration. In order to enhance optical contrast, light shields are made on each shutter to prevent light leak. Shutters are actuated magnetically, latched and addressed electrostatically. The shutter arrays are fabricated using MEMS bulk-micromachining and packaged utilizing a novel single-sided indium flip-chip bonding technology. The MSA flight system consists of a mosaic of 2 x 2 format of four fully addressable 365 x 171 arrays. The system will be placed in the JWST optical path at the focal plane of NIRSpec detectors. MSAs that we fabricated passed a series of qualification tests for flight capabilities. We are in the process of making final flight-qualified MSA systems for the JWST mission.
The James Webb Space Telescope's (JWST) Near Infrared Spectrograph (NIRSpec) incorporates two 5 micron cutoff (lambdaco=5 micron) 2048×2048 pixel Teledyne HgCdTe HAWAII-2RG sensor chip assemblies. These detector arrays, and the two Teledyne SIDECAR application specific integrated circuits that control them, are operated in space at T ~ 37 K. In this article, we provide a brief introduction to NIRSpec, its detector subsystem (DS), detector readout in the space radiation environment, and present a snapshot of the developmental status of the NIRSpec DS as integration and testing of the engineering test unit begins.
The James Webb Space Telescope (JWST) Observatory, the follow-on mission to the Hubble Space Telescope, will yield astonishing breakthroughs in infrared space science. One of the four instruments on that mission, the NIRSpec instrument, is being developed by the European Space Agency with EADS Astrium Germany GmbH as the prime contractor. This multi-object spectrograph is capable of measuring the near infrared spectrum of at least 100 objects simultaneously at various spectral resolutions in the 0.6 micron to 5.0 micron wavelength range. A physical optical model, based on Fourier Optics, was developed in order to simulate some of the key optical performances of NIRSpec. Realistic WFE maps were established for both the JWST optical telescope as well as for the various NIRSpec optical stages. The model simulates the optical performance of NIRSpec at the key optical pupil and image planes. Using this core optical simulation module, the model was expanded to a full instrument performance simulator that can be used to simulate the response of NIRSpec to any given optical input. The program will be of great use during the planning and evaluation of performance testing and calibration measurements.
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.