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NIRSpec Instrument Engineering Test Unit model is completed

NIRSpec Instrument Engineering Test Unit model is completed

14 October 2009

The Engineering Test Unit model of NIRSpec - the innovative and pioneering Near Infrared Spectrograph for the James Webb Space Telescope - has been completed by the prime contractor, EADS Astrium, and is ready to be shipped to NASA for testing.

The James Webb Space Telescope (JWST) is a large (6.5 m), cold (<50 K), infrared-optimised telescope designed to address a number of key topics in modern astronomy, which include identifying the first stars and galaxies and, studying how they have evolved.

The NIRSpec Engineering Test Unit. Credit: EADS Astrium

When launched in 2014 JWST will carry a suite of four scientific instruments including NIRSpec - an innovative multi-object spectrograph designed to obtain spectra of up to 100 objects simultaneously. NIRSpec's multi-object capability combined with the sensitivity of the JWST telescope will be essential for determining the age, chemical composition and distances of faint galaxies. These measurements are key to unravelling the history of galaxy formation in the early Universe – one of the primary science goals of the JWST mission.

The NIRSpec ETU: a representative replica for realistic testing

The NIRSpec demonstration model during vibration tests. Credit: EADS Astrium

The NIRSpec Engineering Test Unit (ETU) model realistically replicates the thermal, mechanical, electrical and optical characteristics (up to the micro-shutter array) of the real flight model instrument. This ETU has been subject to an extensive series of tests at the Astrium and IABG facilities in Munich, Germany. These tests included vibration tests at room temperature, thermal vacuum and optical performance tests at cryogenic temperatures, and electromagnetic characterisation tests at room and cryogenic temperatures. At the end of this test campaign the flight model representative Collimator and Camera optical systems, built from SiC - the material that will be used for the flight elements - were removed and replaced by dummy masses.

The ETU will be shipped, later this year, to NASA's Goddard Space Flight Centre for pre-integration testing with the Integrated Science Instrument Module (ISIM), a key element of the JWST observatory which houses the four science instruments (NIRSpec, NIRCam, MIRI, and TFI), the associated electronics, and other components.

Progress on the NIRSpec flight model

The NIRSpec camera optics during cryo testing at CSL, Belgium. Credit: Sagem Défense Sécurité

In the meantime the NIRSpec flight model optical bench is beginning to take shape with integration and alignment activities for several flight model subsystems underway at Astrium since January this year.

A comprehensive test campaign for the complete flight model will begin mid-2010. In early 2011 the complete NIRSpec flight model is scheduled to be delivered to NASA for integration with the flight model ISIM.

Elements of the observatory begin to take shape

This year has seen a number of key elements of the JWST observatory pass significant milestones:

  • September 2009: The flight model of the ISIM is delivered to GSFC for testing
  • July 2009: The JWST spacecraft passes its Preliminary Design Review
  • April 2009: The first of 18 flight mirrors completes cryogenic testing
  • March 2009: The sunshield passes the Preliminary Design Review and moves to the detailed design phase
  • February 2009: Construction of the telescope backplane begins

JWST and NIRSpec

The JWST observatory is a joint project of NASA, ESA and the Canadian Space Agency. It is scheduled to launch in 2014 and will carry four scientific instruments: NIRSpec (a near-infrared spectrograph), NIRCam (a near-infrared camera ), MIRI (a mid-infrared camera and spectrograph) and TFI (a tunable filter imager).

NIRSpec will be the principal spectrographic instrument on board the observatory. It is built by European industry to ESA's specifications and managed by the ESA JWST Project at ESTEC, the Netherlands. The prime contractor is EADS Astrium GmbH in Ottobrunn, Germany. The NIRSpec detector and Multi-Shutter Array subsystems are provided by NASA's Goddard Space Flight Center.

For more information:

Giorgio Bagnasco, ESA NIRSpec Instrument Manager
Science and Robotic Exploration Directorate, ESA, The Netherlands.
Email:; Phone: +31-71-565-8371

Last Update: 1 September 2019
18-Apr-2021 00:41 UT

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