The Near-Infrared Spectrograph (NIRSpec) is a near infrared multi-object dispersive spectrograph capable of simultaneously observing more than 100 sources over a field-of-view (FOV) larger than 3' x 3'. The NIRSpec will be the first spectrograph in space that has this capability. Targets in the Field of View are normally selected by opening groups of shutters in a micro-shutter array (MSA) to form multiple apertures. The microshutters are arranged in a waffle-like grid that contains more than 62000 shutters with each cell measuring 100 µm x 200 µm. Sweeping a magnet across the surface of the MSA opens all operable shutters. Individual shutters may then be addressed and closed electronically. NIRSpec is also capable of Fixed-slit and Integral-field spectroscopy and provides medium-resolution spectroscopy over a wavelength range of 1 - 5 µm and lower-resolution spectroscopy from 0.6 - 5 µm.
NIRSpec will address all of the four main JWST science themes, and much more. It will enable large spectroscopic surveys of faint galaxies at high redshift, obtain sensitive spectra of transiting exoplanets and image line emission from protoplanetary disks and protostars. NIRSpec is being built for the European Space Agency (ESA) by the Astrium consortium with Dr. Pierre Ferruit guiding its development as the ESA JWST Project Scientist. Peter Jakobsen, the NIRSpec Instrument PI, retired in December 2011.
By late September NIRSpec had completed a series of operational tests at Goddard Space Flight Center. These tests included all of JWST's instruments, assembled for the first time in the Integrated Science Instrument Module (ISIM). This ISIM test cooled the instruments to about 40 K, the expected operation temperature for JWST's instruments once the telescope is launched. This test was successful in providing critical information on how the instruments work individually and together. Following these tests, ISIM was removed from the vacuum chamber and taken apart.
NIRSpec is due to get new sets of detectors and micro-shutter arrays (MSAs) in December of this year. Those new items will be the ones that NIRSpec flies with and are improvements over the parts now in the instrument. Next year there will again be a full test of all the instruments integrated as ISIM, and this time we expect to test scenarios that are similar to science observations after launch.
STScI staff worked with ESA scientists to support this year's ISIM tests over the summer and we will again next year. Meanwhile we have been planning and preparing the software that will enable users to create valid and efficient NIRSpec programs, helping to create the needed Exposure Time Calculators, and so on. The launch of JWST is set at four years from now, but before then many milestones must be reached in order to have an effective observatory as soon as possible.
The entire Integrated Science Instrument Module with NIRSpec in it is now being tested under operational conditions in "CV2" (Cryo-Vac Test 2). As of mid-July all the instruments have cooled to their operational temperatures near or below 40 K. ISIM now starts its Comprehensive Performance Test in which all the instruments are tested for functionality. Later tests will emulate the more varied observations expected when NIRSpec is operational. STScI NIRSpec staff will assist in these tests along with the ESA scientists and engineers.
At STScI, NIRSpec staff have been continuing to work on the many aspects of preparing to support science operations. That includes experiments with documentation and user information systems, observation modeling to simulate realistic instrument usage, and working with software developers on planning tools.
NIRSpec has been integrated into ISIM, making ISIM now complete. Basic functionality tests under ambient conditions have all been successful. As part of ISIM, NIRSpec will be extensively tested during CV2, which runs from mid-June to mid-September. Later this year, after CV2, new detectors and new MSAs will be installed in NIRSpec, leading up to the final ISIM test, CV3, in 2015.