In order to perform spectrometric measurements, the Near Infrared Spectrometer (NIRSpec) aboard the James Webb
Space Telescope (JWST) needs the ability to select various spectral band widths and split these up into its comprised
wavelengths. These functions are achieved by the Filter Wheel Assembly (FWA) and the Grating Wheel Assembly
(GWA). The filters of the FWA select a different bandwidth of the spectrum each while the gratings on the GWA yield
specific diffractive characteristic for spectral segmentation. A high spectral sensitivity as well as the ability to detect the
spectra of various objects at the same time result in high requirements regarding the positioning accuracy of the optics of
both mechanisms in order to link the detected spectra to the 2-dimensional images of the observed objects.
The NIRSpec mechanism including FWA and GWA will operate at temperature levels below 42K which are established
during testing inside of a cryostat. However the alignment and testing of these mechanisms requires a lot of thought since
there is very limited access to the item under test within such a device. Alignment needs to be preloaded based on
simulations and testing is reduced to optical methods and evaluation of electrical signals.
This paper describes the methods used for the various alignment steps, the corresponding tests and their precision of
measurement as well as the achieved accuracies in the mechanism performance.
The Mid Infrared Instrument (MIRI) aboard JWST is equipped with one filter wheel and two dichroic-grating wheel
mechanisms to reconfigure the instrument between observing modes such as broad/narrow-band imaging, coronagraphy
and low/medium resolution spectroscopy. Key requirements for the three mechanisms with up to 18 optical elements on
the wheel include: (1) reliable operation at T = 7 K, (2) high positional accuracy of 4 arcsec, (3) low power dissipation,
(4) high vibration capability, (5) functionality at 7 K < T < 300 K and (6) long lifetime (5-10 years). To meet these
requirements a space-proven wheel concept consisting of a central MoS2-lubricated integrated ball bearing, a central
torque motor for actuation, a ratchet system with monolithic CuBe flexural pivots for precise and powerless positioning
and a magnetoresistive position sensor has been implemented. We report here the final performance and lessons-learnt
from the successful acceptance test program of the MIRI wheel mechanism flight models. The mechanisms have been
meanwhile integrated into the flight model of the MIRI instrument, ready for launch in 2014 by an Ariane 5 rocket.
The High-Definition InfraRed (HDIR) thermal-imaging system is a thermal camera with highest geometrical resolution producing a video signal according to the HDTV (High- Definition TeleVision) standard. The thermal-imaging system is a parallel-scanning device with two fold interlace. Its detector is sensitive within the 7-11 micrometers spectral region and features 576 x n elements (n being the number of TDI stages). It has been carefully optimized in terms of range performance and size of optical entrance pupil as well as feasibility of production and yield. The 16:9 aspect ratio of the HDTV standard together with the high number of 1920 pixels/line and 1152 lines propose a drastic increase in range performance. In fact, model calculations predict an increase of up to 60% for identification range as compared to present-standard TV-compatible thermal imagers with the same vertical field of view. With the HDIR having been integrated into a German main battle tank Leopard 2, trials were undertaken in comparison with other equipment like the OPHELIOS and the Common Module WBG-X.