PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " 2004-08-25 S.McLaughlin Created 2005-02-04 S.McLaughlin Resolved liens from Oct 2004 thermal-vac review; 2006-05-22 DI:McLaughlin Resolved liens from Apr 2006 peer review; " OBJECT = INSTRUMENT INSTRUMENT_HOST_ID = "DIF" INSTRUMENT_ID = "HRII" OBJECT = INSTRUMENT_INFORMATION INSTRUMENT_NAME = "DEEP IMPACT HIGH RESOLUTION INSTRUMENT - IR SPECTROMETER" INSTRUMENT_TYPE = "INFRARED SPECTROMETER" INSTRUMENT_DESC = " Instrument Overview =================== The High Resolution Imager (HRI) consisted of a long-focal-length telescope with a dichroic beam splitter, located in front of the focal plane, that reflected visible (0.3 to 1.0 microns) light through a filter wheel to a CCD for direct, optical imaging. The beam splitter transmitted the near-infrared light (1 to 5 microns) to a 2-prism spectrometer. For convenience, we considered these as two separate instruments, HRIV and HRII, sharing the telescope since the two focal planes operate in parallel asynchronously. The HRI telescope was a classical Cassegrain design with the following parameters: Primary aperture : 30.0 cm diameter, round Primary focal ratio : 4.5 Secondary Obscuration : 9.7 cm diameter, round Secondary magnification : 7.8x (net Cassegrain focal length 1050 cm) Back focal distance : 30.0 cm The beam-splitter was a dichroic with equal transmission and reflection occurring at about 1.05 microns and was placed in front of the telescope focal plane. The spectrometer was a 2-prism design, one of calcium fluoride (CaF_2) and one of zinc selenide (ZnSe) to maximize etendue and minimize problems with order separation. The camera and collimator led to a net demagnification of 3x, for an effective f/ratio of f/12 and effective focal length of 360 cm in the final beam. The entrance slit subtended on the sky 2.53 milliradians by 10 microradians (0.145 degrees by 2 arcseconds), filling the 512-pixel height of the IR array. The slit width matched the binned pixel (2x2) used for most observations. The near-infrared detector was a 1024 (wavelength) x 512 (spatial) pixel mercury cadmium telluride (HgCdTe) device manufactured by Rockwell using the multiplexer originally developed under contract from the University of Hawaii for use in the WFC3 on HST. Physically, it was a 1024 x 1024 device, but only half of the device is active. Pixels were 18 microns square and normal operations included 2x2 binning (post-readout). Spectral resolving power, because of the 2-prism design, varies from greater than 740 at 1.04 microns down to 210 at 2.6 microns, and back up to 385 at 4.8 microns. Due to saturation problems in warm areas of the nucleus, the central quarter of the detector was covered with a neutral density filter. When operated in the 512 x 256 pixel, 2x2 binning mode, the HRII instrument had the following field-of-view characteristics: Spatial ------- Physical Pixel Size : 36 micrometers Effective Pixel FOV : 10.0 microradians Effective FOV : 2.5 milliradians or 0.15 degrees Spectral -------- Effective Pixel FOV : 10.0 microradians Effective FOV : 10.0 microradians (slit width) The three instruments on the flyby spacecraft, HRII, HRIV, and MRI, were mounted on a separate instrument platform together with the star trackers. The three instruments were nominally co-aligned. For a detailed discussion of the instrument, see Hampton, et al. (2005) [HAMPTONETAL2005]. This instrument overview was provided by Dr. Michael A'Hearn, the principal investigator for the Deep Impact mission. Instrument Calibration ====================== The HRII instrument was calibrated by using in-flight data as well as pre-launch data taken during thermal-vacuum tests (TV1, TV2, and TV4) performed in 2002 and 2003. The calibration of the HRII instrument was discussed in the 'Deep Impact Instrument Calibration' paper by Klaasen, et al. (2006) [KLAASENETAL2006]. Flight Performance ================== The HRII instrument generally performed as expected during flight. Small changes in instrumental temperatures affected the dark current more than expected from ground thermal-vacuum tests. For more information, please see the 'Deep Impact Instrument Calibration' paper by Klaasen, et al. (2006) [KLAASENETAL2006]. Early images of stars using the HRI visible CCD indicated the HRI telescope was out of focus. However, this focus problem did not affect the HRII instrument. " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "HAMPTONETAL2005" END_OBJECT = INSTRUMENT_REFERENCE_INFO OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "KLAASENETAL2006" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END