PDS_VERSION_ID = PDS3 LABEL_REVISION_NOTE = " 2004-08-25 S.McLaughlin Created 2005-02-04 S.McLaughlin Resolved liens " 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 = " The instrument overview was provided by Dr. Michael A'Hearn, the principal investigator for the Deep Impact mission. For a detailed discussion of the instrument, see Hampton, et al. (2005) [HAMPTONETAL2005]. Instrument Overview =================== The High Resolution Imager (HRI) consists of a long-focal-length telescope followed by a dichroic beam splitter that reflects visible (0.3 to 1.0 microns) light through a filter wheel to a CCD for direct, optical imaging. The beam splitter transmits the near-infrared light (1 to 5 microns) to a 2-prism spectrometer. For convenience, we consider these as two separate instruments, HRIV and HRII, sharing the telescope since the two focal planes operate in parallel asynchronously. The HRI telescope is 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 m) Back focal distance : 30.0 cm The beam-splitter is a dichroic with equal transmission and reflection occurring at about 1.05 microns and it is placed in front of the telescope focal plane. The spectrometer is a 2-prism design, one of calcium flouride (CaF_2) and one of zinc selenide (ZnSe) to maximize etendue and minimize problems with order separation. The camera and collimator lead 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 subtends 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 matches the binned pixel (2x2) used for most observations. The near-infrared detector is a 1024 (wavelength) x 512 (spatial) pixel silver cadium 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 is a 1024 x 1024 device, but only half of the device is active. Pixels are 18 microns square and normal operations include 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 probable saturation problems in warm areas of the nucleus, the central quarter of the detector is covered with a neutral density filter. When operated in the 512 x 256 pixel, 2x2 binning mode, the HRII instrument has the following field-of-view characteristics: Spatial ------- Pixel Size : 36 micrometers Pixel FOV : 10.0 microradians FOV : 2.5 milliradians or 0.15 degrees Spectral -------- Pixel FOV : 10.0 microradians FOV : 10.0 microradians (slit width) The three instruments on the flyby spacecraft, HRII, HRIV and MRI, are mounted on a separate instrument platform together with the star trackers. The three instruments are nominally co-aligned. " END_OBJECT = INSTRUMENT_INFORMATION OBJECT = INSTRUMENT_REFERENCE_INFO REFERENCE_KEY_ID = "HAMPTONETAL2005" END_OBJECT = INSTRUMENT_REFERENCE_INFO END_OBJECT = INSTRUMENT END