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High Resolution Instrument (HRI)

NSSDCA ID: 2005-001A-01

Mission Name: Deep Impact/EPOXI
Principal Investigator:Dr. Michael F. A'Hearn


The High Resolution Instrument (HRI) is a combination multi-spectral charged-couple device (CCD) camera and infrared (IR) spectrometer. The instrument consists of a 30 cm aperture f/35 telescope and a Spectral Imaging Module (SIM). The telescope is a 35.5 cm diameter graphite composite tube housing light baffles and zerodur glass primary and secondary mirrors. It is a Cassegrain design with a focal length of 10.5 meters. The telescope focuses light into a dichroic beam splitter in the SIM. The beam splitter reflects visible light (0.3 to 1.0 microns) to the camera and transmits near-infrared light (1 to 5 microns) to the IR spectrometer.

The camera has a 1008 x 1008 active pixel split frame transfer CCD with a field of view of 2 milliradians (0.118 degrees or 2 microradians/pixel). It has a filter wheel for multi-spectral capabilities. The wheel contains two clear apertures and seven filters. Five of the filters are centered at 450, 550, 650, 750, and 850 nanometers. A low bandpass filter effectively measures 340 to 400 nm, and a high bandpass filter allows 900 to 960 nm, the low and high ends of the range defined by the beamsplitter reflectivity and the CCD response, respectively. Full frame readout time is 1.8 seconds. At closest approach the camera will be operated in a 128 x 128 pixel sub-frame mode to allow more rapid imaging. The CCD camera will be able to image the comet nucleus with a resolution of about 1.4 meters per pixel when the spacecraft is 700 km away, the approximate distance at final imaging.

The IR spectrometer is designed to measure spectral reflectivity and thermal emission of the nucleus and dust and the emission bands of water, carbon monoxide, and carbon dioxide, the most abundant volatiles. The spectrometer detector uses a 2 prism design (one of CaF2 and one of ZnSe) and a 1024 (wavelength) by 1024 (spatial) HgCdTe focal plane array. Only half the device is active, giving an effective detector area of 1024 x 512. The central quarter of the detector is covered with a neutral density filter due to likely saturation problems imaging warm areas of the nucleus. The entrance slit is 2.53 milliradians by 10 microradians (0.145 degrees by 2 arcseconds). The camera and collimator lead to an effective f/12 with a focal length of 360 cm. It will have a resolution of 10 meters at closest approach. The spectral range is 1.05 to 4.8 microns, spectral resolution varies from 740 (lambda/delta-lambda) at 1.05 microns to a minimum of 210 at 2.5 microns and back up to 385 at 4.8 microns.

Alternate Names

  • Deep Impact High Resolution Instrument - IR Spectrometer
  • Deep Impact High Resolution Instrument - Visible CCD
  • DeepImpact/HRI
  • HRI
  • HRII
  • HRIV
  • urn:nasa:pds:context:instrument:dif.hrii
  • urn:nasa:pds:context:instrument:dif.hriv

Funding Agency

  • NASA-Office of Space Science Applications (United States)


  • Planetary Science: Small Bodies

Additional Information

Questions and comments about this experiment can be directed to: Dr. David R. Williams



NameRoleOriginal AffiliationE-mail
Dr. Michael F. A'HearnPrincipal InvestigatorUniversity of Maryland

Selected References

  • Hampton, D. L., et al., An Overview of the Instrument Suite for the Deep Impact Mission, Space Sci. Rev., 117, No. 1-2, 43-93, Mar. 2005.
  • Wellnitz, D. D., et al., The location of the impact point of the Deep Impact Impactor on Comet 9P/Tempel 1, Icarus, 222, No. 2, 487-491, doi:10.1016/j.icarus.2012.08.003, Feb. 2013.
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