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Composite Infrared Spectrometer (CIRS)

NSSDCA ID: 1997-061A-05

Mission Name: Cassini
Principal Investigator:Mr. Virgil G. Kunde


The Composite Infrared Spectrometer (CIRS) on Cassini is designed to measure infrared emissions from atmospheres, rings, and surfaces over a wavelength range between 7 and 1000 micrometers. Its objectives for Saturn and Titan are to: (1) map the global atmospheric temperature structure; (2) map the global atmospheric gas composition; (3) ascertain global atmospheric haze and cloud distributions; (4) gather information on atmospheric energetic processes; and, (5) search for new atmospheric molecular species. Additional goals are to: (6) map global surface temperatures at Titan; and, (7) to determine the thermal characteristics and composition of Saturn's rings and icy satellites. To accomplish these goals, CIRS consists of a 50.8 cm Cassegrain telescope and three interferometers, a far-infrared, a mid-infrared, and a reference interferometer.

The far-infrared interferometer covers a spectral range from 17-1000 micrometers (10-600/cm). The instrument is a polarizing interferometer with substrate-mounted wire grid polarizers to polarize the radiation and subsequently modulate the polarization. The instrument has a 4.3 milliradian field of view.

The mid-infrared interferometer is of conventional Michelson design and covers a spectral range of 7-17 micrometers (600-1400/cm) in two bands. The first band (9-17 micrometers or 600-1000/cm) is imaged on a 1 x 10 photoconductive HgCdTe detector array. The second band (7-9 micrometers or 1100-1400/cm) is imaged on a 1 x 10 photovoltaic HgCdTe detector array. Each element in each detector array consists of a 0.273 milliradian square pixel.

The reference interferometer provides timing correlation of the science data sampling to the scan mechanism position. Also of a Michelson design, it is used on-axis at the optic center of the mid-infrared interferometer and includes laser diode and LED sources, a quartz beam-splitter/compensator, optics, and a silicon detector.

A 70-80 K cold finger serves as a single-stage passive cooler, radiating to space. There are four commandable set points within the range, but the nominal setting is 80 K. The cold finger has heaters for decontamination and detector annealing.

Alternate Names

  • CIRS
  • Cassini/CIRS

Facts in Brief

Mass: 39.24 kg
Power (avg): 26.4 W
Bit rate (avg): 6 kbps

Funding Agency

  • NASA-Office of Space Science (United States)


  • Planetary Science: Atmospheres

Additional Information

Questions and comments about this experiment can be directed to: Dr. Edwin V. Bell, II



NameRoleOriginal AffiliationE-mail
Dr. Barney J. ConrathCo-InvestigatorNASA Goddard Space Flight Center
Dr. Tobias C. OwenCo-InvestigatorUniversity of Hawaii
Dr. John C. PearlCo-InvestigatorNASA Goddard Space Flight
Dr. Renee M. PrangeCo-InvestigatorInstitut d Astrophysique
Dr. Robert E. SamuelsonCo-InvestigatorNASA Goddard Space Flight Center
Dr. Peter J. GieraschCo-InvestigatorCornell
Dr. Fredric W. TaylorCo-InvestigatorOxford
Dr. Glenn S. OrtonCo-InvestigatorNASA Jet Propulsion
Dr. F. Michael FlasarCo-InvestigatorNASA Goddard Space Flight
Dr. Daniel GautierCo-InvestigatorObservatoire de Paris,
Dr. Donald E. JenningsCo-InvestigatorNASA Goddard Space Flight
Dr. Regis D. CourtinCo-InvestigatorObservatoire de Paris,
Dr. Mian M. AbbasCo-InvestigatorNASA Marshall Space Flight
Dr. Francois RaulinCo-InvestigatorUniversite
Dr. Bruno BezardCo-InvestigatorObservatoire de Paris,
Dr. John C. BrasunasCo-InvestigatorNASA Goddard Space Flight
Dr. Gordon L. BjorakerCo-InvestigatorNASA Goddard Space Flight
Dr. C. CesarskyCo-InvestigatorCentre d'Etudes Nucleaires de
Dr. Paul N. RomaniCo-InvestigatorNASA Goddard Space Flight
Dr. Peter AdeCo-InvestigatorQueen Mary and Westfield College,
Dr. Antonella BarucciCo-InvestigatorObservatoire de Paris,
Dr. Simon CalcuttCo-InvestigatorOxford
Dr. Angioletta CoradiniCo-InvestigatorUniversita la Sapienza
Dr. Athena CoustenisCo-InvestigatorObservatoire de Paris,
Dr. Klaus GrossmanCo-InvestigatorUniversitat-Gesanthochschule
Dr. Emmanuel LellouchCo-InvestigatorObservatoire de Paris,
Dr. Andre MartenCo-InvestigatorObservatoire de Paris,
Dr. Jean-Paul MeyerCo-InvestigatorCentre d'Etudes Nucleaires de
Dr. Peter ReadCo-InvestigatorOxford
Mr. Virgil G. KundePrincipal InvestigatorNASA Goddard Space Flight

Selected References

  • Kunde, V. G., et al., Cassini infrared Fourier spectroscopic investigation, in Proc. SPIE Cassini/Huygens: A Mission to the Saturnian Systems Vol. 2803, 162-177, L. Horn Ed., doi:10.1117/12.253416, Oct. 1996.
  • Flasar, F. M., et al., Exploring The Saturn System In The Thermal Infrared: The Composite Infrared Spectrometer, Space Sci. Rev., 115, 169-297, doi:10.1007/s11214-004-1454-9, 2004.
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