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Thermal Emission Spectrometer (TES)

NSSDC ID: 1992-063A-06
Mission Name: Mars Observer
Principal Investigator: Prof. Philip R. Christensen


The Thermal Emission Spectrometer, or TES, was intended to extend and improve upon measurements of thermal infrared emission instruments carried by earlier missions (Mariners 6, 7, and 9 and Vikings 1 and 2). The primary objectives of the TES were to: (1) determine and map the composition of surface minerals, rocks, and ices; (2) study the composition, size, and spatial and temporal distribution of atmospheric dust; (3) locate and determine the temperature, height, and condensate abundances of Martian clouds; (4) study the advance, retreat, and total energy balance of polar cap deposits; and, (5) measure the thermophysical properties of Martian surface materials.

To accomplish these goals, the investigation utilized three sensors: a Michelson interferometer, a solar reflectance sensor, and a broadband radiance sensor. The instrument had overall dimensions of 23.6 x 35.5 x 40.0 cm and required no cooling system for the detectors. Measurements could be made in a spectral range from 6--50 micrometers, roughly comparable to those made by the IRIS instrument on Mariner 9, but with better spectral resolution (5 and 10/cm), spatial resolution (3 km), near-global coverage, and a better signal-to-noise ratio than all comparable previous experiments.

The interferometer and broadband radiometer were two separate telescopes, but shared a common pointing mirror. The mirror could rotate through a full 360 degrees, permitting the instrument to view space, both limbs, and internal, full-aperture thermal and albedo calibration targets. The telescope for the spectrometer was a 15.2 cm diameter Cassegrain afocal design with a focal ratio of f/4 and an intermediate field stop to limit the admittance of stray light. The output beam of the telescope was 1.524 cm in diameter. After passing through the interferometer, the energy was focused onto a 2 x 3 array of field stops by an off-axis mirror. A separate 1.5 cm diameter, off-axis reflecting telescope was used for the thermal and albedo radiometer channels. A reflecting resonant fork chopper, operating at 30 Hz, was used to separate the solar reflectance (0.3--3.0 micrometers) and thermal emission (3.9--100 micrometers) bands. The TES was programmed to operate in one of four default operating modes to maximize the collection of different types of data. In-flight calibration of the radiometric channels was made using observations of space and an internal blackbody.

Contact with Mars Observer was lost for unknown reasons on August 21, 1993, three days before scheduled orbit insertion, so no data were returned for this investigation. This experiment has been re-scheduled to fly on the Mars Global Surveyor.

Alternate Names

  • TES

Facts in Brief

Mass: 14.4 kg
Power (avg): 15.6 W
Bit rate (avg): 1.664 bps

Funding Agency

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


  • Planetary Science: Atmospheres
  • Planetary Science: Geology and Geophysics

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Barney J. ConrathCo-InvestigatorNASA Goddard Space Flight Center 
Dr. R. Todd ClancyCo-InvestigatorUniversity of Colorado 
Dr. Roger N. ClarkCo-InvestigatorUS Geological
Dr. John C. PearlCo-InvestigatorNASA Goddard Space Flight
Dr. Hugh H. KiefferCo-InvestigatorUS Geological
Mr. Stillman C. Chase, Jr.Co-InvestigatorSanta Barbara Research Center 
Mr. Donald A. AndersonCo-InvestigatorArizona State
Prof. Philip R. ChristensenPrincipal InvestigatorArizona State

Selected References

Komro, F. G., and F. N. Hujber, Mars Observer instrument complement, J. Spacecr. Rockets, 28, No. 5, 501-506, Sep.-Oct. 1991.

Christensen, P. R., et al., Thermal emission spectrometer experiment: Mars Observer mission, J. Geophys. Res., 97, No. E5, 7719-7734, May 1992.

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