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X-ray Spectrometer (XRS)

NSSDCA ID: 2004-030A-03

Mission Name: MESSENGER


The MESSENGER X-Ray Spectrometer (XRS) will detect the K-flourescence X-ray emissions diagnostic of elements (Mg, Al, S, Ca, Ti, and Fe) within 1 mm of the surface. Surface abundances will be mapped with spatial resolutions down to 20 km. The primary objectives of this experiment are to help characterize the chemical composition and geologic history of Mercury. A total data return of about 1.5 Gb is expected.

The XRS is an improved version of the design used on the NEAR-Shoemaker spacecraft. Mounted on the nadir facing instrument deck of MESSENGER, it consists of three cylindrical gas filled proportional counters, each 10 square cm, behind a 25 micrometer Be window. Each counter has a set of anti-coincidence wires to catch penetrating cosmic ray events, an internal Be liner to block x-rays produced by cosmic rays in the detector tube walls, and a 12 degree field of view Be-CU honeycomb collimator. Thin absorption filters (8.5 micrometer Mg and 8.5 micrometer Al) on two of the detectors separate the lower energy x-ray lines (Al, Mg, and Si). Energy spectra from 0.7 to 10 keV with a resolution (full width half maximum) of 350 eV are accumulated. The maximum input rate is 20 kHz and the integration period is 100 s at periapsis and 2000 s at apoapsis. A small (0.1 square mm) sunward pointing Si-PIN X-ray detector with a thin Be foil cover is mounted on the sunshade to measure the time-variable solar flux input to the planet.

Alternate Names

  • XRS
  • urn:nasa:pds:context:instrument:xrs.mess

Facts in Brief

Mass: 3.4 kg
Power (avg): 8 W
Bit rate (avg): 0.049 kbps

Funding Agency

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


  • Planetary Science: Geology and Geophysics

Additional Information

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



NameRoleOriginal AffiliationE-mail
Dr. Richard StarrExperiment ScientistNASA Goddard Space Flight

Selected References

  • Schlemm, C. E., et al., The X-Ray Spectrometer on the MESSENGER Spacecraft, Space Sci. Rev., 131, No. 1-4, 393-415, doi:10.1007/s11214-007-9248-5, Aug. 2007.
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