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Mapping Spectrometer (MS)

NSSDCA ID: 2007-043A-02

Mission Name: Dawn
Principal Investigator:Dr. Maria Christina de Sanctis

Description

The Dawn mapping spectrometer (MS) is a modification of the VIRTIS mapping spectrometer flown on the Rosetta mission. It has two channels, one visible and one infrared and uses a dual arm optical and focal design. The spectrometer consists of four components: an optical system (5.0 kg), proximity electronics (3.0 kg, 5W), a cryocooler and driving electronics (1.3 kg, 12.6 W), and a mechanical and thermal mount (5.0 kg). The primary objective of the experiment is to help determine the mineral composition of the surfaces of the asteroids. It will also be used to determine the physical structure and nature of the surface particles and identify water-bearing minerals, surface ice and frost, and any tenuous atmosphere. The visible and infrared channels share common optics and grating so beam splitters are not required. The optical system is a Shafer telescope combining an inverted Burch off-axis telescope with an Offner relay. A cover in front of the aperture protects the optics and is coated on the inside to be used as a calibration target with two internal calibration lamps. The pupil diameter is 47.5 mm, the field of view is 64 mrad x 64 mrad, and the F# is 5.6 for the visible system and 3.2 for the IR system. The Offner spectrometer is matched to the telescope, which has its exit pupil through a 38 x 9.53 micrometer slit to the grating. The grating is etched with two different groove densities, the central part with high groove density for the visible channel and the outer part with a lower density for the infrared channel. The visible channel uses a silicon CCD array to image over a wavelength range of 250 to 1000 nm. The array is based on the Thomson-CSF type TH 7896 CCD detector using a buried channel design and poly-silicon N-MOS technology. It includes a multipinned phase (MPP) boron implant to operate fully inverted and decrease residual images. The array has 1024 x 1024 sensitive elements and will be operated as a frame transfer device, with a sensitive area and a storage area. The infrared channel utilizes a mercury cadmium telluride infrared focal plane array of 270 x 435 photodiodes coupled to a silicon CMOS multiplexer. The detector covers wavelengths from 950 to 5050 nm at an operating temperature of 70 K. An optical window in the detector housing acts as a substrate for order-sorting filters coated in the window with bandpasses of 900-1600, 1200-1900, 1900-2500, 2400-3750, 3600-4400, and 4300-5000 micrometers. In order to minimize thermal background radiation, the spectrometer needs to be cooled to under 135 K by passively radiating to space. The array itself is cooled to its 70 K operating temperature by a Stirling active cooler.

Alternate Names

  • Dawn/MS
  • MS
  • VIR
  • Visible and Infrared Spectrometer (VIR)

Facts in Brief

Mass: 9.3 kg
Power (avg): 17.6 W

Discipline

  • Planetary Science: Small Bodies

Additional Information

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

 

Personnel

NameRoleOriginal AffiliationE-mail
Dr. Maria Christina de SanctisPrincipal InvestigatorIstituto Nazionale di Astrofisicamariacristina.desanctis@iaps.inaf.it
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