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The APXS System on Mars and Similar SDD Systems

 

 

  The APXS System on Mars and Similar SDD Systems  
         
         
  In January 2004 NASA’s Mars Exploration Rovers ‘Spirit’ and ‘Opportunity’ landed at different sites on Mars and started their scientific tasks to investigate the geology of Mars, to search for traces of water and to find out the conditions for future manned missions. The mission had been scheduled for three months but has been extended due to the great success.In early 2006 both rovers were still alive and collected Marsian data.   Artists impression of a Mars Exploration Rover(Courtesy of the Jet Propulsion Laboratoy in Pasadena)
Figure A
Artist’s impression of a Mars Exploration Rover.
The robotic arm is stretched to the left.
 
         
  The rovers are equipped with an optical panoramic camera, a thermal emission spectrometer as well as a robotic arm (Figure B) that carries a microscope camera for close-up views of samples, an alpha- particle X-ray spectrometer (APXS, Figure C ) for chemical analysis, a Mößbauer spectrometer for the identification of iron minerals and a rock abrasion tool to perform depth profiling.   Two Photos of the APXS system on the robotic arm in operation on Mars (Courtesy of the Jet Propulsion Laboratory in Pasadena)
Figure B, C
Two Photos of the APXS system on the robotic arm
in operation on Mars (A,B,C Courtesy of the
Jet Propulsion Laboratory in Pasadena).
 
     
  The APXS system has been developed and operated by the cosmological-chemistry group of the MPI für Chemie in Mainz. It consists of an arrangement of six radioactive 244Cm sources to excite the sample, an X-ray detector for particle-induced X-ray emission (PIXE) studies, and alpha-particle detectors for Rutherford backscattering measurements. The X-ray sensor is a SDD designed, fabricated, and qualified by MPI HLL. The SDD has a sensitive area of 10 mm² and is mounted together with a thermoelectric cooler in a compact package of one cubic centimeter.  
     
ROSETTA mission  
  A system very similar to APXS and also equipped with a MPI HLL SDD is on board ESA’s ROSETTA mission. ROSETTA has been launched in March 2004 to rendezvous with the comet 67P/Churyumov-Gerasimenko eleven years later. ROSETTA consists of an orbiter satellite and a small lander, the first spacecraft to make a soft landing on the surface of a comet nucleus. As part of the lander’s payload the APXS will contribute to the study of the origin of comets.  
         
‘ExoMars’ mission      
  In 2013 the European Space Agency will launch the ‘ExoMars’ mission with the scientific background to search for traces of life on the red planet. ExoMars will land a mobile rover similar to the one depicted above in Figure A. Among the rover’s instrumentation there will be the miniaturized Mößbauer spectrometer MIMOS2 developed by the Johannes Gutenberg Universität in Mainz.   Schematic layout of SDDs for the MIMOS2 Moessbauer spectrometer of the European ExoMars rover
Figure D
     
  MIMOS2 will analyze the mineralogy of Marsian 36 MPI HLL rocks by Mößbauer spectroscopy in backscatter geometry using the 14.4 keV line of 57Fe and will be equipped with eight SDDs by MPI HLL and PNSensor. The SDDs will have a sensitive area of 45 mm2 each and are grouped in two per chip (Figure D). They will be arranged in a ring shape around a 10 mm collimator through which the sample is irradiated.  
   
  In addition to the Marsian studies MIMOS2 is foreseen to find terrestrial application in the field of archaeology, geology, corrosion studies of buildings, and environmental analytics (Link to external siteSilicon Drift Detectors in Industry Applications).
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Photo of the APXS system (Courtesy of Max-Planck-Institut för Chemie in Mainz).