Bhandari, N.

Crawford, I. A.

Grande, M.

Howe, C. J.

Huovelin, J.

Kellett, B. J.

Maddison, B. J.

Sreekumar, P.

English

Publications of the IAS Fellows

  
 
 
 
 
EPSC Abstracts, 
Vol. 4, EPSC2009-738, 2009 
European Planetary Science Congress,  
© Author(s) 2009 
 
 
 
 
Initial results from the C1XS x-ray spectrometer on Chandrayaan-1  
Manuel Grande1, Brian J. Maddison2, P. Sreekumar3, Johani Huovelin4, Barry J. Kellett2,   Chris J.Howe2,  
Ian. A. Crawford5, and the C1XS Team6, 1Institute of Mathematical and Physical Sciences, University of 
Wales, Aberystwyth, SY23 3BZ,  UK, m.grande@aber.ac.uk, 2Rutherford Appleton Laboratory, Chilton, 
UK, 3Space Astronomy & Instrumentation Division, ISRO Satellite Centre, Bangalore, India, 4The 
Observatory, Univ. of Helsinki, Finland, 5School of Earth Sciences, Birkbeck College London,  London, 
UK,  6The other members of the C1XS  Team are identified in the Acknowledgments 
 
Introduction:  The Chandrayaan-1 lunar 
mission which was cuccessfully launched by the 
Indian Space Research Organisation (ISRO) on 22 
October carried as part of its payload the C1XS 
Chandrayaan-1 X-ray Spectrometer (Grande et al 
2009 [1]). It exploits heritage from the D-CIXS 
instrument (Grande et all, 2007[2]]) on ESA’s 
SMART-1 mission. However, by comparison with 
SMART-1, Chandrayaan-1 is a science oriented 
rather than a technology mission, leading to far 
more favourable conditions for science 
measurements. C1XS is designed to measure 
absolute and relative abundances of major rock-
forming elements (principally Mg, Al, Si, Ca, Ti 
and Fe) in the lunar crust with resolution ~25 km.  
The C1XS hardware was designed and built by 
an international team led from the Rutherford 
Appleton Laboratory (RAL), STFC. The Principal 
Investigator is Prof. M. Grande at Aberystwyth 
University. There is also a major science and 
design contribution from ISRO Satellite Centre, 
Bangalore, India; CESR, Toulouse, France 
provides 3-D Plus video processor integrated 
circuits, and there is an important contribution to 
the detector characterisation from Brunel 
University. The Science team is chaired by Dr. I. 
A. Crawford of Birkbeck College London. In order 
to record the incident solar X-ray flux at the Moon, 
C1XS carries an X-ray Solar Monitor (XSM) 
provided by the University of Helsinki 
Observatory, Finland. C1XS is primarily funded 
by ESA with partial support to RAL from ISRO. 
Instrument   
The baseline instrument design consists of 24 
nadir pointing Swept Charge Device (SCD) 
detectors (Howe et al., forthcoming). A traditional 
box collimator defines the field of view of each 
SCD, resulting in a triangular angular sensitivity 
with 50% of the X-ray signal deriving from 14° of 
the collimator aperture, corresponding to 25 km on 
the lunar surface from Chandrayaan-1’s circular 
100 km orbit. A deployable door protects the 
instrument during launch and cruise, and also 
provides a 55Fe calibration X-ray source for each 
of the detectors, allowing in flight calibration to be 
performed. The source strength is sufficient 
throughout the two year mission for gain 
calibration to be obtained within 10 minutes.  
  
Figure 1: Comparison of in-flight and 
laboratory performance, using the onboard Mn55 
sources. Note similarity between the two spectra. 
                                                         
 
Figure 2: Lunar Spectrum obtained on 12 Dec 
2008, in low illumination conditions. Note the 
excellent resolution achieved in the Magnesium, 
Aluminium and Silicon Lines 
  
 
 
 
 
EPSC Abstracts, 
Vol. 4, EPSC2009-738, 2009 
European Planetary Science Congress,  
© Author(s) 2009 
 
 
 
The Swept Charge Device (SCD) detectors (Gow 
et al 2007) provide high detection efficiency in the 
0.8 to 7 keV range, which contains the X-ray 
fluorescence lines of interest. The principal 
requirement is a spectral resolution sufficient to 
clearly resolve the three common light rock 
forming elements (Mg, Al, Si).   
The X-ray solar monitor (XSM) is based on the 
SMART-1 XSM (Huovelin et al 2002 [3]) and 
consists of a separate silicon detector unit on the 
spacecraft. The non-imaging HPSi PIN sensor has 
a wide field-of-view (FOV) to enable Sun 
visibility during a significant fraction of the 
mission lifetime, which is essential for obtaining 
calibration spectra for the X-ray fluorescence 
measurements by the C1XS spectrometer. The 
energy range (1–20 keV), spectral resolution 
(about 200 eV at 6 keV), and sensitivity (about 
7000 cps at flux level of 10−4 W m−2 in the range 
1–8 keV) are tuned to provide optimal knowledge 
about the solar X-ray flux, matching well with the 
activating energy range for the fluorescence 
measured by C1XS. 
 
In Flight Performance 
The instrument has recently been turned on, 
and is operating nominally. In flight calibration 
has been carried out using the onboard Mn55 
radiation sources, and the results are shown in 
Figure 1, as a comparison with the equivalent lab 
based calibration spectrum.  
It is seen that the flight spectrum matches very 
closely the lab spectrum, indicating that the 
instrument is performing well, and has undergone 
very little degradation as a result of the cruise to 
the Moon, and the consequent radiation belt 
passages. Detailed analysis suggests a broadening 
of the FWHM by 30ev, far less than predicted.   
The Sun continues to show X-ray emission 
characteristic of the Solar minimum, and the onset 
of this solar maximum is significantly delayed. 
However, C1XS has been able to observe the 
Moon even in these very low illumination 
conditions. Figure 2 shows the result of an 
integration during an A class flare on Dec 12, 
2008. The expected lines at Mg, Al and Si are 
clearly seen and resolved. This performance shows 
that the instrument is easily meeting its design 
requirements, and in the higher illumination 
conditions expected during the rest of the mission 
will be capable of meeting its science goals.  
 
Science Goals:  
C1XS will determine the major element 
geochemistry (and especially Mg/Si and/or Mg/Fe 
elemental ratios) in the main lunar terrain types 
(i.e. Procellarum KREEP Terrane, South Pole-
Aitken Basin, and the Farside Highlands; Jolliff et 
al., 2000) and establish the geographical 
distribution of the magnesian suite of rocks. A key 
ambition is to determine the large-scale 
stratigraphy of lower crust (and possibly 
crust/mantle boundary region) by measuring the 
elemental abundances of the floor material of large 
basins not obscured by mare basalts (e.g. SPA and 
other farside basins), and the central rings and 
ejecta of large basins which expose material 
derived from depths of many tens of km. In 
addition, determination of the crustal aluminium 
abundance and distribution is important for the 
assessment of lunar refractory element enrichment, 
and C1XS-derived aluminium abundance maps 
will thus constrain models of lunar origins. 
Conclusions 
The C1XS instrument is optimised to perform 
X-ray spectroscopy in the framework provided by 
the ISRO Chandrayaan-1 mission to the Moon. 
Initial results suggest that its performance as a 
science instrument will be outstanding. 
Acknowledgements 
The C1XS Team: M Grande, A Cook,  M. Wilding, J A 
Carter (University of Wales, Aberystwyth, UK), BJ 
Maddison, BJ Kellett, CJ Howe (Rutherford Appleton 
Lab, UK), P. Sreekumar, A Shrivastava, S Narendranath, 
( ISRO, India), J Huovelin (Helsinki Univ, Finland),  I 
Crawford, K Joy (Birkbeck College London, UK), C L 
Duston , O Gasnaut, S Maurice,   (OMP, Toulouse, 
France), A Holland, D Smith  (Brunel Univ, UK),  D 
Rothery, M Anand (Open University UK),  S Russell, 
Natural History Museum, UK), JN Goswami, 
N.Bhandari (PRL India), D Lawrence, (Los Alamos 
National Lab, USA), V Fernandes, (U Coimbra, 
Portugal), T. Okada, (ISAS, Japan) , O Witasse 
(ESTEC), C Pieters (Brown University), M Wieczorek 
(IPG Paris, France). 
References: [1] Grande M., et al.  The C1XS X-ray 
spectrometer on Chandrayaan-1, Grande M., et al.2009 
Planet. Space. Sci. 57 (2009) 717–724 [2] Grande M., et 
al.  The D-CIXS X-ray spectrometer on the SMART-1 
mission to the Moon—First Results. Planet. Space. 
Sci ,55, 494 (2007) 
 (2007). [3]Huovelin J et al. The SMART-1 X-ray solar 
monitor (XSM): calibrations for D-CIXS and 
independent coronal science. Planet. Space. Sci 2002, 
Vol 50, Iss 14-15, pp 1345-1353  Mission to the Moon, 
Planet. Space. Sci., 2009 doi:10.1016/j.pss.2008.12.00 


Initial results from the C1XS X-ray spectrometer on Chandrayaan-1

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Initial results from the C1XS X-ray spectrometer on Chandrayaan-1

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