The Chandrayaan-1 X-ray Spectrometer (C1XS) is a
compact X-ray spectrometer for the Chandrayaan-1
lunar mission. It exploits heritage from the D-C1XS
instrument on ESA’s SMART-1 mission. C1XS is
designed to measure absolute and relative abundances
of major rock-forming elements (principally Mg, Al,
Si, Ti, Ca and Fe) over the lunar surface. The baseline
design consists of 24 nadir pointing Swept Charge Device
detectors, which provide high detection efficiency
in the 1–7 keV range, which contains the X-ray fluorescence
lines of the above elements of interest. Micromachined
collimators provide a 14 degree FWHM FOV,
equivalent to 25 km from 100 km altitude. A deployable
door protects the instrument during launch and
cruise, and also provides a 55Fe calibration X-ray source
for detector calibration. Additional refinements compared
to D-C1XS will result in a significantly improved
energy resolution. To record the incident solar X-ray
flux at the Moon, C1XS carries an X-ray Solar Monitor
(XSM). C1XS will arrive at the Moon in the run
up to the maximum of the solar cycle 24, and the expected
high incident X-ray flux coupled to a 100 km
circular polar orbit, will provide composition data
accurate to better than 10% of major elemental abundances
over the lunar surface