The high-precision gamma-ray spectrometer (GRS) on the lunar polar orbiter Kaguya (SELENE)
            is designed to measure 200 keV?12 MeV gamma rays in order to determine elemental compositions 
            of the lunar surface. The GRS consists of a large germanium (Ge) crystal as a main detector 
            and a massive bismuth germanate crystal and a plastic scintillator as anticoincidence detectors. 
            The Ge detector is cooled by a Stirling cryocooler with its compressor attached to a passive 
            radiator facing the cold space. The cooling system maintains the Ge detector below 90 K during 
            the observation. The flight model of the GRS has achieved an energy resolution of 3.0 keV 
            (FWHM) at 1333 keV. Energy spectra obtained by the GRS will show sharp gamma-ray lines whose 
            energies identify the elements and whose intensities determine the concentrations of the elements, 
            permitting global mapping of the elemental abundances in the sub-surface of the Moon.