ClONO2 is one of the most important species governing the chemistry of stratosphere, especially ozone depletion, particularly in the polar regions. A compact echelle grating spectrometer (f equals 200 mm) with 0.2 cm-1 spectral resolution around the 780.2 cm-1 chlorine nitrate (ClONO2) absorption band has been designed and tested. This is a part of the flight model of the Improved Limb Atmospheric Spectrometer-II (ILAS-II) mission onboard Advanced Earth Observing Satellite II (ADEOS-II). Using an off axis parabolic collimator and two cylindrical off axis parabolic collecting mirrors, this spectrometer is a compact space-borne instrument optimized for solar occultation measurements. The solar absorption spectra measured with the array detector on the ground are consistent with the designed spectral resolution and the resolution simulated with the Code V optical performance simulator. Radiometric and spectrometric pre-launch calibration results of the spectrometer are discussed. The instrument slit function measurement with a tunable diode laser and integrating sphere is also discussed.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.