Mass spectrometers are valuable tools for the in situ characterization of gaseous exo- and atmospheres and have been operated at various bodies in space. Typical measurements derive the elemental composition, relative abundances, and isotopic ratios of the examined environment. To sample tenuous gas environments around comets, icy moons, and the exosphere of Mercury, efficient instrument designs with high sensitivity are mandatory while the contamination by the spacecraft and the sensor itself should be kept as low as possible. With the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA), designed to characterize the coma of comet 67P/Churyumov-Gerasimenko, we were able to quantify the effects of spacecraft contamination on such measurements. By means of 3D computational modeling of a helium leak in the thruster pressurization tubing that was detected during the cruise phase we examine the physics involved leading to the measurements of contamination. 3 types of contamination can be distinguished: i) Compounds from the decomposition of the spacecraft material. ii) Contamination from thruster firing during maneuvers. iii) Adsorption and desorption of the sampled environment on and from the spacecraft. We show that even after more than ten years in space the effects of i) are still detectable by ROSINA and impose an important constraint on the lower limit of gas number densities one can examine by means of mass spectrometry. Effects from ii) act on much shorter time scales and can be avoided or minimized by proper mission planning and data analysis afterwards. iii) is the most difficult effect to quantify as it changes over time and finally carries the fingerprint of the sampled environment which makes prior calibration not possible.
We describe the performance evaluation of a sample of InGaAs detectors from which the best unit had to be selected for the
flight model of the SIR-2 NIR-spectrometer to be flown on the Chandrayaan-1 mission in 2008.
The near-infrared spectrometer, SIR, is a flexible, compact and low mass (2 kg) instrument designed to measure reflectance spectra in the wavelength range between 935 and 2390 nm with a resolution of 6 nm per pixel. In its current implementation it is part of ESA’s technology mission SMART-1, which will be launched in 2003 and tested in an orbit around the Moon. The SIR spectrometer uses a reflection grating and an InGaAs detector. Its design is optimized to operate under extreme temperature and to withstand extreme vibrational conditions. For the SMART-1 mission its capabilities are of particular importance for the study of features like maria, craters, and fracture ridges that will provide deeper insights into crust and mantel material and therefore, into the development of the Moon and the Earth-Moon system.