The performance of a space-borne water vapour and temperature lidar exploiting the vibrational and pure rotational Raman techniques in the ultraviolet is simulated. This paper discusses simulations under a variety of environmental and climate scenarios. Simulations demonstrate the capability of Raman lidars deployed on-board low-Earth-orbit satellites to provide global-scale water vapour mixing ratio and temperature measurements in the lower to middle troposphere, with accuracies exceeding most observational requirements for numerical weather prediction (NWP) and climate research applications. These performances are especially attractive for measurements in the low troposphere in order to close the most critical gaps in the current earth observation system. In all climate zones, considering vertical and horizontal resolutions of 200 m and 50 km, respectively, mean water vapour mixing ratio profiling precision from the surface up to an altitude of 4 km is simulated to be 10%, while temperature profiling precision is simulated to be 0.40-0.75 K in the altitude interval up to 15 km. Performances in the presence of clouds are also simulated. Measurements are found to be possible above and below cirrus clouds with an optical thickness of 0.3. This combination of accuracy and vertical resolution cannot be achieved with any other space borne remote sensing technique and will provide a breakthrough in our knowledge of global and regional water and energy cycles, as well as in the quality of short- to medium-range weather forecasts. Besides providing a comprehensive set of simulations, this paper also provides an insight into specific possible technological solutions that are proposed for the implementation of a space-borne Raman lidar system. These solutions refer to technological breakthroughs gained during the last decade in the design and development of specific lidar devices and sub-systems, primarily in high-power, high-efficiency solid-state laser sources, low-weight large aperture telescopes, and high-gain, high-quantum efficiency detectors.