We present a spectrometer design based on a novel nanofabricated blazed X-ray transmission grating which is modeled to have superior efficiency. Here we outline a full instrument design proposed for Constellation-X which is expected to give resolving powers ~2000 (HEW). The spectrometer advantages include lower mass budget and smaller diffractor area, as well as order-of-magnitude more relaxed alignment tolerances for crucial degrees of freedom than reflection grating schemes considered in the past1,2,3. The spectrometer readout is based on conventional CCD technology adapted to operate with very high speed and low power. This instrument will enable high resolution absorption and emission line spectroscopy in the critical band between 0.2 and 1.5 keV.© (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.