Angular resolution in the far-infrared (FIR) wavelength regime limits the range of size scales accessible although the FIR range has become of prime importance for astrophysics. Observations of ionic, atomic and molecular lines, many of them only present in the FIR spectral region, provide important and unique information on the star- and planet formation process occurring in interstellar clouds, and more generally on the lifecycle of gas and dust. All these regions are heavily obscured by dust, and (F)IR spectroscopic observations are important means of gaining insight about their physical and chemical environments, and the evolutionary development. Besides the high spectral resolution these investigations require high angular resolution in order to match the small angular sizes of star forming cores and circumstellar disks. The European Space Agency’s (ESA) Herschel satellite will provide the first step towards high spectral resolution. To obtain both high spectral and spatial resolution capabilities, we propose a heterodyne aperture-synthesis mission concept, ESPRIT, to operate in a wavelength regime that is neither accessible from the ground by Atacama Large Millimeter Array (ALMA), nor with James Webb Space Telescope (JWST).
