The Performance and Scientific Rationale for an Infrared Imaging Fourier Transform Spectrograph on a Large Space Telescope

We describe a concept for an imaging spectrograph for a large orbiting observatory such as NASA's proposed Next Generation Space Telescope (NGST) based on an imaging Fourier transform spectrograph (IFTS). An IFTS has several important advantages that make it an ideal instrument to pursue the scientific objectives of NGST. We review the operation of an IFTS and make a quantitative evaluation of the signal-to-noise performance of such an instrument in the context of NGST. We consider the relationship between pixel size, spectral resolution, and diameter of the beam splitter for imaging and nonimaging Fourier transform spectrographs and give the condition required to maintain spectral modulation efficiency over the entire field of view. We give examples of scientific programs that could be performed with this facility.