The imaging FTS performs both as a diffraction limited camera and a multiobject spectrometer. Since the majority of the NGST design reference mission consists of imaging and low resolution spectroscopy this instrument can peform about 80% of NGST science efficiently. Some of the principal science investigations enabled by this IFTS design include galaxy formation and evolution (particularly evolution of IR galaxies), stellar population and chemical abundances in galaxies, merging history of galaxies, better survey and classification of supernovae (and consequently better determination of certain cosmological constants), large scale structure (galaxy clustering, spectra of galaxies with complex morphologies, spectra of lens arcs and images), extragalactic background light studies, protoplanetary disk mapping, mass function studies for sub-stellar objects from brown dwarfs to extra-solar giant planets, and Kuiper Belt object discovery and spectroscopy.
This IFTS design employs dual input ports, one for the telescope and the other for a calibration source. Dual output ports deliver complementary symmetric and antisymmetric interferograms which are differenced to get the final interferogram. The IFTS receives collimated light which is split into near-IR and mid-IR channels. Band-pass filters next select the near-IR and mid-IR wavelength ranges of interest. The near-IR channel covers 0.6-5.6 microns using two 8192 x 8192 InSb arrays, each with a 316 x 316 arc second field of view. The mid-IR channel covers 5.0-15 microns using two 1024 x 1024 HgCdTe arrays each with a 100 x 100 arc second field of view. A heat pump consisting of three staged passive radiators cools the detectors to 35-40 K. With a maximum optical path difference of 1 cm, this IFTS can provide anything from full bandpass imaging up to a spectral resolution (R) of 10,000. For a SNR of 10 at with a 100,000 second integration, the calculated near-IR and mid-IR sensitivities (in nano Janskys) for an object with a spectrum which is flat are 0.2 and 13 for R=1, 1.0 and 65 for R=5, and 35 and 1300 for R=100.