Rice University has been developing a gamma ray telescope to be used for the detection of spectral gamma ray lines from Type I supernovae within one megaparsec in the energy range from 100 keV to 10 MeV. The detector is an actively shielded array of 121 0.5\sp′′ x 0.5\sp′′ x 2.0\sp′′ NaI(Tl) crystals, each optically separated from the remainder of the array independently viewed. Inflight calibration of the 121 individual PMTs will be handled by an on board computer in conjunction with LEDs attached to the crystals. The active shield is constructed of individual blocks viewed separately by one or more photomultiplier tubes acting in anticoincidence with the central detector, providing excellent isolation from non-source gamma ray detections. The telescope uses a coded aperture approach yielding an overall geometrical spatial resolution of 2.6\sp∘ x 2.6\sp∘ FWHM. The energy resolution of the detector is expected to be 12% FWHM at 0.661 MeV. Simulations of the detector/shield assembly yield a projected sensitivity of 1 × 10\sp−4 photons cm\sp−2 sec\sp−1 for a 3 sigma detection at 1 MeV. (Abstract shortened with permission of author.)