One proposal for such a mission, selected for study as a NASA New Mission Concept in Astrophysics, is the Gamma-ray Large Area Space Telescope (GLAST) shown in fig. 4.2.

For the baseline mission parameters given in Table 4.1, a nearly two-order-of-magnitude improvement in flux sensitivity and a factor of 10 improvement in point source location capability will be obtained. Determination of the spectra of the sources over a broad energy range will also be possible. A wide field-of-view telescope will allow the detection of many more transient sources such as AGN flares and high-energy gamma-ray bursts.

The principal scientific objectives for the mission include:

• Active galactic Nuclei: determine the mechanisms of AGN jet formation, particle acceleration, and radiation by studying gamma-ray emission fromall known blazars (and possibly other AGN classes) and correlating these observations with those at other wavelengths.

• Unidentified Gamma-ray Sources: determine the type of object(s) and the mechanisms for gamma-ray emission from the unidentified gamma-ray sources by measuring precise positions of these sources.

• Isotropic Background Radiation: determine if the high-energy background is resolvable into point sources or if there is a true diffuse component, by a deep survey of high-latitude fields.

• Gamma-Ray Bursts: provide constraints on physical mechanisms for gamma-ray bursts by detecting high-energy radiation from 50 - 150 bursts per year and studying the GeV : keV-MeV emission ratio as a function of time; image burst positions to a few arcminutes or better, allowing deep "real-time" multiwavelength observations.

• Endpoints of Stellar Evolution (Supernovae, Neutron Stars, and Black Holes): provide direct evidence of proton cosmic-ray acceleration in supernova remnants by gamma-ray mapping and energy spectral measurements; distinguish between models for high-energy gamma-ray emission from pulsars by measuring detailed phase-resolved spectra. Determine whether or not galactic superluminal jet sources emit significant high-energy gamma radiation.
  
• Molecular Clouds, Normal Galaxies and Clusters: probe the cosmic-ray distribution in dense molecular clouds and in nearby galaxies (LMC, SMC, M31) by gamma-ray mapping and measuring the spectra of diffuse emission from these objects; search for extended emission from possible cold dark matter clouds in the galaxy and from galaxy clusters as a signature of unusual concentrations of unseen gas or cosmic rays.