GRASP: a gamma-ray astronomy mission dedicated to the fine spectroscopy and positioning of celestial gamma-ray sources

The GRASP mission - Gamma Ray Astronomy with Spectroscopy and Positioning - will be the first high resolution spectral imager to operate in the gamma-ray region of the spectrum. The instrument covers the photon energy range from approximately 15 keV to more than 100 MeV. A combination of discrete germanium solid state devices and scintillation counters form a position sensitive gamma-ray detection matrix which is operated in conjunction with a coded aperture mask to create arc minute images of the gamma-ray sky with a spectral resolution of typically λ/Δλ ∼ 1000. The use of a coded mask with a ''zoom'' facility will permit the combination of field of view and angular resolution to be adjusted to suit the scientific aims of each observation. The respective continuum and line sensitivities will be typically 10-8ph cm-2s-1keV-1 and 310-6ph cm-2s-1 for point sources of gamma-rays with photon energies close to 1 MeV