The origin of the cosmic diffuse gamma-ray (CDG) background in the 0.3 – 30 MeV energy range is a mystery that has persisted for over 40 years. The Mini Astrophysical MeV Background Observatory (MAMBO) is a CubeSat mission motivated by the fact that, since the MeV CDG is relatively bright, only a small detector is required to make high-quality measurements of it. Indeed, the sensitivity of space-based gamma-ray instruments to the CDG is limited not by size, but by the locally generated instrumental background produced by interactions of energetic particles in spacecraft materials. Comparatively tiny CubeSat platforms provide a uniquely quiet environment relative to previous gamma-ray science missions. The MAMBO mission will provide the best measurements ever made of the MeV CDG spectrum and angular distribution, utilizing two key innovations: 1) low instrumental background on a 12U CubeSat platform; and 2) an innovative shielded spectrometer design that simultaneously measures signal and background. Enabling technologies include the use of compact silicon photomultipliers (SiPMs) for scintillator readout, and a tagged calibration source for real-time gain adjustment. We describe the MAMBO instrument, readout, commercial 12U bus systems, and mission concept in detail, including simulations and laboratory measurements demonstrating the key measurement concept.
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