We present RAAD (Rapid Acquisition Atmospheric Detector), a detector designed to study Terrestrial Gamma ray Flashes (TGFs) and other fast hard X-ray and soft gamma-ray phenomena. TGFs are bursts of radiation from thunderstorms which occur on sub-microsecond timescales. Most detectors used to study TGFs have been limited by deadtime and timing precision, and sometimes poor calibration at lower energies. We will present calibration and space qualification tests of a detector aimed at the 20 keV - 2500 keV range with ~ 100 ns time response and good spectral resolution. This uses 2 X 2 arrays of two different scintillation crystals, Cerium Bromide and Lanthanum BromoChloride, both of which have very fast decay times. We couple them to both standard photomultiplier tubes (PMTs) and silicon photomultipliers (SiPMs) along with custom electronics designed to provide very fast sampling with very low power consumption per channel. Each crystal array fits into < 1U of a cubesat, and provides ~20 cm<sup>2 </sup>of effective area to photons < 200 keV and ~10 cm<sup>2</sup> at 600 keV. The RAAD concept is the winner of the Mini-satellite competition held by the UAE Space Agency in 2018, largely developed with undergraduates at NYUAD, and is expected to be fully developed and launched by 2020. Two detectors, one with PMTs and one with SiPMs will be deployed on a 3U CubeSat, providing head to head performance tests for both crystal types and light sensor types. This will serve as a proof of concept showing how such detectors could be deployed in a network of CubeSats to study TGFs and other phenomena.