Space qualifying RAAD CubeSat for the study of terrestrial gamma-ray flashes and other short timescale phenomenon

The RAAD (Rapid Acquisition Atmospheric Detector) instrument is a soft Gamma-Ray detector optimized for studying Terrestrial GammaRay Flashes (TGFs). We are testing two configurations which use two different types of scintillating crystals (Cerium Bromide and Lanthanum BromoChloride) coupled to S13361-6050AE-04 Hamamatsu Silicon Photomultipliers (SiPMs) and R11265-200 Photomultiplier Tubes (PMTs). Each detector consists of a 2 x 2 array of crystals and photosensors, each fitting into < 1U of a CubeSat, and provides ~20 cm² of effective area to photons with energy less than 200 keV and ~10 cm² at 600 keV. The detector's unique combination of scintillating crystals and photosensors, along with a custom-designed readout electronics, overcomes the deadtime and timing precision limitations as well as the low resolution at lower energies (< 50 keV) typical of previous missions that had tried to detect TGFs. The custom-designed payload electronics provide the required spectroscopic and timing capabilities within the low power budget constraints (< 4 W on average) of the mission. It is sensitive in the 20 keV - 3000 keV energy range, has a 200 ns time resolution, and good energy resolution (~ 5% @ 511 keV). We present the results of thermal and mechanical space qualification tests on the payload, energy and timing calibrations, and pre-flight particle and signal simulations characterizing the expected response. We also show how such detectors could be deployed in a network of CubeSats to study TGFs and for multi-messenger astronomy. RAAD is the chosen payload for the Light-1 3U CubeSat, the first joint mission between the UAE Space Agency and the Bahraini Space Agency, which is expected to be launched in May 2021 and deployed from the International Space Station.