The Moon Burst Energetics All-sky Monitor (MoonBEAM) is a proposed SmallSat mission to be deployed in a cis-lunar orbit in order to maximize the number of detected astrophysical transients, particularly short-duration gamma-ray burst transients, some of which may be temporally coincident with gravitational-wave signals. The unique mission design permits continuous monitoring of virtually the entire sky, something that is not possible for a single spacecraft in Low-Earth Orbit (LEO). While MoonBEAM is designed to localize transients to an accuracy of a few degrees, the large distance of MoonBEAM from other similar instruments in LEO will enable the use of light-travel time of detected transients to improve the localization of such events, potentially aiding follow-up searches of gravitational-wave signals from binary neutron star mergers.
The current concept for MoonBEAM utilizes five phosphor sandwich (“phoswich”) detectors around the spacecraft. Each phoswich detector comprises two scintillators with intrinsically different temporal and spectral properties, in order to maximize the information from each registered photon. One of the scintillators is used as an active shield to reduce noise from cosmic background photons as well as photons entering the back of the detector. This technology both increases the sensitivity of the detectors and improves the ability of the detectors to perform localization of transients on the sky.
MoonBEAM, led by PI C. Michelle Hui (NASA/MSFC), was selected for a 12-month concept study through the Astrophysics Science SmallSat Studies Call (AS3) with the purpose of clarifying mission and science requirements and determining technical feasibility. Oliver Roberts, through the funding of two USRA IRADs, has led the current phoswich detector design. This included the on-/off-axis response of various detector configurations over the anticipated spectral range of MoonBEAM and how these photon interactions drive the post-processing of the signal. The output of that work is used by other team members to determine the science capability of the detectors. Cori Fletcher and Adam Goldstein will contribute to the concept study by helping model the detector response as a function of arrival angle and energy, estimate the background noise and detector sensitivities, and produce simulations of gamma-ray bursts to study the localization capability of MoonBEAM.