Designed with large FOV and high detection efficiency, GRM is optimized to detect GRBs in the hard X-ray and soft gamma-ray band, and transmit the information of GRB triggers and locations to other onboard payloads real-timely and the ground segment instruments through the VHF channel, a process which is particularly crucial for short and hard GRBs. GRM is composed of three identical NaI(T1) crystal spectrometers (GRDs) pointing in different orientations for onboard localization of GRBs, three auxiliary calibration detectors (GCDs), each one installed on the edge of the top surface of each GRD to stabilize the detector’s gain through high-voltage adjustment and to perform the on-orbit relative energy calibration, one electronics box (GEB) for scientific data collection and management and power supply for other parts of the system, and one particle monitor (GPM) for early warning of charged particle flow on orbit.

The performance requirements of GRM are as table 1:

Table 1: GRM performance requirements