UNDERSTANDING THE RADIATION ENVIRONMENT AT EARTH IS CRITICAL DUE TO BOTH SCIENTIFIC INTERESTS AND PRACTICAL NEEDS. HOWEVER THE ACCELERATION MECHANISM OF EARTH S ENERGETIC PARTICLES CONSISTING OF RADIATION BELTS IS NEITHER FULLY UNDERSTOOD NOR QUANTIFIED BECAUSE OF 1) SPARSE IN-SITU OBSERVATIONS BETWEEN THE ALTITUDE OF ~5.8 RE AND GEOSYNCHRONOUS ORBIT (GEO) AND 2) DIFFICULTIES TO DISENTANGLE THE EFFECT OF DIFFERENT ACCELERATION MECHANISMS. THIS PROPOSAL AIMS TO DEVELOP A MINIATURIZED HIGH-ENERGY-RESOLUTION RELATIVISTIC ELECTRON TELESCOPE (HERT) THAT CAN BE EASILY ACCOMMODATED INTO FUTURE CUBESAT/SMALLSAT MISSIONS TO UNDERSTAND AND QUANTIFY THE EFFECT OF ACCELERATION MECHANISM THROUGHOUT THE ENTIRE RADIATION BELTS TO GEO USING A NOVEL METHOD OF PROBING ELECTRON FLUX OSCILLATIONS. HERT IS A COMPACT (&LT;3U) TELESCOPE WITH THE ABILITY TO PROVIDE HIGH ENERGY RESOLUTION (DE/E&LT;10%) MEASUREMENTS OF 1 7 MEV ELECTRONS. WITH A COMPACT DESIGN AND MUCH HIGHER ENERGY RESOLUTION IN COMPARISON TO PREVIOUS TELESCOPE-TYPE INSTRUMENTS (E.G. REPT ON THE VAN ALLEN PROBES) HERT WILL SIGNIFICANTLY CONTRIBUTE TO THE QUANTITATIVE UNDERSTANDING OF THE RADIATION BELT ELECTRON DYNAMICS.