THE INTENSITY OF ENERGETIC PARTICLES TRAPPED IN EARTH'S RADIATION BELTS VARIES BY ORDERS OF MAGNITUDE ON TIMESCALES FROM MINUTES TO DAYS. THIS DYNAMIC VARIABILITY IS CONTROLLED BY A SHIFTING BALANCE BETWEEN DIFFERENT ACCELERATION AND LOSS MECHANISMS. PRECIPITATION INTO THE ATMOSPHERE HAS BEEN RECOGNIZED FOR DECADES AS A MAJOR LOSS MECHANISM YET CRITICAL QUESTIONS ABOUT THE PHYSICAL PROCESSES REMAIN. SIGNIFICANT PROGRESS HAS BEEN MADE IN IDENTIFYING THE PLASMA WAVES THAT DRIVE ATMOSPHERIC PRECIPITATION [E.G. THORNE 2010 FOR REVIEW]. HOWEVER THE PHYSICAL "MODES" IN WHICH THESE ACT IS NOT WELL SPECIFIED: ELECTRONS MAY BE SCATTERED SLOWLY THROUGH A DIFFUSIVE PROCESS [E.G. SHPRITS ET AL. 2008 REVIEW] OR RAPIDLY THROUGH NONLINEAR PROCESSES [E.G. ALBERT 2000; BORTNIK ET AL. 2008 OMURA ET AL. 2015]. THE PHYSICAL MODE DETERMINES THE SCATTERING RATE AND THUS THE IMPACT ON THE RADIATION BELTS. THEREFORE IT IS IMPORTANT TO ESTABLISH WHERE AND HOW FREQUENTLY LOSS MECHANISMS ACT IN DIFFERENT MODES FOR PARTICLES OF DIFFERENT ENERGIES. THE RELATIVISTIC ELECTRON ATMOSPHERIC LOSS (REAL) CUBESAT MISSION WILL CHARACTERIZE DIFFERENT MODES OF ATMOSPHERIC LOSS BY MAKING HIGH TIME RESOLUTION MEASUREMENTS OF THE ELECTRON PITCH ANGLE AND ENERGY DISTRIBUTIONS IN LOW EARTH ORBIT (LEO) OVER A WIDE ENERGY RANGE FROM KEV TO MEV. LEO IS IDEAL FOR MEASURING PRECIPITATION SINCE THE ATMOSPHERIC LOSS CONE IS LARGER (~60 DEG) THAN AT THE EQUATOR (FEW DEGREES). THE OVERARCHING GOAL OF REAL IS TO IMPROVE OUR UNDERSTANDING OF THE PHYSICAL MECHANISMS RESPONSIBLE FOR SCATTERING RADIATION BELT ELECTRONS INTO THE ATMOSPHERE. REAL WILL INVESTIGATE SPECIFIC ASPECTS OF THESE MECHANISMS BY ANSWERING THE FOLLOWING SCIENCE QUESTIONS: 1.) WHEN AND WHERE DO DIFFERENT PRECIPITATION LOSS MODES (DIFFUSION STRONG DIFFUSION AND NONLINEAR SCATTERING) OCCUR 2.) HOW DO ELECTRON PRECIPITATION LOSS MODES DEPEND ON ENERGY 3.) WHAT IS THE RELATIVE IMPACT OF DIFFERENT PRECIPITATION LOSS MODES ON THE RADIATION BELTS REAL CONTRIBUTES TO THE HELIOPHYSICS OBJECTIVE TO "UNDERSTAND THE SUN AND ITS INTERACTIONS WITH EARTH AND THE SOLAR SYSTEM INCLUDING SPACE WEATHER" BY INVESTIGATING ELECTRON LOSS MECHANISMS IN THE MAGNETOSPHERE. REAL ADDRESSES TWO HELIOPHYSICS SCIENCE GOALS "EXPLORE THE PHYSICAL PROCESSES IN THE SPACE ENVIRONMENT FROM THE SUN TO THE EARTH AND THROUGHOUT THE SOLAR SYSTEM" AND "DEVELOP THE KNOWLEDGE AND CAPABILITY TO DETECT AND PREDICT EXTREME CONDITIONS IN SPACE TO PROTECT LIFE AND SOCIETY AND TO SAFEGUARD HUMAN AND ROBOTIC EXPLORERS BEYOND EARTH" BY IMPROVING OUR UNDERSTANDING OF WAVE-PARTICLE INTERACTIONS IN SPACE PLASMAS LEADING TO IMPROVED PREDICTIVE MODELS OF THE RADIATION BELTS.