THE PROPOSED CUSP ALFVEN AND PLASMA ELECTRODYNAMICS ROCKET---2 (CAPER-2) WILL MAKE SIGNIFICANT ADVANCES IN UNDERSTANDING DAYSIDE MAGNETOSPHERE-IONOSPHERE (MI) COUPLING BUILDING ON THE SMALL NUMBER OF PREVIOUS ROCKET EXPERIMENTS IN THE POLAR CUSP IONOSPHERE TO ADDRESS TWO OF THE THREE BROAD GOALS LAID OUT IN NASA'S 2014 SCIENCE PLAN: EXPLORING THE PHYSICAL PROCESSES IN THE SPACE ENVIRONMENT FROM THE SUN TO THE EARTH AND ADVANCING UNDERSTANDING OF THE CONNECTIONS THAT LINK THE SUN TO THE EARTH. AT HIGH MAGNETIC LATITUDES MAGNETOSPHERE-IONOSPHERE COUPLING GIVES RISE TO AURORA VIA AT LEAST TWO SEPARATE ELECTRON ACCELERATION PROCESSES OF BROAD SIGNIFICANCE TO SPACE PLASMA PHYSICS: ACCELERATION BY QUASISTATIC ELECTRIC FIELDS AND BY THE TIME-VARYING ELECTROMAGNETIC FIELDS ASSOCIATED WITH ALFVEN WAVES. IN ADDITION A HOST OF MICROPHYSICAL WAVE PROCESSES REDISTRIBUTE ENERGY FROM THE RESULTING ELECTRON BEAMS TO THE THERMAL PLASMA INCLUDING MOST UBIQUITOUSLY LANGMUIR WAVES. THE DAYSIDE POLAR CUSP THE SITE OF DIRECT ACCESS OF THE SOLAR WIND PARTICLES TO LOW ALTITUDES AND THE ESCAPE OF IONOSPHERIC PARTICLES TO SPACE HOSTS BOTH TYPES OF PARTICLE ACCELERATION PROCESSES SIMILAR TO THE NIGHTSIDE AURORAL ZONE BUT DOMINATED BY DIFFERENT MAGNETOSPHERIC PROCESSES SUCH AS DAYSIDE RECONNECTION AND INTERACTIONS WITH INTERPLANETARY PRESSURE PULSES AND DISCONTINUITIES. IN PARTICULAR BASED ON FAST SATELLITE ELECTRON PARTICLE SPECTRA AND EVIDENCE FROM OTHER SATELLITES PARTICLE ACCELERATION VIA ALFVEN WAVES IS BELIEVED TO OCCUR VIRTUALLY 100% OF THE TIME IN THE CUSP BUT IN CONTRAST TO ALFVEN ACCELERATION ON THE NIGHTSIDE CUSP ALFVEN ACCELERATION HAS NEVER BEEN DIRECTLY MEASURED WITH COMBINED HIGH RESOLUTION PARTICLE ELECTRIC FIELD AND MAGNETIC FIELD MEASUREMENTS. BY INCLUDING THE SAME KEY INSTRUMENTS FLOWN ON COMPLEMENTARY MISSIONS IN THE NIGHTSIDE AURORA CAPER-2 WILL MAKE THE FIRST COMPLETE MEASUREMENTS OF THE ROLE AND NATURE OF ALFVEN WAVE ACCELERATION IN THE CUSP. CAPER-2 WILL ALSO INCLUDE THE FIRST WAVE-PARTICLE CORRELATOR MEASUREMENTS IN THE CUSP TO PROBE THE DETAILED INTERACTION OF THE ELECTRON BEAMS WITH LANGMUIR WAVE ELECTRIC FIELDS AND DISCOVER THE CAUSES OF THE OBSERVED DIFFERENCES IN THE LANGMUIR WAVES IN THE CUSP VERSUS THE NIGHTSIDE. THROUGH STATE-OF-THE-ART MEASUREMENTS OF WAVE-PARTICLE INTERACTIONS LEADING TO PARTICLE ACCELERATION AT TIME SCALES RANGING FROM ULTRALOW FREQUENCIES TO HIGH FREQUENCIES THE CAPER-2 MISSION WILL ANSWER SIGNIFICANT OUTSTANDING QUESTIONS ABOUT MI COUPLING IN THE POLAR CUSP AND PROCESSES THAT OCCUR WIDELY IN SPACE PLASMAS.