WE PROPOSE A CONCEPT STUDY FOR A SMALLSAT MISSION BASED ON OUR DEVELOPMENT OF A HIGH-RESOLUTION ENERGETIC X-RAY IMAGER (HREXI) OPTIMIZED TO CONDUCT WIDE-FIELD (~30O X 45O) X-RAY IMAGING AND SPECTROSCOPY STUDIES OF BLACK HOLES AND TRANSIENTS WITH HIGH RESOLUTION (<25 ) SOURCE POSITIONS AND SENSITIVITY (FLUXES<1 X 10-10 ERGS CM-2 S-1) OVER A BROAD BAND (3 200 KEV). THE HREXI SMALLSAT PATHFINDER (HSP) MISSION WILL BE A PATHFINDER FOR A FUTURE SMALLSAT CONSTELLATION OF ~20 32 HREXI SMALLSATS TO IMAGE THE FULL SKY (4 SR) CONTINUOUSLY AS A 4PI X-RAY IMAGING OBSERVATORY (4PIXIO). THIS WOULD BE A UNIQUE FACILITY FOR ALL OF TIME DOMAIN ASTROPHYSICS (TDA) AND ENABLE THE THE ULTIMATE SURVEY AND STUDY OF HIGH REDSHIFT GAMMA-RAY BURSTS (GRBS) FROM MASSIVE POP III STARS IN THE EARLY UNIVERSE ALLOWING STUDIES OF BOTH THE STAR FORMATION HISTORY AND THE EPOCH OF REIONIZATION OF THE UNIVERSE (EOR). WITHIN OUR GALAXY SUCH A MISSION WOULD ENABLE THE ULTIMATE WIDE-FIELD DETECTION AND MONITORING OF ACCRETING BLACK HOLES (BHS) FOR BOTH BLACK HOLE LOW MASS X-RAY BINARIES (BH-LMXBS) AND THOSE WITH HIGH MASS (O STAR) COMPANIONS (BH-HMXBS) AS WELL AS THE MERGERS OF STELLAR MASS BHS AND THEIR POSSIBLE ELECTROMAGNETIC COUNTERPARTS IN LIGO/VIRGO GRAVITATIONAL WAVE EVENTS. OUR PROPOSED CONCEPT STUDY FOR A SINGLE (OR POSSIBLY TWO) SMALLSAT FOR HSP WOULD HAVE SIGNIFICANTLY HIGHER SPATIAL RESOLUTION AND ENERGY BAND COVERAGE THAN SWIFT/BAT THE CURRENT (BUT NOT INDEFINITE) PRIME FACILITY FOR TDA STUDIES OF BOTH STELLAR BHS AND SMBHS. THIS PROPOSED CONCEPT STUDY FOR THE HREXI SMALLSAT PATHFINDER (HSP) MISSION WOULD HAVE THE FOLLOWING PRIME SCIENCE OBJECTIVES: 1) STUDIES OF EXTREME NON-RECURRING TRANSIENTS BOTH LONG AND SHORT GRBS (SGRBS) OVER THE BROAD ENERGY BAND NOT PREVIOUSLY AVAILABLE. LIGO/VIRGO SGRBS AS WELL AS BH-BH MERGERS ARE A PRIME AREA OF STUDY. TWO HSP SMALLSATS WOULD NEARLY DOUBLE THE CHANCE FROM SWIFT/BAT FOR DETECTION OF THESE RARE TRANSIENTS. 2) STUDIES OF EXTREME RECURRING TRANSIENTS: I) FLARES FROM M DWARFS (OR OTHER) STARS OF INTEREST FOR EXOPLANET SYSTEMS II) EXTREME FLARES FROM BLAZARS AND III) TIDAL DISRUPTION EVENTS (TDES) FROM THE TIDAL SHREDDING OF A STAR BY CLOSE ENCOUNTER WITH A GALAXY SMBH. AGAIN THE BROAD BAND OF HSP ALLOWS NEW BOTH HARD AND SOFT EVENTS TO BE DISCOVERED. 3) DEEP BH X-RAY BINARY SURVEYS IN THE GALAXY OF I) THE GALACTIC BULGE AND II) THE GALACTIC PLANE (HALF) FOR LOW-LUMINOSITY FLARING FROM BH-LMXBS THAT WOULD REVEAL THE STILL UNCERTAIN VERY LARGE POPULATION OF THESE DORMANT SYSTEMS; AS WELL AS THE LOW LUMINOSITY POPULATION OF BH-HMXBS WHERE THE DONOR O STAR IS STILL ON THE MAIN SEQUENCE (OR RECENTLY EVOLVED OFF) AND HAS A CHARACTERISTICALLY WEAK WIND. THE HSP CONCEPT STUDY WILL MAKE USE OF OUR RECENTLY DEVELOPED HREXI IMAGING DETECTOR SYSTEM WITH EXTENDED LOW-GAP TILING OF DETECTORS READ OUT BY THE NUSTAR ASIC NOW TRANSFORMED INTO A BACK-SIDE READOUT (WITH THROUGH-SILICON VIAS TSVS). AN ENGINEERING MODEL (EM) OF HREXI IS EXPECTED BY THE TIME OF OUR STUDY. WE WILL STUDY THE FULL DETECTOR AND CODED APERTURE TELESCOPE DESIGN WHICH APPEARS TO BE FULLY COMPATIBLE WITH THE SMALLSAT SPACECRAFT BUS MICROSAT_S5 DEVELOPED BY BLUE CANYON TECHNOLOGIES (BCT). BCT WILL WORK WITH US ON OPTIMIZING THE DESIGN FROM THE PLAN PRESENTED HERE. WE WILL USE THE WALLOPS MISSION PLANNING LAB (MPL) TO CONDUCT OUR FULL MISSION DESIGN WHICH INCLUDES A MOC AT GSFC AND A SOC AT SAO. WE SHALL STUDY MISSION-CRITICAL DATA SYSTEMS (ON BOARD PROCESSING) AND DOWNLINK FACILITIES INCLUDING THE POSSIBLE FUTURE WIFI FROM LEO PLANS ENVISAGED BY COMMERCIAL PROVIDERS.