MULTIMESSENGER ASTRONOMY ARRIVED WITH GW170817 THE FIRST DETECTION BY LIGO AND VIRGO OF A BINARY NEUTRON STAR (BNS) MERGER AND THE SUBSEQUENT OBSERVATION BY GROUND AND SPACE-BASED OBSERVATORIES OF ASSOCIATED EM SIGNATURES ACROSS THE SPECTRUM. A SECOND BNS MERGER GW190425 WAS SUBSEQUENTLY ED ALTHOUGH NO SIGNIFICANT EM COUNTERPARTS WERE FOUND. CURRENT ESTIMATES SUGGEST MANY MORE SUCH EVENTS ARE LIKELY TO BE OBSERVED IN THE NEAR FUTURE. IN THE SEARCH FOR EM COUNTERPARTS NASA MISSIONS PLAY AN INDISPENSABLE ROLE DETECTING AND CHARACTERIZING GRBS AND OTHER EM TRANSIENTS. HOWEVER THERE EXIST SIGNIFICANT UNCERTAINTIES IN.THE BNS MERGER MODELS THAT LINK THE BINARY PARAMETERS (EXTRACTED FROM GWS) TO THE EJECTA PROPERTIES THAT DETERMINE EM SIGNATURES LEAVING THE DATA COLLECTED BY THESE NASA MISSIONS WITH SUBSTANTIAL UNREALIZED POTENTIAL. IN PARTICULAR GRAVITATIONAL WAVES (GWS) PROVIDE AN ACCURATE MEASUREMENT OF THE TOTAL MASS OF THE BINARY WHICH DETERMINES THE ULTIMATE FATE OF THE REMNANT. IN THE HIGH MASS CASE THE REMNANT UNDERGOES PROMPT-COLLAPSE ON DYNAMIC TIMESCALES. OBSERVATIONS OF BNS MERGERS SUCH AS GW170817 AND GW190425 HAVE THE POTENTIAL TO NARROW DOWN THIS PROMPT-COLLAPSE THRESHOLD MASS WHICH IN TURN HELPS NARROW DOWN THE NEUTRON.STAR EQUATION OF STATE. HOWEVER AT PRESENT GWS ALONE ARE UNABLE TO SIGNIFICANTLY CONSTRAIN THE SPINS OF THE BINARY AND THE EFFECT OF SPIN ON THE BNS PROMPT-COLLAPSE THRESHOLD MASS IS UNDER-EXPLORED STYMIEING EFFORTS TO LEARN ABOUT THE NEUTRON STAR EQUATION OF STATE THIS WAY. FOR LOWER MASSES THE MERGER REMNANT LIVES LONG ENOUGH TO EMIT SIGNIFICANT NEUTRINO RADIATION THAT HAS A MAJOR EFFECT ON THE POST-MERGER DYNAMICS INCLUDING EJECTA VELOCITIES MASSES AND COMPOSITION. HOWEVER NEUTRINO TRANSPORT (NT) IN THE MERGER AFTERMATH.IS POORLY MODELED BY EXISTING METHODS RESULTING IN AN ORDER-OF-MAGNITUDE DISCREPANCY BETWEEN THE KILONOVAE-INFERRED EJECTA MASS AND NUMERICAL RELATIVITY PREDICTIONS FOR GW170817 AS WELL AS LINGERING QUESTIONS ABOUT THE ROLE NEUTRINOS PLAY IN LAUNCHING THE POST-MERGER JETS BELIEVED TO PRODUCE ASSOCIATED GRBS. TO FIX ALL THESE ISSUES RELIABLE THEORETICAL MODELING IS NEEDED. WE PROPOSE CUTTING-EDGE NUMERICAL RELATIVITY STUDIES OF BNS MERGERS. FIRST A DETAILED STUDY OF THE EFFECT OF SPIN ON BNS PROMPT-COLLAPSE WILL BE.PERFORMED. SIMULTANEOUSLY WE WILL DEVELOP A NOVEL FIRST-PRINCIPLE-BASED NT SOLVER FOR DYNAMICAL SPACETIME DESIGNED TO BE RELIABLE EVEN IN THE EXTREME BNS MERGER ENVIRONMENT. THE PUBLIC RELEASE OF THIS CODE WILL HAVE A MASSIVE IMPACT ON THE FIELD OF NUMERICAL RELATIVITY. WE WILL THEN USE THIS CODE TO CONDUCT THE FIRST BNS MERGER SIMULATIONS FULLY MODELING THE DYNAMICS OF POST-MERGER NEUTRINO WINDS AND THEIR EFFECTS ON EJECTA OUTFLOW AND JET LAUNCHING. THIS WILL GREATLY INCREASE THE SCIENTIFIC RETURN OF EM FOLLOWUP OBSERVATIONS BY MISSIONS SUCH AS FERMI INTEGRAL SWIFT AND OTHERS IN NASAS PHYSICS OF THE COSMOS PROGRAM HELPING TO FULFILL THE PROMISE OF.MULTIMESSENGER ASTRONOMY.