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The joint gravitational wave and electromagnetic detections of the binary neutron star (BNS) merger GW170817 ushered in a new era of astrophysics. In the UV-optical-NIR the emission (a d_commakilonovad_comma) was powered by radioactive decay of nuclei produced via r-process nucleosynthesis. In the gamma-ray comma X-ray comma and radio the emission was instead powered by an off-axis jet typical of short gamma-ray bursts (SGRBs) this connection was previously supported by the HST detection of a kilonova in the short GRB130603B. With only a single joint GW-EM detection and a single kilonova detection in an SGRB comma the key frontier is to begin to map the distribution of merger outcomesdoublePoint ejecta mass comma velocity comma geometry comma and nucleosynthetic yields. Here we propose to achieve this goal with HST observations of a kilonova associated with an SGRBs observations of kilonovae in SGRBs are essential because the orientation is well known (face-on comma along the binary.s angular momentum axis) and the LIGO-Virgo Observing Run 3 has not yielded joint GW-EM detections. Such a study can only be achieved with the sensitivity and resolution of HST comma and it matches one of the d_commaspecial initiativesd_comma comma namely deep NIR monitoring that is essential for informing future JWST follow-ups (d_commaJWST Preparatory Observationsd_comma). We request 10 orbits for 1 SGRB event. The HST observations will be supported by approved programs at Chandra comma VLA comma ALMA comma Gemini comma Keck comma Magellan comma MMT that will provide the targets comma cover optical and early NIR follow-up to establish the baseline behavior comma and complete the multi-wavelength picture of the event. Given the broad interest in this topic we waive the proprietary period.