17264

The exceptional gamma-ray burst GRB 221009A is the brightest GRB ever observed by almost two orders of magnitude comma and rate estimates suggest it is a once per millenium event. It is now the subject of an intensive series of multi-wavelength observations with detections of individual photons with tens to hundreds of TeV to low frequency radio comma including approved NIR spectroscopy from JWST. Remarkably comma it is also a relatively nearby event with a redshift of only z=0.15. The worldwide follow-up is building what will become a legacy data set for the field. The collapsars accompanying such lumonous bursts have been proposed as a source of r-process heavy elements comma and this case offers the best opportunity for the foreseeable future to test this hypothesis. We propose here non-disruptive HST ToO imaging observations at mid- to late-times post burst comma sampling the spectral energy distribution evolution comma in order to characterise the accompanying SN comma compare its properties to those of more ordinary GRBs comma and crucially to seek the signature of r-process nucleosynthesis comma expected to produce NIR excess starting after the SN peak comma that is 3-6 weeks after the GRB. These data will also pinpoint the burst position on its host comma allowing future studies of the GRB progenitor environment. HST data are essential because of the target faintness and crucially because it will not be observable from ground (nor JWST) on the critical epochs requested here.