English: JWST NIRSpec instrument : Micro Shutter Assembly design (MSA). The current MSA is shown projected onto an ACS image at one pointing in Ω Cen. The image on right extracted from the area represented by the blue box on left, shows a sample of the many targets that are accessible to the MSA at a single pointing (sources marked with green plus symbols). Because of spectral overlap by targets in the same row of the MSA, many different MSA onfigurations would be required to obtain spectra of all accessible targets. Small ithers would further enable observation of the inaccessible targets shown in red