Ultraviolet Contrast Performance of the Next Generation Microshutter Arrays in Development to Enable Multi-Object Spectroscopy on the Habitable Worlds Observatory

The use of microshutter arrays (MSAs) to enable multi-object spectroscopy (MOS) on JWST is now well documented and has been used extensively by the scientific community on the NIRSpec instrument. In response to both the design point studies of both LUVOIR and HabEx, the National Academies recognized the value of MOS for next generation science in the capabilities that NASA’s next Flagship mission, the Habitable Worlds Observatory (HWO), could enable for transformational astrophysics. The challenge was that while the original MSAs had been designed for use in the infrared (IR) for JWST, the waveband of particular interest for HWO astrophysics is the far ultraviolet (FUV). As such the design of the MSAs has been completely overhauled with the inclusion of light shields to prevent photons slipping around the edges of closed shutters, and the manufacture advancement needed to prevent buckling in the shutter blades to provide a flat surface that would sit flush against those light shields. We report in this paper the successes achieved in improving the physical and manufacture performance of the next generation MSAs (NGMSAs) to provide a baseline technological solution that will provide a low-risk capability for HWO. As part of this report we will present contrast measurements in a custom TVAC chamber at NASA Goddard that has simulated the expected beam speeds of a UV instrument on HWO and demonstrated the contrast performance.