A design concept for the High Resolution Imager on the Habitable Worlds Observatory
The Habitable Worlds Observatory (HWO) will be NASA's next flagship astrophysics mission, designed to search for signs of life on planets around nearby stars and conduct transformational science across astrophysics. Its High Resolution Imager (HRI) is not only the observatory's main imaging camera, but also provides grism spectroscopy and sub-microarcsecond astrometry, as well as the observatory's fine guidance, wavefront sensing and pupil imaging. We present a design concept for HRI, developed during concurrent design sessions by flowing down science requirements within the envelope of NASA's EAC-1 telescope architecture. Light from a 3'x2' field is collimated by two mirrors, then divided by a dichroic for simultaneous observations in an ultraviolet-to-visible arm covering 200-900 nm and a near-infrared arm covering 0.9-2.2 um. By minimising the number of reflective surfaces upstream of the dichroic, our optical design maximises throughput and stability, while reducing wavefront error. Readout modes can be chosen in orbit to image the entire field in exposures of at least 10 seconds, or in smaller windows for observations up to 1 kHz. Throughout, we emphasise the interplay between subsystems that couple design choices.