Description and ray-tracing simulations of HYPE, a far-ultraviolet polarimetric Spatial-Heterodyne spectrometer

Temperature and velocity-distribution remote-sensing of faint diffuse sources such as the interplanetary medium (IPM), comets and planetary atmospheres, is an instrumental challenge that becomes more pronounced in the ultraviolet. All reflective Spatial-Heterodyne Spectrometers (SHS), an emerging new class of instruments that combines both high étendue and high resolving power (greater than 10⁵), are ideally suited to these types of observations. Their all-reflective configuration and their self-compensating monolithic design enable them to operate under the tight tolerances of the ultraviolet and to survive the rigors of space launch. An in-development sounding-rocket experiment, the Hydrogen Polarimetric Explorer (HYPE), will merge an all-reflective SHS with a half-wave Brewster reflection polarimeter to obtain the first interferometric polarimetry of an ultraviolet emission line source. Its initial flight will target the IPM at the hydrogen Lyman-alpha transition (121.6nm). HYPE's novel optical configuration also combines several improvements in reflective SHS design, including true zero-path interferometry, no aliasing, and one-dimensional imaging. The optical layout and performance of the HYPE prototype will be described along with simulation results from ray-tracing computations.