Design and analysis of an FUV spectrograph for a small satellite

Abstract

The Halo Ultraviolet Explorer (HUE) is a payload aimed at studying the diffuse far ultraviolet sky over a bandpass of 800 -- 1200 Ao. The novel features of HUE include a large effective collecting area (254 cm2) and fast (f/2.2) optics in a compact design optimized for a standard small satellite bus. We have investigated two different models, each with an 18 cm off-axis parabolic primary mirror, but one with an additional folding mirror to decrease the total length of the spectrograph. The spectrograph slit is dumbbell shaped maximizing the spectral resolution in the centre of the slit while increasing the sensitivity to diffuse sources at the edges. The primary scientific goal of the mission is to investigate the distribution of O VI in the Galactic halo. This line is a sensitive indicator of the hot gas in the interstellar medium and is critical in understanding the dynamics and energetics of the Galaxy.