Development of an Extreme Ultraviolet Imager for the Sun Coronal Ejection Tracker (SunCET) CubeSat

The Sun Coronal Ejection Tracker (SunCET) telescope is an extreme ultraviolet imager used to study the dominant physical mechanisms for coronal mass ejection (CME) acceleration profiles as a function of altitude and time. The SunCET mission uses a 6U CubeSat to fill the middle corona (1.5-4 solar radii from the Sun's center) observational gap left by the Heliophysics System Observatory. CMEs are significant because they can affect space weather, impacting satellite operations, communications, and power systems on Earth. SunCET uses a two-mirror Ritchey-Chrétien telescope with a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{2.0}^{\circ}\times \mathbf{2.7}^{\circ}$</tex> full field of view (FOV) to form a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{3.79} \times \mathbf{5.03}$</tex> solar radii image on a backside illuminated CMOS detector. Aluminum filters and aperiodic B4C/Mo/Al mirror coatings are utilized to block visible light and create a 17–20 nm bandpass. SunCET will be the first to fly these novel coatings, which are less susceptible to performance degradation in air than existing formulations. Low coefficient of thermal expansion materials (Zerodur and Invar) are used for the mirrors and structure to maintain focus over temperature. The telescope is 1.87kg and fits within a 10x15x20cm volume. The telescope was assembled and tested at Johns Hopkins Applied Physics Laboratory between February and May 2024. The telescope was measured to have a point spread function (PSF) with an 80% encircled energy radius of less than 30 arcseconds within the inner 3.5 solar radius portion of the FOV. This ensures SunCET's observations complement existing and future coronagraphs and heliospheric imagers for continuity of coverage out to hundreds of solar radii.