IXPE Observatory Integrated Thermal, Power, and Attitude Mission Design Analysis

When the Imaging X-ray Polarimetry Explorer (IXPE) launches in 2021, the world will have a new orbiting Xray observatory capable of examining previously unexplored celestial phenomena. For the first time, an earth-orbiting observatory will be able to resolve the polarization angle of each incoming X-ray photon in an imaged scene, and provide polarization measurements of each source within the instrument's field of view. The two top-level project requirements that drive the mission design and observatory capability are the execution, in a one year period, of a Design Reference Mission (DRM) containing 48 representative targets, and the ability to observe any location on the celestial sphere for 30 days every six months. IXPE exceeds these driving requirements with a straightforward observatory design concept that allows a large instrument field of regard with a fixed solar array. IXPE completed its preliminary design review in June 2018 with a baseline power and thermal design that accommodates all observatory attitudes that maintain a +/- 25 degree angle between the body-fixed solar array and the plane normal to the sun vector. This paper examines how observatory attitude affects power consumption, how the DRM targets drive the observatory power and thermal design, and potential system design trades.