Imaging X-Ray Polarimetry Explorer (IXPE) - Ready for Flight

The Imaging X-Ray Polarimetry Explorer (IXPE) is designed to expand understanding of high-energy astrophysical processes and sources, in support of NASA's first science objective in Astrophysics: “Discover how the universe works.” Polarization measurements and imaging are key capabilities of the IXPE observatory. IXPE, an international collaboration between NASA and the Italian Space Agency (ASI), is a NASA Small Explorer designed as a 2-year mission which launches to a circular LEO orbit at an altitude of 600 km and an inclination of ~0 degrees on a Falcon 9 launch vehicle. The payload uses a single science operational mode to capture the x-ray data from the science targets. The mission design follows a simple observing paradigm: pointed viewing of known x-ray sources (with known locations in the sky) over multiple orbits (not necessarily consecutive orbits) until the observation is complete. IXPE's payload is a set of three identical, imaging, x-ray polarimetry telescopes mounted on a common optical bench and co-aligned with the pointing axis of the spacecraft. The payload is accommodated on the spacecraft top deck. The BCP-Small spacecraft provides the necessary resources to support and operate the payload elements and enable continuous science data collection. The Observatory communicates with ground stations via S-band link. The ground system consists of three major elements: the ground stations for data receipt and command upload to the Observatory; the Mission Operation Center (MOC); and Science Operations Center (SOC). The primary ground station, contributed to the IXPE mission as part of an international collaboration with ASI is at Malindi, Kenya. The back-up ground station is in Singapore through the NEN. TDRSS is used for early operations and contingencies. The MOC is located at CU/LASP using their existing multi-mission MOC. The SOC is located at MSFC and the data archive at the GSFC HEASARC. The IXPE Project completed its Phase A activities in July 2016; Project start occurred in February 2017. Currently, the Project is finishing up Phase D activities, having completed all Observatory environmental testing and launch with final commissioning activities ongoing. Launch occurred on 9 December 2021. This paper summarizes the IXPE mission, describes the Observatory, launch segment, ground system, discusses launch and commissioning and reviews lessons-learned.