The Balloon Borne XL-Calibur Hard X-ray Polarimetry Mission

In this presentation, I will give an overview of the design, assembly, and realization of the XL-Calibur mission. XL-Calibur is a mission designed to perform precision measurements of the polarization of the 15-80 keV emission from bright galactic X-ray sources, i.e. mass accreting black holes, and accretion and rotation powered neutron stars, on Long Duration Balloon (LDB) flights. The mission was first conceived in 2010 with a small team. After the successful Long Duration Balloon flight in December 2018, the supporting collaboration was enlarged and now includes 50 scientists from 20 institutions from the US, Japan, and Sweden. We flew XL-Calibur in July 2022 from Sweden to Canada, and succeeded in fulfilling and even exceeding our expectations, returning high signal to noise ratio data sets on the black hole Cyg X-1 and the Crab Nebula and Pulsar. I will emphasize some of the practical aspects of developing and implementing a LDB flight mission like XL-Calibur, and will also present some of the results from the 2022 flight.