Mirror Assembly Bonded Joints for the POEMMA Balloon with Radio (PBR) NASA Mission

The POEMMA Balloon with Radio (PBR) mission aims to measure ultra-high-energy cosmic rays (UHECRs), neutrinos, and high-altitude, horizontal air showers. The onboard 16-segment concave mirror assembly is joined to the telescope frame using epoxy-bonded Kovar pads. We evaluate the thermal and structural resilience of the epoxy bond to the Kovar flight pads through tensile and shear configuration tests under both shock loads and long-term loads, while replicating the thermal conditions experienced in past POEMMA missions. We find the pad/mirror bonded joint withstands forces of 8G in all test configurations, with greater than a 200% safety factor, greatly exceeding NASA flight requirements for bonded joints. We demonstrate the procedure for the assembly of the individual mirror segments, both the bonding procedure of the flexure assembly to the glass and the integration of the mirror segments into the full mirror assembly.