Flexure Mechanical Testing for PBR

The Probe Of Extreme Multi-Messenger Astrophysics (POEMMA) Balloon with Radio (PBR) is a NASA super-pressure balloon payload set to launch in 2027. PBR will study Ultra-High-Energy Cosmic Rays, Very High Energy Neutrinos, and High-Altitude Horizontal Air-showers from 33 km above the Earth. This telescope uses a hybrid focal surface with both fluorescence and Cherenkov cameras. With a 1.1 m wide aperture, the main optical component of PBR is an array of 12 Borosilicate spherical glass mirror segments that will all be connected to the frame of the telescope with epoxy bonded kovar pads and a complex 3D spring called a flexure to minimize thermal load on the glue joints. All glue joints and the associated support must pass rigorous standards set by NASA so it is crucial to characterize the flexures. This poster presentation will touch on the results of physical tests performed to characterize the flexure's spring constant at room and low temperatures (approximately -70 ℃) as well as the resulting temperature-dependent constitutive model. Additionally, displacement-controlled testing has been done to determine the forces on the glass pad boundary to compare against FEA simulations. Discussion on the test-setup and procedure required to achieve the lower atmospheric testing conditions will also be presented.