2016 Scientific Ballooning Technologies Workshop Title The X-Calibur Telescope Truss and Gondola Author Fabian Kislat (Washington University, St. Louis) Abstract X-Calibur is a scattering hard x-ray polarimeter to be flown on a high-altitude balloon in the fall of 2016. In X-Calibur, the InFOCuS grazing incidence x-ray mirror focusses x-rays onto a 13mmdiameter plastic scintillator, in which they scatter. The scattered photons are detected by CdZnTe detectors surrounding the scattering slab. Polarization can then be inferred from the azimuthal scattering distribution because photons scatter preferentially perpendicular to their polarization direction. The telescope will utilize the Wallops Arc-Second Pointer (WASP). In order to keep systematic uncertainties small, the focal spot of the 8m focal length mirror must stay within 0.5mm of the center of the scattering slab. This places strong requirements on the stiffness and thermal expansion of the telescope truss. In this talk I present the design of the Carbon Fiber Aluminum composite truss for X-Calibur, the in-flight alignment monitoring systems, as well as our approach to actively controlling alignment during flight by heating the Aluminum joints of the truss. Furthermore, the results of laboratory tests of the structure will be discussed, demonstrating that we expect to fulfill the most stringent requirements that will allow us to operat the truss without the active control, making the active control a risk minimization backup option to compensate for unforseen effects.

2016balloontech.umn.edu