Addressing circularity errors in full shell x-ray optics

Recent advances in mandrel polishing have enabled full shell x-ray optics at NASA Marshall Space Flight Center (MSFC) to achieve axial figure errors approaching sub-arcsecond levels. However, azimuthal circularity errors continue to limit angular resolution, contributing approximately 5 arcseconds half-power-diameter (HPD) to the point spread function. In electroformed nickel-cobalt shell optics fabricated via mandrel replication, axial figure accuracy is effectively transferred from the precision-polished mandrels to the replicated shells. Conversely, the electroforming process itself, combined with residual stress relaxation during shell extraction, introduces systematic out-of-roundness deformations in the azimuthal direction. These circularity errors manifest as low spatial frequency slope variations that propagate azimuthally around the shell circumference, representing a dominant contribution to the overall error budget. Understanding the correlation between circularity errors and optical performance degradation is essential for advancing sub-arcsecond x-ray telescope technology. We present comprehensive three-dimensional ray-tracing analyses quantifying the impact of measured circularity error modes on imaging performance. Furthermore, we report on experimental validation and simulation results for several mitigation strategies designed to minimize circularity-induced aberrations.