Design concept for the international x-ray observatory Flight Mirror Assembly

The Flight Mirror Assembly (FMA) mechanical design for NASA's next major x-ray telescope mission, the International X-Ray Observatory (IXO), recently kicked off at NASA. The design presents some unique engineering challenges requiring a novel mirror design due to the high angular resolution and large effective area required to achieve the desired scientific objectives. The Wolter-I x-ray telescope optical design requires about 14,000 0.4 mm thick glass mirror segments to be densely packed into a 3.2 m diameter FMA and supported with micron level accuracy and stability. Key challenges addressed by the FMA design concept include bonding the mirrors into the module without distortion, designing the segment support for glass survivability, keeping the structure light enough to launch, providing a large effective area, and preventing unacceptable thermal distortion. The thin mirror segments are mounted into intermediate wedge shaped structures called modules. Modules are kinematically mounted to the FMA primary structure which is being optimized for minimum mass and maximum projected area in the focal plane. The current design approach appears feasible without new technology development beyond that currently in process.