Light Weight, Scalable Manufacturing of Telescope Optics

NASA's future X-ray astronomy missions will require X-ray optics that have large effective areas, are lightweight, and cost effective. Recent X-ray telescopes, such as the Chandra Observatory, utilized reflectors made from zerodur which were up to 20mm thick. The thickness of the reflector as well as the mass limited the number of nested optics that could be implemented. The current state of the art reflectors are made from electroformed nickel/cobalt which is on the order of 1mm thick. The implementation of these thin optics have greatly increased the number of nested reflectors possible. XMM-Newton uses such optics and consists of 58 nested reflectors compared to 4 for Chandra. Aside from the manufacturing cost of the reflectors themselves, the mass of the telescope is a large factor that determines the overall cost of the mission, mainly due to the requirements of the launch vehicle. The proposed innovation seeks to improve upon the current state of the art by replacing much of the NiCo with a stiff, lightweight ceramic material. A thermal spray process will be developed to allow for the deposition of porosity graded alumina onto the rear surface of the reflector. Several diagnostic techniques will be used to adjust the inflight particle state as well as the resulting residual stress of the coating as to not adversely affect the figure accuracy of the optic. The gradation of the alumina layer will allow for CTE matching with the electroformed shell as well as optimization of the ceramic stiffness. By reducing the NiCo layer from 1mm to less than 100um and adding a 200um alumina layer as the support structure the overall mass of the telescope can be greatly reduced and thus reduce the overall cost of the mission. Additionally the overall thinner optic would allow a greater packing density and increase the capabilities of such X-ray telescopes.

X-ray astronomy is highly dependent upon focusing optics as illustrated by the profound influence that results from the Chandra, XMM-Newton, and Suzaku observatories are having upon astrophysics. X-ray measurements address many of the major scientific objectives of NASA. They involve the entire range of X-ray emitting objects from the most distant supermassive black holes to planets and comets in our own solar system. Any innovation that can reduce the mass, lower the cost or improve the resolution of a telescope would be important as it would allow future missions to occur sooner and be more effective. The development we are proposing includes fabrication and manufacturing techniques that can benefit X-ray telescope technology and the success in fabricating and testing new lighter weight, stronger material optics will allow high throughput X-ray integral mirror shell telescopes to be substantially lighter weight, with improved angular resolution. This endeavor would lead to the design and development of X-ray optics for future NASA missions such as the Advanced X-ray Spectroscopic Imaging Observatory (AXSIO) and the construction of hard X-ray telescopes for future missions, including Explorer missions. Future X-ray astronomy missions such as Smart-X will require large effective area and will utilize a segmented optics approach. Our technology studies to fabricate lighter weight substrates which may also be useful for future missions requiring segmented optics.

While the development focuses on x-ray optics, significant possibilities exist for multi-spectral systems (i.e. UV, visible, infrared). These applications can be applied to the area of defense telescopes, commercial space exploration and medical imaging. The proposed innovation of coating microstructure gradation for supporting the precise x-ray optical surface can be applied to other applications due to highly robustness of thermal spray processes including surface conforming ability, large area deposition, fast deposition rate, and versatile process parameter variation as compared to vacuum deposition coating processes. Free standing multi-layer thick coating pipes and tubes manufactured via thermal spray forming process and separation from a graphite mandrel have already been tested. Residual stress management of the multi-functional layers is critical to achieve the uniform geometry as well as good cohesive strength. In conjunction, microstructure gradation via porosity level will reduce the overall system weight while provide enough structural stiffness. TS process is applicable for membrane-type solid oxide fuel cell fabrication in a consecutive and economical deposition process from dense electrolyte layers to porous electrode layers. Porosity graded microstructure investigation along with residual stress management benefits this SOFC structure development.

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