Polishing of X-Ray Optics

Manufacturing grazing incidence x-ray mirrors costs between $4 to $6 million per square meter of optical surface area. To reduce the cost of making x-ray mirrors, NASA is seeking manufacturing solutions to aid in cost reduction factors of 5 to 50 times. One cost driver is the mandrel-based polishing process that impacts the inside surface of an X-ray mirror shell. Current shells are created through a replication process utilizing an aluminum mandrel. OptiPro is proposing to enhance process solutions to reduce costs required for polishing both the mandrel and the outside shell surface by maintaining constant force during polishing, developing new polishing tools, and optimizing the polishing algorithm. The target platform for these improvements will be on an OptiPros polishing platform. These improvements will be directly applicable to the polishing being done at Marshall Space Flight Center on various equipment including OptiPros UltraForm Finishing platform. OptiPros Phase II will focus on prototyping hardware and software solutions to provide a cost effective deterministic solution when combined with an optimized polishing process. A rotisserie part A-Axis and a new dual tool polishing head will be updated to an existing bridge polishing platform. A force feedback system will be prototyped and integrated into a polisher to provide in-situ adjustments during polishing. Prototype polishing tools will be further refined and optimized. The polishing algorithms are being enhanced for more efficient polishing and achieving tighter tolerances through improvements to correction algorithms and new adaptive learning routines. The software will be upgraded to incorporate all of these changes. All innovations will be tested on a demonstrator mandrel and processing will be refined to improve surface quality as efficiently as possible. The results of this Phase II will enhance fabrication at MSFC and become commercially available solutions at OptiPro. The x-ray mirror assembly (XMA) is the key imaging assembly within any x-ray telescope - including the Lynx mission - and largely defines its performance. All XMA's consist of a series of grazing incidence rotationally-symmetric reflective shells for collecting light and focusing it onto a detector. It has been shown that a series of shells can be fabricated from nickel using mandrels and nickel-replication processes. In this proposal, we offer a means to improve the fabrication economics associated with these techniques, while also substantially improving both the quality of surface finish and surface figure error of shells through the potential use of five innovations we wish to develop in Phase II. In particular, these innovations include 1) updates to the mandrel-based fabrication machine including a dual-tool machining head and rotisserie A-axis, 2) improved use of tools using force/torque sensing and feedback, 3) enhanced tool path algorithms with learning techniques, 4) tool process optimizations transferable to GSFC and MSFC, and 5) upgrades to on-board polishing software. The technical objectives of the Phase II work are to develop the hardware, software, and process solutions to efficiently polish the x-ray mandrels and shells in a single polishing platform. Specifically, the objectives of the Phase II effort include: 1. Design, prototype, and install a new dual tool polishing head on an existing bridge polishing platform for polishing mandrels during the Phase II. 2. Build and install rotisserie axis on existing bridge polishing platform for polishing full-shell mandrels. 3. Refine the tooling concepts developed in Phase I for new polishing tool options. 4. Develop and integrate polishing feedback system that adjusts based on polishing force/torque measured. 5. Develop and evaluate a new correction algorithms to further optimize the error map driven polishing process. 6. Develop and evaluate a learning algorithm for adapting the polishing tool paths for system error. 7. Update on-board polishing software to use the innovations being developed during Phase II. 8. Develop optimized polishing process on a prototype mandrel. The deliverables at the end of the Phase II project are a final report summarizing the work efforts executed in support of the above objectives, the prototype mandrel produced through the completion of those work tasks, and the machine hardware and software developed during the tasks.
Benefits: The proposed system will benefit all projects using x-ray shells and mandrels, both cylindrical and segments that fit within the working envelope that the proposed hardware is installed on. Missions including Lynx and the IR/O/UV space telescope would be among those that would benefit from the technology being developed. These improvements will be applicable to polishing being done at Marshall Space Flight Center on various equipment including OptiPro's UltraForm Finishing platform and polishing being done at Goddard Space Flight Center. The proposed polishing system and hardware improvements would benefit all types of part geometries including the following: Rotationally Symmetric Geometries - Aspheres, Spheres, and Ogive Missile Domes Cylindrical Optics Freeform and Conformal Optics Optics The processes being developed to work with nickel will provide ground work for working on other metal materials, including aluminum.