Future astrophysical missions will require fabrication technology capable of producing high angular resolution x - ray optics . A full - shell direct fabrication approach using modern robotic polishing machines has the potential for producing high resolution , light - weight and affordable x - ray mirrors that can be nested to produce large collecting area . This approach to mirror fabrication , based on the use of the metal substrates coated with nickel phosphorous alloy , is being pursued at MSFC . The design of the polishing fixtures for the direct fabrication , the surface figure metrology techniques used and the results of the polishing experiments are presented .