Figure and Dimension Metrology of Extremely Lightweight X-Ray Mirrors for Space Astronomy Applications

The International X-ray Observatory (IXO) is the next major space X-ray observatory, performing both imaging and spectroscopic studies of all kinds of objects in the Universe. It is a collaborative mission of the National Aeronautics and Space Administration of the United States, the European Space Agency, and Japan Aerospace Exploration Agency. It is to be launched into a Sun-Earth L2 orbit in 2021. One of the most challenging aspects of the mission is the construction of a flight mirror assembly capable focusing X-rays in the band of 0.1 to 40 keY with an angular resolution of better than 5 arc-seconds and with an effective collection area of more than 3 sq m. The mirror assembly will consist of approximately 15,000 parabolic and hyperbolic mirror segments, each of which is approximately 200mm by 300mm with a thickness of 0.4mm. The manufacture and qualification of these mirror segments and their integration into the giant mirror assembly have been the objectives of a vigorous technology development program at NASA's Goddard Space Flight Center. Each of these mirror segments needs to be measured and qualified for both optical figure and mechanical dimensions. In this talk, I will describe the technology program with a particular emphasis on a measurement system we are developing to meet those requirements, including the use of coordinate measuring machines, Fizeau interferometers, and custom-designed, and -built null lens. This system is capable of measuring highly off-axis aspherical or cylindrical mirrors with repeatability, accuracy, and speed.