The future of high angular resolution x-ray optics for astronomy (Conference Presentation)

Beginning with the Einstein Observatory in 1978, continuing with ROSAT in the 1990’s and currently the Chandra X-Ray Observatory, high angular resolution focusing telescopes have been the premier X-ray astronomy instruments of their time. However, as they have acquired larger area and improved angular resolution they have become increasingly massive and expensive. The successor to Chandra planned for the late 2020’s currently named “Lynx” will rely on active optics to allow the use of much lower mass segmented mirrors with the goal of gaining an order of magnitude larger area than Chandra with a lower ratio of mass to effective area and perhaps slightly better angular resolution than Chandra’s 0.5 arc second half power diameter and/or over a somewhat larger field. The goals for Lynx are probably at the limit of what is possible with grazing incidence X-ray optics. Success in the development of higher angular resolution, lower mass telescopes will come at the expense of effective area. A diffractive-refractive pair consisting of a Fresnel zone plate and a diffractive lens that transmits rather than reflects X-rays is capable in theory of achieving mili arc second resolution with a much lower ratio of mass to effective area than the grazing incidence reflective Wolter optics. However, the focal lengths of this system are thousands of kilometers necessitating formation flying between one spacecraft hosting the optics and another hosting the detectors, most likely in a Sun-Earth L2 orbit. The trajectory of one of the two spacecraft can be in a true orbit but the other must be powered by an ion engine to maintain the alignment. The growing interest in deep space astronaut operations may allow the ion engines to be replaced when depleted.