A comparison of different alignment approaches for the segmented grazing incidence mirrors on Constellation-X

Each of the four Spectroscopy X-ray Telescopes (SXT) on Constellation-X contain a mirror assembly comprised of 2600 primary and secondary mirror segments. Critical to the performance of the mirror assemblies is the alignment of secondary to primary, and alignment of mirror pairs to one another. Focus errors must be corrected in order to meet imaging error budgets. The use of segmented mirrors enables unique alignment strategies not feasible with mirror shells of a full revolution. We discuss the relative advantages and disadvantages of two Con-X alignment strategies to minimize focus errors between shells. In the first approach, the mirrors are bent azimuthally to adjust the focal length of the mirror pair. In the second approach, coma is used to compensate for the transverse focus error. We examine the limits of applicability of the two approaches, and also discuss alignment error budgets.