P1 and H1 will be delivered to the Eastman Kodak Corporation (EKC) for alignment and assembly as part of VETA-2. EKC will use these elements to check the alignment equipment and for mechanical tests. Following these tests, all mirror elements will be shipped to Optical Coating Laboratories, Inc. (OCLI) where the final cleaning and coating (with sputtered Iridium) will take place. OCLI first will verify the sputtering geometry on test samples which duplicate the required geometry for the optical elements. The final coating of the optical element (and witness samples) will be performed after satisfactory preliminary qualification runs are obtained. The mirror elements then will be shipped back to EKC for final alignment and assembly.
The final alignment and assembly at EKC will be performed in a vertical tower which is inside a class 100 clean area. The mirror elements, composite support sleeves, and aluminum center aperture plate all must be supported in a strain free manner. The mirror elements will be positioned above an optical flat located at the bottom of the assembly tower. The optical flat will be leveled to gravity, and the optical reference assembly mounted on the center aperture plate will be made parallel to the optical flat. The inner paraboloid (P6) then will be mounted so that its axis of symmetry is normal to the optical flat. The optical alignment sensor used for this purpose illuminates the paraboloid from near its focus; light passes through the paraboloid, reflects from the flat, and returns to a quad cell detector near the paraboloid focus. The software does a fourier decomposition of the centroid coordinates as a function of the azimuthal angle illuminated. The paraboloid is aligned normal to the flat when the centroid of the returned light does not show a dependence upon the azimuth angle (). The paraboloid focus is determined by finding the point where the centroid does not show a dependence upon azimuth angle; proper axial and lateral alignment is achieved when the paraboloid focus is coincident with the center of a sphere which is part of the optical reference assembly mounted on the center aperture plate. This technique was developed on a technology development program, and shown to be sensitive to alignment errors of less than 0.02 arc seconds. The next smaller paraboloid (P4) then is added and aligned so that it is co-axial with P6 and the two paraboloid foci are coincident. The paraboloid focal lengths are about twice the system focal lengths, and this extra length is accommodated by fold flats. These fold flats then are removed and the first hyperboloid (H6) is added. The alignment is similar to that of the paraboloids; a azimuthal dependence of the image centroid indicates that the hyperboloid focus is displaced laterally from that of the associated paraboloid. The position of the system focus can be adjusted laterally without any loss of resolution by rotating the hyperboloid about the common focus it shares with the associated paraboloid; the position of the system focus can be adjusted axially with small loss of resolution by displacing the hyperboloid axially. The position of H6 is adjusted to yield a coma-free (no centroid dependence) image which is coincident with the center of a second sphere on the optical reference assembly. The next paraboloid (P3) then will be aligned so that its focus is coincident with that of P4; then H4 will be added so that its focus is coincident with that of H6, and so forth through P1, H3, and H1.
The mirror then will be shipped to the NASA Marshall Space Flight Center for final X-ray calibration, where the X-ray performance will be determined and compared with the expected results based upon the metrology data and the calculated degradation from gravity, finite source distance, detector resolution, and so forth. We had excellent agreement for the only previous mirror for which metrology adequate for this task existed, and we hope no surprises will be found.