Engineering topics

Melugin, R.

Publications and source records attributed to Melugin, R..

3 records

NASA NTRS1982

Optimum shapes for lightweighted mirrors

Two types of monolithic lightweight mirrors with arched backs, the center-supported single arch and the ring-supported double arch, are discussed. It is shown that, assuming a maximum permissible rms tolerance of 6 x 10 to the -6th in, the single arch mirror weighs about 50 percent of an equivalent solid mirror up to a diameter of 24 in. The single arch is relatively simple to construct and uses a simple center support. Where a better figure is required, or for larger sizes, the double arch is superior in performance to the single arch. The weight of the double arch will vary from about 50 to under 40 percent of an equivalent conventional mirror as the diameter is increased from 20 to 144 in. Further weight reduction for the double arch is possible through the reduction of the size of the support.

Vukobratovich, D.↗

NASA NTRS1982

Gravity deflections of lightweighted mirrors

Two 20-in-diameter lightweight fused-silica mirrors, one having a single arch configuration and the other a double arch configuration, were tested interferometrically at their centers of curvature in both a face-up and face-down support mode. By subtracting the wavefront errors in these two support modes, the gravity deflections were determined in spite of some residual figure error. It is found that the single arch mirror, supported horizontally on three points, has about half the total deflection of the double arch design. The single arch mirror is twice as stiff azimuthally as the double arch, but radially the double arch has four times the stiffness of the single arch. If a more uniform azimuthal support were provided for the double arch, its deflections would be expected to improve significantly.

Anderson, D.↗

NASA NTRS1980

Alignment and evaluation of the cryogenic corrected infrared astronomical satellite /IRAS/ telescope

Room temperature alignment and evaluation techniques for the Infrared Astronomical Satellite (IRAS) telescope, which has a primary mirror figured to correct for surface distortions and the 2 K operating temperature are discussed. Interferometric cryogenic testing of the 0.6 m, f/1.5 lightweighted beryllium primary mirror at its intended operating temperature reveals surface distortions that can be modeled with Zernike polynomials. With this model, it becomes possible to derive the 'inverse' of the cryowavefront error (ideal cryo mirror) and to figure the cryo correction into the primary mirror using Perkin-Elmer's Computer Controlled Polisher. It is recognized that during room temperature assembly of the system, misalignment of the secondary mirror can introduce additional unwanted aberrations that may cancel or distort the wavefront errors purposely introduced by the cryo figuring. To avoid this possible degradation and to ensure optimum telescope performance, the system Zernike polynomial coefficients and wavefront maps generated from the in-process alignment interferograms are monitored and compared to Zernike coefficients and wavefront maps for the cryo corrected primary mirror.

Harned, N.↗