WUPPE Telescope

The WUPPE telescope is a 20-inch classical Cassegrain telescope. As light enters the telescope(from right in the figure above), it encounters an extensive sunshade fabricated by Heath-Tecna, Inc. from aluminum honeycomb with the inner honeycomb exposed and painted black. The sunshade allows for observations of stars brighter than magnitude 6 during the daytime part of the orbit. Next, a latchable aperture door provides for contamination protection during launch and re-entry (cleanliness is maintained on the ground with a dry N₂ gas purge). A Westinghouse deuterium hollow-cathode lamp mounted on a miniature optical bench in the door provides an ultraviolet continuum for checking system response on the ground. The telescope tube itself is fabricated from two rolled and welded aluminum tubes with internal baffles added. The primary mirror, an 0.5 m aperture f/3 parabola, consists of a light-weighted Schott Zerodur blank polished to lambda/4, coated with a standard Al/MgF₂ coating. It is held by a three-point spider which penetrates the central hole of the mirror and which holds an extensive internal baffle. The hyperbolic secondary mirror completes an optical system with an effective f/10 focal ratio. For alignment, offsetting, and focussing, three secondary mirror vanes may be articulated independently. By pivoting the secondary mirror about the "neutral point" approximately 5 cm beyond the primary focal point, an offsetting capability of +/- 15 arcmin is possible without appreciable image degradation (image diameter < 1.5 arcsec). In addition, the secondary mirror cell incorporates tip/tilt image motion compensation (IMC) through two piezo-electric transducers commanded by signals from the Spacelab pointing system. This IMC system together with the pointing performance of the Spacelab Instrument Pointing System (IPS) is specified to provide a pointing jitter of less than +/- 0.2 arcseconds, as required for maintenance of optimum spectral purity.

-taken from Nordsieck et al. 1994, SPIE, Vol. 2010, p.2.