ORFEUS-SPAS - The Berkeley EUV spectrometer

Abstract

The Berkeley EUV spectrometer of ORFEUS-SPAS, a joint project of NASA and the BMFT, incorporates a set of four novel spherically figured, varied line-space gratings used in a geometry that is similar to that of the classic Rowland mount to span an interval of 390 and 1200 A. Two spectral detector units containing curved microchannel plates and delay-line anodes encode the arriving photons in digital format for telemetry. An additional optic directs the image of the source in the entrance aperture onto a sealed FUV detector which is used to track the source as it drifts during an observation, enabling a postflight reconstruction of the spacecraft pointing vector. This in turn makes it possible to define with precision the wavelength of each recorded photon.