A schematic illustration of the IUE scientific instrument is shown in Figure 2.1. The instrument contains two spectrographs which function independently. Each spectrograph has a prime and a redundant camera. The Long-Wavelength Prime (LWP) and Short-Wavelength Prime (SWP) cameras are the standard detectors. The Long-Wavelength Redundant (LWR) camera suffers from some problems, but is still available for users with reduced sensitivity (see section 3.9). The Short-Wavelength Redundant (SWR) camera is not operational. More detailed descriptions of the cameras and spacecraft are given in Boggess et al. (1978a, b) and in the Camera User's Guide (Coleman et al. 1977).
Figure 2.1: Optical schematic of the IUE Scientific Instrument derived from Coleman, et al. (1977). The available detectors are underlined. This schematic does not show two plane mirrors which are located behind the entrance apertures for the long-wavelength spectrograph in order to allow separation of the optical paths.