The Deep Survey/Spectrometer telescope (right) is really two instruments in one. An innovative design allows both of these instruments to share the same gold-plated, grazing-incidence mirrors. This arrangement permits two entirely different observing functions to be carried out within the same compact assembly that weighs 336 kg (741 lb). The telescope's opening, or aperture, is divided into six equal segments. Radiation from three of these segments is focused by the grazing-incidence mirror onto the single deep survey detector. During the survey phase of the mission, this telescope performed long-exposure observations while being pointed along the dark shadow cast by the Earth, allowing it to detect much fainter sources than the all-sky survey scanners. Radiation from the other three aperture segments is intercepted by diffraction gratings that spread the radiation into beams of individual EUV wavelengths. The beams are then directed to the spectrometer's three detectors, called the short wavelength, medium wavelength, and long wavelength spectrometers. During spectroscopy studies, the spectrometer measures the wavelength distribution of radiation from astronomical EUV sources.