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Extreme Ultraviolet Explorer
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Extreme Ultraviolet Explorer
The Extreme Ultraviolet Explorer (EUVE or Explorer 67) was a NASA space telescope for ultraviolet astronomy. EUVE was a part of NASA's Explorer spacecraft series. Launched on 7 June 1992 with instruments for ultraviolet (UV) radiation between wavelengths of 7 and 76 nm (equivalent to 0.016–0.163 keV in energy), the EUVE was the first satellite mission especially for the short-wave ultraviolet range. The satellite compiled an all-sky survey of 801 astronomical targets before being decommissioned on 31 January 2001.
The Extreme-Ultraviolet Explorer (EUVE) was a spinning spacecraft designed to rotate about the Earth/Sun line. EUVE was a part of NASA's Explorer spacecraft series and designed to operate in the extreme ultraviolet (EUV) range of the spectrum, from 70 to 760 Ångström (Å). This spacecraft's objective was to carry out a full-sky survey, and subsequently, a deep survey and pointed observations. Science objectives included discovering and studying UV sources radiating in this spectral region, and analyzing effects of the interstellar medium on the radiation from these sources. The proposal for the craft originated with the Space Astrophysics Group at the University of California Berkeley who had previously been involved with the EUV telescope on the Apollo element of the Apollo–Soyuz mission.
The full-sky survey was accomplished by three Wolter-Schwarzschild grazing-incidence telescopes. During the sky survey, the satellite was spun three times per orbit to image a 2° wide band of sky in each of four EUV passbands. The deep survey was accomplished with a fourth Wolter-Schwarzschild grazing-incidence telescope, within a 2 × 180° region of sky. This telescope was also used for three-EUV bandpass spectroscopy of individual sources, providing ~ 1–2 Å resolution spectra.
The goals of the mission included several different areas of observation using the extreme ultraviolet (EUV) range of frequencies:
The science instruments were attached to a Multi-mission Modular Spacecraft (MMS). The MMS was 3-axis stabilized, with a stellar reference control system and solar arrays.
NASA described these instruments:
The EUVE Spectrometer was a three-fold symmetric slitless objective design based on variable line space grazing incidence reflection gratings. Photon images are accumulated simultaneously in three bandpasses with effective spectral resolutions of 200–400 in 3 bandpasses from 70 to 760 Å. The Spectrometer and Deep Survey instruments share the DS/S mirror. The regions of the mirror devoted to the spectrometer and Deep Survey were defined at the front aperture, which was an annulus divided into six segments. Each of the spectrometer channels receives a beam of light from one of three alternating segments. This division gives each channel a geometric area of 75 cm2 (11.6 sq in). After the mirror, each converging beam then strikes one of three gratings which focus the spectra onto three detectors, arranged in a circle around the central Deep Survey detector. The throughput of the EUVE Spectrometer was determined by the combined effects of the mirrors' and gratings' coating reflectivities, which were functions of both wavelength and grazing angle, the filter transmissions, and the quantum efficiency functions of the detector photocathode materials.
In order to achieve good spectral resolution, any EUV spectrometer must be designed to limit the effect of diffuse sky radiation. The medium and long wavelength channels of the EUVE Spectrometer have wire-grid collimators placed directly after the aperture before the mirror, which limit the grazing angles of the incident light to exclude some of the sky background. They consist of 15 etched molybdenum grids, spaced exponentially and held in a thermally stable claw structure, also of molybdenum. The transmission profile of the stack is triangular in the dispersion direction and limits the beam to 20 arcminutes FWHM. The transmission of each collimator assembly was tested in visible light. The collimator relative transmissions were measured in the EUV by comparing the Spectrometer throughputs, measured as a function of off-axis angle, before and after installation of the collimators in the medium and long wavelength channels. Alignment to the boresight of the instrument was also determined. Both collimators functioned as designed, with peak transmissions of 64.2% and 65.4% in the medium and long wavelength channels, respectively.
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Extreme Ultraviolet Explorer
The Extreme Ultraviolet Explorer (EUVE or Explorer 67) was a NASA space telescope for ultraviolet astronomy. EUVE was a part of NASA's Explorer spacecraft series. Launched on 7 June 1992 with instruments for ultraviolet (UV) radiation between wavelengths of 7 and 76 nm (equivalent to 0.016–0.163 keV in energy), the EUVE was the first satellite mission especially for the short-wave ultraviolet range. The satellite compiled an all-sky survey of 801 astronomical targets before being decommissioned on 31 January 2001.
The Extreme-Ultraviolet Explorer (EUVE) was a spinning spacecraft designed to rotate about the Earth/Sun line. EUVE was a part of NASA's Explorer spacecraft series and designed to operate in the extreme ultraviolet (EUV) range of the spectrum, from 70 to 760 Ångström (Å). This spacecraft's objective was to carry out a full-sky survey, and subsequently, a deep survey and pointed observations. Science objectives included discovering and studying UV sources radiating in this spectral region, and analyzing effects of the interstellar medium on the radiation from these sources. The proposal for the craft originated with the Space Astrophysics Group at the University of California Berkeley who had previously been involved with the EUV telescope on the Apollo element of the Apollo–Soyuz mission.
The full-sky survey was accomplished by three Wolter-Schwarzschild grazing-incidence telescopes. During the sky survey, the satellite was spun three times per orbit to image a 2° wide band of sky in each of four EUV passbands. The deep survey was accomplished with a fourth Wolter-Schwarzschild grazing-incidence telescope, within a 2 × 180° region of sky. This telescope was also used for three-EUV bandpass spectroscopy of individual sources, providing ~ 1–2 Å resolution spectra.
The goals of the mission included several different areas of observation using the extreme ultraviolet (EUV) range of frequencies:
The science instruments were attached to a Multi-mission Modular Spacecraft (MMS). The MMS was 3-axis stabilized, with a stellar reference control system and solar arrays.
NASA described these instruments:
The EUVE Spectrometer was a three-fold symmetric slitless objective design based on variable line space grazing incidence reflection gratings. Photon images are accumulated simultaneously in three bandpasses with effective spectral resolutions of 200–400 in 3 bandpasses from 70 to 760 Å. The Spectrometer and Deep Survey instruments share the DS/S mirror. The regions of the mirror devoted to the spectrometer and Deep Survey were defined at the front aperture, which was an annulus divided into six segments. Each of the spectrometer channels receives a beam of light from one of three alternating segments. This division gives each channel a geometric area of 75 cm2 (11.6 sq in). After the mirror, each converging beam then strikes one of three gratings which focus the spectra onto three detectors, arranged in a circle around the central Deep Survey detector. The throughput of the EUVE Spectrometer was determined by the combined effects of the mirrors' and gratings' coating reflectivities, which were functions of both wavelength and grazing angle, the filter transmissions, and the quantum efficiency functions of the detector photocathode materials.
In order to achieve good spectral resolution, any EUV spectrometer must be designed to limit the effect of diffuse sky radiation. The medium and long wavelength channels of the EUVE Spectrometer have wire-grid collimators placed directly after the aperture before the mirror, which limit the grazing angles of the incident light to exclude some of the sky background. They consist of 15 etched molybdenum grids, spaced exponentially and held in a thermally stable claw structure, also of molybdenum. The transmission profile of the stack is triangular in the dispersion direction and limits the beam to 20 arcminutes FWHM. The transmission of each collimator assembly was tested in visible light. The collimator relative transmissions were measured in the EUV by comparing the Spectrometer throughputs, measured as a function of off-axis angle, before and after installation of the collimators in the medium and long wavelength channels. Alignment to the boresight of the instrument was also determined. Both collimators functioned as designed, with peak transmissions of 64.2% and 65.4% in the medium and long wavelength channels, respectively.
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