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An important part of a balanced future program in space astronomy is a fast, wide-angle telescope (a Space Schmidt) capable of imaging in the ground-inaccessible ultraviolet wave-length range (1100-3000 Å) and capable of reaching substantially fainter background light levels in the visible and near-infrared than are groundbased telescopes (limited by airglow sky background). In 1978, NASA appointed a working group to assess the scientific need and objectives for such a telescope, and to study its feasibility of implementation. In the latter task, the working group was assisted by the Goddard Space Flight Center and by the Perkin Elmer Optical Technology Division (under contract to GSFC). Among the principal observational objectives which were outlined are: Detection of hidden hot objects UV morphology of galaxies Determine presence of dust in galactic fields and extragalactic objects Detection and study of faint extended objects Detection and study of emission line objects Observation of solar system objects (particularly diffuse ones). In addition to the scientific objectives, other concerns such as technical feasibility, complexity, and cost resulted in the following guidelines for the engineering aspects of the feasibility study: Confine space to one orbiter pallet. Use one of the standard pointing systems. Minimize cost. 5 degree field of view 0.75 m diameter aperture, minimum 1.0 arc sec image resolution Fast focal ratio (~ f/3.0) 170 mm diameter detector format (~ 10 μm pixels). The feasibility study determined that all of these specifications could be met with reason-able assurance, and baseline configurations were derived for the telescope optics, structure, and electrographic detector. Supporting studies of these and various other aspects of the telescope system are continuing. Since completion of the study, prospects for a long-duration space platform (as an alternative to extended-duration Spacelab missions) have come to the forefront, resulting in significant changes in the program plan. By far the most important of these is that the baseline scientific objective can now be upgraded (from the observation of a few dozen selected fields of special interest) to a complete full-sky survey in the far-ultraviolet to a limiting V magnitude (for an unreddened BO star) of mv = +27.0. An international consortium of astronomical institutions has now joined together in proposing to carry out this program from instrument development to the production and distribution of the final far-ultraviolet all-sky survey atlas.
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