As part of the planning process for the Orbiting Solar Laboratory (OSL), a proposed NASA space-borne solar
observatory, the authors have developed an instrument concept, the "Active Sun Telescope Array" (ASTA), for a high
resolution soft x-ray/Extreme Ultraviolet (XUV) experiment designed to investigate the phenomenology of the solar
chromosphere and corona. ASTA is an ensemble of six EUV/XUV solar telescopes designed to provide: (i) wide field (i.e.
full disk) solar images in narrow wavelength bands, (ii) high resolution spectroheliograms, and (iii) line profiles, of the
solar plasma in the temperature range from 10,000 K to 30,000,000 K. The ASTA also incorporates specific operational
modes to allow the precise registration of its EUV and XUV images and the visible/ultraviolet and far ultraviolet images
of the other primary OSL instruments. The simplest (baseline) ASTA configuration incorporates six identical telescopes,
which differ only in the reflective coatings used normal incidence multilayer coated optics are used for XUV observations,
principally of the solar plasma from 900,000 K to 30,000,000 K, and SiC optics are used for extreme-ultraviolet
observations of the solar plasma from 20,000 K to 2,000,000 K. An attractive option, which allows the ASTA to extend
its coverage of the solar plasma to material as hot as 100,000,000 K, is the replacement of one or more of the XUV
telescopes with Wolter I grazing incidence telescopes to allow soft x-ray observations down to -1.5 A. The detector used
in the ASTA is the MAMA photon counting array detector.