E. A. Tandberg-Hanssen

The Ultra High Resolution XUV Spectroheliograph

We describe a space-borne solar observatory, the Ultra High Resolution XUV Spectroheliograph (UHRXS), which has been selected by NASA for flight among the initial scientific instruments to be placed on the space station Freedom. The principal UHRXS instruments are nine XUV multilayer Ritchey-Chretien telescopes covering the spectral range from ~70 to ~350 A; each telescope is able to isolate line multiplets, within a narrow wavelength interval, excited over a narrow temperature range, providing full disk images of diagnostic quality covering structures in the solar atmosphere ranging in temperature from T ~ 50,000 K (He II, ? ~ 304 A) to 20,000,000 K (Fe XXIV, ? ~ 192 A). The XUV images will be recorded on high resolution 70 mm format film, allowing resolutions as high as 0.1 arcsec to be achieved for a 1.0° field. The XUV images will be supplemented by (i) full disk high resolution (~0.1 arcsec) far ultraviolet images in H I Ly ? (? - 1216 A) and C IV (? ~ 1548/1550 A), (ii) full disk soft x-ray images in four bands in the interval ?? ~ 6 to 70 A, and (iii) electronically recorded high resolution (?/?? > 10,000) spectrohelio-grams in 2 XUV, 1 EUV (~450 to 1100 A) and 2 FUV (~1100 to 1600 A) bands. The electronically recorded images will use the multi-anode multichannel array detector. We propose to utilize the resulting data sets to address fundamental problems related to the following solar phenomena: (i)the fine structure of the solar chromosphere/corona interface, (ii) the structure, energetics, and evolution of high temperature coronal loops, (iii) the large scale structure and dynamics of the corona, including the solar wind interface, the magnetic field, and coronal mass ejections, and (iv) solar flares, especially the preflare state, the impulsive release of energy, and the evolution of postflare loops.

An ultraviolet polarimeter for the Solar Maximum Mission

The Solar Maximum Mission experiment contingency will include one instrument originally designed and built for OSO-8. The engineering model of the OSO-8 High Resolution Spectrometer has been rebuilt to make it flightworthy and to encompass several new functions, including solar ultraviolet polarimetry. The rebuilt package is designated as the High Resolution Ultraviolet Spectrometer/Polarimeter. The device that enables polarimetry is a dual channel rotating waveplate system. The waveplates are magnesium fluoride and will allow measurements to be made ranging from the Lyman Alpha line to near visible ultraviolet. One waveplate channel will use the polarization characteristics of the spectrometer diffraction grating as the analyzer. The second channel has a built-in four-mirror polarizer. This paper describes the polarimeter design, operation, and calibration.

Solar Chromospheric and Coronal Explorer

The presence of the solar magnetic field has a profound effect on the structure of the lower chromosphere, and is responsible for the formation of the upper chromosphere and the corona, and the acceleration of the solar wind. The variation of the field induces variations in the chromosphere and the corona on time scales from 0.001 seconds to centries. SOHO, and subsequent approved solar missions such as TRACE will bring powerful observational capabilities to bear on critical questions relating to solar variability. However, the most fundamental question--how energy is transferred from the magnetic field into the solar plasma--will require observations of diagnostic quality on a spatial scale of 50 - 100 kilometers; this is an order of magnitude beyond the capability of any planned mission. Our mission concept, the Solar Chromospheric and Coronal Explorer (SCCE) is designed to investigate the mechanisms underlying the variability of the solar atmosphere, by attaining spectroscopic observations of the solar atmosphere over a wide range of temperatures (4,500 K to 100,000,000 K), with very high angular (0.1 arcseconds) and temporal (0.001 seconds) resolution, that will permit models of the physical processes that underlie the phenomena of solar activity to be formulated and tested at the scale, 50 - 75 kilometers that appears to be fundamental. The architecture of the SCCE is based on advances in multilayer optics, which permit broad spectral response, and high angular and spectral resolution to be achieved in a volume, and at a cost that is compatible with deployment within the fiscal and physical constraints of the MIDEX program.

Ultrahigh-resolution XUV spectroheliograph III: a modified configuration for a free-flying platform

The Ultra-High Resolution XUV Spectroheliograph (UHRXS) is a comprehensive solar observatory capable of studying solar phenomena at soft X-ray, XUV, EUV, and VUV wavelengths with normal incidence imaging multilayer telescopes capable of very high angular resolution (about 0.1 arcsec), and spectrographs able to achieve high spectral resolution. This instrument has been selected by NASA for flight as an attached payload on the Space Station Freedom. Recent developments have made it clear that accommodations for attached payloads on Freedom will not become available during the initial operations of Freedom and may never be available. We have studied the changes that must be made to place the UHRXS instrument on a Free Flying Plafform such as the Delta Launched Explorer Bus. We report on the configuration, performance, and accommodation on a free flying platform of the revised UHRXS concept.

Solar/stellar coronal explorer and the solar/stellar coronal observatory

The Solar/Stellar Coronal Explorer (SSCE) carries six identical Ritchey-Chretien Telescopes of 127 mm aperture each; their images will be recorded by multianode microchannel-array detectors. The mirrors of five of the telescopes are coated with multilayer reflecting structures that select narrow XUV wavelength bands corresponding to strong emission lines emitted by solar or stellar coronal plasmas. Also noted here is a larger explorer mission concept, that of the Solar/Stellar Coronal Observatory, which will undertake more extensive spectroscopic observations.