Mission Overview

e Diffuse X-Ray Spectrometer (DXS) experiment was built by the University of Wisconsin-Madison and flown as an attached payload in the January 1993 flight of Space Shuttle Endeavor (STS-54). The DXS's main scientific goal was to obtain spectra of the diffuse soft X-ray background.
Mission Characteristics
Lifetime: January 13, 1993 - January 19, 1993
Energy Range: 0.15 - 0.28 keV

Launch Information

Launch Date: 1993-01-13 at 00:00:00 UTC
Launch Vehicle: Shuttle
Launch Site: Cape Canaveral, United States


Diffuse X-Ray Spectrometer (DXS)

The Diffuse X-ray Spectrometer (DXS) was a single experiment shuttle payload designed to fly on multiple missions. The primary objective of the DXS payload was to obtain measurements on the diffuse soft X-ray background radiation in the Milky Way Galaxy. This low energy X-ray background apparently arises in the local interstellar plasma which has a temperature of about 1 million degrees. In such a plasma, X-ray emission will be due to collisionally excited lines of a number of ions including Si VIII, Mg IX, S VIII and Ne IX. The purpose of DXS was to study the those emission lines to verify that the lines do indeed arise form such a plasma and in turn to use the emissions as diagnostics for the plasma temperature, its element abundances and its ionic populations. If the plasma is shown not to be in ionization equilibrium, then the X-ray emission may be due to a blast wave (i.e. supernova explosion in the solar vicinity) with an age of about 100,000 years.
DXS consisted of two large area Bragg crystal spectrometers, each covering an energy range of 0.15-0.28 keV. The instrument field of view was 15 degrees by 150 degrees (FWHM). The energy resolution was approximately 10 eV while the spectral range covered the interval from 420-840 nm.

Each DXS instrument was mounted on either side of the Shuttle cargo bay. The instruments faced each other to expand the length of the arc on the sky which could be observed at full spectral coverage. Each detector contained a curved panel of Bragg crystals mounted above a position-sensitive proportional counter. A spectrum was dispersed across the counter, resulting in all portions of the spectrum being simultaneously measured. This eliminated false features from being introduced by a time-varying background, a common problem in conventional Bragg spectrometers. In addition, since all wavelengths were measured simultaneously, but the various wavelengths could come from different directions in the sky, the spectrometers were rocked back and forth about an axis perpendicular to the dispersed direction so that complete spectral coverage along an arc of the sky could be obtained. DXS flew as an attached payload using the Hitchhiker avionics and Shuttle Payload of Opportunity Carrier (SPOC) hardware, which provided support systems for power, command, and telemetry to the DXS instruments. DXS was first flown on the STS 54 mission.

2 large area Bragg crystal spectrometers (43-84 Å) with 2.7 Å energy resolution and 15 ° (FWHM) angular resolution


• DXS obtained the first-ever high resolution spectra of the diffuse soft X-ray background in the energy band from 0.15 to 0.28 keV (43-84 Å).