Broad Band X-Ray Telescope

Broad Band X-Ray Telescope. The Broad Band X-Ray Telescope was a pioneering X-ray astronomy instrument flown as a Spacelab payload aboard NASA's Space Shuttle Columbia in 1990. Designed to conduct sensitive, wide-energy-range observations, it provided crucial data on high-energy astrophysical phenomena. Its brief mission yielded significant insights into the nature of celestial X-ray sources, complementing the work of contemporary observatories like the Einstein Observatory.

Overview

The Broad Band X-Ray Telescope was a principal component of the ASTRO-1 observatory, a suite of ultraviolet and X-ray telescopes mounted on a Spacelab pallet. Conceived and managed by scientists at the Goddard Space Flight Center, its primary goal was to perform high-sensitivity spectroscopy and imaging across a broad segment of the X-ray band. This capability was vital for studying the physics of extreme environments, such as those found in supernova remnants, active galactic nuclei, and X-ray binary systems. The mission represented a significant step forward from previous sounding rocket and satellite experiments, offering more detailed spectral data than earlier instruments like those on the HEAO 1 satellite.

Design and instrumentation

The telescope's core was a nested Wolter telescope optics system, fabricated using precision-ground glass surfaces coated with iridium to enhance X-ray reflectivity. This design focused X-rays onto three main focal plane instruments. The High-Throughput Imaging Spectrometer (HITS) provided imaging and moderate-resolution spectroscopy. The Solid State Spectrometer (SSS) offered high spectral resolution for detailed line studies, while the Broad Band Filter Spectrometer (BBFS) used a set of thin-film filters to obtain very low-resolution spectra across its entire energy band. This multi-instrument approach, developed in collaboration with the Smithsonian Astrophysical Observatory and American Science and Engineering, allowed for simultaneous, complementary measurements of source properties, from temperature and density to chemical composition.

Scientific objectives and discoveries

Key objectives included measuring the temperature, density, and elemental abundances in hot astrophysical plasma, probing the structure of accretion disks around compact objects, and investigating the origin of the cosmic X-ray background. Among its notable observations were detailed studies of the Cygnus X-1 black hole candidate, the Crab Nebula pulsar wind nebula, and the Large Magellanic Cloud supernova remnant SNR 0509-67.5. The telescope's data were instrumental in constraining models of thermal radiation and non-thermal radiation processes, and its observations of distant galaxy clusters contributed to understanding the intracluster medium. Findings were later compared with data from subsequent missions like the Advanced Satellite for Cosmology and Astrophysics.

Mission history and operations

Launched on STS-35 aboard the Space Shuttle Columbia from Kennedy Space Center on December 2, 1990, the telescope was deployed as part of the ASTRO-1 payload. The mission faced significant challenges, including failures in the shuttle's Inertial Measurement Unit and the primary star tracker, which complicated pointing. Astronauts, including Vance D. Brand and mission specialist Samuel T. Durrance, performed manual pointing using the shuttle's windows and a Space Shuttle star tracker backup system. Despite these difficulties, over 100 observations of nearly 40 targets were completed during the 9-day flight. The telescope was retrieved and returned to Earth on December 11, 1990, concluding its only flight.

Legacy and impact

The Broad Band X-Ray Telescope demonstrated the feasibility and scientific value of high-throughput, broad-band X-ray spectroscopy from a Space Shuttle platform. Its data archives continue to be used for comparative studies with later observatories such as Chandra, XMM-Newton, and Suzaku. The mission served as a direct technological and operational precursor to the highly successful Advanced X-ray Astrophysics Facility program, which culminated in the Chandra X-ray Observatory. The telescope's development also advanced techniques in X-ray optics fabrication and calibration, influencing the design of instruments for subsequent NASA and European Space Agency missions.

Category:Space telescopes Category:X-ray telescopes Category:NASA space probes Category:1990 in spaceflight