Centroid detector assembly for the AXAF-I alignment test system

The Chandra X-ray Observatory has been operating successfully on orbit for 20 years, providing outstanding astrophysics data to the science community. The telescope’s mission life has been extended well past its required five years due to the robust system design as well as the mission planning skills of the engineers and scientists at the Chandra Operations Control Center (OCC) in Massachusetts. Lessons learned in designing and operating Chandra can significantly benefit the Lynx mission, one of the NASA Strategic Mission concepts under consideration by the 2020 Decadal Survey. This paper reviews the design features that have enabled Chandra’s long mission life, with emphasis on the performance of the thermal and mechanical designs. Impacts of the aging exterior thermal finish are discussed, including drifting internal temperatures and a corresponding loss of the 10C cold bias design surrounding the High Resolution Mirror Assembly (HRMA). Also addressed are the resulting changes to the radiative cold heat sink for the Aspect Determination System (ADS); the increased potential for contamination on optical and focal plane surfaces; and consequences of putting components close to their upper temperature limit. Actions to address the changing conditions by the flight operations team at the OCC are described, showing how thermal constraints have been accommodated. Lessons learned, optimized operations, and new thermal design options are presented as methods to ensure a long life for the Lynx mission.

The X-Ray Telescope High Resolution Mirror Assembly (HRMA) designed by American Science and Engineering (AS&E) and Smithsonian Institution Astrophysical Observatory (SAO) was developed, manufactured, assembled, and tested by Perkin-Elmer under contract to AS&E. This paper describes each phase of its fabrication and testing except for the surface roughness measurement and the optical coating which are discussed in separate papers. Particular emphasis is placed on the achievement of the circumferential variation in slope, A (A R), and its measurement during the loose-abrasive grinding operations. Also discussed, at length, are the optical figuring, surface smoothing via submerged polishing, and figure measurement using a semi-automated fringe scanner and modular interferogram analysis computer programs. The optical testing used during the assembly operation is reviewed and the test equipment and test methods are described. The pertinent specifications of the High Resolution Mirror Assembly and achievements of the program are summarized.

The precision metrology mount is the structural backbone that supports all AXAF metrology at Hughes Danbury Optical Systems. This mount is currently designed to support P1 and Hi optics, the two outermost elements of the High Resolution Mirror Assembly (HRMA)1 . The mount must offload the mirror deterministically in a one-g field with tolerances established on the gram level. The intent of this paper is to quantify the requirements placed on the metrology mount and then to describe the design philosophy used to meet these demanding performance requirements. Finally and most importantly, the paper describes how each of the metrology mount's specifications were addressed and met from a design vantage point.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The evaluation of alternative configurations in developing the AXAF design concept is reviewed. Consideration is given to the overall design (comprising the six-concentric-mirror High-Resolution Mirror Assembly, the focal-plane and spectroscopic instruments, and the spacecraft); problems in accommodating the instruments and providing for their selection; the interfaces between the optical bench, the spacecraft, and the Shuttle Orbiter; and provisions for servicing during the 15-yr AXAF lifetime. Drawings and diagrams are included.

The paper discusses selection of a set of metals for an electrochemical test system used for the detection of sulfur-containing organic substances. Analytical studies of organic sulfur compounds are very important since these compounds are widely used in medicine, biology, oil refining industry, etc. Quantitative determination and identification of sulfur-containing substances is essential for solving environmental problems. The electrochemical test system for analysis of organic substances is a solution containing a set of cations of various metals that have the ability to form complex compounds with analytes. Thereby, a single electrode can be used to carry out electrochemical multisensory analysis because metal cations play the role of sensors. Thus, there is no need to use a set of several working (indicator) electrodes, the number of which determines the number of informative parameters. Since sets of metals for test systems may slightly differ from each other, we need to select an optimal set for a specific problem. According to the study results, a set of metals for sulfur-containing organic substances consists of zinc, gallium and copper. The test system composed of these metals gives reliable results of electroanalytical determination of organic compounds of this class. The expediency of using such a test system is confirmed by comparative estimation of the Euclidean distances between the vector representations of the analytes and sulfur-containing organic compounds presented in the previously created database. Software for experimental data processing, visualization, and comparative analysis of the vector representations and the database components is developed.

The concept, implementation, and performance of the motion detection system (MDS) designed as a diagnostic for X-ray ground testing for AXAF are described. The purpose of the MDS is to measure the magnitude of a relative rigid body motion among the AXAF test optic, the X-ray source, and X-ray focal plane detector. The MDS consists of a point source, lens, centroid detector, transimpedance amplifier, and computer system. Measurement of the centroid position of the image of the optical point source provides a direct measure of the motions of the X-ray optical system. The outputs from the detector and filter/amplifier are digitized and processed using the calibration with a 50 Hz bandwidth to give the centroid's location on the detector. Resolution of 0.008 arcsec has been achieved by this system. Data illustrating the performance of the motion detection system are also presented.

The Constellation X-ray Mission is the next major x-ray- astronomy mission in the NASA Space Science road map. As a follow-on to the Chandra X-ray Observatory--nee, the Advanced X-ray Astrophysics Facility--Constellation X will provide high-throughput, high-resolution spectroscopy to probe the gravitational field, kinematics, temperature, density, composition and ionization state of cosmic sources. The Constellation-X observatory system comprises four separate satellites, each with one large Spectroscopy X-ray Telescope (SXT, with a pixelated microcalorimeter and a reflection-grating-CCD spectrometer) and three smaller Hard X-ray Telescopes (HXTs, with pixelated hard-x-ray detectors). Essential to the success of Constellation X is the development of large (1.6-m-diameter), lightweight optics for the SXT mirror assembly. With the Smithsonian Astrophysical Observatory, teams led by NASA's Marshall Space Flight Center, by NASA's Goddard Space Flight Center, and by Italy's Osservatorio Astronomico di Brera are currently developing competing mirror techniques for lightweight SXT optics, toward achieving the required system-level half-power diameter--better than 15 arcsec.

The alignment and X-ray imaging performance of the Advanced X-ray Astrophysics Facility (AXAF) Verification Engineering Test Article-I(VETA-I) was measured by the VETA-I X-Ray Detection System (VXDS). The VXDS was based on the X-ray detection system utilized in the AXAF Technology Mirror Assembly (TMA) program, upgraded to meet the more stringent requirements of the VETA-I test program. The VXDS includes two types of X-ray detectors: (1) a High Resolution Imager (HRI) which provides X-ray imaging capabilities; and (2) sealed and flow proportional counters which, in conjunction with apertures of various types and precision translation stages, provide the most accurate measurement of VETA-I performance. Herein we give an overview of the VXDS hardware including X-ray detectors, translation stages, apertures, proportional counters and flow counter gas supply system and associated electronics. We also describe the installation of the VXDS into the Marshall Space Flight Central (MSFC) X-Ray Calibration Facility (XRCF). We discuss in detail the design and performance of those elements of the VXDS which have not been discussed elsewhere; translation systems, flow counter gas supply system, apertures and thermal monitoring system.

The advanced X-ray Astrophysics Facility (AXAF)

The energy bandwidth and total throughput of a grazing incidence optics system is a strong function of the X-ray reflectivity of the surface coating. In support of the Advanced X-ray Astrophysics Facility (AXAF), studies are underway to evaluate and characterize the reflectivity of potential AXAF coatings. Here we report on results obtained for Au, Ir, and Ni coatings produced by electron-beam evaporation, evaporation with ion-assist, and sputtering. Effects of coating thickness and deposition angle have been evaluated at 6.4 and 8.1 keV; the highest reflectivities are those of the thinner, about 200 A vs about 700 A, coatings. While considerable variations exist, the best Ir samples have higher reflectivity than any of the Au coatings. Data results have been compared with models for theoretical reflectivity, particularly with regard to the effective density of the coatings. Independent measurements of the coating densities have been carried out for comparison with the reflectivity results.

The Advanced X-ray Astrophysics Facility--Imaging is one of two complementary space-based x-ray observatories being developed by NASA. Utilizing grazing incidence mirror elements in a Wolter Type I configuration, it will image x-ray sources over an energy range of 0.1 to 10 KeV. This paper describes the deposition of iridium/chromium coatings on Zerodur substrates using DC magnetron sputtering for use in grazing incidence configuration. Included are a description of the configuration and parameters of the deposition process, the results of x-ray performance measurements, and the implications of the results for scaling the deposition process to the full scale AXAF-I mirror elements.

With the launches of the Chandra X-ray Observatory (CXO) and the X-ray Multimirror Mission (XMM), high resolution X-ray spectroscopy of cosmic sources has begun. Early, deep observations of three stellar coronal sources will provide not only invaluable calibration data, but will also give us benchmarks for the atomic data under collisional equilibrium conditions. Analysis of the Chandra X-ray Observatory data, and data from other telescopes taken simultaneously, for these stars is ongoing as part of the Emission Line Project. Goals of the Emission Line Project are (1) to determine and verify accurate and robust diagnostics and (2) to identify and prioritize issues in fundamental spectroscopy which will require further theoretical and/or laboratory work. The Astrophysical Plasma Emission Database will be described in some detail, as it is introducing standardization and flexibility into X-ray spectral modeling. Spectral models of X-ray astrophysical plasmas can be generally classified as dominated by eithe...

Properly planned and executed metrology crosschecks at low to mid system test levels can provide up to the same degree of end item performance insurance protection that a top-level end-to-end test can, at a small fraction of the cost, and in a much more timely manner in terms of identifying and correcting problems. This philosophy has been put into rigorous practice on the optics fabrication activity being performed by Hughes Danbury Optical Systems, under contract to TRW, on the Advanced X-ray Astrophysics Facility (AXAF) program being managed by NASA's Marshall Space Flight Center. The process to date, while for the most part having provided confidence that the primary calibrations and tests are correct, has also identified several significant but subtle errors that were corrected. The focus of the paper is on the process itself as an optical quality insurance tool, with examples from AXAF described.

A variety of instruments will be placed at the focus of the Advanced X-ray Astrophysics Facility (AXAF) telescope, either by moving them into focus through the use of an instrument carousel or by moving the telescope assembly. Focal plane instrument categories under consideration for AXAF encompass high and moderate resolution X-ray cameras, X-ray spectrometers, and polarimeters; some of these instruments may require such consumables as a cryogen, in the case of solid state device cooling, or a gas, as in the case of proportional counters. Attention is presently given to interface requirements impacting on the maintenance that must be conducted over the 15-year service life of AXAF, and, especially, on the 'aspect solution' criteria that must be met to minimize stiffness stability criteria.

The general design and performance characteristics of MIT's two dispersive spectrometers, the Bragg Crystal Spectrometer (BCS) and the High Energy Transmission Grating Spectrometer (HETG), now being developed for the Advanced X-ray Astrophysics Facility (AXAF), are described. Particular attention is given to the development of the critical technologies incorporated into these instruments, including BCS diffractors, imaging gas flow proportional counters, and grating elements for the HETG. The principal stages and the current status of the developments are reviewed.