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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

VIEWCACHE: An incremental pointer-based access method for autonomous interoperable databases

One of the biggest problems facing NASA today is to provide scientists efficient access to a large number of distributed databases. Our pointer-based incremental data base access method, VIEWCACHE, provides such an interface for accessing distributed datasets and directories. VIEWCACHE allows database browsing and search performing inter-database cross-referencing with no actual data movement between database sites. This organization and processing is especially suitable for managing Astrophysics databases which are physically distributed all over the world. Once the search is complete, the set of collected pointers pointing to the desired data are cached. VIEWCACHE includes spatial access methods for accessing image datasets, which provide much easier query formulation by referring directly to the image and very efficient search for objects contained within a two-dimensional window. We will develop and optimize a VIEWCACHE External Gateway Access to database management systems to facilitate database search.

Roussopoulos, N.↗
NASA NTRS2000

Optical Performance Modeling of FUSE Telescope Mirror

We describe the Metrology Data Processor (METDAT), the Optical Surface Analysis Code (OSAC), and their application to the image evaluation of the Far Ultraviolet Spectroscopic Explorer (FUSE) mirrors. The FUSE instrument - designed and developed by the Johns Hopkins University and launched in June 1999 is an astrophysics satellite which provides high resolution spectra (lambda/Delta(lambda) = 20,000 - 25,000) in the wavelength region from 90.5 to 118.7 nm The FUSE instrument is comprised of four co-aligned, normal incidence, off-axis parabolic mirrors, four Rowland circle spectrograph channels with holographic gratings, and delay line microchannel plate detectors. The OSAC code provides a comprehensive analysis of optical system performance, including the effects of optical surface misalignments, low spatial frequency deformations described by discrete polynomial terms, mid- and high-spatial frequency deformations (surface roughness), and diffraction due to the finite size of the aperture. Both normal incidence (traditionally infrared, visible, and near ultraviolet mirror systems) and grazing incidence (x-ray mirror systems) systems can be analyzed. The code also properly accounts for reflectance losses on the mirror surfaces. Low frequency surface errors are described in OSAC by using Zernike polynomials for normal incidence mirrors and Legendre-Fourier polynomials for grazing incidence mirrors. The scatter analysis of the mirror is based on scalar scatter theory. The program accepts simple autocovariance (ACV) function models or power spectral density (PSD) models derived from mirror surface metrology data as input to the scatter calculation. The end product of the program is a user-defined pixel array containing the system Point Spread Function (PSF). The METDAT routine is used in conjunction with the OSAC program. This code reads in laboratory metrology data in a normalized format. The code then fits the data using Zernike polynomials for normal incidence systems or Legendre-Fourier polynomials for grazing incidence systems. It removes low order terms from the metrology data, calculates statistical ACV or PSD functions, and fits these data to OSAC models for the scatter analysis. In this paper we briefly describe the laboratory image testing of FUSE spare mirror performed in the near and vacuum ultraviolet at John Hopkins University and OSAC modeling of the test setup performed at NASA/GSFC. The test setup is a double-pass configuration consisting of a Hg discharge source, the FUSE off-axis parabolic mirror under test, an autocollimating flat mirror, and a tomographic imaging detector. Two additional, small fold flats are used in the optical train to accommodate the light source and the detector. The modeling is based on Zernike fitting and PSD analysis of surface metrology data measured by both the mirror vendor (Tinsley) and JHU. The results of our models agree well with the laboratory imaging data, thus validating our theoretical model. Finally, we predict the imaging performance of FUSE mirrors in their flight configuration at far-ultraviolet wavelengths.

Saha, Timo T.↗
NASA NTRS2000

Metrology and Alignment of Light Weight Grazing Incidence X-Ray Mirrors

Metrology and alignment of light weight X-ray optics have been a challenge for two reasons: (1) that the intrinsic mirror quality and distortions caused by handling can not be easily separated, and (2) the diffraction limits of the visible light become a severe problem at the order of one arc-minute. Traditional methods of using a normal incident pencil or small parallel beam which monitors a tiny fraction of the mirror in question at a given time can not adequately monitor those distortions. We are developing a normal incidence setup that monitors a large fraction, if not the whole, of the mirror at any given time. It will allow us to align thin X-ray mirrors to-an accuracy of a few arc seconds or to a limit dominated by the mirror intrinsic quality.

Zhang, William↗
NASA NTRS2000

Performance of The Far Ultraviolet Spectroscopic Explorer Mirror Assemblies

The Far Ultraviolet Spectroscopic Explorer is a NASA astrophysics satellite which produces high-resolution spectra in the far-ultraviolet (90.5-118.7 nm bandpass) using a high effective area and low background detectors. The observatory was launched on its three-year mission from Cape Canaveral Air Station on 24 June 1999. The instrument contains four coaligned, normal incidence, off-axis parabolic mirrors which illuminate separate Rowland circle spectrograph channels equipped with holographically ruled diffraction gratings and delay line microchannel plate detectors. The telescope mirrors have a 352 x 387 mm aperture and 2245 mm focal length and are attached to actuator assemblies, which provide on-orbit, tip, tilt, and focus control. Two mirrors are coated with silicon carbide (SiC) and two are coated with lithium fluoride over aluminum (Al:LiF). We describe mirror assembly in-flight optical and mechanical performance. On-orbit measurements of the far-ultraviolet point spread function associated with each mirror are compared to expectations based on pre-flight laboratory measurements and modeling using the Optical Surface Analysis Code and surface metrology data. On-orbit imaging data indicate that the mirrors meet their instrument-level requirement of 50 percent and 95 percent slit transmission for the high- and mid-resolution spectrograph entrance slits, respectively. The degradation of mirror reflectivity during satellite integration and test is also discussed. The far-ultraviolet reflectivity of the SiC- and AlLiF-coated mirrors decreased about six percent and three percent, respectively, between coating and launch. Each mirror is equipped with three actuators, which consist of a stepper motor driving a ball screw via a two-stage planetary gear train. We also discuss the mechanical performance of the mirror assemblies, including actuator performance and thermal effects.

Ohi, Raymond G.↗
NASA NTRS2001

Constellation-X Cylinder Figuring and Polishing Studies

In support of Goddard's Constellation-X mandrel manufacturing effort a series of fabrication experiments are being performed to determine a best approach. Currently, polishing immediately after diamond turning, produces a RMS surface roughness of 0.31 nm, on a nickel plated aluminum mandrel. Studies currently under way will incorporate an abrasive figuring step followed by a polishing operation. The current diamond turning, figuring and polishing procedures will be described and the results presented.

Waluschka, Eugene↗
NASA NTRS2002

Equal-Curvature X-Ray Telescopes

We introduce a new type of x-ray telescope design; an Equal-Curvature telescope. We simply add a second order axial sag to the base grazing incidence cone-cone telescope. The radius of curvature of the sag terms is the same on the primary surface and on the secondary surface. The design is optimized so that the on-axis image spot at the focal plane is minimized. The on-axis RMS (root mean square) spot diameter of two studied telescopes is less than 0.2 arc-seconds. The off-axis performance is comparable to equivalent Wolter type 1 telescopes.

Saha, Timo T.↗
NASA NTRS2003

Equal-Curvature X-ray Telescope Designs for Constellation-X Mission

We study grazing incidence Equal-Curvature telescope designs for the Constellation-X mission. These telescopes have nearly spherical axial surfaces. The telescopes are designed so that the axial curvature is the same on the primary and secondary. The optical performance of these telescopes is for all practical purposes identical to the equivalent Wolter telescopes.

Saha, Timo T.↗
NASA NTRS2003

Development of Mirror Segments for the Constellation-X Observatory

As NASA's next major X-ray observatory, Constellation-X will have a photon collection area of 30,000 sq cm at 1 keV, which, after folding other instrumental responses, translates into an effective area of 15,000 sq cm. The observatory consists of four identical satellites each of which carries a spectroscopic X-ray telescope mirror assembly (SXT) that is 1.6 m in diameter and has a focal length of 10 m and a collection area of 7,500 sq cm at 1 keV and an angular resolution of 15 sec. HPD (half-power diameter) at the system level. Each mirror assembly consists of a large number of mirror segments precisely assembled together. Our development of the mirror segments is divided into two steps. The first one is to develop the basic approach and fabricate segments within the constraints of existing infrastructure to meet the angular resolution requirement, but not mirror segment size requirement. We have all but successfully completed this part of the development. We are now on the verge of going into the second step, that is to fabricate mirror segments of larger sizes to reduce the number of segments that have to be aligned and integrated. In this paper, we report on the requirements and the development status of the mirror segments. These assembly and other requirements of the SXT are reported elsewhere.

Zhang, W.↗
NASA NTRS2003

Ambient and Cryogenic Alignment Verification and Performance of the Infrared Multi-Object Spectrometer

The Infrared Multi-Object Spectrometer (IRMOS) is a facility instrument for the Kitt Peak National Observatory 4 and 2.1 meter telescopes. IRMOS is a near-IR (0.8 - 2.5 micron) spectrometer with low- to mid-resolving power (R = 300 - 3000). IRMOS produces simultaneous spectra of approximately 100 objects in its 2.8 x 2.0 arc-min field of view using a commercial Micro Electro-Mechanical Systems (MEMS) Digital Micro-mirror Device (DMD) from Texas Instruments. The IRMOS optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the DMD field stop, and the spectrograph images the DMD onto the detector. We describe ambient breadboard subsystem alignment and imaging performance of each stage independently, and the ambient and cryogenic imaging performance of the fully assembled instrument. Interferometric measurements of subsystem wavefront error serve to venfy alignment, and are accomplished using a commercial, modified Twyman-Green laser unequal path interferometer. Image testing provides further verification of the optomechanical alignment method and a measurement of near-angle scattered light due to mirror small-scale surface error. Image testing is performed at multiple field points. A mercury-argon pencil lamp provides spectral lines at 546.1 nm and 1550 nm, and a CCD camera and IR camera are used as detectors. We use commercial optical modeling software to predict the point-spread function and its effect on instrument slit transmission and resolution. Our breadboard test results validate this prediction. We conclude with an instrument performance prediction for first light.

Connelly, Joseph A.↗
NASA NTRS2004

Alignment and Performance of the Infrared Multi-Object Spectrometer

The Infrared Multi-Object Spectrometer (IRMOS) is a principle investigator class instrument for the Kitt Peak National Observatory 4 and 2.1 meter telescopes. IRMOS is a near-IR (0.8 - 2.5 micron) spectrometer with low-to mid-resolving power (R = 300 - 3000). IRMOS produces simultaneous spectra of approximately 100 objects in its 2.8 x 2.0 arc-min field of view (4 m telescope) using a commercial Micro Electro-Mechanical Systems (MEMS) micro-mirror array (MMA) from Texas Instruments. The IRMOS optical design consists of two imaging subsystems. The focal reducer images the focal plane of the telescope onto the MMA field stop, and the spectrograph images the MMA onto the detector. We describe ambient breadboard subsystem alignment and imaging performance of each stage independently, and ambient imaging performance of the fully assembled instrument. Interferometric measurements of subsystem wavefront error serve as a qualitative alignment guide, and are accomplished using a commercial, modified Twyman-Green laser unequal path interferometer. Image testing provides verification of the optomechanical alignment method and a measurement of near-angle scattered light due to mirror small-scale surface error. Image testing is performed at multiple field points. A mercury-argon pencil lamp provides a spectral line at 546.1 nanometers, a blackbody source provides a line at 1550 nanometers, and a CCD camera and IR camera are used as detectors. We use commercial optical modeling software to predict the point-spread function and its effect on instrument slit transmission and resolution. Our breadboard and instrument level test results validate this prediction. We conclude with an instrument performance prediction for cryogenic operation and first light in late 2003.

Connelly, Joseph A.↗
NASA NTRS2004

Optical Metrology for the Segmented Optics on the Constellation-X Spectroscopy X-Ray Telescope

We present the metrology requirements and metrology implementation necessary to prove out the reflector technology for the Constellation X(C-X) spectroscopy X-ray telescope (SXT). This segmented, 1.6m diameter highly nested Wolter-1 telescope presents many metrology and alignment challenges. In particular, these mirrors have a stringent imaging error budget as compared to their intrinsic stiffness; This is required for Constellation-X to have sufficient effective area with the weight requirement. This has implications for the metrology that can be used. A variety of contract and noncontact optical profiling and interferometric methods are combined to test the formed glass substrates before replication and the replicated reflector segments.The reflectors are tested both stand-alone and in-situ in an alignment tower.Some of these methods have not been used on prior X-ray telescopes and some are feasible only because of the segmented approach used on the SXT. Methods discussed include high precision coordinate measurement machines using very low force or optical probe axial interferometric profiling azimuthal circularity profiling and use of advanced null optics such as conical computer generated hologram (CGHs).

Content, David↗
NASA NTRS2005

Technology Development for the Constellation-X Spectroscopy X-Ray Telescope

The Constellation-X Spectroscopy X-ray Telescope (SXT) is a large diameter, high throughput, grazing incidence imaging mirror system, designed to perform high sensitivity spectroscopy of cosmic X-ray sources in the 0.2-10.0 keV band. The baseline effective area requirement is -3 m# at 1 keV. The system-level angular-resolution requirement is a 15-arcseconds half-power diameter, with a 5-arcsecond goal. The effective area is attained through a modular design, involving the nesting of many confocal, thin-walled Wolter I mirror segments. Considerable progress has been made in developing thin, thermally formed, glass mirror substrates that meet or better the angular-resolution requirement. Several approaches to mounting and aligning reflector segments into a mirror system are under investigation. We report here on the progress of the SXT technology development program toward reaching the performance goals.

Petre, Robert↗
NASA NTRS2006

The Constellation-X Spectroscopy X-ray Telescope: Recent Technology Development

We describe recent progress in the technology development program for the mirror system for the Constellation-X Spectroscopy X-ray Telescope (SXT). Development of this mirror represents a significant technology challenge, as it must provide a combination of large effective area (3 sq. m) and modest angular resolution (15 arc second half power diameter requirement; 5 arc second goal) with a limited mass allocation. The baseline design incorporates over 200 nested Wolter 1 mirrors. Each of these in turn is segmented in order to simplify handling of the mirrors and facilitate mass production. The X-ray reflecting surfaces are fabricated from thin, thermally formed glass sheets. Production improvements have yielded mirror segments that approach the performance requirement without the need for epoxy replication. A mounting and alignment approach incorporating piezoelectric actuators has been shown to manipulate mirror segments with the required precision without introducing significant distortion. Substantial improvements in metrology methodology have provided insights into the mirror segment forming and alignment processes. An X-ray demonstration of a mirror segment pair is planned for early 2006.

Petre, Robert↗
NASA NTRS2007

Alignment and Integration Techniques for Mirror Segment Pairs on the Constellation X Telescope

We present the concepts behind current alignment and integration techniques for testing a Constellation-X primary-secondary mirror segment pair in an x-ray beam line test. We examine the effects of a passive mount on thin glass x-ray mirror segments, and the issues of mount shape and environment on alignment. We also investigate how bonding and transfer to a permanent housing affects the quality of the final image, comparing predicted results to a full x-ray test on a primary secondary pair.

Hadjimichael, Theo↗
NASA NTRS2008

Aberrations for Grazing Incidence Optics

Large number of grazing incidence telescope configurations have been designed and studied. Wolte1 telescopes are commonly used in astronomical applications. Wolter telescopes consist of a paraboloidal primary mirror and a hyperboloidal or an ellipsoidal secondary mirror. There are 8 possible combinations of Wolter telescopes. Out of these possible designs only type 1 and type 2 telescopes are widely used. Type 1 telescope is typically used for x-ray applications and type 2 telescopes are used for EUV applications. Wolter-Schwarzshild (WS) telescopes offer improved image quality over a small field of view. The WS designs are stigmatic and free of third order coma and, therefore, the PSF is significantly better over a small field of view. Typically the image is more symmetric about its centroid. As for the Wolter telescopes there are 8 possible combinations of WS telescopes. These designs have not been widely used because the surface equations are complex parametric equations complicating the analysis and typically the resolution requirements are too low to take full advantage of the WS designs. There are several other design options. Most notable are wide field x-ray telescope designs. Polynomial designs were originally suggested by Burrows4 and hyperboloid-hyperboloid designs for solar physics applications were designed by Harvey5. No general aberration theory exists for grazing incidence telescopes that would cover all the design options. Several authors have studied the aberrations of grazing incidence telescopes. A comprehensive theory of Wolter type 1 and 2 telescopes has been developed. Later this theory was expanded to include all possible combinations of grazing incidence and also normal incidence paraboloid-hyperboloid and paraboloid-ellipsoid telescopes. In this article the aberration theory of Wolter type telescopes is briefly reviewed.

Saha, Timo T.↗
NASA NTRS2008

Opto-Mechanics of the Constellation-X SXT Mirrors: Challenges in Mounting and Assembling the Mirror Segments

The Constellation-X Spectroscopy X-Ray Telescopes consists of segmented glass mirrors with an axial length of 200 mm, a width of up to 400 mm, and a thickness of 0.4 mm. To meet the requirement of less than 15 arc-second half-power diameter with the small thickness and relatively large size is a tremendous challenge in opto-mechanics. How shall we limit distortion of the mirrors due to gravity in ground tests, that arises from thermal stress, and that occurs in the process of mounting, affixing and assembling of these mirrors? In this paper, we will describe our current opto-mechanical approach to these problems. We will discuss, in particular, the approach and experiment where the mirrors are mounted vertically by first suspending it at two points.

Chan, Kai-Wing↗
NASA NTRS2007

Mechanical and Thermal Analysis of the Spectroscopy X-ray Telescopes for the Constellation-X Mission

Area and mass requirements for the Constellation-X Spectroscopy X-Ray Telescopes restrict the thickness of the mirror segment to below a mm. Requirement of angular resolution of 15" over the soft x-ray band implies that allowable optic deformation is sub-micrometer for these thin segments. These requirements place stringent constraint on the mounting, alignment and affixing of these mirror segments in both the metrology and integration processes. We present analyses and optimization of the Constellation-X mirrors under relevant mechanical and thermal environments.

Chan, Kai-Wing↗