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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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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Hydrologic applications of Nimbus 5 ESMR data

A region of low brightness temperature lying along the Mississippi River from Cairo, Illinois, to Morganza, Louisiana was observed in early Nimbus 5 Electrically Scanning Microwave Radiometer images. This region, which generally corresponds to an outwash aquifer in the Mississippi Valley, had brightness temperatures, at times as much as 40 K below the surrounding (drier) older uplands. Fluctuations of as much as 30 K were observed during the time interval 15 December 1972 to 28 February 1973. Comparison images taken from the Earth Resources Technology Satellite indicate that the study area is aligned with the Mississippi River floodplain, a region of potentially high soil moisture content. The brightness temperature fluctuations were compared with variations in precipitation and other hydrologic parameters in order to delineate the causative factors.

Schmugge, T. J.↗
NASA NTRS1977

Gregorian all-reflective optical system

An optical heterodyne receiver comprises a system of reflectors forming a folded Gregorian configuration for collecting a signal beam, and an optical detector located at the focus of the system. A paraboloidal primary reflector and an elipsoidal secondary reflector face each other on an optical axis with the focus of the secondary reflector coinciding with the focus of the primary reflector. An auxiliary laser generates a local oscillator beam that is combined with the signal beam after the signal beam emerges from the exit pupil (which is also the aperture stop) of the system, and the resultant is impinged on the detector. A pair of image motion compensators is located as close to the exit pupil as possible for aligning off-axis inputs to the detector.

King, W. L.↗
NASA NTRS1990

IAL SPACE: A test laboratory for the ISO cryogenic payload

The ESA Infrared Space Observatory (ISO) satellite is a 3 axes pointed platform designed to make accurate pointed observations of astronomical objects and sources in the wavelength range between 2.5 and 200 microns. ISO is composed of a service module and a payload module which is a large cylindrical vacuum vessel. The vessel is in fact a cryostat (capacity of 2250 l of liquid He II) which contains the telescope and the four focal scientific instruments. The latter being cooled up to a temperature less than 4 K. The qualification of the payload requires the measurement respectively of: the image quality of the telescope through wave front error (WFE) measurements; and the optical alignment of the scientific instruments with respect to the telescope axis and the telescope focus, and this under cryogenic conditions. Consequently, since 1988, the FOCAL 5 IAL Space facility has been upgraded in order to perform the cryogenic optical tests of the ISO optical subsystems.

Cucchiaro, A.↗
NASA NTRS2000

Discrete and Diffuse Aurora During Varying Activity Levels: Simultaneous Fast and Polar UVI Observations

We examine simultaneous measurements of auroral electron precipitation obtained in-situ by the FAST spacecraft and remotely by Polar Ultraviolet Imagery (UVI) images for activity levels ranging from quiet to storm-time intervals. The incident energy flux measured by FAST and inferred from the UVI images agree well during quiescent periods, particularly in regions of discrete aurora in which the electron precipitation spectra are dominated by the component accelerated by a field-aligned potential. During magnetospheric substorms and active storm periods, such as those following Coronal Mass Ejection (CME) disturbances of the magnetosphere, the energy flux inferred from the UVI images generally exceeds that measured locally by FAST at the same location by as much as an order of magnitude. The auroral electrons during these active periods are dominated by diffuse precipitation which is observed up the to the highest energy channel of FAST (30 keV). These storm-time observations imply that a high energy component above 30 keV not observed by FAST may be contributing significantly to the total energy flux carried by the precipitating electrons. Observations suggest that as magnetospheric activity increases acceleration processes in the magnetosphere and pitch-angle diffusion by wave-particle interactions become more important than the ionospheric acceleration in producing the measured auroral energy fluxes.

Chua, D.↗
NASA NTRS2004

On-orbit performance testing of the Pointing Calibration & Reference Sensor for the Spitzer Space Telescope

We present the on-orbit performance results of the Pointing Calibration and Reference Sensor (PCRS) for the Spitzer Space Telescope. A cryogenic optical (center wavelength 0.55 mu) imager, the PCRS serves as the Observatory's fine guidance sensor by providing an alignment reference between the telescope boresight and the external spacecraft attitude determination system. The PCRS makes precision measurements of the positions of known guide stars; these are used to calibrate measurements from Spitzer's star tracker and gyroscopes to obtain the actual pointing of the Spitzer telescope. The PCRS calibrates out thermomoechanical drifts between the 300 K spacecraft bus and the 5.5 K telescope. By using only 16 pixels, the PCRS provides high precision centroiding with extremely low (`64 mu W) power dissipation, resulting in minimal impact to Spritzer's helium lifetime. We have demonstrated that the PCRS meets its centroiding accuracy requirement of 0.14 arcsec 1-sigma radial, which represents about1/100 pixel centroiding. The Spitzer Space Telescope was launched in 25 August, 2003 and completed its In-Orbit Checkout phase two months later; the PCRS has been operating failure free ever since.

Spitzer↗
NASA NTRS2012

The Astro-H Soft X-Ray Mirror

The Astro-H is led by the Japanese Space Agency (JAXA) in collaboration with many other institutions including the NASA Goddard Space Flight Center. Goddard's contributions include two soft X-ray telescopes (SXTs). The telescopes have an effective area of 562 square cm at 1 keV and 425 square cm at 6 keV with an image quality requirement of 1.7 arc-minutes half power diameter (HPD). The engineering model has demonstrated 1.1 arc-minutes HPD error. The design of the SXT is based on the successful Suzaku mission mirrors with some enhancements to improve the image quality. Two major enhancements are bonding the X-ray mirror foils to alignment bars instead of allowing the mirrors to float, and fabricating alignment bars with grooves within 5 microns of accuracy. An engineering model SXT was recently built and subjected to several tests including vibration, thermal, and X-ray performance in a beamline. Several lessons were learned during this testing that will be incorporated in the flight design. Test results and optical performance are discussed, along with a description of the design of the SXT.

Robinson, David↗
NASA NTRS2012

Cryogenic Photogrammetry and Radiometry for the James Webb Space Telescope Microshutters

The James Webb Space Telescope (JWST) relies on several innovations to complete its five year mission. One vital technology is microshutters, the programmable field selectors that enable the Near Infrared Spectrometer (NIRSpec) to perform multi-object spectroscopy. Mission success depends on acquiring spectra from large numbers of galaxies by positioning shutter slits over faint targets. Precise selection of faint targets requires field selectors that are both high in contrast and stable in position. We have developed test facilities to evaluate microshutter contrast and alignment stability at their 35K operating temperature. These facilities used a novel application of image registration algorithms to obtain non-contact, sub-micron measurements in cryogenic conditions. The cryogenic motion of the shutters was successfully characterized. Optical results also demonstrated that shutter contrast far exceeds the NIRSpec requirements. Our test program has concluded with the delivery of a flight-qualified field selection subsystem to the NIRSpec bench.

Chambers, Victor J.↗
NASA NTRS2018

LUVOIR Primary Mirror Segment Alignment Control With Joint Laser Metrology and Segment Edge Sensing

An approach is developed for the alignment and stability maintenance of the LUVOIR segmented primary mirror using a segment state estimation and wavefront control method based on a hybrid segment motion sensing architecture of laser truss metrology and segment edge sensors. Our current computer model was generated for LUVOIR Architecture Option A with a 15-meter aperture, 120segment primary mirror. The methodology and simulation results will be presented and analyzed. JPL has a long history of technology development in laser metrology and edge sensors, including work in SIM [7], Keck and TMT [8], CCAT [3] and LUVOIR [1]. We will discuss our current efforts of LUVOIR laser metrology and edge-sensor models development, showing sensitivities of sensor measurements to various mirror eigenmodes, removing global modes and strengthening weak modes by performing joint (hybrid) laser-metrology and edge sensing. We will define and derive an important performance metric called wavefront error multiplier (WEM), and show that WEM provides a simple link between sensor errors and the closed-loop (controlled) system wavefront error. We will show WEM values for several hybrid sensor configuration options studied. We will discuss an algorithm for mirror shape control and maintenance through segment state and wavefront estimations using joint edge-metrology sensing. We will compare simulated performance of mirror state estimation, wavefront estimation and wavefront control based on joint edge-metrology sensing among several sensor configurations, and show the impact of sensor error distributions on the segmented mirror alignment performance. Mirror shape control performance will be also be evaluated in terms of imaging contrast between inner working angles (IWA) and outer working angles (OWA) of a LUVOIR coronagraph. The research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. LUVOIR is a mission concept under study for the next astronomy Decadal Survey—the information presented in this paper is pre-decisional and is provided for planning and discussion purposes only.

Shelton, Chris↗
NASA NTRS2019

Technologies to Enable the Next Great Observatory

The Large Ultraviolet/Optical/Infrared Surveyor (LUVOIR) is one of four mission concepts being studied by NASA for the 2020 Decadal Survey in Astronomy and Astrophysics. LUVOIR will be capable of a broad range of science, including: direct imaging and characterization of a wide range of exoplanets and the search for biosignatures on Earth-like planets around sun-like stars; studying galaxy formation and evolution; investigating star and planet formation; and remote sensing of bodies within the Solar System. Enabling a mission as ambitious as LUVOIR requires an array of technologies, such as ultra-stable structures and optics, precision metrology and wavefront sensing, high-contrast imaging techniques, large-format detectors with very low noise, and high-throughput ultraviolet instrumentation. Critically, a systems-level approach must be taken to developing these technologies, guided by architecture studies to place each technology in the appropriate system context.In this poster, we describe LUVOIR's technology needs, as well as current efforts that are actively developing these technologies. We will discuss recent advancements in: measuring picometer-level displacements of optical and structural elements; sub-milli-kelvin thermal sensing and control; non-contact vibration isolation for pointing and dynamic stability; coronagraph design for achieving 10-10 contrast on a segmented system; high-speed metrology for optical system alignment; low-order and out-of-band wavefront sensing for maintaining high-contrast images; low-noise detectors across the ultraviolet, optical, and near infrared bands; broadband coatings with high-reflectivity below Ly. We will also describe a systems approach to coordinating the development of these technologies to achieve the necessary maturity for a LUVOIR mission start in the next decade.

space telescopes↗
NASA NTRS1988

On the relation between photospheric flow fields and the magnetic field distribution on the solar surface

Using the technique of local correlation tracking on a 28 minute time sequence of white-light images of solar granulation, the horizontal flow field on the solar surface is measured. The time series was obtained by the Solar Optical Universal Polarimeter (SOUP) on Spacelab 2 (Space Shuttle flight 51-F) and is free from atmospheric blurring and distortion. The SOUP flow fields have been compared with carefully aligned magnetograms taken over a nine hour period at the Big Bear Solar Observatory before, during, and after the SOUP images. The flow field and the magnetic field agree in considerable detail: vectors which define the flow of the white-light intensity pattern (granulation) point toward magnetic field regions, magnetic fields surround flow cells, and magnetic features move along the flow arrows. The projected locations of free particles ('corks') in the measured flow field congregate at the same locations where the magnetic field is observed.

Simon, George W.↗
NASA NTRS1979

Influence of alignment and surface defects on the performance of X-ray telescopes

The effects of misalignment and surface deformations on the image quality of a grazing incidence telescope with six nested subsystems are investigated. The axial rms-spot size serves as a measure for the image quality. The surface deformations are simulated by ellipsoidal and sinusoidal deviations from the ideal surface. Misalignments are tilts, decenters, and despaces of the individual elements. The effects of each type of defect are analyzed in a single two-element system. The full nested system is then analyzed in the presence of all possible defects on all 12 elements, whereby the magnitude of the defects is randomized within a given upper limit.

Korsch, D.↗
NASA NTRS1992

Optics Alignment Panel

The Optics Alignment Panel (OAP) was commissioned by the HST Science Working Group to determine the optimum alignment of the OTA optics. The goal was to find the position of the secondary mirror (SM) for which there is no coma or astigmatism in the camera images due to misaligned optics, either tilt or decenter. The despace position was reviewed of the SM and the optimum focus was sought. The results of these efforts are as follows: (1) the best estimate of the aligned position of the SM in the notation of HDOS is (DZ,DY,TZ,TY) = (+248 microns, +8 microns, +53 arcsec, -79 arcsec), and (2) the best focus, defined to be that despace which maximizes the fractional energy at 486 nm in a 0.1 arcsec radius of a stellar image, is 12.2 mm beyond paraxial focus. The data leading to these conclusions, and the estimated uncertainties in the final results, are presented.

Schroeder, Daniel J.↗
NASA NTRS2006

Phase Sensor for Aligning a Segmented Telescope Mirror

A phase sensor has been developed for use in aligning a segmented telescope mirror to within a fraction of a wavelength in piston. (As used here, piston signifies displacement of a mirror segment along the optical axis of the telescope.) Such precise alignment is necessary in order to realize the full benefit of the large aperture achievable through segmentation. This phase sensor is achromatic. It is based on two-wavelength shearing interferometry, and can be modified to utilize an extended or broad-band (e.g., white) light source. The sensor optics include a ruled diffraction grating and an imaging lens. The sensor can measure the piston shift between segments as well as aberrations of the segments. It can measure the surface error of an individual segment, making it possible to compensate for the error with optimal amount(s) of piston and/or tilt. The precise capture range of the sensor depends partly on the telescope design; the largest relative piston shifts measurable by use of this sensor are of the order of 100 m. The accuracy of the sensor also depends partly on the telescope design; in general, the accuracy is sufficient to enable alignment to within approximately half a wavelength. The interferometric image is digitized and processed by a simple algorithm in real time, and the output of the algorithm can be used to maintain alignment in real time, even in the presence of atmospheric turbulence. The sensor is robust. Through calibration, it can be made insensitive to (and, hence, tolerant of) misalignments and aberrations of its own optics, most aberrations of the telescope as a whole (in contradistinction to aberrations of individual segments), and most aberrations introduced by atmospheric turbulence

Stahl, Philip↗
NASA NTRS1980

Initial test bed concentrator characterization

The operational characteristics and the mirror alignment technique of the test bed concentrator control system are highlighted. The final design of the TBC control system provided one axis of fast slew capability so that either the Sun acquisition or emergency off-Sun mode could be obtained in a minimum time. The procedure for getting on and off Sun is to run the elevation axis up to the approximate elevation of the Sun for the particular time of acquisition and then slew the concentrator on Sun in azimuth. The automatic Sun-acquisition system is controlled by two Sun sensors, one for each axis; each has a 2deg acquisition cone angle within which the concentrators are programmed to point. The mirror alignment technique chosen utilized a semi-distant incandescent light source which produced a reflected image on the focal point target. The concentrator was boresighted to the light by moving the concentrator while sighting along the cross hairs and through the apertures in the disks to the light source resulting in a maximum point error of 0.11 deg. Test plans to install a solar flux mapper to characterize the solar spot and to measure the size, shape, and intensity of the Sun's image are outlined.

Starkey, D. J.↗
NASA NTRS1984

Rapid Test Bed Concentrator (TBC) Alignment Techniques

A new, labor and cost saving method was developed to eliminate the procedure of covering all (220) mirrors and uncovering then one-by-one in sequence to adjust each to the focal plane. This latest method being used to align mirrors of a parabolic solar concentrator utilizes a computer-derived target of discreet images made up of individual mirror reflections on a plane in front of the intended, nominal, focal point. Incorporating this computer technique increases accuracy and gives potential to develop flux distributions required by different receiver designs.

Argoud, M. J.↗
NASA NTRS1982

Landsat image registration for agricultural applications

An image registration system has been developed at the NASA Johnson Space Center (JSC) to spatially align multi-temporal Landsat acquisitions for use in agriculture and forestry research. Working in conjunction with the Master Data Processor (MDP) at the Goddard Space Flight Center, it functionally replaces the long-standing LACIE Registration Processor as JSC's data supplier. The system represents an expansion of the techniques developed for the MDP and LACIE Registration Processor, and it utilizes the experience gained in an IBM/JSC effort evaluating the performance of the latter. These techniques are discussed in detail. Several tests were developed to evaluate the registration performance of the system. The results indicate that 1/15-pixel accuracy (about 4m for Landsat MSS) is achievable in ideal circumstances, sub-pixel accuracy (often to 0.2 pixel or better) was attained on a representative set of U.S. acquisitions, and a success rate commensurate with the LACIE Registration Processor was realized. The system has been employed in a production mode on U.S. and foreign data, and a performance similar to the earlier tests has been noted.

Wolfe, R. H., Jr.↗
NASA NTRS1994

Imaging The Leading Edge Of A Weld

Proposed optical system integrated into plasma arc welding torch provides image of leading edge of weld pool and welding-arc-initiation point. Welding torch aligned better with joint. System includes coherent bundle of optical fibers and transparent cup.

Mcgee, William F.↗