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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS2017

Characterizing Non-Resolved Debris Through Spectral and Photometric Ground-Based Telescopic Data: What Can Laboratory Ground-truth Data Do for You?

NASA's ODPO has recently collected data of unresolved objects at GEO with the 3.8m UKIRT infrared telescope on Mauna Kea and the 1.3m MCAT visible telescope on Ascension Island. Analyses of SWIR data of rocket bodies and HS-376 solar-panel covered buses demonstrate the uniqueness of spectral signatures. Data of 3 classes of rocket bodies show similarities amongst a given class, but distinct differences from one class to another, suggesting that infrared reflectance spectra could effectively be used toward characterizing and constraining potential parent bodies of uncorrelated targets (UCTs). The Optical Measurements Center (OMC) at NASA JSC is designed to collect photometric signatures in the laboratory that can be used for comparison with telescopic data. NASA also has a spectral database of spacecraft materials for use with spectral unmixing models. Spectral unmixing of the HS-376 bus data demonstrates how absorption features and slopes can be used to constrain material characteristics of debris. Broadband photometry likewise can be compared with MCAT data of non-resolved debris images. Similar studies have been applied to IDCSP satellites to demonstrate how color-color photometry can be compared with lab data to constrain bulk materials signatures of spacecraft and debris.

Lederer, Susan↗
NASA NTRS2002

Cryogenic Reflectance Spectroscopy in Support of Planetary Missions

Present understanding of planetary composition is based primarily on remotely-sensed data, and in particular upon ultraviolet, visible, and infrared spectroscopy. Spectra acquired by telescopic and spacecraft instruments are compared to laboratory measurements of pure materials in order to identify surface components based on characteristic absorption features. Cryogenic spectral measurements are necessary for the study of worlds beyond the Earth's orbit. While some materials exhibit only small spectral changes as a function of temperature, many others are strongly temperature-dependent. For example, hydrated salts exhibit different spectral behavior under conditions appropriate to Europa than at terrestrial temperatures. The icy satellites of the outer solar system contain significant quantities of volatile ices which do not even exist at standard temperature and pressure (STP). A comprehensive spectral database of ices and minerals covering a wide temperature range will have applications ranging from the study of comets and Kuiper Belt objects to outer planet satellites and the polar regions of Mars. Efforts are presently underway at NASA-Ames to develop capabilities which will contribute to such a database. As spacecraft instruments feature increasing spatial and spectral resolution, appropriate laboratory reference spectra become increasingly critical to accurate interpretation of the spacecraft data.

Dalton, J. B.↗
NASA NTRS2019

Experimentally-Derived Bidirectional Reflectance Distribution Function Data in Support of the Orbital Debris Program Office

The NASA Orbital Debris Program Office (ODPO) has used various optical assets to acquire photometric data of Earth-orbiting objects to define the orbital debris environment. To better characterize and model optical data acquired from ground-based telescopes, the Optical Measurements Center (OMC) at NASA Johnson Space Center emulates illumination conditions seen in space by using equipment and techniques that parallel telescopic observations and source-target-sensor orientations. One of the OMC goals is to improve the size calculation used for optical data by developing an optical-based Size Estimation Model. The current size estimation requires applying a Lambertian phase function, a set albedo value, and range to the observed magnitude. The first step to improving the sampled brightness of laboratory targets is to remove aspect-angle dependencies. Then, the volume of possible object viewing angles is sampled at 21 combinations of azimuth and zenith angles for each solar phase angle. Finally, the acquired images are input into an image processing program that generates approximations for the object’s Bidirectional Reflectance Distribution Function (BRDF) and phase function. The BRDF is a radiometric concept that identifies an object’s material composition by matching a BRDF approximated with photometric data collected by ground-based telescopes with a BRDF generated experimentally from a known object in the laboratory. This paper discusses the validation of experimental BRDF and phase function approximations produced in the OMC and how the findings will be incorporated into ODPO models. A Lambertian sphere is imaged and the subsequent experimental functions are scrutinized to confirm that they correspond to an object that has an isotropic luminance. With the image processing algorithm validated, test objects with varying optical properties are then imaged to confirm that the produced photometric functions are both unique and repeatable. Once the validation is complete, the OMC will be used to evaluate a subset of fragments from a hypervelocity impact test of a mock-up satellite and assess the appropriate phase function and size estimates using BRDF measurements for a large volume of targets composed of various shapes, sizes, and materials.

Orbital Debris Program Office (ODPO)↗
NASA NTRS1964

Attachment converts microscope to point source autocollimator

A low-power microscope or telescope provides a simple means of autocollimation. This is done by fitting the instrument with a light source to permit alignment from a reflecting surface normal to the optic axis of the instrument.

Shlichta, P. J.↗
NASA NTRS1986

Star-Viewing Scheduler

Strategy and algorithm produce well-balanced timetable that accommodates many constraints. Strategy for scheduling star observations on Space Shuttle astronomy missions ensures best use of three future ultraviolet telescopes. Strategy, described in report, takes into account such diverse factors as maneuvers of Space Shuttle orbiter, interference by Moon, occultation by Earth, reflections, unstaffed periods during crew rotation, encounters with South Atlantic anomaly, and obscuration during dispersal of ejected water.

Guffin, O. T.↗
NASA NTRS1991

Determination of lunar ilmenite abundances from remotely sensed data

The mineral ilmenite (FeTiO3) was found in abundance in lunar mare soils returned during the Apollo project. Lunar ilmenite often contains greater than 50 weight-percent titanium dioxide (TiO2), and is a primary potential resource for oxygen and other raw materials to supply future lunar bases. Chemical and spectroscopic analysis of the returned lunar soils produced an empirical function that relates the spectral reflectance ratio at 400 and 560 nm to the weight percent abundance of TiO2. This allowed mapping of the lunar TiO2 distribution using telescopic vidicon multispectral imaging from the ground; however, the time variant photometric response of the vidicon detectors produced abundance uncertainties of at least 2 to 5 percent. Since that time, solid-state charge-coupled device (CCD) detector technology capable of much improved photometric response has become available. An investigation of the lunar TiO2 distribution was carried out utilizing groundbased telescopic CCD multispectral imagery and spectroscopy. The work was approached in phases to develop optimum technique based upon initial results. The goal is to achieve the best possible TiO2 abundance maps from the ground as a precursor to lunar orbiter and robotic sample return missions, and to produce a better idea of the peak abundances of TiO2 for benefaction studies. These phases and the results are summarized.

Larson, Stephen M.↗
NASA NTRS1992

Observations of Mars using Hubble Space Telescope

The lack of a continuous record of Martian meteorology or of volatile cycles on Mars for extended periods of several Martian years seriously hinders efforts to understand the physics of the Martian atmosphere and surface system. The spacecraft observations are limited to only a few isolated time periods, and the Earth based record is limited by the relatively short periods surrounding oppositions when telescopic observations can yield useful data. To remedy this situation, the authors have embarked on a three year program of Mars observations using the Hubble Space Telescope (HST). Several scientific investigations are being carried out using the images, including: a study of the albedo variations; unit mapping of spectral reflectances; determination of optical depths due to aerosols and condensates; a study of the properties of condensate clouds and hoods; comparison of surface and atmospheric features; observation of size and shape of the polar caps; and investigation of surface atmospheric phenomena.

James, Philip B.↗
NASA NTRS2012

Chemical Mapping of Vesta

Vesta s surface mineralogy and composition have been studied for decades via telescopic spectroscopy and laboratory analyses of the howardite, eucrite, and diogenite (HED) meteorites, which are thought to originate from Vesta. Visible and infrared reflectance measurements by Dawn have broadly confirmed the paradigm established by Earth-based work, strengthening the Vesta-HED connection. The Dawn mission has achieved a milestone by completing the first chemical measurements of a main-belt asteroid using nuclear spectroscopy. Dawn s Gamma Ray and Neutron Detector (GRaND) has globally mapped the composition of Vesta, including the portions of the northern hemisphere not illuminated by solar radiation. GRaND is sensitive to the composition of the bulk regolith to depths of several decimeters. Abundances and/or detection limits for specific elements and elemental ratios, such as H, Fe, Si, Fe/O, Fe/Si, and K, have been measured. Variations in the average atomic mass and neutron macroscopic absorption cross section have been characterized. The measurements constrain the relative proportions of HED whole-rock end-members, providing measurements of the pyroxene and plagioclase content of the regolith, thereby constraining the processes underlying Vesta s differentiation and crustal evolution. The spatial resolution of GRaND is sufficient to determine basin-average compositions of Veneneia and Rheasilvia, which may contain outcrops of Vesta s olivine-rich mantle. While the elemental composition of Vesta s regolith is similar to the meteorites, there are notable departures from HED whole-rock compositions. While these differences are not sufficient to topple the Vesta-HED paradigm, they provide insight into global-scale processes that have shaped Vesta s surface. Questions addressed by the analysis of GRaND data include: (i) Is Vesta the source of the Fe-rich mesosiderites? (ii) Are evolved, igneous lithologies present on Vesta s surface? (iii) What are the origins of exogenic materials found in Vesta s regolith? (iv) Is the vestan mantle exposed within the southern basins?

Prettyman, Thomas H.↗
NASA NTRS2017

Ground-Based Observing Campaign of Briz-M Debris

In 2015, NASA's Orbital Debris Program Office (ODPO) completed the installation of the Meter Class Autonomous Telescope (MCAT) on Ascension Island. MCAT is a 1.3m optical telescope designed with a fast tracking capability for observing orbital debris at all orbital regimes (Low-Erath orbits to Geosyncronous (GEO) orbits) from a low latitude site. This new asset is dedicated year-round for debris observations, and its location fills a geographical gap in the Ground-based Electro Optical Space Surveillance (GEODSS) network. A commercial off the shelf (COTS) research grade 0.4m telescope (named the Benbrook telescope) will also be installed on Ascension at the end of 2016. This smaller version is controlled by the same master software, designed by Euclid Research, and can be tasked to work independently or in concert with MCAT. Like MCAT, it has a the same suite of filters, a similar field of view, and a fast-tracking Astelco mount, and is also capable of tracking debris at all orbital regimes. These assets are well suited for targeted campagins or surveys of debris. Since 2013, NASA's ODPO has also had extensive access to the 3.8m infrared UKIRT telescope, located on Mauna Kea. At nearly 14,000-ft, this site affords excellent conditions for collecting both photometery and spectroscopy at near-IR (0.9 - 2.5 micrometers SWIR) and thermal-IR (8 - 25 micrometers; LWIR) regimes, ideal for investigating material properties as well as thermal characteristics and sizes of debris. For the purposes of understanding orbital debris, taking data in both survey mode as well as targeting individual objects for more in-depth characterizations are desired. With the recent break-ups of Briz-M rocket bodies, we have collected a suite of data in the optical, near-infrared, and mid-infrared of in-tact objects as well as those classified as debris. A break-up at GEO of a Briz-M rocket occurred in January, 2016, well timed for the first remote observing survey-campaign with MCAT. Access to the 3.8m UKIRT telescope has also allowed for investigating this break-up in the near-infrared at wavelengths where debris is often much more reflective, allowing for the potential detection of a smaller population of these debris. In addition, a suite of near-IR reflectance spectroscopy (0.8-2.5 micrometers) and thermal-IR (8-15 micrometers) of individual in-tact and debris Briz-M objects has been collected. Analysis of the survey data will be discussed.

Lederer, S. M.↗
NASA NTRSDate not supplied

Development of Ni-based Multilayer Coatings for Extended Broadband X-ray Imaging

Next-generation astronomical hard x-ray telescopes require new multilayer coating designs to extend the current imaging capabilities into the 100’s of keV. W/Si and Pt/C demonstrate excellent reflectivity response and effective area up to approximately 70 and 80 keV but are severely limited beyond this due to Kα absorption lines. Lower-density metals provide a promising alternative to Pt and W for broader energy bands as their K-edges occur at significantly lower energies. Ni/C is such a low-density pairing that through modeling can achieve the desired energy responses. However, Ni is a notoriously difficult metal to sputter, often resulting is relatively low deposition rates and rough coating surfaces. The goal of this work is to characterize Ni/C multilayers using a custom deposition chamber at GSFC and determine the feasibility of these designs for future hard x-ray missions such as HEX-P.

Danielle N. Gurgew↗
NASA NTRS1996

The large area modular array of reflections (LAMAR)

The Large Area Modular Array of Reflectors (LAMAR) was selected as an attached payload for the Space Station Freedom in June 1989. It is a high throughput multiple X-ray telescope system that was capable of performing both imaging and dispersive spectroscopy measurements simultaneously. The LAMAR program was halted in 1990 when attached payloads were removed from the Space Station. A technical description of LAMAR is the main body of this report.

Gorenstein, Paul↗
NASA NTRS2014

Bi-static Optical Observations of GEO Objects

A bi-static study of objects at Geosynchronous Earth Orbit (GEO) was conducted using two ground-based wide-field optical telescopes. The University of Michigan's 0.6-m MODEST (Michigan Orbital Debris Survey Telescope) located at the Cerro Tololo Inter- American Observatory in Chile was employed in a series of coordinated observations with the U.S. Naval Observatory's (USNO) 1.3-m telescope at the USNO Flagstaff Station near Flagstaff, Arizona, USA. The goals of this project are twofold: (1) Obtain optical distances to known and unknown objects at GEO from the difference in the observed topocentric position of objects measured with respect to a reference star frame. The distance can be derived directly from these measurements, and is independent of any orbital solution. The wide geographical separation of these two telescopes means that the parallax difference is larger than ten degrees, and (2) Compare optical photometry in similar filters of GEO objects taken during the same time period from the two sites. The object's illuminated surfaces presented different angles of reflected sunlight to the two telescopes.During a four hour period on the night.of 22 February 2014 (UT), coordinated observations were obtained for eight different GEO positions. Each coordinated observation sequence was started on the hour or half-hour, and was selected to ensure the same cataloged GEO object was available in the field of view of both telescopes during the thirty minute observing sequence. GEO objects were chosen to be both controlled and uncontrolled at a range of orbital inclinations, and the objects were not tracked. Instead both telescopes were operated with all drives off in GEO survey mode to discover un-cataloged objects at GEO. The initial results from this proof-of-concept observing run will be presented, with the intent of laying the foundation for future large-scale bi-static observing campaigns of the GEO regime.

Seitzer, Patrick↗
NASA NTRS2010

Shack-Hartmann Phasing of Segmented Telescopes: Systematic Effects from Lenslet Arrays

The segments in the Keck telescopes are routinely phased using a Shack-Hartmann wavefront sensor with sub-apertures that span adjacent segments. However, one potential limitation to the absolute accuracy of this technique is that it relies on a lenslet array (or a single lens plus a prism array) to form the subimages. These optics have the potential to introduce wavefront errors and stray reflections at the subaperture level that will bias the phasing measurement. We present laboratory data to quantify this effect, using measured errors from Keck and two other lenslet arrays. In addition, as part of the design of the Thirty Meter Telescope Alignment and Phasing System we present a preliminary investigation of a lenslet-free approach that relies on Fresnel diffraction to form the subimages at the CCD. Such a technique has several advantages, including the elimination of lenslet aberrations.

segmented mirrors↗
NASA NTRS1998

Study of the Effects of Photometric Geometry on Spectral Reflectance Measurements

The objective of this research is to investigate how the spectrophotometric properties of planetary surface materials depend on photometric geometry by refining and applying radiative transfer theory to data obtained from spacecraft and telescope observations of planetary surfaces, studies of laboratory analogs, and computer simulations. The goal is to perfect the physical interpretation of photometric parameters in the context of planetary surface geological properties and processes. The purpose of this report is to document the research achievements associated with this study.

Helfenstein, Paul↗
NASA NTRS1976

High intensity solar irradiation testing of UV optics

The Orbiting Solar Observatory-I (OSO-8 in orbit) incorporates two high resolution solar pointing spectrometers operating from 1000 A to 4000 A. Energy from the sun enters a Cassegrainian telescope and is focused on a slit while the solar disk is scanned to one arc-second resolution. The stability of the secondary mirrors reflectance was of concern since they would be exposed to intense focused solar energy up to 27 suns. A test program was initiated to simulate this energy input on sample UV mirrors of the MgF2 and LiF types and to evaluate their performance after irradiation. Tests were conducted to simulate the solar spectrum at high intensities (25 suns) and at a single wavelength near Lyman-alpha, but with twenty times the solar intensity at Lyman-alpha. Post-test measurements after every exposure were made at wavelengths from 1025 A to 1849 A. After 75 simulated 'orbits', reflectance changes due to temperature effects were noted to be less than 10%. Reductions in reflectance under high intensity solar radiation were generally greater than 10%. Polymerization of surface contaminations on the LiF mirrors reduced reflectances at short wavelengths by 40%.

Greyerbiehl, J. M.↗
NASA NTRS1981

Infrared Astronomy

Several observational programs in infrared astronomy are described and significant findings are briefly discussed. The near infrared work concentrates largely on the use of the 5 m Hale telescope in spectroscopic and photometric studies of extragalactic sources. Observations of the P alpha line profile in a low redshift quasar, X-ray bursters, reflection nebula, and cataclysmic variables are included. Millimeter continuum observations of dust emission from quasars and galactic molecular clouds are also discussed. Finally, improvements to instrumentation are reported.

Neugebauer, G.↗