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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 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Master-Oscillator/Power-Amplifier Laser System

Master-oscillator/power-amplifier (MOPA) laser system operates in continuous-wave mode or in amplitude-modulation (e.g., pulse) mode by modulation of oscillator current. Power amplifier is laser-diode-pumped neodymium:yttrium lithium fluoride (Nd:YLF) laser; oscillator is laser diode. Offers relatively high efficiency and power. Because drive current to oscillator modulated, external electro-optical modulator not needed. Potential uses include free-space optical communications, coded laser ranging, and generation of high-power, mode-locked pulses.

Yu, Anthony W.↗
NASA NTRS1995

Effect of Microgravity on Material Undergoing Melting and Freezing: the TES Experiment

This experiment is the first to melt and freeze a high temperature thermal energy storage (TES) material under an extended duration of microgravity. It is one of a series to validate an analytical computer program that predicts void behavior of substances undergoing phase change under microgravity. Two flight experiments were launched in STS-62. The first, TES-1, containing lithium fluoride in an annular volume, performed flawlessly in the 22 hours of its operation. Results are reported in this paper. A software failure in TES-2 caused its shutdown after 4 seconds. A computer program, TESSIM, for thermal energy storage simulation is being developed to analyze the phenomena occurring within the TES containment vessel. The first order effects, particularly the surface tension forces, have been incorporated into TESSIM. TESSIM validation is based on two types of results. First is the temperature history of various points of the containment structure, and second, upon return from flight, the distribution of the TES material within the containment vessel following the last freeze cycle. The temperature data over the four cycles showed a repetition of results over the third and fourth cycles. This result is a confirmation that any initial conditions prior to the first cycle had been damped out by the third cycle. The TESSIM simulation showed a close comparison with the flight data. The solidified TES material distribution within the containment vessel was obtained by a tomography imaging process. The frozen material was concentrated toward the colder end of the annular volume. The TESSIM prediction showed the same pattern. With the general agreement of TESSIM and the data, a computerized visual representation can be shown which accurately shows the movement and behavior of the void during the entire freezing and melting cycles.

Namkoong, David↗
NASA NTRS1995

Spectroscopy and excitation dynamics of the trivalent lanthanides Tm(3+) and Ho(3+) in LiYF4

A detailed study of the spectroscopy and excitation dynamics Tm3+ and Ho3+ in yttrium lithium fluoride, LiYF4 (YLF), has been done. Absorption spectroscopy is utilized in the Judd-Ofelt theory to determine radiative transition rates of spontaneous emission. Luminescence spectroscopy is studied under cw diode laser excitation at 785nm. The effect of dopant ion concentration and excitation power on the observed luminescence are considered in these measurements. An analysis of these measurements have been used to determine channels of energy transfer between Tm3+ and Ho3+ ions. The temporal response of Tm and Ho in singly and co-doped YLF to pulsed laser excitation with a Ti:Al2O3 laser and a CoMgF2 laser turned to various wavelengths have also been studied. The energy transfer mechanisms of cross relaxation, upconversion, and resonant energy transfer between Tm3+ and Ho3+ ions have been modeled, and the model parameters extracted by a fitting procedure to the measured temporal response curves. Rate equation approaches to modeling are presented that result in predictions of rate constants for energy transfer processes, as well as more conventional approaches to modeling such as the Forster-Dexter models, which give the interaction strengths in terms of microscopic interaction parameters.

Walsh, Brian M.↗
NASA NTRS1995

Radiative and Nonradiative Transitions of the Rare-Earth Ions Tm(3+) and Ho(3+) in Y3AI5O12 and LiYF4

The optical spectra of rare earth ions in solids arise primarily from electric and magnetic dipole transitions between stark split multiplets of the 4f(sup N) electronic configuration. Electric dipole transitions are parity forbidden between levels of the 4f(sup N) configuration, while those of magnetic dipole origin are allowed. It is known from experiment, however, that the significant contributions to the intensities of most transitions are electric dipole in nature. Judd and Ofelt developed the theory of forced electric dipole transitions of rare-earth ions. This study is devoted to determining electric dipole transition probabilities and branching ratios for Tm(3+) and Ho(3+) ions in Yttrium Aluminum Garnet (YAG) and Yttrium Lithium Fluoride (YLF) using the theory of Judd and Ofelt. The radiative rates determined from the Judd-Ofelt analysis are used with measured lifetimes to find nonradiative rates of relaxation.

Walsh, Brian M.↗
NASA NTRS1996

Design of the Heat Receiver for the U.S./Russia Solar Dynamic Power Joint Flight Demonstration

A joint U.S./Russia program is being conducted to develop, fabricate, launch, and operate a solar dynamic demonstration system on Space Station Mir. The goal of the program is to demonstrate and confirm that solar dynamic power systems are viable for future space applications such as the International Space Station Alpha The major components of the system include a heat receiver, a closed Brayton cycle power conversion unit, a power conditioning and control unit, a concentrator, a radiator, a thermal control system, and a Space Shuttle Carrier. This paper discusses the design of the heat receiver component. The receiver comprises a cylindrical cavity, the walls of which are lined with a series of tubes running the length of the cavity. The engine working fluid, a mixture of xenon and helium, is heated by the concentrated sunlight incident on these tubes. The receiver incorporates integral thermal storage, using a eutectic mixture of lithium fluoride and calcium difluoride as the thermal storage solid-to-liquid phase change materiaL This thermal storage is required to enable power production during eclipse. The phase change material is contained in a series of individual containment canisters.

Strumpf, Hal J.↗
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 NTRSDate not supplied

A New Linear Polarizer Design for Application in the Far-Ultraviolet Spectral Range

New mission concepts that are under consideration by NASA (such as the Polstar MIDEX mission concept) call for the design and implementation of Far Ultraviolet (FUV) polarizer technologies that have not been developed yet. A team that includes members from the NASA Goddard Space Flight Center (GSFC), Arizona State University (ASU), and Woodruff Consulting, worked on the design and development of a polarizer design that may produce extinction ratios higher than have ever been reported before in the FUV spectral range (100-200 nm). This polarizer consists of transmitting linearly polarized light through a series of reflections from a combination of two silicon carbide (SiC) and two lithium fluoride (LiF) crystals positioned at angles of incidence (relative to surface normal) close to the LiF Brewster’s angle. The performance of this polarizer concept was fabricated and tested with an existing McPherson 225 Vacuum Ultraviolet (VUV) spectrometer located in the Optics Branch at NASA-GSFC. Initial testing has shown that in the FUV spectral range, this design can produce state-of-the-art extinction ratios at the Hydrogen Lyman-Alpha (Ly-α) wavelength of 121.6 nm. A polarizer with such a performance has never been reported and it signifies a breakthrough in FUV polarization technology. The levels of effectiveness paired with the design’s compact design allows for a new polarizer capability that would one day be implemented in a future spectropolarimetry space mission. In addition, this polarizer concept could potentially be used to characterize the optical properties of new mirror coatings that will be used in a future Habitable World Observatory (HWO) mission concept as proposed by the 2020 Decadal Survey.2

Far Ultraviolet (FUV), polarimetry, instrumentatio↗
NASA NTRSDate not supplied

Linear Polarizer Design for Application in the Far-Ultraviolet Spectral Range

New mission concepts that are under consideration by NASA (such as the Polstar MIDEX mission concept) call for the design and implementation of Far Ultraviolet (FUV) polarizer technologies that have not been developed yet. A team that includes members from the NASA Goddard Space Flight Center (GSFC), Arizona State University (ASU), and Woodruff Consulting, worked on the design and development of a polarizer design that may produce extinction ratios higher than have ever been reported before in the FUV spectral range (100-200 nm). This polarizer consists of transmitting linearly polarized light through a series of reflections from a combination of two silicon carbide (SiC) and two lithium fluoride (LiF) crystals positioned at angles of incidence (relative to surface normal) close to the LiF Brewster’s angle. The performance of this polarizer concept was fabricated and tested with an existing McPherson 225 Vacuum Ultraviolet (VUV) spectrometer located in the Optics Branch at NASA-GSFC. Initial testing has shown that in the FUV spectral range, this design can produce state-of-the-art extinction ratios at the Hydrogen Lyman-Alpha (Ly-α) wavelength of 121.6 nm. A polarizer with such a performance has never been reported and it signifies a breakthrough in FUV polarization technology. The levels of effectiveness paired with the design’s compact design allows for a new polarizer capability that would one day be implemented in a future spectropolarimetry space mission. In addition, this polarizer concept could potentially be used to characterize the optical properties of new mirror coatings that will be used in a future Habitable World Observatory (HWO) mission concept as proposed by the 2020 Decadal Survey.2

Far Ultraviolet (FUV), polarimetry, instrumentatio↗
NASA NTRSDate not supplied

Linear Polarizer Design for Application in the Far-Ultraviolet Spectral Range

New mission concepts that are under consideration by NASA call for the design and implementation of Far Ultraviolet (FUV) polarizer technologies that have not been developed yet. A team that includes members from the NASA Goddard Space Flight Center (GSFC), Arizona State University (ASU), and Woodruff Consulting, worked on the design and development of a polarizer design that produce very high extinction ratios in the FUV spectral range (100-200 nm). This polarizer consists of reflecting light through a series of mirrors from a combination of two silicon carbide (SiC) and two lithium fluoride (LiF) crystals positioned at angles of incidence (relative to surface normal) close to the average LiF Brewster’s angle in the FUV. The output is a highly linearly polarized beam. This polarizer concept was fabricated and tested in the existing McPherson 225 Vacuum Ultraviolet (VUV) spectrometer located in the Optics Branch at NASA-GSFC. Initial testing using a MgF2 crystal at the Brewster’s angle as an analyzer has shown that this design can produce state-of-the-art extinction ratios at the Hydrogen Lyman-Alpha (Ly-α) wavelength of 121.6 nm, and that the measured extinction ratio of the two crossed polarizers, ≈114, is mostly limited by the MgF2 analyzer. A polarizer with such a performance at this wavelength has never been reported and it signifies a breakthrough in FUV polarization technology. The levels of effectiveness paired with the polarizer’s compact design allows for a new polarizer capability that would one day be implemented in a future FUV spectropolarimetry space mission.

Far Ultraviolet (FUV)↗
NASA NTRSDate not supplied

Metrological and Spectral Characterization of the Aspera Flight Optics

Aspera is a NASA's Astrophysics Pioneers mission, led by the University of Arizona. The aim of this mission is to study the presence of hot gasses (T=10^5-10^6 K) in the circumgalactic medium (CGM) and how the flow of these gasses affects galactic formation. One key enabling technology in the Aspera optical system is the use of more efficient UV-reflective optical coatings particularly at around 103.2 nm where the O VI emission line is located . In order to meet radiometric effective area requirements, the Goddard Space Flight Center (GSFC) code 551 Optics Branch applied Al (aluminum) + eLiF (enhanced lithium fluoride) on these optics, where the Al+LiF is annealed at elevated temperature (~250˚C) after the deposition and thus providing an improved version of the Al+LiF used in FUSE . Furthermore, these optics are encapsulated with a thin film of atomic layer deposited MgF2 at the Jet Propulsion Laboratory for enhanced durability . The efficiency and durability of these coatings depends on the quality of the optical surface in terms of cleanliness and roughness. Roughness increases the scatter off the coating and reduces the specular reflectance, and surface contaminants can accommodate moisture and other contaminants, increase scattering, and are weak points in the coating that may affect adhesion and subsequently the longevity of these coatings. Extensive optical metrology is necessary to minimize and quantify the impact of surface roughness and contaminants on optical surfaces. In this proceeding we report the inspection procedure implemented for Aspera optics at GSFC, from initial receiving of the optics to post-coating. Inspection includes Atomic Force Microscopy (AFM), Scanning White Light Interferometry (SWILI), Dark Field Microscopy (DFM), Phase Shifting Interferometry (PSI), and Vacuum ultraviolet (VUV) spectroscopy. Combinations of these techniques are used to inspect flight optics at each of the following steps: i) as-received, pre-cleaning inspection, ii) pre-coating, post-cleaning inspection, and iii) post-coating inspection. The evolution of roughness and other surface inspections such as contaminants are compared between each step to quantify the effect each step has on the flight optics. The final far ultraviolet (FUV) spectral performance of witness samples coated with the flight optics are presented.

Far Ultraviolet (FUV)↗
NASA NTRS1990

A heat receiver design for solar dynamic space power systems

An advanced heat pipe receiver designed for a solar dynamic space power system is described. The power system consists of a solar concentrator, solar heat receiver, Stirling heat engine, linear alternator and waste heat radiator. The solar concentrator focuses the sun's energy into a heat receiver. The engine and alternator convert a portion of this energy to electric power and the remaining heat is rejected by a waste heat radiator. Primary liquid metal heat pipes transport heat energy to the Stirling engine. Thermal energy storage allows this power system to operate during the shade portion of an orbit. Lithium fluoride/calcium fluoride eutectic is the thermal energy storage material. Thermal energy storage canisters are attached to the midsection of each heat pipe. The primary heat pipes pass through a secondary vapor cavity heat pipe near the engine and receiver interface. The secondary vapor cavity heat pipe serves three important functions. First, it smooths out hot spots in the solar cavity and provides even distribution of heat to the engine. Second, the event of a heat pipe failure, the secondary heat pipe cavity can efficiently transfer heat from other operating primary heat pipes to the engine heat exchanger of the defunct heat pipe. Third, the secondary heat pipe vapor cavity reduces temperature drops caused by heat flow into the engine. This unique design provides a high level of reliability and performance.

Baker, Karl W.↗
NASA NTRS1991

STS lithium/CF(x) battery

Lithium carbon fluoride batteries are used on Space Shuttle Rocket Boosters and external tanks. These batteries have been extremely successful in terms of mission reliability with the exception of cell yield variances. The function/system and battery descriptions are given. A description is given of the battery range safety system.

Gnacek, Dee↗
NASA NTRSDate not supplied

Exposure of Highly Reflective Far-Ultraviolet Coatings to LEO Environment for TRL Advancement for the Habitable Worlds Observatory

Over the past several years, our team at the NASA Goddard Space Flight Center (GSFC), in collaboration with the Jet Propulsion Laboratory (JPL) and the Naval Research Laboratory (NRL), have developed several new protected Al coating technologies with improved Far-Ultraviolet (FUV) reflectance performance and more robust environmental stability. These include Al protected with lithium-based fluoride (LiF) coatings such as hot deposited LiF (eLiF), XeF 2 -passivated LiF coatings (XeLiF), Li 3 AlF 6 overcoats, AlF 3 (plasma passivated), and XeF 2 passivated MgF 2 coatings (XeMgF 2 ). However, despite these developments, relatively little experimental information exists regarding the long-term stability of these coatings after simultaneous exposure to the Low Earth Orbit (LEO) environment. To evaluate their environmental durability and advance their Technology Readiness Level (TRL), representative samples of these coating technologies, Al+XeLiF, Al+eLiF, Al+Li 3 AlF 6 , Al+AlF 3 , Al+XeMgF 2 , and bare Al as reference samples, were flown onboard the International Space Station (ISS) as part of the Materials International Space Station Experiment 20 (MISSE-20). The MISSE platform is operated by Aegis Aerospace for relatively long-duration (e.g. 6 months) external exposure experiments in a space environment. The coatings were deposited on ULE and Zerodur substrates, and witness samples deposited on the same coatings runs, but on glass slides were left on Earth as control. A subset of the flight samples were fitted with MgF 2 windows to reduce direct exposure to atomic oxygen (AO) and charged particles, and still let through UV and other types of radiation on these samples. After approximately 6 months of exposure in the forward-facing (RAM) direction, the samples were returned to Earth and characterized by performing FUV/NUV/VIS/NIR reflectance measurements to quantify degradation, spectroscopic ellipsometry to evaluate coating thickness and optical constants, atomic force microscopy (AFM) to quantify surface roughness evolution during the flight in the ISS. The MgF 2 protective windows were also analyzed through FUV transmission measurements. Comparison with the witness samples left on the ground and with the flown bare Al samples (with just the naturally occurring Al 2 O 3 layer) provided a quantitative assessment of coating thickness variations, optical performance degradation, and morphological changes induced by prolonged exposure to the LEO environment.

Far Ultraviolet (FUV)↗