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NASA NTRS2009

Numerical Optimization of the Thermal Field in Bridgman Detached Growth

The global modeling of the thermal field in two vertical Bridgman-like crystal growth configurations, has been performed to get optimal thermal conditions for a successful detached growth of Ge and CdTe crystals. These computations are performed using the CrysMAS code and expand upon our previous analysis [1] that propose a new mechanism involving the thermal field and meniscus position to explain stable conditions for dewetted Bridgman growth. The analysis of the vertical Bridgman configuration with two heaters, used by Palosz et al. for the detached growth of Ge, shows, consistent with their results, that the large wetting angle of germanium on boron nitride surfaces was an important factor to promote a successful detached growth. Our computations predict that by initiating growth much higher into the hot zone of the furnace, the thermal conditions will be favorable for continued detachment even for systems that did not exhibit high contact angles. The computations performed for a vertical gradient freeze configuration with three heaters representative of that used for the detached growth of CdTe, show favorable thermal conditions for dewetting during the entirely growth run described. Improved thermal conditions are also predicted for coated silica crucibles when the solid-liquid interface advances higher into the hot zone during the solidification process. The second set of experiments on CdTe growth described elsewhere has shown the reattachment of the crystal to the crucible after few centimeters of dewetted growth. The thermal modeling of this configuration shows a second solidification front appearing at the top of the sample and approaching the middle line across the third heater. In these conditions, the crystal grows detached from the bottom, but will be attached to the crucible in the upper part because of the solidification without gap in this region. The solidification with two interfaces can be avoided when the top of the sample is positioned below the middle position of the third furnace.

Stelian, C.↗

NASA NTRS2013

FUN3D Airload Predictions for the Full-Scale UH-60A Airloads Rotor in a Wind Tunnel

An unsteady Reynolds-Averaged Navier-Stokes solver for unstructured grids, FUN3D, is used to compute the rotor performance and airloads of the UH-60A Airloads Rotor in the National Full-Scale Aerodynamic Complex (NFAC) 40- by 80-foot Wind Tunnel. The flow solver is loosely coupled to a rotorcraft comprehensive code, CAMRAD-II, to account for trim and aeroelastic deflections. Computations are made for the 1-g level flight speed-sweep test conditions with the airloads rotor installed on the NFAC Large Rotor Test Apparatus (LRTA) and in the 40- by 80-ft wind tunnel to determine the influence of the test stand and wind-tunnel walls on the rotor performance and airloads. Detailed comparisons are made between the results of the CFD/CSD simulations and the wind tunnel measurements. The computed trends in solidity-weighted propulsive force and power coefficient match the experimental trends over the range of advance ratios and are comparable to previously published results. Rotor performance and sectional airloads show little sensitivity to the modeling of the wind-tunnel walls, which indicates that the rotor shaft-angle correction adequately compensates for the wall influence up to an advance ratio of 0.37. Sensitivity of the rotor performance and sectional airloads to the modeling of the rotor with the LRTA body/hub increases with advance ratio. The inclusion of the LRTA in the simulation slightly improves the comparison of rotor propulsive force between the computation and wind tunnel data but does not resolve the difference in the rotor power predictions at mu = 0.37. Despite a more precise knowledge of the rotor trim loads and flight condition, the level of comparison between the computed and measured sectional airloads/pressures at an advance ratio of 0.37 is comparable to the results previously published for the high-speed flight test condition.

Lee-Rausch, Elizabeth M.↗

NASA NTRS2025

Thermochemical Stability of Ca2Yb8(SiO4)6O2 Apatite in Presence of Molten Calcium-Magnesium-AluminoSilicate (CMAS)

Thermochemical stability of ytterbium silicon oxyapatite Ca 2 Yb 8 (SiO 4 ) 6 O 2 (CYbS) in the presence of molten calcium-magnesium aluminosilicate (CMAS) has been investigated at elevated temperatures. CYbS apatite powder was synthesized from the constituent oxides via solid state reaction method. Hot pressed apatite substrates were exposed to molten CMAS at 1200, 1300, and 1400 °C for 1, 10, and 50 h. Development of phases in the interaction region of the heat-treated specimens was monitored using scanning electron microscopy, transmission electron microscopy, high angle annular dark field imaging, selected area electron diffraction and energy dispersive X-ray spectroscopy. Monoclinic cyclosilicate Ca 3 Yb 2 (Si 3 O 9 ) 2 formed from interaction of CYbS apatite with CaO in the CMAS melt at the apatite-CMAS reaction front and continued to nucleate and grow within the residual CMAS in diffusion couples annealed for 1-50 h at 1200 °C and those heat treated at 1300 °C for 1 h. Residual CMAS was Ca-depleted when cyclosilicate was present. Dendritic wollastonite CaSiO 3 was observed within the residual CMAS in couples annealed at 1200 and 1300 °C. Ingress of molten CMAS, because of its exponential decrease in viscosity, occurred through open pores and along the grain boundaries of the apatite substrates without any detectable chemical reaction at 1300 and 1400 °C. Results of this study indicate that Ca 2 Yb 8 (SiO 4 ) 6 O 2 apatite has the potential to mitigate the CMAS corrosion up to about 1200 °C but not at higher temperatures.

X-ray diffraction↗

DOE OSTI2015

SOFIA infrared spectrophotometry of comet C/2012 K1 (Pan-STARRS)

We present pre-perihelion infrared 8–31 μm spectrophotometric and imaging observations of comet C/2012 K1 (Pan-STARRS), a dynamically new Oort Cloud comet, conducted with NASA's Stratospheric Observatory for Infrared Astronomy facility (+FORCAST) in 2014 June. As a “new” comet (first inner solar system passage), the coma grain population may be extremely pristine, unencumbered by a rime and insufficiently irradiated by the Sun to carbonize its surface organics. The comet exhibited a weak 10 μm silicate feature ≃1.18 ± 0.03 above the underlying best-fit 215.32 ± 0.95 K continuum blackbody. Thermal modeling of the observed spectral energy distribution indicates that the coma grains are fractally solid with a porosity factor D = 3 and the peak in the grain size distribution, a{sub peak} = 0.6 μm, large. The sub-micron coma grains are dominated by amorphous carbon, with a silicate-to-carbon ratio of 0.80{sub −0.20}{sup +0.25}. The silicate crystalline mass fraction is 0.20{sub −0.10}{sup +0.30}, similar to with other dynamically new comets exhibiting weak 10 μm silicate features. The bolometric dust albedo of the coma dust is 0.14 ± 0.01 at a phase angle of 34.°76, and the average dust production rate, corrected to zero phase, at the epoch of our observations was Afρ ≃ 5340 cm.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1996

Compact Solar Simulator with a Small Subtense Angle and Controlled Magnification Optics

The present invention is directed to a method of simulating a pseudosun using a solar simulator. In the present invention the collector and lens of a lamp are designed to properly focus a plurality of light beams onto a segmented turning mirror. The path of light rays are traced from the lamp to the collector and then finally to the lens to control the solid and tangential magnification of the solar simulator. The segmented turning mirror is located at the focal point of the light beam and redirects the light into a vacuum chamber.

Jefferies, Kent S.↗

DOE OSTI2014

Synthesis and characterisation of In-doped MnWO{sub 4}-type solid-solutions: Mn{sub 1−3x}In{sub 2x}□{sub x}WO{sub 4} (x=0–0.11)

Substitution of In{sup 3+} for Mn{sup 2+} in MnWO{sub 4}, which is one of the most studied multiferroics, was conducted systematically by solid-state reactions at 1050 °C to obtain a series of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} solid solutions (x=0–0.11; the box indicates vacancy). The successful In-doping could be proven by electron microprobe, and statically disordered structures of this solid solution series were elucidated by Rietveld analyses with X-Ray powder diffraction (XPD) data. Its average structure maintains the space group P2/c at least up to the replacement of 33 at% Mn. The tendency of their unit cells proportionally enlarging with In-doping is an unexpected observation because In{sup 3+} is smaller than Mn{sup 2+}. This could not be explained alone by average atomic bonding distances and angles evaluated from XPD data analyses. Complimentarily, micro-Raman spectra of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} materials feature a hardening of Raman modes due to stronger atomic bonds in W{sub 2}O{sub 4} and WO{sub 2} units with increasing In-doping. This is considered as an inevitable consequence of broken bonding in directly neighbouring Mn–O bonds as the presence of In{sup 3+} in MnWO{sub 4} accompanies the creation of defects at Mn sites. The current study using XRD and micro-Raman suggests the enlarging local space around the bridging oxygen as the reason for the unexpected cell expansion when smaller In{sup 3+} along with defects replace Mn{sup 2+} in MnWO{sub 4}. - Graphical abstract: Despite of substitution of smaller In{sup 3+} for larger Mn{sup 2+}, the In-rich solid solution Mn{sub 0.71(2)}In{sub 0.19(1)}□{sub 0.10}WO{sub 4} undergoes a volume expansion of 0.4% with respect to MnWO{sub 4}. This could be explained by a local space expansion of 0.13% around bridging oxygen at O2 sites, as illustrated by dashed lines for clarity. - Highlights: • Investigation of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} solid solutions (x=0–0.11). • An unexpected lattice expansion by In-doping. • Strong change in local environment around bridging oxygens. • Enhancement of atomic bonds in W{sub 2}O{sub 4} and WO{sub 2} units with increasing In-doping.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Origins of electronic bands in the antiferromagnetic topological insulator MnBi 2 Te 4

Despite the rapid progress in understanding the first intrinsic magnetic topological insulator MnBi 2 Te 4 , its electronic structure remains a topic under debates. In this work, we perform a thorough spectroscopic investigation into the electronic structure of MnBi 2 Te 4 via laser-based angle-resolved photoemission spectroscopy. Through quantitative analysis, we estimate an upper bound of 3 meV for the gap size of the topological surface state. Furthermore, our circular dichroism measurements reveal band chiralities for both the topological surface state and quasi-2D bands, which can be well reproduced in a band hybridization model. A numerical simulation of energy-momentum dispersions based on a four-band model with an additional step potential near the surface provides a promising explanation for the origin of the quasi-2D bands. Our study represents a solid step forward in reconciling the existing controversies in the electronic structure of MnBi 2 Te 4 , and provides an important framework to understand the electronic structures of other relevant topological materials MnBi 2n Te 3n+1 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2017

Phase field modeling of microstructure evolution and concomitant effective conductivity change in solid oxide fuel cell electrodes

Microstructure evolution plays an important role in the performance degradation of SOFC electrodes. In this work, we propose a much improved phase field model to simulate the microstructure evolution in the electrodes of solid oxide fuel cell. We demonstrate that the tunability of the interfacial energy in this model has been significantly enhanced. Parameters are set to fit for the interfacial energies of a typical Ni-YSZ anode, an LSM-YSZ cathode and an artificial reference electrode, respectively. The contact angles at various triple junctions and the microstructure evolutions in two dimensions are calibrated to verify the model. As a demonstration of the capabilities of the model, three dimensional microstructure evolutions are simulated applying the model to the three different electrodes. The time evolutions of grain size and triple phase boundary density are analyzed. In addition, a recently proposed bound charge successive approximation algorithm is employed to calculate the effective conductivity of the electrodes during microstructure evolution. Furthermore, the effective conductivity of all electrodes are found to decrease during the microstructure evolution, which is attributed to the increased tortuosity and the loss of percolated volume fraction of the electrode phase.

30 DIRECT ENERGY CONVERSION↗

DOE OSTI2013

Observation of atomic scale compositional and displacive modulations in incommensurate melilite electrolytes

The paradigm that functional materials are adequately described as three-dimensional crystal structures is not universally tenable. Gallate melilites are efficient oxide ion conductors at intermediate temperatures (∼750 °C) with non-rational crystallographic modulations presumed to play a key role in significantly enhancing oxygen mobility. Lattice distortions associated with incommensuration are usually extrapolated from diffraction analysis of volumes greatly exceeding the scale of modulation. Therefore, opportunities for making direct nanometric measurements are exceptionally valuable for correlating structure with function. In [CaLn]{sub 2}[Ga]{sub 2}[Ga{sub 2}O{sub 7}]{sub 2} (Ln=Nd, La) melilites, atomic displacive and compositional modulation waves can be imaged by high angle annular dark field and bright field scanning transmission electron microscopy with contrast quantified through electron scattering simulation. Here, we present atomic scale observations of (3+2)-dimensional modulations in gallate melilites which expands our understanding of the ion conduction mechanism and provides guidance for enhancing the performance of solid oxide fuel cells through crystal chemical tailoring. - Highlights: • Characterise the (3+2)-dimensional melilite electrolytes using STEM technique. • Direct observation on displacive and compositional modulation in melilites. • Structural flexibility reduces when increasing interstitial oxygen. • Domain-like incommensurate modulation model is proposed.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2016

SU-F-T-93: Breast Surface Dose Enhancement Using a Clinical Prone Breast Board

Purpose: The use of specialized patient set-up devices in radiotherapy, such as prone breast boards, may have unwanted dosimetric effects. The goal of this study was to evaluate the effect of a clinically used prone breast board on skin dose due to buildup. Methods: GafChromic film (EBT3) was used for dose measurements on the surface of a solid water phantom shaped to mimic the curvature of the breast. We investigated two setup scenarios: the medial field border placed at the medial edge of the board and 1 cm contralaterally from that edge. A strip of film was taped to the medial surface of the phantom. Gantry angles varied from 10 to 30 degrees below the lateral gantry position, representing anterior oblique fields. The measurements were performed with and without the presence of the board; the ratio of their corresponding doses (dose enhancement) was evaluated. Results: For the cases where the field edge is at the edge of the board, the dose enhancement is negligible for all the tested angles. When the field edge is 1 cm inside the board, the maximum surface dose enhancement varies depending on the gantry angle between 2.2 for 30 degrees and 3.2 for 20 degrees. The length on the film at which the presence of the board is detectable (i.e. where there is dose enhancement) is longer for the shallower angles. Conclusion: Even the low-density, thin carbon fiber board with a thin soft foam pad on the top can produce significant dose enhancement on the skin in prone breast treatment due to loss of buildup. However, it happens only when the patient mid-sternum is over the board, i.e. the medial edge of the field traverses through the board and pad. Even then, the effect occurs only at the field edge, i.e. the penumbral region.

60 APPLIED LIFE SCIENCES↗

NASA NTRS1984

Secondary flow spanwise deviation model for the stators of NASA middle compressor stages

A model of the spanwise variation of deviation for stator blades is presented. Deviation is defined as the difference between the passage mean flow angle and the metal angle at the outlet of a blade element of an axial compressor stage. The variation of deviation is taken as the difference above or below that predicted by blade element, (i.e., two-dimensional) theory at any spanwise location. The variation of deviation is dependent upon the blade camber, solidity and inlet boundary layer thickness at the hub or tip end-wall, and the blade channel aspect ratio. If these parameters are known or can be calculated, the model provides a reasonable approximation of the spanwise variation of deviation for most compressor middle stage stators operating at subsonic inlet Mach numbers.

Roberts, W. B.↗

NASA NTRS1990

SAPT units turn-on in an interference-dominant environment

A stand alone pressure transducer (SAPT) is a credit-card-sized smart pressure sensor inserted between the tile and the aluminum skin of a space shuttle. Reliably initiating the SAPT units via RF signals in a prelaunch environment is a challenging problem. Multiple-source interference may exist if more than one GSE (ground support equipment) antenna is turned on at the same time to meet the simultaneity requirement of 10 ms. A polygon model for orbiter, external tank, solid rocket booster, and tail service masts is used to simulate the prelaunch environment. Geometric optics is then applied to identify the coverage areas and the areas which are vulnerable to multipath and/or multiple-source interference. Simulation results show that the underside areas of an orbiter have incidence angles exceeding 80 deg. For multipath interference, both sides of the cargo bay areas are found to be vulnerable to a worst-case multipath loss exceeding 20 dB. Multiple-source interference areas are also identified. Mitigation methods for the coverage and interference problem are described. It is shown that multiple-source interference can be eliminated (or controlled) using the time-division-multiplexing method or the time-stamp approach.

Peng, W.-C.↗

NASA NTRS1992

The study of the thermal behavior of a new semicrystalline polyimide

Thermal properties of a new semicrystalline polyimide synthesized from 3,3',4,4' benzophenone tetracarboxylic dianhydride (BTDA) and 2,2 dimethyl 1,2-(4 aminophenoxy) propane (DMDA) were studied. Heat capacities in the solid and liquid states of BTDA-DMDA were measured. The heat capacity increase at the glass transition temperature (T sub g = 230 C) is 145 J/(C mol) for amorphous BTDA-DMDA. The equilibrium heat of fusion of the BTDA-DMDA crystals was obtained using wide angle X ray diffraction and differential scanning calorimetry measurements, and it is 75.8 kJ/mol. Based on the information of crystallinity and the heat capacity increase at T sub g, a rigid amorphous fraction is identified in semicrystalline BTDA-DMDA samples. The rigid amorphous fraction represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample which should be associated with crystal sizes, and therefore, with crystal morphology. It was also found that this polymer has a high temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies are determined to be 154 and 150 kJ/mol in nitrogen and air, respectively.

Cheng, Stephen Z. D.↗

DOE OSTI2019

Organic-Mineral Interfacial Chemistry Drives Heterogeneous Nucleation of Sr-Rich (Bax, Sr1-x)SO4 from Undersaturated Solution

Sr-bearing marine barite [(Bax, Sr1-x)SO4] cycling has been widely used to reconstruct geochemical evolutions of paleoenvironments. However, an understanding of barite precipitation in the ocean, which is globally undersaturated with respect to barite, is missing. Moreover, the reason for the occurrence of higher Sr content in marine barites than expected for classical crystal growth processes remains unknown. Field data analyses suggested that organic molecules may regulate the formation and composition of marine barites; however, the specific organic–mineral interactions are unclear. Using in situ grazing incidence small-angle X-ray scattering (GISAXS), size and total volume evolutions of barite precipitates on organic films were characterized. The results show that barite forms on organic films from undersaturated solutions. Moreover, from a single supersaturated solution with respect to barite, Sr-rich barite nanoparticles formed on organics, while micrometer-size Sr-poor barites formed in bulk solutions. Ion adsorption experiments showed that organic films can enrich cation concentrations in the adjacent solution, thus increasing the local supersaturation and promoting barite nucleation on organic films, even when the bulk solution was undersaturated. The Sr enrichment in barites formed on organic films was found to be controlled by solid-solution nucleation rates; instead, the Sr-poor barite formation in bulk solution was found to be controlled by solid-solution growth rates. This study provides a mechanistic explanation for Sr-rich marine barite formation and offers insights for understanding and controlling the compositions of solid solutions by separately tuning their nucleation and growth rates via the unique chemistry of solution–organic interfaces.

Deng, Ning↗

NASA NTRS2001

Friction Stir Welding Development at NASA, Marshall Space Flight Center

Friction stir welding (FSW) is a solid state process that pan be used to join materials without melting. The process was invented by The Welding Institute (TWI), Cambridge, England. Friction stir welding exhibits several advantages over fusion welding in that it produces welds with fewer defects and higher joint efficiency and is capable of joining alloys that are generally considered non-weldable with a fusion weld process. In 1994, NASA-Marshall began collaborating with TWI to transform FSW from a laboratory curiosity to a viable metal joining process suitable for manufacturing hardware. While teamed with TWI, NASA-Marshall began its own FSW research and development effort to investigate possible aerospace applications for the FSW process. The work involved nearly all aspects of FSW development, including process modeling, scale-up issues, applications to advanced materials and development of tooling to use FSW on components of the Space Shuttle with particular emphasis on aluminum tanks. The friction stir welding process involves spinning a pin-tool at an appropriate speed, plunging it into the base metal pieces to be joined, and then translating it along the joint of the work pieces. In aluminum alloys the rotating speed typically ranges from 200 to 400 revolutions per minute and the translation speed is approximately two to five inches per minute. The pin-tool is inserted at a small lead angle from the axis normal to the work piece and requires significant loading along the axis of the tool. An anvil or reaction structure is required behind the welded material to react the load along the axis of the pin tool. The process requires no external heat input, filler material, protective shielding gas or inert atmosphere typical of fusion weld processes. The FSW solid-state weld process has resulted in aluminum welds with significantly higher strengths, higher joint efficiencies and fewer defects than fusion welds used to join similar alloys.

McGill, Preston↗

DOE OSTI2019

Enhanced hydrogen storage by a variable temperature process

We present a simple method of variable temperature process that can potentially enhance the hydrogen storage properties of a large variety of solid state materials. In this approach, hydrogen gas is first introduced at about room temperature, which is followed by a gradual increase to a preset maximum temperature value, T max . Using this approach, we investigated hydrogen absorption properties of vertically aligned arrays of magnesium nanotrees and nanoblades fabricated by glancing angle deposition (GLAD) technique, and conventional Mg thin film. Weight percentage (wt%) storage values were measured by quartz crystal microbalance (QCM). After exposing Mg samples to H 2 at 30 bar and 30 °C, dynamic absorption measurements were conducted as the temperature was increased from 30 °C to maximum values of T max = 100, 200, and 300 °C all within 150 min. QCM measurements revealed that variable temperature method results in significant improvements in hydrogen storage values over the ones obtained by conventional constant temperature process. At a low effective temperature T eff = 165 °C (T max = 300 °C), we achieved storage values of 6.19, 4.76, and 2.79 wt% for Mg nanotrees, nanoblades, and thin film, respectively.

08 HYDROGEN↗

DOE OSTI2023

Surface Functional Groups Affect Iron (Hydr)oxide Heterogeneous Nucleation: Implications for Membrane Scaling

Because of its favorable thermodynamics and fast kinetics, heterogeneous solid nucleation on membranes triggers early-stage mineral scaling. Iron (hydr)oxide, a typical membrane scale, initially forms as nanoparticles that interact with surface functional groups on membranes, but these nanoscale phenomena are difficult to observe in real time. In this study, we utilized in situ grazing incidence small angle X-ray scattering and ex situ atomic force microscopy to examine the heterogeneous nucleation of iron (hydr)oxide on surface functional groups commonly used in membranes, including hydroxyl (OH), carboxyl (COOH), and fluoro (F) groups. We found that, compared to nucleation on hydrophilic OH- and COOH-surfaces, the high hydrophobicity of an F-modified surface significantly reduced the extents of both heterogeneously and homogeneously formed iron (hydr)oxide nucleation. Moreover, on the OH-surface, the high functional group density of 0.76 nmol/cm 2 caused faster heterogeneous nucleation than that on a COOH-surface, with a density of 0.28 ± 0.04 nmol/cm 2 . The F-surface also had the highest heterogeneous nucleation energy barrier (26 ± 0.6 kJ/mol), followed by COOH- (23 ±0.8 kJ/mol) and OH- (20 ± 0.9 kJ/mol) surfaces. The kinetic and thermodynamic information provided here will help us better predict the rates and extents of early-stage scaling of iron (hydr)oxide nanoparticles in membrane processes. Finally, this work provides both kinetic and thermodynamic information about iron (hydr)oxide nucleation controlled by membrane-related functional groups (OH, COOH, and F).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

NASA NTRS1993

Multibeam Laser Altimeter for Planetary Topographic Mapping

Laser altimetry provides an active, high-resolution, high-accuracy method for measurement of planetary and asteroid surface topography. The basis of the measurement is the timing of the roundtrip propagation of short-duration pulses of laser radiation between a spacecraft and the surface. Vertical, or elevation, resolution of the altimetry measurement is determined primarily by laser pulse width, surface-induced spreading in time of the reflected pulse, and the timing precision of the altimeter electronics. With conventional gain-switched pulses from solid-state lasers and nanosecond resolution timing electronics, submeter vertical range resolution is possible anywhere from orbital altitudes of approximately 1 km to altitudes of several hundred kilometers. Horizontal resolution is a function of laser beam footprint size at the surface and the spacing between successive laser pulses. Laser divergence angle and altimeter platform height above the surface determine the laser footprint size at the surface, while laser pulse repetition rate, laser transmitter beam configuration, and altimeter platform velocity determine the spacing between successive laser pulses. Multiple laser transmitters in a single laser altimeter instrument that is orbiting above a planetary or asteroid surface could provide across-track as well as along-track coverage that can be used to construct a range image (i.e., topographic map) of the surface. We are developing a pushbroom laser altimeter instrument concept that utilizes a linear array of laser transmitters to provide contiguous across-track and along-track data. The laser technology is based on the emerging monolithic combination of individual, 1-sq cm diode-pumped Nd:YAG laser pulse emitters. Details of the multi-emitter laser transmitter technology, the instrument configuration, and performance calculations for a realistic Discovery-class mission will be presented.

Garvin, J. B.↗