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All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Selection process for trade study: Graphite Composite Primary Structure (GCPS)

This TA 2 document describes the selection process that will be used to identify the most suitable structural configuration for an SSTO winged vehicle capable of delivering 25,000 lbs to a 220 nm circular orbit at 51.6 degree inclination. The most suitable unpressurized graphite composite structures and material selections is within this configuration and will be the prototype design for subsequent design and analysis and the basis for the design and fabrication of payload bay, wing, and thrust structure full scale test articles representing segments of the prototype structures. The selection process for this TA 2 trade study is the same as that for the TA 1 trade study. As the trade study progresses additional insight may result in modifications to the selection criteria within this process. Such modifications will result in an update of this document as appropriate.

Greenberg, H. S.↗
NASA NTRS2003

X-ray single Photon Spectrometers

The research at Yale on superconducting tunnel junctions (STJs) focussed on x-ray detectors, using a 5.9 keV x-ray source. All the Yale tests were carried out at 0.21 K, in a two-stage helium 3 dewar. Careful attention was given to grounding and shielding. All current waveforms were digitially recorded and analyzed subsequently on computer. The imaging device geometry was studied. This allows imaging along the length of the tantalum (Ta) absorber, which is 600 nm thick to provide good x-ray absorption. The quasiparticles produced by single photon absorption rapidly cool to the Ta gap, E(sub g_Ta) = 1.4 meV, and then diffuse. They are trapped in the A1 traps at the two ends (E(sub g_A1) = 0.4 meV), to give two charges that tunnel out of the A1 traps, Q(sub 1) and Q(sub 2). The total charge is Q = Q(sub 1) + Q(sub 2). This lateral trapping is what allows imaging.

Prober, Daniel↗
NASA NTRS2003

Cautionary Notes on Cosmogenic W-182 and Other Nuclei in Lunar Samples

Leya et al. (2000) showed that neutron capture on Ta-181 results in a production rate of Ta-182 (decays with a half-life of 114 days to W-182) sufficiently high to cause significant shifts in W-182 abundances considering the neutron fluences due to the cosmic ray cascade that were known to occur near the lunar surface. Leya et al. concluded that this cosmogenic production of W-182 may explain the large positive epsilon(sub W-182) values that Lee et al. (1997) had reported in some lunar samples rather than being produced from decay of now extinct Hf-182 (bar tau = 13 x 10(exp 6) yr). If the large range in epsilon(sub W-182) of lunar samples (0 to +11 in whole rock samples) was due to decay of now extinct Hf-182, it would require a very early time of formation and differentiation of the lunar crust-mantle system (with high Hf/W ratios) during the earliest stages of Earth s accretion. This result was both surprising and difficult to understand. The ability to explain these results by a more plausible mechanism is therefore very attractive. In a recent report Lee et al. (2002) showed that there were excesses of W-182 and that epsilon(sub W-182) was correlated with the Ta/W ratios in the mineral phases of individual lunar rock samples. This is in accord with W-182 variations in lunar samples being produced by cosmic-ray induced neutron capture on Ta-182.

Yin, Qingzhu↗
NASA NTRS2001

Sensorimotor adaptations to microgravity in humans

Motor function is altered by microgravity, but little detail is available as to what these changes are and how changes in the individual components of the sensorimotor system affect the control of movement. Further, there is little information on whether the changes in motor performance reflect immediate or chronic adaptations to changing gravitational environments. To determine the effects of microgravity on the neural control properties of selected motor pools, four male astronauts from the NASA STS-78 mission performed motor tasks requiring the maintenance of either ankle dorsiflexor or plantarflexor torque. Torques of 10 or 50% of a maximal voluntary contraction (MVC) were requested of the subjects during 10 degrees peak-to-peak sinusoidal movements at 0.5 Hz. When 10% MVC of the plantarflexors was requested, the actual torques generated in-flight were similar to pre-flight values. Post-flight torques were higher than pre- and in-flight torques. The actual torques when 50% MVC was requested were higher in- and post-flight than pre-flight. Soleus (Sol) electromyographic (EMG) amplitudes during plantarflexion were higher in-flight than pre- or post-flight for both the 10 and 50% MVC tasks. No differences in medial gastrocnemius (MG) EMG amplitudes were observed for either the 10 or 50% MVC tasks. The EMG amplitudes of the tibialis anterior (TA), an antagonist to plantarflexion, were higher in- and post-flight than pre-flight for the 50% MVC task. During the dorsiflexion tasks, the torques generated in both the 10 and 50% MVC tasks did not differ pre-, in- and post-flight. TA EMG amplitudes were significantly higher in- than pre-flight for both the 10 or 50% MVC tasks, and remained elevated post-flight for the 50% MVC test. Both the Sol and MG EMG amplitudes were significantly higher in-flight than either pre- or post-flight for both the 10 and 50% MVC tests. These data suggest that the most consistent response to space flight was an elevation in the level of contractions of agonists and antagonists when attempting to maintain constant torques at a given level of MVC. Also, the chronic levels of EMG activity in selected ankle flexor and extensor muscles during space flight and during routine activities on Earth were recorded. Compared with pre- and post-flight values, there was a marked increase in the total EMG activity of the TA and the Sol and no change in the MG EMG activity in-flight. These data indicate that space flight, as occurs on shuttle missions, is a model of elevated activation of both flexor and extensor muscles, probably reflecting the effects of programmed work schedules in flight rather than a direct effect of microgravity.

NASA Experiment Number 284036↗
NASA NTRS2005

RADAR Reveals Titan Topography

The Cassini Titan RADAR Mapper is a K(sub u)-band (13.78 GHz, lambda = 2.17 cm) linear polarized RADAR instrument capable of operating in synthetic aperture (SAR), scatterometer, altimeter and radiometer modes. During the first targeted flyby of Titan on 26 October, 2004 (referred to as Ta) observations were made in all modes. Evidence for topographic relief based on the Ta altimetry and SAR data are presented here. Additional SAR and altimetry observations are planned for the T3 encounter on 15 February, 2005, but have not been carried out at this writing. Results from the T3 encounter relevant to topography will be included in our presentation. Data obtained in the Ta encounter include a SAR image swath

Kirk, R. L.↗
NASA NTRS2001

Reducing software security risk through an integrated approach

The fourth quarter delivery, FY'01 for this RTOP is a Property-Based Testing (PBT), 'Tester's Assistant' (TA). The TA tool is to be used to check compiled and pre-compiled code for potential security weaknesses that could be exploited by hackers. The TA Instrumenter, implemented mostly in C++ (with a small part in Java), parsels two types of files: Java and TASPEC. Security properties to be checked are written in TASPEC. The Instrumenter is used in conjunction with the Tester's Assistant Specification (TASpec)execution monitor to verify the security properties of a given program.

software security↗
NASA NTRS2008

Oxidation of ZrB2 SiC TaSi2 Materials at Ultra High Temperatures

ZrB2 - 20v% SiC - 20v% TaSi2 was oxidized in stagnant air for ten minute cycles for times up to 100 minutes at 1627 C and 1927 C. The sample oxidized at 1627 C showed oxidation resistance better than that of the standard ZrB2 - 20v% SiC. The sample oxidized at 1927 C, however, showed evidence of liquid phase formation and complex oxidation products. The sample exposed at 1927 C was analyzed in detail by scanning electron microprobe and wavelength dispersive spectroscopy to understand the complex oxidation and melting reactions occurring during exposure. The as hot-pressed material shows the formation of a Zr(Ta)B2 phase in addition to the three phases in the nominal composition already noted. After oxidation, the TaSi2 in the matrix was completely reacted to form Ta(Zr)C. The layered oxidation products included SiO2, ZrO2, Ta2O5, and a complex oxide containing both Zr and Ta. Likely reactions are proposed based on thermodynamic phase stability and phase morphology.

Opila, E.↗
NASA NTRS2009

Effects of Tantalum on the Temporal Evolution of a Model Ni-Al-Cr Superalloy During Phase Decomposition

The effects of a 2.0 at.% addition of Ta to a model Ni-10.0Al-8.5Cr (at.%) superalloy aged at 1073 K are assessed using scanning electron microscopy and atom-probe tomography. The gamma'(Ll2)-precipitate morphology that develops as a result of gamma-(fcc)matrix phase decomposition is found to evolve from a bimodal distribution of spheroidal precipitates, to {001}-faceted cuboids and parallelepipeds aligned along the elastically soft {001}-type directions. The phase compositions and the widths of the gamma'-precipitate/gamma-matrix heterophase interfaces evolve temporally as the Ni-Al-Cr-Ta alloy undergoes quasi-stationary state coarsening after 1 h of aging. Tantalum is observed to partition preferentially to the gamma'-precipitate phase, and suppresses the mobility of Ni in the gamma-matrix sufficiently to cause an accumulation of Ni on the gamma-matrix side of the gamma'/gamma interface. Additionally, computational modeling, employing Thermo-Calc, Dictra and PrecipiCalc, is employed to elucidate the kinetic pathways that lead to phase decomposition in this concentrated Ni-Al-Cr-Ta alloy.

Booth, Morrison, Christopher↗
NASA NTRS2003

The Micro-Arcsecond Metrology Testbed

The Micro-Arcsecond Metrology (MAM) testbed is a ground-based system of optical and electronic equipment for testing components, systems, and engineering concepts for the Space Interferometer Mission (SIM) and similar future missions, in which optical interferometers will be operated in outer space. In addition, the MAM testbed is of interest in its own right as a highly precise metrological system. The designs of the SIM interferometer and the MAM testbed reflect a requirement to measure both the position of the starlight central fringe and the change in the internal optical path of the interferometer with sufficient spatial resolution to generate astrometric data with angular resolution at the microarcsecond level. The internal path is to be measured by use of a small metrological laser beam of 1,319-nm wavelength, whereas the position of the starlight fringe is to be estimated by use of a charge-coupled-device (CCD) image detector sampling a large concentric annular beam. For the SIM to succeed, the optical path length determined from the interferometer fringes must be tracked by the metrological subsystem to within tens of picometers, through all operational motions of an interferometer delay line and siderostats. The purpose of the experiments performed on the MAM testbed is to demonstrate this agreement in a large-scale simulation that includes a substantial portion of the system in the planned configuration for operation in outer space. A major challenge in this endeavor is to align the metrological beam with the starlight beam in order to maintain consistency between the metrological and starlight subsystems at the system level. The MAM testbed includes an optical interferometer with a white light source, all major optical components of a stellar interferometer, and heterodyne metrological sensors. The aforementioned subsystems are installed in a large vacuum chamber in order to suppress atmospheric and thermal disturbances. The MAM is divided into two distinct subsystems: the test article (TA), which is the interferometer proper, and the inverse interferometer pseudo-star (IIPS), which synthesizes the light coming from a distant target star by providing spatially coherent wavefronts out of two mirrors, separated by the MAM baseline, that feed directly into two siderostats that are parts of the TA. The two feed mirrors of the IIPS are articulated (in translation and tilt) in order to simulate stars located at different orientations in space, while still illuminating the TA siderostats. The spectrum of the simulated starlight of the IIPS corresponds to that of a blackbody at a temperature of about 3,100 K.

Goullioud, Renaud↗
NASA NTRS2012

The Aquarius Salinity Retrieval Algorithm

The first part of this presentation gives an overview over the Aquarius salinity retrieval algorithm. The instrument calibration [2] converts Aquarius radiometer counts into antenna temperatures (TA). The salinity retrieval algorithm converts those TA into brightness temperatures (TB) at a flat ocean surface. As a first step, contributions arising from the intrusion of solar, lunar and galactic radiation are subtracted. The antenna pattern correction (APC) removes the effects of cross-polarization contamination and spillover. The Aquarius radiometer measures the 3rd Stokes parameter in addition to vertical (v) and horizontal (h) polarizations, which allows for an easy removal of ionospheric Faraday rotation. The atmospheric absorption at L-band is almost entirely due to molecular oxygen, which can be calculated based on auxiliary input fields from numerical weather prediction models and then successively removed from the TB. The final step in the TA to TB conversion is the correction for the roughness of the sea surface due to wind, which is addressed in more detail in section 3. The TB of the flat ocean surface can now be matched to a salinity value using a surface emission model that is based on a model for the dielectric constant of sea water [3], [4] and an auxiliary field for the sea surface temperature. In the current processing only v-pol TB are used for this last step.

Meissner, Thomas↗
NASA NTRS2012

MSFC's Advanced Space Propulsion Formulation Task

In NASA s Fiscal Year 2012, a small project was undertaken to provide additional substance, depth, and activity knowledge to the technology areas identified in the In-Space Propulsion Systems Roadmap, Technology Area 02 (TA-02), as created under the auspices of the NASA Office of the Chief Technologist (OCT). This roadmap was divided into four basic groups: (1) Chemical Propulsion, (2) Non-chemical Propulsion, (3) Advanced (TRL<3) Propulsion Technologies, and (4) Supporting Technologies. The first two were grouped according to the governing physics. The third group captured technologies and physic concepts that are at a lower TRL level. The fourth group identified pertinent technical areas that are strongly coupled with these related areas which could allow significant improvements in performance. There were a total of 45 technologies identified in TA-02, and 25 of these were studied in this formulation task. The goal of this task was to provide OCT with a knowledge-base for decisionmaking on advanced space propulsion technologies and not waste money by unintentionally repeating past projects or funding the technologies with minor impacts. This formulation task developed the next level of detail for technologies described and provides context to OCT where investments should be made. The presentation will begin with the list of technologies from TA-02, how they were prioritized for this study, and details on what additional data was captured for the technologies studied. Following this, some samples of the documentation will be provided, followed by plans on how the data will be made accessible.

Huebner, Lawrence D.↗
NASA NTRS2014

Green Propulsion Auxiliary Power Unit Demonstration at MSFC

In 2012, the National Aeronautics & Space Administration (NASA) Space Technology Mission Directorate (STMD) began the process of building an integrated technology roadmap, including both technology pull and technology push strategies. Technology Area 1 (TA-01) for Launch Propulsion Systems is one of fourteen TA's that provide recommendations for the overall technology investment strategy and prioritization of NASA's space technology activities. Identified within TA-01 was the need for a green propulsion auxiliary power unit (APU) for hydraulic power by 2015. Engineers led by the author at the Marshall Space Flight Center (MSFC) have been evaluating green propellant alternatives and have begun the development of an APU testbed to demonstrate the feasibility of use. NASA has residual APU assets remaining from the retired Space Shuttle Program. Likewise, the F-16 Falcon fighter jet also uses an Emergency Power Unit (EPU) that has similar characteristics to the NASA hardware. Both EPU's and APU components have been acquired for testing at MSFC. In concert with this effort, ATK has been developing green propellant technology based on the Swedish Space Corp ECAPS LMP-103S propellant. Propellant blending and test facilities have been established at ATK's Elkton MD facility with the intent to provide suitable propellant blends for application to green APU systems as well as thrusters. This paper will summarize the status of the testing efforts with ATK for use of the green propellant LMP-103S based on ammonium dinitramide and use of the Air Force Research Laboratory (AFRL) propellant AF-M315E based on hydroxyl ammonium nitrate with these test assets.

Robinson, Joel W.↗
NASA NTRS2014

Green Mono Propulsion Activities at MSFC

In 2012, the National Aeronautics & Space Administration (NASA) Space Technology Mission Directorate (STMD) began the process of building an integrated technology roadmap, including both technology pull and technology push strategies. Technology Area 1 (TA-01) for Launch Propulsion Systems and TA-02 In-Space Propulsion are two of the fourteen TA's that provide recommendations for the overall technology investment strategy and prioritization of NASA's space technology activities. Identified within these documents are future needs of green propellant use. Green ionic liquid monopropellants and propulsion systems are beginning to be demonstrated in space flight environments. Starting in 2010 with the flight of PRISMA, a one Newton thruster system began on-orbit demonstrations operating on ammonium dinitramide based propellant. The NASA Green Propellant Infusion Mission (GPIM) plans to demonstrate both 1 N, and 22 N hydroxyl ammonium nitrate based thrusters in a 2015 flight demonstration. In addition, engineers at MSFC have been evaluating green propellant alternatives for both thrusters and auxiliary power units. This paper summarizes the status of these development/demonstration activities and investigates the potential for evolution of green propellants from small spacecraft and satellites to larger spacecraft systems, human exploration, and launch system auxiliary propulsion applications.

Robinson, Joel W.↗
NASA NTRS2020

Attribution of Chemistry-Climate Model Initiative (CCMI) Ozone Radiative Flux Bias from Satellites

The top-of-atmosphere (TOA) outgoing longwave flux over the 9.6-μm ozone band is a fundamental quantity for understanding chemistry-climate coupling. However, observed TOA fluxes are hard to estimate as they exhibit considerable variability in space and time that depend on the distributions of clouds, ozone (O3), water vapor (H2O), air temperature (Ta), and surface temperature (Ts). Benchmarking present day fluxes and quantifying the relative influence of their drivers is the first step for estimating climate feedbacks from ozone radiative forcing and predicting radiative forcing evolution. To that end, we constructed observational instantaneous radiative kernels (IRKs) under clear-sky conditions, representing the sensitivities of the TOA flux in the 9.6-μm ozone band to the vertical distribution of geophysical variables, including O3, H2O, Ta, and Ts based upon the Aura Tropospheric Emission Spectrometer (TES) measurements. Applying these kernels to present-day simulations from the Chemistry-Climate Model Initiative (CCMI) project as compared to a 2006 reanalysis assimilating satellite observations, we show that the models have large differences in TOA flux, attributable to different geophysical variables. In particular, model simulations continue to diverge from observations in the tropics, as reported in previous studies of the Atmospheric Chemistry Climate Model Inter-comparison Project (ACCMIP) simulations. The principal culprits are tropical mid and upper tropospheric ozone followed by tropical lower tropospheric H2O. Five models out of the eight studied here have TOA flux biases exceeding 100 mWm-2 attributable to tropospheric ozone bias. Another set of five models have flux biases over 50 mWm-2 due to H2O. On the other hand, Ta radiative bias is negligible in all models (no more than 30 mWm-2). We found that AM3 and CMAM have the lowest TOA flux biases globally but are a result of cancellation of opposite biases due to difference processes. Overall, the multi-model ensemble mean bias is –133±98 mWm-2, indicating that they are too atmospherically opaque due to trapping too much radiation in the atmosphere by overestimated tropical tropospheric O3 and H2O. Having too much O3 and H2O in the troposphere would have different impacts on the sensitivity of TOA flux to O3 and these competing effects add more uncertainties on the ozone radiative forcing. We find that the inter-model TOA outgoing longwave radiation (OLR) difference is well anti-correlated with their ozone band flux bias. This suggests that there is significant radiative compensation in the calculation of model outgoing longwave radiation.

Aura Tropospheric Emission Spectrometer (TES) meas↗
NASA NTRS1965

Development of high temperature nickel-base alloys for jet engine turbine bucket applications

A program has been initiated to develop a material with superior properties at elevated temperatures for utilization in turbine blade applications. A nickel-base superalloy can provide the necessary high temperature strength by using the maximum capability of the three available strengthening mechanisms - intermetallic gamma prime precipitation (Ni3Al), solid solution strengthening with refractory and precious metals, and stable carbide formations through the addition of strong carbide forming elements. A stress rupture test at 2000 deg F and 15,000 psi was formulated to approximate the desired properties. By adding varying amounts of refractory metals (Mo, W and Ta) it was possible to statistically analyze the effects of each in a basic superalloy composition containing fixed amounts of Co, Cr, C, B, Sr, and Ni at three separate levels of AL and Ta. Metallographic analysis correlated with the mechanical properties of the alloys; those with few strengthening phases were weak and ductile and those with excessive amounts of intermetallic phases present in undesirable morphologies were brittle.

SUPERALLOY↗
NASA NTRS1971

Experimental physics characteristics of a heavy-metal-reflected fast-spectrum critical assembly

A zero-power critical assembly was designed, constructed, and operated for the purpose of conducting a series of benchmark experiments dealing with the physics characteristics of a UN-fueled, Li-7 cooled, Mo-reflected, drum-controlled compact fast reactor for use with a space-power electric conversion system. The experimental program consisted basically of measuring the differential neutron spectra and the changes in critical mass that accompanied the stepwise addition of (Li-7)3N, Hf, Ta, and W to a basic core fueled with U metal in a pin-type Ta honeycomb structure. In addition, experimental results were obtained on power distributions, control characteristics, neutron lifetime, and reactivity worths of numerous absorber, structural, and scattering materials.

Heneveld, W. H.↗
NASA NTRS1972

Experimental physics characteristics of a heavy-metal-reflected fast-spectrum critical assembly

A zero-power critical assembly was designed, constructed, and operated for the purpose of conducting a series of benchmark experiments dealing with the physics characteristics of a UN-fueled, Li-cooled, Mo-reflected, drum-controlled compact fast reactor for use with a space-power electric conversion system. The range of the previous experimental investigations has been expanded to include the reactivity effects of:(1) surrounding the reactor with 15.24 cm (6 in.) of polyethylene, (2) reducing the heights of a portion of the upper and lower axial reflectors by factors of 2 and 4, (3) adding 45 kg of W to the core uniformly in two steps, (4) adding 9.54 kg of Ta to the core uniformly, and (5) inserting 2.3 kg of polyethylene into the core proper and determining the effect of a Ta addition on the polyethylene worth.

Heneveld, W. H.↗