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NASA NTRS1985

Circuit analysis method for thin-film solar cell modules

The design of a thin-film solar cell module is dependent on the probability of occurrence of pinhole shunt defects. Using known or assumed defect density data, dichotomous population statistics can be used to calculate the number of defects expected in a module. Probability theory is then used to assign the defective cells to individual strings in a selected series-parallel circuit design. Iterative numerical calculation is used to calcuate I-V curves using cell test values or assumed defective cell values as inputs. Good and shunted cell I-V curves are added to determine the module output power and I-V curve. Different levels of shunt resistance can be selected to model different defect levels.

Burger, D. R.↗

NASA NTRS1990

HR 1362 - A test case for stellar dynamo theories

An analysis of 11 yr of photometry of HR 1362 = EK Eri has shown a well-established photometric period of 335 days. This confirms an earlier period determination of about 310 days from 3 yr of APT data and is consistent with a new v sin i determination of 2 + or - 2 km/s. Recent Ca II H and K observations show moderately strong H and K emission lines at a flux level of log F prime (K) of about 6.5 ergs sq m/s. If the photometric period is interpreted as the rotation period, this surface flux is more than one order of magnitude larger than what can be expected from empirical activity versus rotation relationships. The spectrum and the U-B and B-V colors are consistent with a single G8 III-IV spectral classification, while the V-R and V-I values indicate a small color excess, typical of chromospherically active stars.

Strassmeier, Klaus G.↗

NASA NTRS1992

Stratospheric temperature increases due to Pinatubo aerosols

Northern-Hemisphere stratospheric temperatures at 30 and 50 mb beginning in June 1991 are compared with 20-year (1965-1984) and 26-year (1964-1989) monthly means. Significant temperature increases are shown in July, August, September, and October for latitudes from approximately 30 deg N to the equator. In September and October deviations are observed for large areas between the equator and 30 deg N, with temperature increases as high as + 3.5 C occurring at some locations. The monthly averaged zonal mean 30-mb temperatures at 20 deg N in September and October were approximately 2.5 C higher that the 26-year mean, with some daily zonal mean increases of almost 3 C. Higher values occurred equatorward of 20 deg N. These warmings are due to absorption of radiation by the aerosols produced from the June eruptions of the volcano Pinatubo (15.1 deg N, 120.4 deg E) in the Philippines. Stratospheric warmings are expected to be occurring simultaneously at southern latitudes, especially from the equator to about 20 deg S, based on satellite and lidar measurements of the locations of the new aerosol layers. These localized temperature increases should decrease in magnitude and become more global as the cloud disperses globally and spreads in altitude.

Labitzke, K.↗

NASA NTRS1931

A comparison of the aerodynamic characteristics of the normal and three reflexed airfoils in the variable density wind tunnel

An investigation was made of the aerodynamic effects of reflexing the trailing edge of three commonly used airfoils. Six airfoils were used in the investigation: three having the normal profiles of the Navy 60, the Boeing 106, and the Gottingen 398, and three having these profiles modified to obtain a reflexed trailing edge with the mean camber line changed to give Cmc/4=0. The tests were conducted at a value of the Reynolds Number of approximately 3,100,000 in the variable density wind tunnel of the National Advisory Committee for Aeronautics. Measurements of lift, drag, and pitching moment were made on each of the six airfoils. The expected reduction of the center of pressure travel was obtained. The maximum lift was reduced approximately 12 per cent and the minimum profile drag approximately 4 per cent.

Defoe, George L↗

NASA NTRS1994

Multi-application controls: Robust nonlinear multivariable aerospace controls applications

This viewgraph presentation describes the general methodology used to apply Honywell's Multi-Application Control (MACH) and the specific application to the F-18 High Angle-of-Attack Research Vehicle (HARV) including piloted simulation handling qualities evaluation. The general steps include insertion of modeling data for geometry and mass properties, aerodynamics, propulsion data and assumptions, requirements and specifications, e.g. definition of control variables, handling qualities, stability margins and statements for bandwidth, control power, priorities, position and rate limits. The specific steps include choice of independent variables for least squares fits to aerodynamic and propulsion data, modifications to the management of the controls with regard to integrator windup and actuation limiting and priorities, e.g. pitch priority over roll, and command limiting to prevent departures and/or undesirable inertial coupling or inability to recover to a stable trim condition. The HARV control problem is characterized by significant nonlinearities and multivariable interactions in the low speed, high angle-of-attack, high angular rate flight regime. Systematic approaches to the control of vehicle motions modeled with coupled nonlinear equations of motion have been developed. This paper will discuss the dynamic inversion approach which explicity accounts for nonlinearities in the control design. Multiple control effectors (including aerodynamic control surfaces and thrust vectoring control) and sensors are used to control the motions of the vehicles in several degrees-of-freedom. Several maneuvers will be used to illustrate performance of MACH in the high angle-of-attack flight regime. Analytical methods for assessing the robust performance of the multivariable control system in the presence of math modeling uncertainty, disturbances, and commands have reached a high level of maturity. The structured singular value (mu) frequency response methodology is presented as a method for analyzing robust performance and the mu-synthesis method will be presented as a method for synthesizing a robust control system. The paper concludes with the author's expectations regarding future applications of robust nonlinear multivariable controls.

Enns, Dale F.↗

NASA NTRS1993

One-milliarsecond precision parallax studies in the regions of Delta Cephei and EV Lacertae

Trigonometric parallaxes for stars in the regions of the variable stars delta Cephei and EV Lacertae are derived from data collected with the Multichannel Astrometric Photometer (MAP) and the Thaw Refractor of the University of Pittsburgh's Allegheny Observatory. The weighted mean parallax of all trigonometric studies of delta Cephei is now + 0.0030 sec + or - 0.00093 sec, corresponding to a distance modulus of 7.61 + or - 0.67 mag. This indicates that this luminosity standard star is approximately one standard deviation more distance than has been generally accepted. The weighted mean trigonometric parallax of all studies of the variable star EV Lacertae (BD + 43 deg 4305) is + 0.1993 sec + or - 0.00093 sec, implying a distance modulus of - 1.498 + or - 0.0010 mag. The calculated absolute magnitude of this star is almost exactly that predicted by its (R-I)(sub Kron) magnitude and by the Gliese (R-I) main-sequence value for stars in the solar neighborhood. We also find a parallax of 0.0189 sec + or - 0.0008 sec for the FO IVn star, HR 8666 (BD + 43 sec 4300). The derived luminosity of this star is midway between that expected for luminosity class IV and V stars at the indicated temperature.

Gatewood, George↗

NASA NTRS1994

Proximate nutritional composition of CELSS crops grown at different CO2 partial pressures

Two Controlled Ecological Life Support System (CELSS) candidate crops, soybean (Glycine max) and potato (Solanum tuberosum), were grown hydroponically in controlled environments maintained at carbon dioxide (CO2) partial pressures ranging from 0.05 to 1.00 kPa (500 to 10,000 ppm at 101 kPa atmospheric pressure). Plants were harvested at maturity (90 days for soybean and 105 days for potato) and all tissues analyzed for proximate nutritional composition (i.e. protein, fat, carbohydrate, crude fiber, and ash content). Soybean seed ash and crude fiber were higher and carbohydrate was lower than values reported for field-grown seed. Potato tubers showed little difference from field-grown tubers. Crude fiber of soybean stems and leaves increased with increased CO2, as did soybean leaf protein (total nitrogen). Potato leaf and stem (combined) protein levels also increased with increased CO2, while leaf and stem carbohydrates decreased. Values for leaf and stem protein and ash were higher than values generally reported for field-grown plants for both species. Results suggest that CO2 partial pressure should have little influence on proximate composition of potato tubers or soybean seed, but that high ash and protein levels might be expected from leaves and stems of crops grown in controlled environments of a CELSS.

Wheeler, R. M.↗

NASA NTRS1996

Results of a Parametric Study on 10,000 lb. and 50,000 lb. Permanent Magnetic Actuators

The purpose of this study was to generate design data and complete dynamic performance estimates for a high performance permanent magnet actuator. The basic configuration selected for analysis is an axisymmetric Nd-B-Fe permanent magnet actuator capable of providing force in one direction along its major axis. The actuator consisted of two main axisymmetric components separated by an air gap. The design was optimized for each value of force, gap and magnetic field to yield minimum weight and maximum lift to weight ratio. The basic conclusion is that, within parameters considered, the 10,000 lb. and 50,000 lb. actuators are lightweight and compact. As expected for most permanent magnet devices, the smaller ones have higher lift to eight ratios.

Stekly, Z. J. J.↗

NASA NTRS1999

Comparison of TRMM and Global Precipitation Climatology Project (GPCP) Precipitation Analyses

This paper describes recent results of using Tropical Rainfall Measuring Mission (TRMM) (launched in November 1997) information as the key calibration tool in a merged analysis on a 1 x 1' latitude/longitude monthly scale based on multiple satellite sources and raingauge analyses. The TRMM-based product is compared with the community-based Global Precipitation Climatology Project (GPCP) results. The long-term GPCP analysis is compared to the new TRMM-based analysis which uses the most accurate TRMM information to calibrate the estimates from the Special Sensor Microwave/Imager (SSM/I) and geosynchronous IR observations and merges those estimates together with the TRMM and gauge information to produce accurate rainfall estimates with the increased sampling provided by the combined satellite information. The comparison with TRMM results on a month-to-month basis should clarify the strengths and weaknesses of the long-term GPCP product in the tropics and point to how to improve the monitoring analysis. Preliminary results from the TRMM merged satellite analysis indicates fairly close agreement with the GPCP estimates. The GPCP analysis is done at 2.5 degree latitude/longitude resolution and interpolated to a 1 degree grid for comparison with the TRMM analysis. As expected the same features are evident in both panels, but there are subtle differences in the magnitudes. Focusing on the Pacific Ocean Inter-Tropical Convergence Zone (ITCZ) one can see the TRMM-based estimates having higher peak values and lower values in the ITCZ periphery. These attributes also show up in the statistics, where GPCP>TRMM at low values (below 10 mm/d) and TRMM>GPCP at high values (greater than 15 mm/d). The area in the Indian Ocean which shows consistently higher values of TRMM over GPCP needs to be examined carefully to determine if the lack of geosynchronous data has led to a difference in the two analyses. By the time of the meeting over a year of TRMM products will be available for comparison. Global tropical and regional values will be compared. Both products will be compared to TRMM validation site data over land and water. The results should begin to determine the use of the TRMM estimates in the evaluation of the GPCP analysis.

Adler, Robert F.↗

NASA NTRS2003

Performance Expectations of Closed-Brayton-Cycle Heat Exchangers in 100-kWe Nuclear Space Power Systems

Performance expectations of closed-Brayton-cycle heat exchangers to be used in 100-k We nuclear space power systems were forecast. Proposed cycle state points for a system supporting a mission to three of Jupiter's moons required effectiveness values for the heat-source exchanger, recuperator and rejection exchanger (gas cooler) of 0.98, 0.95, and 0.97, respectively. Performance parameters such as number of thermal units (Ntu), equivalent thermal conductance (UA), and entropy generation numbers (Ns) varied from 11 to 19, 23 to 39 kW/K, and 0.019 to 0.023 for some standard heat exchanger configurations. Pressure-loss contributions to entropy generation were significant; the largest frictional contribution was 114% of the heat transfer irreversibility. Using conventional recuperator designs, the 0.95 effectiveness proved difficult to achieve without exceeding other performance targets; a metallic, plate-fin counterflow solution called for 15% more mass and 33% higher pressure-loss than the target values. Two types of gas-coolers showed promise. Single-pass counterflow and multipass cross-counterflow arrangements both met the 0.97 effectiveness requirement. Potential reliability-related advantages of the cross-counterflow design were noted. Cycle modifications, enhanced heat transfer techniques and incorporation of advanced materials were suggested options to reduce system development risk. Carbon-carbon sheeting or foam proved an attractive option to improve overall performance.

Barrett, Michael J.↗

NASA NTRS2012

Redetermination of the Sm-Nd Age and Initial (Epsilon)Nd of Lunar Troctolite 76535: Implications for Lunar Crustal Development

Lunar troctolite 76535 is an old lunar rock predating the era of the lunar cataclysmic bombardment, but its radiometrially determined ages have been discordant [1-3]. The most recent multi-chronometer study [4] gave preferred ages of 4226+/-35 Ma and 4236+/-15 Ma from a Pb-207/Pb-206 isochron and an U-Pb upper concordia intercept, resp. We derive an age of 4323+/-64 Ma from Sm-Nd data reported by [4] for the bulk rock and three mineral separates. They derived an age of approx.4.38 Ga from combined Rb-Sr data [3,4] by omitting data for olivine separates. Ar-39-Ar-40 ages of approx.4.2 Ga are summarized by [5]. New Sm-147-Nd-143 data presented here give an age of 4335+/-71 Ma in agreement with the Sm-Nd age from [4], whereas Sm-146-Nd-142 data give a model age T(sub LEW) = 4439+/-22 Ma. Further, initial (Epsilon)Nd-143 for 76535 conforms to the Nd-143 evolution expected in an urKREEP [6] reservoir, consistent with inheritance of urKREEP Sm-Nd systematics via assimilation. We show that urKREEP Sm-Nd systematics require the lunar initial (Epsilon)Nd-143 to exceed the Chondritic Uniform Reservoir (CHUR) value [7], but are consistent with evolution from initial (Epsilon)Nd-143 like that of the HED meteorite parent body as defined by a 4557+/-20 Ma internal isochron for the cumulate eucrites Y-980433 and Y- 980318 [8].

Nyquist, Laurence E.↗

NASA NTRS2014

High Temperature Lightweight Self-Healing Ceramic Composites for Aircraft Engine Applications

The present research effort was undertaken to develop a new generation of SiC fiber- reinforced engineered matrix composites (EMCs) with sufficient high temperature plasticity to reduce crack propagation and self-healing capabilities to fill surface-connected cracks to prevent the oxygen ingress to the fibers. A matrix engineered with these capabilities is expected to increase the load bearing capabilities of SiCSiC CMCs at high temperatures. Several matrix compositions were designed to match the coefficient of thermal expansion (CTE) of the SiC fibers using a rule of mixture (ROM) approach. The CTE values of these matrices were determined and it was demonstrated that they were generally in good agreement with that of monolithic SiC between room temperature and 1525 K. The parameters to hot press the powders were optimized, and specimens were fabricated for determining bend strength, CTE, oxidation and microstructural characteristics of the engineered matrices. The oxidation tests revealed that some of the matrices exhibited catastrophic oxidation, and therefore, these were eliminated from further consideration. Two promising compositions were down selected based on these results for further development. Four-point bend tests were conducted on these two promising matrices between room temperature and 1698 K. Although theses matrices were brittle and failed at low stresses at room temperature, they exhibited high temperature ductility and higher stresses at the higher temperatures. The effects of different additives on the self-healing capabilities of these matrices were investigated. The results of preliminary studies conducted to slurry and melt infiltration trials with CrSi2 are described.

Silicides↗

NASA NTRS2013

Dynamic Acquisition and Retrieval Tool (DART) for Comet Sample Return : Session: 2.06.Robotic Mobility and Sample Acquisition Systems

The 2011 Decadal Survey for planetary science released by the National Research Council of the National Academies identified Comet Surface Sample Return (CSSR) as one of five high priority potential New Frontiers-class missions in the next decade. The main objectives of the research described in this publication are: develop a concept for an end-to-end system for collecting and storing a comet sample to be returned to Earth; design, fabricate and test a prototype Dynamic Acquisition and Retrieval Tool (DART) capable of collecting 500 cc sample in a canister and eject the canister with a predetermined speed; identify a set of simulants with physical properties at room temperature that suitably match the physical properties of the comet surface as it would be sampled. We propose the use of a dart that would be launched from the spacecraft to impact and penetrate the comet surface. After collecting the sample, the sample canister would be ejected at a speed greater than the comet's escape velocity and captured by the spacecraft, packaged into a return capsule and returned to Earth. The dart would be composed of an inner tube or sample canister, an outer tube, a decelerator, a means of capturing and retaining the sample, and a mechanism to eject the canister with the sample for later rendezvous with the spacecraft. One of the significant unknowns is the physical properties of the comet surface. Based on new findings from the recent Deep Impact comet encounter mission, we have limited our search of solutions for sampling materials to materials with 10 to 100 kPa shear strength in loose or consolidated form. As the possible range of values for the comet surface temperature is also significantly different than room temperature and testing at conditions other than the room temperature can become resource intensive, we sought sample simulants with physical properties at room temperature similar to the expected physical properties of the comet surface material. The chosen DART configuration, the efforts to identify a test simulant and the properties of these simulants, and the results of the preliminary testing will be described in this paper.

Dynamic Acquisition and Retrieval Tool (DART)↗

NASA NTRS2019

Near-infrared Spectroscopy of Galaxies During Reionization: Measuring C III] in a Galaxy at z = 7.5

We present Keck/MOSFIRE H-band spectroscopy targeting C III] λ1907, 1909 in a z = 7.5056 galaxy previously identified via Lyα emission. We detect strong line emission at 1.621 ± 0.002 mm with a line flux of (2.63 ± 0.52) × 10−18 erg s−1cm−2. We tentatively identify this line as [C III] λ1907, but we are unable to detect C III] λ1909 owing to sky emission at the expected location. This gives a galaxy systemic redshift, zsys = 7.5032 ± 0.0003, with a velocity offset to Lyα of DvLya = 88 ± 27 km s−1. The ratio of combined C III]/Lyα is 0.30–0.45, one of the highest values measured for any z > 2 galaxy. We do not detect Si III] λλ1883, 1892, and place an upper limit on Si III]/C III] < 0.35 (2σ). Comparing our results to photoionization models, the C III] equivalent width (WC III] = 16.23 ± 2.32 Å), low Si III]/C III] ratio, and high implied [O III] equivalent width (from the Spitzer/IRAC [3.6]–[4.5] ~- 0.8 mag color) require subsolar metallicities (Z ~- 0.1–0.2 Zsun) and a high ionization parameter, log U >~ 1.5. These results favor models that produce higher ionization, such as the BPASS models for the photospheres of high-mass stars, and that include both binary stellar populations and/or an IMF that extends to 300 Me. The combined C III] equivalent width and [3.6]–[4.5] color are more consistent with ionization from young stars than active galactic nuclei (AGNs); however, we cannot rule out ionization from a combination of an AGN and young stars. We make predictions for James Webb Space Telescope spectroscopy using these different models, which will ultimately test the nature of the ionizing radiation in this source.

reionization↗

NASA NTRS2021

LMI Automated Air Cargo Operations Market Research and Forecast

Air cargo companies and aircraft manufacturers are making significant investments to enable the movement of cargo via various levels of automated aircraft, such as aircraft with simplified operations requiring a pilot, remotely monitored or piloted aircraft, and fully autonomous aircraft. These investments will enable greater utilization of aircraft while unlocking new air markets traditionally served by ground transportation only. Many cargo companies and aerospace experts envision an operating environment where a single pilot can remotely pilot numerous aircraft for significant increases in aircraft utilization. The future operating environment is also expected to include air cargo companies flying smaller aircraft from airports and distribution centers outside of major U.S. cities directly to city centers, avoiding congested roads and increasing the velocity of cargo shipments, particularly those that are high-value, time-sensitive, and security sensitive (e.g., pharmaceuticals). These are just a few benefits and use cases cargo companies and aerospace experts see with the advancement of automated aircraft. To better understand industry’s direction, NASA asked the LMI team to research the forecasted market, timeline, risks, and opportunities for integrating unmanned air cargo vehicles into the National Airspace System (NAS) for the development and prioritization of the NASA Air Traffic Management Exploration’s research portfolio. To begin the market assessment, we gathered data via numerous interviews with key stakeholders and subject matter experts and literature reviews. We then incorporated the data into a custom-developed systems dynamics model and visualization dashboard. The systems dynamics model classifies the size of the market (e.g., overall fleet size of automated aircraft) for four distinct use cases over the next 20 years. The model projects the year in which various types of automated aircraft will enter the commercial cargo market based on our team’s collective research on when the aircraft will become viable due to manufacturing and certification timelines and the lifespan of current, traditional aircraft in service, to name a few factors. While this report defines our team’s estimated timeline of entry and growth, the model is dynamic—it enables NASA users to change variables based on future-year events. If the necessary technology does not mature in accordance with our assumptions, then NASA can change the entry of service point to a future year to evaluate the changes in market size in the out years. This flexibility will be key to deciding when and how NASA should invest in various areas.

air traffic management↗

NASA NTRS1971

Some implications of a new value for the primordial solar deuterium-hydrogen ratio.

Some astrophysical implications of a primordial solar D/H ratio of 0.000015 are investigated. Perhaps the most interesting aspects of the D/H ratio concern galactic evolution and cosmology. It is shown that the initial galactic abundance of deuterium exceeds by at least a factor of 30 the abundance expected from known galactic production mechanisms. If a Friedmann cosmology is a correct description of the universe, it must be an open one unless some as yet unknown mechanism is invo ked to produce deuterium and He-3.

Black, D. C.↗

NASA NTRS1984

Extreme incompatibility of Pb during the crystallization of magmatic iron meteorites

The partitioning behavior of Pb in the three-phase system metal-troilite-sulfide liquid was investigated. Microscopic examination and electron microprobe analysis of a polished section showed three phases--Fe metal, troilite and an Fe-S-Pb-O metallic liquid. The Pb concentration of the metallic liquid was 1.4 wt.%; the Pb contents of both the troilite and the Fe metal were below the detection limit of the electron probe. To better define the Pb concentrations of the solid phases, the same sample was analyzed for Pb and Fe using the M.I.T., Harvard and Brown ion microprobe. Even at this level of precision, some conclusions and speculations are possible: (1) The D(Pb) (troilite/metallic liquid) is low (.01 to .001) and, contrary to expectation, troilite, like metal, excludes Pb very effectively during the crystallization of metallic liquids; (2) Pb in iron meteorites is conceivably concentrated in trace phases which are less susceptible to contamination than metal and troilite; and (3) taken at face value D(Pb)(metal/troilite) is 0.1, but given the Pb and Fe ion yields from simple endmember phases (Fe, FeS, Pb, PbS), this D is more likely to be 0.05 to 0.03.

Jones, J. H.↗

NASA NTRS1986

Aerodynamic characteristics of two-dimensional wing configurations at angles of attack near -90 deg

Wind tunnel tests were conducted to determine the drag of two-dimensional wing sections operating in a near-vertical flow condition. Various leading- and trialing-edge configurations, including plain flaps of 25, 30, and 35% chord were tested at angles of attack from -75 to -105 deg. Reynolds numbers examined ranged from approximately 0.6 x 10 to the 6th power to 1.4 x 10 to the 6th power. The data were obtained using a wind tunnel force and moment balance system and arrays of chordwise pressure orifices. The results showed that significant reductions in drag, beyond what would be expected by virtue of the decreased frontal area, were obtainable with geometries that delayed flow separation. Rapid changes in drag with angle of attack were noted for many configurations. The results, however, were fairly insensitive to Reynolds number variations. Drag values computed from the pressure data generally agreed with the force data within 2%.

Maisel, Martin↗