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NASA NTRS1992

LDEF microenvironments, observed and predicted

Complex protrusions and surface indentations on spacecraft equipment alter exposure environments by casting shadows, producing reflections and scattering incident atomic oxygen flux and UV radiation. A computer model is being developed to predict these effects. The model accounts for any arbitrary shape, size, orientation, or curvature of exposed objects. LDEF offers a unique opportunity to compare model prediction with observations. For this purpose, a study is underway on twelve of LDEF's copper grounding straps. These straps were exposed at various angles from the ram vector during the LDEF flight. Microenvironment variables include shadowing and reflections from clamps and fasteners, and varying exposure caused by bending of the straps. Strap measurements include optical properties, surface film composition by ESCA, and film thickness measurements by optical interference techniques. The features of the microenvironment model and the analytical methods used to examine the straps are discussed. Data are presented showing predicted microenvironmental variations. These variations are compared with observed point to point differences in surface properties of the straps.

Bourassa, R. J.↗

NASA NTRS1992

Global Backscatter Experiment (GLOBE) Results: Aerosol Backscatter Global Distribution and Wavelength Dependence

The GLObal Backscatter Experiment (GLOBE) was initiated by NASA in 1986 as an interagency and international research effort to characterize tropospheric backscatter properties. The primary objective of the program is to develop realistic aerosol backscatter inputs for design and simulation studies for NASA's prospective Laser Atmospheric Wind Sounder (LAWS). To achieve this, GLOBE incorporates several different types of aerosol sensors, which operate from a variety of sensor platforms, covering a wide range of spatial and temporal scales, and measure a diverse set of aerosol physical, chemical, and optical properties. The results of this analysis have provided important new information on the life cycles and physicochemical properties of global scale tropospheric aerosol systems. In addition, GLOBE analytical methods will be useful for the Earth Observing System (EOS) and other studies that involve the assimilation of large, complex atmospheric aerosol databases.

Bowdle, David A.↗

NASA NTRS1992

Nonlinear analyses of composite aerospace structures in sonic fatigue

The primary research effort of this project is the development of analytical methods for the prediction of nonlinear random response of composite aerospace structures subjected to combined acoustic and thermal loads. The progress, accomplishments, and future plans of three random response research topics are discussed, namely acoustics-structure interactions using boundary/finite element methods, nonlinear vibrations of beams and composite plates under harmonic and random excitations, and numerical simulation of the nonlinear response of composite plates under combined thermal and acoustic loading.

Mei, Chuh↗

NASA NTRS1990

Soil surface CO2 fluxes on the Konza Prairie

The utilization of a soil chamber to measure fluxes of soil-surface CO2 fluxes is described in terms of equipment, analytical methods, and estimate quality. A soil chamber attached to a gas-exchange system measures the fluxes every 5-15 min, and the data are compared to measurements of the CO2 fluxes from the canopy and from the soil + canopy. The soil chamber yields good measurements when operated in a closed system that is ported to the free atmosphere, and the CO2 flux is found to have a diurnal component.

Norman, J. M.↗

NASA NTRS1991

Results from a test of a 2/3-scale V-22 rotor and wing in the 40- by 80-Foot Wind Tunnel

A test of a 0.658-scale V-22 rotor and wing was conducted in the 40- by 80-Foot Wind Tunnel at Ames Research Center. The principal objectives of the test were to measure the wing download in hover for a variety of test configurations, and rotor performance in forward flight. Also, a limited amount of data on rotor performance in vertical climb were acquired. This paper presents the results from the test with predictions from appropriate analytical methods. A new method for presenting and interpreting wing surface pressure data in hover is described, and this method shows that the wing flap can produce substantial lift loads in hover. The rotor performance in vertical climb was underpredicted by CAMRAD/JA and by the free wake analysis EHPIC. A simple momentum theory is presented which provides good predictions of rotor performance in forward flight.

Felker, Fort F.↗

NASA NTRS1991

Ongoing development of a computer jobstream to predict helicopter main rotor performance in icing conditions

Work is currently underway at the NASA Lewis Research Center to develop an analytical method for predicting the performance degradation of a helicopter operating in icing conditions. A brief survey is performed of possibilities available to perform such a calculation along with the reasons for choosing the present approach. A complete description of the proposed jobstream is given as well as a discussion of the present state of the development.

Britton, Randall K.↗

NASA NTRS1990

Statistical interference prediction for ground stations from orbiting satellites. I - Simulation of interference duration and analytical approach for the determination of protection ratios

The authors describe simulation and analytical techniques for predicting the interference durations and protection ratios for deep-space ground stations from satellites in circular orbits. The simulation approach employs the characteristics of the ground station receivers in addition to the satellite specifications to calculate the daily statistics of the interference duration. On the other hand, the analytical method employs the ground station specifications to statistically predict the protection ratios as a function of the number of interference satellites and their associated probabilities. The results presented here can be used for both planning the missions and designing satellite communication links. The results can be also be used by spectrum managers and operations personnel to minimize the risk of harmful interference from satellites in low earth orbit to the deep space frequency band.

Gevargiz, John M.↗

NASA NTRS1991

Micromechanical analysis of the failure process in ceramic matrix composites

An analysis of the effectiveness of fiber reinforcement in brittle matrix composites is presented. The analytical method allows consideration of discrete fiber distribution and examination of the development of crack growth parameters on the microscale. The problem associated with bridging zone development is addressed here; therefore, the bridging zone is considered to be smaller than the main preexisting crack, and the small scale approach is used. The mechanics of the reinforcement is accurately accounted for in the process zone of a growing crack. Closed form solutions characterizing the initial failure process are presented for linear and nonlinear force-fiber pullout displacement relationships. The implicit exact solution for the extended bridging zone is presented as well.

Rubinstein, Asher A.↗

NASA NTRS1990

X-29 high angle of attack

Flight test program highlights are discussed for the X-29 high angle-of-attack (AOA) aircraft. The AOA envelope extended from 10 to 66 deg; the X-29 exhibited precise pitch control, allowing AOA to be maintained within 1 deg during stabilized points as well as permitting rapid recoveries from all AOAs. Attention is given to controllability degradation above 40-deg AOA due to asymmetric yawing moments. The use of this aircraft as a fundamental research tool which complements analytical methods is powerfully justified by the obviation of scaling effects.

Ishmael, Stephen D.↗

NASA NTRS1992

Fracture mechanics expert system

Attention is given to fracture mechanics, an analytical method used extensively in the National Space Transportation System to conservatively predict the remaining service life of an article when a flaw or a material defect is detected. These analyses are performed on hardware containing material defects that have been detected by various nondestructive inspection techniques. An expert system being developed to streamline the process so that hardware dispositions may be obtained in a timely and consistent manner is discussed. The expert system reduces the potential for errors due to the manual transcription between the various software programs involved in completing a fracture mechanics analysis. NEXPERT Object, the expert system development shell selected for this purpose, allows the various software programs used in fracture mechanics analyses to be accessed and manipulated from the same platform.

Powers, E.↗

NASA NTRS1992

Impact damage and residual tension strength of a thick graphite/epoxy rocket motor case

Impacters of various masses were dropped from various heights onto thick graphite/epoxy filament-wound cylinders. The cylinders represented filament-wound cases made for the booster motors of the Space Shuttle. Tups of various shapes were affixed to the impacters. Some of the cylinders were filled with inert propellant, and some were empty. The cylinders were impacted numerous times around the circumference and then cut into tension coupons, each containing an impact site. The size of the damage and the residual tension strength were measured. For hemispherical tups, strength was reduced as much as 30 percent by nonvisible damage. The damage consisted of matrix cracking and broken fibers. Analytical methods were used to predict the damage and residual tension strength. A factor of safety to account for nonvisible damage was determined. For corner and rod shaped tups, any damage that resulted in strength loss was readily visible.

Poe, C. C., Jr.↗

NASA NTRS1992

Reflectivity (visible and near IR), Moessbauer, static magnetic, and X ray diffraction properties of aluminum-substituted hematites

The effect of substituting iron by aluminum in polymorphs of Fe2O3 and FeOOH on their reflectivity characteristics was investigated by comparing data on visible and NIR reflectivities and on static magnetic, XRD, and Moessbauer properties for a family of aluminum-substituted hematites alpha-(Fe,Al)2O3, with compositions where the values of the Al/(Al+Fe) ratio were up to 0.61. Samples were prepared by oxidation of magnetite, dehydroxylation of goethite, and direct precipitation. The analytical methods used for obtaining diffuse reflectivity spectra (350-2200 nm), Moessbauer spectra, and static magnetic data are those described by Morris et al. (1989).

Morris, Richard V.↗

NASA NTRS1987

Low speed aerodynamics CFD code validation

The objective of the research project is to develop and validate analytical methods for low-speed aerodynamics. The experimental needs for computational methods are presented. All data and results are presented in viewgraph format.

South, Jerry C.↗

NASA NTRS1992

Uncertainty management by relaxation of conflicting constraints in production process scheduling

Mathematical-analytical methods as used in Operations Research approaches are often insufficient for scheduling problems. This is due to three reasons: the combinatorial complexity of the search space, conflicting objectives for production optimization, and the uncertainty in the production process. Knowledge-based techniques, especially approximate reasoning and constraint relaxation, are promising ways to overcome these problems. A case study from an industrial CIM environment, namely high-grade steel production, is presented to demonstrate how knowledge-based scheduling with the desired capabilities could work. By using fuzzy set theory, the applied knowledge representation technique covers the uncertainty inherent in the problem domain. Based on this knowledge representation, a classification of jobs according to their importance is defined which is then used for the straightforward generation of a schedule. A control strategy which comprises organizational, spatial, temporal, and chemical constraints is introduced. The strategy supports the dynamic relaxation of conflicting constraints in order to improve tentative schedules.

Dorn, Juergen↗

NASA NTRS1991

Real-time simulations for automated rendezvous and capture

Although the individual technologies for automated rendezvous and capture (AR&C) exist, they have not yet been integrated to produce a working system in the United States. Thus, real-time integrated systems simulations are critical to the development and pre-flight demonstration of an AR&C capability. Real-time simulations require a level of development more typical of a flight system compared to purely analytical methods, thus providing confidence in derived design concepts. This presentation will describe Martin Marietta's Space Operations Simulation (SOS) Laboratory, a state-of-the-art real-time simulation facility for AR&C, along with an implementation for the Satellite Servicer System (SSS) Program.

Cuseo, John A.↗

NASA NTRS1993

Measuring the metastatic potential of cancer cells

Cancer cells must secrete proteolytic enzymes to invade adjacent tissues and migrate to a new metastatic site. Urokinase (uPA) is a key enzyme related to metastasis in cancers of the lung, colon, gastric, uterine, breast, brain, and malignant melanoma. A NASA technology utilization project has combined fluorescence microscopy, image analysis, and flow cytometry, using fluorescent dyes, and urokinase-specific antibodies to measure uPA and abnormal DNA levels (related to cancer cell proliferation) inside the cancer cells. The project is focused on developing quantitative measurements to determine if a patient's tumor cells are actively metastasizing. If a significant number of tumor cells contain large amounts of uPA (esp. membrane-bound) then the post-surgical chemotherapy or radiotherapy can be targeted for metastatic cells that have already left the primary tumor. These analytical methods have been applied to a retrospective study of biopsy tissues from 150 node negative, stage 1 breast cancer patients. Cytopathology and image analysis has shown that uPA is present in high levels in many breast cancer cells, but not found in normal breast. Significant amounts of uPA also have been measured in glioma cell lines cultured from brain tumors. Commercial applications include new diagnostic tests for metastatic cells, in different cancers, which are being developed with a company that provides a medical testing service using flow cytometry for DNA analysis and hormone receptors on tumor cells from patient biopsies. This research also may provide the basis for developing a new 'magic bullet' treatment against metastasis using chemotherapeutic drugs or radioisotopes attached to urokinase-specific monoclonal antibodies that will only bind to metastatic cells.

Morrison, Dennis R.↗

NASA NTRS1990

Communications and tracking technology discipline

Viewgraphs on communications and tracking technology discipline for Space Station Freedom are presented. The objective is to develop devices, components, and analytical methods to enhance and enable technology to meet space station evolutionary requirements for multiple access (proximity) communications, space-to-ground communications, and tracking as it pertains to rendezvous and docking as well as potential orbital debris warning systems. Topics covered include: optical communications and tracking; monolithic microwave integrated circuit systems; traveling wave tube technology; advanced modulation and coding; and advanced automation.

Romanofsky, Robert↗

NASA NTRS1993

Nonlinear analyses of composite aerospace structures in sonic fatigue

This report summarizes the semiannual research progress, accomplishments, and future plans performed under the NASA Langley Research Center Grant No. NAG-1-1358. The primary research effort of this project is the development of analytical methods for the prediction of nonlinear random response of composite aerospace structures subjected to combined acoustic and thermal loads. The progress, accomplishments, and future plates on four sonic fatigue research topics are described. The sonic fatigue design and passive control of random response of shape memory alloy hybrid composites presented in section 4, which is suited especially for HSCT, is a new initiative.

Mei, Chuh↗