SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Analysis of bright features in 3840 A and H-alpha shows that for every Ellerman bomb there is a cospatial brightening in the 3840 A network. We give properties of these bright points in both wavelengths as well as describe: (1) the appearance, and subsequent separation, of new elements in the 3840 A network and (2) the direct transition from a 3840 A bright point to a new sunspot.
Using both analytical and Monte Carlo techniques, beam-pointing errors of planar-phased arrays are analyzed. The obtained simple formulas for rms pointing errors are applicable to uniform planar arrays with both uniform and Gaussian uncorrelated phase-error distributions and for any arbitrary scan angle.
The purpose of the Large Space Telescope (LST) program is to place a three-meter diffraction limited telescope in a 270-nautical mile orbit in order to perform astronomical observations that are not presently possible with earth bound telescopes due to atmospheric obscuration. In order to determine whether the stringent pointing requirements could be met, a complex simulation model was defined which consisted of detailed dynamic representations of control moment gyros (CMGs) and reaction wheels including their noise characteristics, dynamic sensor representations with sensor noise, shock mounts for the CMG actuators, and a detailed flexible body structural model with all significant vehicle and solar panel bending modes. On the basis of both stability and performance studies utilizing this model, it was determined that a body pointing system will meet LST requirements.
Measurements are given of the control points on the Mariner 9 pictures which were used in the computation of the June 1973 control net of Mars. The method of making the measurements is discussed along with the picture coordinate system and the removal of distortions. Table are presented of the 9804 measurements of 1645 points on 660 pictures.
A multi-point release mechanism used on the communications technology satellite. The mechanism is designed to jettison one large panel and to release a second panel; both panels have independent multi-point attachments to the spacecraft and require to be released in sequence. The solar array is stowed concertina fashion under 2 psi pressure to ensure that no movement occurs between the stowed folds of the array during the launch. One pair of linear pyrotechnic-actuators releases both the JBSA and the pressure plate via the release mechanism. This release mechanism has successfully passed qualification level vibration launch and thermal environment tests and has accumulated to date close to 30 successful releases.
The use of a digital computer program (MATCH) for automated determination of the flutter velocity and the matched-point flutter density is described. The program is based on the use of the modified Laguerre iteration formula to converge to a flutter crossing or a matched-point density. A general description of the computer program is included and the purpose of all subroutines used is stated. The input required by the program and various input options are detailed, and the output description is presented. The program can solve flutter equations formulated with up to 12 vibration modes and obtain flutter solutions for up to 10 air densities. The program usage is illustrated by a sample run, and the FORTRAN program listing is included.
An analysis capability is described for the three-point-bend test applicable to materials of linear but unequal tensile and compressive stress-strain relations. The capability consists of numerous equations of simple form and their graphical representation. Procedures are described to examine the local stress concentrations and failure modes initiation. Examples are given to illustrate the usefulness and ease of application of the capability. Comparisons are made with materials which have equal tensile and compressive properties. The results indicate possible underestimates for flexural modulus or strength ranging from 25 to 50 percent greater than values predicted when accounting for unequal properties. The capability can also be used to reduce test data from three-point-bending tests, extract material properties useful in design from these test data, select test specimen dimensions, and size structural members.
For many years the Pointe Mouillee State Game Area, located on the Lake Erie shoreline just south of Detroit, has been a prime waterfowl habitat. The usefulness of the site for this purpose has been impaired because of the gradual deterioration of the marshland and severe flooding and storms during the spring of 1973. Also, it has been proposed that a dredge spoils area be located in or near the marsh. To aid the future management of a diked refuge area of 148 hectares within the State Game Area, a detailed vegetation inventory was prepared by photointerpretation and a generalized vegetation inventory was obtained by processing multispectral scanner imagery. Also, an analysis was conducted to determine the magnitude of past losses of marshland and the possibilities of replacing this lost habitat. The analysis indicated that large additions to waterfowl habitat could be provided by changes in management of vegetation in existing sections of the State Game Area, through acquisition and conversion of adjacent land by the Michigan Department of Natural Resources, and by the proposed construction of a barrier dike offshore of Pointe Mouillee. Altogether, the various measures considered in this report could affect a total area of nearly 13 sq. km.
The S193 Rad/Scat, although initially programmed for operating in the earth pointing mode, can be operated in the solar pointing mode as well. The usual coordinate systems for describing the S193 in orbit are defined. The instructions for the operation of the radiometer and scatterometer are presented in terms of standard Euler angles for these coordinate systems. A sample analysis for the scatterometer is described. The relationships between the various Euler angles and physically meaningful orbit parameters are defined.
Techniques using the infrared radiation emitted by a sliding elastohydrodynamic (EHD) point contact to measure oil film and surface temperature are discussed. Temperature distributions in the EHD contact are presented for a naphthenic mineral oil at 1.04 GN/sq m (150,000 psi) Hertz pressure and several sliding velocities. Film temperatures as high as 360 C are reported at locations near the points of minimum film thickness in the contact side lobes.
A theoretical and experimental study is made to investigate the effect on plate vibrations of varying the stiffness of corner elastic point supports. An experiment is conducted in which the bending stiffness of horizontal beams is used to support a square plate at its four corners. The stiffness of these supports can be varied over such a range that the plate fundamental frequency is lowered to 40% of the rigid support frequency. The variation with support stiffness of the frequencies of the first eight plate modes is measured and is compared with results from a theoretical model in which a Rayleigh-Ritz analysis is used which approximates the plate mode shapes as products of free-free beam modes. The elastic point supports are modeled both as massless translational springs and springs with tip masses, which are included to better represent the experimental supports.
A method is described involving the measurement of the viscous desolidification (pour) point of wax-free lubricant fluids. This method is especially useful for pour point testing of experimental quantities, since only six to sixteen drops of the oil are required for a single determination (automatically performed in duplicate) with nearly full recovery of the sample. The technique consists of: (1) rapidly freezing a small, predetermined amount of the oil on the side of a small test tube to form a frozen drop of given dimensions; (2) immersing duplicates of the charged and stoppered tubes into a cold bath; and (3) measuring the temperature when the drop front has moved a predetermined distance as the bath warms up.
The MTF degradation due to lateral diffusion is calculated for a back illuminated CCD imager for typical device parameters. The discrete nature of the CCD and finite size of the photosensitive elements result in an additional MTF degradation. The Fourier transform approach is utilized to calculate the effective point spread function for these processes in the time domain. Experimental data are presented on the point spread function for a three phase, double level anodized aluminum 160 x 100 thinned and back illuminated CCD imager and compared with the theoretical results. A simple modification of the Crowell and Labuda model suggested by these results is presented.
The isothermal elastohydrodynamic lubrication (EHL) of a point contact was analyzed numerically by simultaneously solving the elasticity and Reynolds equations. In the elasticity analysis the contact zone was divided into equal rectangular areas, and it was assumed that a uniform pressure was applied over each area. In the numerical analysis of the Reynolds equation, a phi analysis (where phi is equal to the pressure times the film thickness of the 3/2 power) was used to help the relaxation process. The EHL point contact analysis is applicable for the entire range of elliptical parameters and is valid for any combination of rolling and sliding within the contact.
The concept of a neutral point depends on the physical phenomena described. The regions with B less than about 1 gamma detected by Schindler and Ness may be interpreted as neutral regions for the ion-tearing process. The assumption of the presence of a multiple neutral point structure (with temporal variations) is still the most promising interpretation of the Explorer 34 data. Alternatives suggested by Russell lead to difficulties. Nevertheless, the final answer can come only from multiple satellite systems. A 1-day displacement of the day count in the data discussed by Schindler and Ness is corrected.
The Large Space Telescope (LST) program is aimed at placing a three-meter diffraction-limited telescope in a 270-nm orbit to perform astronomical observations that are not possible with earth-based telescopes. A complex simulation model is described which was developed to determine whether the stringent pointing stability requirements could be met. The model (programmed on a hybrid computer) included detailed dynamic representation of control moment gyros (CMGs) and reaction wheels (RWs), including their noise characteristics; dynamic sensor representation (including noise); shockmounts for the CMG actuators; detailed representation of an image motion compensation system; and a detailed flexible body vehicle model. Stability and performance studies based on the simulation model showed that the body pointing system will meet LST requirements in the presence of CMG vibrational disturbances and sensor noise. The recommended system consists of three orthogonally mounted RWs for primary short-term control, and a cluster of CMG actuators for continuous RW desaturation and vehicle maneuvering.
Based on previous laminar boundary-layer solutions for argon, xenon, nitrogen, and air, it is shown that the effect of gas ionization on stagnation-point heat transfer can be correlated with the variation of the frozen Prandtl number across the boundary layer. A formula is obtained for stagnation-point heat transfer in a noble gas and is shown to be valid from the low-temperature range to the region of strong ionization. It is concluded that the considered effect can be well correlated by the 0.7 power of the Prandtl-number ratio across the boundary layer.
Telescope mount provides torquing for a fine-pointing servosystem in both pitch and yaw. Use of flexure bearings in EPC (experiment pointing control) actuator package offers performance and reliability superior to that of other bearing configurations.