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.
Standard IC chips and digitally tuned oscillator combined. Circuit consists of PROM-based microprogramed control sequencer, which drives group of diode switches to select one of eight tuning capacitors in L-C oscillator. Circuit originally designed to "dither" transmitter frequency of K-band radar at high rates finds application in other areas, as automated test equipment or computer-controlled receiver tuning.
To achieve the program goals, 28 minimodules were fabricated and tested, using 600 cells made from three-inch-diameter wafers processed by the sequence chosen for this purpose. Of these 600 cells, half were made from epitaxially grown layers on potentially low-cost substrates. The other half were made from commercial semiconductor-grade (SG), single-crystal silicon wafers that served as controls. Cell processing was normally performed on mixed lots containing significant numbers of each of these two types of wafers. After evaluation of the performance of all cells, they were separated by types for incorporation into modules that were to be tested for electrical performance and response to environmental stress. A simplified flow chart displaying this scheme, for quantities representing half of the planned total to be processed, is presented.
The launch vehicle, spacecraft, and mission are summarized. Launch window information, vehicle telemetry coverage, real time data flow, telemetry coverage by station, selected trajectory information, and a brief sequence of flight events are included.
The Space Shuttle's avionics system is controlled by five onboard computers, four of which are loaded with the Primary Avionics Software System (PASS), and one of which is loaded with the Backup Flight System (BFS). The Shuttle is nominally controlled by the PASS computers. However, in the event of a PASS generic software failure, the BFS is engaged and assumes control of the Shuttle. The BFS Sequencing System problems presented by the engage requirement and the solutions chosen by the developers are discussed. These solutions constitute a technique which can be applied to the design of any real-time backup system.
IUE satellite and Lick 3 m reflector image tube scanner measurements of the Mg II and Ca II resonance lines in a sample of T Tauri stars are the basis of a discussion of the Mg II h and k line emission and the Ca II H and K line emission, within the context of stellar chromospheres. Corroborative evidence is presented for the chromospheric origin of these resonance lines, and chromospheric radiative loss rates in the Mg II and Ca II resonance lines are derived. It is found that the degree of nonradiative heating present in the outer atmospheres of T Tauri stars generally exceeds that of the RS CVn systems, as well as the dMe stars and other active chromospheric dwarfs, and it is inferred that the surfaces of such pre-main sequence stars are covered by regions similar to solar plages. The mean chromospheric electron density of T Tauri stars is determined as 10 to the 11th/cu cm.
The processing gain of a direct sequence spread spectrum system is approximately the ratio of the spreading code chip rate to the data rate. This paper provides a more accurate understanding of the performance of such systems as a function of the modulation scheme and jammer characteristics.
New sequence data from several protein families and from 5S ribosomal RNA confirm and elaborate a previously proposed description of the phylogenetic connections between a variety of bacteria and the eukaryotes. Probably, the first organisms were nonphotosynthetic anaerobic prokaryotes, which were followed soon by photosynthetic anaerobes. From this photosynthetic stock, the aerobic line to Pseudomonadacae, Rhodospirillaceae, and blue-greens arose. The eukaryotes derived genetic material from the symbioses of at least three separate bacterial lines. Ancestors of Rhodopseudomonas globiformis gave rise to the eukaryote mitochondria, probably through at least three separate symbioses, one early on the flagellate line, one on the ciliate line, and one on the stem to the multicellular forms.
Notched and unnotched geometries at 16, 32, and 64-ply thicknesses of a 90/45/0-45 (ns) laminate and a 45/0/-45/90 (ns) laminate were tested in compression-compression fatigue. The fatigue life and the initiation, type, and progression of damage were determined. Interlaminar stresses generated at straight, free edges of axially loaded laminates were used to interpret the test results. The fatigue lives of the notched specimens did not appear to be a strong function of laminate stacking sequence or specimen thickness. The stress concentration at the hole dominated over the interlaminar stresses at the straight free edge. The unnotched specimens of the 90/45/0/-45 (ns) laminate with tensile interlaminar normal stresses delaminated more readily than did the 45/0/-45/90 (ns) laminate with compressive interlaminar normal stress. The life of the 16-ply unnotched specimens was lower than the 32- and 64-ply specimens. Delaminations were located at the interface where the maximum shear stress occurred regardless of the sense or magnitude of the interlaminar normal stress. An antibuckling fixture was effective in preventing out-of-plane motion without overconstraining the specimen.
The results of equilibrium crystallization experiments at one atmosphere on a sample of the Type B Ca-Al-rich inclusions (CAI) of the Allende meteorite are reported. All the experiments were performed on a synthetic sample approximating the Allende CAI characteristics. The crystallization sequence observed comprised spinel at 1550 C, then melilite at 1400 C, anorthite at 1260 C, and then Ti-Al-rich clinopyroxene, formed at 1230 C. The observation that pyroxenes similar to the titaniferous fassaites found in Type B inclusions can be formed by equilibrium crystallizations of melts with Type B composition indicate that some Type B CAIs were at least partially molten. If the temperatures were not too far above the solidus, the molten condensate compositions would be similar to that occurring in gas-to-solid condensation.
Three 8-base pair (bp) segments of alternating purine-pyrimidine from the simian virus 40 enhancer region form Z-DNA on negative supercoiling; minichromosome DNase I-hypersensitive sites determined by others bracket these three segments. A survey of transcriptional enhancer sequences reveals a pattern of potential Z-DNA-forming regions which occur in pairs 50-80 bp apart. This may influence local chromatin structure and may be related to transcriptional activation.
The pre-main sequence X-ray emitting stars observed in molecular clouds appear to provide the bulk of the ionization. Newly forming stars therefore control the coupling of the magnetic field to the cloud. Since this coupling itself is believed to be responsible for the rate of cloud collapse, it is suggested that there is a natural feedback mechanism, involving observed X-rays, which is capable of regulating molecular cloud evolution and the rate of star formation.
Length and timing of pulse sequences user controlled. Digital circuit generates several pulse streams to control loads that must be synchronized allowing duration and phasing of each stream to be varied independently. Application of circuit to control pump for biomedical applications.
The implications of observational findings on atmospheric and subatmospheric taxonomy, diagnostics, and modeling are explored. The correlations between distinctive radial sequences in stellar atmospheres and the thermodynamic properties of the stars in which they appear are discussed.
The Advanced Flexible Reusable Surface Insulation (AFRSI) test article was wind tunnel tested. The AFRSI was exposed to a simulated ascent airloads environment and data was obtained which could be used to support the AFRSI certification program. The AFRSI sequence of environments also included radiant heating (1500 degrees Fahrenheit) and wind/rain environments. The test article was wind/rain conditioned before each wind tunnel entry and was thermally conditioned after each wind tunnel entry. The AFRSI failed and the test was aborted before reaching the ascent environment. The AFRSI test article sequentially exposed to 50 wind/rain and 49 simulated entry thermal missions, as well as four wind tunnel entries equivalent to 40 ascent missions.
The role of proteins in the origin of living things is discussed. It has been experimentally established that amino acids can sequence themselves under simulated geological conditions with highly nonrandom products which accordingly contain diverse information. Multiple copies of each type of macromolecule are formed, resulting in greater power for any protoenzymic molecule than would accrue from a single copy of each type. Thermal proteins are readily incorporated into laboratory protocells. The experimental evidence for original polyfunctional protocells is discussed.
Prokaryotic and eukaryotic evolutionary trees are developed from protein and nucleic-acid sequences by the methods of numerical taxonomy. Trees are presented for bacterial ferredoxins, 5S ribosomal RNA, c-type cytochromes , cytochromes c2 and c', and 5.8S ribosomal RNA; the implications for early evolution are discussed; and a composite tree showing the branching of the anaerobes, aerobes, archaebacteria, and eukaryotes is shown. Single lines are found for all oxygen-evolving photosynthetic forms and for the salt-loving and high-temperature forms of archaebacteria. It is argued that the eukaryote mitochondria, chloroplasts, and cytoplasmic host material are descended from free-living prokaryotes that formed symbiotic associations, with more than one symbiotic event involved in the evolution of each organelle.
The origin of mitochondria and chloroplasts is investigated on the basis of prokaryotic and early-eukaryotic evolutionary trees derived from protein and nucleic-acid sequences by the method of Dayhoff (1979). Trees for bacterial ferrodoxins, 5S ribosomal RNA, c-type cytochromes, the lipid-binding subunit of ATPase, and dihydrofolate reductase are presented and discussed. Good agreement among the trees is found, and it is argued that the mitochondria and chloroplasts evolved by multiple symbiotic events.
The International Sun-Earth Explorer-3 (ISEE-3) was moved from its mission halo orbit upstream of the earth's magnetosphere on June 10, 1982. Multiple lunar swingby maneuvers were then used to shape the trajectory for extensive exploration of the distant geomagnetic tail and finally to place the spacecraft on a course that will intercept the comet Giacobini-Zinner on September 11, 1985. With this new mission objective, the spacecraft was renamed the International Cometary Explorer (ICE). A double-lunar-swingby control technique involving five passes by the moon was eventually implemented to accomplish this, but in the process of finding this solution several feasible, though less optimal, alternative trajectory sequences implementing the same procedure were discovered. This paper provides a descriptive comparison of these very different orbital profiles and serves to illustrate the utility and great flexibility of this orbital control procedure. Targeting methodology for finding constrained solutions in this space is also presented.