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  • Other Sources  (5,825)
  • SPACECRAFT DESIGN, TESTING AND PERFORMANCE  (5,824)
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  • 1
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    Niphargus-Thiothrix associations may be widespread in sulphidic groundwater ecosystems: evidence from southeastern Romania. (2018)
    Details
    Publication Date: 2021-04-25
    Description: Niphargus is a speciose amphipod genus found in groundwater habitats across Europe. Three Niphargus species living in the sulphidic Frasassi caves in Italy harbour sulphur-oxidizing Thiothrix bacterial ectosymbionts. These three species are distantly related, implying that the ability to form ectosymbioses with Thiothrix may be common among Niphargus. Therefore, Niphargus-Thiothrix associations may also be found in sulphidic aquifers other than Frasassi. In this study, we examined this possibility by analysing niphargids of the genera Niphargus and Pontoniphargus collected from the partly sulphidic aquifers of the Southern Dobrogea region of Romania, which are accessible through springs, wells and Movile Cave. Molecular and morphological analyses revealed seven niphargid species in this region. Five of these species occurred occasionally or exclusively in sulphidic locations, whereas the remaining two were restricted to nonsulphidic areas. Thiothrix were detected by PCR on all seven Dobrogean niphargid species and observed using microscopy to be predominantly attached to their hosts' appendages. 16S rRNA gene sequences of the Thiothrix epibionts fell into two main clades, one of which (herein named T4) occurred solely on niphargids collected in sulphidic locations. The other Thiothrix clade was present on niphargids from both sulphidic and nonsulphidic areas and indistinguishable from the T3 ectosymbiont clade previously identified on Frasassi-dwelling Niphargus. Although niphargids from Frasassi and Southern Dobrogea are not closely related, the patterns of their association with Thiothrix are remarkably alike. The finding of similar Niphargus-Thiothrix associations in aquifers located 1200 km apart suggests that they may be widespread in European groundwater ecosystems.
    Keywords: amphipods; ecology; sulphide; symbiosis; systematics; taxonomy ; 551 ; Amphipoda ; Animals ; DNA, Bacterial ; Ecosystem ; Groundwater ; Molecular Sequence Data ; Phylogeny ; RNA, Ribosomal, 16S ; Romania ; Sequence Analysis, DNA ; Sulfur ; Symbiosis ; Thiothrix
    Language: English , English
    Type: article , publishedVersion
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    CITATION GEO-LEO
  • 2
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    Design considerations and strategies for lunar-based observations (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This paper addresses the design considerations and strategies for astrophysical observations as key elements of an international solar system exploration program. Emphasis is placed on the technical and programmatic challenges and opportunities associated with an evolving program of lunar-based astronomy. Both robotic and human tended facilities are discussed ranging from relatively small meter-class transit telescopes to large interferometer and filled-aperture systems.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Space Technology - Industrial and Commercial Applications (ISSN 0892-9270); 14; 6; p. 355-365
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    NASA TECHNICAL REPORTS
  • 3
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    Structural damage detection of space truss structures using best achievable eigenvectors (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A method is presented by which measured modes and frequencies from a modal test can be used to determine the location and magnitude of damage in a space struss structure. The damage is located by computing the Euclidean distances between the measured mode shapes and the best achievable eigenvectors. The best achievable eigenvectors are the projection of the measured mode shapes onto the subspace defined by the refined analytical model of the structure and the measured frequencies. Loss of both stiffness and mass properties can be located and quantified. To examine the performance of the method when experimentally measured modes are employed, various damage detection studies using a laboratory eight-bay truss structure were conducted. The method performs well even though the measurement errors inevitably make the damage location more difficult.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AIAA Journal (ISSN 0001-1452); 32; 5; p. 1049-1057
    Format: text
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    NASA TECHNICAL REPORTS
  • 4
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    Russian questions remain after space station review (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Following the project's first major design review, some unresolved technical issues, mainly centered on details of how to integrate Russian hardware into the U.S./international space station, remain. No 'show stoppers' were found in the review. Specific open technical issues are discussed in this article.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Aviation Week & Space Technology (ISSN 0005-2175); 140; 13; p. 26-27
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    NASA TECHNICAL REPORTS
  • 5
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    Trajectory-based heating analysis for the European Space Agency/Rosetta Earth Return Vehicle (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A coupled, trajectory-based flowfield and material thermal-response analysis is presented for the European Space Agency proposed Rosetta comet nucleus sample return vehicle. The probe returns to earth along a hyperbolic trajectory with an entry velocity of 16.5 km/s and requires an ablative heat shield on the forebody. Combined radiative and convective ablating flowfield analyses were performed for the significant heating portion of the shallow ballistic entry trajectory. Both quasisteady ablation and fully transient analyses were performed for a heat shield composed of carbon-phenolic ablative material. Quasisteady analysis was performed using the two-dimensional axisymmetric codes RASLE and BLIMPK. Transient computational results were obtained from the one-dimensional ablation/conduction code CMA. Results are presented for heating, temperature, and ablation rate distributions over the probe forebody for various trajectory points. Comparison of transient and quasisteady results indicates that, for the heating pulse encountered by this probe, the quasisteady approach is conservative from the standpoint of predicted surface recession.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Spacecraft and Rockets (ISSN 0022-4650); 31; 3; p. 421-428
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    NASA TECHNICAL REPORTS
  • 6
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    The X-ray astronomy satellite ASCA (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Advanced Satellite for Cosmology and Astrophysics (ASCA) is a high-throughput X-ray astronomy observatory which is capable of simultaneous imaging and spectroscopic observations over a wide energy range 0.5-10 keV. The scientific capabilities of ASCA and some aspects related to its operation and observations are briefly described.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: PASJ: Publications of the Astronomical Society of Japan (ISSN 0004-6264); 46; 3; p. L37-L41
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    NASA TECHNICAL REPORTS
  • 7
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    Estimation of the electromagnetic bias from retracked TOPEX data (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We examine the electromagnetic (EM) bias by using retracked TOPEX altimeter data. In contrast to previous studies, we use a parameterization of the EM bias which does not make stringent assumptions about the form of the correction or its global behavior. We find that the most effective single parameter correction uses the altimeter-estimated wind speed but that other parameterizations, using a wave age related parameter of significant wave height, may also significantly reduce the repeat pass variance. The different corrections are compared, and their improvement of the TOPEX height variance is quantified.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 24,971-24,979
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    NASA TECHNICAL REPORTS
  • 8
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    Comparison of TOPEX/POSEIDON sigma(sub 0) and significant wave height distributions to Geosat (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Monthly Ku band sigma(sub 0) and significant wave height (SWH) histograms from the NASA altimeter on the TOPEX/POSEIDON satellite are preseneted for January through June 1993 for three latitude bands between +/- 60 degrees. The data are compared to distributions from the Geosat mission for the same months in 1987-1989. Generally, the distributions agree quite well, although there are some seasonal/hemispherical differences. The sigma(sub 0) comparison reveals an overall bias between the two altimeters with the TOPEX sigma(sub 0) higher by about 0.7 dB, which is consistent with algorithm improvements for TOPEX. The SWH distributions show strong hemispherical/seasonal changes. The seasonal/hemispherical differences between TOPEX and Geosat are consistent for SWH and sigma(sub 0). The joint distribution of sigma(sub 0) and SWH is extremely stable friom month to month. The typical SWH is independent of sigma(sub 0) for sigma(sub 0) greater than 11.3 dB. The minimum SWH grows exponentially with wind speed. This joint distribution may be useful for understanding electromagnetic bias in altimeter measurements. Finally, altimeter data are compared to buoy values from 21 overflights of the NASA verification site near Pt. Conception, California. Wave heights agree well with an root mean square (RMS) difference of only 0.2 m. Altimeter sigma(sub 0) values are compared to buoy wind speeds. The results are consistent with the -0.7 dB sigma(sub 0) offset from the histogram comparisons.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 25,015-25,024
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    NASA TECHNICAL REPORTS
  • 9
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    Assessment of the TOPEX altimeter performance using waveform retracking (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: To assess the accuracy of the TOPEX altimeter data, we have reprocessed the raw altimeter waveform data using more sophisticated algorithms than those implemented in the altimeter hardware. We discuss systematic contamination of the waveform which we have observed and its effect on very long wavelength errors. We conclude that these systematic errors are responsible for a very long wavelength error whose peak-to-peak magnitude for the Ku band altimeter is of the order of 1 cm. We also examine the ability of retracked data to reduce the repeat pass variance and correct for significant wave height (SWH) and acceleration dependent errors. We find that the ground postprocessing contains SWH dependent biases which depend on the altimeter fine height correction.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 24,957-24,969
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    NASA TECHNICAL REPORTS
  • 10
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    The corrections for significant wave height and attitude effects in the TOPEX radar altimeter (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The routine ground processing of data from the NASA radar altimeter of TOPEX/POSEIDON includes instrument corrections for the effects of significant wave height and attitude angle changes on the altimeter's estimates of range, backscattered power, and significant wave height. This paper describes how these instrument corrections were generated and how they are applied. Detailed waveform fitting to telemetered waveform samples is use to assess the effectiveness of the corrections. There are several altimeter hardware-caused small waveform departures from the model waveforms and these departures, designated waveform 'features', are described in detailed. A consequence of the waveform features, and their positioning relationship to range rate, is that range data for ground tracks moving toward the equator may differ systematically by about a centimeter compared to range data for ground tracks moving away from the equator. The results and discussion are limited to side A of the redundant altimeter, as only side A has been operated on orbit.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: Journal of Geophysical Research (ISSN 0148-0227); 99; C12; p. 24,941-24,955
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    NASA TECHNICAL REPORTS
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