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  • Life Sciences (General)  (26)
  • SPACECRAFT PROPULSION AND POWER  (11)
  • Signal transduction  (4)
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  • 1
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    Linear quadratic servo control of a reusable rocket engine (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 15; 5, Se; 1149-115
    Format: text
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  • 2
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    Spaceflight exposure effects on transcription, activity, and localization of alcohol dehydrogenase in the roots of Arabidopsis thaliana (1997)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Although considerable research and speculation have been directed toward understanding a plant's perception of gravity and the resulting gravitropic responses, little is known about the role of gravity-dependent physical processes in normal physiological function. These studies were conducted to determine whether the roots of plants exposed to spaceflight conditions may be experiencing hypoxia. Arabidopsis thaliana (L.) Heynh. plants were grown in agar medium during 6 or 11 d of spaceflight exposure on shuttle missions STS-54 (CHROMEX-03) and STS-68 (CHROMEX-05), respectively. The analysis included measurement of agar redox potential and root alcohol dehydrogenase (ADH) activity, localization, and expression. ADH activity increased by 89% as a result of spaceflight exposure for both CHROMEX-03 and -05 experiments, and ADH RNase protection assays revealed a 136% increase in ADH mRNA. The increase in ADH activity associated with the spaceflight roots was realized by a 28% decrease in oxygen availability in a ground-based study; however, no reduction in redox potential was observed in measurements of the spaceflight bulk agar. Spaceflight exposure appears to effect a hypoxic response in the roots of agar-grown plants that may be caused by changes in gravity-mediated fluid and/or gas behavior.
    Keywords: Life Sciences (General)
    Type: Plant physiology (ISSN 0032-0889); Volume 113; 3; 685-93
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  • 3
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    Changes in soluble sugar, starch, and alcohol dehydrogenase in Arabidopsis thaliana exposed to N2 diluted atmospheres (1997)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Proper exchange of atmospheric gases is important for normal root and shoot metabolism in plants. This study was conducted to determine how restricted air supply affects foliar carbohydrates, while using the marker enzyme alcohol dehydrogenase (ADH) to report on the oxygenation status of the rootzone. Fourteen-day-old Arabidopsis thaliana (L.) Heynh. plants grown singly in 7-ml tubes containing agarified nutrient medium were placed in coupled Magenta vessels and exposed for six days to either ambient air or one of six different air/nitrogen dilutions. Redox potential of the agar medium was measured immediately after harvesting and freezing leaf tissue, and then root systems were quickly extracted from the agar and frozen for subsequent analyses. Redox potential measurements indicated that this series of gas mixtures produced a transition from hypoxia to anoxia in the root zones. Root ADH activity increased at higher rates as the redox potential neared anoxic levels. In contrast, ADH mRNA expression quickly neared its maximum as the medium became hypoxic and showed little further increase as it became anoxic. Foliar carbohydrate levels increased 1.5- to 2-fold with decreased availability of metabolic gases, with starch increasing at higher concentrations of air than soluble carbohydrate. The results serve as a model for plant performance under microgravity conditions, where absence of convective air movement prevents replenishment of metabolic gases.
    Keywords: Life Sciences (General)
    Type: Plant & cell physiology (ISSN 0032-0781); Volume 38; 12; 1354-8
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  • 4
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    Oxytropism: a new twist in pollen tube orientation (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Chemical gradients and structural features within the pistil have been previously proposed as factors determining the directionality of pollen tube growth. In this study, we examine the behavior of pollen of eight species germinated in a dynamic oxygen gradient. While the germination rates of some species decreased directly with decreasing oxygen tension, other species showed no decrease in germination at oxygen tensions as low as 2 kPa. In one species, germination was consistently greater at decreased oxygen tensions than at ambient atmospheric levels. In three of the eight species tested, the developing pollen tube showed clear directional growth away from the more-oxygenated regions of the growth medium, while in one species growth was towards the more-oxygenated region. The remaining four species showed random tube growth. The pattern of oxytropic responses among the taxa suggests that this tropic behavior is both widespread and phylogenetically unpredictable.
    Keywords: Life Sciences (General)
    Type: Planta (ISSN 0032-0935); Volume 213; 2; 318-22
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  • 5
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    Gravity independence of seed-to-seed cycling in Brassica rapa (2000)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Growth of higher plants in the microgravity environment of orbital platforms has been problematic. Plants typically developed more slowly in space and often failed at the reproductive phase. Short-duration experiments on the Space Shuttle showed that early stages in the reproductive process could occur normally in microgravity, so we sought a long-duration opportunity to test gravity's role throughout the complete life cycle. During a 122-d opportunity on the Mir space station, full life cycles were completed in microgravity with Brassica rapa L. in a series of three experiments in the Svet greenhouse. Plant material was preserved in space by chemical fixation, freezing, and drying, and then compared to material preserved in the same way during a high-fidelity ground control. At sampling times 13 d after planting, plants on Mir were the same size and had the same number of flower buds as ground control plants. Following hand-pollination of the flowers by the astronaut, siliques formed. In microgravity, siliques ripened basipetally and contained smaller seeds with less than 20% of the cotyledon cells found in the seeds harvested from the ground control. Cytochemical localization of storage reserves in the mature embryos showed that starch was retained in the spaceflight material, whereas protein and lipid were the primary storage reserves in the ground control seeds. While these successful seed-to-seed cycles show that gravity is not absolutely required for any step in the plant life cycle, seed quality in Brassica is compromised by development in microgravity.
    Keywords: Life Sciences (General)
    Type: Planta (ISSN 0032-0935); Volume 210; 3; 400-6
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  • 6
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    [Growth and development of plants in a sequence of generations under the conditions of space flight (experiment Greenhouse-3)] (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The purpose was to study characteristic features of growth and development of several plant generations in space flight in experiment GREENHOUSE-3 as a part of the Russian-US space research program MIR/NASA in 1997. The experiment consisted of cultivation of Brassica rapa L. in board greenhouse Svet. Two vegetative cycles were fully completed and the third vegetation was terminated on day 13 on the phase of budding. The total duration of the space experiment was 122 days, i.e. same as in the ground controls. In the experiment with Brassica rapa L. viable seeds produced by the first crop were planted in space flight and yielded next crop. Crops raised from the ground and space seeds were found to differ in height and number of buds. Both parameters were lowered in the plants grown from the space seeds. The prime course for smaller size and reduced organogenic potential of plantTs reproductive system seems to be a less content of nutrients in seeds that had matured in the space flight. Experiment GREENHOUSE-3 demonstrated principle feasibility of plant reproduction in space greenhouse from seeds developed in microgravity.
    Keywords: Life Sciences (General)
    Type: Aviakosmicheskaia i ekologicheskaia meditsina = Aerospace and environmental medicine (ISSN 0233-528X); Volume 35; 3; 43-8
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  • 7
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    Influence of atmospheric oxygen on leaf structure and starch deposition in Arabidopsis thaliana (2001)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Plant culture in oxygen concentrations below ambient is known to stimulate vegetative growth, but apart from reports on increased leaf number and weight, little is known about development at subambient oxygen concentrations. Arabidopsis thaliana (L.) Heynh. (cv. Columbia) plants were grown full term in pre-mixed atmospheres with oxygen partial pressures of 2.5, 5.1, 10.1, 16.2, and 21.3 kPa O2, 0.035 kPa CO2 and the balance nitrogen under continuous light. Fully expanded leaves were harvested and processed for light and transmission electron microscopy or for starch quantification. Growth in subambient oxygen concentrations caused changes in leaf anatomy (increased thickness, stomatal density and starch content) that have also been described for plants grown under carbon dioxide enrichment. However, at the lowest oxygen treatment (2.5 kPa), developmental changes occurred that could not be explained by changes in carbon budget caused by suppressed photorespiration, resulting in very thick leaves and a dwarf morphology. This study establishes the leaf parameters that change during growth under low O2, and identifies the lower concentration at which O2 limitation on transport and biosynthetic pathways detrimentally affects leaf development. Grant numbers: NAG5-3756, NAG2-1020, NAG2-1375.
    Keywords: Life Sciences (General)
    Type: Plant, cell & environment (ISSN 0140-7791); Volume 24; 4; 419-28
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  • 8
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    Linear quadratic servo control of a reusable rocket engine (1991)
    In:  Other Sources
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    Publication Date: 2019-06-28
    Description: The paper deals with the development of a design method for a servo component in the frequency domain using singular values and its application to a reusable rocket engine. A general methodology used to design a class of linear multivariable controllers for intelligent control systems is presented. Focus is placed on performance and robustness characteristics, and an estimator design performed in the framework of the Kalman-filter formalism with emphasis on using a sensor set different from the commanded values is discussed. It is noted that loop transfer recovery modifies the nominal plant noise intensities in order to obtain the desired degree of robustness to uncertainty reflected at the plant input. Simulation results demonstrating the performance of the linear design on a nonlinear engine model over all power levels during mainstage operation are discussed.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: AIAA PAPER 91-1999
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  • 9
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    A demonstration of an intelligent control system for a reusable rocket engine (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: An Intelligent Control System for reusable rocket engines is under development at NASA Lewis Research Center. The primary objective is to extend the useful life of a reusable rocket propulsion system while minimizing between flight maintenance and maximizing engine life and performance through improved control and monitoring algorithms and additional sensing and actuation. This paper describes current progress towards proof-of-concept of an Intelligent Control System for the Space Shuttle Main Engine. A subset of identifiable and accommodatable engine failure modes is selected for preliminary demonstration. Failure models are developed retaining only first order effects and included in a simplified nonlinear simulation of the rocket engine for analysis under closed loop control. The engine level coordinator acts as an interface between the diagnostic and control systems, and translates thrust and mixture ratio commands dictated by mission requirements, and engine status (health) into engine operational strategies carried out by a multivariable control. Control reconfiguration achieves fault tolerance if the nominal (healthy engine) control cannot. Each of the aforementioned functionalities is discussed in the context of an example to illustrate the operation of the system in the context of a representative failure. A graphical user interface allows the researcher to monitor the Intelligent Control System and engine performance under various failure modes selected for demonstration.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA-TM-105794 , E-7224 , NAS 1.15:105794 , AD-A255720
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  • 10
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    Controls concepts for next generation reuseable rocket engines (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Three primary issues will drive the design and control used in next generation reuseable rocket engines. In addition to steady-state and dynamic performance, the requirements for increased durability, reliability and operability (with faults) will dictate which new controls and design technologies and features will be brought to bear. An array of concepts which have been brought forward will be tested against the measures of cost and benefit as reflected in the above 'ilities'. This paper examines some of the new concepts and looks for metrics to judge their value.
    Keywords: SPACECRAFT PROPULSION AND POWER
    Type: NASA-TM-106902 , E-9594 , NAS 1.15:106902 , 1995 American Control Conference; Jun 21, 1995 - Jun 23, 1995; Seattle, WA; United States
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