9,401 research outputs found

    Graphical techniques to assist in pointing and control studies of orbiting spacecraft

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    Computer generated graphics are developed to assist in the modeling and assessment of pointing and control systems of orbiting spacecraft. Three-dimensional diagrams are constructed of the Earth and of geometrical models which resemble the spacecraft of interest. Orbital positioning of the spacecraft model relative to the Earth and the orbital ground track are then displayed. A star data base is also available which may be used for telescope pointing and star tracker field-of-views to visually assist in spacecraft pointing and control studies. A geometrical model of the Hubble Space Telescope (HST) is constructed and placed in Earth orbit to demonstrate the use of these programs. Simulated star patterns are then displayed corresponding to the primary mirror's FOV and the telescope's star trackers for various telescope orientations with respect to the celestial sphere

    Generation of pseudo-random numbers

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    Practical methods for generating acceptable random numbers from a variety of probability distributions which are frequently encountered in engineering applications are described. The speed, accuracy, and guarantee of statistical randomness of the various methods are discussed

    A stochastic model for photon noise induced by charged particles in multiplier phototubes of the space telescope fine guidance sensors

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    The Space Telescope (ST) is subjected to charged particle strikes in its space environment. ST's onboard fine guidance sensors utilize multiplier phototubes (PMT) for attitude determination. These tubes, when subjected to charged particle strikes, generate spurious photons in the form of Cerenkov radiation and fluorescence which give rise to unwanted disturbances in the pointing of the telescope. A stochastic model for the number of these spurious photons which strike the photocathode of the multiplier phototube which in turn produce the unwanted photon noise are presented. The model is applicable to both galactic cosmic rays and charged particles trapped in the Earth's radiation belts. The model which was programmed allows for easy adaption to a wide range of particles and different parameters for the phototube of the multiplier. The probability density functions for photons noise caused by protons, alpha particles, and carbon nuclei were using thousands of simulated strikes. These distributions are used as part of an overall ST dynamics simulation. The sensitivity of the density function to changes in the window parameters was also investigated

    Fluid thrust control system

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    A pure fluid thrust control system is described for a pump-fed, regeneratively cooled liquid propellant rocket engine. A proportional fluid amplifier and a bistable fluid amplifier control overshoot in the starting of the engine and take it to a predetermined thrust. An ejector type pump is provided in the line between the liquid hydrogen rocket nozzle heat exchanger and the turbine driving the fuel pump to aid in bringing the fluid at this point back into the regular system when it is not bypassed. The thrust control system is intended to function in environments too severe for mechanical controls

    Seasonal Patterns of Flight and Attack of Maple Saplings by the Ambrosia Beetle \u3ci\u3eCorthylus Punctatissimus\u3c/i\u3e (Coleoptera: Scolytidae) in Central Michigan

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    Window traps with ethanol were used to observe seasonal flight patterns of Corthylus punctatissimus in central Michigan. Flights peaked in early July with a second peak seven weeks later in late August. Similarly, wilting of attacked maple (Acer) saplings began to appear a week after initial Corthylus flights, and showed twopeaks, one in mid-July and again with another peak, seven weeks later, in early September. The second peak of activity is presumably from reemerged adults, and not a second generation

    A stochastic model for particle impingements on orbiting spacecraft

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    A general methodology for simulating particle impingements on orbiting spacecraft is developed. Major steps in the modeling process are presented as (1) modeling objective, (2) construction of the spacecraft geometrical model, (3) simulation of the particles in the space environment, (4) particle impact and subsequent events of interest, and (5) results of the simulation. A simulation of the expected meteoroid impingements on the Hubble Space Telescope and the resulting angular momentum transfers which can cause telescope pointing disturbances is given to illustrate these methods

    Microwave soil moisture measurements and analysis

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    An effort to develop a model that simulates the distribution of water content and of temperature in bare soil is documented. The field experimental set up designed to acquire the data to test this model is described. The microwave signature acquisition system (MSAS) field measurements acquired in Colby, Kansas during the summer of 1978 are pesented

    Phosphatase Regulation of CFTR

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    The cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel is tightly regulated by the opposing actions of protein kinases and phosphatases. Its phosphorylation and activation by protein kinases A (PKA) and C (PKC) have been studied in some detail but phosphatase regulation of the channel has received less attention. Several phosphatases may control CFTR in various cell types, however in epithelia most deactivation is mediated by a membrane-bound phosphatase with functional properties resembling those of PP2C, the prototypic member of the PPM gene family of serinelthreonine phosphatases. The PP2C-like phosphatase requires Mg2+, is insensitive to the inhibitors okadaic acid and calyculin A, does not require Ca2+ or calmodulin, and is inhibited non-specifically by phenylimidazothiazoles. It is closely associated with CFTR and can be co-immunoprecipitated or co-purified from celllysates by affinity chromatography with, or without, pretreatment with chemical crosslinking reagents. Current efforts are directed towards identifying the phosphatase at the molecular level; i.e., determining if it is a novel isoform or alternatively spliced variant of a known PP2C isoform, or a new membrane-targeted phosphatase in the PPM family. Identifying and characterizing the phosphatase will open many new avenues of investigation into basic aspects of CFTR regulation, and may have clinical significance since the phosphatase is a potential target for pharmacotherapies to treat cystic fibrosis and secretory diarrhea

    Probability and Statistics in Aerospace Engineering

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    This monograph was prepared to give the practicing engineer a clear understanding of probability and statistics with special consideration to problems frequently encountered in aerospace engineering. It is conceived to be both a desktop reference and a refresher for aerospace engineers in government and industry. It could also be used as a supplement to standard texts for in-house training courses on the subject
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