3,425 research outputs found

    Automatic rendezvous and capture system development in a manned environment

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    This paper presents the development of a 'Phase One' AR&C system capability as a logical outgrowth of Rendezvous and Proximity Operations (R&PO) system development for manned space programs. The continuity of the approach to R&PO across the Apollo, Skylab, Apollo-Soyuz, and Shuttle programs is traced and lessons learned which are applicable to AR&C discussed. Use of the Shuttle as a test bed for Automatic Rendezvous and Capture capabilities and technology demonstrations is discussed. A status of the current Phase One System design and brief overview of its capabilities is presented

    Formation of ions and radicals from icy grains in comets

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    Ion and radical formation in comets are thought to occur primarily by photodissociation of gas phase molecules. Experimental evidence and theoretical calculations are presented that show that some of the radical and ions can come directly from ice grains. The experimental evidence suggest that if the frozen molecules on the surface of grains undergo direct dissociation then they may be able to release radicals directly in the gas phase. If the molecules undergo predissociation it is unlikely that they will release radicals in the gas phase since they should be quenched. Calculations of this direct photodissociation mechanism further indicate that even if the parent molecule undergoes direct dissociation, the yield will not be high enough to explain the rays structure in comets unless the radicals are stored in the grains and then released when the grain evaporates. Calculations were also performed to determine the maximum number of ions that can be stored in an icy grain's radius. This number is compared with the ratio of the ion to neutral molecular density. The comparison suggests that some of the ions observed near the nucleus of the comet could have originally been present in the cometary nucleus. It is also pointed out that the presence of these ions in icy grains could lead to radical formation via electron recombination. Finally, an avalanche process was evaluated as another means of producing ions in comets

    The temporal changes in the emission spectrum of Comet 9P/Tempel 1 after Deep Impact

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    The time dependence of the changes in the emission spectra of Comet 9P/Tempel 1 after Deep Impact are derived and discussed. This was a unique event because for the first time it gave astronomers the opportunity to follow the time history of the formation and decay of O(1S), OH, CN, C2, C3, NH, and NH2. Least squares fits of a modified Haser model with constraints using known rate constants were fit to the observed data. In the case of OH a simple two-step Haser model provides a reasonable fit to the observations. Fitting the emissions from O(1S), CN, C2, C3, NH, and NH2 requires the addition of a delayed component to a regular two or three step Haser model. From this information a picture of the Deep Impact encounter emerges where there is an initial formation of gas and dust, which is responsible for the prompt emission that occurs right after impact. A secondary source of gas starts later after impact when the initial dust has dissipated enough so that solar radiation can reach the surface of freshly exposed material. The implications of this and other results are discussed in terms of the implications on the structure and composition of the comet's nucleus.Comment: Accepted for publication in The Astrophysical Journal; 26 pages including 8 figures and 1 tabl

    Photodissociation Cross Sections for the Production of C2 from C2H Using Laser Induced Hg Photosensitization and Tunable Ultraviolet and Visible Lasers

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    The principle goal of our research was to understand the formation of free radicals in comets. To do this we compared laboratory results with cometary observations in attempt to make sure that the cometary observations agree with what is known about the photochemistry of the proposed parent molecule. Initially we concentrated on the CS emission in an effort to show the parent of this molecule was CS2, consistent with cometary observations of the photochemical lifetime. We then started to look into the problem of the C2 formation in comets. We set out to see if we could measure all of the nascent distributions of the C2 products in the hope that they would be a characteristic signature of the formation process

    The price of corporate social responsibility: the case of black economic empowerment transactions in South Africa

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    Since the demise of apartheid in South Africa, corporations have been encouraged to participate in the governmental goal of increasing corporate ownership by the black majority population. One vehicle that has arisen to help facilitate an increase in corporate ownership has been black economic empowerment (BEE) transactions. BEE transactions are essentially private placements of equity. Firms that have taken this socially activist position of selling portions of their equity, usually at a substantial discount, to black empowerment groups have received positive media attention in the name of “good corporate citizenship.” ; This study investigates the market performance of these BEE transactions, specifically addressing three questions. The first question is whether BEE transactions create or destroy wealth. To address this question we use an event study methodology to calculate the cumulative abnormal returns (CARs) associated with public announcements of BEE transactions. The second question is whether specific types of BEE transactions did better or worse than others. We address this question by analyzing the cross-sectional variation in the CARs associated with public announcements of BEE transactions. The third question is whether firms that engage in BEE transactions experience negative post-announcement price performance. This last question is motivated by popular press accounts of the exploitation of black empowerment groups by white-owned South African corporations. To address this question, we test whether BEE transactions have benefited white corporate South Africa at the expense of the participating black empowerment groups.

    Communication and equilibrium in discontinuous games of incomplete information

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    This paper offers a new approach to the study of economic problems usually modeled as games of incomplete information with discontinuous payoffs. Typically, the discontinuities arise from indeterminacies (ties) in the underlying problem. The point of view taken here is that the tie-breaking rules that resolve these indeterminacies should be viewed as part of the solution rather than part of the description of the model. A solution is therefore a tie-breaking rule together with strategies satisfying the usual best-response criterion. When information is incomplete, solutions need not exist; that is, there may be no tie-breaking rule that is compatible with the existence of strategy profiles satisfying the usual best-response criteria. It is shown that the introduction of incentive compatible communication (cheap talk) restores existence

    A phase one AR/C system design

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    The Phase One AR&C System Design integrates an evolutionary design based on the legacy of previous mission successes, flight tested components from manned Rendezvous and Proximity Operations (RPO) space programs, and additional AR&C components validated using proven methods. The Phase One system has a modular, open architecture with the standardized interfaces proposed for Space Station Freedom system architecture

    Economic Impact of the Muskingum Watershed Conservancy District on the Regional Economy, 2014-2022

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    The Muskingum Watershed Conservancy District (MWCD), the largest conservancy district in Ohio, initiated a significant, multi-year capital improvement plan in 2014 in response to increasing revenues associated with Utica Shale development. This study used input-output analysis to estimate the regional economic impact of MWCD’s spending on infrastructure improvements and related operations from 2014 through 2022. Cleveland State University’s Energy Policy Center found that MWCD’s 182.1millionincapitalspendingduringthestudyperiodresultedin182.1 million in capital spending during the study period resulted in 486.8 million of gross output (total economic activity of all sales/revenues), 221.9millionofvalueadded(grossoutputminusintermediateinputs),221.9 million of value added (gross output minus intermediate inputs), 135.6 million in labor income, and 2,287 jobs throughout the conservancy district’s 18-county service area. Additionally, every 1 million spent annually by MWCD during the study period on operations and maintenance (O&M) supported approximately 3.5 million of gross output, 1.9millionofvalueadded,1.9 million of value added, 1.3 million in labor income, and 22 jobs per year on average in the local economy. Altogether, MWCD’s spending on capital improvements and O&M from 2014 through 2022 resulted in $938.3 million of total economic activity for the 18-county region served by the conservancy district
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