Star Tracker Accuracy Improvement and Optimization for Attitude Measurement in Three-Axis

High precision attitude measurement systems obviate the need for the beacon from the receiver making it possible for the spacecraft to beam a laser communications signal to a ground station without the ground station advertising its location. The research presented targets new detection and estimation methods to improve the accuracy in locating stars on a focal plane detector, and an understanding of the effects of changes in the optics design parameters and aberration, including defocus, on the navigation solution itself. This understanding can lead to an optimization of the attitude solution with respect to those optics realm parameter changes. The methodology discussed includes the development of a model of a current star tracker system. Using this model, multiple algorithms are implemented, including a multi-hypothesis method (MHT), to detect and estimate the position of the stars on the focal plane detector. It will be shown that using the MHT for detection and estimation, a greater accuracy can be found for each star estimation from more traditional detection and estimation algorithms. The approach then uses the model to develop statistics of the star tracker and the attitude estimation outputs to understand the accuracy, or variance, of the system's attitude solution. This solution is repeated for a range of defocus aberration, and a lower limit to the variance of the attitude solution is shown. A Cramer Rao lower bound solution is derived for the star tracker system and the results are compared to the Monte Carlo analysis from the model and shown to correlate very well. The approach uses a star image not as a Gaussian spot on the focal plane as done in previous work, and use of an image that includes the effects of aberrations of the optic system, and the effects of under-sampling and noise from the focal plane detector as well. Analysis includes exploring a star tracker's accuracy improvement through the combination of focus error and under-sampling effects alone, possibly contradicting conventional wisdom and approaches

Design and construction of a human powered vehicle seating simulator for diagnostic testing

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references (leaf 24).A seating simulator was built to test the influence of various seating positions on human cycling power output. The simulator measures a rider's physical stress required to produce a certain power output. A heart rate monitor is used to find the rider's physical stress level. The theory is that the best shaped seat will allow the rider to pedal most efficiently. The seat of the simulator can easily be changed by connecting the seat's support strings to a square grid of holes. Mechanical power flows from the simulator's bike pedals through a chain drive to an electric motor. Electrical power flows from the electric motor through a rectifier to a variable bank of resistors. There were issues which came up involving the bike parts used and the dynamics of the chain drive system. The worst problem was that the supports would flex causing the chain to slacken and resonate under the changing forces of the pedaling motion. First a steel pipe was added to make the system more rigid. Then a sliding copper derailleur was used to allow the chain to stay on up to 213 watts. Finally the copper derailleur was replaced with a bike's derailleur which allows the simulator to operate in excess of 450 watts. Initial tests of several different seat configurations were completed with notable influence on the heart rate of the rider.by Harry Lichter.S.B

Chromosomal in situ suppression hybridization of human gonosomes and autosomes and its use in clinical cytogenetics

DNA libraries from sorted human gonosomes were used selectively to stain the X and Y chromosomes in normal and aberrant cultured human cells by chromosomal in situ suppression (CISS-) hybridization. The entire X chromosome was stained in metaphase spreads. Interphase chromosome domains of both the active and inactive X were clearly delineated. CISS-hybridization of the Y chromosome resulted in the specific decoration of the euchromatic part (Ypter-q11), whereas the heterochromatic part (Yq12) remained unlabeled. The stained part of the Y chromosome formed a compact domain in interphase nuclei. This approach was applied to amniotic fluid cells containing a ring chromosome of unknown origin (47,XY; +r). The ring chromosome was not stained by library probes from the gonosomes, thereby suggesting its autosomal origin. The sensitivity of CISS-hybridization was demonstrated by the detection of small translocations and fragments in human lymphocyte metaphase spreads after irradiation with 60Co-gamma-rays. Lymphocyte cultures from two XX-males were investigated by CISS-hybridization with Y-library probes. In both cases, metaphase spreads demonstrated a translocation of Yp-material to the short arm of an X chromosome. The translocated Y-material could also be demonstrated directly in interphase nuclei. CISS-hybridization of autosomes 7 and 13 was used for prenatal diagnosis in a case with a known balanced translocation t(7;13) in the father. The same translocation was observed in amniotic fluid cells from the fetus. Specific staining of the chromosomes involved in such translocations will be particularly important, in the future, in cases that cannot be solved reliably by conventional chromosome banding alone

Continuum Model of Thin-Film Deposition and Growth

A continuum theory for the deposition and growth of solid films is presented. The theory is developed in a coordinate-independent manner and so incorporates the fully nonlinear physics. The evolution of the film is modeled in three steps. First, the adsorption of atoms in the incident beam is modeled as a ballistic process. Second, the random motion of the adatoms is treated as a diffusive process. Finally, sticking of adatoms to the film occurs as a Poisson process. The resulting system of differential equations is examined in several parameter limits. The diffusively dominated limit appears similar to zone 1 of the structure-zone model. Generically the surface slope develops discontinuities; these ‘‘kinks’’ play the role of grain boundaries. In the ballistically dominated case these kinks may be advected along the surface giving rise to columnarlike microstructures, as is observed in zone 2

The Return of the Honeymoon: Television News Coverage of New Presidents, 1981-2009

Content analysis of network evening news coverage during the first year of the Barack Obama presidency revealed coverage that was far more positive in tone than comparable news reports from the first years of the Ronald Reagan, Bill Clinton, and George W. Bush presidencies. Both domestic and international policy evaluations of the Obama presidency were more positive in tone than those of the last three presidents to take office during partisan transfers of power. The findings reveal a revival of the media honeymoon that scholars thought had disappeared during the modern era of a more combative press. An investigation of the “beat sweetening” hypothesis reveals mixed results, suggesting the need for further investigation

News Coverage of New Presidents in \u3ci\u3eThe New York Times\u3c/i\u3e, 1981-2009

Content analysis of front-page The New York Times stories during the first year of the Barack Obama presidency revealed news coverage that was far more positive in tone than that received during the first year of the Ronald Reagan, Bill Clinton, and George W. Bush presidencies. Overall, the Obama findings reveal a media honeymoon in that influential newspaper, a sharp contrast from first-year coverage of other presidents during the modern era of a more combative press. The positive policy coverage Obama received in the Times was also significantly more positive than on evening newscasts of network television and on Fox News’ Special Report

Network Television’s Coverage of the 2008 Presidential Election

Content analysis of network evening news coverage of the 2008 presidential election revealed a slight increase in the amount of coverage and a decline in the coverage of policy matters compared to 4 years earlier. Barack Obama received the most positive coverage recorded for any major party nominee on network television since the Center for Media and Public Affairs started analyzing election news content in 1988. The tonal gap between the Democratic and Republican nominees was also the largest recorded over the past six presidential elections. The one-sided coverage on ABC, CBS, and NBC was in sharp contrast to the more uniformly negative coverage of the two candidates during the evening newscasts on Fox News

Partisan Targets of Media Fact-checking: Examining President Obama and the 113th Congress

An analysis of statements by President Obama and by Democratic and Republican members of Congress selected for analysis by PolitiFact.com and Washington Post Fact Checker reveals that PolitiFact was more likely to find greater deceit in Republican rhetoric and that the Fact Checker was more negative overall in its assessments. Legislators who had more than one statement analyzed during the study period were disproportionally likely to be influential members of the House or Senate leadership or likely 2016 presidential candidates. The lawmakers selected for greater scrutiny were also more likely to be more ideologically extreme than the median members of their party caucuses

Viscous Cross-waves: An Analytical Treatment

Viscous effects on the excitation of cross‐waves in a semi‐infinite box of finite depth and width are considered. A formalism using matched asymptotic expansions and an improved method of computing the solvability condition is used to derive the relative contributions of the free‐surface, sidewall, bottom, and wavemaker viscous boundary layers. This analysis yields an expression for the damping coefficient previously incorporated on heuristic grounds. In addition, three new contributions are found: a viscous detuning of the resonant frequency, a slow spatial variation in the coupling to the progressive wave, and a viscous correction to the wavemaker boundary condition. The wavemaker boundary condition breaks the symmetry of the linear neutral stability curve at leading order for many geometries of experimental interest