13,675 research outputs found

    STR: a student developed star tracker for the ESA-LED ESMO moon mission

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    In the frame of their engineering degree, ISAE’s students are developing a Star Tracker, with the aim of being the core attitude estimation equipment of the European Moon Student Orbiter. This development goes on since several years and is currently in phase B. We intend to start building an integrated breadboard for the end of the academic year. The STR is composed of several sub-systems: the optical and detection sub-system, the electronics, the mechanics and the software. The optical detection part is based on an in-house developed new generation of APS detectors. The optical train is made of several lenses enclosed in a titanium tube. The electronics includes a FPGA for the pre-processing of the image and a microcontroller in order to manage the high level functions of the instrument. The mechanical part includes the electronics box, as well as the sensor baffle. The design is optimized to minimize the thermo-elastic noise of the assembly. Embedded on ESMO platform, this Star Tracker will be able to compute the satellite‘s attitude, taking into account the specific requirements linked to a Moon mission (illumination, radiation requirements and baffle adaptation to lunar orbit). In order to validate the design, software end-to-end simulation will include a complete simulation of the STR in its lunar dynamic environment. Therefore, we are developing a simple orbital model for the mission (including potential dazzling by celestial bodies)

    Explaining heterogeneity in utility functions by individual differences in decision modes

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    The curvature of utility functions varies between people. We suggest that there is a relationship between individual differences in preferred decision mode (intuition vs. deliberation) and the curvature of the individual utility function. If a person habitually prefers a deliberative mode, the utility function should be nearly linear, while it should be curved when a person prefers the intuitive mode. In this study the utility functions of the subjects were assessed using a lottery-based elicitation method and related to a measurement of the habitual mode preference for intuition and deliberation. Results confirm that people who prefer the deliberative mode have a utility function that is more linear than for people who prefer the intuitive mode. Our findings indicate a stronger affective bias of subjective values in intuitive than deliberate decision makers. While deliberative decision makers may have rather used the stated values, intuitive decision makers may have additionally integrated affective reactions towards the stimuli into the decision.

    Explaining heterogeneity in utility functions by individual differences in preferred decision modes

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    The curvature of utility functions varies between people. We suggest that there exists a relationship between the mode in which a person usually makes a decision and the curvature of the individual utility function. In a deliberate decision mode, a decision-maker tends to have a nearly linear utility function. In an intuitive decision mode, the utility function is more curved. In our experiment the utility function is assessed with a lottery-based utility elicitation method and related to a measure that assesses the habitual preference for intuition and deliberation (Betsch, submitted). Results confirm that for people that habitually use the deliberate decision mode, the utility function is more linear than for people that habitually use the intuitive decision mode. The finding and its implications for the research on individual decision behavior in economics and psychology are discussed.

    Onboard utilization of ground control points for image correction. Volume 1: Executive summary

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    Operation of a navigation system, centered around image correction, was simulated and the system performance was analyzed. Onboard utilization of ground control points for image correction is summarized. Simulation results, and recommendations for future mission requirements are presented

    Precision Pointing Control System (PPCS) system design and analysis

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    The precision pointing control system (PPCS) is an integrated system for precision attitude determination and orientation of gimbaled experiment platforms. The PPCS concept configures the system to perform orientation of up to six independent gimbaled experiment platforms to design goal accuracy of 0.001 degrees, and to operate in conjunction with a three-axis stabilized earth-oriented spacecraft in orbits ranging from low altitude (200-2500 n.m., sun synchronous) to 24 hour geosynchronous, with a design goal life of 3 to 5 years. The system comprises two complementary functions: (1) attitude determination where the attitude of a defined set of body-fixed reference axes is determined relative to a known set of reference axes fixed in inertial space; and (2) pointing control where gimbal orientation is controlled, open-loop (without use of payload error/feedback) with respect to a defined set of body-fixed reference axes to produce pointing to a desired target

    Concepts for on-board satellite image registration, volume 1

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    The NASA-NEEDS program goals present a requirement for on-board signal processing to achieve user-compatible, information-adaptive data acquisition. One very specific area of interest is the preprocessing required to register imaging sensor data which have been distorted by anomalies in subsatellite-point position and/or attitude control. The concepts and considerations involved in using state-of-the-art positioning systems such as the Global Positioning System (GPS) in concert with state-of-the-art attitude stabilization and/or determination systems to provide the required registration accuracy are discussed with emphasis on assessing the accuracy to which a given image picture element can be located and identified, determining those algorithms required to augment the registration procedure and evaluating the technology impact on performing these procedures on-board the satellite

    On universality in aging ferromagnets

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    This work is a contribution to the study of universality in out-of-equilibrium lattice models undergoing a second-order phase transition at equilibrium. The experimental protocol that we have chosen is the following: the system is prepared in its high-temperature phase and then quenched at the critical temperature TcT_c. We investigated by mean of Monte Carlo simulations two quantities that are believed to take universal values: the exponent λ/z\lambda/z obtained from the decay of autocorrelation functions and the asymptotic value XX_\infty of the fluctuation-dissipation ratio X(t,s)X(t,s). This protocol was applied to the Ising model, the 3-state clock model and the 4-state Potts model on square, triangular and honeycomb lattices and to the Ashkin-Teller model at the point belonging at equilibrium to the 3-state Potts model universality class and to a multispin Ising model and the Baxter-Wu model both belonging to the 4-state Potts model universality class at equilibrium.Comment: 17 page

    Autonomous flight and remote site landing guidance research for helicopters

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    Automated low-altitude flight and landing in remote areas within a civilian environment are investigated, where initial cost, ongoing maintenance costs, and system productivity are important considerations. An approach has been taken which has: (1) utilized those technologies developed for military applications which are directly transferable to a civilian mission; (2) exploited and developed technology areas where new methods or concepts are required; and (3) undertaken research with the potential to lead to innovative methods or concepts required to achieve a manual and fully automatic remote area low-altitude and landing capability. The project has resulted in a definition of system operational concept that includes a sensor subsystem, a sensor fusion/feature extraction capability, and a guidance and control law concept. These subsystem concepts have been developed to sufficient depth to enable further exploration within the NASA simulation environment, and to support programs leading to the flight test

    An introduction to the interim digital SAR processor and the characteristics of the associated Seasat SAR imagery

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    Basic engineering data regarding the Interim Digital SAR Processor (IDP) and the digitally correlated Seasat synthetic aperature radar (SAR) imagery are presented. The correlation function and IDP hardware/software configuration are described, and a preliminary performance assessment presented. The geometric and radiometric characteristics, with special emphasis on those peculiar to the IDP produced imagery, are described

    A Parametric Analysis of Prospect Theory's Functionals for the General Population

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    This paper presents the results of an experiment that completely measures the utility function and probability weighting function for different positive and negative monetary outcomes, using a representative sample of N = 1935 from the general public. The results confirm earlier findings in the lab, suggesting that utility is less pronounced than what is found in classical measurements where expected utility is assumed. Utility for losses is found to be convex, consistent with diminishing sensitivity, and the obtained loss aversion coefficient of 1.6 is moderate but in agreement with contemporary evidence. The estimated probability weighing functions have an inverse-S shape and they imply pessimism in both domains. These results show that probability weighting is also an important phenomenon in the general population. Women and lower educated individuals are found to be more risk averse, in agreement with common findings. Unlike previous studies that ascribed gender differences in risk attitudes solely to differences in the degree utility curvature, however, our results show that this finding is primarily driven by loss aversion and, for women, also by a more pessimistic psychological response towards the probability of obtaining the best possible outcome.loss aversion, utility for gains and losses, prospect theory, subjective probability weighting
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