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  • 1
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    Vapour Phase Conversion of Glycerol to Acrolein over Supported Copper (2012)
    Springer
    Details
    Publication Date: 2012-11-24
    Print ISSN: 1319-8025
    Electronic ISSN: 2191-4281
    Topics: Natural Sciences in General , Technology
    Published by Springer
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    PAPER CURRENT
  • 2
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    Affordable Care Act and healthcare delivery: A comparison of California and Florida hospitals and emergency departments (2017)
    Public Library of Science
    Details
    Publication Date: 2017-08-03
    Electronic ISSN: 1932-6203
    Topics: Medicine , Natural Sciences in General
    Published by Public Library of Science
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    PAPER CURRENT
  • 3
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    Quadratic Programming for Allocating Control Effort (2005)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A computer program calculates an optimal allocation of control effort in a system that includes redundant control actuators. The program implements an iterative (but otherwise single-stage) algorithm of the quadratic-programming type. In general, in the quadratic-programming problem, one seeks the values of a set of variables that minimize a quadratic cost function, subject to a set of linear equality and inequality constraints. In this program, the cost function combines control effort (typically quantified in terms of energy or fuel consumed) and control residuals (differences between commanded and sensed values of variables to be controlled). In comparison with prior control-allocation software, this program offers approximately equal accuracy but much greater computational efficiency. In addition, this program offers flexibility, robustness to actuation failures, and a capability for selective enforcement of control requirements. The computational efficiency of this program makes it suitable for such complex, real-time applications as controlling redundant aircraft actuators or redundant spacecraft thrusters. The program is written in the C language for execution in a UNIX operating system.
    Keywords: Man/System Technology and Life Support
    Type: NPO-40592 , NASA Tech Briefs, August 2005; 13
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Alternative Attitude Commanding and Control for Precise Spacecraft Landing (2004)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A report proposes an alternative method of control for precision landing on a remote planet. In the traditional method, the attitude of a spacecraft is required to track a commanded translational acceleration vector, which is generated at each time step by solving a two-point boundary value problem. No requirement of continuity is imposed on the acceleration. The translational acceleration does not necessarily vary smoothly. Tracking of a non-smooth acceleration causes the vehicle attitude to exhibit undesirable transients and poor pointing stability behavior. In the alternative method, the two-point boundary value problem is not solved at each time step. A smooth reference position profile is computed. The profile is recomputed only when the control errors get sufficiently large. The nominal attitude is still required to track the smooth reference acceleration command. A steering logic is proposed that controls the position and velocity errors about the reference profile by perturbing the attitude slightly about the nominal attitude. The overall pointing behavior is therefore smooth, greatly reducing the degree of pointing instability.
    Keywords: Astrodynamics
    Type: NPO-40585 , NASA Tech Briefs, December 2004; 27
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    Attitude and Translation Control of a Solar Sail Vehicle (2008)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A report discusses the ability to control the attitude and translation degrees-of-freedom of a solar sail vehicle by changing its center of gravity. A movement of the spacecraft s center of mass causes solar-pressure force to apply a torque to the vehicle. At the compact core of the solar-sail vehicle lies the spacecraft bus which is a large fraction of the total vehicle mass. In this concept, the bus is attached to the spacecraft by two single degree-of-freedom linear tracks. This allows relative movement of the bus in the sail plane. At the null position, the resulting solar pressure applies no torque to the vehicle. But any deviation of the bus from the null creates an offset between the spacecraft center of mass and center of solar radiation pressure, resulting in a solar-pressure torque on the vehicle which changes the vehicle attitude. Two of the three vehicle degrees of freedom can be actively controlled in this manner. The third, the roll about the sunline, requires a low-authority vane/propulsive subsystem. Translation control of the vehicle is achieved by directing the solar-pressure-induced force in the proper inertial direction. This requires attitude control. Attitude and translation degrees-of-freedom are therefore coupled. A guidance law is proposed, which allows the vehicle to stationkeep at an appropriate point on the inertially-rotating Sun-Earth line. Power requirements for moving the bus are minimal. Extensive software simulations have been performed to demonstrate the feasibility of this concept.
    Keywords: Technology Utilization and Surface Transportation
    Type: NPO-44129 , NASA Tech Briefs, May 2008; 35
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 6
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    Powered Flight Design and Reconstructed Performance Summary for the Mars Science Laboratory Mission (2013)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The Powered Flight segment of Mars Science Laboratory's (MSL) Entry, Descent, and Landing (EDL) system extends from backshell separation through landing. This segment is responsible for removing the final 0.1% of the kinetic energy dissipated during EDL and culminating with the successful touchdown of the rover on the surface of Mars. Many challenges exist in the Powered Flight segment: extraction of Powered Descent Vehicle from the backshell, performing a 300m divert maneuver to avoid the backshell and parachute, slowing the descent from 85 m/s to 0.75 m/s and successfully lowering the rover on a 7.5m bridle beneath the rocket-powered Descent Stage and gently placing it on the surface using the Sky Crane Maneuver. Finally, the nearly-spent Descent Stage must execute a Flyaway maneuver to ensure surface impact a safe distance from the Rover. This paper provides an overview of the powered flight design, key features, and event timeline. It also summarizes Curiosity's as flown performance on the night of August 5th as reconstructed by the flight team.
    Keywords: Spacecraft Design, Testing and Performance; Lunar and Planetary Science and Exploration
    Type: AAS 13-424 , AAS/AIAA Spaceflight Mechanics Meeting; Feb 10, 2013 - Feb 14, 2013; Kauai, HI; United States
    Format: text
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    NASA TECHNICAL REPORTS
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