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  • Spacecraft Design, Testing and Performance  (6)
  • Polymer and Materials Science  (3)
  • 1
    Electronic Resource
    Electronic Resource
    Comparison of elasticities of components of a cardiac bioprosthesis leaflet (1996)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 30 (1996), S. 47-52 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The mechanoelastic behavior of calf pericardium employed in cardiac bioprostheses was compared with that of three types of thread (Nylon, Prolene, and silk) used to suture this biological tissue. The elastic limit (EL) of each material was determined by means of tensile tests and the mathematical functions that govern the stress/strain curves within the EL have been described. The first derivative of these functions for each point to the curves allowed the immediate calculation of the elastic modulus (EM), which was considered the best parameter for comparing the elasticities of the materials being assessed. It was observed that the deformation of the pericardium produced by the working stress of a pericardial leaflet was approximately 1000 times greater than that produced in the surgical threads. When the elasticities were compared on the basis of the EM, that of pericardium was 749.06, 626.95, and 1253.17 times greater than that of the Nylon, Prolene, and silk suture threads, respectively. These results demonstrate that the interaction between these materials (pericardium and the threads) could be generating detrimental forces that can diminish the durability of the leaflets of the bioprostheses constructed of calf pericardium. © 1996 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Description of the mathematical law that defines the relaxation of bovine pericardium subjected to stress (1994)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 28 (1994), S. 755-760 
    Details
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: A material subjected to traction stress increases in length; if we maintain the elongation constant, the stress varies over a period of time. This phenomenon has been referred to as relaxation. The purpose of this study was to define a mathematical law that relates the variation in stress to time when elongation remains constant in bovine pericardium. The mathematical function obtained after assaying 34 samples to the point of relaxation, subjected to initial stresses ranging from 0.17-10.07 MPa, responds to the following equation: y = -0.0252 + 0.953 α - (0.0165 + 0.015 α)lnt, where γ is the stress withstood at an instant in time, t, after initial stress α. A normogram, validated by assays of up to 6,340 min duration (4.40 days), is presented for graphic calculation, permitting the computation of the loss of stress due to relaxation of this biomaterial, with initial stresses ranging from 1-10 MPa. © 1994 John Wiley & Sons, Inc.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jbm.820280613
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  • 3
    Electronic Resource
    Electronic Resource
    Selection and interaction of biomaterials used in the construction of cardiac bioprostheses (1998)
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 39 (1998), S. 568-574 
    Details
    ISSN: 0021-9304
    Keywords: biomaterial ; bioprostheses ; suture ; pericardium ; heart valves ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The mechanical behavior of calf pericardium employed in the manufacture of cardiac bioprostheses was assessed according to the region from which it was selected. For this purpose, selected samples of the tissue were sewn with different types of commercially available sutures and subjected to tensile testing, the results of which were compared with the findings in selected, but not sutured, tissue used as a control. The results confirm a loss of resistance - that is, a reduction of the capacity of sutured samples of the biomaterial to withstand breakage stress compared with control samples. Taking into account the marked resistance to breakage of the suture thread, this phenomenon can only be explained as a consequence of the deleterious mechanical interaction between the suture and chemically treated pericardium. This interaction is illustrated by the shearing force which is responsible for the loss of resistance in the tested samples. These trials demonstrate that the results can be improved and the deleterious interaction diminished, although not eliminated, when the pericardium is selected from a given region. © 1998 John Wiley & Sons, Inc. J Biomed Mater Res, 39, 568-574, 1998.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 4
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    Attitude Controller for the Atmospheric Entry of the Mars Science Laboratory (2008)
    In:  Other Sources
    Details
    Publication Date: 2019-08-24
    Description: This paper describes the attitude controller for the atmospheric entry of the Mars Science Laboratory (MSL). The controller will command 8 RCS thrusters to control the 3- axis attitude of the entry capsule. The Entry Controller is formulated as three independent channels in the control frame, which is nominally aligned with the stability frame. Each channel has a feedfoward and a feedback path. The feedforward path enables fast response to large bank commands. The feedback path stabilizes the vehicle angle of attack and sideslip around its trim position, and tracks bank commands. The feedback path has a PD/D control structure with deadbands that minimizes fuel usage. The performance of this design is demonstrated via computer simulations.
    Keywords: Spacecraft Design, Testing and Performance
    Type: 2008 AIAA Guidance, Navigation and Control Conference and Exhibit; Aug 18, 2008 - Aug 21, 2008; Honolulu, HI; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 5
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    From Sojourner to Curiosity, the Guidance, Navigation, and Control Challenges of Landing on Mars (2016)
    In:  Other Sources
    Details
    Publication Date: 2020-01-13
    Description: No abstract available
    Keywords: Spacecraft Design, Testing and Performance
    Type: JPL-CL-16-3842 , IFAC Symposium on Automatic Control in Aerospace; Aug 21, 2016 - Aug 25, 2016; Sherbrooke, Quebec; Canada
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  • 6
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    The Intelligent Landing System for Safe and Precise Landing on Europa (2017)
    In:  Other Sources
    Details
    Publication Date: 2019-12-20
    Description: Europa, the smallest of Jupiters Galilean moons, is thought to harbor a vast liquid water ocean beneath its icy crust, making it one of the most scientifically intriguing targets for a robotic surface sampling mission in our Solar System. However, autonomously landing a spacecraft safely and precisely on Europa poses unique challenges, such as very little existing high-resolution reconnaissance imagery, a surface expected to be very rough and hazardous over a wide range of scales, an extremely intense ionizing radiation environment, and very limited lander resources for mass and volume. To address these challenges, we propose a novel Intelligent Landing System (ILS) combining four Guidance, Navigation & Control (GN&C) sensing functions velocimetry, altimetry, map-relative localization, and hazard detection that would together enable safe and precise landing on Europas surface. The ILS is a smart sensor system, combining an inertial measurement unit (IMU), a monocular, passive-optical camera, and a light detection and ranging (Li-DAR) sensor with dedicated computing resources as well as an onboard 3D terrain map. The ILS leverages more than a decade of technology development from programs such as the Lander Vision System, currently baselined on the Mars 2020 mission. This paper provides a detailed description of the proposed ILS architecture and concept of operations, as well as select preliminary simulation results to assess performance and robustness.
    Keywords: Spacecraft Design, Testing and Performance
    Type: JPL-CL-CL#17-0517 , Annual Guidance and Control Conference; Feb 02, 2017 - Feb 08, 2017; Breckenridge, CO; United States
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  • 7
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    Mars Science Laboratory Entry, Descent, and Landing System Overview (2010)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: In 2012, the Mars Science Laboratory (MSL) mission will pioneer the next generation of robotic Entry, Descent, and Landing (EDL) systems by delivering the largest and most capable rover to date to the surface of Mars. In addition to landing more mass than prior missions to Mars, MSL will offer access to regions of Mars that have been previously unreachable. The MSL EDL sequence is a result of a more stringent requirement set than any of its predecessors. Notable among these requirements is landing a 900 kg rover in a landing ellipse much smaller than that of any previous Mars lander. In meeting these requirements, MSL is extending the limits of the EDL technologies qualified by the Mars Viking, Mars Pathfinder, and Mars Exploration Rover missions. Thus, there are many design challenges that must be solved for the mission to be successful. Several pieces of the EDL design are technological firsts, such as guided entry and precision landing on another planet, as well as the entire Sky Crane maneuver. This paper discusses the MSL EDL architecture and discusses some of the challenges faced in delivering an unprecedented rover payload to the surface of Mars.
    Keywords: Spacecraft Design, Testing and Performance
    Type: International Planetary Probe Workshop; Jun 12, 2010; Barcelona; Spain
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  • 8
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    The Mars Science Laboratory EDL Mode Commander (2011)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Spacecraft Design, Testing and Performance
    Type: International Planetary Probe (IPPW-8) Workshop; Jun 06, 2011 - Jun 10, 2011; Norfolk, VA; United States
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  • 9
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    Mars Science Lander GN&C Design for Entry, Descent, and Landing (2011)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: No abstract available
    Keywords: Spacecraft Design, Testing and Performance
    Type: International ESA Conference on Guidance and Navigation Control Systems; Jun 05, 2011 - Jun 10, 2011; Carlsbad; Czechoslovakia
    Format: text
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