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  • Polymer and Materials Science  (4)
  • SPACECRAFT DESIGN, TESTING AND PERFORMANCE  (4)
  • 1
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 11 (1967), S. 1289-1297 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new method has been developed for measuring the number of molecules of oxygen required (∊) to cause a main chain scission in peroxide vulcanizates of natural rubber. This method is based on experimentally derived relationships and is not dependent on statistical theories of rubber elasticity. The value ∊ is only slightly temperature dependent, ranging from 28 at 65°C. to 22 at 100°C. The effects of several types of antioxidant have been examined, in all cases ∊ was greatly reduced. The effect of antioxidant 2246 has been studied in more detail and the results indicate that there is a high probability of scission occurring at the termination step in the oxidation chain.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 3091-3099 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Blends of cis-1,4-polybutadiene and natural rubber were vulcanized with dicumyl peroxide and a CBS (N-cyclohexylbenzothiazole-2-sulfenamide) accelerated sulfur system. For the peroxide-cured systems, soft vulcanizates had the natural rubber component only very lightly crosslinked and showed pronounced flow at room temperature. The oxidative stress relaxation of the hard vulcanizates at 80°C. in air was intermediate between that of the pure polymers. Intermittent stress relaxation measurements on these vulcanizates showed pronounced crosslinking during the aging of the pure polybutadiene and the 50/50 blend. Soft blends prepared by the accelerated sulfur system also showed flow due to the lightly crosslinked polybutadiene component. The unextracted hard blends resembled the pure polybutadiene vulcanizate in oxidative stress relaxation behavior at 80°C. in air, whereas after extraction to remove residual antioxidant and vulcanization products, etc., the blends were similar to natural rubber at all levels.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 9 (1965), S. 3101-3109 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of high strain on the oxidative stress relaxation of several natural rubber vulcanizates has been investigated. In the case of peroxide and CBS accelerated vulcanizates, the rate of stress relaxation increases with increasing strain, and this increase appears to be due to an increase in the rate of oxidation of the network. TMTD and MBT vulcanizates showed marked premature failure at high strains and no oxidative stress relaxation measurement could be made. It was found that the tensile strength of a TMTD vulcanizate was at least 20% higher in vacuum than in oxygen, due, it is believed, to stress-induced oxidative degradation at the tip of surface flaws in the rubber.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Applied Polymer Science 11 (1967), S. 2201-2214 
    ISSN: 0021-8995
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The oxidation characteristics of protected and unprotected vulcanizates from natural rubber have been examined. With unpurified rubber (RSS1) in the presence or absence of added antioxidants the rate of oxidation of the vulcanizates is: unaccelerated sulfur 〉 accelerated sulfur 〉 TMTD sulfurless or EV 〉 peroxide. This order is obtained because the sulfur compounds present in the sulfurated vulcanizates are antagonistic towards both natural and added antioxidants. The antagonism is greatest with polysulfides, and when they are present they dominate the aging behavior of vulcanizates.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2013-08-29
    Description: The Comet Rendezvous/Asteroid Flyby (CRAF) and Cassini planetary missions provide exciting pointing and control challenges. The mission and science objectives, and an attitude and articulation control concept designed to meet these challenges, are described. CRAF/Cassini mission characteristics which drive pointing and control include: close range flybys of asteroids and icy satellites; Huygens probe guidance and communication; Saturn orbit insertion; comet rendezvous and orbit insertion; closed loop target tracking from a comet orbit perturbed by gas and dust pressure; fine spacecraft pointing for Titan radar mapping and Earth communications; requirements for autonomous failure detection; isolation; recovery; and 13.5 year lifetime. The philosophy and approach chosen to meet these challenges and the overall control architecture are addressed, including operational and autonomous safe modes. Critical functions are highlighted, such as charge coupled device imaging of stars and extended bodies which provide references for inertial and target referenced pointing respectively. Tradeoffs and rationale for the selection and location of sensors and actuators are reviewed.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: ESA, Spacecraft Guidance, Navigation and Control Systems; p 23-32
    Format: text
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  • 6
    Publication Date: 2011-08-19
    Description: The characteristics of the Mariner Mark II Integrated Platform Pointing and Attitude Control System (IPPACS) microstep actuator with momentum compensation and the IPPACS optical reference tracker are examined, and the advantages of this new technology are identified. The momentum-compensated articulation acts to prevent platform articulation activity from disturbing the spacecaft. This guarantees dynamic stability, ensures a quiescent pointing environment, and decouples the design of the platform from the design of the spacecraft. A microstep actuator with harmonic drive provides platform angular step resolution to 0.5 arcsec for precision pointing of instruments. An optical reference tracker boresighted with scientific instruments guarantees accurate target-referenced closed-loop pointing. An IPPACS star and target tracker with 1 to 10 arcsec accuracy and wide 11 x 17 degrees field of view has been derived from Advanced Star and Target Reference Optical Sensor (ASTROS) CCD star tracker technology, greatly enhancing the optical referencing capabilities of future multimission interplanetary spacecraft.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Format: text
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  • 7
    Publication Date: 2019-06-28
    Description: A study of pointing requirements and control approaches for the Earth Observing System, EOS, is presented. The proposed instrument set includes several massive instruments with varied articulation requirements, and pointing control requirements in several cases tighter than 0.01 degrees. Approaches to multipayload control and stability are explored, including: (a) the use of interconnected but dynamically isolated payload modules on a large platform, each with independent inertial control, and (b) precision basebody control of smaller platforms, with momentum compensated articulation and on-orbit dynamic balancing of spin-scan instruments. Results from multibody spacecraft models highlight potential payload dynamic interaction problems and suggest the need for dynamic isolation and disturbance rejection control techniques.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AAS PAPER 85-436
    Format: text
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  • 8
    Publication Date: 2019-06-28
    Description: Performance testing plans, procedures, and initial results for the Galileo Attitude and Articulation Control Subsystem are described. The objectives of performance testing include test bed comparisons, examining the interactions between spacecraft dynamics and controllers, and verifying the ability to tune control algorithms in flight to meet specific performance requirements. Two primary test beds are described. One, the Integration Test Laboratory, drives actual flight hardware components and support equipment with a real time computer simulation of spacecraft dynamics. The other, the Functional Simulator, is a nonreal time computer simulation with high fidelity spacecraft dynamics, including flexible appendages, fuel slosh, and simulated hardware components. Initial Functional Simulator results are presented which illustrate spacecraft response to open loop spin-up and turn commands. A closed loop sun acquisition turn is also demonstrated. Future tests for verifying performance of attitude determination, spacecraft control, and scan platform pointing functions are outlined.
    Keywords: SPACECRAFT DESIGN, TESTING AND PERFORMANCE
    Type: AAS PAPER 83-323
    Format: text
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