Effect of long-term exposure to Low Earth Orbit (LEO) space environment

Data obtained from components and materials from the Solar Maximum Mission satellite are presented and compared to data for similar materials obtained from the Advanced Composite Materials Exposure to Space Experiment (ACOMEX) flown on Shuttle mission STS-41G. In addition to evaluation of surface erosion and mass loss that may be of importance to very long-term missions, comparisons of solar absorptance and thermal emittance measurements for both long and short term exposures were made. Although the ratio of absorptance over emittance can be altered by proper choice of materials to ensure a proper operating environment for the spacecraft, once the thermal design is established, it is important that the material properties not change in order to maintain the operating environment for many payload and bus items such as electronics, batteries, fuel, etc. However, data presented show significant changes after short exposure in low Earth environment. Moreover, the measured changes are shown to differ according to the manner of exposure, i.e., normal or oblique, which also affects the resultant eroded surface morphology. These results identify constraints to be considered in development of flight experiments or laboratory testing

Space environmental effects on polymer matrix composites as a function of sample location on LDEF

This paper presents results on the effect of circumferential location on the variation in solar absorptance (alpha(sub S)) and infrared emittance (epsilon) for five different polymer matrix composites (PMC), and variations in erosion depth due to atomic oxygen (AO) for fourteen different PMC materials. In addition, a chemical content design parameter (gamma) has been found that correlates well with the erosion yield obtained from space flight data and hyperthermal AO tests for hydrocarbon polymeric materials. This parameter defines the ratio of the total number of atoms in a repeat monomer unit to the difference between the total carbon content and the total number of intermolecular oxygen atoms in the same repeat unit

Proposed test program and data base for LDEF polymer matrix composites

A survey of the polymer matrix composite materials that were flown on Long Duration Exposure Facility (LDEF) is presented with particular attention to the effect of circumferential location (alpha) on the measured degradation and property changes. Specifically, it is known that atomic oxygen fluence (AO), VUV radiation dose, and number of impacts by micrometeoroids/debris vary with alpha. Thus, it is possible to assess material degradation and property damage changes with alpha for those materials that are common to three or more locations. Once the alpha-dependence functions were defined, other material samples will provide data that can readily be used to predict damage and property changes as a function of alpha as well. What data can be realistically obtained from these materials, how this data can be obtained, and the scientific/design value of the data to the user community is summarized. Finally, a proposed test plan is presented with recommended characterization methodologies that should be employed by all investigators to ensure consistency in the data base that will result from this exercise

Review of existing numerical methods and validation procedure available for bird strike modelling

Summary This paper reviews numerical methods that are currently available to simulate bird strike as well as the theory of the event. It also summarizes important parameters and provides guidelines as to how to set up the analysis and how to evaluate a model. The information provided is based on physical properties and available results regarding a bird and its behaviour upon impact. The simulations have been performed with LS-DYNA 970 but can be done in similar dynamic finite elements analysis codes

Feasibility Study of the Computer Control of Leaf (ESTEC, Noorwijk, The Netherlands)

NRC publication: Ye

Active Control of Aircraft Cabin Noise

Peer reviewed: YesNRC publication: Ye

A Structural Optimization Program for Wing Flutter

Peer reviewed: YesNRC publication: Ye

Development of the shock simulation methodology for spacecraft components

Spacecraft components encounter mechanical shock from a variety of sources. Components must withstand a series of flight shock pulses and must be designed and tested accordingly to ensure reliability. This paper presents a \u201cDesign for Shock\u201d methodology to accurately analyze the response to shock for components under the short duration dynamic loading to assess component structural integrity and demonstrate design robustness. This methodology uses a more realistic simulation of the response of the component to shock loading using a wave propagation solution based on explicit time integration of the transient shock event rather than a stationary random and (or) quasi-static approach which has been traditionally used for this analysis. This approach was applied to a sensitive scientific instrument to demonstrate its effectiveness. The method is shown to provide a more accurate simulation of the shock event thereby reducing the unknown conservatism of the stationary random and (or) quasi-static approach while providing accurate simulation of the transient dynamic response of the structure.Peer reviewed: YesNRC publication: Ye

Protection of the Radarsat Spacecraft from the Low Earth Orbit Environment

NRC publication: Ye