Computer Science – Performance
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.568h&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Performance
Scientific paper
To verify that the International Space Station (ISS) payload facility racks do not disturb the microgravity environment of neighboring facility racks during any ISS microgravity period, a control integration process must be followed. Currently no facility racks have taken this process from start to finish. The authors are assisting the NASA Glenn Research Center (GRC) Fluids Combustion Facility (FCF) in this process. The major topics to be addressed in this paper are: 1) ISS Program Microgravity Requirements, 2) Rack Microgravity Control Approaches, 3) Integration Process Flow, 4) Required ISS Program Inputs, 5) Facility Analytical Work, 6) Facility Testing Work, 7) Facility Output to ISS Program, and 8) Verification &Validation Process. The ISS payload microgravity requirements are given in PIRN 110H to the ISS Program document SSP 57000. These requirements are based on being a "good neighbor" by limiting the payload disturbances on the environment of adjacent rack payloads during ISS microgravity periods. The ARIS PIRN, which is still pending ISS Program approval, addresses onboard rack disturbances being transmitted to offboard locations and specific ARIS items such as rack sway space and accelerometer saturation. To meet the facilities' microgravity requirements, various active or passive isolation approaches can be utilized. These include the Active Rack Isolation System (ARIS), the Passive Rack Isolation System (PaRIS), damping material inserted into the four external ARIS snubber cups, or local isolation at the individual onboard rack disturbers. ARIS utilizes a controller specifically tuned for the facility and eight pushrods, which will coordinate the racks movement in the low frequency range (.01 Hz to 2 Hz). PaRIS utilizes eight spring / dampers to isolate the rack from the ISS module structure at frequencies above 0.5 Hz. Local onboard rack isolation approaches involve the use of damping materials, isolation grommets, or wire rope isolators for substantial disturbers located within the rack. The assessment of the microgravity levels at various points in the rack requires the use of several analytical tools and models. An on-orbit NASTRAN model of an International Standard Payload Rack (ISPR) is required to accurately model the facility payload rack. Care must be exercised to accurately model both disturber locations and critical science locations. MATLAB Simulink is utilized to determine transfer functions at specific locations in the rack. Offboard rack disturbances are obtained from the 1999 ISS Program Non-Isolated Rack Assessment (NIRA99) predictions for assessment of sway space and ARIS accelerometer saturation. Onboard rack disturbances are input into the Simulink model from either an ISS Program library of typical disturbers or from Microgravity Emission Laboratory (MEL) data for the actual disturber. The ISS module to rack umbilicals are included in the models. Umbilical NASTRAN models or stiffness test data needs to be provided from the ISS Program. These umbilicals are major elements in determining the payload facility rack microgravity performance. Once the facility payload rack and disturbers are properly modeled, an assessment can be made as to whether the ISS Program microgravity levels are achieved. The predicted levels can then be verified by additional ground testing of either a subrack assembly or a facility rack, which can be further verified by on-orbit acceleration measurements.
Grodsinsky Carlos M.
Heese J.
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