Structural Design of the GN&C Navigation Base for the Space Station Freedomby Lavonia Grant, Honeywell Inc, Largo, United States,
Fred Cutting, Honeywell Inc, Largo, United States,
Abstract: The Space Station Freedom (SSF) pointing accuracy budget requires that the Guidance, Navigation and Control hardware maintain alignment within ± 0.1 degrees of arc. The ring laser gyros (RLG) and the inertial sensor assembly (ISA) maintain the SSF's knowledge of its orientation in inertial space. The Star Tracker (ST) sensors identify star positions to compensate for RLG drift, and a Kalman filter compensates for changes in alignment between the Star Trackers and the RLG. The thermal drift of the Star Tracker orientation with respect to SSF is controlled by the mounting base named the 'Nav Base'. The Nav Base is a plate structure designed to support the ISAs and orient the Star Trackers. No electronic compensation is planned for thermally induced changes in Star Tracker orientation. The budgeted allowance for thermal drift of the Nav Base is ±60 arc sec. The design approach to assess Nav Base thermal distortion is to use the TRASYS thermal radiation model and SINDA thermal analyzer to provide Nav Base temperatures and temperature gradients. The mounting of the Nav Base to the SSF will be through thermal and structural isolation springs. Both sides of the Nav Base will be covered with ten layers of multi-layer insulation (MLI). The objective is to create an adiabatic plate with near zero thermally induced strains. The initial efforts were to determine the order of magnitude of the alignment problems between the ISAs and Star Trackers caused by thermally induced strain.
Subject Headings: Space stations | Tracking | Thermal analysis | Inertia | Probe instruments | Thermal effects | Structural design | Navigation (geomatic)
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