Control/structure interactions of Freedom's solar dynamic modules

Solar Dynamic Modules for Space Station Freedom: The Relationship Between Fine-Pointing Control and Thermal Loading of the Aperture Plate: Part I—Analysis

“…Graphite segment in-plane thermal stresses were calculated assuming the segment was free of surface traction forces and that temperature varied only through the thickness of the segment. These are fairly good assumptions as long as: (1) the graphite segments have compliant supports and are free to expand differentially from the HA 188 plate, (2) no diffusion bonding occurs between the graphite segments and the HA 188 plate, and (3) the concentrated solar image remains well focused, i.e., for mispointing angles less than about 1.0°, which validates the use of one-dimensional aperture plate thermal modeling. From [121, the in-plane (IP) or lateral thermal stresses in the bulk material, subject to the aforementioned restrictions, are given by:…”

“…The Freedom configuration shown in figure 1 is a multibody dynamical system. Its control systems include space station attitude and reboost controllers and for the outboard truss power modules control systems: (1) an Alpha joint in the truss to permit orbital sun tracking about the y axis (truss longitudinal axis), (2) a Beta joint between each power module and the truss to permit rotation about an axis normal to the truss for seasonal sun tracking, and (3) two axis joints for fine-pointing (FP) the SD concentrator relative to the sun and relative to the receiver aperture. SD pointing requires alignment of the system consisting of the sun, concentrator, and receiver aperture.…”

“…A control approach was developed for multibody space structures like Freedom where both large, rigid-body motions and vibratory motions are controlled using the same hardware [2]. In this way, SD modules can be targeted and fine-pointed while, simultaneously, structural vibrations are damped.…”