Motion control of free-floating variable geometry truss. I - Kinematics

A variable geometry truss is representative of adaptive structures, whose shape can be intentionally altered through shortening or lengthening its adjustable length members, and so has gained some applications in space engineering including space robots, payload isolation, and so on. A new application of variable geometry trusses is proposed, where variable geometry trusses, as components of some larger space structure, might be expected to construct themselves through their adaptivity. Unlike applications such as space manipulators where a variable geometry truss is considered to be fixed on some platform, in this case a variable geometry truss is free floating in three-dimensional space. To this end, the approach on controlling the motion of a free-floating variable geometry truss is discussed from the standpoint of kinematics. Through taking into account the conservation of momentum of the structural system, a family of compact equations is provided to describe the geometry and motion of freefloating variable geometry trusses. Based on the centroid displacement vector d of a variable geometry truss bay, a group of pseudolinear equations for determining the geometry shape of a free-floating variable geometry truss is obtained. With a simple representation for the angular velocity of a variable geometry truss bay, obtained here, the orientation control for the bay's working plane is made possible. Finally, a simulation is performed to demonstrate the validity of the derived equations.