High-Fidelity Gravity Offloading System for Free-Free Vibration Testing

Abstract

Proposed for the high performance vibration testing of free-flying systems is the Marionette paradigm, a mechanically simple passive gravity compensation scheme characterized by low mass, little interference with specimen response, high imperfection tolerance, and compatibility with up to medium scale specimen kinematics. An introduction to this concept, theory, features, and some practicalities, is offered. The need for and the potential of system optimization are discussed and illustrated. Possible means to generalize the basic concept to adaptive specimen geometries or to the simulation of nonuniform inertial conditions are also discussed. Hardware and numerical illustrations are presented. Nomenclature d = diameter dz = vertical displacement E, = Young's modulus and Poisson's ratio e = fulcrum offset e x , e z = fulcrum offset components in directions x, z h = fly beam arm tip vertical displacement K = geometric nonlinear stiffness against beam tilt L = fly beam span: the distance between arm endpoints M = moment m = mass m= direct mass overhead support structure mass/mass supported r = fly beam arm length S, S i = load tree top and anchor point forces W, w = weight = fly beam arm ratio r 1 =r 2 = density (specific mass) = Force ratio: ratio of fly beam arm loads S 1 =S 2 Subscripts 1, 2 = association with one or the other fly beam arm

Deployment Simulations of Inflatable Tensegrity Structures

“…Air pressure can be removed by testing in vacuum chambers, but they limit the size of the spacecraft to be tested. Gravity effects can be diminished for stiff structures by stateof-the-art gravity compensation systems, [13], but is next to impossible to remove for ultra lightweight and very flexible systems, such as a tensegrity during deployment. Thus, the only remaining option to analyse the deployment behaviour in space is through numerical simulations.…”

Architecture for in-space robotic assembly of a modular space telescope

“…25 Ground-based testing of large deployable structures prior to flight is also complicated by the difficulty of gravity offload. 26 Linearly deploying structures have been demonstrated on a length scale appropriate to large telescopes. The Folding Articulated Square Truss Mast (FASTMast) has been used to deploy the 35-m long solar array wings of the ISS, 27 and the able deployable articulated mast was used to deploy the Shuttle Radar Topography Mission instrument to a distance of 60 m 28 and the NuSTAR optical package to a distance of 10 m. 29 Two-dimensional deployment at this length scale has been demonstrated for membrane and mesh surfaces but not for precision truss structures as required by optical reflectors.…”

Deployment Dynamics of Foldable Thin Shell Space Structures

“…5(a). To avoid the resulting in-plane forces, nested fly beams have been proposed, creating a "marionette"-like suspension [37]. However, this approach is better suited for small displacement experiments, such as vibration testing.…”