Session: 02-06-01: Structural Dynamics and Control of Aerospace Structures

Paper Number: 138370

138370 - Modal Sensitivity Analysis of Self-Deployable Tape-Spring Booms for Cubesats 

The need for using extendable booms to deploy payloads, solar sails and antennas is ever increasing. Their inclusion in future space missions can provide a viable alternative to massive truss-like structures as well as significantly reduce fuel mass requirements for attitude control systems. However, there is a significant knowledge gap in terms of the effect that these deployments have on the chassis of the satellite. As the size of deployable structures increases, this information becomes even more important. Ut ProSat-1 (UPS-1), a 3U cubesat, led by a student team from Virginia Tech, aims to passively self-deploy a parabolic tape-spring boom on orbit. This boom has an inertial measurement unit (IMU) on a flexible circuit at its tip and another one near its root inside the chassis. These two IMUs together will measure the frequency response of the structure in terms of the transverse acceleration due to the deployment of the boom. It also has embedded copper wires inside the composite that run along the length of the boom. These transfer data and power to and from the boom-tip. 

It is to be noted that these booms are complex structural systems with a non-linear response. They are also highly sensitive to geometry defects and density variations introduced during curing. Here, we study the geometric sensitivity of the modal response of the boom using a finite element (FE) approach. Although the cured tape spring has a constant parabolic cross section, the deployed boom has a variable cross section due to its root conditions inside the deployer. This variable cross section comprises an infinite number of parabolic splines. We measured the actual 4-ft long boom specimen at 5 cm intervals, starting from the root to the tip. The base width and height of the parabolas were noted and used to create profiles in Solidworks. Then, the solid loft feature was used to create a continuous boom CAD model from these profiles. To perform the sensitivity analysis, we created several low fidelity FE models with varying numbers of parabolic splines to define the cross section of the boom.  Mechanical properties and total mass of the composite layup were kept constant. Furthermore, a handheld 3D laser scanner was used to capture the exact surface geometry in the form of a point cloud. A shell surface was fitted on this cloud and modal analysis was performed on it in Abaqus. The differences in the computational cost and accuracy were noted for the approximate models and this point-cloud model. Finally, this was compared to the modal analysis of this boom using the PSV-400 scanning laser vibrometer. We suspended the boom vertically downwards by fixing the deployer system to a rigid stand and the laser was directed perpendicular to the boom axis. The velocity and force response of the boom was measured at different locations along the boom by hitting it with an impulse hammer. This data was used to plot the frequency response functions giving us the mode shapes and the natural frequencies of the boom. Therefore, the dynamics of the fully deployed boom was studied on the ground and this data will be compared with the data we obtain on-orbit. 

Presenting Author: Deven Mhadgut Virginia Tech

Presenting Author Biography: Deven is a PhD student at Virginia Tech working with Prof. Jonathan Black and Dr. Austin Phoenix. He has previously obtained an MS in Aerospace Engineering at the University of Colorado, Boulder. His current work involves study of experimental dynamic characterization of thin composite booms for space applications.