Thomas W. Murphey

Design and analysis of a meter-class CubeSat boom with a motor-less deployment by bi-stable tape springs

The increasing demand for greater CubeSat mission capabilities has led to the need for more complex deployable mechanisms within the limited packaged volume. This paper presents a meter-class deployable boom featuring a single burn wire release mechanism and motor-less deployment actuation by the stored strain energy of bi-stable tape springs. Bi-stable tape springs are rolled about two independently rotating central hubs, where the unique and controlled release of strain energy unrolls the hubs and drives boom deployment linearly outward with a nearly constant torque. At the end of deployment, the tape springs lock-out to remove the deployment degree of freedom from the structure while providing structural sti ness, derived from the two inwardly facing and o set bi-stable tape springs, spanning from end to end. The presented device has stowed dimensions measuring 5.0cm by 3.8cm by 3.8cm, well within the packaging requirements of a 1-U CubeSat. The mechanical design and deployment properties are investigated and presented.

Synchronous Deployed Solar Sail Subsystem Design Concept

A solar sail concept has been developed from a common spiral fold pattern in order to enable a simultaneous mast and sail deployment. This novel concept utilizes the stored strain energy in a series of elastic spar members to enforce proper folding kinematics rather than relying on bulky mechanical joints. The critical inner and outer spar networks are secured to four elastically extendible masts anchored to a central drum. Deployment of the solar sail system is actuated by rotating the central drum around which the masts, spars, and film are wrapped. Tensioned radial cords deterministically unfold the membrane film under the authority of the resilient, spring-like spar members. Proper elastic behavior of the spars is an important facet to this design, and thus a significant effort was dedicated their development. This compact ground demonstration concept includes about 7.5 m 2 of reflective membrane film for useful propulsion. Features of this robust, lightweight membrane structure may prove valuable to reducing mass and increasing deployment reliability of other planar subsystems such as sun shades, solar arrays, radiators, or antenna arrays.

Large Deformation Bending of Thin Composite Tape Spring Laminates

The bending stiffness of a thin carbon and glass fiber composite tape spring for deployable space structures was measured and compared to analytical predictions. Testing consisted of subjecting the laminate to bending in a large deformation four point bending test fixture. Bending stiffnesses in the D11 and D22 directions as well as failure curvatures were measured. Coupons failed in a fiber tensile mode at a bending strain of 2.2%. Modified micromechanics and classical lamination theory analysis were used to predict laminate stiffness properties. Test results were 10% less than predicted values.

Development of an Elastically Deployable Boom for Tensioned Planar Structures

This paper reports on the design, analysis and testing of a new elastically deployable boom. The boom is designed such that it flattens and elastically stows around a circular hub. Using finite element analyses, a design trade was performed to determine the boom geometry that maximizes bending stiffness. Predictions of the boom’s bending and torsional stiffness and strength were also made using the finite element model. Mechanical tests of a 0.610 m boom segment were conducted to measure these properties as well. The bending stiffness test results were consistent with the finite element analysis, showing a 3.8% and 6.5% difference in stiffness about the soft axis and stiff axis, respectively. The bending buckling loads and modes shapes corresponded to those predicted by the nonlinear finite element analysis.

Deployable Trusses Based on Large Rotation Flexure Hinges

Formulations for the strength, stiffness, mass efficiency, and packaging of deployable trusses using flexure hinges are developed and comparedwith the experimentwithin. The equations are based on classical buckling theory, Euler buckling with engineering approximations, and finite element-based models to predict the column and bending strengths of solid rod and tubular trusses with slender flexure hinges. Flexure hinge material performance metrics are derived and used to show that, while bothmass efficient trusses of solid rods and trusses of tubes are feasible with existing materials, trusses of solid rods are significantly more strain limited. A representative high compaction ratio deployable truss with pultruded carbon fiber reinforced plastic rods and super elastic nickel-titanium alloy flexure hinges was fabricated and tested. The compressive strength of the truss was 48% less than predicted and the compressive stiffness of the truss was 12% less than predicted.

Large Strain Behavior of Thin Unidirectional Composite Flexures

The large strain flexure of 0.135 mm, 0.259 mm and 0.383 mm thick unidirectional carbon fiber reinforced epoxy plates was investigated. Coupons were folded in a U-shape and compressed between parallel platens while platen separation and load were measured up to failure. The test was modeling numerically using a geometrically nonlinear elastica solution method in combination with a two parameter nonlinear elastic material constitutive model based on graphite crystallite reorientation. Using a curve fitting method, the test data was used to estimate model parameters. Test results show a nonlinear material response resulting in bending stiffness softening as curvature increases. Bending failure strains were larger than expected and increased as coupon thickness decreased, ranging from 2.15% to 2.75%. Also unexpected, the failure occurred in a tensile mode on the outside coupon surface, not in a compressive mode. The results indicate thin flexures can be used at strains and curvatures larger than previously thought.

Development of Deployable Elastic Composite Shape Memory Alloy Reinforced (DECSMAR) Structures

*& The objective of this research is to develop a novel. self-deployable truss architecture composed of carbon fiber reinforced plastic (CFRP) tape-spring elements and embedded shape memory alloy (SMA) flexures; this particular structural system is referred to as deployable elastic composite shape memory alloy reinforced (DECSMAR) and is representative of a concentrated, material deformation based deployable architecture. The scope of this study encompasses applying fundamental principles of rational boom design relevant to all deployable structures, first to define the design space of the individual CFRP tape-spring element, then to conduct an exercise for a point design of a 180 mm radius DECSMAR boom with correlation to experimental analysis, and finally to explore performance implications of scaling the truss radius. Of particular interest was the design of the CFRP tape-spring element elastic-stability and stiffness properties, then to understand how load-path allocation between the frame-like longerons and battens and tension only diagonals proportions energy imparted from global loading through the structural network; thermal response was not investigated. Characterizing the enhancement the SMA flexure features purchase and design issues for package envelop optimization are pertinent to both individual CFRP tape-spring element and system wide design and are discussed throughout. Aspects of the architecture for tackle to further develop DECSMAR, including the selfdeployment scheme, will be focused on in a sequel manuscript to appear. Technology addressed through this research is intended to foster and mature successive large, launchpackaged concentrated strain structures.

Design and Testing of Self-Deploying Membrane Optic Support Structure Using Rollable Composite Tape Springs

The detail mechanical design of a freely-deploying support structure that positions and tensions a membrane primary optic was presented. Rollable composite tape spring members were the main components of the structure that provided the deployment force, controlled the deployment kinematics, and reacted the membrane tension load at full deployment. A simple constraint mechanism locks each tape spring hub in the stowed configuration, and simultaneously releases each hub for deployment. The detailed design and analysis of the self-deployable tape spring mechanism shows that the system provides the necessary deployment force and buckling resistance with margin. A prototype unit was fabricated and deployment tests performed. The deployment tests successfully demonstrate a new architecture based on rolled and freely deployed composite tape spring members that achieves simultaneous deployment in three dimensions without mechanical synchronization.

Experimental and Numerical Identification of a Monolithic Articulated Concentrated Strain Elastic Structure's (MACSES's) Properties

Abstract : The objective of this research is to identify the effective continuum properties of a recently developed, deployable hierarchical truss architecture composed of carbon fiber reinforced plastic (CFRP) tubes and CFRP tape-spring hinge elements with embedded shape memory alloy (SMA) flexures; this particular structural system is referred to as monolithic articulated concentrated strain elastic structure (MACSES) and is representative of a concentrated, material deformation based deployable architecture. The scope of this study encompasses numerically and experimentally identifying the deployed stiffness and strength performance, i.e., bending, shear, torsion, and axial moduli with corresponding critical loads, of a 540 mm radius boom. Bending modulus to linear mass ratio was measured at 145 kNm3kg-1. Of particular interest were the sensitivity of joint composition to global properties and the acceptability of discontinuous load-paths. Developmental aspects of the MACSES architecture, including the concept at the individual element level, the packaging kinematics design, and evaluation and scaling the global performance of the system are reported in a preceding manuscript.

Experimental and Numerical Analysis of a DECSMAR Structure's Deployment and Deployed Performance

Abstract : The objective of this research is to analyze the deployment and deployed performance of a recently developed, self-deployable truss architecture composed of carbon fiber reinforced plastic (CFRP) tape-spring elements and embedded shape memory alloy (SMA) flexures; this particular structural system is referred to as deployable elastic composite shape memory alloy reinforced (DECSMAR) and is representative of a concentrated, material deformation based deployable architecture. The scope of this study encompasses numerically and experimentally mapping the force profile through the deployment path of a 450 mm radius DECSMAR boom and then to numerically determine the effective continuum, deployed stiffness and strength properties, i.e., bending, shear, torsion, and axial moduli with corresponding critical loads, correlated to experimental analysis, of an equivalent radius, five-bay DECSMAR boom. Minimum deployment force to linear mass and bending modulus to linear mass ratios were measured at 2.79 Nmkg-1 and 2.38 MNm3kg-1, respectively. Of particular interest were deleterious effects of the deployment sequencer on the force profile, the deployed performance attributable to the SMA flexure features, and consequences of flattening longeron ends to buy packaging efficiency. Developmental aspects of the DECSMAR architecture, including the design space of the individual CFRP tape-spring element, an exercise for a point design of a 180 mm radius DECSMAR boom with correlation to experimental analysis, and performance implications of scaling the truss radius, are focused on in a prequel manuscript.