Experimental testing of tape springs folded in three dimensions

One of the main drivers in satellite design is the minimization of mass, in the attempt to reduce the large costs involved in the launch of the spacecraft. However, the recent advances in micro electro mechanical systems (MEMS) have allowed a further reduction in the mass of on-board equipment. With advances in micro ion propulsion systems for attitude control, and the miniaturisation of ground based mobile communications, the satellite power requirement does not reduce linearly with mass. This creates the need for photovoltaic cell areas larger than the surface area of the satellite bus. Therefore small satellite deployable structures become increasingly important. The major design requirements for such systems are reliability and low cost. The simpler the components of the system are (i.e. the minimum number of moving parts, lubrication etc), the more chance of the system meeting the design requirements. For this reason, there has been significant investigation into the deployment dynamics of tape springs folded in two dimensions, to form simple hinges which do not require lubrication and automatically locks in the deployed configuration. The present work focuses on using tapes springs to support a new conceptual area deployment design for nano/micro satellites. The deployment of this design incorporates bi-axial folding, which requires the tape springs to unfold in three dimensions. Little research has been carried out in this area. The design of a test rig to determine the properties of this three dimensional deployment is presented in detail. This rig measures both the bending and twisting moments produced from the three- dimensional fold. The combination of these two moments defines the main deployment properties of the tape springs and hence the final array. The experimental results will be compared to theoretical results produced using shell theory and non- linear, finite element analysis

A study of joint damping in metal plates

For satellite applications the determination of the correct dynamic behaviour and in particular the structural damping is important to assess the vibration environment for the spacecraft subsystems and ultimately their capability to withstand the launch vibration environment. Therefore, the object of this investigation is to experimentally analyse a range of aluminium panel configurations to study the effect of joints on the damping of the complete structure. The paper begins with a full description of the experimental method used to accurately determine the modal loss factors for each of the panel configurations analysed. Nine different panels were used in the experimental tests, six of which incorporate lap joints variations. The joint parameters investigated include fastener type, bolt torque, fastener spacing, overlap distance and the effect of stiffeners. The damping results of ten different joint variants are presented for each of the first twelve modes of vibration. This data is directly compared to the damping factors of an equivalent monolithic panel. Various specific conclusions are made with respect to each of the joint parameters investigated. However, the primary conclusion is that the mode shape combined with the joint stiffness and joint location can be suggestive as to the likely magnitude increase of the modal loss factor

Low frequency damping of metal panels in ambient Air

Mathematical models of structural dynamics are widely used and applied in many branches of science and engineering and it has been argued that many of the shortfalls with these models are due to the fact that the physics of joint dynamics are not properly represented. Experimental analyses are therefore widely used to underpin any work in this area. The most renowned model for predicting the damping resulting from air pumping is based on a significant quantity of experimental data and was generally developed and applied to high frequency vibrations of jointed or stiffened panels. This publication applies this model to low frequency panel vibrations, assessing the accuracy of the model for these systems. It is concluded that the theoretical model for high stiffness joints, although generally over approximating the damping magnitude, gives a good conservative estimate of the increase in damping due to air pumping for low frequency vibrations

Development of inflatable structures at the University of Southampton

Inflatable technology for space applications is under continual development and advances in high strength fibres and rigidizable materials have pushed the limitations of these structures. This has lead to their application in deploying large-aperture antennas, reflectors and solar sails. However, many significant advantages can be achieved by combining inflatable structures with structural stiffeners such as tape springs. These advantages include control of the deployment path of the structure while it is inflating (a past weakness of inflatable structure designs), an increased stiffness of the structure once deployed and a reduction in the required inflation volume. Such structures have been previously constructed at the Jet Propulsion Laboratory focusing on large scale booms. However, due to the high efficiency of these designs they are also appealing to small satellite systems. This article outlines ongoing research work performed at the University of Southampton into the field of small satellite hybrid inflatable structures. Inflatable booms have been constructed and combined with tape spring reinforcements to create simple hybrid structures. These structures have been subjected to bending tests and compared directly to an equivalent inflatable tube without tape spring reinforcement. This enables the stiffness benefits to be determined with respect to the added mass of the tape springs. The paper presents these results, which leads to an initial performance assessment of these structures

A study of tape spring fold curvature for space deployable structures

Tape springs, defined as thin metallic strips with an initially curved cross section, are an attractive structural solution and hinge mechanism for small satellite deployable structures due to their low mass, low cost and general simplicity. They have previously been used to deploy booms and array panels in various configurations that incorporate a two dimensional deployment of the tape. However, applications currently exist that incorporate three dimensional tape springs folds. To accurately model the deployment of an appendage mounted with tape spring hinges, it is necessary to accurately model the opening moments produced from the material strains in the tape spring fold. These moments are primarily a function of curvature. This publication uses a photographic method to analyse the curvature assumptions of two dimensional tape spring folds and to define the curvature trends for three dimensional tape spring folds as a basis for calculating the opening moment. It is found that although a variation in the curvature can be seen for three dimensional tape spring folds, its effect is secondary to the tape thickness tolerance. Therefore constant curvature models are concluded to be accurate enough for general tape fold applications

A study into the dynamics of three dimensional tape spring folds

One of the most significant drivers in satellite design is the minimization of mass, in the attempt to reduce the large costs involved in the launch. With technological advances across many fields it is now widely known that very low mass satellites can perform a wide variety of missions. However, the satellite power requirement does not reduce linearly with mass, creating the need for efficient and reliable small satellite deployable structures. One structural solution for this application is tape springs. Tape springs have been previously studied by many countries for space applications focusing on two dimensional systems. This work studies the possible impact of using tape springs folded in three dimensions. By initially analytically determining the static moments created, simple deployment models can be constructed for tape springs in free space. By determining the impact of these moments about an array fold line, a dynamic model of an array can be created which is directly comparable to the two dimensional system. The impact of the three dimensional fold can then be determined