S.J.I. Walker

Study of the Dynamics of Three-Dimensional Tape Spring Folds

One of the most significant drivers in satellite design is the minimization of mass 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 possible structural solution for this application is tape springs. Tape springs have been previously studied in 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 first analytically determining the static moments created, simple deployment models can be constructed for tape springs in free space. Then, determining the impact of these moments about an array fold line allows the creation of a dynamic model of an array that is directly comparable to the two-dimensional system. The impact of the three-dimensional fold can then be determined.

Experimental Investigation of Tape Springs Folded in Three Dimensions

One of the most significant drivers in satellite design is the minimization of mass 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, there is a need for small, efficient, area deployment devices. One possible structural solution for such devices is tape springs. Previous work on tape spring hinges has focused on two-dimensional folds; however, applications exist that incorporate three-dimensional tape spring folds. The properties of three-dimensional tape spring folds are experimentally investigated using a specially designed test rig. The rig is first used to produce comparative two-dimensional data before being used to analyze more complex three-dimensional folds.

A study of tape spring fold curvature for space deployable structures

Abstract 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 because of 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.

Aerostat for electrical power generation -concept feasibility

The current paper examines the feasibility of using a high altitude tethered aerostat as a platform for producing a substantial quantity of electric energy and transmitting it to Earth using the mooring cable. Based on realistic values for the relevant engineering parameters that describe the technical properties of the materials and subsystems, a static analysis of the aerostat in its deployed configuration has been carried out. The results of the computations, although of a preliminary nature, demonstrate that the concept is technically feasible. There are, nevertheless, issues to be addressed to improve the performance. However none of these issues is deemed to negate the technical feasibility of this concept. A test case is investigated in terms of preliminary sizing of the aerostat, including mooring cable and solar cell coverage, and it shows the capability to deliver power to the ground in excess of 95 kW. A brief assessment of the cost has also been carried out to investigate the potential gains offered by this system to produce solar electric energy.

On the use of SEREP for satellite FEM validation

Purpose – The purpose of this paper is to assess the suitability of various methods for the reduction of a large finite element model (FEM) of satellites to produce models to be used for correlation of the FEM with test results. The robustness of the cross‐orthogonality checks (COC) for the correlation process carried out utilizing the reduced model is investigated, showing its dependence on the number of mode shapes used in the reduction process. Finally the paper investigates the improvement in the robustness of the COC that can be achieved utilizing optimality criteria for the selection of the degrees of freedom (DOF) used for the correlation process.Design/methodology/approach – A Monte Carlo approach has been used to simulate inaccuracies in the mode shapes (analysis and experimental) of a satellite FEM that are compared during the COC. The sensitivity of the COC to the parameters utilized during the reduction process, i.e. mode shapes and DOFs, is then assessed for different levels of inaccuracy in ...

Solar Radiation Pressure Hamiltonian Feedback Control for Unstable Libration-Point Orbits

This work investigates a Hamiltonian structure-preserving control that uses the acceleration of solar radiation pressure for the stabilization of unstable periodic orbits in the circular restricted...

Experimental analysis of damping across joints in metal plates

In the current world of engineering, structural vibration problems continue impact the design and construction of a wide range of products. Amid the parameters that determine the dynamic behaviour of a structure the one that takes into account the dissipation of energy resulting in the decay of the vibration is the least understood and the most difficult to quantify [1]. The estimation of damping factors is of interest in most branches of engineering sciences. In the field of aircraft structures the damping directly affects the fatigue life, a parameter which is applied conservatively due to the inherent complexity in modelling the damping of built up structures and the potentially catastrophic consequences of a fatigue failure. One of the most important problems is the limited knowledge of how joints affect the damping of the complete structure. This work therefore addresses this issue and focuses on the damping of joints in metal plates as part of a larger project to investigate the damping of built up structures. Various plate configurations are experimentally investigated using two different approaches. The results from the configurations are compared and discussed along with the advantages and disadvantages of each experimental approach. This enables a link to be identified between the damping magnitudes and the mode shapes and joint stiffnesses.

Guidance, Navigation, and Control for the Eddy Brake Method

Existing active debris removal methods that require physical contact with the target have applicability limitations depending on the maximum angular momentum that can be absorbed. Therefore, a detumbling phase before the capturing phase may be necessary. The aim of this paper is to study the guidance, navigation, and control subsystem of the “eddy brake,” which is an active contactless detumbling method based on the generation of eddy currents. The paper first presents this method and the main requirements for the control module, as well as the necessary sensors for pose estimation on board the chaser. Furthermore, the linear and rotational dynamics based on the magnetic tensor theory are explained in order to model the chaser–target interactions. In addition, the set of three-dimensional nonlinear dynamical equations that model the detumbling process are formulated including a specific control strategy, with possible inaccuracies and delays derived from the onboard sensors and actuators. Moreover, a stab...

Use of multiple SMA wires for morphing of inflatable wings

The concept of inflatable wings has design heritage and they have recently seen renewed interest, largely due to the increased demand in unmanned aerial vehicles (UAVs). They offer design advantages over conventional wings, particularly with regard to stowage and portability, since they can be tightly packed when undeployed. Unfortunately current methods of flight control involve the use of additional control surfaces attached to the trailing edge of the wing, adversely affecting the stowage capabilities. One way of overcoming this restriction is to use the wing itself as a control surface, by morphing the very shape of the wing to achieve the desired results. This article outlines the research performed at the University of Southampton into differing configurations of Shape Memory Alloy (SMA) wires as a controllable actuator for the wing morphing. Specifically the use of multiple wires to further enhance this control was the focus of this work. A simple test rig was constructed in order to evaluate the pulling force achievable by combinations of SMA wires in a number of configurations. The most promising of these configurations was then attached to an inflatable wing model for further testing. Both static testing and wind tunnel testing was undertaken, evaluating the authority of flight control such a system could achieve. The test results are presented in this paper, giving an initial performance assessment of the proposed control method

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 by 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.