Hybrid sliding mode control for motorised space tether spin-up when coupled with axial oscillation

A specialised hybrid controller is applied for the control of motorised space tether spin-up coupled with an axial oscillation phenomenon. A six degree of freedom dynamic model of a motorised momentum exchange tether is used as the basis for interplanetary payload exchange in the context of control. The tether comprises a symmetrical double payload configuration, with an outrigger counter inertia and massive central facility. It is shown that including axial elasticity permits an enhanced level of performance prediction accuracy and a useful departure from the usual rigid body representations, particularly for accurate payload positioning at strategic points. A simulation with a given initial condition data has been devised in a connecting programme between control code written in MATLAB and dynamics simulation code constructed within MATHEMATICA. It is shown that there is an enhanced level of spin-up control for the six degree of freedom motorised momentum exchange tether system using the specialised hybrid controller

Multi-objective optimisation on motorized momentum exchange tether for payload orbital transfer

The symmetrical motorised momentum exchange tether, is intended to be excited by a continuous torque, so that, it can be applied as an orbital transfer system. The motor drive accelerates the tether, and increases the relative velocity of payloads fitted to each end. In order to access better tether performance, a higher efficiency index needs to be achieved. Meanwhile, the stress in each tether sub-span should stay within the stress limitations. The multi-objective optimisation methods of Genetic Algorithms can be applied for tether performance enhancement. The tether's efficiency index and stress are used as multi-objectives, and the analysis of the resulting Pareto front suggests a set of solutions for the parameters of the motorised momentum exchange tether when used for payload transfer, in order to achieve relative high transfer performance, and safe tether strength

Editor's Note : Erratum: Structural damage detection based on the reconstructed phase space for reinforced concrete slab by Zhenhua Nie, Hong Hao, Hongwei Ma (Journal of Sound and Vibration (2013) 332 (1061-1078))

This notice is placed against the above paper at the request of the Editor-in-Chief

Enhanced vibrational energy harvesting using non-linear stochastic resonance

Stochastic resonance has seen wide application in the physical sciences as a tool to understand weak signal amplification by noise. However, this apparently counter- intuitive phenomenon does not appear to have been exploited as a tool to enhance vibrational energy harvesting. In this note we demonstrate that by adding a periodic excitation to a damped energy harvesting mechanism, the power available from the device is apparently enhanced over a conventional unexcited mechanism. A simple model of such a device is proposed and investigated to explore the use of stochastic resonance to enhance vibrational energy harvesting

The Mechanics of Motorised Momentum Exchange Tethers when applied to Active Debris Removal from LEO

The concept of momentum exchange when applied to space tethers for propulsion is well established, and a considerable body of literature now exists on the on-orbit modelling, the dynamics, and also the control of a large range of tether system applications. The authors consider here a new application for the Motorised Momentum Exchange Tether by highlighting three key stages of development leading to a conceptualisation that can subsequently be developed into a technology for Active Debris Removal. The paper starts with a study of the on-orbit mechanics of a full sized motorised tether in which it is shown that a laden and therefore highly massasymmetrical tether can still be forced to spin, and certainly to librate, thereby confirming its possible usefulness for active debris removal (ADR). The second part of the paper concentrates on the modelling of the centripetal deployment of a symmetrical MMET in order to get it initialized for debris removal operations, and the third and final part of the paper provides an entry into scale modelling for low cost mission design and testing. It is shown that the motorised momentum exchange tether offers a potential solution to the removal of large pieces of orbital debris, and that dynamic methodologies can be implemented to in order to optimise the emergent design

The Mechanics of Motorised Momentum Exchange Tethers when applied to Active Debris Removal from LEO

The concept of momentum exchange when applied to space tethers for propulsion is well established, and a considerable body of literature now exists on the on-orbit modelling, the dynamics, and also the control of a large range of tether system applications. The authors consider here a new application for the Motorised Momentum Exchange Tether by highlighting three key stages of development leading to a conceptualisation that can subsequently be developed into a technology for Active Debris Removal. The paper starts with a study of the on-orbit mechanics of a full sized motorised tether in which it is shown that a laden and therefore highly massasymmetrical tether can still be forced to spin, and certainly to librate, thereby confirming its possible usefulness for active debris removal (ADR). The second part of the paper concentrates on the modelling of the centripetal deployment of a symmetrical MMET in order to get it initialized for debris removal operations, and the third and final part of the paper provides an entry into scale modelling for low cost mission design and testing. It is shown that the motorised momentum exchange tether offers a potential solution to the removal of large pieces of orbital debris, and that dynamic methodologies can be implemented to in order to optimise the emergent design

The Suaineadh Project : a stepping stone towards the deployment of large flexible structures in space

The Suaineadh project aims at testing the controlled deployment and stabilization of space web. The deployment system is based on a simple yet ingenious control of the centrifugal force that will pull each of the four daughters sections apart. The four daughters are attached onto the four corners of a square web, and will be released from their initial stowed configuration attached to a central hub. Enclosed in the central hub is a specifically designed spinning reaction wheel that controls the rotational speed with a closed loop control fed by measurements from an onboard inertial measurement sensor. Five other such sensors located within the web and central hub provide information on the surface curvature of the web, and progression of the deployment. Suaineadh is currently at an advanced stage of development: all the components are manufactured with the subsystems integrated and are presently awaiting full integration and testing. This paper will present the current status of the Suaineadh project and the results of the most recent set of tests. In particular, the paper will cover the overall mechanical design of the system, the electrical and sensor assemblies, the communication and power systems and the spinning wheel with its control system

The design of a buoyancy module testing facility

The work reported in this paper details the design of a facility for the water permeability testing of subsea drill-string riser buoyancy modules. The facility has been built and commissioned and is unique in the UK The only other test facility of this sort exists at the South Western Research Institute at San Antonio in Texas, USA. Buoyancy modules are used to reduce the effective weight of a subsea drill-string riser so as to avoid buckling and vibration problems in service. This weight reduction increases the natural frequencies of the riser well above typical frequencies of excitation as a result of drilling. The geometry of the modules depends on the particular riser design but generally approximates to a long, semi-circular section, sleeve which is clamped round the length of the riser. Many modules are used in service to surround the whole length of the riser from the sea bed to the surface. Individual module lengths vary but tend to be around the 5 m mark. The most important module performance characteristics are the effective buoyancy force in water and the ability of the module to resist water ingress at the high hydrostatic pressures encountered in deep water. These pressures can reach up to 345 bar in the deepest water, and are therefore potentially capable of forcing water into the material of the module. The concept behind the testing facility is a computerized data logging system that detects and computes minute weight changes in sample sections of the buoyancy riser module due to the ingress of sea water at very high hydrostatic pressures. The system simulates the hydrostatic conditions found in deep water, and provides a specific printout of pressure and buoyancy quantities over test periods of up to 100 hours; the format of the printout is to the standard generally required by industry. The work was carried out in recognition of the need for a UK facility which would enable manufacturers of the module material, and also customers purchasing the modules, to have confidence that the required buoyancy performance of the modules can be maintained under typical subsea conditions—without necessarily incurring the very high costs of testing in the US