Browsing by Author "Roberts, Peter C. E."
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Item Open Access An aerostable drag-sail device for the deorbit and disposal of sub-tonne, low earth orbit spacecraft(Cranfield University, 2006-10) Harkness, Patrick George; Roberts, Peter C. E.There is an increasing amount of debris in low Earth orbit arising from the disintegration and collision of old spacecraft which have not been removed from orbit. A ‘bolt-on’ deorbit device to be attached to new spacecraft is therefore proposed, which would deploy an aerostable drag sail at end-of-life. This drag sail would interact with the rarefied atmospheric gases and plasma present at altitudes of up to 1,000 km and thus denude energy from the orbit, causing it to become lower and lower until final re-entry of the host becomes inevitable. At this point the drag sail would collapse and both the host and the deorbit device would be destroyed by aerothermodynamic forces. This work develops the deorbit device concept by demonstrating that aerostable drag enhancement is an effective and competitive deorbit mechanism. This is done by: • Calculating the aerodynamic, solar radiation pressure and gravitational influences on the deployed drag sail and using them to model the performance of the device. • Using the results of that modelling to identify the optimum shape, size and deployment conditions of the drag sail. • Further calculating the structural strength required to resist the aerodynamic loads until the desired collapse altitude. • And finally by using that information to assemble a conceptual design which demonstrates the practicability of the system.Item Open Access Computational modelling of aerodynamic disturbances on spacecraft within a concurrent engineering framework(Cranfield University, 2007-09) Graziano, Benjamin P.; Roberts, Peter C. E.This research was motivated by the need to perform an accurate aerodynamic analysis of the drag deorbit device concept under development within the Space Research Centre, Cranfield University. Its purpose is to deorbit satellites from low Earth orbit at the end of the useful lives, in order to help reduce the growing problem of space debris. It has been found that existing spacecraft aerodynamic analysis tools do not adequately support concurrent engineering. Furthermore, use of concurrent engineering in the space industry is currently limited to Phase A (preliminary design studies). To remedy this, the Spacecraft Engineering, Design, and Analysis Tools (SEDAT) Concept has been proposed. Inspired by the approach employed by enterprise applications, it proposes that all the computer tools used on a spacecraft project should be incorporated into one system as separate modules, presented via a single client, and connected to a centralised Relational Database Management System. To demonstrate the concept and assess its potential a SEDAT System and accompanying Free Molecular Flow (FMF) spacecraft aerodynamic analysis module have been developed. The FMF Module is explicitly designed to facilitate concurrent engineering and make use of the maximum variety of Gas-Surface Interaction Models (GSIMs) and their associated data. It also incorporates a new Hybrid method of FMF analysis that combines the Ray-Tracing Panel (RTP) and Test-Particle Monte Carlo (TPMC) methods, enabling it to analyse complex geometries that are subject to surface shielding and multiple molecular reflections. Studies have been performed using a Hybrid version of the Schaaf and Chambre GSIM. One of these studies analysed a drag deorbit device design using a range of accommodation coefficients, including the latest empirically based incidence-dependent coefficients. Based on this analysis, recommendations have been made regarding the material selection and structural design of the device.Item Open Access The Development of high fidelity linearized J2 models for satellite formation flying control(2005-02-16T00:00:00Z) Roberts, Jennifer A.; Roberts, Peter C. E.The inclusion of the linearized J2 effect in the Hill equations of relative motion gives greater insight into satellite formation flying dynamics, and the opportunity to investigate alternative feedback control strategies for the station keeping task. The work of Schweighart and Sedwick is verified and extended as time varying and analytical models are developed to incorporate the J2 perturbation and its effects on the relative motion of two or more satellites in LEO. Analysis is performed in detail to determine the best modelling strategy for satellite formation keeping in the J2 perturbed environment. The analytical J2 model is found to capture relative motion the most accurately, but only given specific initial conditions. The time varying model captures leader-follower motion better than the Hill equation and analytical J2 models. LQR control laws are designed and performance evaluated for the basic Hill equations and the time varying and analytical J2 models using Matlab/Simulink and the Satellite Tool Kit.Item Open Access Manoeuvre Planning Architecture for the Optimisation of Spacecraft Formation Flying Reconfiguration Manoeuvres(Cranfield University, 2010-05) Burgon, Ross; Roberts, Peter C. E.Formation flying of multiple spacecraft collaborating toward the same goal is fast becoming a reality for space mission designers. Often the missions require the spacecraft to perform translational manoeuvres relative to each other to achieve some mission objective. These manoeuvres need to be planned to ensure the safety of the spacecraft in the formation and to optimise fuel management throughout the fleet. In addition to these requirements is it desirable for this manoeuvre planning to occur autonomously within the fleet to reduce operations cost and provide greater planning flexibility for the mission. One such mission that would benefit from this type of manoeuvre planning is the European Space Agency’s DARWIN mission, designed to search for extra-solar Earth-like planets using separated spacecraft interferometry. This thesis presents a Manoeuvre Planning Architecture for the DARWIN mission. The design of the Architecture involves identifying and conceptualising all factors affecting the execution of formation flying manoeuvres at the Sun/Earth libration point L2. A systematic trade-off analysis of these factors is performed and results in a modularised Manoeuvre Planning Architecture for the optimisation of formation flying reconfiguration manoeuvres. The Architecture provides a means for DARWIN to autonomously plan manoeuvres during the reconfiguration mode of the mission. The Architecture consists of a Science Operations Module, a Position Assignment Module, a Trajectory Design Module and a Station-keeping Module that represents a multiple multi-variable optimisation approach to the formation flying manoeuvre planning problem. The manoeuvres are planned to incorporate target selection for maximum science returns, collision avoidance, thruster plume avoidance, manoeuvre duration minimisation and manoeuvre fuel management (including fuel consumption minimisation and formation fuel balancing). With many customisable variables the Architecture can be tuned to give the best performance throughout the mission duration. The implementation of the Architecture highlights the importance of planning formation flying reconfiguration manoeuvres. When compared with a benchmark manoeuvre planning strategy the Architecture demonstrates a performance increase of 27% for manoeuvre scheduling and fuel savings of 40% over a fifty target observation tour. The Architecture designed in this thesis contributes to the field of spacecraft formation flying analysis on various levels. First, the manoeuvre planning is designed at the mission level with considerations for mission operations and station-keeping included in the design. Secondly, the requirements analysis and implementation of Science Operation Module represent a unique insight into the complexity of observation scheduling for exo-planet analysis missions and presents a robust method for autonomously optimising that scheduling. Thirdly, in-depth analyses are performed on DARWIN-based modifications of existing manoeuvre optimisation strategies identifying their strengths and weaknesses and ways to improve them. Finally, though not implemented in this thesis, the design of a Station-keeping Module is provided to add station-keeping optimisation functionality to the Architecture.Item Open Access MUSTANG 2001 Summary of the Group Design Project MSc in Astronautics and Space Engineering 2001/02 Cranfield University(2003-09-18T00:00:00Z) Hobbs, Stephen; Bowling, Tom; Roberts, Peter C. E.MUSTANG (Multi-University Space Technology Advanced Nanosatellite Group) was the group design project for students of the MSc in Astronautics and Space Engineering for the Academic Year 2001/02 at Cranfield University. The project also involved students of Southampton University and Astrium (UK) Ltd. and was supported by BNSC. The project involved the initial design of a nanosatellite to be used as a technology demonstrator for microsystem technology (MST) in space. The project builds on previous work (in 1999/2000 and 2000/01) and is both a critical re-evaluation of the previous work and a development of new design work in specific areas (e.g. electrical subsystem, mechanisms, data handling). By the end of the project, the design has developed to a stage where detailed sub- system design and prototyping / manufacture are the next steps. The goal of launch readiness by 2003/04 is possible, but only achievable with significant extra resources.Item Open Access MUSTANG: A Technology demonstrator for formation flying and distributed systems technologies in space(2005-06-27T00:00:00Z) Roberts, Peter C. E.; Bowling, Tom; Hobbs, StephenFuture astronomical, surveillance and communications concepts are expected to depend heavily upon distributed systems – many satellites flying in formation to form synthesized detector arrays many times the size of each individual spacecraft. Various concepts for these systems are already under development at establishments around the globe. The MUSTANG project is a UK programme funded by the British National Space Centre (BNSC) to demonstrate distributed systems using two nanospacecraft in a low Earth orbit. This will include the demonstration of a variety of formation flying techniques as well as demonstrating various enabling technologies that will facilitate such distributed systems. The use of many small spacecraft in distributed systems greatly increases the potential for the production of large amounts of space debris. Passive end-of-life de-orbit technologies will also be demonstrated to address this probleItem Open Access Spacecraft Flight in the Atmosphere(Cranfield University, 2014-09) Virgili Llop, Josep; Roberts, Peter C. E.Spacecraft that orbit in Low Earth Orbit travel through a tenuous atmosphere and hence experience aerodynamic forces that can become quite significant, specially at low altitudes. The presence of these forces can become a major design driver for missions that fly at very low altitudes. Unfortunately, spacecraft aerodynamics are not well understood. In this dissertation, a CubeSat mission is proposed which will study rarefied-gas aerodynamics, with the objective of determining the effect of surface composition, surface finishing and flow incidence angle on the drag and lift coefficients with an error of less than 5% using a novel method. The CubeSat, has been named ΔDsat, because this study, will be performed using differential measurements of drag and lift coefficients in order to eliminate any measurement bias. ΔDsat carries 4 deployable fins that can rotate independently and expose different surface types to the flow at different incident angles. In addition, in the dissertation four methods to exploit the aerodynamic forces for the missions advantage are proposed and described in detail. The first one is aerostability, which by shaping the spacecraft appropriately, the resulting aerodynamic torques stabilise the attitude spacecraft with respect to the flow. The second method uses aerodynamic drag and lift to change de inclination of a decaying spacecraft in order to maintain the Sun-synchronous aspect of an orbit whilst decaying. The required lift to drag ratio is in the order of 1.0-1.6, which is not currently achievable (it is theoretically possible), but it could be achieved if drag compensating propulsion is used (thus becoming a fuel saving strategy). The third method controls the atmospheric re¬entry interface (the location of the burn-up) by modulating the drag, hence controlling the decay profile. When applied to ΔDsat an error of less than 200 km 3cr on the re-entry location is achieved. Finally, aerostable spacecraft can be used to perform in-situ measurements of the atmospheric winds, by observing their attitude evolution. The aerostable ΔDsat CubeSat would be capable of determining the cross-track winds with an error of less 4 m/s 3cr.