Browsing by Author "Hobbs, Stephen E."

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    A concurrent engineering framework to explore the servicer-client relationship in on-orbit servicing.
    (2018-12) Matos De Carvalho, Tiago; Kingston, Jennifer; Hobbs, Stephen E.
    The implementation of On-Orbit Servicing (OOS) in the development and operation of space systems has been pursued to enable inspection, maintenance, repair and assembly of systems in space. Performing such tasks robotically involves the consideration of two sides, a Servicer satellite performing the necessary tasks and a Client satellite receiving it. A critical point for a realistic consideration of OOS demands the concurrent approach of both sides. Despite the current interests towards OOS, there is still a gap in the research into the relationship of Client and Servicer. This research aims to develop and demonstrate a methodology to technically incorporate On-Orbit Servicing, at a system-level, to the mission design process and operation of current and new satellites. The first objective deals with the systematic arrangement of the current available knowledge. A top-down approach is used to provide a taxonomy of servicing, followed by the functional decomposition of the main tasks. This objective clarifies the main issues observed today in OOS, directly related to the Client-Servicer relationship. The second objective is to establish the proposed framework. Agent Based Modelling and Simulation is used to implement the main guidelines and concept of operation, and to output different metrics to allow users (Servicers and/or Clients) to evaluate the attractiveness of various OOS scenarios. The mathematical background for the different metrics is defined and discussed. This is complemented by a solution exploration feature for specific types of OOS. A set of cases is presented based on current interests of operators, providing coverage of potential scenarios to use the framework. The proposed objectives are met, achieving the main research aim. The results help to illustrate the effects of servicing in the systems design and operation. Features of the framework expand the capacity to identify potentially attractive conditions for both sides. Such characteristics are not observed in the current published research and represent a powerful tool to be employed at early stages of design and procurement.
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    G-CLASS: geosynchronous radar for water cycle science - orbit selection and system design
    (IET, 2019-11-28) Hobbs, Stephen E.; Guarnieri, Andrea Monti; Broquetas, Antoni; Calvet, Jean-Christophe; Casagli, Nicola; Chini, Marco; Ferretti, Rossella; Nagler, Thomas; Pierdicca, Nazzareno; Prudhomme, Christel; Wadge, Geoff
    The mission geosynchronous – continental land atmosphere sensing system (G-CLASS) is designed to study the diurnal water cycle, using geosynchronous radar. Although the water cycle is vital to human society, processes on timescales less than a day are very poorly observed from space. G-CLASS, using C-band geosynchronous radar, could transform this. Its science objectives address intense storms and high resolution weather prediction, and significant diurnal processes such as snow melt and soil moisture change, with societal impacts including agriculture, water resource management, flooding, and landslides. Secondary objectives relate to ground motion observations for earthquake, volcano, and subsidence monitoring. The orbit chosen for G-CLASS is designed to avoid the geosynchronous protected region and enables integration times of minutes to an hour to achieve resolutions down to ∼20 m. Geosynchronous orbit (GEO) enables high temporal resolution imaging (up to several images per hour), rapid response, and very flexible imaging modes which can provide much improved coverage at low latitudes. The G-CLASS system design is based on a standard small geosynchronous satellite and meets the requirements of ESA's Earth Explorer 10 call.
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    Geosynchronous continental land-atmosphere sensing system (g-class): persistent radar imaging for earth science
    (IEEE, 2018-11-05) Hobbs, Stephen E.; Monti-Guarnieri, A.
    More frequent imaging of Earth system processes is recognised as one of the emerging needs in Earth observation. Conventional low Earth orbit satellites are limited in their ability to provide this, whereas satellites in geosynchronous orbit can in principle provide continuous imaging. A new mission de- sign has been developed from studies for a previous geosynchronous radar mission concept (GeoSTARe) to improve its technical feasibility and geographical coverage, and to rein- force its science focus. This new mission (Geosynchronous - Continental Land Atmosphere Sensing System (G-CLASS)) is presented. G-CLASS is in fact a family of missions: we present a version focussed on the diurnal water cycle - G-CLASS:H2O - for which geosynchronous radar has great potential. G-CLASS:H2O is being developed as a proposal for ESA’s Earth Explorer programme.
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    Insar measurements at high latitudes.
    (2014-10) Andra Baduge, Anura Terance Wickramanayake; Hobbs, Stephen E.
    This thesis contributes towards understanding of Interferometric Synthetic Aperture Radar (InSAR) measurements at high latitudes. Luossavaara-Kiirunavaara Aktiebolag (LKAB) mining company, the sponsor of this Ph.D. research, intends to use the InSAR techniques for subsidence measurements around the Kiruna underground iron ore mine. The Kiruna underground iron ore mine is located in direct proximity to the city of Kiruna, with the active mining area currently about 1 km west of the city center (67°51'20" N, 20°13'30 E). At present LKAB is exploring the possibility of using InSAR measurements as an operational technique for subsidence measurements. High latitudes InSAR measurements are known to be particularly affected by long periods of ground snow cover that contributes to temporal de-correlation between subsequent radar images. The objectives of this Ph.D. research are (1) to quantify the seasonal effects in InSAR measurements and (2) to identify techniques to improve the high latitude InSAR measurements. In this research study, spatial coherence was used to quantify the seasonal effects in the Differential InSAR (DInSAR) measurements for Kiruna region. A comparison between Static Global Positioning System (Static-GPS) and Corner Reflector InSAR (CRInSAR) measurements were carried out to quantify the seasonal effects in CRInSAR measurements. Spatial ground deformation patterns were used to improve the DInSAR measurements. A theoretical analysis for compact active transponders (CAT) was carried out to improve the North-South InSAR measurements. DInSAR, CRInSAR and Coherent Target Monitoring (CTM) techniques were used to evaluate the applicability of InSAR techniques for high latitude mining induce deformation measurements. The results show seasonal variations in DInSAR, CTM and CRInSAR measurements. Furthermore, DInSAR measurements around the Kiruna iron ore mine can be improved up to sub-centimeter accuracies by using the spatial ground deformation patterns. Also, the compact active transponders identi ed as a possible candidate to improve the accuracy of the North-South InSAR measurements. It is concluded that, all InSAR techniques (DInSAR, CTM and CRInSAR) were affected by the winter snow condition, and only the summer (snow-free) months are suitable for ground deformation measurements. Moreover, the study shows that without the winter images still it is possible to achieve accurate CTM and CRInSAR time series estimations for Kiruna. The East-West vector is the least noisy deformation vector, and both East-West and vertical vectors can be used to determine the LKAB environmental criterion. At present, every year, LKAB is acquiring 45 Radarsat-2 images from three beam modes. However, this study shows that less than 35% of those data are useful for subsidence measurements.
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    Machine vision and scientific imaging for autonomous air vehicles (UAV).
    (Cranfield University, 2008-08) Jameson, Pierre-Daniel; Cooke, Alastair K.; Hobbs, Stephen E.
    This thesis outlines the necessary requirements to determine an Unmanned Aerial Vehicles (UAV’s) pose relative to a lead aircraft or target, thus enabling a UAV to successfully follow a lead aircraft or target. The use of Machine Vision for Autonomous navigation has been investigated and two flight scenarios were chosen for analysis. Firstly, following a manoeuvring lead aircraft, and secondly, maintaining a steady heading behind a target/lead aircraft (as would be required for in-flight refuelling). In addition, the author has performed a literature review of current research in this field which is significantly dominated by eventual military requirements in order to improve UAV endurance. In addition, experimental work towards developing a passive vision based navigation system has been undertaken. It is hoped that after further research and development this will lead to an eventual flight trial using the flight dynamics department’s UAV’s. The experimental work has been performed using both equipment and software already available within the department and furthermore, it has enabled an analysis of the department’s currently available capabilities for passive visual navigation to be undertaken. Key points for further work have been outlined for the future advancement of the visual navigation project.
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    Multi-fidelity modelling of low-energy trajectories for space mission design.
    (2019-03) Neves, Rita; Sanchez Cuartielles, Joan Pau; Hobbs, Stephen E.
    The proposal of increasingly complex and innovative space endeavours poses growing demands for mission designers. In order to meet the established requirements and constraints while maintaining a low fuel cost, the use of low-energy trajectories is particularly interesting. These paths in space allow spacecraft to change orbits and move with little to no fuel, but they are computed using motion models of a higher fidelity than the commonly used two-body problem. For this purpose, perturbation methods that explore the third-body effect are especially attractive, since they can accurately convey the system dynamics of a three-body configuration with a lower computational cost, by employing mapping techniques or exploring analytical approximations. The focus of this work is to broaden the knowledge of low-energy trajectories by developing new mathematical tools to assist in mission design applications. In particular, novel models of motion based on the third-body effect are conceived and classified by the forces they account for (conservative or non-conservative). The necessary numerical tools to complement the trajectory design are developed: this includes differential correction methods and targeting schemes, which take advantage of the Jacobian matrices derived from the presented models to generate full low-thrust control laws. One application of this analysis focuses on the trajectory design for missions to near- Earth asteroids. Two different projects are explored: one is based on the preliminary design of separate rendezvous and capture missions to the invariant manifolds of libration point L₂. This is achieved by studying two specific, recently discovered bodies and determining dates, fuel cost and final control history for each trajectory. The other covers a larger study on asteroid capture missions, where several asteroids are regarded as potential targets. The candidates are considered using a multi-fidelity design framework. Its purpose is to filter through the trajectory options using models of motion of increasing accuracy, so that a final refined, low-thrust solution is obtained. The trajectory design hinges on harnessing Earth’s gravity by exploiting encounters outside its sphere of influence, the named Earth-resonant encounters. An additional application explored in this investigation is the search and computation of periodic orbits for different planetary systems, following the current interest for missions involving distant retrograde and prograde orbits. In summary, this thesis presents four novel methods to model the third-body perturbation, distinct in their suitability for applications from real-time computations to long-term orbital predictions. These, together with the additionally developed tools for trajectory design, are applied in two asteroid mission cases. The developed Earth-resonant encounters allow for a very large increase in retrievable mass with respect to the state-of-the-art, namely for the cases of six near-Earth asteroids presented.
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    Towards in-orbit hyperspectral imaging of space debris
    (2023-01-26) Hobbs, Stephen E.; Felicetti, Leonard; Leslie, Cameron; Rowling, Samuel; Brydon, George; Dhesi, Mekhi; Harris, Toby; Chermak, Lounis; Soori, Umair
    Satellites are vulnerable to space debris larger than ~1 cm, but much of this debris cannot be tracked from the ground. In-orbit detection and tracking of debris is one solution to this problem. We present some steps towards achieving this, and in particular to use hyperspectral imaging to maximise the information obtained. We present current work related to hyperspectral in-orbit imaging of space debris in three areas: scenario evaluation, a reflectance database, and an image simulator. Example results are presented. Hyperspectral imaging has the potential to provide valuable additional information, such as assessments of spacecraft or debris condition and even spectral “finger-printing” of material types or use (e.g. propellant contamination). These project components are being merged to assess mission opportunities and to develop enhanced data processing methods to improve knowledge and understanding of the orbital environment.