CERES :: Browsing by Author "Bowling, Tom"

Browsing by Author "Bowling, Tom"

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Open Access
An assessment of the autonomous integrity monitoring performance of a combined GPS/Galileo Satellite Navigation System, and its impact on the case for the development of Galileo
(Cranfield University, 2004-03) Loizou, John; Bowling, Tom
In 1999 Europe, through the European Commission and the European Space Agency, began detailed definition of a second generation Global Navigation Satellite System (GNSS). This GNSS development programme, known as “Galileo”, was intended to both complement and compete against the existing US Global Positioning System (GPS). Unlike GPS, Galileo is intended to be privately financed, following the initial development investment from the EC and ESA, which implies that Galileo should provide some revenue-earning services. From its earliest inception, the basis of these services has been assumed to be through the provision of Signal Integrity through an Integrity Flag broadcast through the Galileo system– a service which GPS cannot provide without some external system augmentation. This thesis undertakes a critical evaluation of the value of this integrity system in Galileo. This thesis has two parts. The first demonstrates that the conditions required to attract adequate private finance to the Galileo programme are incompatible with the system architecture derived from the early Galileo system studies and taken forward into the system early deployment phase, which includes an Integrity system within Galileo. The second part of this thesis aims to demonstrate that receivers which can combine the signals from GPS and Galileo may offer a free Integrity service which meet the needs of the majority of users, possibly up to the standards required for aviation precision approach. A novel Receiver Autonomous Integrity Monitoring (RAIM) technique is described, using an Errors in Variables/Total Least Squares approach to the detection of inconsistencies in an over-determined set of GNSS signal measurements. The mathematical basis for this technique is presented, along with results which compare the simulated performance of receivers using this algorithm against the expected performance of Galileo’s internal integrity determination system.
Open Access
Control of colocated geostationary satellites
(Cranfield University, 1996-10) Hardacre, S.; Bowling, Tom
Control of the inter-satellite distances within a cluster of colocated satellites located in the same GEO window is examined with regards to the close approaches between pairs of satellites. Firstly, the orbital evolution and station keeping control of a single GEO satellite is examined and a new IBM PC based software program capable of performing both these functions autonomously from initial values of the orbital position and date is detailed and validated. Cluster design ideas are then examined in detail and the propagation software is used to generate data for a cluster of four satellites. Two test cases are examined to quantify the frequency of close approaches between individual satellite pairs, each test case using a different orbital element separation strategy but the same station keeping control scheme. The results of the study are then compared with previous research and discussions are presented on the advantages of each method. Finally, a cluster geometry correction manoeuvre, based on Hill's equations of relative motion, is presented which requires only those thrusters used by typical station keeping. This manoeuvre is integrated into the computer software and the two test cases noted previously are again propagated and the close approach results analysed to demonstrate the reduction in the number of close approaches below 5 km.
Open Access
Debris mitigation in geostationary earth orbit
(Cranfield University; School of Engineering, 2004-12-18T11:04:06Z) Todd, Laura; Bowling, Tom
The Inter-Agency Debris Committee recommendation for the reorbiting of geostationary satellites at the end of life involves an altitude increase of no more than 300km for most operational satellites. Although this reduces the collision probability in the geostationary ring itself, it does not remove the possibility of fragmentation debris produced in the reorbital region from passing into the geostationary ring. Unless the satellites are reorbited to a higher altitude than the current recommendations, the debris problem will continue to escalate to an unmanageable level. Due to mass and fuel budgets there are a limited number of available propulsive options, which can achieve the necessary reorbit. The research focus selected has been solar sails and this paper describes ongoing research for the reorbit of geostationary satellites using this method.
Open Access
Design and user applications of a low-cost satellite constellation for global daily imaging revisit
(Cranfield University, 2004-03) Boland, Lee; Bowling, Tom; Lane, Robin
There are many varied sources of satellite Earth Observation and Remote Sensing data currently in-orbit. However, in general there is a distinct lack of rapid-response data for timely application. This is particularly of value in disaster situations where the value of information rapidly falls as time progresses after the event. Micro-satellite constellations, with their low-cost and low launch costs provide a potential affordable solution to the issue of data timeliness. This researchp roject, supportedb y Surrey Satellite Technology Limited, addressesth e problem of data timeliness through the development of a solution for a micro-satellite constellation to give global daily imaging revisit opportunities at a Ground Sample Distance of 30-40m in Red, Green and Near Infra-Red bands. This thesis reviews existing Earth Observation capabilities to highlight the niche that exists for this mission. It then describes the development of the mission and spacecraft system solution as well as ground segment characteristics. The spacecraft and mission design is taken from a conceptual phase to launch and validation via in-orbit operations. This is the first micro-satellite constellation for Earth Observation, and the first microsatellite solution to addresst he rapid-responsep roblem. Research into potential applications for the image data is also presented, focussing in particular on disaster management applications. Wildfire management applications and flood monitoring are considered in most detail, whilst other potential application areas are addressed in brief. This research clearly indicates that there is much potential for the DMC imagery to add value, over and above the current available Earth Observation data sources, to a number of applications. It is noted that further work should be performed to validate the use of DMC data in any given application.
Open Access
Drag-free control and technological risk assessment for the LISA gravitational wave space antenna
(Cranfield University, 2000-10-10) Roberts, P.; Bowling, Tom
The quest for the direct detection and observation of gravitational waves remains one of the lasting scientific challenges of the 20th century, and one that will continue on into the 21 st. Concepts and technologies are being developed that will, early in the new millennium, allow their direct observation for the first time. This will be the beginning of the gravitational wave astronomy revolution. The LISA (Laser Interferometer Space Antenna) mISSIOn is one of the cornerstones of this revolution. Observing in the low-frequency band, it will provide information about our universe that cannot be gathered from the ground. This band contains sources fundamental to our understanding of how the universe began and operates. In turn, fundamental to the LISA mission is the concept of drag-free control. This provides the relatively undisturbed environment for the test-masses which form the references for the measurement of the gravitational waves. Without it the effect of gravitational waves would be but a whisper amongst a cacophony of disturbances. It is drag-free control for the LISA mission which forms the basis for the majority of this thesis. The research and development work carried out by the author has involved the development of a control model of the LISA dragfree control system to assess its feasibility. The author proposes a different approach to the problems involved from that suggested by other authors. It is shown that this approach, unlike those suggested in the mission baseline studies, fulfills the control requirements for the LISA mission. Technological risk assessment in general, as well as that associated with the LISA mission, is also considered.
Open Access
FEEP thruster nano-satellite application
(2004-01) Fernando, W. C. P.; Bowling, Tom
Open Access
Figure of merit for satellite constellation design
(Cranfield University, 2002-01-27) Eves, S.; Bowling, Tom
The purpose of this research has been to develop a technique by which satellite constellations in different classes of orbit may be realistically compared. Previous work on constellation design has tended to focus on minimising the number of satellites required to provide coverage of the Earth. The variations in satellite vehicle design, which result from the use of different orbits, have, in general, been neglected in such analyses. The purpose of this research is to bridge this gap between constellation design and satellite design using a Figure of Merit. This Figure of Merit incorporates the coverage value provided by the satellite constellation, measured in terms of percentage coverage time, and the overall mass of the satellites which are required to provide this coverage. The coverage value is measured against a specific requirement, which is defined geographically, and which may be weighted by the user to reflect the relative importance of different regions. This allows arbitrary, asymmetric, real-world requirements to be adequately represented. This also marks something of a departure from previous work, in that the goal of much constellation design work has been to provide un-weighted coverage of the entire globe. Simplified mass models are developed for generic communications and surveillance satellites in a variety of orbits, and are then used to calculate the Figure of Merit for individual satellites. It is shown that the best solution depends crucially upon the geographical distribution of the requirement, and other user-defined parameters, such as the minimum elevation angle which can be tolerated. It is also shown that, for certain typical requirements, the Figure of Merit correctly identifies geostationary orbit (GEO) and low Earth orbit (LEO) as having particular advantages. iii The technique of characterising the requirement geographically may also be used as a means of optimising the orbital parameters of the candidate constellations, and a preliminary description of this procedure is also provided. The Figure of Merit Technique is then applied to representative communications satellite constellations in order to demonstrate its ability to differentiate between candidate options. The Figure of Merit technique is also used to investigate the possibility of using a surveillance satellite at very low altitudes.
Open Access
Long term storage and usage of cryogenic propellants for a manned Mars mission
(Cranfield University, 1996-05-03) Ford, Mark; Bowling, Tom
The research is concerned with investigating the storage and usage of liquid Hydrogen and Oxygen over a long duration. For this purpose a mission was defined where these two propellants are used to transport a six man crew to Mars and back. The mission duration is a total of 972 days in length with a stopover time at Mars of 454 days. A baseline spacecraft is designed. The two driving philosophies behind the design are reliability and reusability. This baseline spacecraft design was used a a basis for analysing the extreme thermal environment and its impact on the propellant storage temperatures. Also it allowed the calculation of mass and propellant budgets. It was found that the Hydrogen fuel undergoes a change of phase when the vehicle is orbiting Mars. Hence a escape manoeuvre trajectory simulation was performed which analysed the escape trajectory, acceleration and duration, and assessed the impact on the initial Earth launch propellant budget. I addition, a number of trade-offs were performed in order to increase the efficiency of the propulsion system from its nominal design in which the Hydrogen gas is allowed to expand directly from the storage tanks through the engine. The optimum arrangement that was found was to bleed the gas into a small high pressure tank and allow the fuel to be heated by waste heat from the onboard nuclear reactor. The results indicated that not only does this provide a performance increase over the nominal system but also the amount of propellant required for this bum is smaller than the storable options considered in the literature. Hence this analysis demonstrates that Hydrogen and Oxygen can be stored and used over long periods, and that they can still provide a better propellant performance than storable options, even with the increased mass penalty associated with using them on a mission such a this one.
Open Access
Modular, reconfigurable approach for a commercial space spacecraft programme
(Cranfield University, 2003-06) Kingston, Jenny; Bowling, Tom
This thesis presents the work performed in producing a system-level design for a modular, multipurpose small satellite platform. A multipurpose platform may be applied to a wide range of missions, and, to be commercially viable, the envelope of missions for which it is suitable should be as large as possible. The research therefore addresses the particular requirements that are specific to different mission types, and produces characteristic requirement sets for each. General design requirements are also derived, such as those for enabling modularity and allowing compatibility with different launch vehicles. The commercial requirements arising from the different market and customer sectors are also examined. Industry analysis allows identification of general market trends, and predictions are made regarding the likely size and characteristics of the market in which the proposed platform would compete. It is anticipated there could be a worldwide demand for more than twenty small satellites each year, for which a flexible small spacecraft platform could potentially compete. After derivation of the necessary requirements has been performed, a system-level design of the spacecraft platform is undertaken. The resulting design is based on a multi-module, reconfigurable concept, which can be adapted to fit the different launch envelopes of Pegasus-XL, Taurus, ASAP-5 and larger launchers, and also to accommodate a wide range of payloads. The subsystems are offered in different capability variants, which may be interchanged in response to different mission requirements. The platform equipment and structure forms a "standard parts lisf', from which the appropriate configuration can be built up. Schedule reductions are obtained due to the modular design allowing more of the integration and testing of the platform to be performed in parallel. The proposed programme for development of the platform uses up-front investment to conduct much of the detailed design of the platform in advance of any actual project. This allows the design effort to be shared across many subsequent projects, and the design phase of each new project to be minimised. The key benefits of the proposed platform and programme are adaptability, ability to rapidly reconfigure to mission requirements, suitability for future upgrading, and reduction of the project schedule.
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.
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, Stephen
Future 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 proble
Open Access
Performance comparison of reusable launch vehicles
(Cranfield University; School of Engineering, 2005-06-27T16:11:27Z) Ayre, Mark; Bowling, Tom
A parameterised generic launch vehicle design is subjected to performance evaluation using the ORBITER model which is capable of optimising both the design and trajectory of the vehicle. The launcher initial mass, flight path angle, velocity and altitude are varied around design points of existing vehicle concepts to investigate the subsequent effect on performance for payload delivery into a 90km by 200km orbit. The performance results suggest that SSTO systems are unfeasible, delivering marginal positive payload performance only when externally accelerated to high speed using a sled mechanism. The optimal vehicle type from a purely performance perspective is deemed to be the TSTO vertically launched configuration.
Open Access
Systems design and control of a freeflying space robotic manipulator system (ATLAS) for in-orbit satellite servicing operations
(1996-08-02) Ellery, Alexander; Bowling, Tom; Lewis, John
This thesis is concerned with a freeflyer robotic spacecraft for in-orbit satellite servicing employing a dedicated attitude control system, ATLAS (Advanced TeLerobotic Actuation System). It adopts a unique control system design to alleviate the reaction coupling between the spacecraft mounting and the manipulator such that control of both the spacecraft attitude and manipulator kinematics may be effected in real-time using present-day space-rated electronics. It has been found that very few additional computations are required to compensate the coupling problem over standard terrestrial resolved motion robot control algorithms and standard spacecraft attitude control techniques. A mathematical proof of the concept is outlined. The technique is also extended for dual-arm operation. Two manipulator arms are necessary for EVA-equivalence to afford maximum flexibility. Mutual collision possibilities will be eliminated by incorporating a modified Zambesi bridge via interrupt software whereby each manipulator is restricted to operations within its own quadrant. This eases the computational burden of monitoring arm-to-arm collisions in the open chain mode with little loss of flexibility. Closed chain mode is shown to be similar to the open chain mode but with the addition of certain kinematic and force constraints. Each arm must be capable of operating independently or cooperatively, necessitating a hierarachical control architecture which is compatible with the NASREM control architecture. Given that the single arm freeflyer is the baseline of this thesis and that dual arm configurations are merely extensions of this, a simulation program of the techniques outlined has been constructed to output some of the parameters o f interest. Consideration is also given to the possible commercial impact of such a system.
Open Access
A Unified framework for spacecraft operations
(Cranfield University, 2001-04) Verrier, David; Bowling, Tom
This work analyses the current state of the art in the Spacecraft Operations domain. It reviews the structure and practices within the European space industry and shows how the industry is generally shaped by national or international non-governmental organisations. Although it draws most material from the author's experience in Europe whilst working on commercial space projects and international scientific projects, it compares and contrasts this with the US manned space programme and the Russian space programme. The space industry in Europe has inefficient working practices and a poor market structure which lacks incentives. The civil service-based organisations that administer the majority of national and European space activity have a poor internal organisation, are often slow to react, exhibit little delegation and reduce individual initiative. Recommendations are made about industrial policy, and how organisations should approach risk management and how teams should be formed and should interact. The spacecraft and instruments are normally built by specialised teams and organisations. This results in a conceptual gap between those who acquire knowledge whilst building and testing the systems and those who will operate the system. It is necessary to explicitly transfer the knowledge to the operations team, and there are weak mechanisms for doing so. At the same time, the operations team also has to prepare the ground segment to control a spacecraft and exploit a payload that, from their point of view, may be poorly defined. It is proposed that the traditional paper-based products (user manual and flight procedures) could be usefully supplemented or replaced by a knowledge base. An ontology to define a vocabulary is developed and it is shown to facilitate knowledge capture and exploration. The availability of such a facility would then also assist future missions (or even missions running in parallel) to understand the problems that their colleagues have, and adapt or incorporate the solution if it was applicable. There is a significant trend for spacecraft to become more complex and to have many computers and a great deal of software on-board. This make the system difficult to operate, and can also lead to unexpected results, since the state space of a software-driven system is so large. For terrestrial systems, formal methods have been developed to try to counteract the trend: by proving certain behaviour in the specification, the number of paths that need to be tested can be significantly pruned. It is proposed here that formal methods could be adopted to test and communicate knowledge, as well as to improve the design. The trend to have increasingly intelligent sub-systems has been occurred in parallel to the trend to have increasingly sophisticated data communication. This is applicable equally to command and monitoring. The information content of parameters is analysed, and the content of flags and simple packets is calculated.

Browsing by Author "Bowling, Tom"

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