Designing and maintaining systems in a dynamic contemporary environment requires a rethinking of how systems provide value to stakeholders over time. Developing either changeable or classically robust systems are approaches to promoting value sustainment. But, ambiguity in definitions across system domains has resulted in an inability to specify, design, and verify to ilities that promote value sustainment. In order to develop domain-neutral constructs for improved system design, the definitions of flexibility, adaptability, scalability, modifiability, and robustness are shown to relate to the core concept of "changeability," described by three aspects: change agents, change effects, and change mechanisms. In terms of system form or function parameter changes, flexibility and adaptability reflect the location of the change agent-system boundary external or internal respectively. Scalability, modifiability, and robustness relate to change effects, which are quantified differences in system parameters before and after a change has occurred. The extent of changeability is determined using a tradespace network formulation, counting the number of possible and decision maker acceptable change mechanisms available to a system, quantified as the filtered outdegree. Designing changeable systems allows for the possibility of maintaining value delivery over a system lifecycle, in spite of changes in contexts, thereby achieving value robustness.

Spacecraft interact with the space environment in ways that may affect the operation of the spacecraft as well as any scientific experiments that are carried out from the spacecraft platform. In turn the study of these interactions provides information on the space environment. The adverse environmental effects, such as the effect of the radiation belts on electronics, and spacecraft charging from the magnetospheric plasma, means that designers need to understand interactive phenomena to be able to effectively design spacecraft. This has led to the new discipline of spacecraft-environment interactions. The emphasis in this book is on the fundamental physics of the interactions. Spacecraft-Environment Interactions is a valuable introduction to the subject for all students and researchers interested in the application of fluid, gas, plasma and particle dynamics to spacecraft and for spacecraft system engineers.

In a three-dimensional device like a stellarator, the ambipolar electric field must be determined self-consistently from the ambipolarity constraint and can have a significant effect on transport through the diffusion coefficients. A differential formulation and an algebraic formulation for the electric field are solved, together with the density and temperature equations. The results are compared, and in both cases multiple electric field solutions can exist, with bifurcations occurring between different solutions. It is shown that heating of the electrons encourages bifurcation to the more favourable positive electric field root.

The inability to approach systematically the high level of ambiguity present in the early design phases of space systems causes long, highly iterative, and costly design cycles. A process is introduced and described to capture decision maker preferences and use them to generate and evaluate a multitude of space system designs, while providing a common metric that can be easily communicated throughout the design enterprise. Communication channeled through formal utility interviews and analysis enables engineers to better understand the key drivers for the system and allows for a more thorough exploration of the design tradespace. Multi-attribute tradespace exploration with concurrent design, a process incorporating decision theory into model-and simulation-based design, has been applied to several space system projects at the Massachusetts Institute of Technology. Preliminary results indicate that this process can improve the quality of communication to resolve more quickly project ambiguity and to enable the engineer to discover better value designs for multiple stakeholders. The process is also integrated into a concurrent design environment to facilitate the transfer of knowledge of important drivers into higher fidelity design phases. Formal utility theory provides a mechanism to bridge the language barrier between experts of different backgrounds and differing needs, for example, scientists, engineers, managers, etc. Multi-attribute tradespace exploration with concurrent design couples decision makers more closely to the design and, most important, maintains their presence between formal reviews. Nomenclature K= multi-attribute utility normalization constant k i = multi-attribute utility scaling factor for attribute i N = number of attributes U (X) = multi-attribute utility function U i (X i ) = single attribute utility function i X = set of multiple attributes 1, . . . , N X i = single attribute i Introduction SPACE system engineers have been developing effective systems for about 50 years, and their accomplishments are a testament to human ingenuity. In addition to tackling the complex technical challenges in building these systems, engineers must also cope with the changing political and economic context for space system design and development. The history, scope, and scale of space systems results in a close tie with government and large budgets. The postCold War era has resulted in much smaller budgets and a space industry that needs to do more with less. Time and budget pressures can result in corner cutting (such as the Mars program) and careless accounting (such as the International Space Station program).Space system design often starts with needs and a concept. Engineers perform trade studies by setting baselines and making minor changes to seek improvement in performance, cost, schedule, and risk. The culture of an industry that grew through an Apollo race to the moon and large defense contracts in the 1970s and 1980s is slow to adapt a better way to design systems to ensure competitiveness in a r...

Abstract. Over the past five years, researchers working on a number of system design projects in the Space Systems, Policy, and Architecture Research Consortium (SSPARC) at the Massachusetts Institute of Technology (MIT) have developed a process of value-focused, broad tradespace exploration for the development of space systems. The broad tradespace framework has provided insights into communicating and quantifying the impact of changing requirements, uncertainty, and system properties such as flexibility and robustness. Additionally, insights have been made in applications to more complex cases, such as analyzing policy effects on system cost and performance, as well as understanding the time-dependent effects of architecture and design choices for spiral development. The tradespace exploration paradigm both broadens the perspective of designers in conceptual design to better understand the "physics" of the proposed solutions relative to one another, and focuses the designer on delivering systems of value to key system stakeholders.

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All spacecraft interact in some manner with the plasma environment in space, either the natural environment or a self‐induced environment. Early work on plasma spacecraft interactions focused on geosynchronous altitudes where the primary effect is spacecraft charging from the non‐Maxwellian high‐energy plasma environment. This work has been extensively reviewed. In the last several years, there have been a number of measurements in low Earth orbit (LEO) which, when combined with models, have revealed a rich variety of plasma interaction phenomena at these low altitudes. These are reviewed in this work. These include charging on polar orbits, ram and wake flows, use of high‐voltage power systems in space, arcing on high‐voltage solar arrays, noise generation in self induced plasma clouds around large, active spacecraft such as the shuttle, anomalous ionization of emitted neutral gases, use of electrodynamic tethers and plasma contactors and phenomena associated with the use of electrically propelled rockets.

The use of humans to service satellites designed for servicing has been adequately demonstrated on the Hubble Space Telescope and International Space Station. Currently, robotic on-orbit servicing technology is maturing with risk reduction programs such as Orbital Express. Robotic servicing appears to be technically feasible and provides a set of capabilities which range from satellite inspection to physical upgrade of components. However, given the current design and operation paradigms of satellite architectures, it appears that on-orbit servicing will not be heavily used, and, as a result, is not likely to be economically viable. To achieve the vision of on-orbit servicing, the development of a new value proposition for satellite architectures is necessary. This new value proposition is oriented around rapid response to technological or market change and design of satellites with less redundancy. Nomenclature a phase = semimajor axis of the phasing orbit for the servicer a target = semimajor axis of the target satellite orbit CP Ser = servicing cost penalty C op = cost of satellite operations C sat = cost of satellite development k servicer = no. of phasing revolutions of the servicer k target = no. of phasing revolutions of the target satellite N Trans = no. of transponders P markup = markup for serviceable satellite RIFR = interest free discount rate RINF = inflation rate RINS = insurance premium RIRR = internal rate of return t H = expected end-of-life year of the satellite t k= decision year t 0 = initial launch year X 0 = initial value of a GEO satellite communications market V phase = velocity change necessary for servicer to adjust its phase to match target satellite V proximity = velocity change necessary for servicer to adjust to proximity operations at target satellite # = initial angular separation between servicer and target satellite