Theory of plasma contactors in ground-based experiments and low Earth orbit

Previous theoretical work on plasma contactors as current collectors has fallen into two categories: collisionless double layer theory (describing space charge limited contactor clouds) and collisional quasineutral theory. Ground based experiments at low current are well explained by double layer theory, but this theory does not scale well to power generation by electrodynamic tethers in space, since very high anode potentials are needed to draw a substantial ambient electron current across the magnetic field in the absence of collisions (or effective collisions due to turbulence). Isotropic quasineutral models of contactor clouds, extending over a region where the effective collision frequency upsilon sub e exceeds the electron cyclotron frequency omega sub ce, have low anode potentials, but would collect very little ambient electron current, much less than the emitted ion current. A new model is presented, for an anisotropic contactor cloud oriented along the magnetic field, with upsilon sub e less than omega sub ce. The electron motion along the magnetic field is nearly collisionless, forming double layers in that direction, while across the magnetic field the electrons diffuse collisionally and the potential profile is determined by quasineutrality. Using a simplified expression for upsilon sub e due to ion acoustic turbulence, an analytic solution has been found for this model, which should be applicable to current collection in space. The anode potential is low and the collected ambient electron current can be several times the emitted ion current

Assessing Changeability in Aerospace Systems Architecting and Design Using Dynamic Multi-Attribute Tradespace Exploration

A framework for assessing changeability in the context of dynamic Multi-Attribute Tradespace Exploration (MATE) is proposed and applied to three aerospace systems. The framework consists of two parts. First, changeability concepts such as flexibility, scalability, and robustness are defined in a value-centric context. These system properties are shown to relate “real-space to value-space” dynamic mappings to stakeholder-defined subjective “acceptable cost” thresholds. Second, network analysis is applied to a series of temporally linked tradespaces, allowing for the quantification of changeability as a decision metric for comparison across system architecture and design options. The quantifiable is defined as the filtered outdegree of each design node in a tradespace network formed by linking design options through explicitly defined prospective transition paths. Each of the system application studies are assessed in the two part framework and within each study, observations are made regarding the changeability of various design options. The three system applications include a hypothetical low Earth orbit satellite mission, a currently deployed weapon system, and a proposed large astronomical on-orbit observatory. Preliminary cross-application observations are made regarding the embedding of changeability into the system architecture or design. Results suggest that the low Earth orbit satellite mission can increase its changeability by having the ability to readily change its orbit. The weapon system can increase its changeability by continuing to embrace modularity, use of commercial off-the-shelf parts (COTS), and simple, excess capacity interfaces. The large astronomical observatory can increase its potential changeability by having the ability to reconfigure its physical payloads and reschedule its observing tasks. The analysis approach introduced in this paper is shown to be a powerful concept for focusing discussion, design, and assessment of the changeability of aerospace systems

Extracting the Essence of Flexibility in System Design

The modest purpose of this paper is to review the concept of flexibility as discussed in various fields of investigations, and to extract its characteristic features. In order to discuss any subject matter clearly, it is necessary to begin with a clear set of definitions. Indeed much can be gained through careful and consistent definitions of terms alone. Flexibility however is a word rich with ambiguity. While it is being increasingly used in various fields, few attempts have been made to formally define, quantify, and propose ways for achieving flexibility. This paper proposes to fill in part this gap by synthesizing a clear and consistent definition of flexibility. It will do so by reviewing the usage of the term in various fields of inquiries, and show that it is indeed possible to clearly and unambiguously characterize flexibility, and to disentangle it from closely related concepts

Defining System Changeability: Reconciling Flexibility, Adaptability, Scalability, and Robustness for Maintaining System Lifecycle Value

Designing and maintaining systems in a dynamic contemporary environment requires a rethinking of how systems provide value to stakeholders over time. Classically, two different approaches to promoting value sustainment may include developing either alterable or robust systems. The first accomplishes value delivery through altering the system to meet new needs, while the second accomplishes value delivery through maintaining a system to meet needs in spite of changes. The definitions of flexibility, adaptability, scalability, and robustness are shown to be different parts of the core concept of “changeability,” which can be described by three aspects: change agents, change effects, and change mechanisms. Cast in terms of system parameter changes, flexibility and adaptability are shown to relate to the origin of the change agent (external or internal to a system boundary respectively). Scalability and robustness, along with the additional property of modifiability, are shown to relate to change effects. The extent of changeability is determined by the number of possible change mechanisms available to the system as accepted by decision makers. Creating changeable systems, which can incorporate both classical notions of alterability and robustness, empowers systems to maintain value delivery over their lifecycle, in spite of changes in their contexts, thereby achieving value robustness to stakeholders over time

The Space Weather Threat to Situational Awareness, Communications, and Positioning Systems

A recent space weather headline has cast doubt in the minds of some as to whether space weather is the source of spacecraft anomalies, and thus, whether it is important in the design and operation of critical situational awareness, communications, and positioning systems. In this paper, we reiterate the evidence for the importance of space weather, its role in producing spacecraft and ground anomalies, and the threat it poses to critical systems. In addition, we report new studies broken down by anomaly types and suggest the sources of the anomalies (surface charging or interior charging). Finally, we suggest spacecraft charging and ground effects mitigation strategies for design and operations of systems critical to our modern civilization

Screening for Real Options “In” an Engineering System: A Step Towards Flexible System Development

The goal of this research is to develop an analytical framework for screening for real options “in” an engineering system. Real options is defined in the finance literature as the right, but not the obligation, to take an action (e.g. deferring, expanding, contracting, or abandoning) at a predetermined cost and for a predetermined time. These are called "real options" because they pertain to physical or tangible assets, such as equipment, rather than financial instruments. Real options improve a system’s capability of undergoing classes of changes with relative ease. This property is often called “flexibility.” Recently, the DoD has emphasized the need to develop flexible system in order to improve operational, technical, and programmatic effectiveness. The aim of this research is to apply real options thinking to weapon acquisitions in order to promote the ability of weapon system programs to deftly avoid downside consequences or exploit upside opportunities

Screening for Real Options “In” an Engineering System: A Step Towards Flexible System Development; PART I: The Use of Design Matrices to Create an End-to-End Representation of a Complex Socio-Technical System

The goal of this research is to develop an analytical framework for screening for real options “in” an engineering system. Real options is defined in the finance literature as the right, but not the obligation, to take an action (e.g. deferring, expanding, contracting, or abandoning) at a predetermined cost and for a predetermined time. These are called "real options" because they pertain to physical or tangible assets, such as equipment, rather than financial instruments. Real options improve a system’s capability of undergoing classes of changes with relative ease. This property is often called “flexibility.” Recently, the DoD has emphasized the need to develop flexible system in order to improve operational, technical, and programmatic effectiveness. The aim of this research is to apply real options thinking to weapon acquisitions in order to promote the ability of weapon system programs to deftly avoid downside consequences or exploit upside opportunities. The practice of real options in systems engineering is a nascent field of inquiry. One of the most significant challenges in applying real options to engineering systems is the problem of identifying the most efficacious points within the system to create options. In order to identify the points of interest, systems engineers require knowledge about the physical and non physical aspects of the system, insight into sources of change, and the ability to examine the dynamic behavior of the system. We propose a two-phase process to perform this analysis. The first phase is a system representation phase that seeks to create an end-to-end representation of engineering system that includes endogenous interactions across system views and interactions with a systems environment. The next phase is an analysis phase that models the evolution of the engineering system in order to identify the real options in the system. This paper presents the system representation phase and proposes a methodology for creating an end-to-end representation of an engineering system. The methodology for representing an engineering system extends existing systems engineering and architecting methods in two dimensions. First, the framework couples traditional architecting views to represent traceability and endogenous interactions within an engineering system. Second, the framework includes views of the system not represented in traditional engineering frameworks that includes social networks and environmental interactions. The framework uses coupled Design Structure Matrices (DSM) to represent the traditional and new architecting views. The coupled DSMs are organized into an Engineering System Matrix (ESM), which is a holistic representation of an engineering system that captures all of the critical variables and causal interactions across architectural elements. The result is an analytic framework that captures the qualitative understanding of the system into a single view that is conducive for deep quantitative inquiry. This paper presents a discussion of pertinent literature, an overview of the ESM framework and underlying theory. In addition, this paper previews ongoing research using the ESM to identify options for a mini-air vehicle (MAV) weapon development system

A Logical Approach to Real Options Identification with Application to UAV Systems

Complex systems are subject to uncertainties that may lead to suboptimal performance or even catastrophic failure if unmanaged. Uncertainties may be managed through real options that provide a decision maker with the right, but not the obligation, to exercise actions in the future. While real options analysis has traditionally been used to quantify the value of such flexibility, this paper is motivated by the need for a structured approach to identify where real options are or can be embedded for uncertainty management. We introduce a logical model-based approach to identification of real option mechanisms and types, where the mechanism is the enabler of the option, while the type refers to the flexibility provided by the option. First, we extend the classical design structure matrix and the more general multiple-domain matrix (MDM), commonly used in modeling and analyzing interdependencies in complex socio-technical systems, to the more expressive Logical-MDM that supports the representation of flexibility. Second, we show that, in addition to flexibility, two new properties, namely, optionability and realizability, are relevant to the identification of real options. We use the Logical-MDM to estimate flexibility, optionability, and realizability metrics. Finally, we introduce the Real Options Identification (ROI) method based on these metrics, where the identified options are valued using standard real options valuation methods to support decision making under uncertainty. The expressivity of the logic combined with the structure of the dependency model allows the effective representation and identification of mechanisms and types of real options across multiple domains and lifecycle phases of a system. We demonstrate this approach through a series of unmanned air vehicle scenarios

The Short Rotation Period of Hi'iaka, Haumea's Largest Satellite

Hi'iaka is the larger outer satellite of the dwarf planet Haumea. Using relative photometry from the Hubble Space Telescope and Magellan and a phase dispersion minimization analysis, we have identified the rotation period of Hi'iaka to be ~9.8 hrs (double-peaked). This is ~120 times faster than its orbital period, creating new questions about the formation of this system and possible tidal evolution. The rapid rotation suggests that Hi'iaka could have a significant obliquity and spin precession that could be visible in light curves within a few years. We then turn to an investigation of what we learn about the (presently unclear) formation of the Haumea system and family based on this unexpectedly rapid rotation rate. We explore the importance of the initial semi-major axis and rotation period in tidal evolution theory and find they strongly influence the time required to despin to synchronous rotation, relevant to understanding a wide variety of satellite and binary systems. We find that despinning tides do not necessarily lead to synchronous spin periods for Hi'iaka, even if it formed near the Roche limit. Therefore the short rotation period of Hi'iaka does not rule out significant tidal evolution. Hi'iaka's spin period is also consistent with formation near its current location and spin up due to Haumea-centric impactors.Comment: 21 pages with 6 figures, to be published in The Astronomical Journa

Real Options in Enterprise Architecture: A Holistic Mapping of Mechanisms and Types for Uncertainty Management

Uncertaintymanagement is crucial for achieving high performance in enterprises that develop or operate complex engineering systems. This study focuses on flexibility as a means of managing uncertainties and builds upon real options analysis (ROA) that provides a foundation for quantifying the value of flexibility. ROA has found widespread applications ranging from strategic investments to product design. However, these applications are often isolated to specific domains. Furthermore, ROA is focused on valuation, rather than the identification of real options. In this paper, we introduce a framework for holistic consideration of real options in an enterprise context. First, to enable a holistic approach, we use a generalized enterprise architecture framework that considers eight views: strategy, policy, organization, process, product, service, knowledge, and information technology (IT). This expands upon the classical IT-centric view of enterprise architecture. Second, we characterize a real option as a mechanism and type. This characterization disambiguates among mechanisms that enable flexibility and types of flexibility to manage uncertainties. Third, we propose mapping of mechanisms and types to the enterprise architecture views.We leverage this mapping in an integrated real options framework and demonstrate its benefit over the traditional localized approach to ROA.Singapore. Defence Science & Technology AgencySingapore. DSO National Laboratorie