An Approach to Analyze Tradeoffs for Aerospace System Design and Operation

There are important tradeoffs that need to be considered for the design and operation of aerospace systems. In addition to tradeoffs, there may also be multiple stakeholders of interest to the system and each may have different preferences as to the balance amongst the tradeoffs under consideration. A tradeoff hyperspace is created when there are three or more tradeoff dimensions and this increases the challenge associated with resolving the hyperspace in order to determine the best design and operation of a system. The corresponding objectives of this research are to develop a framework to analyze tradeoff hyperspaces and to account for the preferences of multiple stakeholders in this framework.This work was supported by the National Aeronautics and Space Administration (NASA) under grant NRA- #NNX10AN92A (NASA Ames). The authors are grateful to Dr. Neil Y. Chen and Dr. Banavar Sridhar in the Aviation Systems Division at NASA Ames for their valuable guidance and feedback in managing this project

Assessing the impacts of fractionation on pointing-intensive spacecraft

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, February 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 165-168).Fractionated spacecraft consist of physically independent, "free-flying" modules composed of various subsystems. Thus, a fractionated spacecraft might consist of one-module responsible for the power generation and storage, another module responsible for the communications and computing, another module responsible for the attitude and guidance determination, another module responsible for the payload, and so on. Fractionated spacecraft are of particular interest for pointing-intensive, remote sensing mission spacecraft because of their ability to physically decouple subsystems and payloads that truly need precise pointing, thereby potentially reducing the lifecycle cost of fractionated spacecraft relative to a comparable monolithic spacecraft, for a given space mission. Additionally, using fractionation to decouple pointing-intensive subsystems and payloads may potentially reduce the mass and size of the module containing the payload in a fractionated spacecraft (i.e., Payload Module) relative to that of a comparable monolithic spacecraft. If fractionated spacecraft prove to reduce the mass and size associated with the Payload Module, for a given pointing-intensive, remote sensing mission, it may enable pointing-intensive fractionated spacecraft to have longer space mission lifetimes than comparable monolithic spacecraft.(cont.) This research seeks to quantitatively assess the impacts of various fractionated spacecraft architecture strategies on the lifecycle cost, mass, propellant usage, and mission lifetime of pointing-intensive, remote sensing mission spacecraft. A dynamic lifecycle simulation and parametric model was used to assess the lifecycle cost impacts, while the mass, propellant usage, and mission lifetime impacts were assessed using a non-parametric, physics-based computer model. Results from the research demonstrate that fractionated spacecraft can be both more and less expensive than a comparable monolithic spacecraft performing the same space mission. Additionally, the results show that due to the ability of fractionated spacecraft to decouple subsystems and payloads that truly need precise pointing, the mass and propellant usage of the Payload Module can be appreciably less than that of a comparable monolithic spacecraft. Subsequently, fractionated spacecraft can attain longer mission lifetimes than a monolithic spacecraft, and in certain instances, do so with a lesser lifecycle cost than the monolith at its respective shorter mission lifetime.by Michael Gregory O'Neill.S.M

An approach to analyze tradeoffs for aerospace system design and operation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2013.This electronic version was submitted and approved by the author's academic department as part of an electronic thesis pilot project. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from department-submitted PDF version of thesis.Includes bibliographical references (p. 181-189).There are important tradeoffs that need to be considered for the design and operation of aerospace systems. In addition to tradeoffs, there may also be multiple stakeholders of interest to the system and each may have different preferences as to the balance amongst the tradeoffs under consideration. A tradeoff hyperspace is created when there are three or more tradeoff dimensions and this increases the challenge associated with resolving the hyperspace in order to determine the best design and operation of a system. The corresponding objectives of this research are to develop a framework to analyze tradeoff hyperspaces and to account for the preferences of multiple stakeholders in this framework. The framework developed in this research is called the Tradeoff Analysis Framework and its applicability was evaluated through analyzing three different case studies in the aerospace domain, each progressively more complex in terms of applying the framework and exploring the impact of certain types or change, or innovation in the system of interest. The first case study analyzed the impact of changing aircraft cruise operations and one facet of the case study explored the impact of imposing a hypothetical tax on aircraftproduced contrails. From this study it was determined that airlines will change their behavior (i.e., their perceived value-optimal cruise trajectory) in response to a tax placed on producing contrails where, the higher the tax, the less contrails they choose to produce. The second case study explored the impact of changes in aircraft approach procedures into Boston-Logan airport. In this study, there were multiple stakeholders, each with different preferences as to the balance amongst the performance and environmental tradeoffs considered. A key result from this study was that competing stakeholder preferences could be partially resolved, which led to the design new approach procedures that were beneficial to all stakeholders. The third and last case study examined the tradeoffs associated with using fractionated spacecraft for remote sensing space missions. Here, the current paradigm is monolithic spacecraft and it was found that despite fractionated spacecraft demonstrating more value-robustness than a comparable monolith, they fail to stay value-competitive to monoliths in terms of absolute value delivered. In particular, this occurs because presently the enabling technologies required for fractionated spacecraft are not yet mature and reliable enough at the performance levels needed for them to become viable alternatives to monoliths. Along with insights gained in the case studies about the systems of interest, through applying the Tradeoff Analysis Framework insights were gained with respect to implementing the framework. These insights form the methodological contributions of this research since they offer opportunities to learn about the breadth of potential framework applicability and areas for subsequent improvements in the framework for future use.by Michael Gregory O'Neill.Ph.D

Non-invasive molecular imaging of inflammatory macrophages in allograft rejection.

BackgroundMacrophages represent a critical cell type in host defense, development and homeostasis. The ability to image non-invasively pro-inflammatory macrophage infiltrate into a transplanted organ may provide an additional tool for the monitoring of the immune response of the recipient against the donor graft. We therefore decided to image in vivo sialoadhesin (Sn, Siglec 1 or CD169) using anti-Sn mAb (SER-4) directly radiolabelled with (99m)Tc pertechnetate.MethodsWe used a heterotopic heart transplantation model where allogeneic or syngeneic heart grafts were transplanted into the abdomen of recipients. In vivo nanosingle-photon emission computed tomography (SPECT/CT) imaging was performed 7 days post transplantation followed by biodistribution and histology.ResultsIn wild-type mice, the majority of (99m)Tc-SER-4 monoclonal antibody cleared from the blood with a half-life of 167 min and was located predominantly on Sn(+) tissues in the spleen, liver and bone marrow. The biodistribution in the transplantation experiments confirmed data derived from the non-invasive SPECT/CT images, with significantly higher levels of (99m)Tc-SER-4 observed in allogeneic grafts (9.4 (±2.7) %ID/g) compared to syngeneic grafts (4.3 (±10.3) %ID/g) (p = 0.0022) or in mice which received allogeneic grafts injected with (99m)Tc-IgG isotype control (5.9 (±0.6) %ID/g) (p = 0.0185). The transplanted heart to blood ratio was also significantly higher in recipients with allogeneic grafts receiving (99m)Tc-SER-4 as compared to recipients with syngeneic grafts (p = 0.000004) or recipients with allogeneic grafts receiving (99m)Tc-IgG isotype (p = 0.000002).ConclusionsHere, we demonstrate that imaging of Sn(+) macrophages in inflammation may provide an important additional and non-invasive tool for the monitoring of the pathophysiology of cellular immunity in a transplant model

Multi-temperature state-dependent equivalent circuit discharge model for lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are described extensively in the literature, but existing computational models aimed at scientific understanding are too complex for use in applications such as battery management. Computationally simple models are vital for exploitation. This paper proposes a non-linear state-of-charge dependent Li-S equivalent circuit network (ECN) model for a Li-S cell under discharge. Li-S batteries are fundamentally different to Li-ion batteries, and require chemistry-specific models. A new Li-S model is obtained using a ‘behavioural’ interpretation of the ECN model; as Li-S exhibits a ‘steep’ open-circuit voltage (OCV) profile at high states-of-charge, identification methods are designed to take into account OCV changes during current pulses. The prediction-error minimization technique is used. The model is parameterized from laboratory experiments using a mixed-size current pulse profile at four temperatures from 10 °C to 50 °C, giving linearized ECN parameters for a range of states-of-charge, currents and temperatures. These are used to create a nonlinear polynomial-based battery model suitable for use in a battery management system. When the model is used to predict the behaviour of a validation data set representing an automotive NEDC driving cycle, the terminal voltage predictions are judged accurate with a root mean square error of 32 mV

Policy initiatives to address low-income households’ nutritional needs in the UK

Members of low-income households in the UK are more likely to have patterns of food and nutrient intakes that are less inclined to lead to good health outcomes in the short and long term. Health inequalities, including the likelihood of child and adulthood obesity, have long been documented in the UK and show little sign of improving so far, despite 10 years of attention from a government that has committed itself to addressing them. Following the Acheson Inquiry into Inequalities in Health (1998) in England a number of initiatives to tackle inequalities in food and diet were established, both nationally and within the devolved nations of Scotland, Wales and Northern Ireland. Nevertheless, until recently, there has been no overall strategic policy addressing the food and nutritional needs of low-income households. The present paper reviews how the problems have been constructed and understood and how they have been addressed, briefly drawing on recent evaluations of food and nutrition policies in Scotland and Wales. The contemporary challenge is to frame cross-cutting policy initiatives that move beyond simple targeting and local actions, encompass a life-course approach and recognise both the diversity of households that fall into ‘low-income’ categories and the need for ‘upstream’ intervention

Uniqueness of de Sitter space

All inextendible null geodesics in four dimensional de Sitter space dS^4 are complete and globally achronal. This achronality is related to the fact that all observer horizons in dS^4 are eternal, i.e. extend from future infinity scri^+ all the way back to past infinity scri^-. We show that the property of having a null line (inextendible achronal null geodesic) that extends from scri^- to scri^+ characterizes dS^4 among all globally hyperbolic and asymptotically de Sitter spacetimes satisfying the vacuum Einstein equations with positive cosmological constant. This result is then further extended to allow for a class of matter models that includes perfect fluids.Comment: 22 pages, 2 figure

Saturation behavior of superoxide dismutation catalyzed by the iron containing superoxide dismutase of E. coli B

SummaryThe iron containing superoxide dismutase from E. coli B is shown to catalyze superoxide dismutation by a mechanism which exhibits saturation kinetics. This behavior is quite different from that observed previously with bovine Zn/Cu- and iron-containing superoxide dismutase from P. leiognathi. Two parameters of catalysis were measured in the pH range 7.2 to 10.4: kcat was found to be independent of pH and Km varied with the function Km = Km(low pH) [1 + exp(pH -- 8.8)]. These results implicate a group in the catalytic mechanism which ionizes with pKa = 8.8.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24375/1/0000644.pd