A Systems Engineering Tool for Small Satellite Design

The growing popularity of small satellites for applications of all kinds has lead to a marked increase in the number of requests from customers of The Aerospace Corporation for studies involving small satellites. The existing design tools used by the Corporation for concept evaluation of large spacecraft have, in many cases, proven inadequate for these small spacecraft studies. As a result, Aerospace is developing a systems engineering tool to support the conceptual design of small satellites. The Aerospace Corporation’s small satellite systems engineering tool utilizes a spreadsheet-based approach to efficiently track information regarding the mass, power, and volume of the satellite subsystems. This subsystem information is derived through a variety of means, including analytical relationships, iterative solvers, and databases of components appropriate for small satellites. Physics based models for such factors as solar illumination and external torques have been incorporated into the tool to aid in the analysis of the design. In addition to data tracking, the spreadsheet approach used makes it easier for a concurrent engineering methodology to be applied to the design process. This means the effects of a change in one subsystem are immediately propagated to the other subsystems, and system-level effects are more easily identified. The end result is a tool that facilitates rapid systems-level concept evaluation and trade-space exploration in support of the small satellite design process. This paper describes The Aerospace Corporation’s small satellite systems engineering tool. The approach underlying the tool, as well as an overview of the implementation, relationships between the subsystems, and the flow of information are presented

A Model-Based Design Tool for Systems-Level Spacecraft Design

It is standard practice to mathematically model and analyze the various subsystems that make up a spacecraft, to ensure that they will function correctly when built. However, the system-level behavior of the spacecraft is generally understood in much less rigorous terms. This leaves the spacecraft system far more vulnerable than the subsystems to unforeseen design errors which may not manifest themselves until the integration and test phase, when design changes are most expensive in terms of cost and schedule. In this paper, we present Spacecraft Design Workbench, an extensible graphical design tool built upon the Generic Modeling Environment (GME) tool infrastructure, and intended to allow spacecraft systems engineers to model and analyze proposed spacecraft system designs in a rigorous manner. The graphical models defined by our tool have an underlying formal behavior semantics rooted in the Communicating Sequential Processes process algebra, which permits these models to be analyzed using off-the-shelf tools. As a proof-of-concept, we provide a small example that illustrates the application of our tool to the specification of a simple scientific spacecraft

Data-Driven Classification of Coronal Hole and Streamer Belt Solar Wind

We present two new solar wind origin classification schemes developed independently using unsupervised machine learning. The first scheme aims to classify solar wind into three types: coronal-hole wind, streamer-belt wind, and ‘unclassified’ which does not fit into either of the previous two categories. The second scheme independently derives three clusters from the data; the coronal-hole and streamer-belt winds, and a differing unclassified cluster. The classification schemes are created using non-evolving solar wind parameters, such as ion charge states and composition, measured during the three Ulysses fast latitude scans. The schemes are subsequently applied to the Ulysses and the Advanced Compositional Explorer (ACE) datasets. The first scheme is based on oxygen charge state ratio and proton specific entropy. The second uses these data, as well as the carbon charge state ratio, the alpha-to-proton ratio, the iron-to-oxygen ratio, and the mean iron charge state. Thus, the classification schemes are grounded in the properties of the solar source regions. Furthermore, the techniques used are selected specifically to reduce the introduction of subjective biases into the schemes. We demonstrate significant best case disparities (minimum ≈8%, maximum ≈22%) with the traditional fast and slow solar wind determined using speed thresholds. By comparing the results between the in- (ACE) and out-of-ecliptic (Ulysses) data, we find morphological differences in the structure of coronal-hole wind. Our results show how a data-driven approach to the classification of solar wind origins can yield results which differ from those obtained using other methods. As such, the results form an important part of the information required to validate how well current understanding of solar origins and the solar wind match with the data we have

Ecosystem service assessment of selected wetlands of Kolkata and the Indian Gangetic Delta: multi-beneficial systems under differentiated management stress

© 2019, The Author(s). A structured literature review using the search term ‘ecosystem services’ found few relevant studies relating to three contrasting wetlands in West Bengal: the unpopulated Sudhanyakhali Island in the Sundarbans National Park, the populated Gosaba Island separated from Sudhanyakhali Island by a narrow channel, and the East Kolkata Wetland (EKW). Subsequent structured review focused on the EKW using specific service-related terms located only 2 provisioning, 6 regulating, 1 cultural and 3 supporting services. Few services are currently recognized in the literature, with significant gaps in whole service categories. Significantly, there was no published evidence of a systemic overview of service production at these sites. Field observations and stakeholder dialogue informed assessment of ecosystem services using the Rapid Assessment of Wetland Ecosystem Services (RAWES) approach, adopted by the Ramsar Commission, on both islands and three discretely different areas of the EKW. The RAWES surveys found that 32 of 36 ecosystem services were produced from at least one assessed wetland site. Despite low sample size, statistically significant differences were observed in the range of services produced between the five wetland sites and the geographical range at which benefits accrued, explained by differing wetland characteristics and management regimes. Were decisions based solely on evidence provided by existing published knowledge, few ecosystem services would be considered and, potentially, whole ecosystem service categories might be overlooked. Importantly, there would also be no systemic account of service production and interdependencies. RAWES assessment serves as a practical, rapid and systemic approach, taking account of interdependent ecosystem services, supporting protection of the ecological character and achievement of wise use of wetlands. RAWES can also help redress perceptions that the values of peri-urban wetlands are currently under-represented

Of Bounces, Branes and Bounds

Some recent studies have considered a Randall-Sundrum-like brane world evolving in the background of an anti-de Sitter Reissner-Nordstrom black hole. For this scenario, it has been shown that, when the bulk charge is non-vanishing, a singularity-free ``bounce'' universe will always be obtained. However, for the physically relevant case of a de Sitter brane world, we have recently argued that, from a holographic (c-theorem) perspective, such brane worlds may not be physically viable. In the current paper, we reconsider the validity of such models by appealing to the so-called ``causal entropy bound''. In this framework, a paradoxical outcome is obtained: these brane worlds are indeed holographically viable, provided that the bulk charge is not too small. We go on to argue that this new finding is likely the more reliable one.Comment: 15 pages, Revtex; references added and very minor change

Physician Awareness of Drug Cost: A Systematic Review

From a review of data from 24 studies, Michael Allan and colleagues conclude that doctors often underestimate the price of expensive drugs and overestimate the price of those that are inexpensive

Service use of older people who participate in primary care health promotion: a latent class analysis

Background: Recruiting patients to health promotion programmes who will benefit is crucial to success. A key policy driver for health promotion in older people is to reduce health and social care use. Our aim was to describe service use among older people taking part in the Multi-dimensional Risk Appraisal for Older people primary care health promotion programme. Methods: A random sample of 1 in 3 older people (≥65 years old) was invited to participate in the Multi-dimensional Risk Appraisal for Older people project across five general practices in London and Hertfordshire. Data collected included socio-demographic characteristics, well-being and functional ability, lifestyle factors and service use. Latent class analysis (LCA) was used to identify groups based on use of the following: secondary health care, primary health care, community health care, paid care, unpaid care, leisure and local authority resources. Differences in group characteristics were assessed using univariate logistic regression, weighted by probability of class assignation and clustered by GP practice. Results: Response rate was 34% (526/1550) with 447 participants presenting sufficient data for analysis. LCA using three groups gave the most meaningful interpretation and best model fit. About a third (active well) were fit and active with low service use. Just under a third (high NHS users) had high impairments with high primary, secondary and community health care contact, but low non-health services use. Just over a third (community service users) with high impairments used community health and other services without much hospital use. Conclusion: Older people taking part in the Multi-dimensional Risk Appraisal for Older people primary care health promotion can be described as three groups: active well, high NHS users, and community service users