Optimization of Propulsion Systems With Real-Time Precise Orbit Determination Technology to Enable Proximity Operations and Advanced Mission Capabilities

Precise orbit determination technologies are an increasingly important enabler for the validation of critical in-space satellite propulsion systems. Advanced maneuvers require precise knowledge of impulse to optimize operations related to rendezvous, docking, in-orbit refueling, debris removal, formation flying and optical intersatellite-links optimization. These applications can benefit greatly from enhanced knowledge of the precise position of the satellite performing the work, and the precise position of the target. Thruster-intensive missions benefit from this ability to optimize thruster use and calculate and optimize actual fuel use. The authors have combined these technologies to offer a precision 6DOF cold-gas propulsion solution with simultaneous, real time enhanced position/velocity accuracy. In this paper, we present the case for a mission where positioning technology matching Fugro\u27s POD service is used for in-orbit validation of a CubeSat equipped with a propulsion system matching the specifications of GomSpace\u27s 6DOF cold-gas technology. The case study outlines a set of operations that constitute a test campaign for successful in-orbit technology demonstration. The paper concludes with a discussion on how this combination of technologies can be used in advanced missions for in-orbit docking, refueling, cross-link communications optimization and debris capture

Increasing Campus Sense of Belonging through LLC Participation: To Gems Camp We Go

Gemstone seeks to develop students’ research and collaboration skills, foster leadership opportunities, and provide a sense of belonging on a large campus utilizing the Best Practices Model (BPM) and a variety of high impact practices (HIPs), like a Gemstone-specific orientation program called Gems Camp. While studies have demonstrated that LLCs increase students’ sense of belonging, the goal of this study is to explicitly test via propensity score matching if (a) enrollment in the Gemstone Honors Program increases sense of belonging compared to university students not in Gemstone and (b) attendance at Gems Camp increases sense of belonging in Gemstone students. Gemstone students (N=221) had an increased sense of belonging compared to matched university students (N=221). Moreover, Gemstone students who attended Gems Camp (N=92) had an increased sense of belonging compared to matched Gemstone students who did not attend Gems Camp (N=92). In conclusion, the Gemstone Honors Program is an example of an LLC with scaffolded high impact practices, such as intentional first year programming, undergraduate research, and collaborative projects, that promotes an increase in students’ sense of belonging, providing a model for other LLCs to consider in their programming efforts

The Use of Official Statistics in Self-Selection Bias Modeling

Official statistics are a fundamental source of publicly available information that periodically provides a great amount of data on all major areas of citizens’ lives, such as economics, social development, education, and the environment. However, these extraordinary sources of information are often neglected, especially by business and industrial statisticians. In particular, data collected from small businesses, like small and medium-sized enterprizes (SMEs), are rarely integrated with official statistics data

Applications of sensitivity analysis for probit stochastic network equilibrium

Network equilibrium models are widely used by traffic practitioners to aid them in making decisions concerning the operation and management of traffic networks. The common practice is to test a prescribed range of hypothetical changes or policy measures through adjustments to the input data, namely the trip demands, the arc performance (travel time) functions, and policy variables such as tolls or signal timings. Relatively little use is, however, made of the full implicit relationship between model inputs and outputs inherent in these models. By exploiting the representation of such models as an equivalent optimisation problem, classical results on the sensitivity analysis of non-linear programs may be applied, to produce linear relationships between input data perturbations and model outputs. We specifically focus on recent results relating to the probit Stochastic User Equilibrium (PSUE) model, which has the advantage of greater behavioural realism and flexibility relative to the conventional Wardrop user equilibrium and logit SUE models. The paper goes on to explore four applications of these sensitivity expressions in gaining insight into the operation of road traffic networks. These applications are namely: identification of sensitive, ‘critical’ parameters; computation of approximate, re-equilibrated solutions following a change (post-optimisation); robustness analysis of model forecasts to input data errors, in the form of confidence interval estimation; and the solution of problems of the bi-level, optimal network design variety. Finally, numerical experiments applying these methods are reported

Factors Determining Mortality of Adult Chaparral Shrubs in an Extreme Drought Year in California

We measured dieback and mortality in a chaparral shrub community at a chaparral/desert ecotone following four years of below-average rainfall. Ecotones are important systems in which to examine plant and community responses to extreme and prolonged drought conditions and the potential impact of global change on plant distributions and community composition. Following a particularly severe drought year, dieback and mortality were documented for seven co-dominant shrub species. We examined whether mortality was related to species ecology, leaf traits, or water relations. Dieback and mortality were greatest in two non-sprouting species. These species also had high xylem cavitation resistance and low specific leaf area compared to several sprouting species. Among two sprouting congeners, mortality was greater in the more shallowly rooted species, even though this species was more cavitation resistant. Across all species, those that were more resistant to cavitation had greater mortality. Evidently, high resistance to xylem cavitation does not prevent adult plant mortality at chaparral/desert ecotones. A series of extreme drought years could preferentially reduce or eliminate non-sprouting species from mixed chaparral populations, causing a shift in community structure and contributing to desertification

Hordenine : pharmacology, pharmacokinetics and behavioural effects in the horse

Hordenine is an alkaloid occurring naturally in grains, sprouting barley, and certain grasses. It is occasionally found in post race urine samples, and therefore we investigated its pharmacological actions in the horse. Hordenine (2.0 mgkg bodyweight [bwt]) was administered by rapid intravenous (iv) injection to 10 horses. Typically, dosed horses showed a tlehmen response and defecated within 60 secs. All horses showed substantial respiratory distress. Respiratory rates increased about 250 per cent and heart rates were approximately double that of resting values. All animals broke out in a sweat shortly after iv injection, but basal body temperature was not affected. These effects were transient, and the animals appeared normal within 30 mins of dosing. Tkeated horses were tested in a variable interval responding apparatus 30 mins after dosing and no residual stimulation or depressant effects of hordenine were apparent. Animals dosed orally with 2.0 mgkg bwt of hordenine showed no changes in heart rate, respiratory rate, basal body temperature or behaviour. After iv injection of hordenine, (2.0 mgkg bwt) plasma reached a maximum value of about 1.0 pglml, and declined thereafter in a biexponential fashion. Kinetics of plasma concentration satisfied the concept of a two compartment open system, with an a-phase half-life of about 3 mins, and a P-phase half-life of about 35 mins. Total urinary concentrations of hordenine (free and conjugated) peaked at about 400 pg/ml, and then declined exponentially to background levels by 24 h after dosing. Oral administration of hordenine (2.0 mgkg bwt) showed peak plasma levels of about 0.15 pg/ml 1 h after dosing, followed by a slow multi-exponential decline in blood levels of the drug. Total urinary concentrations of hordenine (free and conjugated) peaked at about 200 pg/ml, remained at this level for about 8 h, and then declined to background levels. Plasma levels of hordenine were reflected by a kinetic model which assumed very slow absorption of hordenine from the gastrointestinal tract and no effect on behaviour, heart rate or respiratory rate were noted after oral administration. Because of the low plasma levels, it would appear to be particularly difficult to obtain a pharmacological effect of hordenine after oral administration

Land management explains major trends in forest structure and composition over the last millennium in California's Klamath Mountains

For millennia, forest ecosystems in California have been shaped by fire from both natural processes and Indigenous land management, but the notion of climatic variation as a primary controller of the pre-colonial landscape remains pervasive. Understanding the relative influence of climate and Indigenous burning on the fire regime is key because contemporary forest policy and management are informed by historical baselines. This need is particularly acute in California, where 20th-century fire suppression, coupled with a warming climate, has caused forest densification and increasingly large wildfires that threaten forest ecosystem integrity and management of the forests as part of climate mitigation efforts. We examine climatic versus anthropogenic influence on forest conditions over 3 millennia in the western Klamath Mountains—the ancestral territories of the Karuk and Yurok Tribes—by combining paleoenvironmental data with Western and Indigenous knowledge. A fire regime consisting of tribal burning practices and lightning were associated with long-term stability of forest biomass. Before Euro-American colonization, the long-term median forest biomass was between 104 and 128 Mg/ha, compared to values over 250 Mg/ha today. Indigenous depopulation after AD 1800, coupled with 20th-century fire suppression, likely allowed biomass to increase, culminating in the current landscape: a closed Douglas fir–dominant forest unlike any seen in the preceding 3,000 y. These findings are consistent with precontact forest conditions being influenced by Indigenous land management and suggest large-scale interventions could be needed to return to historic forest biomass levels