In this paper, the hit-to-kill strategy is introduced to solve the three-dimensional (3D) robust head-pursuit (HP) interception problem considering the line-of-sight (LOS) angle constraints. Firstly, a target based re...
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In this paper, the hit-to-kill strategy is introduced to solve the three-dimensional (3D) robust head-pursuit (HP) interception problem considering the line-of-sight (LOS) angle constraints. Firstly, a target based relative dynamic model is proposed to be the nominal model for designing the robust HP guidance laws, where the HP interception problem is formulated as a target passively chases after the interceptor missile. Secondly, the 3D retro-proportional navigation (RPN) guidance law is reinterpreted from the point of control theory, which forces the corresponding guidance system asymptotically stable. Meanwhile, the concept of nullifying the LOS angular rates is successfully introduced to solve the 3D robust HP guidance problem via the sliding mode control. Thirdly, the LOS angles constrained robust HP guidance law is proposed based on the nonsingular terminal sliding mode control. The stabilities of the presented guidance laws are analyzed via the Lyapunov approach. The simulation results are in agreement with the theoretical statements.
Immersive virtual environments (IVEs) have been extensively investigated for applications in education and man-power training because of the benefits of immersion-driven experiences as immersion becomes a factor that ...
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Immersive virtual environments (IVEs) have been extensively investigated for applications in education and man-power training because of the benefits of immersion-driven experiences as immersion becomes a factor that can both accelerate and hamper learning depending on the user's area of focus, which supports the importance of engagement. In this paper, two fundamental approaches to visual engagement in IVE are compared: discipline and guidance. The approaches aim to foster the learner's engagement to predefined area to be focused by either subtracting visual stimuli (discipline) or appending visual indicators pointing to the area (guidance). The experimental results showed no significant improvement in memory recall accuracy and time. However, the guidance group showed superior performances in usability metrics. Interestingly, a significant difference was found in the objective measure of the participants' gaze pattern revealing that the discipline makes the user's gaze consistent and stable.
This paper employs a nonlinear cooperative deviated pursuit guidance strategy, for multiple interceptors, to ensure salvo interception. The problem of ensuring salvo is transformed into one of achieving consensus in t...
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This paper employs a nonlinear cooperative deviated pursuit guidance strategy, for multiple interceptors, to ensure salvo interception. The problem of ensuring salvo is transformed into one of achieving consensus in time-to-go within a finite time, over a directed cycle. By using a deviated pursuit-based guidance approach, the computation of exact time-to-go is facilitated based on interceptors' present states, thereby avoiding the need for estimation of time-to-go and small-angle approximations. Greater flexibility in controlling consensus value and time can be achieved by the choice of heterogeneous gains in the consensus algorithm. The stability and performance of the proposed nonlinear guidance are analysed using Lyapunov-based methods. A sensitivity analysis of time-to-go with respect to various engagement parameters is also carried out. Effectiveness of the proposed salvo guidance strategy is demonstrated through numerical simulations on constant speed, and also realistic, time-varying speed interceptor models.
We are developing guidance for space domain assurance personnel on how to assure Artificial intelligence (AI) and Machine Learning (ML) systems. Key to such guidance will be an assurance process for these personnel, w...
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ISBN:
(纸本)9781665476799
We are developing guidance for space domain assurance personnel on how to assure Artificial intelligence (AI) and Machine Learning (ML) systems. Key to such guidance will be an assurance process for these personnel, who may be unfamiliar with such systems, to follow. We are investigating one such process, the "Assurance of Machine Learning in Autonomous Systems (AMLAS)" from the University of York, UK. To gauge its suitability, we are (retrospectively) applying it to a safety critical AI/ML system in the space domain. We report here on our experience so far in applying this process.
The ability to return a sample or small payload from International Space Station to a target on the ground will be in high demand in the near future. To satisfy this demand, several universities and NASA centers have ...
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ISBN:
(纸本)9788993215243
The ability to return a sample or small payload from International Space Station to a target on the ground will be in high demand in the near future. To satisfy this demand, several universities and NASA centers have been researching such a sample return system. One of the main features of the sample return systems is that they aim to deliver payloads at a designated position on the ground without using a thruster;thus, onboard guidance is essential in improving targeting accuracy of this passive system. This paper presents a trajectory analysis to develop a novel guidance scheme that can determine an optimal ballistic coefficient and phase transition states for the passive sample return system. Numerical simulations show that the ballistic coefficient of the system highly affects the orbital decay rate and the targeting accuracy. Hence, if the novel onboard guidance scheme optimizes the ballistic coefficient and phase transition state, high targeting accuracy can be achieved. Furthermore, an onboard surrogate model that can estimate the vehicle's ballistic coefficient air density along the trajectory will assist the onboard guidance scheme in successfully guiding the sample return system.
This paper considers the combination of an analytical reference trajectory with linear state feedback control to allow for autonomous guidance and control of a spacecraft for coplanar circle-to-circle transfers with a...
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This paper considers the combination of an analytical reference trajectory with linear state feedback control to allow for autonomous guidance and control of a spacecraft for coplanar circle-to-circle transfers with a stage-based propulsion system. Staging of electric propulsion components, such as tanks and thrusters, could allow small spacecraft to achieve high-Delta V capabilities with current propulsion technology. In order to utilize these propulsion systems, further developments in guidance and control of such spacecraft are required due to limitations in computational power and communications. Analytical approximations for low-thrust trajectories could allow for computationally simple guidance and control of autonomous spacecraft for circle-to-circle transfers around large central bodies. Many trajectories have been developed for conventional propulsion systems, based either on their shape or input thrust, and applied for preliminary mission design. A previously developed analytical trajectory is extended to account for the effects of staging propulsion system components. In order to stabilize the trajectory in the presence of disturbances, a linear state feedback control law is designed with linear quadratic regulator methods. Finally, a methodology for determining the correct phasing between the spacecraft and a target object is developed and is practical to implement on power-limited computers. The use of the analytical reference trajectory is simulated on an orbit transfer from low-Earth orbit to geostationary orbit.
EFSA has prepared a guidance document on the assessment of studies on the nature and magnitude of pesticide residues in rotational crop studies as defined in Section 6.6 of the Annex to Regulation (EU) No 283/2013. Th...
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EFSA has prepared a guidance document on the assessment of studies on the nature and magnitude of pesticide residues in rotational crop studies as defined in Section 6.6 of the Annex to Regulation (EU) No 283/2013. This guidance document supports the practical implementation of the relevant OECD Test Guidelines (TGs) and OECD guidance Documents in a harmonised way, respecting the EU regulatory framework for the pesticide assessments. The individual steps of the assessment are illustrated by examples, figures and flow charts. Sources of uncertainty in these assessments are identified and recommendations for further work are provided.
Assisted human reproduction has undergone rapid advances since its inception 45 years ago. To keep pace with these advances, assisted reproduction laboratories should adhere to a quality management system that address...
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Assisted human reproduction has undergone rapid advances since its inception 45 years ago. To keep pace with these advances, assisted reproduction laboratories should adhere to a quality management system that addresses staffing and training, physical space and air quality, equipment maintenance and other operational matters, and ensures gamete and embryo handling in accordance with the latest quality and safety standards. Accordingly, this review aims to provide a reference document that highlights the critical aspects to consider when establishing and operating an ART laboratory. The review collates and expands upon published national and international guidelines and consensus documents, providing easier access to this large body of important information.
The EXTREMA THruster-In-the-Loop Experiment (ETHILE) is a facility designed for testing the effectiveness and robustness of spacecraft guidance algorithms through hardware actuation. Initially designed to simulate in ...
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The EXTREMA THruster-In-the-Loop Experiment (ETHILE) is a facility designed for testing the effectiveness and robustness of spacecraft guidance algorithms through hardware actuation. Initially designed to simulate in an accelerated framework the actuation of interplanetary transfers with low-thrust, the system is highly configurable as it can simulate different thruster behaviours with a thruster balance equipped with a compressed air nozzle. An overview of the system and its performance is given, highlighting through a practical example its possible use for research and educational purposes.
Internet-based cognitive behavioral therapy (ICBT) is promising in alleviating loneliness in adults. Identifying individuals who benefit from ICBT for loneliness is pivotal to offering this intervention in a more targ...
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Internet-based cognitive behavioral therapy (ICBT) is promising in alleviating loneliness in adults. Identifying individuals who benefit from ICBT for loneliness is pivotal to offering this intervention in a more targeted way and improving the intervention for those who do not benefit. This secondary analysis of a randomized controlled trial (RCT) aimed to identify predictors and moderators of outcome of an ICBT with guidance or automated messages for loneliness. In the RCT, 243 participants suffering from loneliness were randomly assigned to an ICBT with guidance (n = 98), automated messages (n = 97), or a waitlist-control condition (n = 48). In total, 180 participants completed the post-assessment (i.e., 10 weeks post-randomization). Outcomes were treatment outcome assessed with the UCLA-9 Loneliness Scale at post-assessment and treatment response, i.e., reliable improvement on the UCLA-9 from pre- to post. The relationship between a wide range of patient characteristics (grouped into socio-demographic, clinical, loneliness-specific, and treatment-related variables) and outcome was analyzed using multiple linear and logistic regressions. Feeling less burdened by loneliness resulted in higher odds of reliable improvement in guided ICBT compared to the waitlist-control condition. No treatment outcome or response moderators were identified for ICBT with automated messages compared to the waitlist-control group. Across active intervention groups, loneliness at baseline, age and fit between the tasks and goals of the intervention and participants' need predicted treatment outcome. Predictors of treatment response for ICBT with guidance and automated messages were not identified, and no variables differentially predicted the effects of ICBT with guidance or automated messages on the outcomes. In conclusion, individuals less burdened by their feelings of loneliness benefited more from guided ICBT. Lower baseline loneliness scores, younger age, and a better match between
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