Space Frontier Research Articles

Bayesian Optimization of Multiobjective Functions Using Multiple Information Sources

Multiobjective optimization is often a difficult task owing to the need to balance competing objectives. A typical approach to handling this is to estimate a Pareto frontier in objective space by identifying nondominated points. This task is typically computationally demanding owing to the need to incorporate information of high enough fidelity to be trusted in design and decision-making processes. In this work, we present a multi-information source framework for enabling efficient multiobjective optimization. The framework allows for the exploitation of all available information and considers both potential improvement and cost. The framework includes ingredients of model fusion, expected hypervolume improvement, and intermediate Gaussian process surrogates. The approach is demonstrated on a test problem and an aerostructural wing design problem.

Higher order hyperbolic quadrature method of moments for solving kinetic equations

This work attempts to solve two fundamental problems that can be encountered when solving kinetic equations using quadrature based moment methods (QBMM). These two problems are considered crucial problems since they are observed even in the simplest particulate systems. On the one hand, we have that particle trajectory crossing (PTC) events can lead to non-physical accumulation of particles in the solution when the system of transport equations is weakly hyperbolic (i.e. delta-shock formation). On the other hand, the fact that particle segregation events can create moment sets close to the frontier of moment space. These, in turn, can produce non-physical high-velocity fluxes that will significantly reduce the computational efficiency. Given that both problems are fundamental, we limit the framework to one-dimensional free transport of particles. For the first problem we create a novel hyperbolic quadrature moment closure. Although we lack formal analytic proof for a quadrature order (N) higher than three, the numerical examples presented clearly show a well-behaved solution, absent of delta-shocks up to an eight-order quadrature. Our solution to the second problem consists of two minor, though effective, modifications to the general numerical algorithm frequently used for solving kinetic equations using QBMM. The performance of the new algorithm is remarkably stable and efficient, shown by a numerical example.

New books & media

New books & media

Characterisation of 6DOF natural and controlled relative dynamics in cislunar space

At the 50th anniversary of Apollo 11, the Moon is back to the scene of scientific and commercial space exploration interests. During the next decade, the establishment of a Gateway in cislunar non-Keplerian orbits will open the space frontiers to sustainable manned and robotic missions on and around the Moon. Such infrastructure will require several logistic operations for its assembly and maintenance, which lean on rendezvous and docking capabilities. Even if few missions have flown on non-Keplerian orbits, Rendezvous and Docking (RV&D) operations have not been performed but in Low Earth Orbit (LEO). Investigations about 6 Degrees Of Freedom (DOF) relative dynamics in non-Keplerian environment are now mandatory to highlight criticalities in the design of the cislunar gateway and to translate RV&D protocols, consolidated in LEO for the International Space Station (ISS), to the new non-Keplerian environment. In this direction, the paper analyses the 6DOF natural orbit-attitude dynamics within the Circular Restricted Three-Body Problem (CR3BP) framework. A novel perspective of the dynamical structures, constituting 6DOF manifolds, allows to better characterise the natural relative dynamics in proximity of non-Keplerian orbits. The importance of orbit-attitude manifolds exploitation is underlined for designing reliable and efficient rendezvous trajectories, enhanced by natural cislunar dynamics.Then, an ephemeris cislunar dynamical model is exploited to address guidance laws for proximity operations. The control capability is included in the dynamics of a chaser vehicle, which is employed to solve the 6DOF guidance problem in proximity of a target spacecraft. The results obtained with the controlled dynamics are compared to those available thanks to natural motion, discussing the energetic and time costs to complete the manoeuvres. A control parametrisation to solve the optimal energy rendezvous problem is proposed.Finally, a feasible operational rendezvous scenario is discussed about the identified favourable locations along the non-Keplerian orbit to perform complex proximity operations. Significant relations between RV&D time and non-Keplerian orbit’s period are discussed as well.

Space: Science & Technology—Promoting Academic Exchange and Exploring the Frontiers of Space

Space: Science & Technology—Promoting Academic Exchange and Exploring the Frontiers of Space

Quantifying the impact of uncertainty in embedded systems mapping for NoC based architectures

We describe a modeling framework to capture and account for uncertainty in design parameters in embedded systems. We then develop an uncertainty-aware solution to the problem of mapping in embedded systems that uses Network-on-Chip (NoC) based architecture platforms. The problem of mapping is formulated as a multi-objective - reliability, performance, and energy consumption - optimization problem. To solve this problem, we propose a solution based on the NSGA-II genetic algorithm and Monte Carlo simulation techniques. The solution is implemented as a computer-aid design tool that can generate robust 3D Pareto frontiers in the solution space formed by the design objectives of reliability, performance, and energy consumption. Comparison to several state-of-the-art models and solutions for the mapping problem, indicate that significant differences in the actual values of the design attribute of interest exist when one considers uncertainty in design parameters. For example, in the case of mapping with reliability as the only objective, 10% uncertainty in design parameters can lead to a 10.06% difference in MTTF estimation. In the case of mapping with execution time and energy consumption as objectives, the difference in 2D Pareto frontiers due to 10% uncertainty in design parameters can be up to 7.9%. These differences are important because they can mislead the overall optimization process of mapping toward suboptimal solution points. The DESUU-NOC tool that implements the proposed multi-objective mapping algorithm has as a main feature and contribution of this paper the ability to generate 3D Pareto frontiers comprised of robust solution points.

Graph‐based subterranean exploration path planning using aerial and legged robots

AbstractAutonomous exploration of subterranean environments remains a major challenge for robotic systems. In response, this paper contributes a novel graph‐based subterranean exploration path planning method that is attuned to key topological properties of subterranean settings, such as large‐scale tunnel‐like networks and complex multibranched topologies. Designed both for aerial and legged robots, the proposed method is structured around a bifurcated local‐ and global‐planner architecture. The local planner utilizes a rapidly exploring random graph to reliably and efficiently identify paths that optimize an exploration gain within a local subspace, while simultaneously avoiding obstacles, respecting applicable traversability constraints and honoring dynamic limitations of the robots. Reflecting the fact that multibranched and tunnel‐like networks of underground environments can often lead to dead‐ends and accounting for the robot endurance, the global planning layer works in conjunction with the local planner to incrementally build a sparse global graph and is engaged when the system must be repositioned to a previously identified frontier of the exploration space, or commanded to return‐to‐home. The designed planner is detailed with respect to its computational complexity and compared against state‐of‐the‐art approaches. Emphasizing field experimentation, the method is evaluated within multiple real‐life deployments using aerial robots and the ANYmal legged system inside both long‐wall and room‐and‐pillar underground mines in the United States and in Switzerland, as well as inside an underground bunker. The presented results further include missions conducted within the Defense Advanced Research Projects Agency (DARPA) Subterranean Challenge, a relevant competition on underground exploration.

On Imposing ESG Constraints of Portfolio Selection for Sustainable Investment and Comparing the Efficient Frontiers in the Weight Space

Sustainable investment is typically fulfilled by screening of environmental, social, and governance (ESG); the screening strategies are practical and expedite sustainable-investment development. However, the strategies typically build portfolios by a list of good stocks and ignore portfolio completeness. Moreover, there has been limited literature to study the portfolio weights of sustainable investment in the weight space. In such an area, this article contributes to the literature as follows: We extend a conventional portfolio-selection model and impose ESG constraints. We analytically solve our model by computing the efficient frontier and prove that the frontier’s portfolio weights all lie on a ray (half line). By the ray structure, we prove that portfolio selection for sustainable investment and conventional portfolio selection fundamentally possess highly different portfolio weights. Overall, our aim is comparing the portfolio weights of sustainable portfolio selection and of conventional portfolio selection; the comparison result has been unknown until now. The result is important for sustainable investment because portfolio weights are the foundation of portfolio selection and investments. We sample the component stocks of Dow Jones Industrial Average Index from 2004 to 2013 and find that our efficient frontier and the conventional efficient frontier are quite similar. Therefore, in plain financial language, investors can still obtain risk-return performance similar to conventional portfolio selection after imposing strong ESG requirements, although the portfolio weights can be totally different. The result is both an endorsement and a reminder for sustainable investment.

Investigating the ratio of risk-to-return changes in efficient portfolio to achieve a new efficient portfolio

Given that not all points on the efficient portfolio frontier in the mean-variance space have constant returns to scale, and investments are determined according to the investor’s preferences, as investors may have conflicting preferences regarding the return and risk. Thus, risk-taking and expected returns are the criteria that determine the utility amount of the investment from selecting a portfolio of investment in assets. As a result, we may have a significant increase (reduction) in the return (risk) of efficient portfolio obtained with a small increase (reduction) in the amount of risk aversion (expected return). Two models presented in this paper are used to investigate this issue. The models are as follows: after obtaining an efficient portfolio, the first model maximises the ratio of the reduction of the risk rate to the reduction of the return rate. Also the second model maximises the ratio of increase in the return rate to the increase of the risk rate. If the optimal value is greater than one, the return (the risk) can be reduced (increased) to the extent obtained from this model to further reduce the risk (increase the return).

The quest for space capabilities and military security in Africa

ABSTRACT Many African nations are increasingly exploring the space frontier in pursuit of their development and security aspirations, with some 30 space agencies, 41 satellites and several ground facilities sponsored across the continent. Although most space programmes in Africa are administered by civilians and designed for research and development purposes, there is also a military-security dimension. During the Cold War, some African countries (prominently South Africa, Egypt and Libya) pursued space, missile and nuclear weapon triad capabilities until domestic and international political dynamics halted or softened those quests. From the second decade of 21st century, however, a new quest for military space capabilities has become evident in Africa. Several African states are embracing space support for military-security purposes. Hence, this study seeks to assess the growing interest and commitment to the acquisition of space capabilities in the military-security framework in Africa, considering the trajectories, opportunities, motivations and possible implications.

Harvesting Macroeconomic Risk Premia

The authors measure the aggregate state of the economy using variables motivated by the macro-finance literature. In particular, they focus on three specific measures: macro-growth, fragility, and volatility. Macro-growth, a procyclical measure, combines information from a series of macroeconomic variables related to economic growth. Fragility, a procyclical measure, is a proxy for the distance to default of the median firm in the economy. Volatility, a countercyclical measure, summarizes the volume of information produced by investors in equity markets. The authors find that these variables are associated with economically large risk premia, which can be harvested using portfolios composed of stocks, global index exchange-traded funds (ETFs), and cross-asset ETFs. <b>TOPICS:</b>Volatility measures, analysis of individual factors/risk premia, exchange-traded funds and applications <b>Key Findings</b> • The measures of macro-growth, fragility, and volatility summarize information related to multiple aspects of the business cycle. This information can be used to construct portfolios that compensate investors for exposure to such aggregate sources of risk. • Long–short equity portfolios with exposures to macro-growth, fragility, and volatility earn 5.43%, 2.26%, and −2.40% per annum, respectively. • Traded versions of the three factors expand the efficient frontier in the factor space, allowing for significant improvements in risk-adjusted performance.

Thule as Frontier

Located in Northwest Greenland, the Thule region is a remarkable frontier zone. This article focusses on the undecided nature of the frontier in both time and space. The article explores the unstable ground upon which ‘resources’ emerge as such. The case is made in three analytical parts: The first discusses the notion of commons and the implicit issue of spatiality. The second shows how the region’s living resources were perceived and poses a question of sustainability. The third centres on the Arctic as a ‘contact zone’; a place for colonial encounters and a meeting ground between human and nonhuman agents.

Observation of extremely efficient terahertz generation from mid-infrared two-color laser filaments

Extreme nonlinear interactions of THz electromagnetic fields with matter are the next frontier in nonlinear optics. However, reaching this frontier in free space is limited by the existing lack of appropriate powerful THz sources. Here, we experimentally demonstrate that two-color filamentation of femtosecond mid-infrared laser pulses at 3.9 μm allows one to generate ultrashort sub-cycle THz pulses with sub-milijoule energy and THz conversion efficiency of 2.36%, resulting in THz field amplitudes above 100 MV cm−1. Our numerical simulations predict that the observed THz yield can be significantly upscaled by further optimizing the experimental setup. Finally, in order to demonstrate the strength of our THz source, we show that the generated THz pulses are powerful enough to induce nonlinear cross-phase modulation in electro-optic crystals. Our work paves the way toward free space extreme nonlinear THz optics using affordable table-top laser systems.

Fractal structures in the parameter space of nontwist area-preserving maps.

Fractal structures are very common in the phase space of nonlinear dynamical systems, both dissipative and conservative, and can be related to the final state uncertainty with respect to small perturbations on initial conditions. Fractal structures may also appear in the parameter space, since parameter values are always known up to some uncertainty. This problem, however, has received less attention, and only for dissipative systems. In this work we investigate fractal structures in the parameter space of two conservative dynamical systems: the standard nontwist map and the quartic nontwist map. For both maps there is a shearless invariant curve in the phase space that acts as a transport barrier separating chaotic orbits. Depending on the values of the system parameters this barrier can break up. In the corresponding parameter space the set of parameter values leading to barrier breakup is separated from the set not leading to breakup by a curve whose properties are investigated in this work, using tools as the uncertainty exponent and basin entropies. We conclude that this frontier in parameter space is a complicated curve exhibiting both smooth and fractal properties, that are characterized using the uncertainty dimension and basin and basin boundary entropies.

Chechen Frontier in the Socio-Cultural Space of East Kazakhstan in Conditions of Deportation

The article covers the history of the totalitarian regime in the 40s of the 20thCentury on the territory of the Soviet Union, including Kazakhstan as an integral part of the Soviet empire. The chronological framework of events is connected with the Second World War, namely with the aggression of the Third Reich against the USSR. The regime of everyday military life reinforced the repressive actions of the Soviet government, the point was directed against the peoples accused of loyalty to the German troops. Chechens who were deported to Kazakhstan, including East Kazakhstan on 23 February 1944, became one of such ethnic groups affected by the totalitarian policy. The methodological basis of the study was an interdisciplinary approach, theoretical and methodological concepts of ‘collective memory’ in the projection of collective-individual, ‘cultural memory’, and ‘generational memory’. In the article, based on a wide range of sources and materials, the integration processes of Chechens and the ethnic dialogue with the Kazakh ethnic group and ethnic palette residing in East Kazakhstan in terms of production and outside its sphere are analysed. The research introduces to the scientific circulation archival and documentary sources and records of materials collected as a result of field expeditions, allowing to show the interaction of Chechens with the local population in conditions of deportation, with an attempt to improve social status by participating in socio-economic processes and preserving ethnic identity. The authors believe that the strategy of behaviour and the adaptation of the Chechen ethnos differed by their internal attitude to the status of the deported; their dispersed state and frontier conditions determined the individual strategy and tactics of survival.

Robustness of full revelation in multisender cheap talk

This paper studies information transmission in a two‐sender, multidimensional cheap talk setting where there are exogenous constraints on the (convex) feasible set of policies for the receiver, and where the receiver is uncertain about both the directions and the magnitudes of the senders' bias vectors. With the supports of the biases represented by cones, we prove that whenever there exists an equilibrium that fully reveals the state, there exists a robust fully revealing equilibrium (FRE), i.e., one in which small deviations result in only small punishments. We provide a geometric condition—the local deterrence condition—that relates the cones of the biases to the frontier of the policy space, which is necessary and sufficient for the existence of a FRE. We also construct a specific policy rule for the receiver—the min rule—that supports a robust FRE whenever one exists.

Fuzzy multivariate mean square error in equispaced pareto frontiers considering manufacturing process optimization problems

This paper proposes a combined approach using the normal boundary intersection (NBI) and multivariate mean square error (MMSE) that is an alternative approach to outperform the traditional NBI driving to an equispaced Pareto Frontier in a low-dimension space with a considerable reduction in the number of iterations. The method participating in the evolutionary stage of creating a uniformly spread Pareto Frontier for a nonlinear multi-objective problem is the NBI using normalized objective functions allied to MMSE. In sequence, the fuzzy MMSE approach is utilized to determine the optimal point of the multi-objective optimization. For sake of comparison, the performance of arc homotopy length, global criterion method, and weighted sums were explored. To illustrate this proposal, a multivariate case of AISI H13 hardened steel-turning process is used. Experimental results indicate that the solution found by NBI-MMSE approach is a more appropriate Pareto frontier that surpassed all the competitors and also provides the best-compromised solution to set the machine input parameters. Further, this algorithm was also tested in benchmark functions to confirm the NBI-MMSE efficiency.

Um nada fica a lembrar-se para sempre. Seis razões para gostar dos romances de Vergílio Ferreira

Os romances de Vergílio Ferreira fazem da nossa existência um romance que começa a ser escrito, obrigam a atravessar fronteiras (espaciais, filosóficas, genológicas), elucidam sobre a nossa condição de meta-animais físicos, dão-nos a linguagem segundo um modo análogo ao do jazz, ensinam que o amor vem só depois do fim e que o mundo é habitável se o olharmos a partir do impoder, dessa capacidade de levarmos o nosso abandono pela mão.

Robot Explorers

Robotic space probes have proven themselves to be capable explorers, roaming the solar system, observing the galaxy, and pushing back the boundaries of the final frontier. Those looking for a return to the glory days of human space exploration will need patience. NASA is aiming for a human landing on Mars in the 2030s, though cynics might contend that a Mars mission has been “just over the horizon” for a generation. Private-sector efforts in the near term are limited to suborbital tourism. Fortunately, NASA, the European Space Agency, and groups from other countries are readying a variety of missions that should answer some of astronomy’s biggest questions, all while keeping human feet firmly on the ground. In this article, we review nine unmanned missions that will explore new frontiers in space over the next decade.

Walking through the Energy-Error Pareto Frontier of Approximate Multipliers

In this article, we target approximate computing for arithmetic circuits, focusing on the most complex and power-hungry units: hardware multipliers. Driven by the lack of a clear solution on the energy-error efficiency of existing approximate multiplication techniques, we present a new, efficient, and easily applied approximation design, as well as explore the current state-of-the-art design space. We show that the proposed approximation scheme can be equally applied at design time to enable synthesis of customized approximate multiplier circuits and at runtime to support dynamic approximation tuning scenarios. We achieve significant gains-up to 69-percent energy and 64-percent area savings with respect to accurate designs-by proposing hybrid approximation performed by two independent techniques that reduce both the depth (through perforation) and the width (through rounding) of the partial products accumulation tree. The corresponding runtime approximation solution delivers energy gains of up to 47 percent, introducing negligible area. More importantly, we show that design solutions configured through the proposed approach form the Pareto frontier of the energy-error space when considering direct quantitative comparisons with existing state of the art.