Deflection Strategies Research Articles

Hole-Finding Learning Strategy for a Robot Assembly With Keyed Circular Peg

Taking the gear assembly of the reducer assembly line as a research background, the hole-finding strategy for robot assembly with keyed circular pegs is proposed to solve the problem of low hole-finding efficiency and success rate. in the circular hole-finding task, deviation domains were divided based on a static mechanism, position vector trajectory optimization in the step distance and direction was designed, and a deviation domain-force mapping relationship was established using a genetic algorithm-support vector machine (GA-SVM) classification algorithm; the accuracy of this algorithm is approximately 90.00%. Thirty groups completed the circular hole-finding task in an average time of 5.4 s. For the square hole-finding task, dual monocular cameras were integrated to identify corner points of the flat key and keyway. Image semantic segmentation based on deep learning was used for the corner-point recognition of the flat key to suppress the effect of changes in light intensity; the recognition has an average error of 0.39 mm. Coarse and fine adjustment circumferential deflection strategies were adopted sequentially. The 30 groups of square hole-finding tasks exhibited a 96.70% success rate in an average time of 10.2 s. The proposed hole-finding strategy improves the efficiency and success rate of the gear assembly.

Optimal deflection strategy of potential hazard asteroids by impacting small asteroids

In this paper, an optimal deflection strategy is proposed to deflect potential hazard asteroids (PHAs) by impacting small asteroids. In this method, the spacecraft is first launched to rendezvous with a candidate asteroid. The candidate asteroid is selected by analyzing the maximum fuel consumption of the spacecraft. The spacecraft flies with the small asteroid, and then it moves the small asteroid to impact the PHA. The particle swarm optimization algorithm (PSO) is applied to search for the optimal impact angle between the small asteroid and the PHA after determining the initial mass of the spacecraft that meets the requirements by using genetic algorithm (GA). Finally, optimizations are carried out to obtain the maximum deviation of the PHA’s orbit to the Earth. Numerical results show that the optimal impact angle plays a significant role in deflecting the PHA. Furthermore, the comparison between the approach with the optimal impact direction and the indirect impact method with centroid impact shows different deflection performances. In addition, direct impact strategies are compared with the method proposed in this paper. The result shows that the deviation of PHA with our approach is better than the direct kinetic impact method when the proper small asteroid is selected and the initial mass of the spacecraft is more than a specific value.

Intelligent selection of NEO deflection strategies under uncertainty

This paper presents an Intelligent Decision Support System (IDSS) that can automatically assess the suitable robust deflection strategies to respond to a Near Earth Objects (NEO) impact scenario. The input to the IDSS is the warning time, the orbital parameters and mass of the NEO and the corresponding uncertainties. The output is the deflection strategies that are more likely to offer a successful deflection. Both aleatory and epistemic uncertainties on ephemerides and physical properties of the NEO are considered.The training data set is produced by generating thousands of virtual impactors, sampled from the current distribution of NEO. For each virtual impactor we perform a robust optimisation, under mixed aleatory/epistemic uncertainties, of the deflection scenario with different deflection strategies. The robust performance indices is considered by the deflection effectiveness, which is quantified by Probability of Collision post deflection. The IDSS is based on a combination Dempster-Shafer theory of evidence and a Random Forest classifier that is trained on the data set of virtual impactors and deflection scenarios. Five deflection strategies are modelled and included in the IDSS: Nuclear Explosion, Kinetic Impactor, Laser Ablation, Gravity Tractor and Ion Beam Shepherd. Simulation results suggest that the proposed decision support system can quickly provide robust decisions on which deflection strategies are to be chosen to respond to a NEO impact scenario. Once trained the IDSS does not require re-running expensive simulations to make decisions on which deflection strategies are to be used and is, therefore, suitable for the rapid pre-screening or reassessment of deflection options.

Teaching about Fascism(s): The Relationship between Fascist Italy and Nazi Germany in Italian, West German, and East German Textbooks, 1950–60

The parallels and interconnections between Fascist Italy and Nazi Germany are not merely a matter of contemporary scholarly interest, but also were and still are a charged political and societal question. Through an analysis of discourse in school history textbooks, this article analyzes how scholars, students, teachers and state authorities perceived these parallels and interconnections during the immediate postwar period. The article investigates how the earliest history textbooks – published in the post-fascist successor states of Italy, West Germany, and East Germany between 1950 and 1960 – evaluated the relationship between Mussolini's Italy and Hitler's Germany during the 1930s. The 1930s are key because they began with Mussolini as the senior fascist dictator; over the course of the decade – with the war in Ethiopia, the Spanish Civil War, the passage of antisemitic racial laws, and the creation of the Pact of Steel – Hitler's Germany eclipsed Mussolini's Italy as the preeminent fascist power. By looking at postwar textbooks’ representations of the Fascist Italy–Nazi Germany relationship during the 1930s, we can see that the postwar post-fascist states often blamed each other for the emergence of the especially imperialist, racist and violent elements of fascism. Thus, this article illustrates how educational materials marshalled deflection strategies during the long process of Vergangenheitsbewältigung.

Feminist Sociology Confluences With Sport Science: Insights, Contradictions, and Silences in Interviewing Elite Women Athletes About Low Energy Availability

This article explores the socio-cultural dimensions of elite sportswomen’s experiences of low energy availability (LEA), focusing particularly on elite track cyclists. With a multidisciplinary research team (two sport scientists and a feminist sociologist), the project began with a suite of quantitative measures that identified five of eight women track cycling athletes categorized with LEA and three athletes categorized with sub-optimal energy availability. This was then followed by semi-structured interviews that revealed the athletes’ complex relationships with body image, menstruation, and nutrition practices, and varied experiences of LEA. Bringing the qualitative data into dialogue with the previously collated physiological data, however, helped us acknowledge the silences and deflection strategies among those with more severe cases of LEA. Ultimately, this article offers original insights both into elite track cyclists’ understandings of body image, menstruation, and nutrition as associated with LEA, and important reflections on the challenges of doing interviews with sportswomen on sensitive topics in high-performance sporting environments.

On the Delivery of DART-ejected Material from Asteroid (65803) Didymos to Earth

Abstract The Double Asteroid Redirection Test (DART) spacecraft is planned to impact the secondary of the binary asteroid (65803) Didymos in 2022 to assess deflection strategies for planetary defense. The impact will create a crater and release asteroidal material, some of which will escape the Didymos system. Because the closest point of approach of Didymos to Earth’s orbit is only 6 million km (about 16 times the Earth–Moon distance), some ejected material will make its way sooner or later to our planet, and the observation of these particles as meteors would increase the scientific payout of the DART mission. The DART project may also represent the first human-generated meteoroids to reach Earth and is a test case for human activity on asteroids and its eventual contribution to the meteoroid environment and spacecraft impact risk. This study examines the amount and timing of the delivery of meteoroids from Didymos to near-Earth space. This study finds that very little DART-ejected material will reach our planet, and most of that only after thousands of years. But some material ejected at the highest velocities could be delivered to Earth-crossing trajectories almost immediately, though at very low fluxes. Timing and radiant directions for material reaching Earth are calculated, though the detection of substantial numbers would indicate more abundant and/or faster ejecta than is expected. The DART impact will create a new meteoroid stream, though probably not a very dense one. However, larger, more capable asteroid impactors could create meteoroid streams in which the particle flux exceeds that naturally occurring in the solar system, with implications for spacecraft safety.

Asteroid de-spin and deflection strategy using a solar-sail spacecraft with reflectivity control devices

Various asteroid mitigation strategies have been proposed to avoid destructive impact events. In such a mission, the spinning motion of an asteroid can prevent a precise and effective deflection maneuver. To circumvent this problem, this study investigates a novel de-spin method using a solar sail spacecraft that is attached to the surface of an asteroid. In this approach, the solar radiation pressure torque induced by reflectivity control devices on the sail membrane is exploited to cancel out the spin rate of an asteroid without requiring fuel. In addition, once attitude control is achieved after the de-spin, the trajectory of the asteroid can be deflected by leveraging the solar radiation pressure force acting on the sail attached to the asteroid. This paper constructs general theories on the proposed asteroid de-spin and deflection methods and provides evidence that this novel strategy would be a feasible option for mitigating small and slow-spinning asteroids.

Strategy as nonsense: strategies for hunting the snark

PurposeThe purpose of this paper is to argue that there is a degree of nonsense in the idea that that an organisation has a strategy, since firms have no mind, heart or soul they cannot have a sense of purpose about themselves and their futures. The lecture considers the ways that those working in organisations, and those responsible for strategy, deflect their thoughts from this idea and the nonsense that results from it.Design/methodology/approachThe paper recasts Whittington’s Schools of Strategy as deflection strategies, arguing that they are coherent means of displacing attention from the absurdities that result from attributing strategies to organisations rather than people. The key points are illustrated by quotes from Lewis Carroll’s The Hunting of the Snark, as the leader of the heroic band faces and overcomes most of the key strategizing problem experience in business strategy.FindingsImportant issues such rationality, benchmarking, learning, leadership, followership and corporate social responsibility crumble into nonsense when it is recalled that these are all human, rather than organisational qualities.Practical implicationsMost strategies do not succeed and most management of change seldom achieves the changes desired. The paper argues that this is chiefly because pragmatic stratagems are frequently idealised into truth claims and prescriptions of doubtful provenance. Scholars of management must bear some responsibility for the resulting nonsense.Social implicationsThe paper argues that it is not possible to do strategy and change without invoking nonsense. Yet, this is a remarkable achievement, nonetheless, for a creature that evolved to chase small game across a savannah.Originality/valueThe paper raises important ontological and epidemiological issues of strategy and change in ways that neither create impenetrable language barriers nor require a philosophical background to grasp.

An efficient algorithm for global periodic orbits generation near irregular-shaped asteroids

Periodic orbits (POs) play an important role in understanding dynamical behaviors around natural celestial bodies. In this study, an efficient algorithm was presented to generate the global POs around irregular-shaped uniformly rotating asteroids. The algorithm was performed in three steps, namely global search, local refinement, and model continuation. First, a mascon model with a low number of particles and optimized mass distribution was constructed to remodel the exterior gravitational potential of the asteroid. Using this model, a multi-start differential evolution enhanced with a deflection strategy with strong global exploration and bypassing abilities was adopted. This algorithm can be regarded as a search engine to find multiple globally optimal regions in which potential POs were located. This was followed by applying a differential correction to locally refine global search solutions and generate the accurate POs in the mascon model in which an analytical Jacobian matrix was derived to improve convergence. Finally, the concept of numerical model continuation was introduced and used to convert the POs from the mascon model into a high-fidelity polyhedron model by sequentially correcting the initial states. The efficiency of the proposed algorithm was substantiated by computing the global POs around an elongated shoe-shaped asteroid 433 Eros. Various global POs with different topological structures in the configuration space were successfully located. Specifically, the proposed algorithm was generic and could be conveniently extended to explore periodic motions in other gravitational systems.

Effect of the finite size of an asteroid on its deflection using a tether–ballast system

Potentially hazardous near-Earth objects which can impose a significant threat on life on the planet have generated a lot of interest in the study of various asteroid deflection strategies. There are numerous asteroid deflection techniques suggested and discussed in the literature. This paper is focused on one of the non-destructive asteroid deflection strategies by attaching a long tether–ballast system to the asteroid. In the existing literature on this technique, very simplified models of the asteroid-tether–ballast system including a point mass model of the asteroid have been used. In this paper, the dynamical effect of using a finite size asteroid model on the asteroid deflection achieved is analyzed in detail. It has been shown that considering the finite size of the asteroid, instead of the point mass approximation, can have significant influence on the deflection predicted. Furthermore the effect of the tether-deployment stage, which is an essential part of any realistic asteroid deflection mission, on the predicted deflection is studied in this paper. Finally the effect of cutting the tether on the deflection achieved is analyzed and it has been shown that depending on the orbital properties of the asteroid as well as its size and rotational rate, cutting the tether at an appropriate time can increase the deflection achieved. Several numerical examples have been used in this paper to elaborate on the proposed technique and to quantitatively analyze the effect of different parameters on the asteroid deflection.

Deflection by kinetic impact: Sensitivity to asteroid properties

Impacting an asteroid with a spacecraft traveling at high speed delivers an impulsive change in velocity to the body. In certain circumstances, this strategy could be used to deflect a hazardous asteroid, moving its orbital path off of an Earth-impacting course. However, the efficacy of momentum delivery to asteroids by hypervelocity impact is sensitive to both the impact conditions (particularly velocity) and specific characteristics of the target asteroid. Here we numerically model asteroid response to kinetic impactors under a wide range of initial conditions, using an Adaptive Smoothed Particle Hydrodynamics code. Impact velocities spanning 1–30 km/s were investigated, yielding, for a particular set of assumptions about the modeled target material, a power-law dependence consistent with a velocity-scaling exponent of μ = 0.44. Target characteristics including equation of state, strength model, porosity, rotational state, and shape were varied, and corresponding changes in asteroid response were documented. The kinetic-impact momentum-multiplication factor, β, decreases with increasing asteroid cohesion and increasing porosity. Although increased porosity lowers β, larger porosities result in greater deflection velocities, as a consequence of reduced target masses for asteroids of fixed size. Porosity also lowers disruption risk for kinetic impacts near the threshold of disruption. Including fast (P = 2.5 h) and very fast (P = 100 s) rotation did not significantly alter β but did affect the risk of disruption by the impact event. Asteroid shape is found to influence the efficiency of momentum delivery, as local slope conditions can change the orientation of the crater ejecta momentum vector. These results emphasize the need for asteroid characterization studies to bracket the range of target conditions expected at near-Earth asteroids while also highlighting some of the principal uncertainties associated with the kinetic-impact deflection strategy.

Nuclear cycler: An incremental approach to the deflection of asteroids

This paper introduces a novel deflection approach based on nuclear explosions: the nuclear cycler. The idea is to combine the effectiveness of nuclear explosions with the controllability and redundancy offered by slow push methods within an incremental deflection strategy. The paper will present an extended model for single nuclear stand-off explosions in the proximity of elongated ellipsoidal asteroids, and a family of natural formation orbits that allows the spacecraft to deploy multiple bombs while being shielded by the asteroid during the detonation.

Simulations of Defense Strategies for Bennu: Material Characterization and Impulse Delivery

Assessments of asteroid deflection strategies depend on material characterization to reduce the uncertainty in predictions of the deflection velocity resulting from impulsive loading. In addition to strength, equation of state, the initial state of the material including its competency (i.e. fractured or monolithic) and the amount of micro- or macroscopic porosity are important considerations to predict the thermomechanical response. There is recent interest in observing near-Earth asteroid (101955) Bennu due to its classification of being potentially hazardous with close approaches occurring every 6 years. Bennu is relatively large with a nominal diameter of 492 m, density estimates ranging from 0.9-1.26 g/cm3 and is composed mainly of carbonaceous chondrite. There is a lack of data for highly porous carbonaceous chondrite at very large pressures and temperatures. In the absence of the specific material composition and state (e.g. layering, porosity as a function of depth) on Bennu we introduce a continuum constitutive model based on the response of granular materials and provide impact and standoff explosion simulations to investigate the response of highly porous materials to these types of impulsive loading scenarios. Simulations with impact speeds of 5 km/s show that the shock wave emanating from the impact site is highly dispersive and that a 10% porous material has a larger compacted volume compared with a 40% porous material with the same bulk density due to differences in compaction response. A three-dimensional simulation of a 190 kT standoff explosion 160 m off the surface of a shape model of Bennu estimated a deflection velocity of 10 cm/s.

The Experience of Relationship Dissolution among British South Asian Gay Men: Identity Threat and Protection

Relationship dissolution has generally been associated with decreased psychological well-being, but little is known about how ethnic and religious minority gay men experience and cope with relationship dissolution. This article examines interview data from sixteen self-identified British South Asian gay men who provided insights into how they experienced and coped with relationship dissolution and into the potential effects of this for identity. Data were analyzed qualitatively using interpretative phenomenological analysis and identity process theory. The following themes are outlined: (i) constructing identity around the relationship; (ii) relationship breakdown and threats to identity; and (iii) repairing identity in silence. The data indicate the centrality of the relationship to identity because of its ability to enhance identity processes and the detrimental effect for identity processes that dissolution can therefore have. Individuals relied heavily upon intrapsychic, deflection strategies for coping with identity threat, which was due to a general lack of social support. Minority group members who are fearful of disclosing their sexual identity to others may cope inadequately with relationship dissolution, exposing identity to chronic threat.

Selecting asteroids for a targeted spectroscopic survey

Asteroid spectroscopy reflects surface mineralogy. There are few thousand asteroids whose surfaces have been observed spectrally. Determining the surface properties of those objects is important for many practical and scientific applications, such as for example developing impact deflection strategies or studying history and evolution of the Solar System and planet formation. The aim of this study is to develop a pre-selection method that can be utilized in searching for asteroids of any taxonomic complex. The method could then be utilized im multiple applications such as searching for the missing V-types or looking for primitive asteroids. We used the Bayes Naive Classifier combined with observations obtained in the course of the Sloan Digital Sky Survey and the Wide-field Infrared Survey Explorer surveys as well as a database of asteroid phase curves for asteroids with known taxonomic type. Using the new classification method we have selected a number of possible V-type candidates. Some of the candidates were than spectrally observed at the Nordic Optical Telescope and South African Large Telescope. We have developed and tested the new pre-selection method. We found three asteroids in the mid/outer Main Belt that are likely of differentiated type. Near-Infrared are still required to confirm this discovery. Similarly to other studies we found that V-type candidates cluster around the Vesta family and are rare in the mid/oter Main Belt. The new method shows that even largely explored large databases combined together could still be further exploited in for example solving the missing dunite problem.

A simplified approach to uncertainty quantification for orbits in impulsive deflection scenarios

For the majority of near-Earth Asteroid (NEA) impact scenarios, optimal deflection strategies use a massive impactor or a nuclear explosive, either of which produce an impulsive change to the orbit of the object. However, uncertainties regarding the object composition and the efficiency of the deflection event lead to a non-negligible uncertainty in the deflection delta-velocity. Propagating this uncertainty through the resulting orbit will create a positional uncertainty envelope at the original impact epoch. We calculate a simplified analytic evolution for impulsively deflected NEAs and perform a full propagation of uncertainties that is nonlinear in the deflection delta-velocity vector. This provides an understanding of both the optimal deflection velocities needed for a given scenario, as well as the resulting positional uncertainty and corresponding residual impact probability. Confidence of a successful deflection attempt as a function of launch opportunities is also discussed for a specific case.

The ion beam shepherd: A new concept for asteroid deflection

A novel slow push asteroid deflection strategy has been recently proposed in which an Earth threatening asteroid can be deflected by exploiting the momentum transmitted by a collimated beam of quasi-neutral plasma impinging against the asteroid surface. The beam can be generated with state-of-the art ion engines from a hovering spacecraft with no need for physical attachment or gravitational interaction with the celestial body. The spacecraft, placed at a distance of a few asteroid diameters, would need an ion thruster pointed at the asteroid surface as well as a second propulsion system to compensate for the ion engine reaction and keep the distance between the asteroid and the shepherd satellite constant throughout the deflection phase. A comparison in terms of required spacecraft mass per total imparted deflection impulse shows that the method outperforms the gravity tractor concept by more than one order of magnitude for asteroids up to about 200m diameter. The two methods would yield comparable performance for asteroids larger than about 2km.

Accurate analytical approximation of asteroid deflection with constant tangential thrust

We present analytical formulas to estimate the variation of achieved deflection for an Earth-impacting asteroid following a continuous tangential low-thrust deflection strategy. Relatively simple analytical expressions are obtained with the aid of asymptotic theory and the use of Peláez orbital elements set, an approach that is particularly suitable to the asteroid deflection problem and is not limited to small eccentricities. The accuracy of the proposed formulas is evaluated numerically showing negligible error for both early and late deflection campaigns. The results will be of aid in planning future low-thrust asteroid deflection missions.

Mixing Convergence and Deflection Strategies for Packet Routing in All-Optical Networks

We present two routing algorithms based on deflection and convergence, which are able to provide high bandwidth and an ending guarantee for the end-to-end delay in a core network. We study the performance of these routing techniques by using simulations, and we prove the bounds on the delay.

WHY IRAQ?*

The US claim that the invasion and occupation of Iraq was a necessary component of the war on terror has been roundly criticized in both popular and scholarly discourse, while many major US allies were unsupportive. However, the present article argues that the US strategy can be viewed as a rational approach to combating transnational terrorist attacks on the American homeland. By deploying a large, activist contingent of troops in a geographical location relatively close to the terrorists' base of operations, a target country can, under certain specified circumstances, successfully deflect terrorist attacks away from domestic civilians, even if the effect of such deployment is not directly to diminish the terrorists' capacity to launch attacks. The interaction between the target government and a terrorist organization is characterized as a sequential move game, the solution to which identifies the conditions under which a deflection strategy maximizes the expected payoff to the target government. It is shown that the deflection strategy makes most sense when the perceived cost of a terrorist attack on the homeland is high and when the target nation is militarily strong and confident of success, has a relatively small proportion of its domestic population that is sympathetic to the terrorists' cause, and is geographically distant from the main base of terrorist operations. Target countries for which one or more of these conditions are absent might be expected to rationally reject such a strategy. *The authors are grateful for helpful comments from Qihong Liu, from participants in a session of the 2005 Public Choice Society annual conference in New Orleans, LA, and from the editors and referees of this journal. All errors and omissions remain the responsibility of the authors.