Journal articles on the topic 'Spacecraft path planning'

In order to solve the problem of path planning for the spacecraft cluster to reach the dynamic target point under the premise of considering obstacle avoidance. In view of the fixed search radius, it will be difficult for the spacecraft to find a better value when it is close to the target point. This paper converts the orbital dynamics of each member spacecraft into an optimization problem considering constraints, and proposes an improved CPSO algorithm based on coordination. The path planning method of the traditional particle swarm optimization (CPSO): The dynamic radius search method that changes the search radius by changing the distance between them, and improves the CPSO algorithm based on this. The improved CPSO algorithm autonomously finds the optimal path of each member spacecraft at the current moment through the dynamic search radius, thereby obtaining the optimal solution for the dynamic path planning of the spacecraft cluster in three-dimensional space. The simulation results show that the use of the improved CPSO algorithm can not only obtain the optimal solution to the spacecraft cluster dynamic path planning problem, but also greatly reduce the fuel consumption in its path planning and improve the path stability of each member spacecraft.

Considering the complex of space environment, the influence of flexible attachments, the restraint of measurement and control precision, it makes difficult to control the attitude precisely. In order to improve the attitude maneuver's rapidity and its stability, this paper studied the attitude maneuver's path programming method of satellite with the flexible attachments. Through the establishment of the dynamic model of flexible satellites, and using multi-objective optimization algorithm to select the optimal parameter, an asymmetric sinusoidal maneuver path was planned. Simulation results show that the planned path could suppress flexible appendages vibration which brought by attitude changes, then the effectiveness of the planning algorithm is demonstrated.

An adaptive learning pigeon-inspired optimization based on mutation disturbance (ALPIO) is proposed for solving the problems of fuel consumption and threat avoidance in spacecraft cluster orbit reconstruction. First, considering the constraints of maintaining a safe distance between adjacent spacecraft within the spacecraft cluster and of avoiding space debris, the optimal performance index for orbital reconfiguration is proposed based on the fuel consumption required for path planning. Second, ALPIO is proposed to solve the path planning. Compared with traditional pigeon-inspired optimization, ALPIO uses the initialization of chaotic and elite backward learning to increase the population diversity, using a nonlinear weighting factor and adjustment factor to control the speed and accuracy of prepopulation convergence. The Cauchy mutation was implemented in the map and compass operator to prevent the population from falling into local optima, and the Gaussian mutation and variation factor were utilized in the landmark operator to prevent the population from stagnating in the late evolution. Through simulation experiments using nine test functions, ALPIO is shown to significantly improve accuracy when obtaining the optimum compared with PSO, PIO, and CGAPIO, and orbital reconfiguration consumes less total fuel. The trajectory of path planning for ALPIO is smoother than those of other optimization methods, and its obstacle avoidance path is the most stable.

In many space missions, spacecraft are required to have the ability to avoid various obstacles and finally reach the target point. In this paper, the path planning of spacecraft attitude maneuver under boundary constraints and pointing constraints is studied. The boundary constraints and orientation constraints are constructed as finite functions of path evaluation. From the point of view of optimal time and shortest path, the constrained attitude maneuver problem is reduced to optimal time and path solving problem. To address this problem, a metaheuristic maneuver path planning method is proposed (cross-mutation grey wolf algorithm (CMGWO)). In the CMGWO method, we use angular velocity and control torque coding to model attitude maneuver, which increases the difficulty of solving the problem. In order to deal with this problem, the grey wolf algorithm is used for mutation and evolution, so as to reduce the difficulty of solving the problem and shorten the convergence time. Finally, simulation analysis is carried out under different conditions, and the feasibility and effectiveness of the method are verified by numerical simulation.

In this paper, the dynamic modelling of a new configuration spacecraft is investigated. The significance of dumbbell-shaped spacecraft to deep space exploration and the configuration of dumbbell-shaped spacecraft are introduced firstly. Then, the vibration problem of the dumbbell-shaped spacecraft of large-angle attitude maneuver is investigated, and a control program based on the combination of adaptive robust control (ARC) and component synthesis vibration suppression method-seven-section path planning (CSVS-SPP) is proposed. The large-angle attitude maneuver route of the spacecraft, which serves as the reference path, is planned using the CSVS-SPP approach, and the attitude controller is designed using the ARC. This program can effectively reduce the influence of external disturbance and parameter uncertainty on the system performance while completing attitude maneuver and suppress the vibration of the flexible beam during large-angle attitude maneuver. The numerical simulations show the superiority and effectiveness of the proposed ARC+CSVS-SPP.

In order to eliminate plume impingement on the target satellite, a free-floating space robot (also known as a chaser), which has the advantage of executing on-orbit service, is always used. This paper develops a path planning method for a safe rendezvous of chaser with a noncooperative target satellite in orbital coordinates. Safety principles for rendezvous in terminal approaching phase are proposed. Grasp points on the target satellite are analyzed and classified into two categories, and a moving ellipse trajectory is adopted to approach a rotating and uncontrolled target satellite. This method guarantees that the chaser can successfully escape if unexpected error occurs or capture fails. The simulation results show that, with this novel autonomous rendezvous method, the chaser can approach the noncooperative target satellite along the designated trajectory in any quadrant of the orbital plane.

Various path planning algorithms have been used to deduce optimal manipulator joint trajectories for spacecraft attitude regulation using arm motion. However, few papers have considered the unexpected factors when applying those planned path into actual situations. Even though conventional feedback control would drive the arm dynamics to the desired one, this only appears when time evolves to infinity which means during some time the actual joint paths deviate from the desired ones. However, the spacecraft attitude change is related to the entire process of arm motion. So, even a small deviation of the actual joint movement from the desired one would cause the failure of spacecraft attitude regulation task. In this paper, sliding mode control technique is adopted to force the actual joint moves along the desired trajectory from the start. Further, saturation function is used to eliminate the chattering phenomenon. Moreover, the relation between attitude regulation accuracy and controller parameters is deduced which gives instructions in tuning the controller parameters. In the end, numerical simulation is conducted to show the feasibility of the proposed controllers.

PurposeThe purpose of this paper is to propose an attitude control algorithm for spacecraft with geometric constraints.Design/methodology/approachThe geometric constraint is reformulated as a quadratic form when quaternion is used as attitude parameter, then the constraint is proved to be nonconvex and is further transformed to a convex one. By designing a new constraint formulation to satisfy the real constraint in the predictive horizon, the attitude control problem is reshaped to a convex planning problem which is based on receding horizon control.FindingsThe proposed algorithm is more effective in handling geometric constraints than previous research which used single step planning control.Practical implicationsWith novel improvements to current methods for steering spacecraft from one attitude to another with geometric constraints, great attitude maneuver path can be achieved to protect instruments and meanwhile satisfy mission requirements.Originality/valueThe attitude control algorithm in this paper is designed especially for the satisfaction of geometric constraints in the process of attitude maneuver of spacecraft. By the application of this algorithm, the security of certain optical instruments, which is critical in an autonomous system, can be further assured.

An analysis of the current pace of development of hypersonic technologies for the means of launching spacecraft into Earth orbit, as well as for unmanned weapons systems, which embody both impact properties and reconnaissance functions. In order to better understand the strategic importance of technologies based on direct-flow jet engines, fragmentary coverage of the impressive path of achievements of aerospace technology, given some of the highlights of the history of its formation. The presented article analyzes the current problem - increasing the reliability, reliability and accuracy of the definition and classification of moving targets by autonomous means of aircraft on combat duty. The results of the research cover the features of the starting positions and functional action on the combat duty of aircraft of different classes and bases and are able to serve as a reliable scientific basis for improving military equipment on hypersonic technologies

Abstract Rapid attitude path planning is the key technique in autonomous spacecraft operation missions. An efficient method is proposed for energy-optimal spacecraft attitude control in presence of constraints. Firstly, Gauss pseudospectral method is utilized to discretize and transcribe the primal continuous problem to a nonlinear programming problem. Then a set of convexification techniques are used to convexity the nonlinear programming problem to a series of second-order cone programming problems, which can be solved iteratively by the interior-point method. A solution to the nonlinear programming problem is obtained as the iteration converges. Numerical results show the method could obtain a valid energy-optimal attitude control plan more rapidly than traditional methods.

AbstractLeading space agencies are increasingly investing in the gradual automation of space missions. In fact, autonomous flight operations may be a key enabler for on-orbit servicing, assembly and manufacturing (OSAM) missions, carrying inherent benefits such as cost and risk reduction. Within the spectrum of proximity operations, this work focuses on autonomous path-planning for the reconstruction of geometry properties of an uncooperative target. The autonomous navigation problem is called active Simultaneous Localization and Mapping (SLAM) problem, and it has been largely studied within the field of robotics. Active SLAM problem may be formulated as a Partially Observable Markov Decision Process (POMDP). Previous works in astrodynamics have demonstrated that is possible to use Reinforcement Learning (RL) techniques to teach an agent that is moving along a pre-determined orbit when to collect measurements to optimize a given mapping goal. In this work, different RL methods are explored to develop an artificial intelligence agent capable of planning sub-optimal paths for autonomous shape reconstruction of an unknown and uncooperative object via imaging. Proximity orbit dynamics are linearized and include orbit eccentricity. The geometry of the target object is rendered by a polyhedron shaped with a triangular mesh. Artificial intelligent agents are created using both the Deep Q-Network (DQN) and the Advantage Actor Critic (A2C) method. State-action value functions are approximated using Artificial Neural Networks (ANN) and trained according to RL principles. Training of the RL agent architecture occurs under fixed or random initial environment conditions. A large database of training tests has been collected. Trained agents show promising performance in achieving extended coverage of the target. Policy learning is demonstrated by displaying that RL agents, at minimum, have higher mapping performance than agents that behave randomly. Furthermore, RL agent may learn to maneuver the spacecraft to control target lighting conditions as a function of the Sun location. This work, therefore, preliminary demonstrates the applicability of RL to autonomous imaging of an uncooperative space object, thus setting a baseline for future works.

For autonomous spacecraft close proximity under environments containing multiple obstacles and complicated constraints, incrementally rapid planning approaches stemming from sampling-based methods are investigated in this paper. Exploring planners are separately developed for the impulsive maneuvered translation and the piecewise constant controlled rotation, which, however, is constrained by the pointing limits coupling with relative positions during the proximity. Using a cost-informed parent-connecting strategy originating from dynamic programming as well as a sweeping growth fashion balanced between tree-based and graph-based methods, an asymptotically optimal unidirectional exploration method is proposed to search energy-efficient translational trajectory without collision. As for the rotation planning, the pointing constraints are taken as virtual obstacles in the state-space augmented with time horizon planned by the translation and, accordingly, a bidirectional exploration method is developed to generate constraint-satisfied slew paths with fast convergence rate. Numerical experiments indicate that the proposed sampling-based methods can rapidly return asymptotic optimal translation trajectory and rotation path satisfying collision avoidance and sensor field-of-view constraints.

As a new on-orbit detection platform, the space robot could ensure stable and reliable operation of spacecraft in complex space environments. The tracking accuracy of the space manipulator end-effector is crucial to the detection precision. In this paper, the Cartesian path planning method of velocity level inverse kinematics based on generalized Jacobian matrix (GJM) is proposed. The GJM will come across singularity issue in path planning, which leads to the infinite or incalculable joint velocity. To solve this issue, firstly, the singular value decomposition (SVD) is used for exposition of the singularity avoidance principle of the damped least squares (DLS) method. After that, the DLS method is improved by introducing an adaptive damping factor which changes with the singularity. Finally, in order to improve the tracking accuracy of the singularity-robust algorithm, the objective function is established, and two adaptive parameters are optimized by genetic algorithm (GA). The simulation of a 6-DOF free-floating space robot is carried out, and the results show that, compared with DLS method, the proposed method could improve the tracking accuracy of space manipulator end-effector.

This paper presents a model-based planner called the Probabilistic Sulu Planner or the p-Sulu Planner, which controls stochastic systems in a goal directed manner within user-specified risk bounds. The objective of the p-Sulu Planner is to allow users to command continuous, stochastic systems, such as unmanned aerial and space vehicles, in a manner that is both intuitive and safe. To this end, we first develop a new plan representation called a chance-constrained qualitative state plan (CCQSP), through which users can specify the desired evolution of the plant state as well as the acceptable level of risk. An example of a CCQSP statement is ``go to A through B within 30 minutes, with less than 0.001% probability of failure." We then develop the p-Sulu Planner, which can tractably solve a CCQSP planning problem. In order to enable CCQSP planning, we develop the following two capabilities in this paper: 1) risk-sensitive planning with risk bounds, and 2) goal-directed planning in a continuous domain with temporal constraints. The first capability is to ensures that the probability of failure is bounded. The second capability is essential for the planner to solve problems with a continuous state space such as vehicle path planning. We demonstrate the capabilities of the p-Sulu Planner by simulations on two real-world scenarios: the path planning and scheduling of a personal aerial vehicle as well as the space rendezvous of an autonomous cargo spacecraft.

The problem of artificial potential function (APF) safety and obstacle avoidance guidance for autonomous rendezvous and docking of chaser spacecraft with noncooperative spacecraft is studied. The relative motion equation of the chaser and the target is established based on the line-of-sight coordinate system, the reference state is designed, and the corresponding state error is deduced. The attitude motion equation of the noncooperative target spacecraft in space is established. The safety and obstacle avoidance guidance problem of autonomous rendezvous and docking with noncooperative target is transformed into a path planning problem in a dynamic environment. The attractive potential function is designed according to the state error. In order to ensure that the chaser can safely approach the noncooperative target spacecraft, a safe corridor with ellipse cissoid is designed in the final approaching stage of autonomous rendezvous and docking. The obstacle is assumed to be a sphere with a certain radius to avoid its influence in the approach, and the obstacle potential function is designed based on the Gaussian function method. The total potential function of the system is designed according to the attractive potential function, the safe potential function, and the obstacle potential function. The total potential function of the system is modified to ensure that the reference state is the minimum of the total potential function of the system. The stability of the system is proven according to the Lyapunov stability principle, and the conditions for satisfying the monotonic decrease in the total potential function of the system are deduced. Finally, the effectiveness of the proposed method is verified by three sets of numerical simulations.

Unary operator domains -- i.e., domains in which operators have a single effect -- arise naturally in many control problems. In its most general form, the problem of STRIPS planning in unary operator domains is known to be as hard as the general STRIPS planning problem -- both are PSPACE-complete. However, unary operator domains induce a natural structure, called the domain's causal graph. This graph relates between the preconditions and effect of each domain operator. Causal graphs were exploited by Williams and Nayak in order to analyze plan generation for one of the controllers in NASA's Deep-Space One spacecraft. There, they utilized the fact that when this graph is acyclic, a serialization ordering over any subgoal can be obtained quickly. In this paper we conduct a comprehensive study of the relationship between the structure of a domain's causal graph and the complexity of planning in this domain. On the positive side, we show that a non-trivial polynomial time plan generation algorithm exists for domains whose causal graph induces a polytree with a constant bound on its node indegree. On the negative side, we show that even plan existence is hard when the graph is a directed-path singly connected DAG. More generally, we show that the number of paths in the causal graph is closely related to the complexity of planning in the associated domain. Finally we relate our results to the question of complexity of planning with serializable subgoals.

A robust adaptive constrained control scheme is proposed for flexible spacecraft attitude maneuver and vibration suppression, in which multiple constraints are simultaneously considered, such as uncertain inertia parameters, external disturbance, unmeasured elastic vibration, actuator saturation, and even actuator misalignment. More specifically, a novel path planning scheme based on quintic polynomial transition is firstly developed to realize smooth acceleration variate and therefore decrease the vibration of flexible appendages. Secondly, an elastic modal estimator is employed to estimate the unmeasured variables, such as the modal position and velocity. Thirdly, an adaptive updating technique is used to spare the extra knowledge of system parameters and the bound of the external disturbance. In addition, an auxiliary design system is constructed to address the actuator saturation problem, and a compensation term is synthesized and integrated into the controller to handle the actuator misalignment. Finally, overall system stabilization is proved within the framework of Lyapunov theory, and numerical simulation results are presented to illustrate the effectiveness of the proposed scheme.

‘Intercontinental Space Flight – Learning from the Concorde’ understands that intercontinental earth-to-earth flights by spacecraft may operate in a legal quagmire where either or both space law or aviation law might apply. However, to the extent that the object of the flight is the intercontinental air transport of paying passengers, air law is more likely to apply to such flights. In such an event, any operator planning to offer inter-continental flights by spacecraft should learn from the difficulties the Concorde faced in launching supersonic trans-Atlantic flights to the United States in the 1970s. Despite the fact that the Concorde’s manufacturers had sought a US type certificate for the aircraft in 1965, it was not until Braniff, a US carrier, began to work with Air France and British Airways to operate Concorde between Washington and Dallas that Concorde’s fortunes improved. The complexity of the legal arrangements, which enabled Concorde to operate between Washington and Dallas, required the re-registration of the aircraft and the issuance of a US type certificate for Concorde. The issues examined during the issuance of the US type certificate cleared the path for a quarter century of US-Europe Concorde service. Since that incident, environmental and noise standards have become more stringent and issues such as social license require genuine commitment to deal with societal concerns. This is the context in which inter-continental space flight will operate, and the lessons of the Concorde’s entry into the US market provide useful guidance.

This paper proposes a planning method of the theoretically fastest slew path, and correspondingly, an analytical open-loop control law for the minimum-time eigenaxis rotation of spacecraft with three reaction wheels. The path planning and the control law are based on the angular momentum conservation of the spacecraft system. Then, a control scheme is also proposed to correct the maneuver error caused by model uncertainties. The control law and control scheme are verified in numerical simulation cases. The results show that the control law would realize the fastest slew path for an eigenaxis rotation, and the control scheme is feasible in shortening the slew time.

Abstract To solve the problem of spacecraft attitude manoeuvre planning under dynamic multiple mandatory pointing constraints and prohibited pointing constraints, a systematic attitude manoeuvre planning approach is proposed that is based on improved policy gradient reinforcement learning. This paper presents a succinct model of dynamic multiple constraints that is similar to a real situation faced by an in-orbit spacecraft. By introducing return baseline and adaptive policy exploration methods, the proposed method overcomes issues such as large variances and slow convergence rates. Concurrently, the required computation time of the proposed method is markedly reduced. Using the proposed method, the near optimal path of the attitude manoeuvre can be determined, making the method suitable for the control of micro spacecraft. Simulation results demonstrate that the planning results fully satisfy all constraints, including six prohibited pointing constraints and two mandatory pointing constraints. The spacecraft also maintains high orientation accuracy to the Earth and Sun during all attitude manoeuvres.

AbstractSolar phase scintillation is of major interest in deep space mission operations for designing a communications system capable of transmitting signals when the path is close to the Sun, but also for improving the navigation under these conditions. The basis of this work is Woo’s solar phase scintillation theory which reported a useful model for the spectral power density of phase scintillations of a signal traveling through a medium close to the Sun. In this paper, Woo’s solar phase scintillation formula is used for the simulation of the spectral density of phase fluctuations induced by the Sun on coherent signals (uplink and downlink carriers are coherently related by a fractional ratio implemented by the spacecraft’s transponder), for the two downlink frequency bands supported by the ESA deep space mission BepiColombo. In particular, the model has been compared to measurement data collected at low Sun Earth Probe (SEP) angles during the superior solar conjunction campaign in March 2021 (in its cruise phase to Mercury). The comparison shows a good match between the phase noise spectral densities of the modified formula and measurement data, therefore, confirming that the formula can be used for the planning and verification of the future near Sun measurements.

Abstract China is planning to construct a new space-borne gravitational-wave (GW) observatory, the TianQin project, in which the spaceborne telescope is an important component in laser interferometry. The telescope is aimed to transmit laser beams between the spacecrafts for the measurement of the displacements between proof-masses in long arms. The telescope should have ultra-small wavefront deviation to minimize noise caused by pointing error, ultra-stable structure to minimize optical path noise caused by temperature jitter, ultra-high stray light suppression ability to eliminate background noise. In this paper, we realize a telescope system design with ultra-stable structure as well as ultra-low wavefront distortion for the space-based GW detection mission. The design requirements demand extreme control of high image quality and extraordinary stray light suppression ability. Based on the primary aberration theory, the initial structure design of the mentioned four-mirror optical system is explored. After optimization, the maximum RMS wavefront error is less than λ/300 over the full field of view (FOV), which meets the noise budget on the telescope design. The stray light noise caused by the back reflection of the telescope is also analyzed. The noise at the position of optical bench is less than 10-10 of the transmitted power, satisfying the requirements of space gravitational-wave detection. We believe that our design can be a good candidate for TianQin project, and can also be a good guide for the space telescope design in any other similar science project.

In Charged Particle Therapy (PT) proton or 12C beams are used to treat deep-seated solid tumors exploiting the advantageous characteristics of charged particles energy deposition in matter. For such projectiles, the maximum of the dose is released at the end of the beam range, in the Bragg peak region, where the tumour is located. However, the nuclear interactions of the beam nuclei with the patient tissues can induce the fragmentation of projectiles and/or target nuclei and needs to be carefully taken into account when planning the treatment. In proton treatments, the target fragmentation produces low energy, short range fragments along all the beam path, that deposit a non-negligible dose especially in the first crossed tissues. On the other hand, in treatments performed using 12C, or other (4He or 16O) ions of interest, the main concern is related to the production of long range fragments that can release their dose in the healthy tissues beyond the Bragg peak. Understanding nuclear fragmentation processes is of interest also for radiation protection in human space flight applications, in view of deep space missions. In particular 4He and high-energy charged particles, mainly 12C, 16O, 28Si and 56Fe, provide the main source of absorbed dose in astronauts outside the atmosphere. The nuclear fragmentation properties of the materials used to build the spacecrafts need to be known with high accuracy in order to optimise the shielding against the space radiation. The study of the impact of these processes, which is of interest both for PT and space radioprotection applications, suffers at present from the limited experimental precision achieved on the relevant nuclear cross sections that compromise the reliability of the available computational models. The FOOT (FragmentatiOn Of Target) collaboration, composed of researchers from France, Germany, Italy and Japan, designed an experiment to study these nuclear processes and measure the corresponding fragmentation cross sections. In this work we discuss the physics motivations of FOOT, describing in detail the present detector design and the expected performances, coming from the optimization studies based on accurate FLUKA MC simulations and preliminary beam test results. The measurements planned will be also presented.

IntroductionIt has been nearly half a century since the appearance of Susan Sontag’s landmark essay “The Imagination of Disaster.” The critic wrote of the public fascination with science fiction disaster films, claiming that, on the one hand “from a psychological point of view, the imagination of disaster does not greatly differ from one period in history to another [but, on the other hand] from a political and moral point of view, it does” (224). Even if Sontag is right about aspects of the imagination of disaster not changing, the types, frequency, and magnitude of disasters and their representation in media and popular culture suggest that dynamic conditions prevail on both counts. Disaster has become a significantly urban phenomenon, and highly publicised “worst case” scenarios such as Hurricane Katrina and the Haiti earthquake highlight multiple demographic, cultural, and environmental contexts for visualising cataclysm. The 1950s and 60s science fiction films that Sontag wrote about were filled with marauding aliens and freaks of disabused science. Since then, their visual and dramatic effects have been much enlarged by all kinds of disaster scenarios. Partly imagined, these scenarios have real-life counterparts with threats from terrorism and the war on terror, pan-epidemics, and global climate change. Sontag’s essay—like most, if not all of the films she mentions—overlooked the aftermath; that is, the rebuilding, following extra-terrestrial invasion. It ignored what was likely to happen when the monsters were gone. In contrast, the psychological as well as the practical, social, and economic aspects of reconstruction are integral to disaster discourse today. Writing about how architecture might creatively contribute to post-conflict (including war) and disaster recovery, for instance, Boano elaborates the psychological background for rebuilding, where the material destruction of dwellings and cities “carries a powerful symbolic erosion of security, social wellbeing and place attachment” (38); these are depicted as attributes of selfhood and identity that must be restored. Similarly, Hutchison and Bleiker (385) adopt a view evident in disaster studies, that disaster-struck communities experience “trauma” and require inspired responses that facilitate “healing and reconciliation” as well as material aid such as food, housing, and renewed infrastructure. This paper revisits Sontag’s “The Imagination of Disaster,” fifty years on in view of the changing face of disasters and their representation in film media, including more recent films. The paper then considers disaster recovery and outlines the difficult path that “creative industries” like architecture and urban planning must tread when promising a vision of rebuilding that provides for such intangible outcomes as “healing and reconciliation.” We find that hopes for the seemingly positive psychologically- and socially-recuperative outcomes accompanying the prospect of rebuilding risk a variety of generalisation akin to wish-fulfilment that Sontag finds in disaster films. The Psychology of Science Fiction and Disaster FilmsIn “The Imagination of Disaster,” written at or close to the height of the Cold War, Sontag ruminates on what America’s interest in, if not preoccupation with, science fiction films tell us about ourselves. Their popularity cannot be explained in terms of their entertainment value alone; or if it can, then why audiences found (and still find) such films entertaining is something that itself needs explanation.Depicted in media like photography and film, utopian and dystopian thought have at least one thing in common. Their visions of either perfected or socially alienated worlds are commonly prompted by criticism of the social/political status quo and point to its reform. For Sontag, science fiction films portrayed both people’s worst nightmares concerning disaster and catastrophe (e.g. the end of the world; chaos; enslavement; mutation), as well as their facile victories over the kinds of moral, political, and social dissolution the films imaginatively depicted. Sontag does not explicitly attribute such “happy endings” to wish-fulfilling phantasy and ego-protection. (“Phantasy” is to be distinguished from fantasy. It is a psychoanalytic term for states of mind, often symbolic in form, resulting from infantile wish-fulfilment, desires and instincts.) She does, however, describe the kinds of fears, existential concerns (like annihilation), and crises of meaning they are designed (purpose built) to allay. The fears are a product of the time—the down and dark side of technology (e.g. depersonalisation; ambivalence towards science, scientists, and technology) and changes wrought in our working and personal lives by urbanisation. In short, then as now, science fictions films were both expressions of deep and genuine worries and of the pressing need to inventively set them to rest.When Sontag claims that “the imagination of disaster does not greatly differ” (224) from one period to another, this is because, psychologically speaking, neither the precipitating concerns and fears (death, loss of love, meaninglessness, etc.), nor the ways in which people’s minds endeavour to assuage them, substantively differ. What is different is the way they are depicted. This is unsurprisingly a function of the political, social, and moral situations and milieus that provide the context in which the imagination of disaster unfolds. In contemporary society, the extent to which the media informs and constructs the context in which the imagination operates is unprecedented.Sontag claims that there is little if any criticism of the real social and political conditions that bring about the fears the films depict (223). Instead, fantasy operates so as to displace and project the actual causes away from their all too human origins into outer space and onto aliens. In a sense, this is the core and raison d’etre for such films. By their very nature, science fiction films of the kind Sontag is discussing cannot concern themselves with genuine social or political criticism (even though the films are necessarily expressive of such criticism). Any serious questioning of the moral and political status quo—conditions that are responsible for the disasters befalling people—would hamper the operation of fantasy and its production of temporarily satisfying “solutions” to whatever catastrophe is being depicted.Sontag goes on to discuss various strategies science fiction employs to deal with such fears. For example, through positing a bifurcation between good and evil, and grossly oversimplifying the moral complexity of situations, it allows one to “give outlet to cruel or at least amoral feelings” (215) and to exercise feelings of superiority—moral and otherwise. Ambiguous feelings towards science and technology are repressed. Quick and psychologically satisfying fixes are sought for these by means of phantasy and the imaginative construction of invulnerable heroes. Much of what Sontag says can straightforwardly be applied to catastrophe in general. “Alongside the hopeful fantasy of moral simplification and international unity embodied in the science fiction films lurk the deepest anxieties about contemporary existence” (220). Sontag writes:In the films it is by means of images and sounds […] that one can participate in the fantasy of living through one’s own death and more, the death of cities, the destruction of humanity itself. Science fiction films are not about science. They are about disaster, which is one of the oldest subjects in art. In science fiction films disaster is rarely viewed intensively; it is always extensive. It is a matter of quality and ingenuity […] the science fiction film […] is concerned with the aesthetics of disaster […] and it is in the imagery of destruction that the core of a good science fiction film lies. (212–13)In science fiction films, disaster, though widespread, is viewed intensively as well as extensively. The disturbances constitutive of the disaster are moral and emotional as well as material. People are left without the mental or physical abilities they need to cope. Government is absent or useless. We find ourselves in what amounts to what Naomi Zack (“Philosophy and Disaster”; Ethics for Disaster) describes as a Hobbesian second state of nature—where government is inoperative and chaos (moral, social, political, personal) reigns. Science fiction’s way out is to imaginatively construct scenarios emotionally satisfying enough to temporarily assuage the distress (anomie or chaos) experienced in the film.There is, however, a tremendous difference in the way in which people who face catastrophic occurrences in their lives, as opposed to science fiction, address the problems. For one thing, they must be far closer to complex and quickly changing realities and uncertain truths than are the phantastic, temporarily gratifying, and morally unproblematic resolutions to the catastrophic scenarios that science fiction envisions. Genuine catastrophe, for example war, undermines and dismantles the structures—material structures to be sure but also those of justice, human kindness, and affectivity—that give us the wherewithal to function and that are shown to be inimical to catastrophe as such. Disaster dispenses with civilization while catastrophe displaces it.Special Effects and Changing StorylinesScience fiction and disaster film genres have been shaped by developments in visual simulation technologies providing opportunities for imaginatively mixing fact and fiction. Developments in filmmaking include computer or digital techniques for reproducing on the screen what can otherwise only be imagined as causal sequences of events and spectacles accompanying the wholesale destruction of buildings and cities—even entire planets. Indeed films are routinely promoted on the basis of how cinematographers and technicians have advanced the state of the art. The revival of 3-D movies with films such as Avatar (2009) and Prometheus (2012) is one of a number of developments augmenting the panoramas of 1950s classics featuring “melting tanks, flying bodies, crashing walls, awesome craters and fissures in the earth, plummeting spacecraft [and] colourful deadly rays” (Sontag 213). An emphasis on the scale of destruction and the wholesale obliteration of recognisable sites emblematic of “the city” (mega-structures like the industrial plant in Aliens (1986) and vast space ships like the “Death Star” in two Star Wars sequels) connect older films with new ones and impress the viewer with ever more extraordinary spectacle.Films that have been remade make for useful comparison. On the whole, these reinforce the continuation and predictability of some storylines (for instance, threats of extra-terrestrial invasion), but also the attenuation or disappearance of other narrative elements such as the monsters and anxieties released by mid-twentieth century atomic tests (Broderick). Remakes also highlight emerging themes requiring novel or updated critical frameworks. For example, environmental anxieties, largely absent in 1950s science fiction films (except for narratives involving colliding worlds or alien contacts) have appeared en masse in recent years, providing an updated view on the ethical issues posed by the fall of cities and communities (Taylor, “Urban”).In The Invasion of the Bodysnatchers and its remakes (1956, 1978, 1993), for example, the organic and vegetal nature of the aliens draws the viewer’s attention to an environment formed by combative species, allowing for threats of infestation, growth and decay of the self and individuality—a longstanding theme. In the most recent version, The Invasion (2007), special effects and directorial spirit render the orifice-seeking tendrils of the pod creatures threateningly vigorous and disturbing (Lim). More sanctimonious than physically invasive, the aliens in the 1951 version of The Day the Earth Stood Still are fed up with humankind’s fixation with atomic self-destruction, and threaten global obliteration on the earth (Cox). In the 2008 remake, the suave alien ambassador, Keanu Reeves, targets the environmental negligence of humanity.Science, including science as fiction, enters into disaster narratives in a variety of ways. Some are less obvious but provocative nonetheless; for example, movies dramatising the arrival of aliens such as War of the Worlds (1953 and 2005) or Alien (1979). These more subtle approaches can be personally confronting even without the mutation of victims into vegetables or zombies. Special effects technologies have made it possible to illustrate the course of catastrophic floods and earthquakes in considerable scientific and visual detail and to represent the interaction of natural disasters, the built environment, and people, from the scale of buildings, homes, and domestic lives to entire cities and urban populations.For instance, the blockbuster film The Day After Tomorrow (2004) runs 118 minutes, but has an uncertain fictional time frame of either a few weeks or 72 hours (if the film’s title is to taken literally). The movie shows the world as we know it being mostly destroyed. Tokyo is shattered by hailstones and Los Angeles is twisted by cyclones the likes of which Dorothy would never have seen. New York disappears beneath a mountainous tsunami. All of these events result from global climate change, though whether this is due to human (in) action or other causes is uncertain. Like their predecessors, the new wave of disaster movies like The Day After Tomorrow makes for questionable “art” (Annan). Nevertheless, their reception opens a window onto broader political and moral contexts for present anxieties. Some critics have condemned The Day After Tomorrow for its scientific inaccuracies—questioning the scale or pace of climate change. Others acknowledge errors while commending efforts to raise environmental awareness (Monbiot). Coincident with the film and criticisms in both the scientific and political arena is a new class of environmental heretic—the climate change denier. This is a shadowy character commonly associated with the presidency of George W. Bush and the oil lobby that uses minor inconsistencies of science to claim that climate change does not exist. One thing underlying both twisting facts for the purposes of making science fiction films and ignoring evidence of climate change is an infantile orientation towards the unknown. In this regard, recent films do what science fiction disaster films have always done. While freely mixing truths and half-truths for the purpose of heightened dramatic effect, they fulfil psychological tasks such as orchestrating nightmare scenarios and all too easy victories on the screen. Uncertainty regarding the precise cause, scale, or duration of cataclysmic natural phenomena is mirrored by suspension of disbelief in the viability of some human responses to portrayals of urban disaster. Science fiction, in other words, invites us to accept as possible the flight of Americans and their values to Mexico (The Day After Tomorrow), the voyage into earth’s molten core (The Core 2003), or the disposal of lava in LA’s drainage system (Volcano 1997). Reinforcing Sontag’s point, here too there is a lack of criticism of the real social and political conditions that bring about the fears depicted in the films (223). Moreover, much like news coverage, images in recent natural disaster films (like their predecessors) typically finish at the point where survivors are obliged to pick up the pieces and start all over again—the latter is not regarded as newsworthy. Allowing for developments in science fiction films and the disaster genre, Sontag’s observation remains accurate. The films are primarily concerned “with the aesthetics of destruction, with the peculiar beauties to be found in wreaking havoc, in making a mess” (213) rather than rebuilding. The Imagination of Disaster RecoverySontag’s essay contributes to an important critical perspective on science fiction film. Variations on her “psychological point of view” have been explored. (The two discourses—psychology and cinema—have parallel and in some cases intertwined histories). Moreover, in the intervening years, psychological or psychoanalytical terms and narratives have themselves become even more a part of popular culture. They feature in recent disaster films and disaster recovery discourse in the “real” world.Today, with greater frequency than in the 1950s and 60s films arguably, representations of alien invasion or catastrophic global warming serve to background conflict resolutions of a more quotidian and personal nature. Hence, viewers are led to suspect that Tom Cruise will be more likely to survive the rapacious monsters in the latest The War of the Worlds if he can become less narcissistic and a better father. Similarly, Dennis Quaid’s character will be much better prepared to serve a newly glaciated America for having rescued his son (and marriage) from the watery deep-freezer that New York City becomes in The Day After Tomorrow. In these films the domestic and familial comprise a domain of inter-personal and communal relations from which victims and heroes appear. Currents of thought from the broad literature of disaster studies and Western media also call upon this domain. The imagination of disaster recovery has come to partly resemble a set of problems organised around the needs of traumatised communities. These serve as an object of urban governance, planning, and design conceived in different ways, but largely envisioned as an organic unity that connects urban populations, their pasts, and settings in a meaningful, psychologically significant manner (Furedi; Hutchison and Bleiker; Boano). Terms like “place” or concepts like Boano’s “place-attachment" (38) feature in this discourse to describe this unity and its subjective dimensions. Consider one example. In August 2006, one year after Katrina, the highly respected Journal of Architectural Education dedicated a special issue to New Orleans and its reconstruction. Opening comments by editorialist Barbara Allen include claims presupposing enduring links between the New Orleans community conceived as an organic whole, its architectural heritage imagined as a mnemonic vehicle, and the city’s unique setting. Though largely unsupported (and arguably unsupportable) the following proposition would find agreement across a number of disaster studies and resonates in commonplace reasoning:The culture of New Orleans is unique. It is a mix of ancient heritage with layers and adaptations added by successive generations, resulting in a singularly beautiful cultural mosaic of elements. Hurricane Katrina destroyed buildings—though not in the city’s historic core—and displaced hundreds of thousands of people, but it cannot wipe out the memories and spirit of the citizens. (4) What is intriguing about the claim is an underlying intellectual project that subsumes psychological and sociological domains of reasoning within a distinctive experience of community, place, and memory. In other words, the common belief that memory is an intrinsic part of the human condition of shock and loss gives form to a theory of how urban communities experience disaster and how they might re-build—and justify rebuilding—themselves. This is problematic and invites anachronistic thinking. While communities are believed to be formed partly by memories of a place, “memory” is neither a collective faculty nor is it geographically bounded. Whose memories are included and which ones are not? Are these truly memories of one place or do they also draw on other real or imagined places? Moreover—and this is where additional circumspection is inspired by our reading of Sontag’s essay—does Allen’s editorial contribute to an aestheticised image of place, rather than criticism of the social and political conditions required for reconstruction to proceed with justice, compassionately and affectively? Allowing for civil liberties to enter the picture, Allen adds “it is necessary to enable every citizen to come back to this exceptional city if they so desire” (4). However, given that memories of places and desires for their recovery are not univocal, and often contain competing visions of what was and should be, it is not surprising they should result in competing expectations for reconstruction efforts. This has clearly proven the case for New Orleans (Vederber; Taylor, “Typologies”)ConclusionThe comparison of films invites an extension of Sontag’s analysis of the imagination of disaster to include the psychology, politics, and morality of rebuilding. Can a “psychological point of view” help us to understand not only the motives behind capturing so many scenes of destruction on screen and television, but also something of the creative impulses driving reconstruction? This invites a second question. How do some impulses, particularly those caricatured as the essence of an “enterprise culture” (Heap and Ross) associated with America’s “can-do” or others valorised as positive outcomes of catastrophe in The Upside of Down (Homer-Dixon), highlight or possibly obscure criticism of the conditions which made cities like New Orleans vulnerable in the first place? The broad outline of an answer to the second question begins to appear only when consideration of the ethics of disaster and rebuilding are taken on board. If “the upside” of “the down” wrought by Hurricane Katrina, for example, is rebuilding of any kind, at any price, and for any person, then the equation works (i.e., there is a silver lining for every cloud). If, however, the range of positives is broadened to include issues of social justice, then the figures require more complex arithmetic.ReferencesAllen, Barbara. “New Orleans and Katrina: One Year Later.” Journal of Architectural Education 60.1 (2006): 4.Annan, David. Catastrophe: The End of the Cinema? London: Lorrimer, 1975.Boano, Camillo. “‘Violent Space’: Production and Reproduction of Security and Vulnerabilities.” The Journal of Architecture 16 (2011): 37–55.Broderick, Mick, ed. Hibakusha Cinema: Hiroshima, Nagasaki and the Nuclear Image in Japanese Film. London: Kegan Paul, 1996.Cox, David. “Get This, Aliens: We Just Don’t Care!” The Guardian 15 Dec. 2008 ‹http://www.guardian.co.uk/film/filmblog/2008/dec/15/the-day-the-earth-stood-still›. Furedi, Frank. “The Changing Meaning of Disaster.” Area 39.4 (2007): 482–89.Heap, Shaun H., and Angus Ross, eds. Understanding the Enterprise Culture: Themes in the Work of Mary Douglas. Edinburgh: Edinburgh University Press, 1992. 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New York: Rowman and Littlefield, 2009.———. “Philosophy and Disaster.” Homeland Security Affairs 2, article 5 (April 2006): ‹http://www.hsaj.org/?article=2.1.5›.FilmographyAlien. Dir. Ridley Scott. Brandywine Productions, 1979.Aliens. Dir. James Cameron. Brandywine Productions, 1986.Avatar. Dir. James Cameron. Lightstorm Entertainment et al., 2009.The Core. Dir. Jon Amiel. Paramount Pictures, 2003.The Day after Tomorrow. Dir. Roland Emmerich. 20th Century Fox, 2004.The Invasion of the Body Snatchers. Dir. Don Siegel. Allied Artists, 1956; also 1978 and 1993.The Invasion. Dirs. Oliver Hirschbiegel and Jame McTeigue. Village Roadshow et al, 2007.Prometheus. Dir. Ridley Scott. Scott Free and Brandywine Productions, 2012Star Wars Episode IV: A New Hope. Dir. George Lucas. Lucasfilm, 1977.Star Wars Episode VI: Return of the Jedi. Dir. George Lucas. Lucasfilm, 1983.Volcano. Dir. Mick Jackson. 20th Century Fox, 1997.War of the Worlds. Dir. George Pal. Paramount, 1953; also Steven Spielberg. Paramount, 2005.Acknowledgments The authors are grateful to Oenone Rooksby and Joely-Kym Sobott for their assistance and advice when preparing this article. It was also made possible in part by a grant from the Australian Research Council.