Survey of the electrostatic tractor research for reorbiting passive GEO space objects

COBRA is the proposed technique to control the motion of a non-cooperative target by means of the interaction between the thruster exhaust gases from the chaser and the target object. In the original ESA SysNova study, the COBRA concept was investigated as an active debris removal system, using contactless technology to deorbit a space debris object and to control its attitude. It was found that the concept is more effective for controlling the attitude of a debris object. An on-orbit experiment was proposed to have a chaser modify the attitude state of a space object in ESA’s COBRA IRIDES project, which has now been canceled due to the lack of propellant in the chaser spacecraft. This study presents the results of an internal follow-up study on how to effectively use the COBRA concept for detumbling a large debris object and controlling its attitude motion prior to capture operations in an active debris removal mission.

This paper introduces a method of prioritizing orbital debris for future active debris removal missions, based on the evaluation of the total collision probability of each cataloged debris. The United States Space Surveillance Network actively monitors, tracks, and catalogs space debris orbiting Earth. The catalog is updated routinely, and is available to the public in the form of two-line element data. The total collision probability of a debris is defined as the overall probability of the debris colliding with any other debris in a given time window. The proposed method uses the two-line element data pertaining to each debris in the catalog to project the future state of the debris, i.e., the classical orbital elements, at predefined time steps for a given time window. The effects of orbital perturbations are considered wherever applicable. The relative distances between all debris are estimated in each time step, and pairwise collision probabilities are calculated for any two debris objects in the catalog. To obtain the total collision probability for a debris, the pairwise collision probabilities pertaining to the debris are summed. Further, for every debris object the trend in the total collision probability as the time window progresses is quantified, and debris objects are ranked based on their chance of collision in the time window. The outcome of the study is compared with target debris proposed in other studies.

Evidence from experiments with single objects indicates that perceiving objects leads to automatic extraction of affordances. Here we examined the influence of implied between-object actions on affordance processing. Images of task-irrelevant object pairs (e.g., a spoon and a bowl) were followed by imperative central targets. Participants made speeded left/right responses to targets, and the responses randomly aligned with the affordance of one of the objects. The orientation of one object was manipulated across trials, leaving the colocation between objects correct or incorrect for potential interaction. Four experiments demonstrated that positioning the objects correctly for between-object actions led to a prioritization of the object active in the action (e.g., the spoon) over the passive (e.g., the bowl) object. Moreover, there was an inhibitory effect on responses to the passive object: responses congruent with the passive object were slower when pairs of objects were shown as if in interaction, compared with when they were not. The effects did not change in the single-hand response task but disappeared when the passive objects were absent-though an affordance should still have been presented by the active object. These results present evidence for affordance selection in action-related object pairs, and suggest inhibition of the action afforded by the passive objects under conditions of affordance competition.

With the increasing use of active object systems, agents and concurrent object oriented languages like Java, the problem of garbage collection of unused resources has become more complicated. Since Active objects are standalone computational agents identifying garbage in active objects system cannot be based on reachability from a root set (which we use for passive objects). We have to go for separate algorithm to collect garbage on system which uses active objects. For the systems which use both active and passive objects we have to use 2 separate methods for collecting garbage. To avoid this we can use a transformation algorithm that can transfer active object reference graph into passive object reference graph, after which we can apply the passive object algorithm to collect garbage from the entire system. An attempt is made to travel through the transformation algorithms.KeywordsActive ObjectsGarbage CollectionPassive ObjectsDistributed Garbage CollectionTransformation Algorithm

This paper focuses on the attitude dynamics of a defunct axisymmetric satellite under the action of Coulomb forces to enable active space debris removal. Touchless Coulomb interaction occurs between an active spacecraft and the passive satellite at a fixed separation distance. The recently developed multi-sphere method of Schaub and Stevenson allows providing a simplified electrostatic force and torque model between non-spherical space objects. The existence of torques between charged bodies makes it necessary to study the attitude motion of the passive satellite for ensuring the safety of the space debris removal. The goal is first to deduce the equations of motion in the canonical form which is suitable for analytical analysis and then to construct a phase portrait, and to obtain exact solutions using Jacobi elliptic functions. Finally, for the disturbed motion of the system of two bodies, when the distance between the active spacecraft and the defunct satellite (or) and charge voltage changes slowly over time, adiabatic invariants are found in terms of the complete elliptic integrals. In this case, the adiabatic invariants are approximately first integrals of the disturbed system and they remain approximately constant for long time intervals during which the parameters change considerably. For a plane motion, the adiabatic invariants used to obtain an analytical solution for envelope of a deflection angle of the defunct satellite. This work extends the theory to the three-dimensional tumbling motion of a satellite on an orbit. The obtained results can be applied to study an opportunity of the space debris removal by the Coulomb interaction with the active spacecraft as a pusher.

Orbital debris has become an increasingly severe problem, and active debris removal (ADR) missions are gaining progressively more attention. The first step in an ADR mission would be approaching the debris, which is usually a non-cooperative target. In a non-cooperative rendezvous, obtaining continuous sensor measurements for navigation is quite difficult due to the loss of sensor lock or the effect of solar reflection on the optical camera. It is essential to ensure passive abort (PA) safety and to guarantee robustness against collisions in the case of off-nominal thruster burns caused by spacecraft anomalies such as navigation sensor or actuator failures. In the proximity phase, sensors and navigation algorithms need to be switched according to the distance between the chaser and the target, considering the field of view and range of the rendezvous sensors. At the sensor-switching point, the navigation values before and after the switchover are compared, and if the health of the sensor is confirmed, the system proceeds to the next approach sequence. This paper proposes a design method of robust relative trajectories in low Earth orbits that considers PA safety and the ease of troubleshooting and transition to the backup relative orbits in the spiral trajectory.

An analysis of cost savings that could be realized on active debris removal (ADR) missions through the use of reusable launch vehicles (RLVs) has been performed. Launch vehicle price estimates were established for three levels of RLV development, based on varying levels of technological development and market competition. An expendable launch vehicle (ELV) price estimate was also established as a point of comparison. These price estimates were used to form two separate debris removal mission cost estimates, based on previously proposed debris removal mission concepts. The results of this analysis indicate that RLVs could reduce launch prices to levels between 19.6% and 92.8% cheaper than ELVs, depending on the level of RLV maturity. It was also determined that a RLV could be used to realize total ADR mission cost savings of between 2.8% (for a partially RLV in an uncompetitive market) and 21.7% (for a fully RLV in a competitive market).

Large-scale distributed computing applications require concurrent programming models that support modular and compositional software development. The actor model supports the development of independent software components with its asynchronous message-passing communication and state encapsulation properties. Automatic actor garbage collection is necessary for high-level actor-oriented programming, but identifying live actors is not as intuitive and easy as identifying live passive objects in a reference graph. However, a transformation method can turn an actor reference graph into a passive object reference graph, which enables the use of passive object garbage collection algorithms and simplifies the problem of actor garbage collection. In this paper, we formally define potential communication by introducing two binary relations - the may-talk-to and the may-transitively-talk-to relations, which are then used to define the set of live actors. We also devise two vertex-preserving transformation methods to transform an actor reference graph into a passive object reference graph. We provide correctness proofs for the proposed algorithms. The experimental results also show that the proposed algorithms are efficient.

Trajectory optimization for multi-target Active Debris Removal missions

In recent years, space debris has become a threat for satellites operating in low Earth orbit. Even by applying mitigation guidelines, their number will still increase over the course of the century. As a consequence, active debris removal missions and on-orbit servicing missions have gained momentum at both academic and industrial level. The crucial step in both scenarios is the capability of navigating in the neighborhood of a target resident space object. This problem has been tackled many times in literature with varying level of cooperativeness of the target required. While several techniques are available when the target is cooperative or its shape is known, no approach is mature enough to deal with uncooperative and unknown targets. This paper proposes a hybrid method to tackle this issue called Coarse Model-Based Relative Navigation (CoMBiNa). The main idea of this algorithm is to split the mission into two phases. During the first phase, the algorithm constructs a coarse model of the target. In the second phase, this coarse model is used as a reference for a relative navigation technique, effectively shifting the focus toward state and inertia estimation. In addition, this paper proposes a strategy to leverage the structure of the selected navigation method to detect and reject outliers. To conclude, CoMBiNa is tested on a simulated environment to highlight its benefits and its shortcomings, while also assessing its applicability on a limited-resource single-board computer.

Landscape architecture is unique as a design practice in its engagement with living nonhumans as instrumental media. However, contemporary landscape architecture theory has struggled to integrate fauna as components of the designed landscape beyond calls to provide and preserve habitat and address the philosophical implications of such a gesture. Animals and other mobile entities, when recognized as integral components of landscapes rather than occasional inhabitants, challenge static notions of landscapes as passive spaces and instead invigorate them as lively events. Some early writings on landscape practice and theory, dating back to the picturesque movement, acknowledge the presence of animals in the landscape. More recently, some landscape designers have imagined new roles for animals. No longer are they passive objects or visitors or inhabitants, blindly providing ecosystem services. Increasingly, these designers have explored the role of animals as active agents shaping the landscape, in ways that reimagine interspecies relationships and subjectivities. Provocations for “animal-aided design” are emblematic of this novel take on the animal in the landscape. Using animacy as a tool for revealing various relational qualities of landscapes, this article joins with calls to attend to the liveliness of other beings as productive and creative agents.

A model of the forces and the torque operating on a ball that is flying with rotation in the atmosphere of the Earth, and the resulting system of ordinary differential equations, are derived from mechanics and aerodynamics.The system of equations allows the theoretical aspects of the flight of a ball, such as the boundedness of its kinetic energy, the curvature of the orbit or the velocity function, to be investigated using certain transformations of the variables.The solutions of the corresponding ordinary or boundary value problems, computed numerically, are used to treat certain tasks in international ball games, for example, the maximum and minimum velocities of a volleyball service.

This paper presents the feasibility study of the REMORA CubeSat mission concept with an integrated miniature robotic payload to prevent large debris collisions. While orbital debris poses a threat to spacecraft, a collision between the largest space debris objects is of significant concern. The DARPA Catcher's Mitt study compiled a list of the highest priority large debris objects. By annually removing 5-10 of these high priority objects, it may be possible to stabilize the medium sized debris population. Instead of deorbiting objects, REMORA would use COTS CubeSat components and secondary payload launches as a cost-effective solution for mitigating large debris collisions. The REMORA CubeSat could rendezvous with a piece of debris and use the robotic manipulator to anchor itself to the target object. Once anchored, the CubeSat could track the debris and, if needed, alter the debris object's trajectory to prevent a collision. Aspects discussed include the mission and robotic payload baseline designs. Many of the highest priority objects identified in the DARPA Catcher's Mitt study are located in the 71°-75° inclination range and in sun-synchronous orbit. An initial mission design concept targets sun-synchronous objects due to the large number of launch opportunities to this orbit. The mission was simulated with a combination of MATLAB, GMAT, and STK. A CubeSat robotic payload was designed to provide a decreased chance of collision between the CubeSat and debris object during attachment, augment the ACS during approach, and provide the ability to orient the thrust vector through the center of mass while pushing. This robotic payload includes a computing element, cameras, miniature robotic arm, and end-effector. An initial miniature arm prototype was designed and built to demonstrate feasibility and inform future designs. An end-effector trade study was performed to explore different end-effectors that could be used to for attaching to the common graspable features on large debris objects. Grasping methods, including mechanical prehension, gecko grippers, electrostatic grippers, and magnetic grippers, were investigated.

Simulation of robotic space operations with minimum base reaction manipulator

Most large space debris has large residual angular momentum, and the de-tumbling and capturing operation can easily cause instability and failure of tracking satellites. Therefore, it is necessary to perform real-time dynamic parameter identification of space debris prior to the imminent de-tumbling and capture operation, thus improving the efficiency and success of active debris removal (ADR) missions. A method for identifying dynamic parameters based on the fusion of visual and inertial data is proposed. To obtain the inertial data, the inertial measurement units (IMU) with light markers were fixed on the debris surface by space harpoon, which has been experimentally proven in space, and the binocular vision was placed at the front of a tracking satellite to obtain coordinates of the light markers. A novel method for denoising inertial data is proposed, which will eliminate the interference from the space environment. Furthermore, based on the denoised data and coordinates of the light markers, the mass-center location is estimated. The normalized angular momentum is calculated using the Euler–Poinsot motion characteristics, and all active debris removal parameters are determined. Simulations with Gaussian noise and experiments in the controlled laboratory have been conducted, the results indicate that this method can provide accurate dynamic parameters for the ADR mission.