Defunct Satellites Research Articles

Bioinspired flexible gripper for vacuum non-cooperative target capture

With the development of space exploration activities, the proliferation of non-cooperative targets in space, such as defunct satellites and space debris, has made the development of efficient and reliable non-cooperative target capture technologies in space a priority for space exploration. In this paper, a flexible gripper inspired by the dermo-muscular sac found in flatworms is presented to address the challenges of non-cooperative target capture in the vacuum environment of space. The gripper design leverages magnetorheological fluid and a magnetic field to enable adjustable stiffness, facilitating the effective grasping of delicate target objects while ensuring a stable connection post-capture. Extensive tests demonstrate the strong potential of the gripper for space applications, showcasing its ability to adjust pre-grip contact force and increase gripping force by adjusting indentation depth. The simplicity of the design contributes to ease of manufacturing, making it a promising tool for future space missions.

Dynamic analysis of tethered defunct satellites with solar panels

Dynamic analysis of tethered defunct satellites with solar panels

Design, fabrication and experimental verification of a drag sail based on thermal-driven controllable bi-stable shape memory polymer composite booms

Deployable drag sails are used for passively deorbiting defunct satellites and other spacecraft. Designing the deployable boom is the main challenge in this technology. We present a bi-stable shape memory polymer composite (Bi-SMPC) boom with high stiffness, a high unfolding/folding ratio, and consistent roll-out deployment. It was designed and fabricated by a strategy of controlling the gradual release of elastic energy stored in a bi-stable composite structure through thermal-driven SMP matrix. Two heating layer strategies were investigated experimentally to determine the optimal driving layer and driving parameters. Based on these parameters, verification tests of a four-stage deployment Bi-SMPC boom were conducted. Meanwhile, a proof-of-concept prototype of a four-stage deployment drag sail based on the Bi-SMPC booms was designed and fabricated. Tests were conducted to verify the effectiveness of the drag sail deployed by the booms. It was found that SMPs can effectively control the deployment of bistable composite structures. The nickel-chromium alloy heating layer offers a more uniform driving temperature field compared to carbon fiber. The drag sail can be deployed successfully under the driving of four Bi-SMPC booms.

Micro-Doppler Signature Analysis for Space Domain Awareness Using VHF Radar

The large quantity of resident space objects orbiting Earth poses a threat to safety and efficient operations in space. Radar sensors are well suited to detecting objects in space including decommissioned satellites and debris, whereas the more commonly used optical sensors are limited by daylight and weather conditions. Observations of three non-operational satellites using a VHF radar system are presented in this paper in the form of micro Doppler signatures associated with rotational motion. Micro Doppler signatures are particularly useful for characterising resident space objects at VHF given the limited bandwidth resulting in poor range resolution. Electromagnetic simulations of the micro Doppler signatures of the defunct satellites are also presented using simple computer-aided design (CAD) models to assist with interpretation of the radar observations. The simulated micro Doppler results are verified using the VHF radar data and provide insight into the attitude and spin axis of the three resident space objects. As future work, this approach will be extended to a larger number of resident space objects which requires a automated processing.

COSMIC: a UK Active Debris Removal Mission

In recent years, the escalation of space activities has led to an alarming surge in space debris within low Earth orbit (LEO). This paper addresses the pressing need for Active Debris Removal (ADR), a two-pronged strategy to stabilize space debris: maintaining shorter satellite lifetimes and actively removing defunct satellites. In 2022, the UK Space Agency issued funding to explore the launch of a 2026 mission to remove uncooperative debris in LEO. Astroscale’s COSMIC (Cleaning Outer Space Mission through Innovative Capture) mission has been conceived to meet this challenge. Leveraging Astroscale’s expertise and heritage from the ELSA-M mission, which is designed for magnetically capturing prepared clients, COSMIC advances the field of ADR by transitioning from magnetic capture to robotic capture, enabling the removal of unprepared and uncooperative debris. This paper explores the development of COSMIC and its mission to pioneer institutionally funded debris removal with robotic capture, representing a significant milestone in ADR and the broader realm of space exploration. Keywords: Active Debris Removal, In-orbit Servicing, Rendezvous Proximity Operations, Spacecraft Detumbling, Robotic Capture

Deflection of dangerous middle-size LEO debris with autonomous space-based laser brooms via surgical actions

There is a consensus that the increasingly large number of LEO debris objects represents a major threat to both active and defunct satellites and that means a potential runaway collisional cascading. This problem urgently demands to be addressed immediately, since the number of satellites in LEO is also dramatically increasing.Many active space debris removal programs have been proposed and those based on using laser from space appear to be really promising, taking into account that one of the most challenging issues from the orbital standpoint is to guarantee the appropriate accuracy for the laser beams that are shot from space-based LEO trackers.In this work, we propose how to build up space-based laser brooms consisting of a significant number of autonomous LEO trackers aimed at performing surgical local shooting actions to deflect the most dangerous middle-size debris objects into the Atmosphere by means of laser ablation.The precision of these brooms lies in the use of the post-Newtonian equations for the computation of absolute and relative positions and velocities, as well as ranges.

Spacecraft Materials’ Reflectivity and Surface Morphology: Aging Caused by Proton Irradiation

The radiation environment in Low Earth Orbit (LEO) is dominated by protons captured by Earth’s magnetic field in the Inner Van-Allen belt. Defunct satellites and other space debris objects can be resident in this environment for several decades and even centuries. So far, there is little knowledge about the impact of long-duration proton exposure to the surface morphology and reflectivity in LEO environment. We report on a laboratory test campaign exposing typical spacecraft materials with protons of 100 keV and 2.5 keV kinetic energy and a fluence corresponding to an in-orbit duration of 100 years and 120 years, respectively, in an 800 km sun-synchronous orbit. Although we find microscopic changes in surface morphology, reflectivity changes of all tested materials were smaller than 15%. This result brings positive news for on-going efforts to use optical methods, e.g. lightcurve measurements or active polarimetry, for characterizing space objects, since it suggests that data can - to a good approximation - be analyzed without accounting for proton induced aging effects that might affect the materials’ optical properties over time.

Metals from spacecraft reentry in stratospheric aerosol particles

Large increases in the number of low earth orbit satellites are projected in the coming decades [L. Schulz, K.-H. Glassmeier, Adv. Space Res. 67, 1002-1025 (2021)] with perhaps 50,000 additional satellites in orbit by 2030 [GAO, Large constellations of satellites: Mitigating environmental and other effects (2022)]. When spent rocket bodies and defunct satellites reenter the atmosphere, they produce metal vapors that condense into aerosol particles that descend into the stratosphere. So far, models of spacecraft reentry have focused on understanding the hazard presented by objects that survive to the surface rather than on the fate of the metals that vaporize. Here, we show that metals that vaporized during spacecraft reentries can be clearly measured in stratospheric sulfuric acid particles. Over 20 elements from reentry were detected and were present in ratios consistent with alloys used in spacecraft. The mass of lithium, aluminum, copper, and lead from the reentry of spacecraft was found to exceed the cosmic dust influx of those metals. About 10% of stratospheric sulfuric acid particles larger than 120 nm in diameter contain aluminum and other elements from spacecraft reentry. Planned increases in the number of low earth orbit satellites within the next few decades could cause up to half of stratospheric sulfuric acid particles to contain metals from reentry. The influence of this level of metallic content on the properties of stratospheric aerosol is unknown.

Numerical simulation and behavior prediction of a space net system throughout the capture process: Spread, contact, and close

AbstractIn this paper, we develop an exhaustive numerical simulator for the dynamic visualization and behavior prediction of the tether‐net system during the whole space debris capture phases, including spread, contact, and close. First of all, to perform its geometrically nonlinear deformation, discrete different geometry theory is applied to model the mechanical response of a flexible net. Based on the discretization of the whole structure into multiple vertexes and lines, the internal force and associated Hession are derived in a closed form to solve a series of nonlinear dynamic equations of motion. The spread and deployment of a packaged net can be realized using this well‐established net solver. Next, a multidimensional incremental potential formulation is selected to achieve the intersection‐free boundary nonlinear contact and collision between the deformable net and rigid debris. Finally, for the closing mechanism analysis, a log‐like barrier functional is derived to achieve the nondeviation condition between the ring–rod linkage system. The continuous log barrier functionals constructed for both the contact model and the linkage system are smooth and differentiable, and, therefore, the nonlinear net capture dynamic system can be efficiently solved through a fully implicit time integrator. Overall, as a demonstration, the whole capture process of a defunct satellite using a hexagon net is simulated through our well‐established numerical framework. We believe that our comprehensive numerical methods could provide new insight into the optimal design of active debris removal systems and promote further development of the online control of tether tugging systems.

Contact dynamic analysis of tether-net system for space debris capture using incremental potential formulation

An efficient computational method is proposed to combine the discrete differential geometry (DDG) method with the multi-dimensional incremental potential (IP) formulation to simulate the contact dynamics between a shooting net and a defunct satellite. The geometrically nonlinearity of the elastic net is described using the DDG method, which discretizes the flexible net into multiple nodes and connected edges. The internal elastic forces and the associated Jacobians are derived analytically. The multi-dimensional incremental potential formulation is used to achieve the intersection-free condition during the physical collision between deformable tether-net and rigid space debris. The smooth IP barrier functional constructed for contact simulation is differentiable, such that the nonlinear elastodynamic system can be robustly solved through a fully implicit time-marching scheme. Our numerical approach is first applied to simple examples, and demonstrating its effectiveness in dealing with non-penetration contacts of elements with different dimensions, such as ‘edge-to-edge’ and ‘edge-to-surface’. Next, the dynamic interaction between the deploying net and defunct satellite is analysed. A parameter sweep is performed with our robust and efficient simulator to show the configuration evolution of the net shot from different relative locations of the target object. Our numerical results can provide an optimal deployment strategy for tether-net capture systems during the active debris removal missions.

Design and Robustness Analysis of a Wave-Based Controller for Tethered Towing of Defunct Satellites

A microgravity environment in space, the elasticity of the tether, and complex flexible appendages make the tethered-towing system a nonlinear and underactuated system, which is sensitive and difficult to stabilize. This letter develops a controller based on wave propagation for tethered towing of defunct satellites, and carries out a robustness analysis of the controller via numerical simulation.

General Tumbling-Averaged Rotational Dynamics for Defunct Satellites

Understanding and predicting the long-term spin state evolution of defunct satellites and rocket bodies is important for solar radiation pressure modeling, space domain awareness, and active debris removal (ADR). Dynamical modeling and observations indicate that defunct geosynchronous satellite spin states are primarily driven by solar radiation torques via the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect. In our two recent papers, we uncovered dynamically rich YORP-driven behavior including cycling between uniform rotation and non-principal axis tumbling, angular momentum sun tracking, and tumbling period resonances. These papers only considered the YORP effect. However, tumbling satellites are also subject to energy dissipation from residual fuel slosh and flexure. Gravitational torques and other environmental perturbations may affect long-term evolution as well. In this paper, the third in our series, we develop semi-analytical tumbling-averaged models for internal energy dissipation and gravity gradient torques and combine them with the earlier YORP models. Accounting for YORP and dissipation, we find asymptotically stable tumbling states with constant angular momentum and kinetic energy and a pole fixed in the rotating sun-satellite orbit frame. With gravity gradients, these asymptotic states become stable limit cycles with yearly periodicity. We discuss the implications of these findings for the space debris population, ADR, and satellite decommission procedures.

A high-fidelity high-efficiency model for electrodynamic tether system based on recursive algorithm

The electrodynamic tether (EDT) system is used as one of the end-of-life disposal technologies to deorbit defunct satellites with the benefit of Earth's magnetic field and plasma environment. However, due to the flexibility of the conductive tether, the orbit-attitude coupling effects as well as the influence of Multiphysics fields, this system suffers from time-consuming computations using complicated mathematical model in long-term simulations. Therefore, this paper proposes a high-fidelity high-efficiency dynamics model for the EDT system, in which the tether libration and transverse motions are described by the articulated model, and the system equations are formulated using recursive dynamics algorithm. Computational cost of the recursive method is compared with a nonrecursive method, and the result shows that with the number of tether elements larger than 15, the recursive method would show better computational efficiency. Since the conductive tether tends to be kilometers long in application, this new model would definitely contribute to the numerical efficiency. In addition, simulations are conducted with 2 and 16 tether elements solutions. By comparing the obtained results, it is found that the two cases show large differences over time. For a long tether, it is reasonable to use a larger number of elements in the dynamics analysis. Besides, in order to suppress the libration motion and avoid unstable states in the EDT system, a current control strategy is proposed and verified by a deorbit simulation in low Earth orbit.

The chemo-dynamical groups of Galactic globular clusters

ABSTRACT We introduce a multicomponent chemo-dynamical method for splitting the Galactic population of globular clusters (GCs) into three distinct constituents: bulge, disc, and stellar halo. The latter is further decomposed into the individual large accretion events that built up the Galactic stellar halo: the Gaia–Enceladus–Sausage, Kraken and Sequoia structures, and the Sagittarius and Helmi streams. Our modelling is extensively tested using mock GC samples constructed from the auriga suite of hydrodynamical simulations of Milky Way (MW)-like galaxies. We find that, on average, a proportion of the accreted GCs cannot be associated with their true infall group and are left ungrouped, biasing our recovered population numbers to $\sim 80{{\ \rm per\ cent}}$ of their true value. Furthermore, the identified groups have a completeness and a purity of only $\sim 65{{\ \rm per\ cent}}$. This reflects the difficulty of the problem, a result of the large degree of overlap in energy-action space of the debris from past accretion events. We apply the method to the Galactic data to infer, in a statistically robust and easily quantifiable way, the GCs associated with each MW accretion event. The resulting groups’ population numbers of GCs, corrected for biases, are then used to infer the halo and stellar masses of the now defunct satellites that built up the halo of the MW.

Practical System to Remove Lethal Untracked Orbital Debris

The environment in low Earth orbit (LEO) is congested with orbital debris threatening the safety of all states, actors, and enterprises who wish to use space. Removing orbital debris is unquestionably one of the top space challenges facing space actors of this generation, one that demands cross-disciplinary solutions to solve this complex systems engineering problem. Based on a review of past and recent approaches to active debris removal, many of the currently proposed technologies and systems focus on removing defunct satellites and other large derelict objects in LEO that are actively cataloged and tracked. While removing the larger space objects is a necessary goal, space sustainability experts agree that the orbital debris ranging from 4 mm to 9 cm poses the greatest risk to operational spacecraft and presents unique challenges for its removal. This paper offers a novel technical approach for the development and near-term deployment of an orbital debris removal system based on existing technology that would be capable of reducing lethal untracked orbital debris in LEO.

Resonance-Averaged Solar Torque Dynamics for Tumbling Satellites

Observations indicate that the spin states of retired and otherwise defunct satellites are diverse and can change significantly over time. Understanding defunct satellite spin state evolution is important for solar radiation pressure modeling, active debris removal, satellite servicing, and space situational awareness. Research has shown that many defunct satellites in geosynchronous earth orbit (GEO) are primarily driven by solar radiation torques via the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect. Recent exploration of YORP-driven nonprincipal axis tumbling has uncovered rich dynamic behavior, including tumbling cycles, spin–orbit coupling, and tumbling period resonances. Radar and optical observations of the defunct Geostationary Operational Environmental Satellite (GOES) 8 strongly suggest that it has been captured in a tumbling resonance at least once since 2018. Motivated by these findings, we develop a numerical resonance-averaged dynamic model to understand YORP-driven resonance capture, building on our earlier nonresonant averaging framework. This resonance-averaged model illuminates resonance capture mechanisms. Also, by averaging over the satellite’s rotation, this model is roughly 20 times faster to propagate than the full (Euler) dynamics. Overall, this allows for rapid, broad exploration to determine resonance capture durations, spin states changes, and the influence of initial spin rate and resonance order on resonance strength. This resonance-averaged model can be easily applied to other environmental perturbations.

Electromagnetic Interaction Between a Slowly Rotating Conducting Shell and Magnetic Dipoles: A Theoretical and Numerical Study

The non-contact electromagnetic detumbling technologies for space debris and defunct satellites attract a lot of interest from many researchers, in which service satellites use one or two electromagnetic devices onboard to generate a controllable torque to reduce the rotation of the target so that the robotic arm can capture the target without hazardous collisions. However, there are many challenges in modeling the interactions between electromagnetic devices and the target. In this study, the electromagnetic devices and the target are simplified as magnetic dipoles and a slowly rotating conducting shell with typical shape, respectively. The interactions of one and two magnetic dipoles with a slowly rotating conducting spherical shell are derived. Then, the interaction between a slowly rotating conducting non-spherical geometry (a cube or a cylinder) and two magnetic dipoles is calculated numerically. The numerical results show that non-spherical geometries can be regarded as spherical shells in terms of calculating the electromagnetic interactions when the magnetic dipoles are far away from the geometries.

Full attitude state reconstruction of tumbling space debris TOPEX/Poseidon via light-curve inversion with Quanta Photogrammetry

The tumbling motion of defunct satellite TOPEX/Poseidon (T/P) is governed by the μ-scale Solar Radiation Pressure (SRP) torque that spun up the satellite from the initial, nadir-pointing to the current fast spinning state [1]. In this paper, we advance the methods of Quanta Photogrammetry (QPM) in an effort to determine satellite attitude parameters – the inertial orientation of the body angular momentum vector L, the rotational phase and rate as well as the object pole coordinates with respect to L; the determined pole offset is 3.52°. The presented data support the hypothesis that the full characteristics of the satellite attitude dynamics can be obtained from a single radiant photogram measured by the photon-counting system of the Graz Satellite Laser Ranging (SLR) Observatory during an overhead pass.The analysis of the observed radiant signature of T/P gives the elevation angle of the normal vector to the solar array front surface at −1.7°, RMS = 0.63°, in the spacecraft body-centered reference frame. This information, along with the pole position, is used to model the SRP forces and torques on the satellite and determine the T/P moment of inertia I=69728,σI=75.2[kgm2], by best-fitting long-term spin simulation to the observed trend.

Adaptive saturated control for spacecraft rendezvous and docking under motion constraints

This paper investigates the problem of position tracking and attitude synchronization for spacecraft rendezvous and docking with a tumbling target, in which kinematic couplings, unknown disturbances, motion constrains, and input saturation are considered. A novel artificial potential function (APF) is developed to encode both three-dimensional pose information and two-dimensional image information regarding path constraint and field of view constraint, respectively. By integrating the APF into the sliding mode technique, an adaptive control strategy is proposed to realize the arrival of the chaser at the docking port without any risk of collision or loss of target features. In addition, a linear anti-windup compensator is introduced to compensate for the input saturation effect. Uniformly ultimately bounded of the closed-loop system is guaranteed through Lyapunov analysis. A specific simulation scenario of docking with the defunct satellite Envisat is created to demonstrate the effectiveness and robustness of the proposed control strategy.

The Basic Shape Classification of Space Debris with Light Curves

We study the machine learning method for classifying the basic shape of space debris in both simulated and observed data experiments, where light curves are used as the input features. In the dataset for training and testing, simulated light curves are derived from four types of debris within different shapes and materials. Observed light curves are extracted from Mini-Mega TORTORA (MMT) database which is a publicly accessible source of space object photometric records. The experiments employ the deep convolutional neural network, make comparisons with other machine learning algorithms, and the results show CNN (Convolutional Neural Network) is better. In simulational experiments, both types of cylinder can be distinguished perfectly, and two other types of satellite have around 90% probability to be classified. Rockets and defunct satellites can achieve 99% success rate in binary classification, but in further sub-classes classifications, the rate becomes relatively lower.