Uncontrolled Satellite Research Articles

Magnetic Attitude Control Scheme for Drag Sail Deorbiting with Limited Sensors

As concerns over space debris in the Low Earth orbit (LEO) intensify, deorbit strategies for small satellites becomes evident because many lack an effective deorbit mechanism. After successfully demonstrating their effectiveness in flight tests, aerodynamic drag sails emerge as a superior deorbit solution, significantly reducing the time required for deorbiting. To maximize the aerodynamic drag, it is crucial to maintain the drag sail perpendicular to the atmospheric flow. This becomes especially challenging with the potential threat of sensor failure. This paper introduces a magnetic control scheme for deorbiting using drag sails. Relying solely on magnetometers as sensors, the control scheme uses magnetorquers, bias momentum wheels, and an onboard geomagnetic field model to keep the sail perpendicular to the satellite’s velocity. Furthermore, a backup control scheme that does not require the onboard geomagnetic field model is proposed. This control scheme uses magnetometers in conjunction with just another common small satellite sensor, such as the GPS, gyroscopes, or sun sensors as sensors. A stability criterion, based on a linearized analytical model, validates the feasibility of this backup control scheme. Numerical simulations confirm the efficacy of both control schemes. Both schemes reduce the deorbit time by approximately 40% compared to the uncontrolled satellite deorbiting.

DragSail systems for satellite deorbit and targeted reentry

The safe disposal of spacecraft upon mission completion is necessary to preserve the utility of high-value orbits. Small satellite launches to low Earth orbit and plans for large commercial constellations for global internet service have the potential to exacerbate the orbital debris problem. A dragsail provides an efficient method for accelerating deorbit following the completion of a satellite's operational mission. Unlike propulsive deorbit approaches that require an active host satellite, the passive deorbit approach offered by dragsails does not require a functional host, and dragsails can offer mass savings for deorbit relative to chemical propulsion. Previous dragsail systems have employed flat square sails, which tend to tumble due to atmospheric and solar pressure perturbations. In this paper, a square pyramid geometry for the drag sail is evaluated. The pyramid geometry offers the benefit of passive aerodynamic stability about the maximum drag attitude. Through a six degree-of-freedom simulation, the passive aerodynamic stability provided by the square pyramid geometry is shown, and the deorbit performance of the square pyramid geometry is benchmarked against a typical square sail design. Uncontrolled satellite reentry results in large entry corridor uncertainties, with the range of possible re-entry trajectories often extending over multiple orbits and spanning groundtrack swaths that encompass large portions of the globe. To reduce this uncertainty, dragsails can be applied to achieve targeted reentry capability. The change in ballistic coefficient provided by sail deployment can be used as a control parameter to initiate reentry from a very low orbit, thereby reducing the uncertainty in the reentry corridor and the surface impact footprint. The ability to control the reentry corridor to within a fraction of an orbit reduces the impact of satellite reentry on the air traffic control system and can be used to constrain the probability of debris impact in populated areas. In this work, parametric studies show the efficacy of targeted reentry using dragsail deployment as a control parameter.

Determination of the Orientation of an Artificial Satellite from Magnetic Field Data in Orbit

At present, the determination of the position of satellite axes from data obtained via measurement of the magnetic field in orbit is an urgent task. This task is important, because the satellite equipment, on the one hand, is minimal, and, on the other hand, it always includes magnetometers. Generally speaking, it is not possible to determine the position of a satellite based solely on magnetic measurements—it is easy to consider the case of a satellite rotating around a magnetic field vector. Conversely, such movement is very special; it is not carried out in an actual situation with an uncontrolled satellite. The combined method proposed below makes it possible to determine the angles and angular velocities of an object based on measurements of only the magnetic field.

Detumbling Method for Uncontrolled Satellite Based on Eddy Currents

For the capture and removal of a large uncontrolled rotating satellite, a detumbling method based on the electromagnetic principle is developed and verified. A numerical method, which applies to arbitrary shapes and a nonuniform field, is used to calculate the eddy current torque of a rotating conductor in magnetic field. The numerical result of a spinning cylinder in uniform field is compared with the analytical solution, and two sets of experiment for spinning cylinder and cuboid shell with open ends are carried out to verify the numerical results in a nonuniform field. The numerical results are in good agreement with the experiments. A detumbling strategy is proposed, and a numerical simulation is carried out taking a spinning cylinder as the hypothetical target of detumbling. The results show that the detumbling strategy is effective and the detumbling rate is greatly improved by applying the detumbling magnetic field.

An Application of Eddy Current Effect on the Active Detumble of Uncontrolled Satellite With Tilt Air Gap

The active removal of expired satellites on orbit is essential to ensure the safety of functional spacecrafts on orbit. The high tumbling rates of the uncontrolled satellites hinder the direct removal operation. Consequently, a non-contact method based on the eddy current effect is applied to despin and detumble the uncooperative satellite. A magnetic vector-based 3-D field model under the mean radius assumption is established to calculate the eddy current forces and torques. The honeycomb structure of the target surface and tilt air gap during detumbling are considered in the theoretical model. An underactuated detumble control model is applied to stabilize the nutation angle and attitude of the target. The simulation results show that the control strategy can stabilize the target’s attitude in a reasonable time. Controlling the tilt angle will generate despin and detumble torques simultaneously. The linear relationship between the despin torque and rotational velocity at several hundreds of rpm is verified by experiments. This article provides a new solution for detumbling an uncooperative satellite with a rotational magnetic field.

Modeling and planning of a space robot for capturing tumbling target by approaching the Dynamic Closest Point

Space debris or uncontrolled satellites bring new and critical challenges for space robots to capture and remove them, especially when the targets are tumbling. In the face of these challenges, most existing research only focused on capturing a fixed point on the target. Distinguished from previous research, this paper attempts to investigate an autonomous tumbling target capturing method by approaching the “Dynamic Closest Point” (DCP), that is, the most suitable point on the target to be grasped and always closest to the end effector. First, an uncontrolled space object and a space robotic system are modeled, and the existence of the DCP is proved. For a practical malfunction spacecraft, the motion characteristics of the DCP and a fixed point are theoretically analyzed and compared as regards different motion types and rotation vectors. Furthermore, the desired trajectory is generated for the end effector of the space robot to approach the DCP autonomously, based on the position and velocity of the DCP estimated in real-time by hand-eye cameras. The joint velocities and angles are then resolved by combining the differential kinematics and movement constraints on the end effector. Finally, an Adams-Simulink co-simulation system is developed. Based on this, the proposed method is verified by single-arm and dual-arm capturing cases. Simulation results demonstrate that the capture time and movement ranges of the end effector are both greatly reduced with the DCP method. In contrast with traditional capturing methods, the efficiency of this proposed method is largely improved.

On-orbit servicing of geosynchronous satellites based on low-thrust transfers considering perturbations

The goal of this paper is to investigate the on-orbit servicing (OOS) of geosynchronous satellites based on low-thrust transfers while considering the different demands of the satellites and the effects of perturbations. One or more servicing spacecraft start from a parking orbit and service the satellites in sequence via low-thrust orbit transfers, and return to the parking orbit in the end. The different demands lead to different service requirements of time and mass, while the perturbations affect the control solution of servicing spacecraft during each transfer, and induce orbit drifts of uncontrolled target satellites during the mission. An analytical method that can efficiently calculate the fuel consumption of low-thrust transfer is proposed, and methods for evaluating the orbit drifts of uncontrolled satellites are presented. The impact of perturbations on OOS mission is investigated in detail, showing that non-negligible factors include lunisolar attraction and tessral harmonic. Based on the dynamic models, a string-based simulated annealing algorithm is adopted to schedule the OOS mission. The efficiency of the proposed dynamic models and optimization method are verified through ample simulations. Results show that it is much more efficient and reasonable to take orbit drift calculations as corrections on the scheduling result assuming no orbit drifts. The proposed models and methods make it possible to schedule the OOS mission with low-thrust transfers, while achieving high accuracy under the effects of J2 perturbation, lunisolar attracion, tesseral harmonic and solar radiation pressure.

Monitoring of Space Debris Rotation Based on Photometry

The number of spacecraft and space debris (SD) in orbit has become so great that there is a real threat to flight safety. The task of precision calculation of the upcoming positions of any space objects (SO) in orbit in order to predict dangerous mutual approaches and to solve practical tasks has become topical. For the development of a modern orbit propagation model and the associated unified forecast of the evolution of orientation and rotation of an uncontrolled satellite, it is necessary to rely on long-term series of high-quality measurements and their analysis. At present, the direction of research on determining the state of SO rotation around a center of mass has become more and more developed. In our work, we analyze the results of photometric observations of several large objects of space debris obtained at the Astronomical Observatory of Odessa University using the KT-50 telescope during the last six years or more. The results of the evolution of the rotation rate and orientation of the Topex/Poseidon, Envisat, Oicets, Cosmos-2487 (Kondor-E) and Sich-2 satellites are presented.

Satellite angular motion classification for active on-orbit debris removal using robots

PurposeThis paper aims to present a novel method for identification and classification of rotational motion for uncontrolled satellites. These processes are shown in context of close proximity orbital operations. In particular, it includes a manipulator arm mounted on chaser satellite and used to capture target satellites. In such situations, a precise extrapolation of the target’s docking port position is needed to determine the manipulator arm motion. The outcome of this analysis might be used in future debris removal or servicing space missions.Design/methodology/approachNonlinear, and in some special cases, chaotic nature of satellite rotational motion was considered. Four parameters were defined: range of motion toward docking port, dominant frequencies, fractal dimension of the motion and its time dependencies.FindingsThe qualitative analysis was performed for presented cases of spacecraft rotational motion and for each case the respective parameters were calculated. The analysis shows that it is possible to detect the type of rotational motion.Originality/valueA novel procedure allowing to estimate the type of satellite rotational motion based on fractal approach was proposed.

Fault-tolerant feature-based estimation of space debris rotational motion during active removal missions

One of the key functionalities required by an Active Debris Removal mission is the assessment of the target kinematics and inertial properties. Passive sensors, such as stereo cameras, are often included in the onboard instrumentation of a chaser spacecraft for capturing sequential photographs and for tracking features of the target surface. A plenty of methods, based on Kalman filtering, are available for the estimation of the target's state from feature positions; however, to guarantee the filter convergence, they typically require continuity of measurements and the capability of tracking a fixed set of pre-defined features of the object. These requirements clash with the actual tracking conditions: failures in feature detection often occur and the assumption of having some a-priori knowledge about the shape of the target could be restrictive in certain cases. The aim of the presented work is to propose a fault-tolerant alternative method for estimating the angular velocity and the relative magnitudes of the principal moments of inertia of the target. Raw data regarding the positions of the tracked features are processed to evaluate corrupted values of a 3-dimentional parameter which entirely describes the finite screw motion of the debris and which primarily is invariant on the particular set of considered features of the object. Missing values of the parameter are completely restored exploiting the typical periodicity of the rotational motion of an uncontrolled satellite: compressed sensing techniques, typically adopted for recovering images or for prognostic applications, are herein used in a completely original fashion for retrieving a kinematic signal that appears sparse in the frequency domain. Due to its invariance about the features, no assumptions are needed about the target's shape and continuity of the tracking. The obtained signal is useful for the indirect evaluation of an attitude signal that feeds an unscented Kalman filter for the estimation of the global rotational state of the target. The results of the computer simulations showed a good robustness of the method and its potential applicability for general motion conditions of the target.

A simplex method for the orbit determination of maneuvering satellites

A simplex method of orbit determination (SMOD) is presented to solve the problem of orbit determination for maneuvering satellites subject to small and continuous thrust. The objective function is established as the sum of the nth powers of the observation errors based on global positioning satellite (GPS) data. The convergence behavior of the proposed method is analyzed using a range of initial orbital parameter errors and n values to ensure the rapid and accurate convergence of the SMOD. For an uncontrolled satellite, the orbit obtained by the SMOD provides a position error compared with GPS data that is commensurate with that obtained by the least squares technique. For low Earth orbit satellite control, the precision of the acceleration produced by a small pulse thrust is less than 0.1% compared with the calibrated value. The orbit obtained by the SMOD is also compared with weak GPS data for a geostationary Earth orbit satellite over several days. The results show that the position accuracy is within 12.0 m. The working efficiency of the electric propulsion is about 67% compared with the designed value. The analyses provide the guidance for subsequent satellite control. The method is suitable for orbit determination of maneuvering satellites subject to small and continuous thrust.

Role of the solar wind parameters in changing orbital motion of the Earth’s satellites

The investigation of the solar wind and geomagnetic activity parameters' effect on variations of the orbital motion periods of artificial satellites has been continued. The periods of orbital motion of uncontrolled satellites from the database of the Ukrainian network of optical stations (UNOS) for 2012–2014 was used. The data have been compared with the values of geomagnetic planetary index K and the energy spectra of protons and electrons obtained by the GEOS satellites in events during which the orbital periods have changed. It is shown that, in the energy spectra of the proton and electron fluxes, there is no effect of softening the spectrum with time at the time of the flare appearance. This indicates the possibility of particle accumulation above the active region (AR), which entails further continuous energy emission of the solar flare from AR. Dependences have been obtained between the geomagnetic activity and the solar wind speed at a given interplanetary magnetic field strength during the periods under study for the changes in the orbital motion periods of satellites. The corresponding correlation coefficients are 0.93–0.96.

Safe path planning for free-floating space robot to approach noncooperative spacecraft

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.

Reconstruction of spacecraft rotational motion using a Kalman filter

Quasi-static microaccelerations of four satellites of the Foton series (nos. 11, 12, M-2, M-3) were monitored as follows. First, according to measurements of onboard sensors obtained in a certain time interval, spacecraft rotational motion was reconstructed in this interval. Then, along the found motion, microacceleration at a given onboard point was calculated according to the known formula as a function of time. The motion was reconstructed by the least squares method using the solutions to the equations of satellite rotational motion. The time intervals in which these equations make reconstruction possible were from one to five orbital revolutions. This length is increased with the modulus of the satellite angular velocity. To get an idea on microaccelerations and satellite motion during an entire flight, the motion was reconstructed in several tens of such intervals. This paper proposes a method for motion reconstruction suitable for an interval of arbitrary length. The method is based on the Kalman filter. We preliminary describe a new version of the method for reconstructing uncontrolled satellite rotational motion from magnetic measurements using the least squares method, which is essentially used to construct the Kalman filter. The results of comparison of both methods are presented using the data obtained on a flight of the Foton M-3.

Secular resonances as a source of dynamic chaoticity in the long-term orbital evolution of uncontrolled satellites

We present the results of MEGNO analysis of the long-term orbital evolution of uncontrolled objects of satellite radio navigation systems in medium Earth orbits and geostationary orbits. It is shown that secular resonances affecting these objects may give rise to dynamic randomness in their long-term orbital evolution.

Modelling and Optimal Control of a Docking Maneuver with an Uncontrolled Satellite

AbstractCapturing disused satellites in orbit and their controlled reentry is the aim of the DEOS space mission. Satellites that ran out of fuel or got damaged pose a threat to working projects in orbit. Additionally, the reentry of such objects endangers the population as the place of impact cannot be controlled anymore. This paper demonstrates the modelling of a rendezvous szenario between a controlled service satellite and an uncontrolled target. The situation is modelled via first order ordinary differental equations where a stable target is considered. In order to prevent a collision of the two spacecrafts and to ensure both satellites are docked at the end of the maneuver, additional state constraints, box contraints for the control and a time dependent rendezvous condition for the final time are added. The problem is formulated as an optimal control problem with Bolza type cost functional and solved using a full discretization approach in AMPL/IpOpt. Last, simulation results for capturing a tumbling satellite are given.

A Study of the Achievable Geosynchronous Angles-Only Orbit Estimation Accuracy

This analysis investigates the geosynchronous orbit estimation accuracy that can be achieved given short-term dedicated tracking by a single ground-based optical sensor. Two Global Positioning System (GPS) Wide Area Augmentation System (WAAS) satellites are chosen for this case study because highly-accurate WAAS reference position and velocity point solutions are available for public use and present the opportunity to experimentally assess the effect of orbit perturbations to the meter level. Simulated optical (angles-only) observations are generated from these experimental reference ephemerides. By varying the tracking parameters of nightly tracking arc length, sampling rate, and orbit epoch, and fitting to two consecutive days of observations, a batch estimation analysis is performed that characterizes the expected level of two-day solution accuracy given an imperfect dynamic model and a satellite which is performing small, frequent maneuvers. The results show that the estimated solution fits over the two-day period to better than 10 meters. An analysis of one month of data for an uncontrolled satellite is performed to statistically determine the solution uncertainty and mean accuracy. It is shown that 10-meter accuracy is possible given short sampling intervals (10 to 30 seconds) and long nightly track lengths (three or more hours per night). Several tracking scenarios are found to meet accuracy requirements on the order of 10 to 100 meters.

Geostationary orbit occupancy and results of its control

The variation of a risk of collision on geostationary orbit is determined during last 8 years. On the average he has changed poorly except for two strong jumps. Is established, that the returning of orbit of drifting object in an equatorial plane can be found not only after 53 years after he became to uncontrolled state, but also through 2 - 4 years after unsuccessful launch of a satellite into orbit. In particular, at the end of December, 2009 the inclination of orbit of the satellite 97016A has passed through zero value. As a result of this risk of collisions of uncontrolled satellites with active satellites was increased in 3 - 4 times. His maximum does not coincide with the moment of returning of object in an equatorial plane. Such maximum of collision risk probability can be two.

Computational methods for reentry trajectories and risk assessment

The trajectory modeling of uncontrolled satellites close to reentry in the atmosphere is still a challenging activity. Tracking data may be sparse and not particularly accurate, the objects’ complicate shape and unknown attitude evolution may render difficult the aerodynamic computations and, last but not the least, the models used to predict the air density at the altitudes of interest, as a function of solar and geomagnetic activity, are affected by significant uncertainties. After a brief overview of the relevance of the risk related to satellite reentries and debris survival down to the ground, the paper describes some of the methods and techniques developed in support of the reentry predictions carried out for civil protection purposes. An appropriate management of the intrinsic uncertainties of the problem is in fact critical for the dissemination of the information, avoiding, as much as possible, misunderstandings and unjustified alarm. Special attention is paid to the evaluation of the risk, the availability of orbit determinations, the uncertainties of the residual lifetime estimation, and the definition of reentry and risk windows. When possible, the discussion is supported by real data, results and examples, often based on the authors’ direct experience and researches.

SPACE ROBOTIC MISSION CONCEPTS FOR CAPTURING STRAY OBJECTS

Abstract The capture and recovery of an expensive satellite that has lost its attitude control function can be an important class of future missions for space robots. Moreover, there are tens of thousands of pieces of debris in orbit from previous missions. These orbiting debris such as the uncontrolled pieces of booster stages and obsolete satellites are a serious hazard to future orbiting spacecrafts. Thus, the use of robotic systems to capture and de-orbit uncontrolled materials from earth orbit has the potential to be another important future class of missions for space robots which should be technically similar to satellite capture. This paper describes on-orbit service system that utilizes multiple space robots for capturing and recovering valuable satellite system and for removing and changing the orbit to avoid collision from space debris. 1. Introduction Researchers have suggested that robots will be crucial components of future orbital missions [1]. While human astronauts are invaluable for their judgment and intelligence, transporting and maintaining them in space is expensive and potentially dangerous. Robotic systems, while having many limitations, offer important advantages to augment or in some cases replace astronauts in orbit. Robots have lower cost, require minimal support infrastructure, and have an indefinite work life in orbit. This paper outlines two potential orbital space missions suited to robots, and possibly teams of robots. These missions are the capture of an uncontrolled satellite and collection or deflection of space debris. The technologies required to perform these missions are currently under study as part of a joint MIT/NASDA research program. An important issue is to identify potential tasks within these missions that are most effectively done by robots.