Strategies For Non-Planar Configurations Of Geostationary Tethered Collecting Solar Power Satellite Systems

To collect additional solar energy during the hours of darkness and to overcome the limited Terrestrial solar power due to the diurnal day night cycle, the concept of a Geostationary Tethered Collecting Solar Power Satellite System has been proposed by several authors in the last years. This tethered system consists of a long tether used to link two bodies: a single large panel with a capability of collecting solar energy, and an Earth-pointing microwave transmitting satellite. In this manner, the solar energy would be collected directly from the space and beamed back down to any point on Earth. Planar configurations, when the panel and the microwave transmitting satellite are placed on geostationary orbits, have been usually investigated to maintain the tethered system around the Earth. However, this configuration implies that the panel and the microwave transmitting satellite must to orbit the Earth in exactly the same orbital plane of all geostationary satellites

Tethered subsatellite study

The results are presented of studies performed relating to the feasibility of deploying a subsatellite from the shuttle by means of a tether. The dynamics, the control laws, the aerodynamics, the heating, and some communication considerations of the tethered subsatellite system are considered. Nothing was found that prohibits the use of a subsatellite joined to the shuttle by a long (100 km) tether. More detailed studies directed at specific applications are recommended

Tethers in space handbook

The handbook provides a list and description of ongoing tether programs. This includes the joint U.S.-Italy demonstration project, and individual U.S. and Italian studies and demonstration programs. An overview of the current activity level and areas of emphasis in this emerging field is provided. The fundamental physical principles behind the proposed tether applications are addressed. Four basic concepts of gravity gradient, rotation, momentum exchange, and electrodynamics are discussed. Information extracted from literature, which supplements and enhances the tether applications is also presented. A bibliography is appended

Hybrid fuzzy sliding mode control for motorised space tether spin-up when coupled with axial and torsional oscillation

A specialised hybrid controller is applied to the control of a motorised space tether spin-up space coupled with an axial and a torsional oscillation phenomenon. A seven-degree-of-freedom (7-DOF) dynamic model of a motorised momentum exchange tether is used as the basis for interplanetary payload exchange in the context of control. The tether comprises a symmetrical double payload configuration, with an outrigger counter inertia and massive central facility. It is shown that including axial and torsional elasticity permits an enhanced level of performance prediction accuracy and a useful departure from the usual rigid body representations, particularly for accurate payload positioning at strategic points. A simulation with given initial condition data has been devised in a connecting programme between control code written in MATLAB and dynamics simulation code constructed within MATHEMATICA. It is shown that there is an enhanced level of spin-up control for the 7-DOF motorised momentum exchange tether system using the specialised hybrid controller. hybrid controller

A Small-Satellite Demonstrator for Generating Artificial Gravity in Space via a Tethered System

It is well-known that prolonged exposure in humans to a microgravity environment leads to significant loss of bone and muscle mass; this presents a formidable obstacle to human exploration of space, particularly for missions requiring travel times of several months or more, such as a 6 to 9mon th trip to Mars. Artificial gravity may be produced by spinning a spacecraft about its center of mass, but since the g– force generated by rotation is equal to “omega-squared times r” (where omega is its angular velocity and r is the distance from the center of rotation), we have that unless the distance from the center of rotation is several kilometers, the rotation rate required to generate “1 − g” would induce vertigo in the astronauts as they moved about the capsule (e.g. if the distance from the center of rotation is 10 meters, the required rotation rate for 1 − g would be 9.5 rpm). By tethering the crew capsule to an object of nearly equal mass (such as the spent final rocket stage) at a distance of 1 to 2 kilometers, the necessary rotation rate would be sufficiently small as to not cause discomfort for the astronauts. For example, if the distance from the center of rotation is 2 kilometers, the required rotation rate for 1−g would be 0.67 rpm; at 1 kilometer the rate is still only 0.95 rpm. 1 rpm is considered an acceptable spin rate for the human body to withstand for extended periods of time. This paper gives an overview of the Tethered Artificial Gravity (TAG) satellite program, a 2-part program to study the operation and dynamics of an artificial-gravity-generating tethered satellite system. Phase I of the program will culminate in a flight of a model spacecraft in a non-ejected Get-Away-Special (GAS) Canister on the Space Shuttle. It is to be operated under the aegis of the Texas Space Grant Consortium. The purpose of the Phase I flight is to test key components of the system to be flown in Phase II of the program. Phase I will also involve detailed modeling and analysis of the dynamics of the spacecraft to be flown in Phase II of the program; the Phase II spacecraft will be a small, 65 kg, tethered satellite system which will be boosted into low-earth orbit, deployed and then spun-up to produce artificial gravity. In addition to a description of the TAG program, results of parametric studies related to TAG will be presented in this paper

Tethers in space handbook, second edition

The Tethers in Space Handbook, Second Edition represents an update to the initial volume issued in September 1986. As originally intended, this handbook is designed to serve as a reference manual for policy makers, program managers, educators, engineers, and scientists alike. It contains information for the uninitiated, providing insight into the fundamental behavior of tethers in space. For those familiar with space tethers, it includes a summary of past and ongoing studies and programs, a complete bibliography of tether publications, and names, addresses, and phone numbers of workers in the field. Perhaps its most valuable asset is the brief description of nearly 50 tether applications which have been proposed and analyzed over the past 10 years. The great variety of these applications, from energy generation to boosting satellites to gravity wave detection is an indication that tethers will play a significant part in the future of space development. This edition of the handbook preserves the major characteristics of the original; however, some significant rearrangements and additions have been made. The first section on Tether Programs has been brought up to date, and now includes a description of TSS-2, the aerodynamic NASA/Italian Space Agency (ASI) mission. Tether Applications follows, and this section has been substantially rearranged. First, the index and cross-reference for the applications have been simplified. Also, the categories have changed slightly, with Technology and Test changed to Aerodynamics, and the Constellations category removed. In reality, tether constellations may be applicable to many of the other categories, since it is simply a different way of using tethers. Finally, to separate out those applications which are obviously in the future, a Concepts category has been added. A new section included here on Conference Summaries recognizes the fact that the tether community is growing internationally, and that meetings provide a means of rapid communication and interaction. Finally, the Bibliography section has been considerably updated to include all known references. These are listed by author and by subject and include the papers to be presented at the Third International Conference in May 1989

Nonlinear dynamics and control of electrodynamic tether for deorbiting space debris

The ever increasing population of space debris poses a great threat to the sustainable development of space industry. Electrodynamic tether has been recognized as a promising technology for the active removal of space debris from overpopulated orbital regions. A typical electrodynamic tether system consists of two end-bodies connected by a conductive tether in space. The electric current flowing in the tether will interact with the magnetic field of the Earth to generate the Lorentz force, by which the system can be deorbited almost without expending propellant. The dynamics and control of any electrodynamic tether system is highly nonlinear by nature and have two critical aspects for practical application: the deployment of electrodynamic tether and the attitude stability during the deorbiting process. This paper summarizes some recent efforts made to address these two issues by the authors’ research team in Nanjing University of Aeronautics and Astronautics. Moreover, some open problems deserving future investigation are discussed

Dynamical modelling of a flexible motorised momentum exchange tether and hybrid fuzzy sliding mode control for spin-up

A space tether is a long cable used to couple satellites, probes or spacecrafts to each other or to other masses, such as a spent booster rocket, space station, or an asteroid. Space tethers are usually made of thin strands of high-strength fibres or conducting wires, which range from a few hundred metres to several kilometres and have a relatively small diameter. Space tethers can provide a mechanical connection between two space objects that enables a transfer of energy and momentum from one object to the other, and as a result they can be used to provide space propulsion without consuming propellant. Additionally, conductive space tethers can interact with the Earth's magnetic field and ionospheric plasma to generate thrust or drag forces without expending propellant. The motorised momentum exchange tether (MMET) was first proposed by Cartmell in 1996 and published in 1998. The system comprises a specially designed tether connecting two payload modules, with a central launcher motor. For the purposes of fundamental dynamical modelling the launcher mass can be regarded as a two part assembly, where the rotor is attached to one end of each tether subspan, and the other side is the stator, which is attached to the rotor by means of suitable bearings. Both the launcher and the payload can be attached to the tether by means of suitable clamps or bearing assemblies, dependent on the requirements of the design. The further chapters in this thesis focus on a series of dynamical models of the symmetrical MMET syste, including the dumbbell MMET system, the solid massless MMET system, the flexible massless MMET system, the solid MMET system and the discretised flexible MMET system. The models in this context have shown that including axial, torsional and pendular elasticity, the MMET systems have a significant bearing on overall performance and that this effect should not be ignored in future, particularly for control studies. All subsequent analyses for control applications should henceforth include flexible compliance within the modelling procedure. Numerical simulations have been given for all types of MMET models, in which, accurate and stable periodic behaviours are observed, including the rigid body motions, the tether spin-up and the flexible motions, with proper parameter settings. The MMET system's spin-up control methods design and analysis will henceforth be referenced on the results. For the non-linear dynamics and complex control problem, it was decided to investigate fuzzy logic based controllers to maintain the desired length and length deployment rate of the tether. A standard two input and one output fuzzy logic control (FLC) is investigated with numerical simulations, in which the control effects on the MMET system's spin-up are observed. Furthermore, to make the necessary enhancement to the fuzzy sliding mode control, a specialised hybrid control law, named F$\alpha$SMC is proposed, which combines fuzzy logic control with a SkyhookSMC control law together, then it is applied for the control of motorised space tether spin-up coupled with an flexible oscillation phenomenon. It is easy to switch the control effects between the SkyhookSMC and the FLC modes when a proper value of $\alpha$ is selected $(0<\alpha<1)$ to balance the weight of the fuzzy logic control to that of the SkyhookSMC control, and the hybrid fuzzy sliding mode controller is thus generated. Next, the simulations with the given initial conditions have been devised in a connecting programme between the control code written in $MATLAB$ and the dynamics simulation code constructed within $MATHEMATICA$. Both the FLC and the hybrid fuzzy sliding mode control methods are designed for the control of spin-up of the discretised flexible MMET system with tether-tube subspans, and the results have shown the validated effects of both these control methods for the MMET system spin-up with included flexible oscillation. To summarise, the objectives of this thesis are, firstly, to propose a series of new dynamical models for the motorised momentum exchange tethers; secondly, to discuss two types of control methods for the spin-up behaviour of a flexible motorised momentum exchange tether, which include a fuzzy logic control and a hybrid fuzzy sliding mode control. By the weight factor $\alpha$, fuzzy logic control and SkyhookSMC controllers can be balanced from one to each other, and there is observed difference for each of the elastic behaviour in the MMET system involving these MMET systems with different controllers - FLC($\alpha = 1$), F$\alpha$SMC($\alpha = 0.5$) and SkyhookSMC($\alpha = 0.0$). The results state the control effects for FLC, F$\alpha$SMC and FLC, which lead to stable spin-up behaviour with flexible oscillations

Analysis of Propellantless Tethered System for the De-Orbiting of Satellites at End of Life

The increase of orbital debris and the consequent proliferation of smaller objects through fragmentation is driving the need for mitigation strategies that address this issue at its roots. The present guidelines for mitigation point out the need to deorbit new satellites injected into low Earth orbit (LEO) within a 25-year time. The issue is then how to deorbit the satellite with an efficient system that does not impair drastically the propellant budget of the satellite and, consequently, reduces its operating life. In this contest a passive system, which makes use of an electrodynamics tether to deorbit a satellite through Lorentz forces, has been investigated. The system collects electrons from the ionosphere at its anodic end (the conductive tether itself left bare) and emits electrons through a plasma contactor at the cathodic end. The current that circulates in the tether produces the Lorentz drag force through the interaction with the Earth’s magnetic field. Power can also be tapped from the tether for running the cathode and other ancillary on-board equipment. The deorbiting system will be carried by the satellite itself at launch and it will be deployed from the satellite at the end of its life. From that moment onward the system operates passively without requiring any intervention from the satellite itself. This thesis summarizes the results of the analysis carried out to show the deorbiting performance of the system starting from different orbital scenarios and for satellite configurations, and describing the tethered system by means of different mathematical models in order to include the lateral flexibility and increase the accuracy of the results, which can be easily scaled. Moreover high-fidelity and latest environmental routines has been used for magnetic field, ionospheric density, atmospheric density and a 4×4 gravity field model, since the environment is very important for describing appropriately each external interaction, in particular the electrodynamic one. The electric properties of the wire depends on its temperature, which is computed dynamically by a thermal model that considers all the major input fluxes and the heat emitted by the tether itself. At last the electric current along the rope is constantly evaluated during the reentry, since large variations happens passing from sunlight to shadow regions, and vice-versa. Without any control the system goes rapidly into instability, because the electrodynamic torque pumps continuously energy into the system enlarging the libration of the tether. So ad hoc strategies must be thought and included. In the past several techniques have been proposed, but with a lot of assumptions and limitations. In this work a new concept has been implemented, mounting in the satellite at the basis of the tether a damping mechanism for dissipating the energy associated with the lateral motion. At last the whole deployment of a tape tether has been analyzed. Several configurations have been studied, and the tradeoff analysis concluded that a non-motorized reeling deployer is well suited for a 1-3 cm wide tape like the tapes. Optimal reference profiles have been evaluated for two class of tether (3 and 5km), and are then used to regulate the brake mechanism mounted on the deployer itself to control the deployment. Different conditions have been analyzed to demonstrate the capabilities of the control law to provide a successful deployment in the presence of various error