Search NASA⌕ Search

SEARCH · Search NASA

Results for “Tethering”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Tethered aerothermodynamic research for hypersonic waveriders

This paper describes the concept of a space-tethered atmospheric system, a hybrid craft consisting of an orbiting spacecraft and a downward-deployed aerodynamically-configured satellite. Such a system could conduct both hypersonic aerothermodynamics research and atmospheric science research in the outer atmosphere (about 150-90 km). Descriptions of specific space-tethered atmospheric systems, scheduled tether flight validation experiments, and a development strategy for a three-phased aerothermodynamics research capability culminating in a 'flying wind tunnel' are provided.

Anderson, John L.↗
NASA NTRS1991

Space-tethered atmospheric systems

This paper describes the concept of a space-tethered atmospheric system, a hybrid craft consisting of an orbiting spacecraft and a downward-deployed aerodynamically-configured satellite. Such a system could conduct hypersonic aerothermodynamics and atmospheric science research in the lower thermosphere (150-90 km). Descriptions of specific tethered atmospheric systems, scheduled tether flight validation experiments, candidate research topics and envisioned capabilities and benefits are provided.

Anderson, J. L.↗
NASA NTRS1990

Tethered satellite systems - The 1991 STS-46 mission

The scope of a collaborative mission involving the implementation of a tethered satellite is described. The 1991 STS-46 mission, sponsored jointly by NASA, the ESA, and the Italian Space Agency involves the deployment of a tethered satellite on a Space Shuttle Discovery flight. The concept behind the tethered satellite is described, and extensive graphic descriptions of the mission profile and specifications are presented. The payload, the European Retrievable Carrier (Eureca), is explained in terms of its features and capabilities, as well as emergency considerations. A study of atmospheric composition will be the primary objective of the satellite project.

Chang Diaz, Franklin↗
NASA NTRS1991

Aerodynamic calculations related to tethered sub-satellite experiments

The results are presented of four aerodynamic studies that were in support of a broader, preliminary inquiry concerning the potential use of downward-deployed tethered sub-satellites for in-flight aerothermodynamic research. There are a multitude of questions regarding the general tethered satellite concept and the present report addresses only a few of these. A method for estimating drag and local surface pressure and shear on orbiting or re-entereing bodies is described, and examples based on the planned TSS-2 (Tethered Satellite System) are given. The problem of pressure measurement are explored, taking into account thermal transpiration, lag time, and the disturbed flow field created by the satellite body. The performance of an aerodynamic stabilizer, a ring-tail design, is calculated and its influence on satellite motion is illustrated. A method for optimizing future satellite shapes for desired aerodynamic properties is transitional rarefied flow with given geometric constraints is proposed and examples are shown.

Potter, J. Leith↗
NASA NTRS1992

The first mission of the Tethered Satellite System

The era of space-age tethered operations moves toward reality with the launch of Tethered Satellite System-1 (TSS-1). The primary objective of this mission is to demonstrate the technology of long tethered systems in space and to demonstrate, through scientific investigations, that such systems are useful for research.

Powers, C. Blake↗
NASA NTRS1990

Investigation of nonlinear E.M. phenomena in the tethered magnetospheric cloud

Nonlinear effects of parametric and of heating type, produced in a plasma under the action of an electric field E(sub 0)(e exp i(omega)t), are considered in this work in connection with the Tethered Magnetospheric Cloud (TMC) accompanying the Tether Satellite System (TSS). The theoretical results show that these phenomena should appear in the ionosphere at high altitudes Z greater than or = (150-200) km, particularly, at Z approximately = 300 km of the TSS system orbit. Therefore, it is of a special interest to search these phenomena by such a unique experiment as the forthcoming first TSS-I and by the future, perhaps modified TSS missions. Because of the parametric decay instability, new branches of wave may be excited both around the electron and ion Lengmuir frequencies Omega (sub 0) = 2(pi)f(sub 0) and Omega (sub 0) = 2(pi)f(sub 0) under the influence of high frequency (HF), (f less than or = 10(exp 6) to few 10(exp 6) Hz), strong electric waves. The heating of all the kinds of particles is growing up very quickly in the ionosphere with altitude in the extra low and very low frequency ranges, F approximately = (1 to 10(exp 4) Hz, discussed below. The temperatures (energies), for example, of the electrons accelerated by the electric field become larger than the ionization potential in this frequency range already at altitudes Z greater than or = (150 - 200) km when the amplitude of the electric field is the absolute value of E(sub 0) approximately = (1-2) mV/m. The sources of these electric fields may be in the TSS-I mission, that so called Phantom Loop (PL) - the Tethered Electrodynamic Tail (TET), and the different kind of electromagnetic oscillations produced by different kinds of instabilities in the TMC plasma. The growth rates of these instabilities will become very high in the TSS surrounding magnetoplasma. However, in the future TSS missions, special artificial sources (generators) of electric fields should be used for these investigations.

Alpert, Yakov L.↗
NASA NTRS1991

Estimating radiated power from a conducting tethered satellite system

In anticipation of the upcoming TSS-1 experiment, theoretical calculations are made of radiated power from a conducting tethered satellite system. The radiation results from the steady motion of the system through the ionospheric plasma and it is stimulated by collection and emission of charge by the noninsulated surfaces of the tethered end connectors. A model of the current system is developed which incorporates the tether wire, satellite surfaces, and sheath currents. The radiation impedance of the current model is calculated using the previously developed theory of Barnett and Olbert (1986). The results confirm the low-frequency Alfven wave description with a predicted radiation impedance of a few tenths of an ohm in the Alven wave limit. Calculations are also made in the lower hybrid and whistler wave band. A larger impedance of about 13 ohm is found for the frequency range 5-50 kHz. By estimating the passive ion current drawn by the system a prediction of the total radiated power is also made. The result of 0.38 mW raises the question of whether or not wave emissions from a passive current collecting system may be detectable by either ground- or space-based platforms.

Donohue, D. J.↗
NASA NTRS1992

Linear adaptive control of a single-tether system

A control law for a single-tether orbiting satellite system based on a reduced order linear adaptive control technique is presented. The main advantages of this technique are its design simplicity and the facts that specific system parameters and model linearization are not required when designing the controller. Two controllers are developed: one which uses only tension in the tether as control actuation and one which uses both tension and in-plane thrusters as control actuation. Both a sixth-order nonlinear and an 11th-order bead model of a tethered satellite system are used for simulation purposes, demonstrating the ability of the controller to manage an uncertain system. Retrieval and stationkeeping results using these nonlinear models and the linear adaptive controller demonstrate the feasibility of the method. The robustness of the controller with respect to parameter uncertainties is also demonstrated by changing the nonlinear model and parameters within the model without redesigning the controller.

Greene, M. E.↗
NASA NTRS1992

Application of space-time neural networks to detect tether skiprope phenomenon in space operations

The feasibility of operating tethered payloads in earth orbit will be studied during a space shuttle flight scheduled for 1992. Tethered systems may exhibit a circular transverse oscillation or skiprope phenomenon due to interaction between the earth's magnetic field and current pulsing through the tether. Effective damping of this skiprope motion depends on rapid and accurate detection of its magnitude and phase. Satellite attitude motion has characteristic oscillations as well as many other perturbations and therefore the relationship between skiprope parameters and attitude time history is very complex and nonlinear. A space-time neural network (STNN) for filtering satellite rate gyro data is proposed for rapid detection and prediction of skiprope magnitude and phase. A validated orbital operations simulator and STNN software will be used for training and testing of this skiprope detection system. The advantages of STNNs are discussed and STNN configurations and preliminary results are presented.

Lea, Robert N.↗
NASA NTRS1993

Space time neural networks for tether operations in space

A space shuttle flight scheduled for 1992 will attempt to prove the feasibility of operating tethered payloads in earth orbit. due to the interaction between the Earth's magnetic field and current pulsing through the tether, the tethered system may exhibit a circular transverse oscillation referred to as the 'skiprope' phenomenon. Effective damping of skiprope motion depends on rapid and accurate detection of skiprope magnitude and phase. Because of non-linear dynamic coupling, the satellite attitude behavior has characteristic oscillations during the skiprope motion. Since the satellite attitude motion has many other perturbations, the relationship between the skiprope parameters and attitude time history is very involved and non-linear. We propose a Space-Time Neural Network implementation for filtering satellite rate gyro data to rapidly detect and predict skiprope magnitude and phase. Training and testing of the skiprope detection system will be performed using a validated Orbital Operations Simulator and Space-Time Neural Network software developed in the Software Technology Branch at NASA's Lyndon B. Johnson Space Center.

Lea, Robert N.↗
NASA NTRS1992

Clustering of tethered satellite system simulation data by an adaptive neuro-fuzzy algorithm

Recent developments in neuro-fuzzy systems indicate that the concepts of adaptive pattern recognition, when used to identify appropriate control actions corresponding to clusters of patterns representing system states in dynamic nonlinear control systems, may result in innovative designs. A modular, unsupervised neural network architecture, in which fuzzy learning rules have been embedded is used for on-line identification of similar states. The architecture and control rules involved in Adaptive Fuzzy Leader Clustering (AFLC) allow this system to be incorporated in control systems for identification of system states corresponding to specific control actions. We have used this algorithm to cluster the simulation data of Tethered Satellite System (TSS) to estimate the range of delta voltages necessary to maintain the desired length rate of the tether. The AFLC algorithm is capable of on-line estimation of the appropriate control voltages from the corresponding length error and length rate error without a priori knowledge of their membership functions and familarity with the behavior of the Tethered Satellite System.

Mitra, Sunanda↗
NASA NTRS1992

Downward-deployed tethered satellite systems, measurement techniques, and instrumentation - A review

This paper describes a number of scheduled and proposed Shuttle-based downward-deployed tethered satellite systems (TSSs) the purpose of which is to determine the structure of the lower thermosphere and to measure the atmospheric and aerodynamic effects in the vicinity of the satellite, the aerothermodynamic effects on the satellite's surface, and the dynamics of the tether and its endmass, the satellite. The instruments for the downward-deployed tethered missions will include mass spectrometers and other density sensors, plasma instrumentation, optical spectrophotometers, magnetometers, and instrumentation to measure the effects on satellite surface (such as the surface temperature, heat transfer, and pressure; gas adsorption on surfaces, chemistry with other gas molecules and surface material, and desorption from the surface; and surface charging).

Brown, Kenneth G.↗
NASA NTRS1992

The flight of the Tethered Satellite System

The U.S.-Italian Tethered Satellite System (TSS) Electrodynamics Mission flew aboard ST-46; the 500-kg satellite will be extended from the Shuttle Orbiter, to which it will remain connected via conducting insulated wire tether. TSS-1 constitutes the first effort to resolve the problem postulated in the 1920s by Langmuir, involving the determination of the dynamic current-voltage characteristics of a body that is charged to high potential and located in a magnetized plasma in the absence of physical boundaries. TSS-1 is also a first step to the use of tethers for space power generation and propulsion.

Papadopoulos, Dennis↗
NASA NTRS1994

Three-dimensional currents of electrodynamic tethers obtained from laboratory models

Magnetic probe measurements in three dimensions (greater than 15,000 positions) and time in a large laboratory plasma (n(sub e) greater than or equal to 10(exp 11)/cc, kTe greater than or equal to 1eV, B(sub 0) = 20 G, 1 m diam. x 2.5 m length) reveal the plasma currents J = del(vector differential operator) x B/mu(sub 0) excited by a pulsed (delta-t = 100 ns), stationary, tethered pair of electrodes (approximately equals 1 cm diam., 20 cm spacing perpendicular to B(sub 0)). The plasma currents for a moving, dc-current carrying electrodynamic tether are obtained by a superposition of delayed pulses emitted at successively displaced tether positions. The transient plasma currents are carried by low-frequency whistlers instead of Alfven waves and form a 3D wing structure but no long phantom loop due to cross-field Hall current shunting.

Urrutia, J. M.↗
NASA NTRS1995

Plasma turbulence enhanced current collection: Results from the plasma motor generator electrodynamic tether flight

The plasma motor generator (PMG) experiment, launched June 26, 1993, was a tethered system of two identical plasma contactors connected via a 500-m conducting tether. The experiment was designed to demonstrate the ability of plasma contactors to provide a low-impedance connection between a spacecraft and the ionosphere for both the electron emission and collection. The flight data indicate that plasma contactors enhance electron collection and emission by both neutralizing the electron space charge and scattering electrons across the geomagnetic field lines. Up to a 0.3 A steady current flowed along the tether in a curcuit completed through the ionosphere. An analytical model for plasma contactor interaction with a background plasma which incorporates electron scattering by plasma waves is compared with the flight data. Good agreement between the model and the data is achieved for an effective scattering frequency equal to one twentieth of the local plasma contactor plasma frequency.

Katz, I.↗
NASA NTRS1996

A Magnetic Bumper-Tether System Using ZFC Y123

We consider the use of magnetic forces in a bumper system, to soften docking procedures. We investigate a system which exhibits no magnetic field except during the docking process, which, if desired, can automatically tether two craft together, and which provides lateral stability during docking. A system composed of zero field cooled Y(1.7)Ba2Cu3O(7-delta) (Y123) tiles and electromagnets is proposed. The Y123 high temperature superconductor (HTS) is mounted on one craft, and the electromagnet on the other. Results of small prototype laboratory experiments are reported. The electromagnet has, for convenience, been replaced by a permanent SmCo ferromagnet in these measurements. When the two craft approach, a mirror image of the ferromagnet is induced in the Y123, and a repulsive bumper force, F(sub B), results. F(sub B) is velocity dependent, and increases with v. For presently available HTS materials, bumper pressure of approx. 3.7 N/cm(exp 2) is achieved using SmCo. This extrapolates to approx. 18 N/cm(exp 2) for an electromagnet, or a force of up to 20 tons for a 1 m(exp 2) system. After reaching a minimum distance of approach, the two colliding craft begin to separate. However, the consequent change of SmCo magnetic field at the Y123 results in a reversal of current in the Y123 so that the Y123 is attractive to the SmCo. The attractive (tether) force, F(sub T), is a function of R = B(sub Fe)/B(sub t, max), where B(sub Fe) is the field at the surface of the ferromagnet, and B(sub t, max) is the maximum trapped field of the Y123, i.e., the trapped field in the so-called critical state. For R greater than or equal to 2, F(sub T) saturates at a value comparable to F(sub B). For a range of initial approach velocities the two craft are tethered following the bumper sequence. Most of the kinetic energy of the collision is first converted to magnetic field energy in the Y123, and then into heat via the creep mechanism. About 15% of the work done against magnetic forces during collision remains stored as magnetic energy after 1 hour. Experiments have also been conducted on the spatial range of the bumper force for arrays of HTS tiles. For a single HTS tile approx. 2 cm in diameter, the range of F(sub B) is approx. l cm. For a l m(exp 2) array the range of F(sub B) will be circa 50 cm.

Weinstein, Roy↗
NASA NTRS1998

Electrodynamic Tether Propulsion and Power Generation at Jupiter

The results of a study performed to evaluate the feasibility and merits of using an electrodynamic tether for propulsion and power generation for a spacecraft in the Jovian system are presented. The environment of the Jovian system has properties which are particularly favorable for utilization of an electrodynamic tether. Specifically, the planet has a strong magnetic field and the mass of the planet dictates high orbital velocities which, when combined with the planet's rapid rotation rate, can produce very large relative velocities between the magnetic field and the spacecraft. In a circular orbit close to the planet, tether propulsive forces are found to be as high as 50 N and power levels as high as 1 MW.

Gallagher, D. L.↗
NASA NTRS1998

The TSS-1R Electrodynamic Tether Experiment: Scientific and Technological Results

The Tethered Satellite System (TSS) program was designed to provide the opportunity to explore certain space plasma-electrodynamic processes (associated with high-voltage bodies and electrical currents in space) and the orbital mechanics of a gravity-gradient stabilized system of two satellites linked by a long conducting tether. A unique data set was obtained during the TSS-1 R mission in which the tether emf and current reached values in excess of 3500 volts and 1 amp, respectively. The insight this has allowed into the current collection process and the physics of high-voltage plasma sheaths is significant. Previous theoretical models of current collection were electro-static assuming that the orbital motion of the system, which is highly sub-sonic with respect to electron thermal motion, was unimportant. This may still be acceptable for the case of relatively slow-moving sounding rockets. However, the TSS-1 R results show that motion relative to the plasma does affect current collection and must be accounted for in orbiting systems.

Stone, Nobie H.↗