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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.

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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Applications of tethers for planetary missions

Ideas of deep space exploration are considered. The role of tethers in deep space is of most concern. A proposal of a tethered instrument package in orbit about the Moon is explored. The idea of a sling on the surface of the Moon which would take solar energy and build up momentum of the sling is studied. The NASA idea of a Mars Aeronomy Orbiter which would use a tether to enhance the planned Mars Orbiter is reviewed. It is also proposed that a tether can be attached to an asteroid during a spacecraft flyby. The possibility of using tethers to provide a transportation system for payloads which are coming to the surface from escape, and which are leaving Mars and escaping from Mars itself is also studied. A proposal from the Jet Propulsion Lab. on collecting comet or asteroid samples and returning them to Earth is reviewed. A tethered penetrator which could collect core samples is the proposed way. Also considered is the area of electrodynamic tethers at Jupiter.

Penzo, P.↗
NASA NTRS1987

Tethers in space; Proceedings of the International Conference, Arlington, VA, Sept. 17-19, 1986

A collection of papers on the applications of tethers in space is presented. Tether flight experiments of the past, in planning stages, and in the future are examined. Tether dynamics and the applications and technical aspects of electrodynamic tethers are addressed. The use of tethers on the Space Station and applications in the Space Station era are considered. Individual tether technology issues, including tether materials and instrumentation for atmospheric measurements are discussed.

Bainum, Peter M.↗
NASA NTRS1986

Tether applications

For a range of tether lengths, end masses, and orbits, tether deployment concepts were defined and/or analyzed from the Orbiter for steady state/dynamic and up/down deployments and from circular/elliptical orbits. Orbits were defined and/or analyzed for end mass releasing concepts with steady state and dynamic releases taking into account tether and end mass motion before and after release. For a range of tether lengths, end masses, and orbits, tether retrieving or disposing concepts were defined and/or analyzed for both reusable and disposable tethers. Tether programs were installed or updated on the MSFC VAX 11/780 computer.

Source record↗
NASA NTRS1989

Theoretical investigation of EM wave generation and radiation in the ULF, ELF, and VLF bands by the electrodynamic orbiting tether

The problem of electromagnetic wave generation by an electrodynamic tethered satellite system is important both for the ordinary operation of such systems and for their possible application as orbiting transmitters. The tether's ionospheric circuit closure problem is closely linked with the propagation of charge-carrying electromagnetic wave packets away from the tethered system. Work is reported which represents a step towards a solution to the problem that takes into account the effects of boundaries and of vertical variations in plasma density, collision frequencies, and ion species. The theory of Alfen wave packet generation by an electrodynamic tethered system in an infinite plasma medium is reviewed, and brief summary of previous work on the problem is given. The consequences of the presence of the boundaries and the vertical nonuniformity are then examined. One of the most significant new features to emerge when ion-neutral collisions are taken into account is the coupling of the Alfven waves to the fast magnetosonic wave. This latter wave is important, as it may be confined by vertical variations in the Alfven speed to a sort of leaky ionospheric wave guide, the resonances of which could be of great importance to the signal received on the Earth's surface. The infinite medium solution for this case where the (uniform) geomagnetic field makes an arbitrary angle with the vertical is taken as the incident wave-packet. Even without a full solution, a number of conclusions can be drawn, the most important of which may be that the electromagnetic field associated with the operation of a steady-current tethered system will probably be too weak to detect on the Earth's surface, even for large tethered currents. This is due to the total reflection of the incident wave at the atmospheric boundary and the inability of a steady-current tethered system to excite the ionospheric wave-guide. An outline of the approach to the numerical problem is given. The use of numerical integrations and boundary conditions consistent with a conducting Earth is proposed to obtain the solution for the horizontal electromagnetic field components at the boundary of the ionosphere with the atmospheric cavity.

Estes, Robert D.↗
NASA NTRS1988

Simulation and measurement of disturbance propagation in a single tether system

One of the missions of the Getaway Tether Experiment (GATE) is to investigate disturbance propagation and control in a tethered system. In order to understand the nature of the propagation, simulation of the tether response is vital. A single finite duration pulse is the source of the disturbance. A bead model is used to predict the motion of the tether and the end masses (modeled as point masses). System response is checked for different magnitudes of force and for different points of impact on the tether. Along with simulation, hardware development is needed, especially in the area of tension measurement. At this time, hardware is being developed to measure the tension in the tether, so that the tethered system can be controlled via tension feedback. The hardware will then be tested in conjunction with the Dynamics and Control Mission of the GATE project.

Greene, Michael↗
NASA NTRS1990

Tethered gravity laboratories study

The scope of the study is to investigate ways of controlling the microgravity environment of the International Space Station by means of a tethered system. Four main study tasks were performed. First, researchers analyzed the utilization of the tether systems to improve the lowest possible steady gravity level on the Space Station and the tether capability to actively control the center of gravity position in order to compensate for activities that would upset the mass distribution of the Station. The purpose of the second task was to evaluate the whole of the experiments performable in a variable gravity environment and the related beneficial residual accelerations, both for pure and applied research in the fields of fluid, materials, and life science, so as to assess the relevance of a variable g-level laboratory. The third task involves the Tethered Variable Gravity Laboratory. The use of the facility that would crawl along a deployed tether and expose experiments to varying intensities of reduced gravity is discussed. Last, a study performed on the Attitude Tether Stabilizer concept is discussed. The stabilization effect of ballast masses tethered to the Space Station was investigated as a means of assisting the attitude control system of the Station.

Lucchetti, F.↗
NASA NTRS1990

In-orbit experimentation with the Small Expendable-Tether Deployment System

The Small Expendable-Tether Deployment System (SEDS) is a light-weight deployer capable of deploying instrumented packages and other tethered payloads up to a distance of 20 km. The system is simple and inexpensive because it does not retrieve the tethered payloads. The deployer is attached to the second stage of a Delta II which acts as a stabilized platform for the deployment of tethered payloads. SEDS is particularly suitable for complementing the Tethered Satellite missions by providing a flexible system for experimenting with the tether-in-space technology. SEDS can also provide a convenient way for testing instruments and/or procedures which require the use of long tethers.

Lorenzini, Enrico C.↗
NASA NTRS1993

Precision attitude control for tethered satellites

Tethered spacecraft are particularly well suited to serve as isolation platforms for space-borne observatories. It has previously been shown that, due to the relatively large tether force, conventional means of performing attitude control for tethered satellites are inefficient for any mission with pointing requirements more stringent than about 1 deg. A particularly effective method of implementing attitude control for tethered satellites is to use the tether tension force to generate control moments by moving the tether attach point relative to the subsatellite center of mass. This paper presents the development of a precision pointing control algorithm for tethered satellites and the simulation of the control system with laboratory hardware. The control algorithm consists of a linear quadratic regulator feedback law and a Kalman filter. The control algorithm has been shown to regulate the vehicle orientation to within 0.60 arcsec rms. This level of precision was achieved only after including a mass center estimator and accurately modeling the effects of the nonlinear attach point motion actuator.

Kline-Schoder, Robert J.↗
NASA NTRS1997

Space Tethers: Design Criteria

This document is prepared to provide a systematic process for the selection of tethers for space applications. Criteria arc provided for determining the strength requirement for tether missions and for mission success from tether severing due to micrometeoroids and orbital debris particle impacts. Background information of materials for use in space tethers is provided, including electricity-conducting tethers. Dynamic considerations for tether selection is also provided. Safety, quality, and reliability considerations are provided for a tether project.

Tomlin, D. D.↗
NASA NTRS1997

SEDS Tether M/OD Damage Analyses

The Small Expendable Deployer System (SEDS) was designed to deploy an endmass at the end of a 20-km-long tether which acts as an upper stage rocket, and the threats from the meteoroid and orbital debris (M/OD) particle environments on SEDS components are important issues for the safety and success of any SEDS mission. However, the possibility of severing the tether due to M/OD particle impacts is an even more serious concern, since the SEDS tether has a relatively large exposed area to the M/OD environments although its diameter is quite small. The threats from the M/OD environments became a very important issue for the third SEDS mission, since the project office proposed using the shuttle orbiter as a launch platform instead of the second stage of a Delta II expendable rocket, which was used for the first two SEDS missions. A series of hyper-velocity impact tests were performed at the Johnson Space Center and Arnold Engineering Development Center to help determine the critical particle sizes required to sever the tether. The computer hydrodynamic code or hydrocode called CTH, developed by the Sandia National Laboratories, was also used to simulate the damage on the SEDS tether caused by both the orbital debris and test particle impacts. The CTH hydrocode simulation results provided the much needed information to help determine the critical particle sizes required to sever the tether. The M/OD particle sizes required to sever the tether were estimated to be less than 0.1 cm in diameter from these studies, and these size particles are more abundant in low-Earth orbit than larger size particles. Finally, the authors performed the M/OD damage analyses for the three SEDS missions; i.e., SEDS-1, -2, and -3 missions, by using the information obtained from the hypervelocity impact test and hydrocode simulations results.

Hayashida, K. B.↗
NASA NTRS1998

Tether System for Exchanging Payloads Between the International Space Station and the Lunar Surface

Systems composed of several rotating and/or hanging tethers may provide a means of exchanging supplies between low Earth orbit facilities and lunar bases without requiring the use of propellant. This work develops methods for designing a tether system capable of repeatedly exchanging payloads between a LEO facility such as the International Space Station or a Space Business Park and a base on the lunar surface. In this system, a hanging tether extended upwards from the LEO facility, places a payload into a slightly elliptical orbit, where it is caught by a rotating tether in a higher elliptical orbit. This rotating tether then tosses the payload to the moon. At the moon, a long rotating "Lunavator" tether catches the payload and deposits it on the surface of the moon. By transporting an equal mass of lunar materials such as oxygen back down to the LEO facility through the tether transport system, the momentum and energy of the system is conserved, allowing frequent traffic between LEO and the lunar surface with minimal propellant requirements.

Robert P. Hoyt↗
NASA NTRS1998

Technology of Bare Tether Current Collection

The outstanding problem for useful applications of electrodynamic tethers is obtaining sufficient electron current from the ionospheric plasma. Bare tether collectors, in which the conducting tether itself, left uninsulated over kilometers of its length, acts as the collecting anode, promise to attain currents of 10 A or more from reasonably sized systems. Current collection by a bare tether is also relatively insensitive to drops in electron density, which are regularly encountered on each revolution of an orbit. This makes nighttime operation feasible. We show how the bare tether's high efficiency of current collection and ability to adjust to density variations follow from the orbital motion limited collection law of thin cylinders. We consider both upwardly deployed (power generation mode) and downwardly deployed (reboost mode) tethers, and present results that indicate how bare tether systems would perform as their magnetic and plasma environment varies in low earth orbit.

Estes, Robert D.↗
NASA NTRS2005

Analysis of Bare-Tether Systems as a Thruster for MXER Studies

The concept of the electrodynamic propulsion has a number of attractive features and has been widely discussed for different applications. A number of system designs have been proposed and compared during the last ten years. In spite of this, the choice of the proper design, for a specific mission, is far from evident. Such characteristics of tether performance as system acceleration, efficiency, etc. should be calculated and compared. The code that calculates the current for bare and partly insulated tethers with circular (wire) and rectangle (tape) cross-sections is presented. It takes into account the corrections to the OML current due to the tether cross-section geometry and the magnetic field produced by the tether current. There are two options in this code: for current calculation with the prescribed energy supply and with the prescribed end-point potential. This permits to calculate the parameters characterizing tether performance. Results for the current calculated for tethers with different designs for the currently proposed Momentum exchange Electrodynamic Reboost (MXER) Tether System are presented.

Khazanov, G. V.↗
NASA NTRS2005

Analysis of Bare-Tether Systems as a Thruster for MXER Studies

The concept of the electrodynamic propulsion has a number of attractive features and has been widely discussed for different applications. A number of system designs have been proposed and compared during the last ten years. In spite of this, the choice of the proper design, for a specific mission, is far from evident. Such characteristics of tether performance as system acceleration, efficiency, etc. should be calculated and compared. The code that calculates the current for bare and partly insulated tethers with circular (wire) and rectangle (tape) cross-sections is presented. It takes into account the corrections to the OML current due to the tether cross-section geometry and the magnetic field produced by the tether current. There are two options in this code: for current calculation with the prescribed energy supply and with the prescribed end-point potential. This permits us to calculate the parameters characterizing tether performance. Results for the current calculated for tethers with different designs for the currently proposed Momentum exchange Electrodynamic Reboost (MXER) Tether System are presented.

Khazanov, G. V.↗
NASA NTRS2005

Design Concept for a Reusable/Propellantless MXER Tether Space Transportation System

The Momentum Exchange/Electrodynamic Reboost (MXER) tether facility is a transformational concept that significantly reduces the fuel requirements (and associated costs) in transferring payloads above low earth orbit (LEO). Facility reboost is accomplished without propellant by driving current against a voltage created by a conducting tether's interaction with the Earth's magnetic field (electrodynamic reboost). This system can be used for transferring a variety of payloads (scientific, cargo, and human space vehicles) to multiple destinations including geosynchronous transfer orbit, the Moon or Mars. MXER technology advancement requires development in two key areas: survivable, high tensile strength non-conducting tethers and reliable, lightweight payload catch/release mechanisms. Fundamental requirements associated with the MXER non-conducting strength tether and catch mechanism designs will be presented. Key requirements for the tether design include high specific-strength (tensile strength/material density), material survivability to the space environment (atomic oxygen and ultraviolet radiation), and structural survivability to micrometeoroid/orbital debris (MM/OD) impacts. The driving mechanism key,gequirements include low mass-to-capture-volume ratio, positional and velocity error tolerance, and operational reliability. Preliminary tether and catch mechanism design criteria are presented, which have been used as guidelines to "screen" and down-select initial concepts. Candidate tether materials and protective coatings are summarized along with their performance in simulated space environments (e.g., oxygen plasma, thermal cycling). A candidate catch mechanism design concept is presented along with examples of demonstration hardware.

McCandless, B., II↗
NASA NTRS2005

Formation Flying of Tethered and Nontethered Spacecraft

A paper discusses the effect of the dynamic interaction taking place within a formation composed of a rigid and a deformable vehicle, and presents the concept of two or more tethered spacecraft flying in formation with one or more separated free-flying spacecraft. Although progress toward formation flight of nontethered spacecraft has already been achieved, the document cites potential advantages of tethering, including less consumption of fuel to maintain formation, very high dynamic stability of a rotating tethered formation, and intrinsically passive gravity-gradient stabilization. The document presents a theoretical analysis of the dynamics of a system comprising one free-flying spacecraft and two tethered spacecraft in orbit, as a prototype of more complex systems. The spacecraft are modeled as rigid bodies and the tether as a mass-less spring with structural viscous damping. Included in the analysis is a study of the feasibility of a centralized control system for maintaining a required formation in low Earth orbit. A numerical simulation of a retargeting maneuver is reported to show that even if the additional internal dynamics of the system caused by flexibility is considered, high pointing precision can be achieved if a fictitious rigid frame is used to track the tethered system, and it should be possible to position the spacecraft with centimeter accuracy and to orient the formation within arc seconds of the desired direction also in the presence of low Earth orbit environmental perturbations. The results of the study demonstrate that the concept is feasible in Earth orbit and point the way to further study of these hybrid tethered and free-flying systems for related applications in orbit around other Solar System bodies.

Quadrelli, Marco B.↗
NASA NTRS2005

Elastic-Tether Suits for Artificial Gravity and Exercise

Body suits harnessed to systems of elastic tethers have been proposed as means of approximating the effects of normal Earth gravitation on crewmembers of spacecraft in flight to help preserve the crewmembers physical fitness. The suits could also be used on Earth to increase effective gravitational loads for purposes of athletic training. The suit according to the proposal would include numerous small tether-attachment fixtures distributed over its outer surface so as to distribute the artificial gravitational force as nearly evenly as possible over the wearer s body. Elastic tethers would be connected between these fixtures and a single attachment fixture on a main elastic tether that would be anchored to a fixture on or under a floor. This fixture might include multiple pulleys to make the effective length of the main tether great enough that normal motions of the wearer cause no more than acceptably small variations in the total artificial gravitational force. Among the problems in designing the suit would be equalizing the load in the shoulder area and keeping tethers out of the way below the knees to prevent tripping. The solution would likely include running tethers through rings on the sides. Body suits with a weight or water ballast system are also proposed for very slight spinning space-station scenarios, in which cases the proposed body suits will easily be able to provide the equivalency of a 1-G or even greater load.

Torrance, Paul↗
NASA NTRS2012

Application of the NASCAP Spacecraft Simulation Tool to Investigate Electrodynamic Tether Current Collection in LEO

Recent interest in using electrodynamic tethers (EDTs) for orbital maneuvering in Low Earth Orbit (LEO) has prompted the development of the Marshall ElectroDynamic Tether Orbit Propagator (MEDTOP) model. The model is comprised of several modules which address various aspects of EDT propulsion, including calculation of state vectors using a standard orbit propagator (e.g., J2), an atmospheric drag model, realistic ionospheric and magnetic field models, space weather effects, and tether librations. The natural electromotive force (EMF) attained during a radially-aligned conductive tether results in electrons flowing down the tether and accumulating on the lower-altitude spacecraft. The energy that drives this EMF is sourced from the orbital energy of the system; thus, EDTs are often proposed as de-orbiting systems. However, when the current is reversed using satellite charged particle sources, then propulsion is possible. One of the most difficult challenges of the modeling effort is to ascertain the equivalent circuit between the spacecraft and the ionospheric plasma. The present study investigates the use of the NASA Charging Analyzer Program (NASCAP) to calculate currents to and from the tethered satellites and the ionospheric plasma. NASCAP is a sophisticated set of computational tools to model the surface charging of three-dimensional (3D) spacecraft surfaces in a time-varying space environment. The model's surface is tessellated into a collection of facets, and NASCAP calculates currents and potentials for each one. Additionally, NASCAP provides for the construction of one or more nested grids to calculate space potential and time-varying electric fields. This provides for the capability to track individual particles orbits, to model charged particle wakes, and to incorporate external charged particle sources. With this study, we have developed a model of calculating currents incident onto an electrodynamic tethered satellite system, and first results are shown here.

Adams, Mitzi↗