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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 253 records · Page 14

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NASA NTRS1988

Study of Plasma Motor Generator (PMG) tether system for orbit reboost

A progress report is given on a system study by TRW begun in January 1987 of a 2 kW Plasma Motor Generator Tether to be used for orbit reboost. Following the completion of the initial phase in September 1987, additional tasks were agreed on and work on them begun in March 1988. These tasks fell into three categories: tests on the prototype tether fabricated during the first phase, simulations of the spacecraft and tether system after deployment using GTOSS, and a brief investigation of the impact and feasibility of increasing the system to 20 kW and hosting it on the Orbital Maneuvering Vehicle. The subcontractor, Energy Sciences Laboratory, was assigned the responsibility of performing the simulations and some mechanical tests on the prototype tether to supplement those done at TRW. A summary of the significant findings and issues from each task follows. Recommendations for future work constitutes the third section. A copy of the final briefing is in Appendix A, plus additional reports for each task and additional analysis.

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NASA NTRS1987

Plasma contactors for use with electrodynamic tethers for power generation

Plasma contactors have been proposed as a means of making good electrical contact between biased surfaces such as found at the ends of an electrodynamic tether and the space environment. A plasma contactor is a plasma source which emits a plasma cloud which facilitates the electrical connection. The physics of this plasma cloud is investigated for contactors used as electron collectors and it is shown that contactor clouds in space will consist of a spherical core possibly containing a shock wave. Outside of the core the cloud will expand anisotropically across the magnetic field leading to a turbulent cigar shape structure along the field. This outer region is itself divided into two regions by the ion response to the electric field. A two dimensional theory of the motion of the cloud across the magnetic field is developed. The current voltage characteristic of an Argon plasma contactor cloud is estimated for several ion currents in the range of 1-100 Amperes. It is shown that small ion current contactors are more efficient than large ion current contactors. This suggests that if a plasma contactor is used on an electrodynamic tether, then a multiple tether array will be more efficient than a single tether.

Hastings, D. E.↗

NASA NTRS1987

Results from a series of tethered rocket experiments

This paper reports the results of three tethered rocket experiments conducted as part of a U.S.-Japan joint program under way since 1980. The major purpose of the experiments is to obtain technical and scientific data supporting the figure electrodynamic tethered subsatellite experiments by the Space Shuttle. Vehicle charging due to dc beam emission up to 80 mA in the 150-200 km altitude range was repeatedly measured by both Langmuir and floating probes, and was found to be usually less than 10 V. During the 80 mA emission, clear evidence for the ignition of a beam-plasma discharge was obtained. In a tether deployment experiment, it was found that the tether wire acted as an antenna whose impedance decreased with the extension of the wire both in high-frequency and very low-frequency bands. Substantial rocket charging was observed during periods of electron-beam very low-frequency pulsing.

Sasaki, S.↗

NASA NTRS1988

Comments on the 'early experimental validation' session of the Second International Conference on Tethers in Space

The paper summarizes the 'early experiment aspects' of the session which focused on the need for low cost, simple flight experiments to verify tether concepts, analysis methods and simulations and to build a data base for future application of tethers. The papers discussed six well thoughtout new space experiments, a modest start toward obtaining the data needed before tether concepts can be realistically expected to be adopted in real designs. Of the ninety-five papers included in the Venice conference, only six new small experiments were discussed. In-space verification of the data base needed to design operational tethers continues to be a step in the future.

Harris, Leonard A.↗

NASA NTRS1988

The tethered satellite electrodynamics experiment project

NASA and Italy's PSN have undertaken the Tethered Satellite Electrodynamics Experiment, in which two tethered bodies will be equipped with data-collecting scientific instruments, as the first stage of the development of the Tethered Satellite System that can be deployed by the Space Shuttle. The experiment will give attention to the electromagnetic interaction between the satellite/tether/orbiter system and the ambient space plasma, and should demonstrate the operation of both satellite- and Shuttle-borne electrodynamic instruments with a conductive tether.

Price, John M.↗

NASA NTRS1988

Alfven waves from an electrodynamic tethered satellite system

The ionospheric plasma currents associated with the operation of an orbiting, constant current electrodynamic tethered satellite system are calculated using linear cold plasma theory and a tethered system current distribution model that takes into account the peculiar dumbbell shape of the system. The field line current calculations show plasma sheet currents at each end of the tethered system whose structure is roughly that of the Alfven wings. The disturbance caused by the moving tethered system extends behind its dimensions along the line of sight. The form of the wings alters as they travel away from the system. The front boundary becomes sharper while the ripples in J(z) in the wake extend to greater distances with larger amplitude. The wave impedance is calculated for a wide range of system dimension values. The expression is in sharp disagreement with a recently published result by Dobrowolny and Veltri (1986).

Estes, Robert D.↗

NASA NTRS1987

Cosmic dust collection with a sub satellite tethered to a Space Station

The number concentration and density of 1 micron and submicron sized grains in interplanetary space, as well as their relation to the larger zodical dust particles, and the importance of the beta meteoroid phenomenon are currently being questioned. The best approach to collecting large numbers of intact micron and submicron sized cosmic dust particles in real time while avoiding terrestrial and man made contamination would be to employ a tethered subsatellite from a space station down into the earth's atmosphere. Such a subsatellite tied to the space shuttle by a 100 km long tether is being developed. It is also possible that a permanent space station would allow the use of a tether even longer than 100 km. It should be noted that the same tethered collectors could also be employed to study the composition and flux of man made earth orbiting debris in any direction within 100 km or so of the space station.

Corso, George J.↗

NASA NTRS1988

The use of the tethered satellite system to perform low density aerothermodynamics studies

The Tethered Satellite System (TSS) is a cooperative space system development activity of the U.S.A. and Italy. It is comprised of the Tether Satellite (TS) and the deployer. Within TSS, the Shuttle Tethered Aerothermodynamic Research Facility (STARFAC) concept has the potential to provide access to vast portions of the upper atmosphere for atmospheric and aerothermodynamic research. The feasibility and capability of the TSS to operate as a continuous open wind tunnel and to perform low density aerothermodynamic studies are investigated. This is accomplished through a modified version of the TS simulation program (SKYHOOK). The results indicate that STARFAC concept is both feasible and practical. The TS can go below 100 km but, if thrust is used, large velocity variation (delta V) maneuvers and an attitude control are required; if a satellite lift is considered, large tether tension is produced and an attitude control is required.

Carlomagno, Giovanni M.↗

NASA NTRS1989

Dynamics and control of the tether elevator/crawler system

This paper investigates the dynamics and acceleration levels of a new tethered system for micro- and variable-gravity applications. The system consists of two platforms tethered on opposite sides to the Space Station. A fourth platform, the elevator, is placed in between the Space Station and the upper platform. Variable-g levels on board the elevator are obtained by moving this facility along the upper tether, while microgravity experiments are carried out on board the Space Station. By controlling the length of the lower tether the position of the system center of mass can be maintained on board the Space Station despite variations of the system's distribution of mass. The paper illustrates the mathematical model, the environmental perturbations and the control techniques which have been adopted for the simulation and control of the system dynamics. Two sets of results from two different simulation runs are shown. The first set shows the system dynamics and the acceleration spectra on board the Space Station and the elevator during station-keeping. The second set of results demonstrates the capability of the elevator to attain a preselected g-level.

Lorenzini, E. C.↗

NASA NTRS1989

Tethered Satellite System-2 - A proposed program

A second mission (TSS-2) has been proposed for the reusable Tethered Satellite System (TSS) being developed jointly by the U.S. and Italy. The TSS-2 flight demonstration would use the TSS deployer/retriever system to deploy a research spacecraft attached to the end of a 100-km-long tether. The deployment would take place downward from the Space Shuttle into the outer atmosphere to an altitude of approximately 130 km. The objectives of the mission would be to demonstrate the atmospheric deployment of a tethered system, conduct scientific and aerothermodynamic research measurements, and conduct engineering measurements to verify flight system performance. Analytical studies have shown the feasibility of the TSS-2 mission from both the technology and operational dynamics standpoint. The TSS-1 mission (a 20 km tether deployed upward to conduct electrodynamic experiments) will validate the TSS itself as well as deployment and retrieval operations.

Anderson, John L.↗

NASA NTRS1989

Tethered Satellite System control system design

This paper discusses the control aspects of the Tethered Satellite System mission. The deployer controls system uses length-error and tension-error feedback to control in-plane libration, length, and length rate. The satellite's reaction control system is used to augment tether tension, control rates and attitude about the tether axis, and to damp in-plane and out-of-plane libration. The orbiter's reaction control system is also used to control in-plane and out-of-plane libration. Results of simulations are presented for the flight portion of the Tethered Satellite System mission.

Tomlin, Donald D.↗

NASA NTRS1989

Development testing of TSS-1 Deployer tether control system mechanisms

Successful tether deployment and retrieval, consistent with established control laws, is predicated upon statusing real time tether dynamic conditions. This paper reports on the initial phase of engineering tests performed on various components and subassemblies integral to the TSS-1 tether control system as part of the TSS Deployer. The tests were conducted as part of the tether control system development and verification plan to confirm the functionality and map the performance of the hardware in both ambient and environmental test conditions. The result of this development effort is a lessons-learned list and design upgrades to both the flight and test hardware and to the test methods and procedures.

Bentley, D. P.↗

NASA NTRS1988

Interaction of the Space Shuttle on-orbit autopilot with tether dynamics

The effect of Orbiter flight control on tether dynamics is studied by simulation. Open-loop effects of Orbiter jet firing on tether dynamics are shown, and the potential for closed-loop interaction between tether dynamics and Orbiter flight control is determined. The significance of these effects on Orbiter flight control and tether control is assessed.

Bergmann, Edward V.↗

NASA NTRS1988

Tether as a dynamic transmission line

The effect of longitudinal impulses on a satellite when a continuum tether from the Shuttle or Space Station is included is investigated. It is demonstrated that, taking the continuum nature of the tether into account, the sharp onset of a forcing impulse at the Shuttle end is perceived on board the satellite. The magnitude of the satellite response is diminished from that of the forcing impulse, and the response exhibits a broadened exponential tailoff. These are due primarily to the coupling between the tether and the satellite and its influence on an impinging impulsive wave, and not on the whole system as in the spring-mass model. The full impulse response function can be quite complex, showing repeated impulses as the tether wave bounces back and forth between the satellite and Shuttle, and having a different shape at each impingement on the satellite.

Gullahorn, Gordon E.↗

NASA NTRS1988

Shuttle electrodynamic tether system

The Shuttle Electrodynamic Tether System (SETS), an investigation of the interaction of a tethered satellite, a conducting tether, and the Orbiter with each other and with their environments is discussed. The historical development of SETS and its objectives are reviewed. The SETS instrumentation is described, including the Tether Current and Voltage Monitor, Fast Pulse Electron Gun, Spherical Retarding Potential Analyzer and Langmuir Probe, Charge Current Probe, Digital Control and Interface Unit, and Dedicated Experiment Processor. The measurements to be made by SETS are examined, and its operations are briefly addressed.

Williamson, P. R.↗

NASA NTRS1988

A two-dimensional theory of plasma contactor clouds used in the ionosphere with an electrodynamic tether

Plasma contactors have been proposed as a means of making good electrical contact between biased surfaces such as found at the ends of an electrodynamic tether and the space environment. A plasma contactor is a plasma source which emits a plasma cloud which facilitates the electrical connection. The physics of this plasma cloud is investigated for contactors used as electron collectors and it is shown that contactor clouds in space will consist of a spherical core possibly containing a shock wave. Outside of the core the cloud will expand anisotropically across the magnetic field leading to a turbulent cigar shape structure along the field. This outer region is itself divided into two regions by the ion response to the electric field. A two-dimensional theory of the motion of the cloud across the magnetic field is developed. The current voltage characteristic of an Argon plasma contactor cloud is estimated for several ion currents in the range of 1-100 Amperes. It is shown that small ion current contactors are more efficient than large ion current contactors. This suggests that if a plasma contactor is used on an electrodynamic tether then a miltiple tether array will be more efficient than a single tether.

Hastings, D. E.↗

NASA NTRS1988

Outer atmospheric research - One tether capability

One specific tether application of far-reaching promise would be to conduct outer atmospheric research by using a tethered subsatellite deployed downward from an orbiting 'mother' craft such as the Shuttle Orbiter. This capability would gather scientific and engineering/technology information about the outer atmosphere, primarily from 150 km down to perhaps 90 km. This paper presents current determinations of specific user needs, tether capabilities, and technological and program requirements to fulfill this application of tethers in space.

Anderson, John L.↗

NASA NTRS1988

Acceleration levels on board the Space Station and a tethered elevator for micro and variable-gravity applications

This paper investigates the dynamics and acceleration levels of a new tethered system for micro and variable-gravity applications. The system consists of two platforms tethered on opposite sides to the Space Station. A fourth platform, the elevator, is placed in between the Space Station and the upper platform. Variable-g levels on board the elevator are obtained by moving this facility along the upper tether, while micro-g experiments are carried out on board the Space Station. By controlling the length of the lower tether the position of the system CM can be maintained on board the Space Station despite variations of the station's distribution of mass. The paper illustrates the mathematical model, the environmental perturbations and the control techniques which have been adopted for the simulation and control of the system dynamics. Two sets of results from two different simulation runs are shown. The first set shows the system dynamics and the acceleration spectra on board the Space Station and the elevator during station-keeping. The second set of results demonstrates the capability of the elevator to attain a preselected g-level.

Lorenzini, E. C.↗