SEARCH · Search NASA

Results for “Tether”

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.

SourceResearch connectionFrom yearThrough year

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

At least 595 records · Page 33

All sources NASA NTRS DOE OSTI

NASA NTRS1988

Plasma contactors for use with electodynamic tethers for power generation

Plasma contactors are 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. The plasma contactor emits a plasma cloud which facilitates the electrical connection. The physics of this plasma cloud is investigated for contactors used as electron collectors. The central question addressed is whether the electrons collected by a plasma contactor come from the far field or by ionization of local neutral gas. This question is important because the system implications are different for the two mechanisms. 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 for the outer regions of the cloud is developed. The current voltage characteristic of an Argon plasma contactor cloud is estimated for several ion currents in the range of 1 to 100 Amperes. It is suggested that the major source of collected electrons comes by ionization of neutral gas while collection of electrons from the far field is relatively small.

Hastings, D. E.↗

NASA NTRS1988

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

The goal is to extend the previous analysis of electromagnetic wave generation by an electrodynamic tethered satellite system to a more realistic model that includes the effects on wave propagation and reflection to the boundaries between ionosphere, atmosphere, and earth. One of the major activities was searching the scientific literature for publications that might be relevant to the problem. The software developed as SAO to follow the path of waves along field lines through the ionosphere to the atmosphere starting from an arbitary position in the atmosphere is described. Some preliminary results are presented from applying the code to the location of wave reception hot spots on the earth's surface for satellites operating at 300 and 600 km altitudes. A generalization of the Alfven wing analysis is presented to allow for arbitrary angles between the velocity vector, geomagnetic field, and the veritcal. This will be utilized in the modeling of the problem with boundaries included.

Estes, Robert D.↗

NASA NTRS1988

Power transmission studies for tethered SP-100

The tether and/or transmission line connecting the SP-100 to space station presents some unorthodox challenges in high voltage engineering, power transmission, and distribution. The line, which doubles as a structural element of this unusual spacecraft, will convey HVDC from SP-100 to the platform in low Earth orbit, and environment where the local plasma is sufficient to cause breakdown of exposed conductors at potentials of only a few hundred volts. Its anticipated several years operation, and continuously accumulating exposure to meteoroids and debris, raises an increasing likelihood that mechanical damage, including perforation, will be sustained in service. The present concept employs an array of gas insulated solid wall aluminum coaxial tubes; a conceptual design which showed basic feasibility of the SP-100 powered space station. Practical considerations of launch, deployment and assembly have lead to investigation of reel deployable, dielectric insulated coaxial cables. To be competitive, the dielectric would have to operate reliably in a radiation environment under electrical stresses exceeding 50 kV/cm. The SP-100 transmission line high voltage interfaces are also considered.

Bents, David J.↗

NASA NTRS1988

Recent developments in gravity gradiometry from the Space-Shuttle-borne tethered satellite system

This paper describes the current development of a noncryogenic gravity gradiometer for future use on board the tethered satellite system (TSS). The paper also proposes a way of testing a single-axis prototype of such an instrument that makes use of the free-fall technique in vacuum. This gravity gradiometer has a design sensitivity of the order of 0.01 EU in 10-s integration time. Because of the small size and light weight, a noncryogenic gravity gradiometer is a valid candidate to fit the limited accommodation capability of the TSS deployed from the Shuttle and maintained, for several days, at an altitude of 120-130 km. This unique capability improves the resolution and accuracy achievable in reconstructing the earth gravity field, in particular at short wavelengths. A preliminary analysis of the dynamics of the TSS satellite indicates the potential of such satellite as a low-altitude research platform for gravity gradiometry.

Lorenzini, Enrico C.↗

NASA NTRS1988

Downward-deployed tethered platforms for high enthalpy aerothermodynamic research

The data on aerothermodynamic and aerodynamic interactions at altitudes above 50 km is extremely limited because of the relative inaccessibility of the region to research vehicles of any sort. This paper addresses the practicability of using downward deployed satellites tethered to an orbiting host vehicle in order to obtain steady-state data in the upper reaches of the region above 80 or 90 km.

Wood, George M.↗

NASA NTRS1988

Power transmission studies for tethered SP-100

The tether and/or transmission line connecting the SP-100 to Space Station presents some unorthodox challenges in high voltage engineering, power transmission, and distribution. The line, which doubles as a structural element of this unusual spacecraft, will convey HVDC from SP-100 to the platform in low Earth orbit, and environment where the local plasma is sufficient to cause breakdown of exposed conductors at potentials of only a few hundred volts. Its anticipated several years operation, and continuously accumulating exposure to meteoroids and debris, raises an increasing likelihood that mechanical damage, including perforation, will be sustained in service. The present concept employs an array of gas insulated solid wall aluminum coaxial tubes; a conceptual design which showed basic feasibility of the SP-100 powered Space Station. Practical considerations of launch, deployment and assembly have led to investigation of reel deployable, dielectric insulated coaxial cables. To be competitive, the dielectric would have to operate reliably in a radiation environment under electrical stresses exceeding 50 kV/cm. The SP-100 transmission line high voltage interfaces are also considered.

Bents, David J.↗

NASA NTRS1988

Study of an orbiting tethered dumbbell system having positive orbital energy

For very long tethered systems the sum of the kinetic and potential energy can be positive. The system remains in a circular orbit as long as the masses remain vertically aligned. The system is unstable without constant control of the alignment. If the upper mass rotates forward in the direction of the orbital motion, the system escapes out of orbit. If the upper mass rotates backward, the system falls out of orbit and the lower mass impacts the body around which the system is orbiting.

Arnold, David A.↗

NASA NTRS1988

Tethered space recovery vehicle deployment/re-entry demonstration

The feasibility of utilizing existing Space Re-entry Vehicle (SRV) hardware for a Shuttle Orbiter-based tethered SRV deployment and re-entry demonstration using the Small Expendable Deployer System has been investigated. Options for mounting the SRV in the Orbiter, modifications and additions required to the existing SRV hardware have been defined. Flight demonstration scenarios from the Orbiter have been investigated, and re-entry motion and targeting uncertainties have been determined.

Florence, D.↗

NASA NTRS1988

Optimization of motion control laws for tether crawler or elevator systems

Based on the proposal of a motion control law by Lorenzini (1987), a method is developed for optimizing motion control laws for tether crawler or elevator systems in terms of the performance measures of travel time, the smoothness of acceleration and deceleration, and the maximum values of velocity and acceleration. The Lorenzini motion control law, based on powers of the hyperbolic tangent function, is modified by the addition of a constant-velocity section, and this modified function is then optimized by parameter selections to minimize the peak acceleration value for a selected travel time or to minimize travel time for the selected peak values of velocity and acceleration. It is shown that the addition of a constant-velocity segment permits further optimization of the motion control law performance.

Swenson, Frank R.↗

NASA NTRS1990

Current collection model on tether satellite system

Results are reported from numerical simulations of current collection by a tethered satellite moving in the earth magnetic field. The focus is on the instruments of the Research on Orbital Plasma Electrodynamics (ROPE) experiment planned for the TSS-1 mission (scheduled launch 1991). The derivation of the governing equations is outlined, and the results of simulations with and without the geomagnetic field are presented in graphs. It is predicted that beam-beam interaction will occur when no magnetic effect is present, especially when the instrument bias is lower than the local potential; with the magnetic effect, there should be complex multiple-stream interactions, magnetic-field shielding covering 30 percent or more of the satellite surface when the B field is greater than 0.35 G, and nearly complete collection of the electrons by the instrument arm.

Hwang, K. S.↗

NASA NTRS1990

Analysis of tethered balloon, ceilometer and class sounding data taken on San Nicolas Island during the FIRE project

During the FIRE Marine Stratocumulus Program on San Nicolas Island, Colorado State University (CSU) and the British Meteorological Office (BMO) operated separate instrument packages on the NASA tethered balloon. The CSU package contained instrumentation for the measurement of temperature, pressure, humidity, cloud droplet concentration, and long and short wave radiation. Eight research flights, performed between July 7 and July 14, are summarized. An analysis priority to the July 7, 8 and 11 flights was assigned for the purposes of comparing the CSU and BMO data. Results are presented. In addition, CSU operated a laser ceilometer for the determination of cloud base, and a CLASS radiosonde site which launched 69 sondes. Data from all of the above systems are being analyzed.

Schubert, Wayne H.↗

NASA NTRS1990

NRL tethered balloon measurements at San Nicolas Island during FIRE IFO 1987

An overview is given of the tethered balloon measurements made during the First ISCCP Regional Experiment (FIRE) marine stratocumulus intensive field observations (IFO) at San Nicolas Island in 1987. The instrument utilized on the balloon flights, the 17 flights over a 10 day period, the state of the data analysis, and some preliminary results are described. A goal of the measurements with the Naval Research Laboratory (NRL) balloon was to give a unique and greatly improved look at the microphysics of the clear and cloud-topped boundary layer. For this goal, collocated measurements were made of turbulence, aerosol, cloud particles, and meteorology. Two new instruments which were expected to make significant contributions to this effort were the saturation hygrometer, capable of measuring 95 percent less than RH 105 percent (with an accuracy of 0.05 percent near 100 percent) and used for the first time in clouds; and the forward scatter meter which gives in situ LWC measurements at more than 10 Hz. The data set, while unfortunately only partially simultaneous with the bulk of the FIRE stratocumulus observations, is unique and worthwhile in its own right. For the first time accurate RH measurements near 100 percent have been made in-cloud; although, the use of the saturation hygrometer reflected a learning experience which will result is substantially better performance the next time. These measurements were made in conjunction with other microphysical measurements such as aerosol and cloud droplet spectra, and perhaps most important of all, they were all collocated with bivane turbulence measurements thus permitting flux calculations. Thus the analysis of this data set, which consisted of about 50 percent stratocumulus cases including increasing and decreasing partial cloud cover, should lead to new insights on the physical mechanisms which drive the boundary-layer/cloud/turbulence system.

Gerber, Hermann↗

NASA NTRS1990

Turbulence measurements using tethered balloon instrumentation during FIRE 1987

As part of the surface-based observations conducted on San Nicolas Island, the U.K. Meteorological Office operated a set of turbulence probes attached to a balloon tether cable. Typically six probes were used, each capable of measuring momentum, heat, and humidity fluxes. Two probes were fitted with net radiometers, one positioned above cloud and the other below; a third probe carried a Lyman-alpha hygrometer fitted with a pre-heater for the measurement of total water content. Some preliminary results are presented from the 14th July describing the variation in structure of the cloudy boundary layer during the daytime. This day was characterized by a complete cloud cover, an inversion height of approximately 600 m. and north-westerly winds of approximately 6 m.s(-1). As an illustration the equivalent potential temperature derived from a profile ascent made between approximately 0830 and 0930 (PDT) is shown. The data has been smoothed to a height resolution of about 4 metres. At this time the cloud base was approximately 200 m. and very light drizzle was reaching the surface. The vertical velocity variance and potential temperature flux for two periods are shown; the first (shown by full lines) immediately follows the profile and the second (shown by dashed lines) is central around 1400 (PDT). The data have been normalized by their maximum values in the first period. Cloud base has now risen to approximately 300 m. There is a marked variation during the morning, particularly in sigma w. The net radiative flux above cloud top has by now reached its maximum value.

Hignett, Phillip↗

NASA NTRS1991

Magnetoplasma sheath waves on a conducting tether in the ionosphere with applications to EMI propagation on large space structures

A recent space experiment confirmed sheath-wave propagation of a kilometer-long insulated wire in the ionosphere, oriented parallel to the Earth's magnetic field. This space tether experiment, Oedipus-A, showed a sheath-wave passband up to about 2 MHz and a phase velocity somewhat slower than the velocity of light in a vacuum, and also demonstrated both ease of wave excitation and low attenuation. The evidence suggests that, on any large structure in low Earth orbit, transient or continuous wave electromagnetic interference, once generated, could propagate over the structure via sheath waves, producing unwanted signal levels much higher than in the absence of the ambient plasma medium. Consequently, there is a need for a review of both electromagnetic interference/electromagnetic compatibility standards and ground test procedures as they apply to large structures in low Earth orbit.

Balmain, K. G.↗

NASA NTRS1990

Role of current driven instabilities in the operation of plasma contactors used with electrodynamic tethers

The collection of current to an electrodynamic tether in low LEO is enhanced by a plasma cloud surrounding the anode (called a plasma contactor). The main mechanism by which this is achieved is the scattering, perpendicular to the lines of the magnetic field, of the electrons which enter the plasma cloud. The scattering may be a result of the interaction between the electrons and unstable EM waves, one example being lower-hybrid waves. The boundaries of instability are found for the lower-hybrid waves in a parametric study where, for the cases of Ar and NH3 clouds, the density, the ratio of electron to ion temperature, and the composition of the electron population, are varied. The main conclusion is that the lower-hybrid waves will be confined to the outer regions of the cloud and have the right properties to scatter electrons.

Gioulekas, A.↗

NASA NTRS1991

Current collection and current closure in the Tethered Satellite System

Current collection and closure-path modeling are examined analytically with respect to the Tethered Satellite System (TSS). A particle-in cell code is compared with a one-dimensional unmagnetized fluid code to model the behavior of a positively charged satellite in the ionosphere. The morphology of the sheath and the sheath-region processes are thus examined, and the influence of ions leaving the sheath region is found to cause the attraction of an electron current that is 40 times greater than the steady state value. The enhancement is transient and enhances the acceleration of the electrons in the sheath. A set of modified MHD equations, including those for ion inertia, quasineutrality, and electron drift, is employed to model TSS current closure. Whistler modes are found to exist and can be excited as the TSS passes through the ionosphere. Important conclusions include a significant fluctuation level in the steady state sheath, an ion void which affects the electron population, and some long-lived electrons trapped in the settled sheath with respect to two directions.

Drobot, Adam↗

NASA NTRS1992

Numerical simulations of the electrodynamic interactions between the Tethered-Satellite-System and space plasma

The first Tethered-Satellite-System (TSS-1), scheduled for a flight in late 1992, is expected to provide relevant information related to the concept of generating an emf in a 20-km-long (or longer) conducting wire. This paper presents numerical simulations of the electrodynamic interactions between the TSS system and space plasma, using a 2D and 3D models of the system. The 2D case code simulates the motion of a long cylinder past a plasma, which is composed of electrons and H(+) ions. The system is solved by allowing the plasma to flow past the cylinder with an imposed magnetic field. The more complex 3D case is considered to study the dynamics in great detail. Results of 2D simulation show that the interaction of a satellite with plasma flowing perpendicularly to the magnetic field results in an enhancement in the current collection.

Vashi, Bharat I.↗

NASA NTRS1993

Snags hit tethered satellite mission

The processing and course of the STS-46 Space Shuttle Atlantis mission are described. Problems experienced by the astronaut team in deploying the Tethered Satellite System during the mission are recounted.

Schuiling, Roelof↗