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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 NTRS1987

Plasma interactions in the Space Shuttle Orbiter environment

Attempts to measure the ambient ionospheric plasma environment in the vicinity of the payload bay of the Space Shuttle Orbiter have shown that the plasma is quite different, in a variety of characteristics, from the ionospheric plasma at low earth orbit altitudes. It appears that the large size, complex geometry and various outgassing characteristics of a typical Orbiter payload can all contribute to modifications of the plasma environment of the Space Shuttle Orbiter. The measurements indicate that the plasma is often quite turbulent and contains populations more energetic than the ambient ionospheric plasma. Pronounced wake and ram effects have been observed, and at times the data can be interpreted as plasma number density enhancements of an order of magnitude or greater over the ambient, undisturbed plasma concentration. There is evidence that this enhanced plasma concentration contains molecular ions, not occurring naturally at low earth orbit altitudes. In addition to describing the observations, the electrodynamics of enhanced Orbiter-generated plasma and its possible impact on optical measurements from the Space Shuttle Orbiter will be discussed.

Raitt, W. J.↗

NASA NTRS1987

Electric fields in the middle atmosphere

Middle atmospheric electrodynamics is characterized by discussing the present understanding of the background electrical conductivity and the sources for electric fields and currents within the medium. Results of recent research that contradicts the historical view of the region are presented. Of principal interest to the present direction of the field is the attempt to quantize the low and high altitude electric generators such as thunderstorms or ionospheric convection. It is noted that the many-fold increase in available electric parameter data from within the middle atmosphere has been a great stimulus to recent research; however, these measurements have tended to raise more questions than they give answers.

Holzworth, Robert H.↗

NASA NTRS1987

Structureborne noise in aircraft

The amount of noise reaching an aircraft's interior by structureborne paths, when high levels of other noises are present, involves the measurement of transfer functions between vibrating levels on the wing and interior noise. The magnitude of the structureborne noise transfer function is established by exciting the aircraft with an electrodynamic shaker; a second transfer function is measured using the same sensor locations with the aircraft engines operating. Attention is given to the case of a twin-turboprop OV-10A aircraft; the resulting transfer function values at the discrete frequencies corresponding to the propeller blade passage frequency and its first four harmonics are tabulated and illustrated.

Clevenson, S. A.↗

NASA NTRS1987

Prospective lunar, planetary and deep space applications of tethers

Projected flights of an internationally managed Tethered Satellite System from the Space Shuttle in the early 1990s will investigate the behavior, first, of an insulated conducting wire 20 km long as it travels at orbital speeds through the ionosphere and earth magnetic field; subsequently, a nonconducting tether will be used to lower an instrumented 'subsatellite' 100 km downward to investigate upper-atmosphere conditions. Further consideration is presently given to other scientific, electrodynamic, transportational, and artificial gravity-generating applications of the tether concept.

Penzo, Paul A.↗

NASA NTRS1988

Space tethers

The principles involved in various applications of space tethers are discussed, with emphasis placed on tethers approved for flight on the US Shuttle. Special consideration is given to the NASA-Italy Tethered Satellite System (TSS) experiment, which will consist of three missions. The purposes of these missions and the types of experiments planned for the TSS are described. Other scientific applications of thether use in the fields of aeronomy and aerodynamics, geodynamics and remote sensing, electrodynamics, physics, astronomy, and life sciences are discussed together with particulars inolved in the measurements.

Ionasecu, Rodica↗

NASA NTRS1988

Ambipolar diffusion drifts and dynamos in turbulent gases

Ambipolar drift in turbulent fluids are considered. Using mean-field electrodynamics, a two-scale theory originally used to study hydromagnetic dynamos, it is shown that magnetic fields can be advected by small-scale magnetosonic (compressional) turbulence or generated by Alfvenic (helical) turbulence. A simple dynamo theory is made and is compared with standard theories in which dissipation is caused by turbulent diffusion. The redistribution of magnetic flux in interstellar clouds is also discussed.

Zweibel, Ellen G.↗

NASA NTRS1988

Ion beam releases at rocket altitudes

NASA Flight 29.015 was the third in a series of flights to study the electrodynamics of man-produced ion beams in the ionosphere. Much like an earlier flight (Moore at al., 1982 and 1983; Kaufman et al., 1985), plasma releases perpendicular to the earth's B field result in ions being measured, often at reduced energies, several hundred meters from the source along the magnetic field. Releases at 200-eV energy parallel to B, however, result in over-200-eV ions measured above the source. In addition, parallel ion releases result in two additional populations of ions seen near 90-deg pitch angle; one near the energy of the generator, and the other at considerably lower energy. The energization of parallel ions could result from the same process by which electrons were accelerated to the generator payload as measured on an earlier flight, presumably due to blockage of natural field-aligned currents by gun-related wave turbulence. This turbulence is also undoubtedly inherent in the mechanism by which a parallel beam of ions creates a perpendicular component.

Pollock, C. J.↗

NASA NTRS1988

Opportunities for Space Station wave experiments

The solar terrestrial observatory (STO) concept is discussed as well as Space Station accommodations for STO. Instruments for the initial STO which can be used to excite and detect waves include the electrodynamic tether, waves in space plasmas, space experiments with particle accelerators, vehicle charge and potential experiments, recoverable plasma diagnostics package, magnetospheric multiprobes, and theoretical and experimental beam plasma physics. An example is given of a typical campaign mode of operation which is appropriate for active experiments.

Shawhan, Stanley D.↗

NASA NTRS1987

Flexible structure control laboratory development and technology demonstration

An experimental structure is described which was constructed to demonstrate and validate recent emerging technologies in the active control and identification of large flexible space structures. The configuration consists of a large, 20 foot diameter antenna-like flexible structure in the horizontal plane with a gimballed central hub, a flexible feed-boom assembly hanging from the hub, and 12 flexible ribs radiating outward. Fourteen electrodynamic force actuators mounted to the hub and to the individual ribs provide the means to excite the structure and exert control forces. Thirty permanently mounted sensors, including optical encoders and analog induction devices provide measurements of structural response at widely distributed points. An experimental remote optical sensor provides sixteen additional sensing channels. A computer samples the sensors, computes the control updates and sends commands to the actuators in real time, while simultaneously displaying selected outputs on a graphics terminal and saving them in memory. Several control experiments were conducted thus far and are documented. These include implementation of distributed parameter system control, model reference adaptive control, and static shape control. These experiments have demonstrated the successful implementation of state-of-the-art control approaches using actual hardware.

Vivian, H. C.↗

NASA NTRS1988

Preparative electrophoresis for space

A premise of continuous flow electrophoresis is that removal of buoyance-induced thermal convection caused by axial and lateral temperature gradients results in ideal performance of these instruments in space. Although these gravity dependent phenomena disturb the rectilinear flow in the separation chamber when high voltage gradients or thick chamber are used, distortion of the injected sample stream due to electrodynamic effects cause major broadening of the separated bands. The electrophoresis separation process is simple, however flow local to the sample filament produced by the applied electric field were not considered. These electrohydrodynamic flows distort the sample stream and limit the separation. Also, electroosmosis and viscous flow combine to further distort the process. A moving wall concept is being proposed for space which will eliminate and control the disturbances. The moving wall entrains the fluid to move as a rigid body and produces a constant residence time for all samples distributed across the chamber thickness. The moving wall electrophoresis chamber can only be operated in space because there is no viscous flow in the chamber to stabilize against thermal convection.

Rhodes, Percy H.↗

NASA NTRS1989

Active vibration control for flexible rotor by optimal direct-output feedback control

Experimental research tests were performed to actively control the rotor vibrations of a flexible rotor mounted on flexible bearing supports. The active control method used in the tests is called optimal direct-output feedback control. This method uses four electrodynamic actuators to apply control forces directly to the bearing housings in order to achieve effective vibration control of the rotor. The force actuators are controlled by an analog controller that accepts rotor displacement as input. The controller is programmed with experimentally determined feedback coefficients; the output is a control signal to the force actuators. The tests showed that this active control method reduced the rotor resonance peaks due to unbalance from approximately 250 micrometers down to approximately 25 micrometers (essentially runout level). The tests were conducted over a speed range from 0 to 10,000 rpm; the rotor system had nine critical speeds within this speed range. The method was effective in significantly reducing the rotor vibration for all of the vibration modes and critical speeds.

Nonami, Kenzou↗

NASA NTRS1989

Middle Atmosphere Program. Handbook for MAP, volume 27

The proceedings are presented from the MAP program of July 1988. It is intended to be a quick synopsis of the symposium. General topics include: New International Equatorial Observatory; Dynamics of the Middle Atmosphere in Winter (DYNAMICS); Global Budget of Stratospheric Trace Constituents (GLOBUS); Gravity Waves and Turbulence in the Middle Atmosphere Program (GRATMAP); Middle Atmosphere Electrodynamics (MAE); Winter in Northern Europe (WINE); Atmospheric Tides Middle Atmosphere Program (ATMAP); and many others.

Edwards, Belva↗

NASA NTRS1989

Middle atmosphere electrical energy coupling

The middle atmosphere (MA) has long been known as an absorber of radio waves, and as a region of nonlinear interactions among waves. The region of highest transverse conductivity near the top of the MA provides a common return for global thunderstorm, auroral Birkeland, and ionospheric dynamo currents, with possibilities for coupling among them. Their associated fields and other transverse fields map to lower altitudes depending on scale size. Evidence now exists for motion-driven aerosol generators, and for charge trapped at the base of magnetic field lines, both capable of producing large MA electric fields. Ionospheric Maxwell currents (curl H) parallel to the magnetic field appear to map to lower altitudes, with rapidly time-varying components appearing as displacement currents in the stratosphere. Lightning couples a (primarily ELF and ULF) current transient to the ionosphere and magnetosphere whose wave shape is largely dependent on the MA conductivity profile. Electrical energy is of direct significance mainly in the upper MA, but electrodynamic transport of minor constituents such as smoke particles or CN may be important at other altitudes.

Hale, L. C.↗

NASA NTRS1988

Coherent HF radar backscatter from small-scale irregularities in the dusk sector of the subauroral ionosphere

This paper describes the characteristics of backscatter from decameter-scale ionospheric plasma density irregualarities, observed with an impressive regularity by the Goose Bay (Labrador) high-frequency (HF) radar in the dusk sector of the winter ionosphere, and discusses the relation of the scatter to the midlatitude trough. It is shown that this dusk scatter can be readily distinguished from other types of late afternoon/early evening scatter by the extreme equatorward position of its source region and by the low values of its associated radar Doppler velocities (not above 200 m/s) and spectral widths (not more than 200 m/s). A comparison of the radar observations with nearly simultaneous particle precipitation data obtained with the DMSP F6 satellite demonstrated that the source region of the backscatter lies within the subauroral ionosphere. It is shown that the characteristics of dusk scatter are compatible with the Spiro et al. (1978) model of the electrodynamics of the midlatitude trough.

Ruohoniemi, J. M.↗

NASA NTRS1988

Theoretical energies for the n = 1 and 2 states of the helium isoelectronic sequence up to Z = 100

The unified method described previously for combining high-precision nonrelativistic variational calculations with relativistic and quantum electrodynamic corrections is applied to the 1s2 1S0, 1s2s 1S0, 1s2s 1S0, 1s2s 3S1, 1s2p 1P1, and 1s2p 3P(0.1,2) states of helium-like ions. Detailed tabulations are presented for all ions in the range Z = 2-100 and are compared with a wide range of experimental data up to (Kr-34)+. The results for (U-90)+ significantly alter the recent Lamb shift measurement of Munger and Gould (1986) from 70.4 + or - 8.3 to 71.0 + or - 8.3 eV, in comparison with a revised theoretical value of 74.3 + or - 0.4 eV. The improved agreement is due to the inclusion of higher order two-electron corrections in the present work.

Drake, G. W.↗

NASA NTRS1988

Novel tether-connected two-dimensional structures for low earth orbits

This paper proposes novel tether-connected two-dimensional structures with a size of several hundred square kilometers for low earth orbits. The attitude of these structures is gravitationally stabilized with respect to an earth-oriented reference frame. A stable shape is obtained by utilizing environmental forces such as differential air drag or electrodynamic forces which stiffen the system. Configurations which differ in geometry and in the number of connecting tethers are presented in the paper. The static stability of each configuration is analyzed as a function of design and orbital parameters. A brief discussion of the applications of such tethered systems is provided at the end of the paper.

Lorenzini, Enrico C.↗

NASA NTRS1989

Magnetosphere-thermosphere coupling - An experiment in interactive modeling

The present use of the Rice convection model to investigate the electrodynamic coupling of the thermosphere to the inner magnetosphere encompasses the effects of EUV-driven and convection-driven neutral winds under quasi-equilibrium conditions. Convection-driven winds are included self-consistently and interactively; a steady-state wind parameterization is written analytically in terms of the electrostatic potential, which is in turn included in a closed-loop calculation for the electric potential itself. The simulations conducted show that, as the neutral system approaches a quasi-equilibrium state, the neutral winds play a much more significant role.

Forbes, Jeffrey M.↗