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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

DE 1 RIMS operational characteristics

The Retarding Ion Mass Spectrometer (RIMS) on the Dynamics Explorer 1 spacecraft observes both the thermal and superthermal (50 eV) ions of the ionosphere and inner magnetosphere. It is capable of measuring the detailed species distribution function of these ions in many cases. It was equipped with an integral electrometer to permit in-flight calibration of the detector sensitivities and variations thereof. A guide to understanding the RIMS data set is given. The reduction process from count rates to physical quantities is discussed in some detail. The procedure used to establish in-flight calibration is described, and results of a comparison with densities from plasma wave measurements are provided. Finally, a discussion is provided of various anomalies in the data set, including changes of channeltron efficiency with time, spin modulation of the axial sensor heads, apparent potential differences between the sensor heads, and failures of the radial head retarding potential sweep and of the -Z axial head aperture plane bias. Studies of the RIMS data set should be conducted only with a thorough awareness of the material presented here, or in collaboration with one of the scientists actively involved with RIMS data analysis.

Olsen, R. C.↗
NASA NTRS1986

Theoretical analysis of the electrical aspects of the basic electro-impulse problem in aircraft de-icing applications

A summary of modeling the electrical system aspects of a coil and metal target configuration resembling a practical electro-impulse deicing (EIDI) installation, and a simple circuit for providing energy to the coil, was presented. The model was developed in sufficient theoretical detail to allow the generation of computer algorithms for the current in the coil, the magnetic induction on both surfaces of the target, the force between the coil and target, and the impulse delivered to the target. These algorithms were applied to a specific prototype EIDI test system for which the current, magnetic fields near the target surfaces, and impulse were previously measured.

Henderson, R. A.↗
NASA NTRS1986

Joule heating and field-aligned currents: Preliminary results from DE-2

There are three main processes by which energy is transferred from the magnetosphere to the thermosphere: (1) charge exchange of the ring current particles; (2) precipitation of charged particles; and (3) joule dissipation by the magnetosphere-ionosphere current systems. The importance of this last process has been recognized and the rate of joule heating has been estimated by many workers. Observations of the electric (E) and magnetic (B) fields from Dynamics Explorer Satellite 2 are providing a new set of data on field-aligned currents. One of the remarkable features found in these observations is the high correlation between an orthogonal pair of the E and B field components. In recent years, observational data have accrued concerning the relationship between the interplanetary magnetic field and the size of the polar cap and also about the evolution of a substorm or a magnetic storm. It is suggested that these findings be incorporated in future model calculations.

Sugiura, M.↗
NASA NTRS1985

DE-1/Siple VLF wave-injection experiments

Results of Siple/DE-1 VLF wave-injection/reception experiments indicate that the injected signals, while propagating in the magnetosphere in the non-ducted mode, are on occasion amplified, generate sidebands and trigger VLF emissions. The propagation paths include direct non-ducted paths as well as reflected modes involving propagation initially in a 'duct' followed by a reflected non-ducted path up to the satellite. Calibrated measurements of the wave magnetic and electric intensities are used to estimate the local refractive index.

Inan, U. S.↗
NASA NTRS1986

Designing an electro-impulse de-icing system

Basic principles and parameters for a system to deice aircraft with electromagnetic impulses are described. The physical basis for deicing by such impulses is explained, and the requirements involved in the electrodynamic design, structural dynamic design, and system design are discussed. Some manufacturing and testing problems and techniques are described.

Zumwalt, G. W.↗
NASA NTRS1986

Measurements of Siple transmitter signals on the DE 1 satellite - Wave normal direction and antenna effective length

A new experimental technique is developed to simultaneously measure the wave propagation direction and the effective length of a small (L value much smaller than wavelength) electric dipole antenna on a spin-stabilized satellite in the magnetosphere. The technique relies on the near simultaneous measurement of single components of the electric and magnetic fields of a coherent VLF signal injected into the medium from a ground-based source. The spin fading characteristics of the signal received by the electric dipole and the magnetic loop antenna permit the measurement of the wave normal direction assuming whistler-mode propagation. In-situ and remote measurements of the local cold plasma density are used to determine the refractive index. The wave electric field is then inferred from the wave magnetic field as measured on the loop antenna, the refractive index and the direction of propagation. Comparing this electric field with the measured voltage across the dipole antenna leads to the determination of the effective length of the receiving electric dipole. The technique is applied to data from the Dynamics Explorer 1 satellite observations of whistler mode signals injected into the magnetosphere from the Siple, Antarctica, VLF transmitter. In one case, with the measured background cold plasma density being 15 el/cu cm, the effective length of the 200 m-long electric dipole antenna is found to be 222 + or - 56 m, i.e., about twice the conventional value.

Sonwalker, V. S.↗
NASA NTRS1986

The Tasseled Cap de-mystified

The fundamental concepts on which the Tasseled Cap transformations of MSS and TM data are based - particularly the identification of inherent data structures - are explained and discussed. Emphasis on the structures present in data from any given sensor, which are themselves the expression of physical characteristics of scene classes, provides a number of advantages, including (a) reduction in data volume with minimal information loss; (b) spectral features which can be applied, without re-definition or adjustment, to any data set for a given sensor; (c) spectral features which can be directly associated with important physical parameters; and (d) easier integration of data from multiple sensors.

Crist, E. P.↗
NASA NTRS1986

DE-2 mass spectrometer observations relevant to the Shuttle glow

A comparison of satellite mass spectrometer data from Dynamics Explorer-2 and Atmosphere Explorer-C and -D provides new evidence supporting the hypothesis that NO2 is the source of the observed continuum glow near ram-facing surfaces of the Space Shuttle. Surface reactions of thermospheric N and O in mass spectrometer ion sources produce NO and NO2 in amounts highly dependent on surface temperature and composition, with direct exposure of ion source surfaces to rammed gas a necessary condition for the production of large amounts of NO2. Initial orbit data indicate that a period of surface conditioning is necessary before these odd nitrogen molecules can be produced efficiently.

Engebretson, M. J.↗
NASA NTRS1986

Ionospheric convection signatures observed by DE 2 during northward interplanetary magnetic field

Observations of the ionospheric convection signature at high latitudes are examined during periods of prolonged northward interplanetary magnetic field (IMF). The data from Dynamics Explorer 2 show that a four-cell convection pattern can frequently be observed in a region that is displaced to the sunward side of the dawn-dusk meridian regardless of season. In the eclipsed ionosphere, extremely structured or turbulent flow exists with no identifiable connection to a more coherent pattern that may simultaneously exist in the dayside region. The two highest-latitude convection cells that form part of the coherent dayside pattern show a dependence on the y component of the IMF. This dependence is such that a clockwise circulating cell displaced toward dawn dominates the high-latitude region when B(Y) is positive. Anti-clockwise circulation displaced toward dusk dominates the highest latitudes when B(Y) is negative. Examination of the simultaneously observed energetic particle environment suggests that both open and closed field lines may be associated with the high-latitude convection cells. On occasions these entire cells can exist on open field lines. The existence of closed field lines in regions of sunward flow is also apparent in the data.

Heelis, R. A.↗
NASA NTRS1986

Lidar stratospheric ozone measurements at the observatoire de Haute Provence (France)

Strastospheric ozone monitoring is of particular importance to confirm present day theories predicting a maximal ozone depletion, due to chlorofluorocarbon emission, in the 35 to 45 km altitude range. Measurements presently rely on both ground based and satellite-borne passive experiments. Such systems have been recently shown to have intrinsic limitations mainly due to atmospheric aerosol presence and calibration problems. During the last few years, active lidar profiling of the ozone vertical distribution by the Differential Absorption Laser technique (DIAL) in the UV wavelength range has been developed using two different laser sources: a Nd-YAG pumped dye laser which enables a large tuning range of the UV emitted wavelengths; and exciplex laser sources using xenon chloride as an active medium and emitting at 308 nm, the off wavelength being usually generated by Raman shifting techniques. Advantages and limitations of using both of these systems are briefly discussed.

Godin, S.↗
NASA NTRS1986

Comet Halley: The Curtis Schmidts-Isla de Pascua observations

Halley's comet plasma tail disturbances and attendant tail phenomena were observed. Nearly simultaneous exposures with two telescopes serve to correlate information obtained with the two instruments. Photographs of 14 pre-Halley comets taken on 54 nights were examined with a view to cross-interpretation of phenomena seen in Halley with the earlier comets, as recorded on a homogenous collection of plates taken with the same instrument. The tail of Halley was highly active. This contrasts sharply with pre-Halley comets where undisturbed tails are the rule. During March and April, disturbances appeared in the tail of Halley at an average of 1 new distrubance every 3.7 days. It is considered that 10 of the 11 observed disturbances had common characteristics which allow them to be characterized as disconnections.

Miller, Freeman D.↗
NASA NTRS1987

GIOTTO's antenna de-spin mechanism: Ots lubrication and thermal vacuum performance

Except in the near Earth phase of GIOTTO's mission to Comet Halley, the HGA (high gain antenna) on board GIOTTO was the only designed means of up/down communications. The spacecraft spin stabilization required that the HGA be despun at the same rotational rate of nominally 15 rpm in order to keep the HGA pointing accurately to a Earth. A dual servomotor despin mechanism was designed and built by SEP of France for this purpose. The expected thermal environment suggested that dry lubrication was preferable to wet for the ball bearings but there existed no relevant data on the torque noise spectrum of candidate solid lubricants. Therefore ad hoc torque noise tests were run with two solid lubricants: ion plated lead film plus lead bronze cage (retainer) and a PTFE composite cage only. The lead lubrication showed the better spectrum up to the mission lifetime point so it was selected for continued test over some 20 times the Halley mission life, with periodic torque spectrum monitoring. The spectrum remained well within the pointing error budget over the 100 million revolutions covered.

Todd, M. J.↗
NASA NTRS1986

Nightside plasmapause positions observed by DE-1 as a function of geomagnetic indices - Comparison with whistler observations and model calculations

The paper analyzes 28 plasmapause crossings made by the DE1 satellite in the night local time sector (from January to March 1982). Different signatures obtained by the Retarding Ion Mass Spectrometer instrument have been used for this analysis. The observed plasmapause positions (Lpp) have been organized as a function of geomagnetic indices. They are compared with the empirical relationship deduced by Carpenter and Parks (1973) from whistler observations. Moreover, the dependence of Lpp versus Kp has been inferred from model calculations using Kp dependent electric and magnetic fields derived from McIlwain's (1974) E3H electric field model and M2 magnetic field model respectively. Stationary models as well as time dependent ones, have been used to determine the positions of the plasmapause. The results of the model calculations are compared to the observations.

Decreau, P. M. E.↗
NASA NTRS1987

New test of general relativity - Measurement of de Sitter geodetic precession rate for lunar perigee

According to general relativity, the calculated rate of motion of lunar perigee should include a contribution of 19.2 msec/yr from geodetic precession. It is shown that existing analyses of lunar-laser-ranging data confirm the general-relativistic rate for geodetic precession with respect to the planetary dynamical frame. In addition, the comparison of earth-rotation results from lunar laser ranging and from VLBI shows that the relative drift of the planetary dynamical frame and the extragalactic VLBI reference frame is small. The estimated accuracy is about 10 percent.

Bertotti, Bruno↗
NASA NTRS1986

DE-1 observations of solar wind-magnetosphere coupling processes in the polar cusp

Measurements of hot plasma distribution functions in the midaltitude polar cusp by the Dynamics Explorer-1 spacecraft have provided new information on the processes of magnetosheath plasma injection and transport and the dependence of these phenomena on solar-wind parameters. Results on magnetosheath plasma injection have included: (1) localization of the region of plasma injection to the high-latitude cusp-magnetosheath interface, (2) movement of this region toward lower latitudes as B(z) becomes more southward, (3) maintenance of quasi-neutrality of suprathermal plasmas within the cusp, and (4) support for merging-type injection at the high-latitude cusp boundary for northward IMF. Plasma flow measurements from Dynamics Explorer-1 have led to a global IMF-dependent convection model which contains both merging and viscous driving forces.

Burch, J. L.↗
NASA NTRS1988

Investigation of the diffuse ultraviolet background with DE data

The imaging instrumentation on the Dynamics Explorer 1 satellite is used to measure the intensity of the diffused ultraviolet radiation on two great circles about the sky. It was found that the extragalactic component of the diffuse ultraviolet radiation has an intensity of 530 + or - 15 units (a unit is one photon/(sq cm s A sr) at a wavelength of 150 nm. The galactic component of the diffuse ultraviolet radiation has a dependence on galactic latitude which requires strongly forward scattering particles if it is produced by dust above the galactic plane.

Fix, John D.↗
NASA NTRS1988

Electro-impulse de-icing electrodynamic solution by discrete elements

This paper describes a technique for analyzing the electrodynamic phenomena associated with electro-impulse deicing. The analysis is done in the time domain and utilizes a discrete element formulation concept expressed in state variable form. Calculated results include coil current, eddy currents in the target (aircraft leading edge skin), pressure distribution on the target, and total force and impulse on the target. Typical results are presented and described. Some comparisons are made between calculated and experimental results, and also between calculated values from other theoretical approaches. Application to the problem of a nonrigid target is treated briefly.

Bernhart, W. D.↗