Engineering topics

Olsen, R. C.

Publications and source records attributed to Olsen, R. C..

At least 37 records · Page 2

NASA NTRS1986

Plasma and field observations of a Pc 5 wave event

The particle detector and electric field data collected by the Dynamo Explorer 1 on the Pc 5 wave event encounter on July 14, 1982 are presented, yielding a nearly complete picture of the event. The overall structure of the Pc 5 seems to order the event into two distinct halves, suggesting a temporal or spatial variation of the micropulsation. Thermal plasma measurements showed that the dominant ion throughout both lobes was H(+). Significant quantities of He(+), O(+), N(+), and O(2+) were also observed to be present and rotating together in a plane normal to the magnetic field direction, due to the Pc5 E x B drift. The plasma parameters determined for the two lobes were used in theoretical calculations to predict the period of the observed resonance.

Waite, J. H.↗

NASA NTRS1986

Calibration of the ISEE plasma composition experiment

The Plasma Composition experiment on the ISEE-1 satellite was designed to measure ions from 1 to 16 amu, at energies from near zero to 16 keV. The two nearly identical flight instruments were calibrated by means of preflight laboratory tests and in-flight data comparisons. This document presents most of the details of those efforts, with special emphasis on the low energy (0 to 100 eV) portion of the instrument response. The analysis of the instrument includes a ray-tracing calculation, which follows an ensemble of test particles through the detector.

Baugher, C. R.↗

NASA NTRS1986

Aperture plane potential control for thermal ion measurements

The effects produced by the addition of an aperture plane to control the bias around an instrument for low-energy ion measurements on satellites collecting data in the plasmasphere and over the polar cap are analyzed. The analysis is based on the design and functions of the retarding ion mass spectrometer (RIMS) on the DE 1 satellite. The NASA Charging Analyzer Program, which treats the spacecraft as a cylinder, was used to generate one set of predictions. A second model involves solution of the Laplace equation with the spacecraft treated as a sphere. Both models were used to predict the barrier height expected at the aperture in response to the bias induced to offset the potential. Comparisons with plasma data show that in the thin sheath regime of the plasmasphere the detectors act as if the potential is shifted, thereby lowering the energy resolution of the instrument. Outside the plasmasphere the barrier height dominates the spin curve variations more than the potential. Partial potential control is available from induced bias apertures if control is active and guided by electron detectors with sensitivities in the 0.5-50.0 eV energy range.

Olsen, R. C.↗

NASA NTRS1986

Conical ion distributions at one earth radius - Observations from the acceleration region?

Thermal ion measurements from the retarding ion mass spectrometer (RIMS) on Dynamics Explorer 1 (DE 1) in the night side auroral region were surveyed for evidence of ion acceleration. The RIMS measurements showed evidence for ion acceleration in the 2-10,000 km altitude range, with ion distributions peaked near 90 deg, and with temperatures of 1 to 10 eV. Two illustrations of the RIMS data for such observations are given. The conical distributions are found at the low latitude edge of the auroral region, just outside the plasmapause. In the first example, the three major ion species (H+, He+, and O+) show evidence of acceleration. The angular distributions are peaked at different pitch angles, indicating that the different species have been accelerated at different altitudes. The H+ flux is higher than the O+ flux in this first example, in the RIMS energy range (0-50 eV). This is apparently typical of the RIMS observations on the night side. In the second example, only O+ is transversely accelerated.

Olsen, R. C.↗

NASA NTRS1985

The hidden ion population - Revisited

In an investigation conducted by Olsen (1982) on the basis of particle data taken with an electrostatic analyzer, it was found that a cold plasma population with a density between 10 and 100 per cu cm appeared suddenly when the satellite was eclipsed, but was hidden in sunlight. The present paper has the objective to show further measurements of ordinarily 'hidden' ion populations, in order to resolve some of the questions raised in connection with the Scatha satellite data reported by Olsen. It is found that the retarding ion mass spectrometer (RIMS) detector is capable of measuring the core of the plasma distribution in sunlight and eclipse, though the task is more easily done in eclipse. There are, however, limitations concerning the ability of the detector to measure all the plasma, all the time. It is, therefore, pointed out that continuous effective measurements of the 'hidden' ion population of the magnetosphere still awaits satellites with effective means of potential control.

Olsen, R. C.↗

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 NTRS1985

Observations of molecular ions in the earth's magnetosphere

The retarding ion mass spectrometer on Dynamics Explorer 1 operating over the polar cap during a large magnetic storm has measured fluxes of up to 10 to the 6th ions/sq cm s of the molecular ions N2(+), NO(+), and O2(+). These ions were measured beginning low in the satellite orbit (1.1 earth radii) and extending to about 3 earth radii geocentric altitude. Near perigee, the ions have a rammed distribution indicating a cold Maxwellian plasma (1000-2000 K). The molecular ions gradually shift to a field-aligned distribution at the higher alitudes. An upward flow of 5-10 km/s is found in these field-aligned measurements. The density of the molecular ions is on the order of 2/cu cm at all altitudes, and the energy of the ions generally increases as the satellite moves sunward across the southern polar cap. Kinetic energies of at least 20 eV were found at 2.5 earth-radii geocentric distance.

Craven, P. D.↗

NASA NTRS1985

Experiments in charge control at geosynchronous orbit - ATS-5 and ATS-6

In connection with existing theoretical concepts, it was difficult to explain the negative potentials found in sunlight, first on Applied Technology Satellite-5 (ATS-5) and then on ATS-6. The problem became important when an association between spacecraft charging and anomalies in spacecraft behavior was observed. A study of daylight charging phenomena on ATS-6 was conducted, and an investigation was performed with the objective to determine effective methods of charge control, taking into account the feasibility to utilize the ATS-5 and ATS-6 ion engines as current sources. In the present paper, data and analysis for the ion engine experiments on ATS-5 and ATS-6 are presented. It is shown that electron emission from a satellite with insulating surfaces is not an effective method of charge control because the increase in differential charging which results limits the effectiveness of electron emitters and increases the possibility of electrostatic discharges between surfaces at different potentials.

Olsen, R. C.↗

NASA NTRS1985

Anomalously high potentials observed on ISEE

Data from two electric field experiments and from the plasma composition experiment on ISEE-1 are used to show that the spacecraft charged to close to -70 V in sunlight at 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely. Modeling of this event is required to determine if the barrier was produced by the presence of space charge.

Whipple, E. C.↗

NASA NTRS1984

First measurements of supersonic polar wind in the polar magnetosphere

Measurements from the Retarding Ion Mass Spectrometer on the Dynamics Explorer have, for the first time, revealed a supersonic polar wind along polar cap field lines. The observations reported were obtained on the nightside (22:30 to 23:30 MLT) from 65 to 81 deg invariant latitude and at altitudes near 2 earth radii. Fitting the data using a thin-sheath model gives a range of temperatures of 0.1 to 0.2 eV with corresponding flow velocities of 25 to 16 km/s over the estimated range of spacecraft potential of +3 to +5 V. For these values the Mach number ranged from 5.1 to 2.6 (with a most likely value of 3). Characteristics of the H(+) flow are in general agreement with those predicted by 'classical' polar wind theory, but high variabilty of the He(+)/H(+) ratio was observed.

Nagai, T.↗

NASA NTRS1984

Anomalously high potentials observed on ISEE

Data from the two electric field experiments and from the plasma composition experiment on ISEE-1 show that the spacecraft charged to close to -70 V in sunlight at about 0700 UT on March 17, 1978. Data from the electron spectrometer experiment show that there was a potential barrier of some -10 to -20 V about the spacecraft during this event. The potential barrier was effective in turning back emitted photoelectrons to the spacecraft. Potential barriers can be formed because of differential charging on the spacecraft or because of the presence of space charge. The stringent electrostatic cleanliness specifications imposed on ISEE make the presence of differential charging unlikely, if these precautions were effective. Modeling of this event is required to determine if the barrier was produced by the presence of space charge.

Whipple, E. C.↗

NASA NTRS1983

Observations of charging dynamics

Plasma data from the University of California, San Diego, Auroral Particles experiments on Applied Technology satellites 5 and 6 are used to investigate the dynamics of natural charging events. Both eclipse and daylight charging events are considered, and typical responses are illustrated by data from specific events. Two different physical processes are found to be involved in the charging process. One of these is straightforward: the spacecraft structure potential responds rapidly to changes in the environment, typically changing by hundreds of volts in a few seconds. The other process is more subtle: differential charging and potential barrier formation precede structural charging and determine the time scale; typically, tens of minutes are required for the potential to change by several hundreds of volts. The latter process is found to be predominately responsible for daylight charging on both spacecraft.

Olsen, R. C.↗

NASA NTRS1983

A threshold effect for spacecraft charging

The borderline case between no charging and large (kV) negative potentials for eclipse charging events on geosynchronous satellites is investigated, and the dependence of this transition on a threshold energy in the ambient plasma is examined. Data from the Applied Technology Satellite 6 and P78-2 (SCATHA) show that plasma sheet fluxes must extend above 10 keV for these satellites to charge in eclipse. The threshold effect is a result of the shape of the normal secondary yield curve, in particular the high energy crossover, where the secondary yield drops below 1. It is found that a large portion of the ambient electron flux must exceed this energy for a negative current to exist.

Olsen, R. C.↗

NASA NTRS1983

Plasma source for spacecraft potential control

A stable electrical ground which enables the particle spectrometers to measure the low energy particle populations was investigated and the current required to neutralize the spacecraft was measured. In addition, the plasma source for potential control (PSPO C) prevents high charging events which could affect the spacecraft electrical integrity. The plasma source must be able to emit a plasma current large enough to balance the sum of all other currents to the spacecraft. In ion thrusters, hollow cathodes provide several amperes of electron current to the discharge chamber. The PSPO C is capable of balancing the net negative currents found in eclipse charging events producing 10 to 100 microamps of electron current. The largest current required is the ion current necessary to balance the total photoelectric current.

Olsen, R. C.↗

NASA NTRS1982

The discovery of nitrogen ions in the earth's magnetosphere

Operating in a mass scanning mode, the Retarding Ion Mass Spectrometer (RIMS) has measured N(+) and N(++) ions in the magnetosphere. Both N(+) and N(++) are observed in the plasmasphere, with N(+) ions also seen flowing out of the northern polar cap at altitudes up to 3 earth radii. The N(+) fluxes are 5 to 10% of the O(+) fluxes with the N(++) fluxes at 1-5% of the N(+) fluxes.

Chappell, C. R.↗

NASA NTRS1982

The hidden ion population of the magnetosphere

The presence of a cold ion population in the magnetosphere which is normally hidden from particle detector observation by the positive charging of the spacecraft is reported. Ion and electron data were obtained from particle detectors on the ATS 6 and SCATHA satellites designed to measure the 1-eV to 80-keV plasma population. The cold, isotropic ion population, with temperature 1 eV and density 10-100/cu cm, was detected only when the spacecraft were in eclipse, when spacecraft potential had dropped from +10 V in sunlight to +4 to +5 V. The hidden ion population was found at geosynchronous altitude only during geomagnetically quiet times and when there has been an absence of geomagnetic activity for several hours, and appears to coexist with the plasma sheet. More consistent measurements of the cold ion population at midnight or at other local times would require the biasing of the ion detector with respect to the spacecraft, or the controlling of spacecraft potential.

Olsen, R. C.↗

NASA NTRS1982

Field-aligned ion streams in the earth's midnight region

Plasma measurements from the University of California at San Diego auroral particles experiment on the geosynchronous Applied Technology Satellite 6 in the midnight region show that the low-energy ion fluxes (1-100 eV) are field aligned and are well characterized as thermal populations (1-10 eV) with a streaming velocity of 30-100 km/s along the magnetic field line. The lowest energies are found prior to injections, on quiet days, with an increase of the streaming velocity evident when an injection occurs near the satellite. Multiple peaks in the ion distribution functions are attributed to the presence of different ions species (H/+/, He/+/, O/+/, O/2+/) streaming at similar velocities, both during quiet times and as the plasma velocity increases in response to an injection.

Olsen, R. C.↗

NASA NTRS1981

Modification of spacecraft potentials by thermal electron emission on ATS-5

Electron emission experiments on Applied Technology Satellite 5 using a thermal electron emitter are reported and analyzed. Operations in eclipse charging environments showed that electron emission could partially discharge a negatively charged satellite. Typical operations resulted in kilovolt potentials being reduced to hundreds of volts for a few tens of seconds, followed by a gradual recharging over a period of minutes. Equilibrium currents were modeled with a one-dimensional current balance model. Currents on the order of 1 microampere were found, significantly below emitter capabilities. Application of a three-dimensional, time-dependent computer model showed that differential charging on the solar arrays was limiting the emitted current, preventing the complete discharge of the satellite, and allowing it to recharge in spite of the electron emitter.

Olsen, R. C.↗