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NASA NTRS1987

Radio emissions from Uranus

The hardware of the Planetary Radio Astronomy Experiment aboard Voyager 2 and the results of the measurements of radio emissions from Uranus are described. Strong 40-kHz to 850-kHz radio emissions were detected after closest approach on the day-side of Uranus. The time variations of these emissions were periodic, with a period of 17.24 h closely matching that of Uranus's rotation and evidently being controlled by the strength and shape of its magnetic field. The instrument also recorded possible Uranian electrostatic discharges, vertex early arcs occurring in sequences of more than a dozen events with approximately 10-min period, and very intense isolated bursts lasting tens of minutes.

Warwick, J. W.↗

NASA NTRS1988

Laboratory investigations

Laboratory studies related to cometary grains and the nuclei of comets can be broken down into three areas which relate to understanding the spectral properties, the formation mechanisms, and the evolution of grains and nuclei: (1) Spectral studies to be used in the interpretation of cometary spectra; (2) Sample preparation experiments which may shed light on the physical nature and history of cometary grains and nuclei by exploring the effects on grain emissivities resulting from the ways in which the samples are created; and (3) Grain processing experiments which should provide insight on the interaction of cometary grains with the environment in the immediate vicinity of the cometary nucleus as the comet travels from the Oort cloud through perihelion, and perhaps even suggestions regarding the relationship between interstellar grains and cometary matter. A summary is presented with a different view of lab experiments than is found in the literature, concentrating on measurement techniques and sample preparations especially relevant to cometary dust.

Russell, Ray W.↗

NASA NTRS1989

Magnetospheric plasma pressures in the midnight meridian - Observations from 2.5 to 35 R(E)

Plasma pressure data from the ISEE 2 fast plasma experiment (FPE) are statistically analyzed to determine the plasma sheet pressure versus distance in the midnight local time sector of the near-earth (12-35 earth radii) magnetotail plasma sheet. In regions where the bulk of the plasma pressure is contributed by particles in the energy range of the FPE (70 eV to 40 keV for ions), the statistically determined peak plasma pressures vary with distance similarly to previously determined lobe magnetic pressures. Estimates of plasma pressures in the 'transition' region (7-12 earth radii), where the magnetic field topology changes rapidly from a dipolar to a taillike configuration, are compared with the observed pressure profiles. Quiet time observations and estimates are combined to provide profiles of the equatorial plasma pressure along the midnight meridian between 2.5 and 35 earth radii.

Spence, Harlan E.↗

NASA NTRS1990

Space Station Freedom pressurized element interior design process

The process used to develop the on-orbit working and living environment of the Space Station Freedom has some very unique constraints and conditions to satisfy. The goal is to provide maximum efficiency and utilization of the available space, in on-orbit, zero G conditions that establishes a comfortable, productive, and safe working environment for the crew. The Space Station Freedom on-orbit living and working space can be divided into support for three major functions: (1) operations, maintenance, and management of the station; (2) conduct of experiments, both directly in the laboratories and remotely for experiments outside the pressurized environment; and (3) crew related functions for food preparation, housekeeping, storage, personal hygiene, health maintenance, zero G environment conditioning, and individual privacy, and rest. The process used to implement these functions, the major requirements driving the design, unique considerations and constraints that influence the design, and summaries of the analysis performed to establish the current configurations are described. Sketches and pictures showing the layout and internal arrangement of the Nodes, U.S. Laboratory and Habitation modules identify the current design relationships of the common and unique station housekeeping subsystems. The crew facilities, work stations, food preparation and eating areas (galley and wardroom), and exercise/health maintenance configurations, waste management and personal hygiene area configuration are shown. U.S. Laboratory experiment facilities and maintenance work areas planned to support the wide variety and mixtures of life science and materials processing payloads are described.

Hopson, George D.↗

NASA NTRS1989

Magnetic fields at Neptune

The Voyager 2 magnetic field experiment discovered a complex and powerful magnetic field in Neptune, as well as an associated magnetosphere and magnetic tail. As the spacecraft exited the magnetosphere, the magnetic tail appeared to be monopolar. The auroral zones are probably located far from the rotation poles, and may possess complex geometry. The Neptune rings and all its known moons are imbedded deep within the magnetosphere (except for Nereid, which is outside when it lies sunward of the planet); the radiation belts have a complex structure due to the absorption of energetic particles by the moons and rings of Neptune, as well as losses associated with the significant changes in the diurnally varying magnetosphere configuration.

Ness, Norman F.↗

NASA NTRS1989

Visual scanning with or without spatial uncertainty and time-sharing performance

An experiment is reported that examines the pattern of task interference between visual scanning as a sequential and selective attention process and other concurrent spatial or verbal processing tasks. A distinction is proposed between visual scanning with or without spatial uncertainty regarding the possible differential effects of these two types of scanning on interference with other concurrent processes. The experiment required the subject to perform a simulated primary tracking task, which was time-shared with a secondary spatial or verbal decision task. The relevant information that was needed to perform the decision tasks were displayed with or without spatial uncertainty. The experiment employed a 2 x 2 x 2 design with types of scanning (with or without spatial uncertainty), expected scanning distance (low/high), and codes of concurrent processing (spatial/verbal) as the three experimental factors. The results provide strong evidence that visual scanning as a spatial exploratory activity produces greater task interference with concurrent spatial tasks than with concurrent verbal tasks. Furthermore, spatial uncertainty in visual scanning is identified to be the crucial factor in producing this differential effect.

Liu, Yili↗

NASA NTRS1990

The sheath structure around a negatively charged rocket payload

The sheath structure around a rocket payload charged up to 460 V negative relative to the ambient ionospheric plasma is investigated experimentally and by computer simulations. The experimental results come from the Charge 2 sounding rocket experiment in which the payload was split into two separate sections (mother and daughter) connected with a conducting, insulated tether. In one of the experimental modes, the voltage between the payloads was increased linearly from 0 to 460 V in 2.5 s. A floating probe array was mounted on the mother with probes located 25, 50, 75, and 100 cm from the rocket surface. The internal impedance of the array was smaller than the probe/plasma impedance, which influenced the potential measurements. The measurements contain signatures, resulting from the outward expansion of the ion sheath with increasing negative mother potential. This conclusion is substantiated by computer simulations of space charge limited flow.

Neubert, T.↗

NASA NTRS1990

The interaction of an artificial electron beam with the earth's upper atmosphere - Effects on spacecraft charging and the near-plasma evironment

The ionization created in the earth's upper atmosphere by an electron beam emitted from a low altitude spacecraft is described by two coupled nonlinear differential electron transport equations for the up-going and down-going differential energy flux. The equations are solved numerically, yielding estimates of the differential electron energy flux density at the spacecraft location. At altitudes below 200-250 km and for beam energies around 1 keV, it is shown that secondary electrons supply a significant contribution to the return current to the spacecraft and thereby reduce the spacecraft potential. The numerical results are in good agreement with observations from the Charge 2 sounding rocket experiment.

Neubert, T.↗

NASA NTRS1990

Space Station Freedom pressurized element interior design process

Hopson, George D.↗

NASA NTRS1991

Phobos - Spectrophotometry between 0.3 and 0.6 micron and IR-radiometry

A 0.3 - 0.6 micron UV-visible spectrophotometer and a 5 - 50 micron radiometer in the KRFM experiment on Phobos 2 measured two groundtracks in the equatorial region of Phobos. Preliminary results indicate that three surface units can be recognized on the basis of differing UV-visible spectral reflectance properties. One of the units is most comparable spectrally to optically darkened mafic material, and a second is comparable either to anhydrous carbonaceous chondrite or to blackened mafic material. Spectral properties of the third unit do not resemble those of known meteorite types. Brightness temperatures measured by the radiometer are consistent with a typical surface thermal inertia of 1 - 3 x 10 to the -3 cal/(sq cm deg s exp 1/2), as suggested by previous investigations, implying a lunar-like regolith texture. At least one area of possibly higher thermal inertia has been tentatively identified, where a large degraded crater is crossed by several grooves. These results indicate significant lateral heterogeneity in the optical and textural properties of Phobos' surface.

Ksanfomality, L.↗

NASA NTRS1991

Studies of low-energy Galactic cosmic-ray composition at 22 AU. I - Secondary/primary ratios

Data from the High Energy Telescope of the CRS experiment on Voyager 2 have been used to measure the intensity, spectra, and elemental abundances of Galactic cosmic rays from Be to Ni at about 100 MeV/n. The charge resolution of this telescope varies from sigma = 0.034 for oxygen to sigma = 0.11 for iron. The solar modulation deceleration parameter Phi relevant for these data is estimated to be around 300 MV (Phi = 150 MeV/n for particles with A/Z = 2), an unprecedently low level for such measurements. This low modulation parameter is a result of the measurements being made in the outer heliosphere at a heliocentric distance of 22 AU, and centered on the solar minimum period of cycle 21. The results on secondary/primary ratios are used to test the Leaky-Box model of cosmic ray propagation, using the most recent cross sections data in hydrogen and helium, and taking into account the effects of the ionized fraction of the interstellar medium. It is found that all the secondary/primary ratios up to P/S are completely consistent with an exponential pathlength distribution (PLD). This PLD shape also accounts for the Sc-V/Fe ratio.

Ferrando, P.↗

NASA NTRS1991

Restrictions on the characteristics of Neptunian lightning

Although lightning-triggered whistlers were detected by the Voyager 2 plasma wave experiment at Neptune, only four possible lightning sferics were detected by the planetary radio astronomy instrument. This low level of detection places strict limits on the characteristics of Neptunian lightning, ruling out lightning with power levels as high as those observed at Saturn or Uranus, but leaving the intriguing possibility that lightning slightly stronger than normal terrestrial lightning flashes but with much lower occurrence rate could exist. Possible scenarios to explain the observations are examined, including reduced NH3 concentration in the planet's atmosphere and an unusually slow risetime discharge process.

Kaiser, M. L.↗

NASA NTRS1991

Voyager 2 electron observations in the magnetosphere of Neptune

This paper describes electron data obtained during the Neptune encounter by the Voyager 2 plasma science experiment. The densities and temperatures of low-energy (10-5950 eV) electrons and the electrostatic potential of the spacecraft near Neptune are derived. The data indicate that the escape of charged particles from Triton and the local ionization of atoms in the neutral torus originating from Triton are the major plasma sources. It is inferred that this neutral torus of hydrogen atoms has a density of about 300/cu cm and an inner boundary at 8 R(N). The data near Neptune exhibit signatures suggesting that both precipitation into Neptune's atmosphere and ring absorption are important plasma loss mechanisms. Plasma transport in the magnetosphere appears to be very fast; the diffusion coefficient is 1 x 10 exp -7 L exp 3 R(N) exp 2/sec.

Zhang, Ming↗

NASA NTRS1993

Thermal protection materials at NASA Ames Research Center

The topics addressed are: (1) Space Exploration Initiative (SEI); (2) Aeroassist Flight Experiment (AFE); (3) Mars Environmental Survey (MESUR); (4) National Aero-space Plan (NASP); (5) Pegasus and Pegasus/SWERVE Hypersonic Testing; and (6) Personnel Launch System TPS evaluation.

Rasky, Daniel J.↗

NASA NTRS1993

Design of an air traffic computer simulation system to support investigation of civil tiltrotor aircraft operations

The TATSS Project's goal was to develop a design for computer software that would support the attainment of the following objectives for the air traffic simulation model: (1) Full freedom of movement for each aircraft object in the simulation model. Each aircraft object may follow any designated flight plan or flight path necessary as required by the experiment under consideration. (2) Object position precision up to +/- 3 meters vertically and +/- 15 meters horizontally. (3) Aircraft maneuvering in three space with the object position precision identified above. (4) Air traffic control operations and procedures. (5) Radar, communication, navaid, and landing aid performance. (6) Weather. (7) Ground obstructions and terrain. (8) Detection and recording of separation violations. (9) Measures of performance including deviations from flight plans, air space violations, air traffic control messages per aircraft, and traditional temporal based measures.

Rogers, Ralph V.↗

NASA NTRS1993

Ion temperature profiles in the horns of the plasma sheet

The plasma sheet horns are the low-altitude extensions of the plasma sheet that lie poleward of the plasmasphere and equatorward of the tail lobes. Within the horns, magnetic field lines of increasing geomagnetic latitudes map to increasing distances into the downtail plasma sheet. Plasma data from the fast plasma experiment on ISEE 2 have been analyzed for 11 outbound crossings of the horns in the premidnight sector of the magnetosphere at typical altitudes of 2-4 R(E). These crossings typically occurred on time scales of less than 1 hour, providing almost instantaneous snapshots of plasma gradients within the horns. Ion temperatures observed during these crossings generally decreased by a factor of four to eight as magnetic field lines of increasing geomagnetic latitude were traversed. If we make the reasonable assumption that the ion temperatures are constant along the field lines within the plasma sheet, then this result implies that the ion temperatures in the downtail plasma sheet also commonly decrease by this same factor over the radial range extending from the inner edge of the plasma sheet at the plasmapause boundary to the outer edge at a neutral line in the distant tail.

Suszcynsky, D. M.↗

NASA NTRS1983

Low background IR detector and detector array evaluations

A technology program has been underway at Ames since 1978 to develop and evaluate detectors and integrated detector arrays for low-background astronomical applications. The approach is to evaluate existing (less than 24 micron) array technology under low-background conditions, with the aim of adapting and optimizing existing devices. For longer wavelengths, where the technology is much less mature, development is sponsored and devices are evaluated, in both discrete and array formats, for eventual applications. The status of this program has been reported previously. We rely on industrial and university sources for the detectors. Typically, after a brief functionality check in the supplier's laboratory, we work with the device at Ames to characterize its low-background performance. In the case of promising arrays or detectors, we conduct ground-based telescope testing to face the problems associated with real applications. A list of devices tested at Ames is given. In the array category, accumulation-mode charge-injection-devices (AMCIDs) appear repeatedly; this reflects our recent experience with the 2 x 64 and 16 x 16 arrays. Results from the 1 x 16 CID and InSb CCD have been reported. The status of our tests of the discrete Ge:x detectors from Lawrence Berkeley Laboratory are described below. Tests of a 1 x 2 switched sample photoconductor array are just beginning. A 32-channel CMOS multiplexer has been tested at 10 K. Low-temperature silicon MOSFETs and germanium JFETs have also been tested, primarily at Ball Aerospace. This paper describes results to date on three elements of this program: AMCID array, discrete Ge:Ga detectors, and Ge JFET preamplifiers.

Goebel, J. H.↗

NASA NTRS1995

Characteristics of low energy ions in the Heavy Ions In Space (HIIS) experiment

We present preliminary data on heavy ions (Z greater than or equal to 10) detected in the topmost Lexan sheets of the track detector stacks of the Heavy Ions in space (HIIS) experiment (M0001) on LDEF. The energy interval covered by these observations varies with the element, with (for example) Ne observable at 18-100 MeV nuc and Fe at 45-200 MeV/nuc. All of the observed ions are at energies far below the geomagnetic cutoff for fully-ionized particles at the LDEF orbit. Above 50 MeV/nuc (where most of our observed particles are Fe), the ions arrive primarily from the direction of lowest geomagnetic cutoff. This suggests that these particles originate outside the magnetosphere from a source with a steeply-falling spectrum and may therefore be associated with solar energetic particle (SEP) events. Below 50 MeV/nuc, the distribution of arrival directions suggests that most of the observed heavy ions are trapped in the Earth's magnetic field. Preliminary analysis, however, shows that these trapped heavy ions have a very surprising composition: they include not only Ne and Ar, which are expected from the trapping of anomalous cosmic rays (ACR's), but also Mg and Si, which are not part of the anomalous component. Our preliminary analysis shows that trapped heavy ions at 12 less than or equal to Zeta less than or equal to 14 have a steeply-falling spectrum, similar to that reported by the Kiel experiment (exp 1,2,3) on LDEF (M0002) for trapped Ar and Fe at E less than 50 MeV/nuc. The trapped Mg, Si, and Fe may also be associated with SEP events, but the mechanism by which they have appeared to deep in the inner magnetosphere requires further theoretical investigation.

Kleis, Thomas↗