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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.

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At least 271 records · Page 15
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NASA NTRS1985

Angle-of-attack estimation for analysis of CAT encounters

Recent studies of clear-air turbulence (CAT) encounters involving wide-body airliners have been based upon flight-path wind estimates made by analyzing digital flight-data-recorder (DFDR) records and radar records. Such estimates require a time history of the aircraft angle of attack, a record that is not usually included in the DFDR measurement set. This paper describes a method for reconstructing angle of attack that utilizes available flight record and aircraft-specific information associated with an aerodynamic model of the lift coefficient. Results from two wide-body incidents in which vane measurements of angle of attack were recorded show good agreement between measured and calculated time histories. This research has been performed in cooperation with the National Transportation Safety Board to provide a better understanding of the CAT phenomenon.

Bach, R. E., Jr.↗
NASA NTRS1986

Voyager engineering improvements for Uranus encounter

Engineering changes made on the Voyager spacecraft during their explorations of the outer solar system are discussed. A recovery from a scan actuator fault, achieved by ground testing, in flight capability enhancement and testing, conservation of actuator usage and a set of contingency plans to substitute roll motion of the spacecraft for motion of the scan platform in the AZ direction, is discussed. General engineering improvements made are addressed, including a scan platform anticreep patch modification, an improvement of dynamic performance during maneuvers, and adaptive control of the attitude control deadband. Changes made in the power management are described. Finally, engineering improvements made in order to enhance scientific findings at the Uranus encounter are reviewed in detail. The two most important were the increased gyro drift turn rate capability to accommodate image motion compensation for the close fly-by of Miranda and the reduction in spacecraft rates to accommodate increased imaging exposure times without incurring excessive image smear.

Marderness, H. P.↗
NASA NTRS1986

VLA feedhorn for Voyager encounter of Neptune

A high gain, low noise corrugated feedhorn was designed and developed by JPL for use in Very Large Array (VLA) antennas, near Soccoro, New Mexico. The new feedhorn will enable the VLA to support the Voyager encounter of Neptune in August of 1989. This will significantly enhance the receiving capability of the United States for that historic event.

Manshadi, F.↗
NASA NTRS1986

Voyager Uranus encounter 0.2lbf T/VA short pulse test report

The attitude control thrusters on the Voyager spacecraft were tested for operation at electrical pulse widths of less than the current 10-millisecond minimum to reduce impulse bit and, therefore, reduce image smear of pictures taken during the Uranus encounter. Thrusters with the identical configuration of the units on the spacecraft were fired in an altitude chamber to characterize impulse bit and impulse bit variations as a function of electrical pulse widths and to determine if the short pulses decreased thruster life. Pulse widths of 4.0 milliseconds provide approximately 45 percent of the impulse provided by a 10-ms pulse, and thruster-to-thruster and pulse-to-pulse variation is approximately plus or minus 10 percent. Pulse widths shorter than 4 ms showed wide variation, and no pulse was obtained at 3 ms. Three thrusters were each subjected to 75,000 short pulses of 4 ms or less without performance degradation. A fourth thruster exhibited partial flow blockage after 13,000 short pulses, but this was attributed to prevous test history and not short pulse exposure. The Voyager attitude control thrusters should be considered flight qualified for short pulse operation at pulse widths of 4.0 ms or more.

Source record↗
NASA NTRS1986

CO near the Pleiades: Encounter of a star cluster with a small molecular cloud

Although there is a large amount of interstellar matter near the Pleiades star cluster, the observed dust and gas is not a remnant of the placental molecular cloud from which the star cluster was formed. Carbon monoxide (CO) associated with the visible reflection nebulae was discovered by Cohen (1975). Its radial velocity differs from that of the cluster by many times the cluster escape velocity, which implies that the cloud-cluster association is the result of a chance encounter. This circumstance and the proximity of the Pleiades to the sun creates an unique opportunity for study of interstellar processes at high spatial resolution. To study the molecular component of the gas, a 1.7 square degree field was mapped with the AT&T Bell Laboratories 7-meter antenna (1.7' beam) on a 1' grid in the J=1.0 C(12)O line, obtaining over 6,000 spectra with 50 kHz resolution. The cloud core was mapped in the J=1-0 line of C(13)O. Further observations include an unsuccessful search for CS (J=2-1) at AT&T BL, and some C(12)O J=2-1 spectra obtained at the Millimeter Wave Observatory of the University of Texas.

Bally, J.↗
NASA NTRS1986

Pointing calibration of the MKIVA DSN antennas Voyager 2 Uranus encounter operations support

The MKIVA DSN introduced significant changes to the pointing systems of the 34-meter and 64-meter diameter antennas. To support the Voyager 2 Uranus Encounter, the systems had to be accurately calibrated. Reliable techniques for use of the calibrations during intense mission support activity had to be provided. This article describes the techniques used to make the antenna pointing calibrations and to demonstrate their operational use. The results of the calibrations are summarized.

Stevens, R.↗
NASA NTRS1986

The Voyager encounter with Uranus and Neptune

Voyager 2 approaches Uranus at a relative low phase angle and high southerly latitude. Only when the spacecraft is very close to Uranus does the geometry change appreciably. Most of the important observations occur within six hours of closest approach. Voyager flies through an Earth and solar occulation zone and leaves Uranus at a relatively high phase angle of about 145 degrees. There isn't much of an opportunity to look at the equatorial region of the planet. At Neptune, on the other hand, the approach is more nearly equatorial (about 35 deg S lat). Voyager 2 will come much closer to Nepture than to any of the other gas giants as it skims within about 2000 km of Neptune's cloudtops. It will pass through earth and solar occultation zones at both Neptune and its satellite, Triton. Again, Voyager 2 will leave Neptune at about 35 deg S latitude. Voyager operational instrument, interplanetary trajectories and planetary encounters are briefly discussed.

Miner, Ellis D.↗
NASA NTRS1986

Ultraviolet spectrophotometry of comet Giacobini-Zinner during the ICE encounter

The IUE spectrophotometry of Comet P/Giacobini-Zinner was acquired in support of the International Cometary Explorer (ICE) mission. The abundances (or upper limits) of UV-active species were calculated. During the ICE encounter the H2O production rate was 3 times 10 to the 28th power/sec, + or - 50%, consistent with values derived from the ICE experiments. Comparison of the abundance of CO2(+) ions with the total electron density measured by the plasma electron experiment on ICE indicates a deficiency of ions relative to electrons indicating a population of ions not detected by remote sensing. The absence of detectable Mg(+) rules out this species as a possible ion of M/Q = 24 detected by the Ion Composition Instrument, part of the ICE complement of instruments.

Ahearn, Michael F.↗
NASA NTRS1986

The variability of Halley's Comet during the Vega, Planet-A, and Giotto encounters

Narrowband photometry of Halley obtained at Cerro Tololo Inter-American Observatory (CTIO), Mauna Kea Observatory (MKO), and Perth Observatory was combined to determine the relative level of activity during the interval spanning the spacecraft encounters. Measurements of the flux from the comet in emission bands of OH, NH, CN, C3, and C2, as well as at 2 continuum points, were obtained at CTIO on each night between 5 March and 17 March 1986. Observations were made on many of these same dates at MKO and Perth using comparable interference filters. The date clearly show variation of a factor of 2.5 in the production of all observed species with a characteristic time scale of a few days.

Schleicher, D. G.↗
NASA NTRS1986

Mass distribution of particulates measured by Giotto's Dust Impact Detection System (DIDSY) in the close encounter period

The cumulative mass distribution of the comet Halley dust efflux in the close encounter period -300 to +300 sec was analyzed. Analysis of the cumulative mass distribution index (alpha) shows considerable short time scale variation. There is clear evidence from the flux rates of passage through at least one major dust enhancement (dust jet) just after closest approach and this is associated with a steepening of the alpha. Comparison with measurements from other sources, and with preencounter predictions, is also made.

Zarnecki, J. C.↗
NASA NTRS1986

Measurements of thermal ion energy spectra from the Giotto encounter with Comet Halley

Ram ion measurements made by the Giotto neutral mass spectrometer show the spatial evolution of the composition and energy spectrum of coma ions. Near the nucleus the plasma is cold and has many constituents, but at distances of the order of 200,000 km the main ions are the terminal products of water dissociation, H(+) and O(+). The ion velocity distribution at the time of the Giotto encounter is highly anisotropic. Ion flow is generally away from the comet with energies increasing with distance to the order of 100 eV in the comet frame of reference. Similarities in the proton and oxygen ion energy spectra in the comet frame suggest an acceleration mechanism other than v x B pickup.

Hodges, R. R.↗
NASA NTRS1987

DSS 43 antenna gain analysis for Voyager Uranus encounter: 8.45-GHz radio science data correction

A malfunction of the Deep Space Network (DSN) 64-meter antenna in Australia forced the antenna to operate with a mispositioned subreflector during the Voyager Uranus encounter period (January 24, 1986). Because of changing main reflector shape and quadripod position as a function of elevation angle, the antenna gain and pointing were not as expected, and the 8.45 GHz received signal level changed during the pass. The study described here used the Geometrical Theory of Diffraction (GTD) analysis to determine actual antenna gain and pointing during that period in an attempt to reconstruct the radio science data. It is found that the 1.4 dB of signal variation can be accounted for by antenna geometry changes and pointing error. Suggested modifications to the values measured during the pass are presented. Additionally, an extremely useful tool for the analysis of gravity deformed reflectors was developed for use in future antenna design and analysis projects.

Slobin, S. D.↗
NASA NTRS1987

Ultraviolet spectrophotometry of Comet Giacobini-Zinner during the ICE encounter

The IUE's UV spectrophotometer was used to monitor Comet Giacobini-Zinner's H2O production rate from June to October, 1985, in support of the International Cometary Explorer (ICE) mission. Observation results for the spatial and temporal variation and the abundance or upper limits of C, CO, CO(+), CO2(+), CS, H, Mg(+), O, OH, and S, between September 9 and 12, included the time of the ICE encounter: at this time, the H2O production rate obtained was consistent with a number of gas production rates derived indirectly from the ICE experiments. A comparison of the CO2(+) ion abundance with the total electron density measured by the plasma electron and radio science experiments on ICE implies an ion deficiency relative to electrons, so that the satisfaction of charge balance criteria requires the presence of a major ion population not detected by remote sensing.

Mcfadden, Lucy A.↗
NASA NTRS1988

Intelligent guidance and control for wind shear encounter

The principal objective is to develop methods for assessing the likelihood of wind shear encounter, for deciding what flight path to pursue, and for using the aircraft's full potential for combating wind shear. This study requires the definition of both deterministic and statistical techniques for fusing internal and external information, for making go/no-go decisions, and for generating commands to the aircraft's cockpit displays and autopilot for both manually controlled and automatic flight. The program has begun with the development of a real-time expert system for pilot aiding that is based on the results of the FAA Windshear Training Aids Program. A two-volume manual that presents an overview, pilot guide, training program, and substantiating data provides guidelines for this initial development. The Expert System to Avoid Wind Shear (ESAWS) currently contains over 140 rules and is coded in the LISP programming language for implementation on a Symbolics 3670 LISP machine.

Stengel, Robert F.↗
NASA NTRS1987

The dust distribution within the inner coma of comet P/Halley 1982i - Encounter by Giotto's impact detectors

Analyses are presented of Giotto's Dust Impact Detection System experiment measurements of dust grains incident on the Giotto dust shield along its trajectory through the coma of comet P/Halley on March 13 and 14, 1986. Ground-based CCD imagery of the inner coma dust continuum at the time of the encounter are used to derive the area of grains intercepted by Giotto. Data obtained at large masses show clear evidence of a decrease in the mass distribution index at these masses within the coma; it is shown that such a value of the mass index can furnish sufficient mass for consistency with an observed deceleration.

Mcdonnell, J. A. M.↗
NASA NTRS1988

Abundances in Comet Halley at the time of the spacecraft encounters

Spectrophotometric observations of Comet Halley obtained in March 1986 at the time of the spacecraft encounters with the comet are described, and the column densities derived from the integrated emission band fluxes are presented. The scale lengths are determined from the spatial profiles of the observed species. Production rates are derived and the parent identities and abundance ratios of the studied species are discussed. The data indicate that the abundance of the primordial condensate NH3 comprises about 0.2 percent of the total volatile fraction of the comet nucleus. The ratio of production rates Q(NH2)/Q(H2O) = 0.003 indicates that Q(NH3)/Q(H2O) is roughly 0.3 percent, which is nearly 10 times lower than the value determined from Giotto ion mass spectrometer data. The production rate Q(CH)/Q(H2O) of 0.007 and the CH spatial profile indicate that CH cannot derive entirely from direct photodissociation of CH4.

Wyckoff, Susan↗
NASA NTRS1987

The Voyager-2 Neptune encounter

Aspects of the encounter of Voyager 2 with Neptune which will occur during the summer of 1989 are discussed. The major scientific objectives and the resulting trajectory characteristics are reviewed. The technological requirements for transmitting the scientific data to earth are addressed, and the hardware and software aboard the satellite which will accomplish the transmission are described.

Kosman, William J.↗
NASA NTRS1988

Galilean satellite ephemeris improvement using Galileo tour encounter information

Accurate navigation of the satellite tour portion of the Galileo mission requires an accurate ephemeris of the Galilean satellites. The ephemeris is updated using radiometric and optical tracking data acquired during the satellite tour. The improved accuracy of the satellite ephemeris leads to improved targeting accuracy at subsequent encounters. The Galileo mission will benefit from improved targeting accuracy through reduced propellant costs and improved pointing accuracy. The predicted error in the updated ephemeris can be less than approximations inherent in the analytical theory used for the ephemeris, so an alternate numerical representation is applied. This alternate description shows promise but also raises questions of numerical stability.

Murrow, D. W.↗