Engineering topics

Intriligator, D. S.

Publications and source records attributed to Intriligator, D. S..

At least 55 records · Page 3

NASA NTRS1980

Preliminary results on the plasma environment of Saturn from the Pioneer 11 plasma analyzer experiment

The Ames Research Center Pioneer 11 plasma analyzer experiment provided measurements of the solar wind interaction with Saturn and the character of the plasma environment within Saturn's magnetosphere. It is shown that Saturn has a detached bow shock wave and magnetopause quite similar to those at earth and Jupiter. The scale size of the interaction region for Saturn is roughly one-third that at Jupiter, but Saturn's magnetosphere is equally responsive to changes in the solar wind dynamic pressure. Saturn's outer magnetosphere is inflated, as evidenced by the observation of large fluxes of corotating plasma. It is postulated that Saturn's magnetosphere may undergo a large expansion when the solar wind pressure is greatly diminished by the presence of Jupiter's extended magnetospheric tail when the two planets are approximately aligned along the same solar radial vector.

Wolfe, J. H.↗

NASA NTRS1980

The Pioneer Venus Orbiter plasma analyzer experiment

The plasma analyzer experiment on the Pioneer Venus Orbiter was designed to determine the basic characteristics of the plasma environment of Venus and the nature of the solar wind interaction at Venus. The plasma analyzer experiment is an electrostatic energy-per-unit charge (E/Q) spectrometer which measures ions and electrons. There is a curved plate electrostatic analyzer system with multiple collectors. The experiment obtains the three dimensional plasma distribution function. Some of the scientific objectives of the instrument are briefly discussed, the general characteristics of the experiment are summarized, and some of the analyses based on the data are presented.

Intriligator, D. S.↗

NASA NTRS1980

Transient phenomena originating at the sun - An interplanetary view

Analyses of several transient phenomena which occurred in 1978 and 1979 are presented using data from the Pioneer Venus, ISEE, and Pioneer 10 and 11 spacecraft. The interplanetary phenomena studied are associated with solar flares and coronal holes. The observations show that phenomena originating at the sun affect the structure of the particle and field regimes throughout the explored solar system, extending out to at least 17-20 AU in the vicinity of the elliptic plane over a range of azimuthal angles greater than 90 deg. High frequency fluctuations in the interplanetary medium appear beyond 1 AU, indicating that transient phenomena are significantly modified by their passage through this medium.

Intriligator, D. S.↗

NASA NTRS1979

Mars in the solar wind

Recent spacecraft observations and model calculations of the solar wind interaction (SWI) at Mars have shown that the particle pressure is not large enough to stand off the solar wind unless the electron temperature is 4 times the ion temperature in the ionosphere, but the additional pressure is presumably magnetic, provided by a planetary magnetic field. In addition, a planetary field corresponding to a surface field of about 20 gammas, and a dipole moment of about 8 x 10 to the 21st gauss per cu cm are implied. Calculations indicate that 60-70% of the pressure is supplied by the magnetic field, and 30-40% by the ionosphere. Thus, the SWI at Mars is unique, being an interaction both with the atmosphere and with the planetary magnetic field.

Intriligator, D. S.↗

NASA NTRS1979

Position and shape of the Venus bow shock - Pioneer Venus Orbiter observations

Magnetometer data from the Pioneer Venus Orbiter is used to examine the position and shape of this planet's bow shock. Utilizing crossings identified on 86 occasions during the first 65 orbits a mean shock surface is defined for sun-Venus-satellite angles of 60-110 deg. Both the shock shape and variance in location are found to be very similar to the terrestrial case for the range in SVS angle considered. However, while the spread in shock positions at the earth is due predominantly to the magnetopause location varying in response to solar wind dynamic pressure, ionopause altitude variations can have little effect on total obstacle radius. Thus, the Cytherean shock is sometimes observed much closer to or farther from the planet than previously predicted by gasdynamic theory applied to the deflection of flow about a blunt body which acts neither as source nor sink for any portion of the flow.

Slavin, J. A.↗

NASA NTRS1979

Electron observations and ion flows from the Pioneer Venus Orbiter plasma analyzer experiment

Additional plasma measurements in the vicinity of Venus are presented. It is shown that (1) there are three distinct plasma electron populations - solar wind electrons, ionosheath electrons, and nightside ionosphere electrons; (2) the plasma ion flow pattern in the ionosheath is consistent with deflected flow around a blunt obstacle; (3) the plasma ion flow velocities near the downstream wake may, at times, be consistent with the deflection of plasma into the tail, closing the solar wind cavity downstream from Venus at a relatively close distance (within 5 Venus radii) to the planet; (4) there is a separation between the inner boundary of the downstream ionosheath and the upper boundary of the nightside ionosphere; and (5) during the first 4.5 months in orbit the measured solar wind plasma speed continued to vary, showing a number of high-speed, but generally nonrecurrent, streams.

Intriligator, D. S.↗

NASA NTRS1979

Evidence for earth magnetospheric tail associated phenomena at 3100 R sub E

Examination of Pioneer 7 NASA Ames Research Center plasma analyzer data obtained in February 1977 at about 3100 earth radii, downstream from earth in the vicinity of the expected extended geomagnetic tail indicate that tail-related phenomena may have been observed. These observations are characterized by intermittent intervals of extremely low levels of plasma ion flux. Corresponding Prognoz 5 Space Research Institute plasma ion data obtained in the vicinity of earth indicate typical solar-wind flux levels and a relatively steady character of the solar wind during this time. These recent Pioneer 7 observations in the vicinity of the expected geomagnetic tail at about 3100 earth radii are consistent with earlier Pioneer 7 observations in September 1966 at about 1000 earth radii and Pioneer 8 observations in January 1968 at about 500 earth radii and represent the most extended positive observational information of the extended nature of the geomagnetic tail. These measurements suggest that at times Jupiter's magnetosphere may have tail-associated phenomena extending to distances of about 10 AU downstream from the planet. These measurements also raise the possibility that at times comets may have tail-associated phenomena extending downstream from the visible tail.

Intriligator, D. S.↗

NASA NTRS1979

Initial observations of the Pioneer Venus orbiter solar wind plasma experiment

The ionosphere, ionosheath, ionopause, and bow shock wave of Venus are characterized. Venus is found to have a well-defined strong standing bow shock wave. In the ionosheath, downstream from the shock, compressed and heated postshock plasma apparently interacts directly with the ionosphere. Plasma ion velocity deflections suggest that the ionopause has a blunt shape. The positions of the bow shock and ionopause are variable and appear to respond to changes in the external solar wind pressure.

Wolfe, J.↗

NASA NTRS1978

Additional evidence consistent with solar cycle variations in the solar wind

Analyses of solar-wind observations from mid-1964 through 1973 confirm the earlier results reported by Intriligator (1974) that there were statistically significant variations in the solar wind in 1968 and 1969, years of solar maximum. These variations were in phase with the solar cycle and consistent with a solar-cycle variation in the solar wind. High-speed stream parameters show that the number of high-speed streams in the solar wind in 1968 and 1969 and the total duration (in days) of high-speed streams in 1968 were considerably more than the predicted yearly average, and in 1965 and 1972 considerably less. Histograms of solar-wind speed from 1964 through 1973 indicate that in 1968 there was the highest percentage of elevated solar-wind speeds, and in 1965 and 1972 the lowest. Studies by others confirm these results, although their authors did not indicate this fact. The duration of the streams and the histograms for 1973 may imply a shifting in the primary stream source.

Intriligator, D. S.↗

NASA NTRS1978

The radial evolution of the bulk properties of the solar wind

Simultaneous solar-wind proton data obtained at several heliocentric distances during radial alignments are compared. The radial variations associated with two high-speed streams in the solar wind are studied as examples of the radial evolution of the solar-wind speed distribution and of high-speed streams in the solar wind as observed in the ecliptic plane in 1973. Pioneer 11 data on high-speed streams in the solar wind observed at about 1.5 and 3.7 AU are compared with the corresponding high-speed-stream data obtained at earth. These analyses indicate that as these high-speed streams propagated to these extended heliocentric distances, there was an erosion of the highest speeds and a general narrowing of the speed distribution. These observations are consistent with the exchange of momentum in the solar wind between high-speed streams and low-speed streams as they propagate outward from the sun.

Intriligator, D. S.↗

NASA NTRS1978

Evidence for a constant speed of shock propagation between 0.8 AU and 2.2 AU

The results of preliminary analysis of the in situ observations of solar wind plasma and interplanetary magnetic field data are presented. It is indicated that two planetary shocks associated with the August 1972 solar events propagated at approximately constant speed between 0.8 AU and 2.2 AU. This result is contrary to some theoretical expectations and earlier reports for these events of a strong deceleration of these shocks with increasing heliocentric distance. One example given is the difference between observed shock speeds of 700 km/sec and the estimated speeds of 2200 km/sec for Pioneer 9 and 1000 km/sec for Pioneer 10. These higher average speeds associated with the propagation of the shocks from the sun to the spacecraft, therefore, imply an extremely strong deceleration closer to the sun (within 0.8 AU).

Intriligator, D. S.↗

NASA NTRS1977

Plasma electron measurements in the outer Jovian magnetosphere

The existence of the plasma electrons in the outer Jovian magnetosphere reported by Intriligator and Wolfe (1974) is consistent with (1) the additional pressure needed to supplement the magnetospheric magnetic field in the outer magnetosphere so as to balance the solar wind and interplanetary magnetic field dynamic pressure across the magnetopause, (2) the drastic change in the plasma electron spectrum as soon as Pioneer 10 crossed the magnetopause from the magnetosheath into the magnetosphere, (3) the fact that the instrument aperture was at spacecraft ground, and (4) the fact that beyond about 2 AU the continuous observations of all ambient electron fluxes (solar wind electrons, secondary electrons, photoelectrons, etc.) are below the instrument threshold.

Intriligator, D. S.↗

NASA NTRS1977

The Venus ionosphere and solar wind interaction

The current state of knowledge of the chemistry, dynamics and energetics of the upper atmosphere and ionosphere of Venus is reviewed together with the nature of the solar wind-Venus interaction. Because of the weak, though perhaps not negligible, intrinsic magnetic field of Venus, the mutual effects between these regions are probably strong and unique in the solar system. The ability of the Pioneer Venus Bus and Orbiter experiments to provide the required data to answer the questions outstanding is discussed in detail.

Bauer, S. J.↗

NASA NTRS1977

Pioneer 9 and Pioneer 10 observations of the solar wind associated with the August 1972 events

Observations are presented of the changes in the solar wind proton parameters at 0.8 and 2.2 AU as a result of the solar flares in August 1972. These observations were obtained by the NASA Ames Research Center solar wind plasma analyzer experiments on Pioneer 9 and Pioneer 10. High time resolution measurements are presented of the solar wind proton speed associated with the arrival of the interplanetary shocks at Pioneer 9 and Pioneer 10. For these events, differential ion energy per unit charge spectra are shown which indicate the changes in the solar wind ion distribution function associated with the arrival of each of the interplanetary shocks. Four fast shocks are identified at Pioneer 9, and it is found that previously the time of arrival of the first interplanetary shock at Pioneer 9 was not correctly identified. Two fast shocks and one reverse shock are identified at Pioneer 10.

Intriligator, D. S.↗

NASA NTRS1976

The August 1972 solar-terrestrial events - Solar wind plasma observations

Solar-wind observations associated with the enhanced levels of solar activity in August 1972 are reviewed with emphasis on recent analyses which more unambiguously characterize the changes in the interplanetary medium. Observations from Pioneer 9 at about 0.8 AU, Pioneer 10 at 2.2 AU, and in the vicinity of earth are reviewed and reinterpreted in the light of new data. Recent calculations of local shock velocities are reviewed, and their implications are discussed. These results indicate that, contrary to previously published observations, there is no significant deceleration of the interplanetary shocks between 0.8 AU and 2.2 AU.

Intriligator, D. S.↗

NASA NTRS1976

Results of the plasma analyzer experiment on Pioneers 10 and 11

The plasma-analyzer experiments on Pioneers 10 and 11 have determined that the characteristics of the solar-wind interaction with the Jovian magnetosphere are basically similar to those observed for the solar-wind interaction of earth and differ mainly in terms of the scale size of the interaction. The Jovian magnetosheath flow field and the calculated normals to the Jovian magnetosphere indicate that the Jovian magnetosphere is extremely thick and blunt in shape. The size of the Jovian magnetosphere in the sunward (dayside) direction can change by as much as a factor of two in response to relatively minor changes in solar-wind dynamic pressure. The outer dayside Jovian magnetosphere is inflated with a high-beta thermal plasma.

Intriligator, D. S.↗

NASA NTRS1975

Pioneer 11 encounter - Preliminary results from the Ames Research Center plasma analyzer experiment

Pioneer 11 observations of the interaction of Jupiter's magnetosphere with the distant solar wind have confirmed the earlier Pioneer 10 observations of the great size and extreme variability of the outer magnetosphere. The nature of the plasma transitions across Jupiter's bow shock and magnetopause as observed on Pioneer 10 have also been confirmed on Pioneer 11. However, the northward direction of the Pioneer 11 outbound trajectory and the distance of the final magnetopause crossing (80 Jupiter radii) now suggest that Jupiter's magnetosphere is extremely broad with a half-thickness (normal to the ecliptic plane in the noon meridian) which is comparable to or greater than the sunward distance to the nose.

Mihalov, J. D.↗

NASA NTRS1975

A search for solar wind velocity changes between 0.7 and 1 AU

Observations are presented concerning the radial variations of the solar wind velocity between 0.7 and 1 AU in late 1968 and early 1969. The observations were made with instruments carried by Pioneer 9 and the earth-orbiting satellite OGO 5. The Pioneer and OGO velocity measurements are compared. It is found that the same basic solar wind velocity structure was seen at both spacecraft. No statistically significant dependence of average velocity on the radial distance from the sun could be observed.

Intriligator, D. S.↗