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NASA NTRS1976

Observations of velocity shear driven plasma turbulence

Electrostatic and magnetic turbulence observations from Hawkeye 1 during the low-altitude portion of its elliptical orbit over the Southern Hemisphere are presented. The magnetic turbulence is confined near the auroral zone and is similar to that seen at higher altitudes by Heos 2 in the polar cusp. The electrostatic turbulence is composed of a background component with a power spectral index of 1.89 + or - 0.26 and an intense component with a power spectral index of 2.80 + or - 0.34. The intense electrostatic turbulence and the magnetic turbulence correlate with velocity shears in the convective plasma flow. Since velocity-shear instabilities are most unstable to wave vectors perpendicular to the magnetic field, the shear-correlated turbulence is anticipated to be two-dimensional in character and to have a power spectral index of 3, which agrees with that observed in the intense electrostatic turbulence.

Kintner, P. M., Jr.↗

NASA NTRS1976

The August 1972 solar-terrestrial events - Interplanetary magnetic field observations

Interplanetary-magnetic-field measurements made by Pioneers 9 and 10, HEOS 2, and Explorer 41 during early August 1972 are reviewed. It is noted that the two Pioneers were nearly radially aligned during the flare events, with Pioneer 9 at a distance of 0.78 AU from the sun and Pioneer 10 at a distance of 2.2 AU. The data obtained by Pioneer 9, Pioneer 10, and the two near-earth satellites are analyzed separately, and the major flare-associated shocks are identified. An attempt is made to identify corresponding shocks at the different locations and to determine their propagation velocities in the region between 0.8 and 2.2 AU. It is found that there was an obvious tendency for the average shock velocities to decrease with increasing radial distance from the sun and that the local velocities at the Pioneer locations were significantly smaller than the appropriate average values. A comparison of these local velocities indicates that there was a large deceleration of the shocks between the sun and some distance within 0.8 AU but little, if any, deceleration beyond that distance. A plot of average shock velocities from the sun to 1.0 AU as a function of longitude separation between the flares and Pioneer 9 is shown to suggest a pronounced deviation of the shock fronts from spherical symmetry.

Smith, E. J.↗

NASA NTRS1977

Structure of a quasi-parallel, quasi-laminar bow shock

A thick quasi-parallel bow shock structure was observed on February 14, 1969, with field and particle detectors of both Heos 1 and Ogo 5. The typical magnetic pulsation structure was at least 1-2 R-E thick radially and was accompanied by irregular but distinct (average) plasma distributions characteristic of neither the solar wind nor the magnetosheath. There appeared to be a separate 'interpulsation' regime occurring between bursts of large amplitude oscillations. This regime was magnetically similar to the upstream wave region but was characterized by disturbed plasma flux and enhanced noise around the ion plasma frequency. The shock structure appeared to be largely of an oblique whistler type, probably complicated by counterstreaming high-energy protons.

Greenstadt, E. W.↗

NASA NTRS1978

Sources of magnetic fields in recurrent interplanetary streams

The paper examines sources of magnetic fields in recurrent streams observed by the Imp 8 and Heos spacecraft at 1 AU and by Mariner 10 en route to Mercury between October 31, 1973 and February 9, 1974, during Carrington rotations 1607-1610. Although most fields and plasmas at 1 AU were related to coronal holes and the magnetic field lines were open in those holes, some of the magnetic fields and plasmas at 1 AU were related to open field line regions on the sun which were not associated with known coronal holes, indicating that open field lines may be more basic than coronal holes as sources of the solar wind. Magnetic field intensities in five equatorial coronal holes, certain photospheric magnetic fields, and the coronal footprints of the sector boundaries on the source surface are characterized.

Burlaga, L. F.↗

NASA NTRS1979

Molecules of significance in planetary aeronomy

This monograph is basically devoted to spectroscopic information of the molecules of planetary interest. Only those molecules have been dealt with which have been confirmed spectroscopically to be present in the atmosphere of major planets of our solar system and play an important role in the aeronomy of the respective planets. An introduction giving the general conditions of planets and their atmospheres including the gaseous molecules is given. Some typical planetary spectra is presented and supported with a discussion on some basic concepts of optical absorption and molecular parameters that are important to the study of planetary atmospheres. Quantities like dipole moments, transition probabilities, Einstein coefficients and line strengths, radiative life times, absorption cross sections, oscillator strengths, line widths and profiles, equivalent widths, growth curves, bond strengths, electronic transition moments, Franck-Condon factors and r-centroids, etc., are discussed. Spectroscopic information and relevant data of 6 diatomic (HF, HCL, CO, H2, O2, N2) and 6 polyatomic (CO2, N2), O3, HeO, NH3, CH4) molecules are presented.

Mohan, H.↗

NASA NTRS1979

A correlative study of magnetic flux transfer in the magnetosphere

The applied magnetic flux of the southward component of the IMF in GSM coordinates (Bz-) which impinges upon the sunward magnetopause is compared to the time integral of the auroral AL index during 56 intervals within a 3-month period in 1969 when interplanetary records from Heos 1 and Explorer 35 were available. The periods of magnetic activity were those for which Bz was greater than 0 and AL was less than 20gamma at the beginning and end of the interval. It was found that for these intervals, the time integral of the AL index was proportional to the applied magnetic flux with a correlation coefficient of 0.94. In addition, the empirical relationships between magnetic flux transfer, applied southward flux, and the time integral of AL arrived at by Holzer and Slavin (1978) on the basis of expansion and contractions of the forward magnetosphere observed with OGO 5 are reexamined and improved.

Holzer, R. E.↗

NASA NTRS1979

Interplanetary medium data book, supplement, 1975 - 1978

Since the issurance of the Interplanetary Medium Data Book (NSSDC/WDC-A-R&S 77-04, 1977) which contains plots and listings of hourly average interplanetary field and plasma parameters covering the period November 27, 1963 through December 30, 1975, additional data are available which fill some 1975 data gaps and which extend the data coverage well into 1978. This supplement contains all the presently available data for the years 1975-1978, Interplanetary magnetic field (IMF) data are from the IMP 8 triaxial fluxgate magnetometer experiment. Derived plasma parameters are form the IMP 7 and IMP 8 instruments. Some of the early 1975 IMF data are from a HEOS 1 experiment.

King, J. H.↗

NASA NTRS1980

Dynamics of micrometeoroids

The spatial and orbital distributions of meteoroids of mass less than 10 to the -8 g are discussed. Pioneer 8 and 9, HEOS-2 and Helios 1 observations of the smallest meteoroids leaving the solar system in hyperbolic orbits due to radiation pressure (beta particles), intermediate mass particles arriving from the heliocentric spacecraft apex direction (alpha meteoroids) and the largest micrometeoroids observed with no preferred directionality (sporadic meteoroids) are reviewed, and evidence for the three groups of dynamically different micrometeoroids in lunar microcrater statistics is indicated. The collisional model of the origin of dust particles from the dispersion of sporadic meteoroids of cometary origin due to the Poynting-Robertson effect and collisions is then applied to account for the dynamics of the beta and alpha micrometeoroids.

Gruen, G.↗

NASA NTRS1982

System design concepts and requirements for aeroassisted orbital transfer vehicles

The Orbital Transfer Vehicle (OTV) is an advanced upper stage concept which will deliver spacecraft from operating systems at Low Earth Orbit (LEO) such as Space Shuttle, Earth-To-Orbit (ETO) vehicles, and Space Operations Center (SOC), to High Earth Orbit (HEO) and planetary excursions. The OTV will be driven by the need to achieve significant reductions in the operational costs for delivering payloads to Geostationary Equatorial Orbit (GEO). Aeroassist is a technological capability that has a potential for OTV's ranging from mission enhancing (reusable OTV for payload delivery) to mission enabling (manned GEO and some DOD). It is shown that the use of aeroassist for OTV's is a high leverage technology which can potentially reduce space transportation costs and enable a number of highly desirable missions.

Austin, R. E.↗

NASA NTRS1983

Optimal trajectories for aeroassisted orbital transfer

Consideration is given to classical and minimax problems involved in aeroassisted transfer from high earth orbit (HEO) to low earth orbit (LEO). The transfer is restricted to coplanar operation, with trajectory control effected by means of lift modulation. The performance of the maneuver is indexed to the energy expenditure or, alternatively, the time integral of the heating rate. Firist-order optimality conditions are defined for the classical approach, as are a sequential gradient-restoration algorithm and a combined gradient-restoration algorithm. Minimization techniques are presented for the aeroassisted transfer energy consumption and time-delay integral of the heating rate, as well as minimization of the pressure. It is shown that the eigenvalues of the Jacobian matrix of the differential system is both stiff and unstable, implying that the sequential gradient restoration algorithm in its present version is unsuitable. A new method, involving a multipoint approach to the two-poing boundary value problem, is recommended.

Miele, A.↗

NASA NTRS1985

In-situ detection of micron-sized dust particles in near-Earth space

In situ detectors for micron sized dust particles based on the measurement of impact ionization have been flown on several space missions (Pioneer 8/9, HEOS-2 and Helios 1/2). Previous measurements of small dust particles in near-Earth space are reviewed. An instrument is proposed for the measurement of micron sized meteoroids and space debris such as solid rocket exhaust particles from on board an Earth orbiting satellite. The instrument will measure the mass, speed, flight direction and electrical charge of individually impacting debris and meteoritic particles. It is a multicoincidence detector of 1000 sq cm sensitive area and measures particle masses in the range from 10 to the -14th power g to 10 to the -8th power g at an impact speed of 10 km/s. The instrument is lightweight (5 kg), consumes little power (4 watts), and requires a data sampling rate of about 100 bits per second.

Gruen, E.↗

NASA NTRS1985

The influence of quiet asymmetric magnetosphere on the cutoff rigidities of the main cone

Some earlier studies show that cutoff rigidities of cosmic-ray particles in the model magnetospheric fields of internal and external sources have daily variations caused by asymmetry of the magnetic field due to the currents induced at the magnetopause and tail currents. Cutoff rigidities of the charged particles coming down at the middle latitudes are examined in this paper. The mathematical model of the magnetospheric field is based on the merged IMP-HEOS experimental data set and includes all known at the present time current systems of the magnetosphere: magnetopause, ring, and magnetotail currents.

Tyasto, M. I.↗

NASA NTRS1986

Space solar cell research: Problems and potential

The value of a passive, maintenance-free, renewable energy source was apparent in the early days of the space program, and the silicon solar cell was pressed into service. Efficiencies of those early space solar arrays were low, and lifetimes shorter than hoped for, but within a decade significant advances had been made in both areas. Better performance was achieved through improvements in silicon single crystal material, better device designs, and a better understanding of the factors that affect the performance of a solar cell in space. Chief among the latter, particularly for the mid-to-high altitude (HEO) and geosynchronous (GEO) orbits, are the effects of the naturally occurring particulate radiation environment. Although not as broadly important to the photovoltaic community at large as increased efficiency, the topic of radiation damage is critically important to use of solar cells in space, and is a major component of the NASA research program in space photovoltaics. A brief overview of some of the opportunities and challenges for space photovoltaic applications is given, and some of the current research directed at achieving high efficiency and controlling radiation damage in space solar cells is discussed.

Flood, D. J.↗

NASA NTRS1986

Space solar cell research - Problems and potential

The value of a passive, maintenance-free, renewable energy source was immediately recognized in the early days of the space program, and the silicon solar cell, despite its infancy, was quickly pressed into service. Efficiencies of those early space solar arrays were low, and lifetimes shorter than hoped for, but within a decade significant advances had been made in both areas. Better performance was achieved because of a variety of factors, ranging from improvements in silicon single crystal material, to better device designs, to a better understanding of the factors that affect the performance of a solar cell in space. Chief among the latter, particularly for the mid-to-high altitude (HEO) and geosynchronous (GEO) orbits, are the effects of the naturally occurring particulate radiation environment. Although not as broadly important to the photovoltaic community at large as increased efficiency, the topic of radiation damage is critically important to use of solar cells in space, and is a major component of the NASA research program in space photovoltaics. This paper will give a brief overview of some of the opportunities and challenges for space photovoltaic applications, and will discuss some of the current reseach directed at achieving high efficiency and controlling the effects of radiation damage in space solar cells.

Flood, Dennis J.↗

NASA NTRS1987

Cusp displacement at the magnetopause for large IMF Y component

The magnetic field orientation just earthward of the dayside magnetopause from 95 ISEE and 11 HEOS crossings with /By/ greater than /Bz/ in the adjacent magnetosheath indicate a statistically significant-1-earth-radius shift of the cusps toward dawn (dusk) in the Northern Hemisphere and dusk (dawn) in the Southern Hemisphere for positive (negative) By. This small shift near the magnetopause and the contrasting large shifts of some reported ionospheric cusp signatures are explained in terms of a finite thickness magnetopause model through which the cusps shift gradually from the inner to the outer edge.

Crooker, N. U.↗

NASA NTRS1989

Fuel-optimal trajectories of aeroassisted orbital transfer with plane change

The problem of minimization of fuel consumption during the atmospheric portion of an aeroassisted, orbital transfer with plane change is addressed. The complete mission has required three characteristic velocities, a deorbit impulse at high earth orbit (HEO), a boost impulse at the atmospheric exit, and a reorbit impulse at low earth orbit (LEO). A performance index has been formulated as the sum of these three impulses. Application of optimal control principles has led to a nonlinear, two-point, boundary value problem which was solved by using a multiple shooting algorithm. The strategy for the atmospheric portion of the minimum-fuel transfer is to start initially with the maximum positive lift in order to recover from the downward plunge, and then to fly with a gradually decreasing lift such that the vehicle skips out of the atmosphere with a flight path angle near zero degrees.

Naidu, Desineni Subbaramaiah↗

NASA NTRS1989

Fuel-optimal trajectories of aeroassisted orbital transfer with plane change

Naidu, D. S.↗

NASA NTRS1990

Mission optimization of the Space Infrared Telescope Facility

The Space Infrared Telescope Facility (SIRTF) mission based on a cryogenically cooled telescope is described. The SIRTF makes it possible to perform background limited measurements with three focal plane instruments in the wavelength range 2-700 microns over the entire celestial sphere for at least five years. A telescope performance limited by the natural astrophysical background between 2 to 300 microns is achieved by using a superfluid helium cryogenic system for maintaining the forebaffle temperature below 8 K. The attitude control system based on Extreme Ultra-Violet Explorer reaction wheels meets the large and small angle slew requirements and provides 0.15 arc sec pointing stability. The present HEO baseline configuration has a mass of 4370 kg. The future Titan IV/Centaur launch capability to 100,000 km for a SIRTF-sized payload is at least 5770 kg.

Brooks, Walter F.↗