Search NASA⌕ Search

Engineering topics

Beard, D. B.

Publications and source records attributed to Beard, D. B..

16 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Solar pressure and molecular decay in cometary atmospheres

The effects of solar pressure and molecular decay on number density in cometary atmospheres are rigorously separated and scale lengths for each are determined from an analysis of observed brightness profiles in the solar and antisolar directions. It is found that the pressure scale length of CN is approximately 160,000 km and that of C2 is approximately 110,000 km. The scale length for molecular decay, heretofore incorrectly inferred from the observational data, is approximately 3 times as long as the pressure scale lengths. It is difficult to determine adequately from observations that extend no more than about 100,000 km from the comet nucleus. The scale length for molecular decay by photodissociation or whatever cause is found to be about 350,000 km for C2 and 500,000 km for CN.

Beard, D. B.↗
NASA NTRS1985

Electric and magnetic drift of non-adiabatic ions in the earth's geomagnetic tail current sheet

It has been shown recently that nonadiabatic particles in the earth's magnetotail drift across the tail roughly as predicted for adiabatic particles with 90 deg pitch angles. In this paper it is shown that this result implies the existence of an approximate invariant of the motion. Adding the effect of convection associated electric fields, the approximate bounce averaged motion of nonadiabatic particles in the magnetotail can be obtained. Thus the particle motion and energization due to combined magnetic and electric drifts in the magnetotail are easily predicted.

Beard, D. B.↗
NASA NTRS1984

Cross-tail ion drift in a realistic model magnetotail

By integrating the exact equations of motion, particle orbits have been followed in a good model magnetospheric field consisting of a planetary dipole, forward magnetosphere, and magnetotail current system. Proton energies from 2 eV to 20 keV were used for the full range of equatorial pitch angles and phase. Despite considerable pitch angle scattering in the equatorial plane crossings, it is found, first, that the bounce-averaged cross-tail drift velocity is approximately independent of pitch angle. Second, it is found that, averaged over initial gyrophase, the drift velocity (due to field curvature and gradient) is proportional to proton energy and is given to good approximation by adiabatic approximations, even up to 20 keV, despite the extreme lack of meeting the adiabatic criteria.

Propp, K.↗
NASA NTRS1982

The tailward magnetopause field beyond 10 RE

The geomagnetic field in the near-earth magnetotail is made up of three major contributions related to the dipole field, the magnetotail current system, and the magnetopause current system exclusive of the return currents in the magnetotail current system. The present investigation is concerned with the third contribution. The calculation of the magnetospheric field is discussed, taking into account the calculation of the field inside the magnetopause on the basis of the numerical integration of the Biot Savart integral. The representation of the field for distances greater than 10 earth radii on the dark side of the magnetosphere is considered. The field internal to the magnetopause is expressed as the negative gradient of a scalar potential which is expressed as a sum of solutions to Laplace's equation in cylindrical coordinates. The origin of coordinates is the earth.

Beard, D. B.↗
NASA NTRS1973

Precise calculation of the magnetosphere surface for a tilted dipole.

The shape of the magnetosphere has been calculated self-consistently for inclinations of the earth's magnetic dipole from perpendicular to the solar wind. Inclination angles of 0-35 deg have been chosen in steps of 5 deg and various smooth trends in the surface characteristics with increasing inclination angle noted. The surface points and the complete field at the surface points have been calculated for the entire surfaces. The neutral point region has been given precise study in one degree steps and is found to be tangent to the solar wind velocity and to have a smooth continuous curvature.

Choe, J. Y.↗
NASA NTRS1972

The F and K components of the solar corona.

Numerical calculations of the F component are conducted for a large range of parameters, particle size distribution, minimum particle size, minimum approach to the sun, albedo, and spatial distribution. Various parametrized functional forms for the electron spatial distribution are assumed, and the parametrical elongation dependence of the K component is calculated. New and old data are analyzed by fitting the theoretical parametrized elongation dependence to observations of the total intensity of the solar corona. The orbital behavior of the dust is estimated together with the temperature and thermal emission.

Calbert, R.↗
NASA NTRS1972

Discussion of the reliability of electron densities and energies interpreted from data and limits on the proton energy and density

Analysis of radio observations of Jupiter were changed to take into account the antenna resolution. A dipole magnetic field with a surface equatorial value of 7 gauss is assumed. The electron temperature is found to increase for r 2.5 Jupiter radii with decreasing r as 1/r cubed, reaching a peak of about 100 MeV at r = 2.5 Jupiter radii. For r 2.5 Jupiter radii, the electron temperature goes as r to the 6th power because of energy lost to radiation. The consequences of making an upper estimate on the proton flux by assuming the magnetic field is loaded with all the energetic protons it can hold are described. The upper limits of proton energy, density, flux, and energy flux are calculated for 1, 2, 2.5, 3, and 6 Jupiter radii. The proton energy and velocity estimates are considered to be fairly reliable; the upper limit to the number density is probably much higher than actuality.

Beard, D. B.↗