A review of the perturbation theory as applied to the determination of geopotential
Satellite theory to determine geopotential from orbital motion of artificial earth satellites
Khan, M. A.↗
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Results for “orbital motion”
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Friction between mantle and core of the earth as a cause of the secular change in obliquity.
Earth mantle and core friction interaction suggested as cause of secular change in orbital motion obliquity
Aoki, S.↗
On the behavior of low density plasma in the presence of cylindrical Langmuir probes
Low density plasma in region of orbital-motion- limited /OML/ currents in presence of cylindrical Langmuir probes
Szuszczewicz, E. P.↗
Structure and evolutionary history of the solar system. I
Solar system origin, structure and evolution, discussing planet and satellite orbital motion, resonance effects, tides and postaccretional changes
Alfven, H.↗
Anchoring spacecraft to planets
For planet tracking, the immense mass relative to applied nongravitational forces (for even the smaller asteroids) removes limitations on the ability to model orbital motion mathematically. A lander on a natural satellite (other than the moon) would not suffer from nongravitational effects, and would further have a large mean motion, which is important for observing gravitational effects. The tracking of a Mars lander over a long period would yield conclusions in the areas of relativity (determination of the parameter beta), the inertial framework, Mars' internal structure (based on the polar moment), and Mars' physical ephemeris.
Cain, D. L.↗
Multispectral image dissector camera system
A sensor system which provides registered high-solution multispectral images from a single sensor with no mechanical moving parts is reported, and the operation of an image dissector camera (IDC) is described. An earth scene 100 nautical miles wide is imaged through a single lens onto a photocathode surface containing three spectral filters, thereby producing three separate spectral signatures on the photocathode surface. An electron image is formed, accelerated, focused, and electromagnetically, deflected across an image plane which contains three sampling apertures, behind which are located three electron multipliers. The IDC system uses electromagnetic deflection for cross-track scanning and spacecraft orbit motion for along-track scanning, thus eliminating the need for a mechanical scanning mirror.
Johnson, B. L.↗
Preliminary study of the application of the Timation 3 satellite to earth physics
The Timation 3 is a timing and navigation satellite originally planned for launch in December 1972 into a circular orbit at 98 deg inclination 14,000 km altitude with gravity gradient stabilization. An error analysis indicates a satellite position uncertainty of about one meter, 80 percent of which is attributable to the assumed gravity model errors. The remaining uncertainties have a period equal to that of the satellites and can be filtered out yielding an effective uncertainty of about 10 cm in the study of phenomena having different periodicities. The accomplishment of these results depends on a careful consideration of solar radiation pressure taking account of the spacecraft reflecting properties and variations in the presentation area. Consideration is also given to the displacement of the laser reflectors from the center of mass of the spacecraft and to the dynamic coupling of any libration in attitude with the orbital motion. The results indicate that a good set of well distribution laser observations of Timation 3 could yield determinations of polar motion, sea floor spreading, solid earth tides, and earth rotation at the 10 cm level.
Carpenter, L.↗
Lyman-alpha measurements of neutral hydrogen in the outer geocorona and in interplanetary space.
Results of hydrogen Lyman-alpha (1216 A) measurements made on a continuous basis by a two-channel photometer on Ogo 5 from March 1968 to June 1971. The highly elliptical orbit provided measurements of both the outer geocorona and of the 1216-A sky background emission, since geocoronal scattering is minimal at the apogee distance of 150,000 km. Selected data (through 1970) are presented, as well as an interpretation of the three principal discoveries to date - namely, (1) a pronounced antisolar enhancement of the geocoronal scattering beyond 70,000 km, which is regarded as evidence for a hydrogen 'geotail' produced by solar Lyman-alpha radiation pressure; (2) a clear correlation of periodic variations in the sky background emission with solar activity associated with solar rotation; and (3) an annual variation of the 1216-A sky background emission, caused by the earth's orbital motion within the cavity created by the solar wind in the nearby interstellar hydrogen.
Thomas, G. E.↗
The estimation of masses of individual galaxies in clusters of galaxies.
Three different methods of estimating masses are discussed. The 'density method' is based on the analysis of the density distribution of galaxies around the object whose mass is to be found. The 'bound-galaxy method' gives estimates of the mass of a double, triple, or quadruple system from analysis of the orbital motion of the components. The 'virial method' utilizes the formulas derived for the second method to obtain estimates of the virial-theorem masses of whole clusters, and thus to obtain upper limits on the mass of an individual galaxy in a cluster. The analytic formulas are developed and compared with computer experiments, and some applications are given.
Wolf, R. A.↗
Nonthermal radio observations of the major planets.
The complex and intriguing source of emission over the entire radio spectrum that Jupiter represents is reviewed in the light of ground radio observation data gathered over a period of seventeen years. The observations indicate the presence of intense radiation belts and a strong magnetic field inclined to the axis of rotation. At decametric wavelengths, several remarkably powerful sources are correlated with the rotation of the planet and the orbital motion of the satellite Io. There is at most marginal evidence of nonthermal emission from Saturn, and no such evidence as yet from Uranus and Neptune.
Smith, A. G.↗
Physical parameters of the Cen X-3 system
Photographic spectra of Cen X-3 show that the primary star has a spectral type near 06.5 with weak, variable emission at wavelength 4640 and 4686. No orbital motion of the emission or absorption lines is detected; for the latter the upper limit is approximately + or - 50 km/s. Analysis of the available data indicates that the primary is a factor of 2-3 less massive than expected from normal evolutionary models while the X-ray source has a solar mass near 1.5.
Osmer, P. S.↗
Influence of thermal distortion on the anomalous behavior of a gravity gradient satellite
Consideration of the problem of determining the influence of solar heating on the low-frequency dynamic stability of a gravity-gradient satellite. The scope of the effort includes the development of a computer program that uses a quasi-static approach for describing a satellite's unsteady orbital motion. The essential feature of the quasi-static approach is that the satellite's long, slender booms reach their thermal equilibrium position solely as a result of thermal bending without consideration of the dynamic effects of boom vibration. A nonlinear analytical model and a corresponding computer program have been developed to study the effect of absorptivity, sun angle, and hinge stiffness on the stability of a satellite's motion.
Goldman, R. L.↗
Physical parameters of the Centaurus X-3 system
Photographic spectra of Cen X-3 show that the primary star has a spectral type near O6.5 with weak, variable emission at 4640 and 4686 A. No orbital motion of the emission or absorption lines is detected; for the latter the upper limit is about plus or minus 50 km/sec. Analysis of the available data indicates that the primary is a factor of 2-3 less massive than expected from normal evolutionary models while the X-ray source has a mass near 1.5 times the solar mass.
Osmer, P. S.↗
Models of Jovian decametric radiation
A critical review is presented of theoretical models of Jovian decametric radiation, with particular emphasis on the Io-modulated emission. The problem is divided into three broad aspects: (1) the mechanism coupling Io's orbital motion to the inner exosphere, (2) the consequent instability mechanism by which electromagnetic waves are amplified, and (3) the subsequent propagation of the waves in the source region and the Jovian plasmasphere. At present there exists no comprehensive theory that treats all of these aspects quantitatively within a single framework. Acceleration of particles by plasma sheaths near Io is proposed as an explanation for the coupling mechanism, while most of the properties of the emission may be explained in the context of cyclotron instability of a highly anisotropic distribution of streaming particles.
Smith, R. A.↗
Geometrical procedures for the analysis of spacecraft attitude and bias determinability
Geometrical procedures are presented for predicting the determinability of spacecraft attitude and bias parameters. An analysis is presented on three common attitude measurements: sun angle, nadir angle, and sun-to-earth mid-scan rotation angle. First, the geometry of these measurements is considered for an arbitrary fixed location of the spacecraft; then the effect of orbital motion is analyzed. The results are summarized in a set of simple geometrical rules. The application of these rules to the Synchronous Meteorological Satellite-2 (SMS-2) is discussed. As a result of this geometrical analysis, modifications were made to the SMS-2 bias determination schedule which substantially enhanced the determinability of attitude sensor biases.
Wertz, J. R.↗
Skylab ultraviolet stellar spectra - A new white dwarf, HD 149499 B
The letter reports the discovery of a cool star with excess brightness in the vacuum ultraviolet on an objective-prism photograph obtained during the second Skylab mission. This star, HD 149499, is of type K0 V and has a companion with an apparent magnitude of about 11.8; the relatively flat UV spectrum observed at the position of HD 149499 is characteristic of a 10th or 11th magnitude unreddened O- or early B-type star. It is shown that the excess VUV brightness is due to the companion, HD 149499B, which probably lies in the region of the H-R diagram occupied by the hot white dwarfs. Inspection of white dwarf lists indicates that this star is the sixth or seventh brightest white dwarf known. A maximum orbital motion of 0.025 arcsec/yr is estimated along with a period of just under 500 yr.
Parsons, S. B.↗
Recent decametric and hectometric observations of Jupiter
Observational results on Jupiter's high-frequency radiation, for the range 1-35 MHz (10 to 100 m), obtained over the past six years with the aid of orbited telescopes, are surveyed. Spectral distributions, periodic effects, burst waveforms and dynamic spectra of storms, polarization effects, high-resolution interferometry, and possible correlations with solar activity are discussed. Related spacecraft experiments are described. Close attention is given to long-term accumulation of occurrence probability data as functions of time and frequency (synoptic monitoring) on Jovian HF emission, and to dominating effects of the Jovian satellite Io, as well as modulation of periodicities by the 11.9-year orbital motion period of Jupiter. Possible effects of the other four Jovian satellites immersed in the Jovian magnetosphere are also taken into consideration. Absence of a Jovian Faraday effect and polarization of fine burst structure are discussed.
Carr, T. D.↗
Models of Jovian decametric radiation
We present a critical review of theoretical models of Jovian decametric radiation, with particular emphasis on the Io-modulated emission. The problem is divided into three broad aspects: the mechanism coupling Io's orbital motion to the inner exosphere, the consequent instability mechanism by which electromagnetic waves are amplified, and the subsequent propagation of the waves in the source region and the Jovian plasmasphere. At present there exists no comprehensive theory that treats all of these aspects quantitatively within a single framework. Acceleration of particles by plasma sheaths near Io appears to be a promising explanation for the coupling mechanism, while most of the properties of the emission may be explained in the context of cyclotron instability of a highly anisotropic distribution of streaming particles. The present state of the theory is evaluated, and some suggested approaches for future work are discussed.
Smith, R. A.↗