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Recent experiments are described which directly intercompare very long baseline interferometry (VLBI) with laser ranging to artificial satellites by measuring the vector lengths of the same intercontinental baselines. These experiments are part of the VLBI/Laser-Intercomparison Project, a continuing task to assess the suitability of VLBI to various geophysical applications.
Based on Wilson's (1977) article on the magnetic effects on space vehicles and other celestial bodies, the magnetic damping of rotation is considered. The inadequacy of the interstellar magnetic field in overcoming solar wind shielding and thus influencing the rotation of bodies is described. The ionospheric shielding of the interstellar field is discussed along with the permeability and magnetic damping by the solar or stellar wind. Star formation and angular momentum is discussed and attention is given to the magnetic damping of unshielded small bodies. Calculations of the rate for damping through random particle impact are made. Theories concerning the rotation of asteroids and the origin of meteorites are reviewed. The shielding process of ionospheric plasmas is outlined and the damping effect of the geomagnetic field on the rotation of artificial satellites is evaluated.
An overview of NASA's involvement in developing systems for precise determination of polar motion, earth rotation, and position on the earth's surface is given. The observational methods discussed are laser ranging to the moon and to artificial satellites, and very long baseline microwave interferometry. A plan for a geodynamics program to apply space technology to research in earth dynamics is outlined.
In cooperation with other Federal government agencies, and the governments of other countries, NASA is undertaking a program of research in geodynamics. The present program activities and plans for extension of these activities in the time period 1979-1985 are described. The program includes operation of observatories for laser ranging to the Moon and to artificial satellites, and radio observatories for very long baseline microwave interferometry (VLBI). These observatories are used to measure polar motion, earth rotation, and tectonic plate movement, and serve as base stations for mobile facilities. The mobile laser ranging and VLBI facilities are used to measure crustal deformation in tectonically active areas.
Frequency of mutations in postflight air-dry Crepis capillaris seeds, kept for five days aboard an artificial satellite was 36.0 + or - 1.9%, vs. 19.01 + or - 1.2% for seeds in a similar ground experiment. Both groups of seeds were prepared in identical concentrations and were treated by the same mutagen. The spectrum of mutations in postflight Crepis capillaris seeds contained a large number of chromosome-type mutations and some cells showed multiple alterations. Postflight seeds not treated with mutagens had a slightly higher level of mutability.
A space object traveling through an atmosphere is governed by two forces: aerodynamic and gravitational. On this premise, equations of motion are derived to provide a set of universal entry equations applicable to all regimes of atmospheric flight from orbital motion under the dissipate force of drag through the dynamic phase of reentry, and finally to the point of contact with the planetary surface. Rigorous mathematical techniques such as averaging, Poincare's method of small parameters, and Lagrange's expansion, applied to obtain a highly accurate, purely analytic theory for orbit contraction and ballistic entry into planetary atmospheres. The theory has a wide range of applications to modern problems including orbit decay of artificial satellites, atmospheric capture of planetary probes, atmospheric grazing, and ballistic reentry of manned and unmanned space vehicles.
Earth artificial satellite methods are extended by means of two way Doppler data, to the computation of very accurate orbiter trajectories around another planet, and to the determination of its gravity field. It is reported that in the case of Mars, all observations collected by 10 Deep Space Network stations located at three different sites during the Mariner 9 and Viking 1 and 2 missions have been processed and used to compute a full twelfth degree and order spherical harmonic model of the gravitational potential. It is concluded that the aeroid derived from the model shows very large correlations with the Martian topography, raising questions as to the deep structure of the planet which cannot be interpreted on the basis of topographic and isostatic considerations alone.
Very long base interferometry (VLBI) and laser ranging to artificial satellites and the Moon were used to determined vector baselines between stations with precisions of about one part in 10 to the 8th power. Deformations and strain accumulations in active earthquake regions were determined by making frequent measurements of baselines between many stations in active areas near plate boundaries.
As the techniques of lunar and artificial satellite laser ranging mature, emphasis is being placed upon the use of these observations to monitor the earth's rotation. It is important to note, however, that at the present time neither technique alone can furnish all three components of this rotation to an accuracy which surpasses those results obtained from classical techniques. The present study represents the first stages of an investigation which has the objective to combine Lageos satellite and lunar laser ranging observations. It is hoped that the proper implementation of such a process might eliminate the shortcomings inherent in each technique, while accentuating the advantages of each. Attention is given to data and model compatibilities, analysis techniques, and numerical results. The presented results are indicative of the great progress which has been realized recently concerning an appropriate combination of Lageos and lunar laser ranging results
Advanced methods involving observations of extraterrestrial objects, such as artificial satellites or quasars, may make it possible to monitor geometrical variations in survey networks of regional, continental, and global scale with a spatial resolution of a few centimeters and a temporal resolution of better than one day. However, in connection with a realization of this potential, it is necessary to account for variations in the orientation of the earth in space. The accuracy provided by the conventional approaches for determining the orientation of the earth is not sufficient in this case. However, an appropriate method could be based on the utilization of independent clock radio interferometry (commonly referred to as VLBI) observations of extragalactic radio sources. The project POLARIS (Polar-motion Analysis by Radio Interferometric Sampling) is concerned with an implementation of this method. The MERIT (Monitor Earth Rotation and Intercompare the Techniques of observation and analysis) observations represent an aid to project POLARIS. Attention is given to details regarding these programs and the results obtained thus far.
This bibliography lists the publications sponsored by the NASA Wallops Flight Center/NASA Goddard Space Flight Center, Wallops Flight Facility during the period 1980 through 1983. The compilation contains citations listed by type of publication; i.e., NASA formal report, NASA contractor report, journal article, or presentation; by contract/grant number; and by accession number. Oceanography, astrophysics, artificial satellites, fluid mechanics, and sea ice are among the topics covered.
The classical methods of initial orbit determination are brought together within a larger viewpoint. This new synthesis stresses that all such techniques follow one of three approaches. Either they seek to compute the orbital element set, or its equivalent, by attacking the differential equations of motion (Laplace), the first integrals of the equations of motion (Taff), or the solution itself (Gauss). The particular technique pursued within a given type of approach should depend upon the nature of the observational data, the amount of a priori information one is willing to presume, and the object of the exercise. This might be a binary star system, a moon, a minor planet, or an artificial satellite. The efficacy of some algorithms for each approach is discussed briefly. Unfortunately, none of them work very well. Extensions of these techniques to radars or laser radars are trivial and have provided no new insights into the overall problem.
Major achievements in space sciences and exploration are briefly reviewed. Artificial satellites, space missions, planetology and space law are among the topics discussed.
Calculations include drag, nonsphericity, and other perturbations. Artificial Satellite Analysis Program (ASAP) is general orbit-prediction program that incorporates sufficient orbit-modeling accuracy for mission design, maneuver analysis, and mission planning. Suitable for studying planetary orbit missions with spacecraft trajectories of exploratory (mapping) nature. Sample data included for study of drift cycle of geosynchronous station, strategy for mapping Venus by radar, frozen orbit about Mars, and repeat-ground-trace orbit. ASAP written in FORTRAN 77.
After a brief description of the experiment to detect the gravitomagnetic field using high altitude laser ranged artificial satellites, several nongravitational perturbations that affect the LAGEOS nodal longitude are studied. It is shown that the error in the calculated value of the secular nodal precession or the value of the secular nodal precession itself is, for each perturbation, less than 1 percent of the gravitomagnetic drag.
The current state of understanding of the biosphere is reviewed, the major scientific issues to be addressed are discussed, and techniques, existing and in need of development, for the science are evaluated. It is primarily concerned with developing the scientific capabilities of remote sensing for advancing the subject. The global nature of the scientific objectives requires the use of space-based techniques. The capability to look at the Earth as a whole was developed only recently. The space program has provided the technology to study the entire Earth from artificial satellites, and thus is a primary force in approaches to planetary biology. Space technology has also permitted comparative studies of planetary atmospheres and surfaces. These studies coupled with the growing awareness of the effects that life has on the entire Earth, are opening new lines of inquiry in science.
A technique is described to estimate the area-to-mass ratio of debris fragments using orbital fragments obtained by radar. The area-to-mass ratio of about 2600 fragments arising from the breakup of 24 artificial satellites was determined; an analysis of the data on about 200 objects with known mass, size, and shape has been made, and a calibration of the observed radar cross-section (RCS) to the effective area of these objects has provided a method to estimate the effective area of debris fragments. From the knowledge of the effective area and the estimated area-to-mass ratio, the mass and area distribution of each of the known breakup has been obtained. As a function of time, the orbital elements can be used to invert any propagation algorithm to yield the area-to-mass ratio of an orbiting object.
Rotating shield steers thrust in desired direction. Report discusses use of thrust-vector deflectors (TVD's) to enhance controllability and reduce number of small rocket engines (thrustors) needed to control attitudes of artificial satellites. Developed in aircraft industry for use in jet engines. Principal advantages gained, lower cost and greater simplicity.