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NASA NTRS1982

Solar wind energy transfer through the magnetopause of an open magnetosphere

An expression is derived for the total power, transferred from the solar wind to an open magnetosphere, which consists of the electromagnetic energy rate and the particle kinetic energy rate. The total rate of energy transferred from the solar wind to an open magnetosphere mainly consists of kinetic energy, and the kinetic energy flux is carried by particles, penetrating from the solar wind into the magnetosphere, which may contribute to the observed flow in the plasma mantle and which will eventually be convected slowly toward the plasma sheet by the electric field as they flow down the tail. While the electromagnetic energy rate controls the near-earth magnetospheric activity, the kinetic energy rate should dominate the dynamics of the distant magnetotail.

Lee, L. C.↗

NASA NTRS1982

On the three-dimensional magnetic structure of the plasmoid created in the magnetotail at substorm onset

The magnetic field in the plasmoid which is created by the reconnection of magnetic field lines at a neutral line formed in the near-earth region of the plasma sheet at substorm onset, and which flows out of the magnetotail into the magnetosphere's wake, displays a strong positive or negative Y(SM) component that has been difficult to reconcile with the standard, two-dimensional reconnection geometry. It is shown that this deviation of the magnetic field is a manifestation of the newly-reconnected field line loop's draping toward the tail's central or midnight meridian, and that the draping is a consequence of the three-dimensional plasma flow associated with the reconnection process.

Hones, E. W., Jr.↗

NASA NTRS1982

Model simulations of possible electromagnetic induction effects at Magsat activities

Model simulations are used in a consideration of whether terrestrial induced-current magnetic field effects are significant for near-earth satellite observation, and the nature of the effect at satellite altitudes of lateral differences in the gross conductivity structure of the earth. It is shown that induction in a spherical earth by distant magnetospheric sources can contribute magnetic field fluctuations at Magsat orbit altitudes which are 30-40% of external field amplitudes. It is found that, when phenomenon dimensions are small by comparison with the earth's radius, the earth may be approximated by a plane, horizontal half-space by which electromagnetic energy is reflected with nearly 100% efficiency from the surface. This implies that while the total horizontal field is twice the source field when the source is above the satellite, it is reduced to values smaller than the source field when the source is below the satellite and tends to enhance gross electrical discontinuity signatures in the lithosphere.

Hermance, J. F.↗

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 NTRS1982

Mean gravity anomalies from a combination of Apollo/ATS 6 and GEOS 3/ATS 6 SST tracking campaigns

Advances in satellite tracking data accuracy and coverage over the past 15 years have led to major improvements in global geopotential models. But the spacial resolution of the gravity field obtained solely from satellite dynamics sensed by tracking data is still of the order of 1000 km. Attention is given to an approach which will provide information regarding the fine structure of the gravity field on the basis of an application of local corrections to the global field. According to this approach, a basic satellite to satellite tracked (SST) range-rate measurement is constructed from the link between a ground station, a geosynchronous satellite (ATS 6), and a near-earth satellite (Apollo or GEOS 3). Attention is given to a mathematical model, the simulation of SST gravity anomaly estimation accuracies, a gravity anomaly estimation from GEOS 3/ATS 6 and Apollo/ATS 6 SST observations, and an evaluation of the mean gravity anomalies determined from SST.

Kahn, W. D.↗

NASA NTRS1982

A catalog of gamma-ray bursts with earth crossing times

A catalog of 111 confirmed gamma-ray bursts detected between 1967 July and 1979 June is presented. Both localization information and earth crossing times for the gamma-ray wave fronts are given. Data which have appeared in some previous catalogs have been revised; many previously unpublished events detected by an international network of dedicated deep space and near-earth experiments since 1976 are also presented.

Klebesadel, R.↗

NASA NTRS1982

NASA space photovoltaic research and technology programs

The NASA programs for increasing conversion efficiency, reduced mass and cost, and extending operating life of photovoltaic converters and arrays and for evaluating advanced solar array concepts are outlined. Research into radiation resistance and annealing, development of thin blankets, high-power low-cost arrays, and lightweight structures for near-Earth and planetary applications are discussed.

Mullin, J. P.↗

NASA NTRS1982

Radio frequency selection and interference prevention

The bands available for deep-space communications, and the choice of particular mission frequencies are discussed. The more general susceptibility of deep-space Earth stations to various kinds of interference is then presented. An associated topic is the development of protection criteria that specify maximum allowable levels of interference. Next, the prediction of interference from near-Earth satellites is described, with particular emphasis on the problems and uncertainties of such predictions. Finally, a brief description of other activities aimed at the prevention or avoidance of interference to deep-space radio communications is given.

Degroot, N. F.↗

NASA NTRS1982

Requirements for a space station

Near-term requirements which will guide the design of a manned space station in near-earth orbit are considered. A primary focus will be establishing a base for astronomical observations which demand long term integration times. Earth observation systems such as the thematic mappers and SAR can be utilized by a free flyer in sunsynchronous orbit. Biological experiments can be carried out only with pressurized modules, ultimately large enough for humans habitation. At first, expendables would be ferried up from earth, while over time the space station would become a closed-loop system. An orbital transfer vehicle is necessary for the repair of satellites stationed in higher energy orbits. The operations of the station would include checking out communications satellites before boost into GEO. Finally, the station would be the final staging point for interplanetary and/or asteroid intercept missions.

Herman, D. H.↗

NASA NTRS1982

Magsat data availability

It is pointed out that a new era in near-earth magnetic field measurements began with NASA's launch of Magsat in October 1979 into a twilight, sun-synchronous orbit with 96.76 deg inclination, 561-km apogee, and 352-km perigee. A cesium vapor and a fluxgate magnetometer were employed to measure the magnetic field. A measurement of the spacecraft attitude to 20 arcseconds was required to achieve 6 nT (nanotesla) accuracy in the component measurements. This was accomplished with the aid of two star cameras on board the spacecraft and a sun sensor attached to the vector magnetometer. Magsat remained in orbit until June 11, 1980. Magsat has conducted the first truly global geomagnetic survey since the studies performed by the Polar Orbiting Geophysical Observatory (POGO) satellites. A global vector survey was provided of the main geopotential field and lower altitude measurements of crustal anomalies were conducted. Details concerning the availability of these data are discussed.

Langel, R. A.↗

NASA NTRS1983

Trajectory analysis of radiative heating for planetary missions with aerobraking of spacecraft

The aerodynamic drag generated during a grazing pass through a planetary atmosphere can be used to expend energy which a spacecraft has in excess of that required to achieve a closed orbit. The propulsion fuel mass saved by eliminating retropropulsive braking maneuvers makes possible missions which are otherwise impossible or impractical. The present investigation has the objective to examine the influence of atmospheric entry trajectory parameters on the magnitude of the radiative heating rates for both the Titan aerocapture and near-earth orbital transfer missions. Calculations are performed for a wide range of entry conditions encompassing those of many conceptual mission scenarios for both Titan and earth. It is found that the nonequilibrium radiative heating is enhanced over that for equilibrium and generally exceeds that for convection for most mission profiles. Nonequilibrium radiation heating is, therefore, an important factor in the design of the corresponding thermal protection systems.

Menees, G. P.↗

NASA NTRS1981

Array-fed reflector antenna design and applications

One phase of the spacecraft antenna research carried out at the Jet Propulsion Laboratory for deep space and near-earth communications is described. Array-fed reflector antenna designs have been elaborated for beam scanning, power amplification, and multiple beam applications. The antenna designs derive from similar optical concepts. Each antenna comprises a relatively small plane-wave array feeding a near-field dual-reflector system. The main reflector and the the subreflector are confocal paraboloids having identical focal length to diameter ratios. The array feed is positioned in such a way that the subreflector is in the near-field (collimated beam) region of the feed. The field distribution of the feed aperture is thereby recreated approximately in the main reflector aperture. The detailed design concepts of the antennas (beam-scanning, high-power, and mutliple-beam) are discussed, and the calculated and measured RF performances of the antennas are presented.

Woo, K.↗

NASA NTRS1982

Particle acceleration by coronal and interplanetary shock waves

Utilizing many years of observation from deep space and near-earth spacecraft a theoretical understanding has evolved on how ions and electrons are accelerated in interplanetary shock waves. This understanding is now being applied to solar flare-induced shock waves propagating through the solar atmosphere. Such solar flare phenomena as gamma-ray line and neutron emissions, interplanetary energetic electron and ion events, and Type II and moving Type IV radio bursts appear understandable in terms of particle acceleration in shock waves.

Pesses, M. E.↗

NASA NTRS1982

Geological implications of impacts of large asteroids and comets on the earth

The present conference discusses such topics as large object fluxes in near-earth space and the probabilities of terrestrial impacts, the geological record of impacts, dynamics modeling for large body impacts on continents and oceans, physical, chemical, and biological models of large impacts' atmospheric effects, dispersed impact ejecta and their signatures, general considerations concerning mass biological extinctions, the Cretaceous/Tertiary boundary event, geochemical signatures in the stratigraphic record, and other phanerozoic events. Attention is given to terrestrial impact rates for long- and short-period comets, estimates of crater size for large body impact, a first-order estimate of shock heating and vaporization in oceanic impacts, atmospheric effects in the first few minutes after an impact, a feasibility test for biogeographic extinction, and the planktonic and dinosaur extinctions.

Silver, L. T.↗

NASA NTRS1960

A Two-Impulse Plan for Performing Rendezvous on a Once-A-Day Basis

An investigation of a two-impulse plan for performing rendezvous on a once-a-day basis with a near-earth satellite station indicates that launch into rendezvous from slightly less than maximum satellite latitude is an unusually favorable circumstance in that no appreciable expense in mass ratio is incurred. In addition, it was found for the two-impulse maneuver employed in this study that the optimum angular travel of the ferry vehicle to rendezvous was considerably less than the 1800 transfer which is optimum for the two-impulse in-plane launch.

Bird, John D.↗

NASA NTRS1970

HELIOS Third Joint Working Group Meeting

During the past six months since the Second Helios Joint Working Group Meeting held 27-30 April 1970 at Goddard Space Flight Center, the TDS Sub-Group supported the Helios Project Office and the other Sub-Groups in the timely disposition of action items and the dissemination of information pertinent to the development of interface documentation. Of particular importance during this time period was the Project's decision to incorporate a single-channel telemetry system design aboard the spacecraft. The TDS Sub-Group participated actively in the process that led to this decision. Still under active study with TDS participation is the pending Project Office decision regarding the incorporation of a ranging capability within the telecommunications design. The TDS Sub-Group assisted the Mission Analysis and Operations Sub-Group in establishment of a study effort concerning the Near-Earth Sequence of Events from launch to launch plus 8 hours. This study, which will provide valuable data for the spacecraft telecommunications design, will include participation by the Experiment, Launch Vehicle, Spacecraft, as well as the TDS and MA&O Sub-Groups. Also during the past 6-month period, the TDS, in conjunction with the Spacecraft Sub-Group, initiated activity to develop the Helios Spacecraft/TDS Compatibility Test Plans and Procedures. Activity concerning the foregoing interface discussions has been and will continue to be based upon the "TDS Estimated Capabilities Document for the Helios Missions" (613-1), and the "DSN/Flight Project Interface Design Handbook" (810-5). These will continue to be considered TDS controlling documents until specific Helios Project/TDS interface documentation is generated and signed off by the respective parties. In addition to the above, the DSN continued the Helios Trainee Program with seven GfW/DFVLR trainees in residence at JPL. Two trainees will complete their year's residency concurrent with the Third Helios Joint Working Group Meeting, while four new trainees are expected to arrive following the Third Helios Joint Working Group Meeting. These and other activities are reported in detail in the paragraphs that follow.

Ousley, Gilbert↗

NASA NTRS1961

Determination of the Required Number of Randomly Spaced Communication Satellites

An investigation has been made f o r determining the minimum number of passive satellites i n near-earth orbits required t o provide given percentages of communication time between two selected ground stations. The study is limited to the geometrical and probability aspects of the problem. An application of the analysis i s made f o r an assumed transatlantic communication system. The satellites are considered t o be i n circular, randomly spaced orbits with fixed inclination and altitude considered range from 1,000 t o 3,000 statute miles.

Bennett, Floyd V.↗

NASA NTRS1961

Flight Performance Handbook for Orbital Operations: Orbital Mechanics and Astrodynamics Formulae, Theorems, Techniques, and Applications

This handbook provides parametric data useful both to the space vehicle designer and mission analyst. It provides numerical and analytical relationships between missions and gross vehicle characteristics as a function of performance parameters. The effects of missile constraints and gross guidance limitations plus operational constraints such as launch site location, tracking net location, orbit visibility and mission on trajectory and orbit design parameters are exhibited. The influence of state-of- the-art applications of solar power as compared to future applications of nuclear power on orbit design parameters, such as eclipse time, are among the parameters included in the study. The principal aim, however, is in providing the analyst with useful parametric design information to cover the general area of earth satellite missions in the region of near-earth to cislunar space and beyond and from injection to atmospheric entry and controlled descent. The chapters are organized around the central idea of orbital operations in the 1961-1969 era with emphasis on parametric flight mechanics studies for ascent phase and parking orbits, transfer maneuvers, rendezvous maneuver, operational orbit considerations, and operational orbit control. The results are based almost entirely on the principles of flight and celestial mechanics. Numerous practical examples have been worked out in detail. This is especially important where it has been difficult or impossible to represent all possible variations of the parameters. The handbook contains analytical formulae and sufficient textual material to permit their proper use. The analytic methods consist of both exact and rapid, approximate methods. Scores of tables, working graphs and illustrations amplify the mathematical models which, together with important facts and data, cover the engineering and scientific applications of orbital mechanics. Each of the five major chapters are arranged to provide a rapid review of an entire astrodynamic subject. By the use of compact graphical and tabular presentation the full scope of the material is made available in an easy-to-use style. Throughout the volume the analyst is shown, by means of suitable introductions, notes, authoritative examples, and cross-references the vital interrelation of the various orbital mechanics topics in the general field of earth satellites and satellite rendezvous. The handbook is designed to give the analyst rapid, reliable access to the mathematics of orbital mechanics needed for virtually any working requirements.

Ambrosio, Alphonso↗