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At least 397 records · Page 22

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NASA NTRS1972

Performance of recoverable single and multiple Space Tugs for missions beyond earth escape.

A recoverable Space Tug launched by the Space Shuttle can provide the required post-orbital propulsion needed for placement of unmanned satellites. The Space Tug will also be used to launch interplanetary spacecraft from low earth orbit. This study summarizes the performance of single and multiple Space Tugs (in tandem) for launching spacecraft beyond earth escape. Trajectories are developed that allow recovery of the Tugs whenever practical. The effects of important Tug and trajectory parameters on performance are presented. It is concluded that a single Tug can inject spacecraft to Mars or Venus and still be recovered. The use of several Tugs in tandem can provide a significant increase in capability over the use of a single Tug. The more difficult missions involve a mix of recovered and expended Tugs.

Zimmerman, A. V.↗

NASA NTRS1974

Blowoff and escape of H2

It is shown that a pure hydrogen atmosphere cannot be retained by Titan, but will blow off in a few hours. Addition of a heavier gas, such as CH4 or N2, in comparable abundance gives a great improvement, although the escape rate can still be large. Moreover, the actual flux can be predicted with confidence from the mixing ratio of H2 to heavy gas.

Hunten, D. M.↗

NASA NTRS1975

Dynamic-stability tests on an aircraft escape module at Mach numbers from 0.40 to 2.16

Wind-tunnel measurements of the aerodynamic damping and oscillatory stability of a model of a proposed escape module for a military aircraft have been made using a small-amplitude forced-oscillation technique in pitch and yaw at Mach numbers from 0.40 to 2.16 and in roll at Mach numbers from 0.40 to 1.20. The results in pitch indicate regions in the angle-of-attack range where the model exhibits large and rapid changes in both damping and stability with angle of attack, probably caused by vortex flow over the fins. There was no pronounced effect of change in angle of attack on damping in yaw. Except for the highest Mach number, negative damping in roll was produced at high negative angles of attack.

Davenport, E. E.↗

NASA NTRS1976

Longitudinal asymmetry of the Jovian magnetosphere and the periodic escape of energetic particles

An earlier model of the Jovian magnetosphere is utilized in which the centrifugal stress of corotating plasma distends the outer magnetosphere and opens the tail field. Because of a longitudinal asymmetry in the ionospheric plasma source strength, caused principally by the nonaxisymmetric surface field, the closed-field region in the tail expands and contracts with the rotation period, resulting in a 10-hour modulation of the flux of energetic particles escaping from the magnetosphere into interplanetary space.

Hill, T. W.↗

NASA NTRS1977

Longitudinal and lateral-directional static aerodynamic characteristics of an unpowered escape system extraction rocket model

An escape system extraction rocket proposed for use on the Rotor Systems Research Aircraft was tested at Mach numbers of 0.1 and 0.3 through an angle of attack range from -2 deg to 102 deg and an angle of sideslip range from 0 deg to 15 deg in the Langley 7- by 10-foot high speed tunnel.

Huffman, J. K.↗

NASA NTRS1977

Longitudinal and lateral-directional static aerodynamic characteristics of an unpowered escape system extraction rocket model with attached launch tubes

Huffman, J. K.↗

NASA NTRS1977

Charge exchange in a planetary corona - Its effect on the distribution and escape of hydrogen

The theory for a spherical collisionless planetary corona is extended to include charge-exchange collisions between H(+) and H, which are assumed to constitute intermingled gases with different kinetic temperatures. The treatment is based on the conventional concept of a critical level (or exobase) above which the only collisions considered in the Boltzmann equation are those that resonantly exchange charge. Although the geometry treated is an oversimplification for a real planet, numerical examples are given for an idealized earth and Venus. For earth, an ion temperature of 4 times the neutral temperature, an ion density at the exobase of 14,000 per cu cm, and a plasmapause at 1.5 earth radii will raise the escape flux of H by a factor of 6. The total H above the exobase is changed by less than 1%. For Venus, conditions are examined that would account for the peculiar H distribution observed from Mariner 5. The plasma conditions required are not obviously outrageous by terrestrial standards, but the Mariner 5 ionosphere measurements did not show a high plasmapause at, say, 1.25 or 1.5 planetary radii, a fact that might argue against a charge-exchange model.

Chamberlain, J. W.↗

NASA NTRS1978

Rigidity-independent coronal propagation and escape of solar protons and alpha particles

In a study of rigidity-independent coronal propagation processes, data on the azimuthal variation of the solar proton/alpha-particle ratio were obtained. Sources for the data included a statistical analysis of events observed by Heos-2, a comparative study of events recorded by both Heos-2 and Pioneer-10 and -11, and a multiday survey of individual events observed by Heos-2 and Pioneer-10. The statistical investigation of Heos-2 events reveals an increase of the lower value of the proton/alpha-particle ratio away from the well-connected region. The data from one or two spacecraft connected at different heliolongitudes indicates no azimuthal dependence of the proton/alpha-particle ratio. All the data appear to suggest rigidity-independent propagation or escape processes.

Perron, C.↗

NASA NTRS1977

Lightning tests of the orbiter pyrotechnic escape system

An experimental test program was undertaken to demonstrate that the Space Shuttle Orbiter Vehicle pyrotechnics actuated Crew Escape System was not subject to failure resulting from a lightning strike in the vicinity of the cockpit. A test sample representing a full-scale portion of the Orbiter Outer Panel was preheated to 325 F and struck with three different current waveforms to simulate the various effects of lightning: (1) 2 micro sec risetime, to 180 kA pulse to evaluate fast current rise shock effects; (2) a 205 kA, 100 micro sec wide pulse to evaluate full energy shock effects; and (3) a 490 ampere, 370 msec continuing current to evaluate the thermal effects of a lightning strike. These tests show that the Orbiter outer panel pyrotechnics are adequately protected against damage resulting from a lightning strike.

Cohen, R.↗

NASA NTRS1979

Helicopter /RSRA/ in-flight escape system - Component qualification

The paper describes the design, development, and qualification approach for the RSRA (Rotor Systems Research Aircraft) system explosive and pyrotechnic components. The approach was based on previous experience and included: (1) the application of good design practice and quality control, (2) a thorough examination of component interfaces through demonstration testing of functional margins, (3) the carrying out of thorough real-world sequential environmental testing, and (4) the operation of environmentally exposed units in subsystem-level tests at temperature, force, and energy limits. Owing largely to this approach, the RSRA became the first helicopter system to contain a fully qualified and operational in-flight escape system.

Bement, L. J.↗

NASA NTRS1980

Energetic particle recurrence and escape during solar cycle 20

Low-energy solar particle data have been combined from a multi-spacecraft near-earth data set covering most of solar cycle 20 (1966-1976). Particle intensity profiles have been ordered in the natural heliographic coordinate system of the estimated high coronal connection longitude of the foot point of the interplanetary field line. The recurrence trends of approximately 1-MeV solar particles become more apparent in this coordinate system than when plotted versus time, and thereby extend the evidence for regions of continual injection and escape from the corona. Intercomparison of solar particles and solar wind streams in heliographic longitude suggests that the origin of stream-associated spatial particle events seen at 1 AU is solar rather than interplanetary.

Gold, R. E.↗

NASA NTRS1981

The effects of CO and HCN on pole-jump avoidance-escape behavior

The effects of carbon monoxide and mixtures of carbon monoxide and hydrogen cyanide at different concentrations and times of exposure were studied in a pole-jump apparatus. The time to loose the avoidance and escape response for mice exposed to these atmospheres was obtained. Correlations to predict the loss as a function of dosage are presented.

Winslow, W.↗

NASA NTRS1983

Pupillary escape intensified by large pupillary size

Pupil responses to light are greatly influenced by initial pupil size. Small pupils, operating under photopic conditions, show tonic responses to step increases of light and high gains; thus the pupil is a good regulator of light. Large pupils, operating under mesopic or scotopic conditions show phasic responses, 'pupillary escape', and smaller gains: the pupil only transiently influences retinal flux. By using accommodation level to set the size of the pupil, the mechanism of the 'pupil size effect' is shown to be dependent on retinal light level only so far as retinal activity sets pupil size.

Stark, L.↗

NASA NTRS1983

A two-stage mechanism for escape of Na and K from Io

A two-stage process is presented to identify Io as the source of Na and K ions in the Io plasma torus. The Voyager I IRIS experiment recorded an SO2 abundance of 0.2 cm atm in the Io subsolar region, and further calculations determined that the S(+) and O(+) would have sufficient energy to penetrate the Io atmosphere and produce sputtering of surface atoms at a rate of 800 million/sq cm per sec. If K, Na, and S are present on the surface in cosmic proportions, then an evenly applied sputter distribution would produce the same abundances of sputtered Na and K as observed in the Na and K clouds around Io. Sputtered into the atmosphere, the ions undergo thermal Jean's escape and attain velocities of at least 2.6 km/sec. The sputtering ions are a factor of two greater on the Jupiter side than on the solar side, in agreement with asymmetries measured by the Voyager.

Summers, M. E.↗

NASA NTRS1983

Nitrogen escape from Mars

The escape rate of nitrogen from Mars is calculated to be 2.3 x 10 to the 5th per sec for low solar flux conditions and 8.9 x 10 to the 5th per sec for high solar flux conditions. The major source of energetic atoms is dissociative recombination of ground state and vibrationally excited N2(+) ions. The measured N-15/N-14 isotope ratio can be reproduced by postulating an early dense atmosphere during which little differentiation occurred.

Fox, J. L.↗

NASA NTRS1984

Photon escape probabilities in a semi-infinite plane-parallel medium

It is shown in this work how to obtain the probabilities of photons escaping from a cold electron plasma environment after having undergone an arbitrary number of scatterings. This is done by retaining the exact differential cross section for Thomson scattering as opposed to using its polarization and angle averaged form. The results are given in the form of recursion relations. The geometry used is the semi-infinite plane-parallel geometry witlh a photon source located on a plane at an arbitrary optical depth below the surface. Analytical expressions are given for the probabilities which are accurate over a wide range of initial optical depth. These results can be used to model compact X-ray galactic sources which are surrounded by an electron-rich plasma.

Williams, A. C.↗

NASA NTRS1984

Electron escape depth variation in thin SiO2 films measured with variable photon energy

A double crystal monochromator at the Stanford Synchrotron Radiation Laboratory is used to study the Si/SiO2 interface, using photon energies of hv = 1950-3700 eV. This photon energy range allows interfaces to be observed through oxide layers 50 A thick or more. Variations in electron escape depth and/or oxide density as a function of distance from the interface are observed over the entire kinetic energy range (100-3600 eV). These differences are attributed to a strained oxide layer near the interface.

Hecht, M. H.↗

NASA NTRS1984

First-flight escape from spheres with R(-2) density distribution

Energy-independent first-flight transport kernels are evaluated for a spherical region with an R(-2) density distribution. The uncollided angular-flux distribution is obtained and integrated for a source distribution that is proportional to the density to give the uncollided emitted particle flux and current density. These are useful for the calculation of mass, energy, and momentum carried away by fast particles born in the medium. The data are relevant to estimate escape from weakly bound atmospheres such as comet comae, dilute circumstellar envelopes, and some unconfined laboratory plasmas.

Huebner, W. F.↗