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The Near Earth Asteroid Rendezvous (NEAR) spacecraft was occulted by the solar disk on February 19, 1997. During the period between February 7 and March 3, 1997, the Near X-band telecommunications system was used to carry out a combination of engineering and radio science measurements through the solar corona.
NASA has successfully used debris avoidance maneuvers to protect our spacecraft for more than 20 . years. This process which started out using parametric data and maneuver boxes has seen considerable evolution and now allows us to continue nominal operations for all but the most threatening objects. This has greatly reduced the interruptions to the critical mission objectives being pursued by NASA s Space Station, Space Shuttle, and robotic satellites.
Mars Mission profile options and mission requirements data are presented for earth-Mars opposition and conjuction class round-trip flyby and stopover mission opportunities. The opposition class flyby and sprint mission uses direct transfer trajectories to and on return from Mars. The opposition-class stopover mission employs the gravitational field of Venus to accelerate the space vehicle on either the outbound or inbound leg in order to reduce the propulsion requirement associated with the opposition-class mission. The conjuction-class mission minimizes propulsion requirements by optimizing the stopover time at Mars. Representative interplanetary space vehicle systems are sized to compare and show sensitivity of the initial mass required in low earth orbit to one mission profile option and mission opportunity to another.
Dislocation climb is an important high temperature process in metals plasticity, responsible for the phenomena such as creep, swelling, or hardening. Climb is defined by the ability of dislocations to leave their original glide plane by interacting with point defects. As such, dislocation climb is controlled by point defect diffusion/absorption/emission, all of which involve thermal activation. The existing thermodynamically consistent models for climb are generally formulated in a continuum framework, through the definition of effective defect fluxes and climb propensities in response to thermodynamic driving forces. However, the point-wise discrete nature of vacancies (and/or self-interstitials) confers a highly discrete nature to the climb dynamics, which is also strongly affected by elastic forces. The combination of discreteness, thermal activation, and elasticity makes this process too challenging for direct atomistic methods such as molecular dynamics. Here we develop a kinetic Monte Carlo model that captures vacancy generation and transport kinetics acting in conjuction with the evolving elastic fields provided by discrete dislocation dynamics simulations. The two models are coupled via the applied stresses and stress gradients generated by dislocation structures at vacancy locations. Our simulations reveal two surprising results. First that climb is dominated by vacancy emission even when the background vacancy concentration is much higher than the equilibrium one. And, second, that climb velocities might be much faster than otherwise believed when one uses the classical theories of climb. These effects are due to the locality of vacancy-dislocation processes, which are not captured in classical treatments that assume smooth vacancy fluxes and homogeneous concentrations. We apply the method to study elementary climb processes in body-centered cubic iron and furnish climb mobility functions to be used in parametric dislocation dynamics and/or crystal plasticity simulations. Here, we apply the technique to study non-conservative plastic bypass of spherical precipitates by edge dislocations and point out the differences between our discrete approach and existing continuum formulations.
Reliable prediction of freezing point depression in liquid electrolytes will accelerate the development of improved Li-ion batteries which can operate in low temperature environments. In this work we establish a computational methodology to calculate activity coefficients and liquidus lines for battery-relevant liquid electrolytes. Electronic structure methods are used in conjuction with classical molecular dynamics simulations and theoretical expressions for Born solvation energy, ion-atmosphere effects from Debye-Hückel theory and solvent entropic effects. The framework uses no a priori knowledge beyond neat solvent properties and the concentration of salt. LiPF 6 in propylene carbonate (PC), LiPF 6 in dimethyl carbonate (DMC) and LiClO 4 in DMC are investigated up to 1 molal with accuracy better than 3 °C when compared to experimental freezing point measurements. Finally, we find that the difference in freezing point depression between the propylene carbonate-based electrolyte and the dimethyl carbonate electrolytes originates from the difference in the solvent dielectric constant.
Load weighing cell used in conjuction with a hoist is isolated during lifting and manipulation of the load. A simple mechanism, attached to a crane hook, provides a screw adjustment for engaging the load cell during weighing of the load and isolating it from lift forces during hoisting of the load.
A comprehensive, Del V (magnitude of impulsive velocity-change vector) study of short staytime (0 to 30 days), short total trip time (10 to 160 days) round trip landing missions (fast missions) is presented. The characteristics of the following selected round trip landing missions are described: mission A (fast mission) with 120-day total trip time, 0-day stay-time, and 73,000-fps total mission Del V; mission B (opposition class) with 380-day total trip time, 0-day staytime, and 52,000-fps total mission Del V; and mission C (conjuction class) with 540-day total trip time, 175-day staytime, and 39,000-fps total mission Del V. A study of large-tank Agena, chemical propulsion stage (CPS), and nuclear stage was conducted. A payload of 5000 pounds was assumed. The propulsion requirements for mission A were found to be two large-tank Agenas and ten CPSs (or alternatively, two large-tank Agenas and five nuclear stages) while mission B required two large-tank Agenas and two CPSs. Mission C can be performed with one large-tank Agena and one CPS.
The activities leading to a tentative concept selection for a pressure-fed engine and propulsion support are outlined. Multiple engine concepts were evaluted through parallel engine major component and system analyses. Booster vehicle coordination, tradeoffs, and technology/development aspects are included. The concept selected for further evaluation has a regeneratively cooled combustion chamber and nozzle in conjuction with an impinging element injector. The propellants chosen are LOX/RP-1, and combustion stabilizing baffles are used to assure dynamic combustion stability.
The development of a control system to accommodate the scientific payload of the High Energy Astronomy Observatory (HEAO) is discussed. One of the critical elements of the system is the star tracker subsystem, which defines an accurate three-axis attitude reference. A digital computer program has been developed to evaluate the ability of a particular star tracker configuration to meet the requirements for attitude reference at various vehicle orientations. Used in conjuction with an adequate star catalog, the computer program provides information on availability of stars for each tracker and on the ability of the system to maintain three-axis attitude reference throughout a representative sequence of vehicle orientations.
A technique has been developed to detect the characteristic spectral signatures of healthy and infected St. Augustine grass. It is possible to predict the coverage of the infected area provided ground truth coverage shows positive St. Augustine grass turf. Qualitative measurements from photographs of plants in the blue and red regions with polarization show that light reflected from healthy plants is more strongly polarized than that from diseased plants. Photographs taken through the blue Wratten 47 filter in conjuction with a polarizer show an excellent differentiation. A large photographic difference also appears in the red region. Much smaller differences were noted in the 540 to 550 nm region. Although the intensity in the near-IR region is much higher than the visible region of the spectrum, differences in the healthy and diseased plants' reflectance were quite small.
A definition of the expendable second stage and space shuttle booster separation system is presented. Modifications required on the reusable booster for expendable second stage/payload flight and the ground systems needed to operate the expendable second stage in conjuction with the space shuttle booster are described. The safety, reliability, and quality assurance program is explained. Launch complex operations and services are analyzed.
A method for computing the lifting pressure distribution on a wing with partial span, swept control surfaces is presented. This method is valid within the framework of linearized, steady, potential flow theory and consists of using conventional lifting surface theory in conjuction with a flap pressure mode. The cause of a numerical instability that can occur during the quadrature of the flap pressure mode is discussed, and an efficient technique to eliminate the instability is derived. This technique is valid for both the flap pressure mode and regular pressure modes and could be used to improve existing lifting surface methods. Examples of the use of the flap pressure mode and comparisons among this method, other theoretical methods, and experiments are given. Discrepancies with experiment are indicated and candidate causes are presented. It is concluded that the method can lead to an efficient and accurate solution of the mathematical problem when a partial span, trailing edge flap is involved.
Previous work in the development of quantitative models for the prediction of passenger reaction to motion and vehicle environment parameters in flight was extended to include a class of aircraft appropriate for low-density, short-haul service. The results indicate that it is possible to obtain quantitative response inputs from an usually small special test-subject group which will be representative of the general traveling public. Additional data which indicate the importance of comfort as a factor in evaluating ride quality was obtained, and identification of the factors which contribute to judgments regarding comfort level was improved. Seat comfort and seat spacing is very vital in the smaller aircraft. Mathematical modeling applied in conjuction with passenger reaction data was shown to be very useful for establishing ride-quality design criteria.
Comparisons and analyses were carried out through the use of detailed gravimetric geoids which we have computed by combining models with a set of 26,000 1 deg x 1 deg mean free air gravity anomalies. The accuracy of the detailed gravimetric geoid computed using the most recent Goddard earth model (GEM-6) in conjunction with the set of 1 deg x 1 deg mean free air gravity anomalies is assessed at + or - 2 meters on the continents of North America, Europe, and Australia, 2 to 5 meters in the Northeast Pacific and North Atlantic areas, and 5 to 10 meters in other areas where surface gravity data are sparse. The R.M.S. differences between this detailed geoid and the detailed geoids computed using the other satellite gravity fields in conjuction with same set of surface data range from 3 to 7 meters.
A finite element stress analysis was performed for the film cooled throat section of an attitude control thruster. The anlaysis employed the RETSCP finite element computer program. The analysis included thermal and pressure loads, and the effects of temperature dependent material properties, to determine the strain range corresponding to the thruster operating cycle. The configuration and operating conditions considered, correspond to a flightweight integrated thruster assembly which was thrust pulse tested. The computed strain range was used in conjuction with Haynes 188 Universal Slopes minimum life data to predict throat section fatigue life. The computed number of cycles to failure was greater than the number of pulses to which the thruster was experimentally subjected without failure.
Treatment is given of system response evaluation, especially in application to subcritical flight and wind tunnel flutter testing of aircraft. An evaluation is made of various existing techniques, in conjuction with a companion survey which reports theoretical and analog experiments made to study the identification of system response characteristics. Various input excitations are considered, and new techniques for analyzing response are explored, particularly in reference to the prevalent practical case where unwanted input noise is present, such as caused by gusts or wind tunnel turbulence. Further developments are also made of system parameter identification techniques.
Frequency bands that best discriminate the Korotkov sounds at systole and at diastole from the sounds immediately preceding these events are defined. Korotkov sound data were recorded from five normotensive subjects during orthostatic stress (lower body negative pressure) and bicycle ergometry. A spectral analysis of the seven Korotkov sounds centered about the systolic and diastolic auscultatory events revealed that a maximum increase in amplitude at the systolic transition occurred in the 18-26-Hz band, while a maximum decrease in amplitude at the diastolic transition occurred in the 40-60-Hz band. These findings were remarkably consistent across subjects and test conditions. These passbands are included in the design specifications for an automatic blood pressure measuring system used in conjuction with medical experiments during NASA's Skylab program.
Vectorcardiograms were recorded via a modified Frank lead system from all crewmen of the three Skylab missions in conjuction with the Lower Body Negative Pressure - M092 Experiment. Data were analyzed by a specially developed computer program (VECTAN). Design of the test sequences allowed direct comparisons of supine resting, Earth based (reference) vectorcardiograms with those taken during lower body negative pressure stress and those obtained at rest in orbit, as well as combinations of these conditions. Results revealed several statistically significant space flight related changes; namely, increased testing and lower body negative pressure stressed heart rates, modestly increased PR interval and corrected QTC interval, and greatly increased P and QPS loop maximal amplitudes. In addition, orientation changes in the QRS maximum vector and the J-vector at rest in space seem quite consistent among crewmen and different from those caused by the application of lower body negative pressure. No clinical abnormalities were observed. Etiology of these findings is conjectured to be, at least in part, related to fluid mass shifts occurring in weightlessness and attendant alterations in cardiovascular dynamics and myocardial autonomic control mechanisms.