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In the early twenty-first century, astronauts will return to the Moon and establish a permanent base. To achieve this goal safely and economically, B&T Engineering has designed an unmanned, reusable, self-unloading lunar lander. The lander is designed to deliver 15,000-kg payloads from an orbital transfer vehicle (OTV) in a low lunar polar orbit and at an altitude of 200 km to any location on the lunar surface.
For the next-generation packet switched communications satellite system with onboard processing and spot-beam operation, a reliable onboard fast packet switch is essential to route packets from different uplink beams to different downlink beams. The rapid emergence of point-to-point services such as video distribution, and the large demand for video conference, distributed data processing, and network management makes the multicast function essential to a fast packet switch (FPS). The satellite's inherent broadcast features gives the satellite network an advantage over the terrestrial network in providing multicast services. This report evaluates alternate multicast FPS architectures for onboard baseband switching applications and selects a candidate for subsequent breadboard development. Architecture evaluation and selection will be based on the study performed in phase 1, 'Onboard B-ISDN Fast Packet Switching Architectures', and other switch architectures which have become commercially available as large scale integration (LSI) devices.
The final Postflight Hardware Evaluation Report 360T025, Appendix B is presented. The Postflight Observation Record (PFOR) for case, seals, and joints are included.
Numerous features of glaciological significance appear on two adjoining SPOT High Resolution Visible (HRV) images that cover the onset region of ice stream B. Many small-scale features, such as crevasses and drift plumes, have been previously observed in aerial photography. Subtle features, such as long flow traces that have not been mapped previously, are also clear in the satellite imagery. Newly discovered features include ladder-like runners and rungs within certain shear margins, flow traces that are parallel to ice flow, unusual crevasse patterns, and flow traces originating within shear margins. An objective of our work is to contribute to an understanding of the genesis of the features observed in satellite imagery. The genetic possibilities for flow traces, other lineations, bands of transverse crevasses, shear margins, mottles, and lumps and warps are described.
The region in the mouth of Ice Stream B (the ice plain) and that in the vicinity of Crary Ice Rise are experiencing large and rapid changes. Based on velocity, ice thickness, and accumulation rate data, the patterns of net mass balance in these regions were calculated. Net mass balance, or the rate of ice thickness change, was calculated as the residual of all mass fluxes into and out of subregions (or boxes). Net mass balance provides a measure of the state of health of the ice sheet and clues to the current dynamics.
Research that creates techniques to automatically obtain dimensional geometric parameters from the nonuniform B-spline surface description of an object is presented. These techniques have been implemented successfully in the aircraft design software, ACSYNT, a computer-aided design system for conceptual aircraft design created at Virginia Tech and NASA Ames. The techniques created and implemented in this research are also of significance to general-purpose design.
The forcing capabilities of systems composed of many actuators are analyzed in this paper. Multiactuator systems can generate higher forces in some directions than in others. Techniques are developed to find the force in the weakest direction. This corresponds to the worst-case output and is defined as the 'minimum control authority'. The minimum control authority is a function of three things: the actuator configuration, the actuator controller and the way in which the output of the system is limited. Three output limits are studied: (1) fuel-flow rate, (2) power, and (3) actuator output. The three corresponding actuator controllers are derived. These controllers generate the desired force while minimizing either fuel flow rate, power or actuator output. It is shown that using the optimal controller can substantially increase the minimum control authority. The techniques for calculating the minimum control authority are applied to the Gravity Probe-B spacecraft thruster system. This example shows that the minimum control authority can be used to design the individual actuators, choose actuator configuration, actuator controller, and study redundancy.
A Type B Ca-, Al-rich 6-m-diam inclusion (CAI) found in the Vigarano C3V chondrite was inspected using optical and scanning electron microscopies and ion microprobe analyses. It was found that the primary constituents of the CAI inclusion are (in percent), melilite (52), fassaite, (20), anorthite (18), spinel (10), and trace Fe-Ni metal. It is noted that, while many of the properties of the inclusion indicate solidification from a melt droplet, the Al-26/Mg-26 isotopic systematics and some textural relationships are incompatible with single-stage closed system crystallization of a homogeneous molten droplet, indicating that the history of this inclusion must have been more complex than melt solidification alone. Moreover, there was unusually high content of Na in melilite, suggesting that the droplet did not form by melting of pristine high-temperature nebular condensates.
The fracture toughness of an Nb-40Al-8Cr - 1W-1Y-0.05B intermetallic material was evaluated by indentation techniques at room temperature. Two widely used indentation methods, crack size measurement and indent strength, yielded excellent agreement with a conventional fracture toughness technique using straight-through precracked specimens, despite the occasional formation of poorly configured cracks. However, the modified indentation technique, using dummy indent flaws, resulted in a low fracture toughness compared to that evaluated by the other methods. The material did not exhibit rising R-curve behavior, as evaluated from the indentation strength data. These results indicate that indentation fracture principles are applicable to this brittle intermetallic material without modification of the residual contact stress term originally calibrated for ceramic materials.
The design of power magnetic components such as transformers, inductors, motors, and generators, requires specific knowledge about the magnetic and electrical characteristics of the magnetic materials used in these components. Limited experimental data exists that characterizes the performance of soft magnetic materials for the combined conditions of high temperature and high frequency over a wide flux density range. An experimental investigation of a 2V-49-Fe-49Co (Supermendur) and a grain oriented 3 Si-Fe (Magnesil) alloy was conducted over the temperature range of 23 to 300 C and frequency range of 0.1 to 10 kHz. The effects of temperature, frequency, and maximum flux density on the core loss and dynamic B-H loops for sinusoidal voltage excitation conditions are examined for each of these materials. A comparison of the core loss of these two materials is also made over the temperature and frequency range investigated.
We describe the status of the development and testing program for the inertial reference system for the Gravity Probe B gyroscopes. The gyroscope housings are attached to a cryogenic telescope with a 14 cm aperture that continuously points at a guide star. The star image is split to provide quadrant pointing information which is used to steer the spacecraft. This data is also combined with the gyro readout data to provide an absolute precession measurement. Motion of the guide star is independently checked by reference to background galaxies. Room temperature testing of a prototype telescope has been completed and preparations are being made for low temperature tests.
The electron excitation function for the H2(a 3Sigma(g)(+) - b 3Sigma(u)(+)) continuum emission has been measured from 11 to 30 eV at 195.0 nm. The emission cross, section data have been combined with electron energy loss cross section measurements to extend the experimental data to 60 eV. The excitation cross section has been estimated by normalizing the data to the electron energy loss cross section at 20 eV and using a model to account for emission from the entire band system. The spin forbidden excitation of the a 3Sigma(g)(+) state is a major dissociative channel of H2 at low energy with a peak cross section of 1.7 +/- 0.85 x 10 exp -17 sq cm at 15.5 eV. The FWHM of the cross section is 7 eV. The high energy dependence of the cross section has a rapid 1/E-cubed fall off with electron energy, E, above 50 eV. A modified Born approximation analysis was applied to the data to provide an analytic model.
The dynamical behavior of fluids, in particular the effect of surface tension on partially-filled rotating fluids (cryogenic liquid helium and helium vapor) in a full scale Gravity Probe-B Spacecraft propellant dewar tank imposed by various frequencies of gravity jitters have been investigated. Fluid stress distribution, caused by the excitation of slosh waves and their associated large amplitude disturbances on the liquid-vapor interface, exerted on the outer and inner walls of rotating dewar container also have been investigated. Results show that fluid stress distribution exerted on the outer and inner walls of rotating dewar are closely related to the characteristics of slosh waves excited on the liquid-vapor interface in the rotating dewar tank.
We have constructed a series of models of Alpha Centauri A and Alpha Centauri B for the purposes of testing the effects of convection modeling both by means of the mixing-length theory (MLT), and by means of parameterization of energy fluxes based upon numerical simulations of turbulent compressible convection. We demonstrate that while MLT, through its adjustable parameter alpha, can be used to match any given values of luminosities and radii, our treatment of convection, which lacks any adjustable parameters, makes specific predictions of stellar radii. Since the predicted radii of the Alpha Centauri system fall within the errors of the observed radii, our treatment of convection is applicable to other stars in the H-R diagram in addition to the sun. A second set of models is constructed using MLT, adjusting alpha to yield not the 'measured' radii but, instead, the radii predictions of our revised treatment of convection. We conclude by assessing the appropriateness of using a single value of alpha to model a wide variety of stars.
We report the discovery of the brightest nonsolar source of EUV emission: the B2 II star Epsilon Canis Majoris. This source has been detected by the Extreme Ultraviolet Explorer satellite's all-sky photometric survey. It is approximately 30 times brighter at 600 A than the predicted emission from the hot white dwarf star HZ 43, previously believed to be the brightest EUV source. We have fitted a simple B star photospheric model to the observed broadband EUV fluxes to explain this emission. Assuming a stellar temperature of 25,000 K and a gravity (log g) of 3.3, we derive an interstellar hydrogen column density of 1.05 +/- 0.05 x 10 exp 18/sq cm over the 187 pc to the star. This corresponds to a line-of-sight number density of hydrogen, of 0.002/cu cm, which is comparable to values found in the rarefied Local Bubble region which surrounds the sun.
Four models of outboard floats (N.A.C.A. models 51-A, 51-B, 51-C, and 51-D) were tested in the N.A.C.A. tank to determine their hydrodynamic characteristics and in the 20-foot wind tunnel to determine their aerodynamic drag. The results of the tests, together with comparisons of them, are presented in the form of charts. From the comparisons, the order of merit of the models is estimated for each factor considered. The best compromise between the various factors seems to be given by model 51-D. This model is the only one in the series with a transverse step.
The effects of inlet-air-flow distortions on the performance of the J65-B-3 turbojet engine were determined over a range of altitudes from 15,000 to 50,000 feet at a flight Mach number of 0.8. Radial inlet-air-flow distortions apparently do not affect the radial distribution of pressure after the first few compressor stages, while the circumferential inlet-air-flow distortion carried completely through the engine. For the distortions investigated, at rated exhaust-gas temperature and fixed-area exhaust-nozzle operation, the primary effect of the radial inlet-air-flow distortions was to reduce the engine air flow, and the primary effect of the circumferential distortion was to impose a temperature profile on the turbine, both resulting in reduction of thrust.
During geometry processing, tangent directions at the data points are frequently readily available from the computation process that generates the points. It is desirable to utilize this information to improve the accuracy of curve fitting and to improve data reduction. This paper presents a curve fitting method which utilizes both position and tangent direction data. This method produces G(exp 1) non-rational B-spline curves. From the examples, the method demonstrates very good data reduction rates while maintaining high accuracy in both position and tangent direction.