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Virginia Tech has several activities which support the NASA Langley effort in the area of large aperture radiometric antenna systems. This semi-annual report discusses the major areas of research and progress made.
A new method of analyzing the kinematics of joint motion is developed. Magnetic Resonance Imaging (MRI) offers several distinct advantages. Past methods of studying anatomic joint motion have usually centered on four approaches. These methods are x-ray projection, goniometric linkage analysis, sonic digitization, and landmark measurement of photogrammetry. Of these four, only x-ray is applicable for in vivo studies. The remaining three methods utilize other types of projections of inter-joint measurements, which can cause various types of error. MRI offers accuracy in measurement due to its tomographic nature (as opposed to projection) without the problems associated with x-ray dosage. Once the data acquisition of MR images was complete, the images were processed using a 3D volume rendering workstation. The metacarpalphalangeal (MCP) joint of the left index finger was selected and reconstructed into a three-dimensional graphic display. From the reconstructed volumetric images, measurements of the angles of movement of the applicable bones were obtained and processed by analyzing the screw motion of the MCP joint. Landmark positions were chosen at distinctive locations of the joint at fixed image threshold intensity levels to ensure repeatability. The primarily two dimensional planar motion of this joint was then studied using a method of constructing coordinate systems using three (or more) points. A transformation matrix based on a world coordinate system described the location and orientation of a local target coordinate system. Future research involving volume rendering of MRI data focusing on the internal kinematics of the hand's individual ligaments, cartilage, tendons, etc. will follow. Its findings will show the applicability of MRI to joint kinematics for gaining further knowledge of the hand-glove (power assisted) design for extravehicular activity (EVA).
The 1-percent calibration accuracy goal of the Advanced X-ray Astrophysics Facility is being approached by way of an experiment at the National Synchrotron Light Source that will demonstrate the accuracy achievable in reflectance measurements conducted on coated flat mirrors in the 50 eV-12 keV energy range. The coatings will be of commercially produced Au, Ni, and Ir, deposited either by sputtering or by e-beam deposition. Optical constants will be estimated via the reflectance vs. angle-of-incidence method.
A new method for analyzing the kinematics of joint motion using magnetic resonance imaging (MRI) is described. The reconstruction of the metacarpalphalangeal joint of the left index finger into a 3D graphic display is shown. From the reconstructed volumetric images, measurements of the angles of movement of the applicable bones are obtained and processed by analyzing the screw motion of the joint. Landmark positions are chosen at distinctive locations of the joint at fixed image threshold intensity levels to ensure repeatability. The primarily 2D planar motion of this joint is then studied using a method of constructing coordinate systems using three or more points. A transformation matrix based on a world coordinate system describes the location and orientation of the local target coordinate system. The findings show the applicability of MRI to joint kinematics for gaining further knowledge of the hand-glove design for EVA.
The addition of a large movable horizontal tail surface to the control system of a rotorcraft in-flight simulator being developed from a Sikorsky UH-60A Black Hawk Helicopter is evaluated. The capabilities of the control surface as a trim control and as an active control are explored. The helicopter dynamics are modeled using the Generic Helicopter simulation program developed by Sikorsky Aircraft. The effect of the horizontal tail on the helicopter trim envelope is examined by plotting trim maps of the aircraft attitude and controls as a function of the flight speed and horizontal tail incidence. The control power of the tail surface relative to that of the other controls is examined by comparing control derivatives extracted from the simulation program over the flight speed envelope. The horizontal tail's contribution as an active control is evaluated using an explicit model following control synthesis involving a linear model of the helicopter in steady, level flight at a flight speed of eighty knots. The horizontal tail is found to provide additional control flexibility in the longitudinal axis. As a trim control, it provides effective control of the trim pitch attitude at mid to high forward speeds. As an active control, the horizontal tail provides useful pitching moment generating capabilities at mid to high forward speeds.
Two solid-state phase transitions in troilite (FeS) can be readily measured by differential scanning calorimetry (DSC) on samples of only a few milligrams. Troilite from the Mundrabilla iron meteorite displays a DSC fingerprint which is distinct from that of terrestrial troilite from Del Norte Co., California; their response to subsequent heating also differ significantly. Further work may establish whether troilite thermometry of meteorites is possible using DSC.
A concept for an orbiting laboratory for testing Controls-Structures Integration (CSI) technology is described. The CSI-Star concept reflects a lower cost, higher risk approach. The concept supports demonstration and validation testing for critical CSI technologies at a cost of $20M to $26M with a 1-year reliability of approximately 0.9. The Ball Aerospace QuickStar bus is the carrier for the CSI test article. QuickStar is launched as a secondary payload on the McDonnell Douglas Delta 2. The QuickStar/Delta 2 approach is flight proven. The CSI test article is a 20 foot, 1 Hz, truss beam which is deployed from the QuickStar bus. The test article is well instrumented for quality system identification. The laboratory provides three layers of active control consisting of global vibration suppression along the truss beam, vibration isolation between the beam and instrument platforms, and vibration compensation through the use of gimbaled platforms which point lasers relative to optical sensor targets. The configuration simulates the dynamics of multi-instrument science platforms such as those of the Earth Observation System (EOS) while maintaining strong ties to astrophysics missions such as the Optical Interferometer. Uplink/downlink services and a reprogrammable computer provide flexibility for long-term investigations by members of the CSI community (NASA, DoD, academia, and industry). CSI-Star fills the gap between short-term experiments, which have been conducted primarily on the Shuttle, and future science missions which require the technology. The on-orbit maturity of CSI technology must be established to obtain acceptance by project managers and to promote injection of the technology into future science missions.
The manpower on this effort was reduced during this reporting period. Activity in the past six months is summarized. The Type 1 antenna is complete and documentation is in final phases. The Type 2 antenna design is complete and a journal article was prepared and was accepted for publication in EEE Transactions on Antennas and Propagation. The spherical antenna configurations are complete and a journal article will appear in the June 1993 issue of EEE Transactions on Antennas and Propagation. In addition, a patent for the spherical antenna is being pursued. The final current activity is that of optimization techniques and they are approaching completion as well. The Tri-Reflector synthesis code (TSAP) was put into user friendly format. A user's guide (Report 93-13) was written and distributed to LaRC. Work continues on EASY7. EASY7 is a user friendly code used to create an input file to GRASP7.
The optical properties associated with small particles, which include aerosols, hydrosols and solid microspheres have an impact on several areas of science and engineering. Since the advent of high-speed computers and lasers, the interaction of light with matter in the form of small particles with a discontinuous optical boundary relative to the surroundings has been much better understood. Various nonlinear optical effects have been observed involving interaction of a laser beam with both solid microspheres and liquid microdroplets. These include observation of second and third harmonic generation, four wave mixing, optical visibility, two photon absorption, observation of stimulated emission and lasing, and Stimulated Raman Scattering. Many of these effects are observed with laser intensities which are orders of magnitude less than that required by threshold condition for interactions in macroscopic bulk medium. The primary reason for this is twofold. The front surface of the microsphere acts as a thick lens to enhance the internal intensity of the input laser radiation, and the spherical shape of the droplet acts as an optical cavity to provide feedback at specific wavelengths corresponding to the whispering gallery modes or the morphology dependent resonances (MDR's). The most interesting and significant recent finding in this field is undoubtedly the existence of resonance peaks in linear and nonlinear optical spectra. Such resonance peaks are only dependent on the particle morphology, which means the size, shape and refractive index of the particle. Because of the simultaneous presence of these resonances, they have been referred to by many names, including structural resonances, whispering modes or whispering gallery modes, creeping waves, circumferential waves, surfaces modes, and virtual modes. All of these names refer to the same phenomena, i.e. morphology dependent resonances (MDR's) which has already been described and predicted precisely by electromagnetic theory and Loentz-Mie theory since 1908. MDR's can become important when the particle size (radius a) approaches and exceeds the wavelength of the electromagnetic wave (lambda) and the refractive index of the particle is greater than that of the surrounding medium. Such resonances are easiest to observe from a single particle with high symmetry, such as a sphere, spheroid, or cylinder. MDR's correspond to solutions of the characteristic equations of the electromagnetic fields in the presence of a sphere.
There were several tangible products that resulted from the reflector antenna research program. The initial technical effort was to develop techniques to compensate for distortions over the surface of the main reflector of a large reflector antenna system. An in-depth investigation of this problem resulted in a new technique for the electronic correction of surface errors. A journal article on the findings describe the use of the iterative sampling method. Shortly after the 'Mission to Planet Earth' program started, we began investigating the use of large reflector antennas in geostationary orbit for passive earth remote sensing. A study panel was coordinated by Virginia Tech to set technical goals for the effort. These were used to guide the design of several antennas. The original interest stemmed from an industrial (Reynolds Metals) need and currently involves work with industry (Prodelin Corporation) on high technology, low cost reflectors. The intervening years (1987 - 1993) is the period of this report and Virginia Tech's reflector antenna activity then was exclusively with NASA LaRC.
This report is the final product of an environmental study conducted by Western Commercial Space Center, Inc. under contract to Tennessee-Calspan Center for Space Transportation and Applied Research. The purpose of this investigation is to accurately document the current environmental and permitting processes associated with commercial space launch activity at Vandenberg AFB, and make recommendations to streamline those processes. The particular areas of interest focus on: identifying applicable Federal, state, and local laws, Department of Defense directives, and Air force regulations; defining the environmental process on Vandenberg AFB and how it relates with other agencies, including Federal and state regulatory agencies; and defining the air quality permit process. Study investigation results are applied to an example Pilot Space Launch Vehicle (PSLV) planning to launch from Vandenberg AFB. The PSLV space hardware is analyzed with respect to environmental and permitting issues associated with vehicle processing, facilities required (existing or new), and launch. The PSLV verified the earlier findings of the study and gave insight into streamlining recommendations.
An improved understanding of low gravity subcritical cryogenic fluid behavior is critical for the continued development of space based systems. Although early experimental programs provided some fundamental understanding of zero gravity cryogenic fluid behavior, more extensive flight data are required to design space based cryogenic liquid storage and transfer systems with confidence. As NASA's mission concepts evolve, the demand for optimized in-space cryogenic systems is increasing. Cryogenic Orbital Nitrogen Experiment (CONE) is an attached shuttle payload experiment designed to address major technological issues associated with on-orbit storage and supply of cryogenic liquids. During its 7 day mission, CONE will conduct experiments and technology demonstrations in active and passive pressure control, stratification and mixing, liquid delivery and expulsion efficiency, and pressurant bottle recharge. These experiments, conducted with liquid nitrogen as the test fluid, will substantially extend the existing low gravity fluid data base and will provide future system designers with vital performance data from an orbital environment.
The Operational Television system at Kennedy Space Center operates hundreds of video cameras, many remotely controllable, in support of the operations at the center. This study was undertaken to determine if commercial NABTS (North American Basic Teletext System) teletext transmission in the vertical blanking interval of the genlock signals distributed to the cameras could be used to send remote control commands to the cameras and the associated pan and tilt platforms. Wavelength division multiplexed fiberoptic links are being installed in the OTV system to obtain RS-250 short-haul quality. It was demonstrated that the NABTS transmission could be sent over the fiberoptic cable plant without excessive video quality degradation and that video cameras could be controlled using NABTS transmissions over multimode fiberoptic paths as long as 1.2 km.
A study has been completed to examine the potential reduction of aircraft flyover noise by the method of active noise control (ANC). It is assumed that the ANC system will be designed such that it cancels discrete tones radiating from the engine fan inlet or fan exhaust duct. Thus, without considering the engineering details of the ANC system design, tone levels are arbitrarily removed from the engine component noise spectrum and the flyover noise EPNL levels are compared with and without the presence of tones. The study was conducted for a range of engine cycles, corresponding to fan pressure ratios from 1.3 to 1.75. The major conclusions that can be drawn are that, for a fan pressure ratio of 1.75, ANC of tones gives about the same suppression as acoustic treatment without ANC, and for a fan pressure ratio of 1.45, ANC appears to offer less effectiveness than passive treatment. Additionally, ANC appears to be more effective at sideline and cutback conditions than at approach. Overall EPNL suppressions due to tone removal range from about 1 to 3 dB at takeoff engine speeds and from 1 to 5 db at approach speeds. Studies of economic impact of the installation of an ANC system for the four engine cases indicate increases of DOC ranging from 1 to 2 percent, favoring the lower fan pressure ratio engines. Further study is needed to confirm the results by examining additional engine data, particularly at low fan pressure ratios, and studying the details of the current results to obtain a more complete understanding. Further studies should also include determining the effects of combining passive and active treatment.
To locate the accessory pathway(s) in preexicitation syndromes, epicardial and endocardial ventricular mapping is performed during anterograde ventricular activation via accessory pathway(s) from data originally received in signal form. As the number of channels increases, it is pertinent that more automated detection of coherent/incoherent signals is achieved as well as the prediction and prognosis of ventricular tachywardia (VT). Today's computers and computer program algorithms are not good in simple perceptual tasks such as recognizing a pattern or identifying a sound. This discrepancy, among other things, has been a major motivating factor in developing brain-based, massively parallel computing architectures. Neural net paradigms have proven to be effective at pattern recognition tasks. In signal processing, the picking of coherent/incoherent signals represents a pattern recognition task for computer systems. The picking of signals representing the onset ot VT also represents such a computer task. We attacked this problem by defining four signal attributes for each potential first maximal arrival peak and one signal attribute over the entire signal as input to a back propagation neural network. One attribute was the predicted amplitude value after the maximum amplitude over a data window. Then, by using a set of known (user selected) coherent/incoherent signals, and signals representing the onset of VT, we trained the back propagation network to recognize coherent/incoherent signals, and signals indicating the onset of VT. Since our output scheme involves a true or false decision, and since the output unit computes values between 0 and 1, we used a Fuzzy Arithmetic approach to classify data as coherent/incoherent signals. Furthermore, a Mean-Square Error Analysis was used to determine system stability. The neural net based picking coherent/incoherent signal system achieved high accuracy on picking coherent/incoherent signals on different patients. The system also achieved a high accuracy of picking signals which represent the onset of VT, that is, VT immediately followed these signals. A special binary representation of the input and output data allowed the neural network to train very rapidly as compared to another standard decimal or normalized representations of the data.
Least-squares inverse filters have found widespread use in the deconvolution of seismograms and the removal of multiples. The use of least-squares prediction filters with prediction distances greater than unity leads to the method of predictive deconvolution which can be used for the removal of long path multiples. The predictive technique allows one to control the length of the desired output wavelet by control of the predictive distance, and hence to specify the desired degree of resolution. Events which are periodic within given repetition ranges can be attenuated selectively. The method is thus effective in the suppression of rather complex reverberation patterns. A back propagation(BP) neural network is constructed to perform the detection of first arrivals of the multiples and therefore aid in the more accurate determination of the predictive distance of the multiples. The neural detector is applied to synthetic reflection coefficients and synthetic seismic traces. The processing results show that the neural detector is accurate and should lead to an automated fast method for determining predictive distances across vast amounts of data such as seismic field records. The neural network system used in this study was the NASA Software Technology Branch's NETS system.
Advanced X-ray Astrophysics Facility - Imaging (AXAF-I) is a spacecraft for X-ray emitting sources observation and has been tentatively scheduled for a space shuttle launch in late 1998 at the Kennedy Space Center. Its main objectives are 'to determine the nature of astronomical objects ranging from normal stars to quasars, to understand the nature of the physical processes which take place in and between astronomical objects, and to add to our understanding of the history and evolution of the universe.' The AXAF-I will have an expected five year life time for the science mission phase. During the science mission phase, the monitoring and management operation of the flight and ground systems is personnel intensive, requiring system experts on duty around the clock. The purpose of the expert system presented in this report is intended to reduce the level of expertise, training, and personnel requirement for the mission operation. The telemetry data from the spacecraft can be divided into two categories: the science observation data and the engineering status data. The science data contains the outputs from the X-ray sensing devices and will be forwarded to the AXAF-I Science Center for interpretation; while the engineering status data will be monitored by the Operation Control Center (OCC) for the operation diagnosis of the spacecraft. The expert system is designed to assist the operation controllers at the OCC to perform the daily mission operations. Since there are hundreds of engineering telemetry data points and the interpretation of the telemetry depends on many factors, e.g., sun or eclipse, the monitoring of the AXAF-I is not a trivial task. In this phase of expert system development, the focus has been limited to the engineering data interpretation, i.e., warnings will be provided to the operation controllers to signal any anomaly. The system is hosted in a Silicon Graphics Indigo-2 workstation running the IRIX operating system. The expert system tool used is the G2 system from Gensym (Gensy).
An extension of a prior study has been completed to examine the potential reduction of aircraft flyover noise by the method of active noise control (ANC). It is assumed that the ANC system will be designed such that it cancels discrete tones radiating from the engine fan inlet or fan exhaust duct, at least to the extent that they no longer protrude above the surrounding broadband noise levels. Thus, without considering the engineering details of the ANC system design, tone levels am arbitrarily removed from the engine component noise spectrum and the flyover noise EPNL levels are compared with and without the presence of tones. The study was conducted for a range of engine cycles, corresponding to fan pressure ratios of 1.3, 1.45, 1.6, and 1.75. This report is an extension of an effort reported previously. The major conclusions drawn from the prior study, which was restricted to fan pressure ratios of 1.45 and 1.75, are that, for a fan pressure ratio of 1.75, ANC of tones gives about the same suppression as acoustic treatment without ANC. For a fan pressure ratio of 1.45, ANC appears to offer less effectiveness from passive treatment. In the present study, the other two fan pressure ratios are included in a more detailed examination of the benefits of the ANC suppression levels. The key results of this extended study are the following observations: (1) The maximum overall benefit obtained from suppression of BPF alone was 2.5 EPNdB at high fan speeds. The suppression benefit increases with increase in fan pressure ratio (FPR), (2) The maximum overall benefit obtained from suppression of the first three harmonics was 3 EPNdB at high speeds. Suppression benefit increases with increase in FPR, (3) At low FPR, only about 1.0 EPNdB maximum reduction was obtained. Suppression is primarily from reduction of BPF at high FPR values and from the combination of tones at low FPR, (4) The benefit from ANC is about the same as the benefit from passive treatment at fan pressure ratios of 1.75 and 1.60. At the two lower fan pressure ratios, the effectivness of treatment is much greater than that of ANC, and (5) No significant difference in ANC suppression behavior was found from the QCSEE engine database analysis compared to that of the E3 engine database, for the FPR = 1.3 engine cycle. The effects of ANC on EPNL noise reduction are difficult to generalize. It was found that the reduction obtained in any particular case depended upon the frequency of the tones and their shift with rpm, the amount of ANC suppression received by each tone (which depended on its protrusion from the background), and the NOY-value of the tone relative to the NOY-value of other tones and the peak broadband levels, because PNL is determined from the sum of the NOY-values.