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NASA NTRS1995

Experimental Demonstration of Microwave Signal/Electric Thruster Plasma Interaction Effects

An experiment was designed and conducted in the Electric Propulsion Laboratory of NASA Lewis Research Center to assess the impact of ion thruster exhaust plasma plume on electromagnetic signal propagation. A microwave transmission experiment was set up inside the propulsion test bed using a pair of broadband horn antennas and a 30 cm 2.3 kW ion thruster. Frequency of signal propagation covered from 6.5 to 18 GHz range. The stainless steel test bed when enclosed can be depressurized to simulate a near vacuum environment. A pulsed CW system with gating hardware was utilized to eliminate multiple chamber reflections from the test signal. Microwave signal was transmitted and received between the two hours when the thruster was operating at a given power level in such a way that the signal propagation path crossed directly through the plume volume. Signal attenuation and phase shift due to the plume was measured for the entire frequency band. Results for this worst case configuration simulation indicate that the effects of the ion thruster plume on microwave signals is a negligible attenuation (within 0.15 dB) and a small phase shift (within 8 deg.). This paper describes the detailed experiment and presents some of the results.

Zaman, Afroz J.↗

NASA NTRS1998

Comparison of Martian Meteorites and Martian Regolith as Shield Materials for Galactic Cosmic Rays

Theoretical calculations of radiation attenuation due to energetic galactic cosmic rays behind Martian rock and Martian regolith material have been made to compare their utilization as shields for advanced manned missions to Mars because the detailed chemical signature of Mars is distinctly different from Earth. The modified radiation fields behind the Martian rocks and the soil model were generated by solving the Boltzmann equation using a HZETRN system with the 1977 Solar Minimum environmental model. For the comparison of the attenuation characteristics, dose and dose equivalent are calculated for the five different subgroups of Martian rocks and the Martian regolith. The results indicate that changes in composition of subgroups of Martian rocks have negligible effects on the overall shielding properties because of the similarity of their constituents. The differences for dose and dose equivalent of these materials relative to those of Martian regolith are within 0.5 and 1 percent, respectively. Therefore, the analysis of Martian habitat construction options using in situ materials according to the Martian regolith model composition is reasonably accurate. Adding an epoxy to Martian regolith, which changes the major constituents of the material, enhances shielding properties because of the added hydrogenous constituents.

Kim, Myung-Hee Y.↗

NASA NTRS1998

Bio-Optical Properties of the Arabian Sea as Determined by In-Situ and SeaWifs Data

The overall objective of this work was to characterize optical and fluorescence properties in the euphotic zone during two British Ocean Flux Study (BOFS) Arabian Sea cruises. This was later expanded in 1995 to include three U.S. Joint Global Ocean Flux Study (JGOFS) Arabian Sea Cruises. The region was to be divided into one or more "bio-optical provinces", within each of which a single set of regression models was to be developed to relate the vertical distribution of irradiance attenuation and normalized fluorescence (SF and NF) to remote sensing reflectance and diffuse attenuation coefficient [K(490)]. The working hypothesis was that over relatively large spatial and temporal scales, the vertical profiles of bio-optical properties were predictable.

Trees, Charles C.↗

NASA NTRS1999

Some Acoustic Results from the Pratt and Whitney Advanced Ducted Propulsor: Fan 1

Noise measurements were obtained for the Advanced Ducted Propulsor (ADP) - Fan 1, with and without nacelle acoustic treatment. The fan was tested with no acoustic treatment (hard wall) and with acoustic treatment installed in three configurations in the nacelle (mid, mid plus aft, fully treated). The hard wall results showed that the radiated noise from the fan came primarily from the aft end of the nacelle. At takeoff and higher speeds, the noise measured at the inlet angles was also found to be dominated by noise from the aft end. Significant amounts of attenuation were observed with acoustic treatment installed and comparison with predictions showed the treatment gave more attenuation than predicted. Effective Perceived Noise Levels were determined for a large hypothetical 4 engine airplane. These levels showed that the installed acoustic treatment provided as much as 5 EPNdB of noise reduction. A traverse with a probe having three microphones, one above the other, showed azimuthal variations in the noise that need to be further investigated.

Dittmar, James H.↗

NASA NTRS1999

Hybrid Active/Passive Jet Engine Noise Suppression System

A novel adaptive segmented liner concept has been developed that employs active control elements to modify the in-duct sound field to enhance the tone-suppressing performance of passive liner elements. This could potentially allow engine designs that inherently produce more tone noise but less broadband noise, or could allow passive liner designs to more optimally address high frequency broadband noise. A proof-of-concept validation program was undertaken, consisting of the development of an adaptive segmented liner that would maximize attenuation of two radial modes in a circular or annular duct. The liner consisted of a leading active segment with dual annuli of axially spaced active Helmholtz resonators, followed by an optimized passive liner and then an array of sensing microphones. Three successively complex versions of the adaptive liner were constructed and their performances tested relative to the performance of optimized uniform passive and segmented passive liners. The salient results of the tests were: The adaptive segmented liner performed well in a high flow speed model fan inlet environment, was successfully scaled to a high sound frequency and successfully attenuated three radial modes using sensor and active resonator arrays that were designed for a two mode, lower frequency environment.

Parente, C. A.↗

NASA NTRS1989

Potentiation of Hormonal Responses to Hemorrhage and Fasting, but not Hypoglycemia in Conscious Adrenalectomized Rats

Bilateral adrenalectomy (ADRX) in rats removes the source of two major stress-responsive hormones, corticosterone and epinephrine. To test how ADRX rats with-stand stress, we performed the following experiments in adult male rats provided with indwelling femoral arterial and venous cannulae and either ADRX or sham-adrenalectomized (Sham) 3 days later and given 0.5% NaCl to drink. Five to 6 days after adrenal surgery the rats were studied after either a 15 ml/kg.5 min hemorrhage or after an overnight fast followed by insulin-induced hypoglycemia. In fed unstressed ADRX rats, basal mean arterial blood pressure was slightly decreased; heart rate was increased; blood volume, vasopressin, and oxytocin concentrations were not different from sham values; and renin and norepinephrine were significantly elevated. The recovery of arterial pressure after hemorrhage in the ADRX rats was similar to that in the sham group over a 5-h period; however, the responses of vasopressin and oxytocin were significantly greater, and those of renin and norepinephrine were markedly potentiated in the ADRX group. Heart rate recovered faster in the ADRX group and was elevated, compared to the sham value, for most of the 5-h period. Restitution of blood volume was attenuated in the ADRX group, although the restitution of plasma protein was not different between the groups. A significant difference in the change in plasma osmolality between groups after hemorrhage may account for the attenuated restitution of blood volume. After an overnight fast, which reduced blood volume in both groups of rats, the plasma renin concentration rose still further in ADRX rats; the differences in other measured variables observed between fed ADRX and sham groups remained the same. The insulin-induced 50% decrease in glucose caused minor effects on arterial blood pressure and heart rate and occasioned responses in renin and norepinephrine of similar magnitudes in the two groups. We conclude that in the absence of the adrenals, rats restore arterial pressure after hemorrhage remarkably well through potentiation of the responses of other vasoactive neural and hormonal systems. In these studies the marked potentiation of the renin response suggests that the renin-angiotensin system may be important in the maintenance of arterial blood pressure after reductions in blood volume.

Darlington, Daniel N.↗

NASA NTRS1993

Observation of Intense Wave Bursts at Very Low Altitudes Within the Venus Nightside Ionosphere

Intense ELF (100 Hz) bursts were detected by the Pioneer Venus Orbiter plasma wave instrument during the final operations of the spacecraft prior to atmospheric entry. These bursts were detected at approx. 130 km altitude around 0400 local time. The wave activity lasted for several tens of seconds. Furthermore the bursts were not symmetric about periapsis, unlike instrument noise caused by neutral impacts on the spacecraft. The bursts had a vertical attenuation scale height of the order 1 km, consistent with that expected for whistler-mode waves propagating through a collisional ionosphere. Since the decay of the signals appears to be due to attenuation, the source must persist for several tens of seconds. The wave bursts could therefore be the signature of electromagnetic radiation entering the bottomside ionosphere from several distant sources, as would be expected if lightning were a relatively persistent phenomenon within the Venus atmosphere.

Strangeway, R. J.↗

NASA NTRS1999

Improved Spacecraft Materials for Radiation Shielding

In the execution of this proposal, we will first examine current and developing spacecraft materials and evaluate their ability to attenuate adverse biological mutational events in mammalian cell systems and reduce the rate of cancer induction in mice harderian glands as a measure of their protective qualities. The HZETRN code system will be used to generate a database on GCR attenuation in each material. If a third year of funding is granted, the most promising and mission-specific materials will be used to study the impact on mission cost for a typical Mars mission scenario as was planned in our original two year proposal at the original funding level. The most promising candidate materials will be further tested as to their transmission characteristics in Fe and Si ion beams to evaluate the accuracy of the HZETRN transmission factors. Materials deemed critical to mission success may also require testing as well as materials developed by industry for their radiation protective qualities (e.g., Physical Sciences Inc.) A study will be made of designing polymeric materials and composite materials with improved radiation shielding properties as well as the possible improvement of mission-specific materials.

Wilson, J. W.↗

NASA NTRS1978

Aspirin- and Indomethacin-Induced Ulcers and their Antagonism by Anthihistamines

Gastric ulceration produced by aspirin and indomethacin was compared in acutely stressed and non-stressed rats. We found a synergism between these anti-inflammatory agents and acute stress in the production of gastric ulcers. Even at relatively high doses, neither agent caused appreciable gastric damage in non-stressed rats, whereas moderate doses of both agents produced massive ulceration in stressed rats. The synergism appears unrelated to the effect of these agents on the pituitary-adrenal response. The size and regional distribution of ulcers produced by aspirin and indomethacin in stressed rats were comparable. However, the dose--response curves of the two drugs were markedly dissimilar. Furthermore, the ulceration produced by indomethacin was attenuated by both H(sub 1) and H(sub 2) histamine receptor antagonists, whereas ulceration produced by aspirin was attenuated only by an H(sub 2) antagonist. The results suggest that the ulcerogenic mechanism of indomethacin may differ from that of aspirin and add to the growing evidence on the importance of endogenous histamine in various forms of gastric ulceration.

Brown, Patricia A.↗

NASA NTRS1999

Advanced Communications Technology Satellite (ACTS) Fade Compensation Protocol Impact on Very Small-Aperture Terminal Bit Error Rate Performance

The Advanced Communications Technology Satellite (ACTS) communications system operates at Ka band. ACTS uses an adaptive rain fade compensation protocol to reduce the impact of signal attenuation resulting from propagation effects. The purpose of this paper is to present the results of an analysis characterizing the improvement in VSAT performance provided by this protocol. The metric for performance is VSAT bit error rate (BER) availability. The acceptable availability defined by communication system design specifications is 99.5% for a BER of 5E-7 or better. VSAT BER availabilities with and without rain fade compensation are presented. A comparison shows the improvement in BER availability realized with rain fade compensation. Results are presented for an eight-month period and for 24 months spread over a three-year period. The two time periods represent two different configurations of the fade compensation protocol. Index Terms-Adaptive coding, attenuation, propagation, rain, satellite communication, satellites.

Cox, Christina B.↗

NASA NTRS1996

Optimal Estimation of Rain-Rate Profiles from Single-Frequency Radar Echoes

The significant ambiguities inherent in the determination of a particular vertical rain intensity profile from a given time profile of radar echo powers measured by a downward-looking (spaceborne or airborne) radar at a single attenuating frequency are well documented. Indeed, one already knows that by appropriately varying the parameters of the reflectivity-rain rate (Z-R) and/or attenuation-rain rate (k- R) relationships one can produce several substantially different rain-rate profiles that would produce the same radar power profile. Imposing the additional constraint that the path-averaged rain rate be a given fixed number does reduce the ambiguities but falls far short of eliminating them. While formulas to generate all mutually ambiguous rain-rate profiles from a given profile of received radar reflectivities have already been derived, there remains to be produced a quantitative measure to assess how likely each of these profiles is, what the appropriate "average" profile should be, and what the "variance" of these multiple solutions is. To do this, one needs to spell out the stochastic constraints that can allow us to make sense of the words "average" and "variance" in a mathematically rigorous way. Such a quantitative approach would be particularly well suited for such systems as the planned precipitation radar of the Tropical Rainfall Measuring Mission (TRMM). Indeed, one would then be able to use the radar reflectivities measured by the TRMM radar to estimate the rain-rate profile that would most likely have produced the measurements, as well as the uncertainty in the estimated rain rates as a function of range. Such an optimal approach is described in this paper.

Haddad, Ziad S.↗

NASA NTRS1999

Tissue Engineered Skeletal Myofibers can Directly "Sense" Gravitational Force Changes

Long-term manned space flight requires a better understanding of skeletal muscle atrophy resulting from microgravity. Atrophy most likely results from changes at both the systemic level (e.g. decreased circulating growth hormone, increased circulating glucocorticoids) and locally (e.g. decreased myofiber resting tension). Differentiated skeletal myofibers in tissue culture have provided a model system over the last decade for gaining a better understanding of the interactions of exogenous growth factors, endogenous growth factors, and muscle fiber tension in regulating protein turnover rates and muscle cell growth. Tissue engineering these cells into three dimensional bioartificial muscle (BAM) constructs has allowed us to extend their use to Space flight studies for the potential future development of countermeasures. Embryonic avian muscle cells were isolated and BAMs tissue engineered as described previously. The myoblasts proliferate and fuse into aligned postmitotic myofibers after ten to fourteen days in vitro. A cylindrical muscle-like structure containing several thousand myofibers is formed which is approximately 30 mm in length, 2-3 mm in diameter, and attached at each end. For the Space Shuttle experiments, the BAMs were transferred to 55 mL bioreactor cartridges (6 BAMs/cartridge). At Kennedy Space Center, the cartridges were mounted in two Space Tissue Loss (STL) Modules (three to four cartridges per Module) and either maintained as ground controls or loaded in a Mid-Deck locker of the Space Shuttle. The BAM cartridges were continuously perfused during the experiment at 1.5 mL/ min with tissue culture medium. Eighteen BAMs were flown for nine days on Mission STS66 while eighteen BAMs served as ground controls. The complete experiment was repeated on Mission STS77 with twenty four BAMs in each group. BAMs could be maintained in a healthy state for at least 30 days in the perfusion bioreactor cartridges. The BAM muscle fibers directly detected both the loss of gravity and the reloading effects of 1 x g. While total cellular metabolism and total protein degradation rates were not altered during 9 to 10 days in Space, protein synthesis rates were significantly reduced and resulted in significant myofiber atrophy compared to ground controls. One g reloading of the flight muscle cells post-flight significantly increased protein synthesis rates and the synthesis rates of myosin heavy chain, fibronectin, and collagen. Tissue cultured muscle cells can directly "sense" changes in gravity and provide a valid model to begin the study of countermeasures. Based on our ground based experiments, and the experiments of others, growth hormone and/or insulin-like growth factors are attractive protein therapeutics which may assisting attenuating skeletal muscle wasting in space. Our laboratory is developing a new cell-based delivery system for this and other potential therapeutic factors for attenuating muscle and bone wasting.

Vandenburgh, Herman H.↗

NASA NTRS1999

A Plasma Instability Theory of Gamma-Ray Burst Emission

A plasma instability theory is presented for the prompt radiation from gamma-ray bursts. In the theory, a highly relativistic shell interacts with the interstellar medium through the filamentation and the two-stream instabilities to convert bulk kinetic energy into electron thermal energy and magnetic field energy. The processes are not efficient enough to satisfy the Rankine-Hugoniot conditions, so a shock cannot form through this mechanism. Instead, the interstellar medium passes through the shell, with the electrons radiating during this passage. Gamma-rays are produced by synchrotron self-Compton emission. Prompt optical emission is also produced through this mechanism, while prompt radio emission is produced through synchrotron emission. The model timescales are consistent with the shortest burst timescales. To emit gamma-rays, the shell's bulk Lorentz factor must be $\simg 10(exp 3)$. For the radiative processes to be efficient, the interstellar medium density must satisfy a lower limit that is a function of the bulk Lorentz factor. Because the limits operate as selection effects, bursts that violate them constitute new classes. In particular, a class of optical and ultraviolet bursts with no gamma-ray emission should exist. The lower limit on the density of the interstellar medium is consistent with the requirements of the Compton attenuation theory, providing an explanation for why all burst spectra appear to be attenuated. Several tests of the theory are discussed, as are the next theoretical investigations that should be conducted.

Brainerd, Jerome J.↗

NASA NTRS1996

Stochastic Filtering of Rain Profiles Using Radar, Surface-Referenced Radar, or Combined Radar-Radiometer Measurements

This paper describes a computationally efficient nearly optimal Bayesian algorithm to estimate rain (and drop size distribution) profiles, given a radar reflectivity profile at a single attenuating wavelength. In addition to estimating the averages of all the mutually ambiguous combinations of rain parameters that can produce the data observed, the approach also calculates the n-ns uncertainty in its estimates (this uncertainty thus quantifies "the amount of ambiguity" in the "solution"). The paper also describes a more general approach that can make estimates based on a radar reflectivity profile together with an approximate measurement of the path-integrated attenuation, or a radar reflectivity profile and a set of passive microwave brightness temperatures. This more general "combined" algorithm is currently being adapted for the Tropical Rainfall Measuring Mission.

Haddad, Ziad S.↗

NASA NTRS1998

Commercial Production of Heavy Metal Fluoride Glass Fiber in Space

International Space Station Alpha (ISSA) will provide a platform not only for materials research but also a possible means to produce products in space which cannot be easily produced on the ground. Some products may even be superior to those now produced in unit gravity due to the lack of gravity induced convection effects. Our research with ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN glass) has shown that gravity does indeed play a major role in the crystallization behavior of this material. At the present time ZBLAN is being produced on earth in fiber optic form for use in surgical lasers and fiber optic lasers among other applications. High attenuation coefficients, however, have kept this material from being used in other applications such as long haul data transmission links. The high attenuation coefficients are due to impurities which can be removed through improved processing techniques and crystals which can only be removed or prevented from forming by processing in a reduced gravity environment.

Tucker, Dennis S.↗

NASA NTRS1999

The Effects of Gravity on ZBLAN Glass

Heavy metal fluoride glass fibers show promise in applications such as surgical lasers, spectroscopy and imaging fiber bundles. ZBLAN, which is within this class has been studied for a number of years. ZBLAN's theoretical attenuation coefficient is approximately 0.002 dB/km which is much better than that of fused silica at 0.2 dB/km. However, due to impurities and crystallites the attenuation coefficients achieved to date are considerably larger than those of fused silica. Impurities can be controlled with better processing techniques. Crystallization has been found to be a function of gravity. It is found that heating to the crystallization temperature in unit gravity results in crystallization while heating in reduced gravity does not. The exact mechanism for this phenomenon is not known but is speculated to be related to stress.

Tucker, Dennis S.↗

NASA NTRS2000

Autonomous, Full-Time Cloud Profiling at Arm Sites with Micro Pulse Lidar

Since the early 1990's technology advances permit ground based lidar to operate full time and profile all significant aerosol and cloud structure of the atmosphere up to the limit of signal attenuation. These systems are known as Micro Pulse Lidars (MPL), as referenced by Spinhirne (1993), and were first in operation at DOE Atmospheric Radiation Measurement (ARM) sites. The objective of the ARM program is to improve the predictability of climate change, particularly as it relates to cloud-climate feedback. The fundamental application of the MPL systems is towards the detection of all significant hydrometeor layers, to the limit of signal attenuation. The heating and cooling of the atmosphere are effected by the distribution and characteristics of clouds and aerosol concentration. Aerosol and cloud retrievals in several important areas can only be adequately obtained with active remote sensing by lidar. For cloud cover, the height and related emissivity of thin clouds and the distribution of base height for all clouds are basic parameters for the surface radiation budget, and lidar is essetial for accurate measurements. The ARM MPL observing network represents the first long-term, global lidar study known within the community. MPL systems are now operational at four ARM sites. A six year data set has been obtained at the original Oklahoma site, and there are several years of observations at tropical and artic sites. Observational results include cloud base height distributions and aerosol profiles. These expanding data sets offer a significant new resource for cloud, aerosol and atmospheric radiation analysis. The nature of the data sets, data processing algorithms, derived parameters and application results are presented.

Spinhirne, James D.↗

NASA NTRS1999

Cardiovascular Session Summary

It was apparent that the bed-rest and spaceflight data indicated that decreases in plasma volume and cardiac atrophy along with cardiac remodeling were fundamental changes which predisposed many astronauts to post flight orthostatic intolerance. Despite the recently acquired in-flight and post-flight muscle sympathetic nerve activity findings suggesting that the sympathetic nerve responses were appropriate there remains significant contrary data from bed-rest studies, post- flight stand tests and hind-limb unweighted rat studies that suggest that the vasoconstrictive responses were compromised at least insufficient in susceptible individuals. The key issues raised is whether a diminished increase in sympathetic activity from baseline without changes in 254 First Biennial Space Biomedical Investigators'Workshop Cardiovascular peak response or receptor adaptations is an abnormal response or is an individual variance of response to the accentuated decrease in stroke volume. Data relating autonomic neural control of heart rate were presented to suggest that the vagal and sympathetic control of heart rate was attenuated. Also, bed-rest and space flight induced attenuated baroreflex control of heart rate was shown to be restored to pre-bedrest function by one bout of maximal dynamic exercise. However, these data were confounded by relying on the use of R-R interval as a measure of efferent responses of the baroreflex during a condition in which the baseline heart rate was changed. Clearly the idea that the autonomic control of heart rate may be changed by microgravity needs further investigation. This direction is suggested despite the fact that in the triple product (HR x SV x TPR = MAP) assessment of the regulation of arterial blood pressure during orthostasis the role of the HR reflex may be less influential than that associated. with cardiac atrophy (SV changes) and aberrant sympathetic vasoconstriction (resistance) changes. Although sympathetic nerve activity responses in-flight and post-flight on neurolab appeared appropriate, enough bed-rest and post-flight stand test data, along with animal model data suggest that vasoconstriction was compromised. The mechanism of this compromised vasoconstriction needs to be delineated. Other major findings concerning microgravity and physiological regulatory systems are that: I . Thermoregulatory adaptation appear to suggest some decrements in the control of cutaneous vasodilation and sweating; 2. Calcium resorption and dietary calcium need to be defined for differing durations of spaceflight, especially as the effects of excess calcium on vasomotor function appears to be detrimental; 3. Neurohumoral mechanisms of microgravity induced changes in neural function and the regulation of plasma volume and total body water, bone resorption and autonomic neural control of the circulation need further delineation; 4. As performance of work tasks become prolonged, the mechanisms of blood pressure regulation in microgravity needs to be used in the recovery period from prolonged work tasks.

Raven, Peter↗