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At least 1,045 records · Page 58
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NASA NTRS2007

The Use of Heavy Ion Radiation as an Analog for Space Radiation Environment and Its Effects on Drug Stability

While it is common knowledge that electromagnetic radiation such as x-rays and gamma rays affect physical-chemical characteristics (PC) of compounds in addition to their toxic and mutagenic effects on biological systems, there are no reports on the effects of cosmic radiation encountered during space missions on stability of pharmaceuticals. Alterations in PC of drug formulations can adversely affect treatment with medications in space. Preliminary evaluation of stability and shelf-life of select pharmaceuticals (12) flown on space missions revealed that 37% and 40% of the formulations failed to meet USP requirements after shuttle and ISS flights, respectively. Based on these results, the current investigation is designed to examine the effect of proton (P) and heavy ion (Fe) radiation on 20 pharmaceutical preparations flown aboard the shuttle and ISS. The objectives of this project are: 1) Examine susceptibility of pharmaceuticals to short acute bouts of high intensity ionizing radiation species encountered during space flights; 2) Estimate extent of degradation of susceptible formulations as a function of intensity of each beam (P & Fe); and 3) compare and contrast the effects of single beam irradiation to that of a combined beam (P + Fe) that simulates space craft environment on drug stability. Irradiations were conducted at the Brookhaven National Laboratories (BNL) with beam strengths of 10 cGy, 10 or 50Gy of P and Fe beams separately. Preliminary evaluation of results revealed a reduction in the chemical content of label claim ranging 12-55 % for Augmentin, 7% for promethzine tablets and 9% for ciprofloxacin ointment. These results are in agreement, although less in magnitude than those observed during space flight and after gamma irradiation.

Vaksman, Z.↗
NASA NTRS2007

Pharmacovigilance in Space: Stability Payload Compliance Procedures

Pharmacovigilance is the science of, and activities relating to the detection, assessment, understanding, and prevention of drug-related problems. Over the lase decade, pharmacovigilance activities have contributed to the development of numerous technological and conventional advances focused on medication safety and regulatory intervention. The topics discussed include: 1) Proactive Pharmacovigilance; 2) A New Frontier; 3) Research Activities; 4) Project Purpose; 5) Methods; 6) Flight Stability Kit Components; 7) Experimental Conditions; 8) Research Project Logistics; 9) Research Plan; 10) Pharmaceutical Stability Research Project Pharmacovigilance Aspects; 11) Security / Control; 12) Packaging/Containment Actions; 13) Shelf-Life Assessments; 14) Stability Assessment Parameters; 15) Chemical Content Analysis; 16) Preliminary Results; 17) Temperature/Humidity; 18) Changes in PHysical and Chemical Assessment Parameters; 19) Observations; and 20) Conclusions.

Daniels, Vernie R.↗
NASA NTRS2004

Stochastic Stability of Nonlinear Sampled Data Systems with a Jump Linear Controller

This paper analyzes the stability of a sampled- data system consisting of a deterministic, nonlinear, time- invariant, continuous-time plant and a stochastic, discrete- time, jump linear controller. The jump linear controller mod- els, for example, computer systems and communication net- works that are subject to stochastic upsets or disruptions. This sampled-data model has been used in the analysis and design of fault-tolerant systems and computer-control systems with random communication delays without taking into account the inter-sample response. To analyze stability, appropriate topologies are introduced for the signal spaces of the sampled- data system. With these topologies, the ideal sampling and zero-order-hold operators are shown to be measurable maps. This paper shows that the known equivalence between the stability of a deterministic, linear sampled-data system and its associated discrete-time representation as well as between a nonlinear sampled-data system and a linearized representation holds even in a stochastic framework.

Gonzalez, Oscar R.↗
NASA NTRS2005

Atmospheric Stability & Turbulence from Temperature Profiles over Sicily During Summer 2002 & 2003 HASI Balloon Campaigns

Experimental results and interpretation of the temperature measurements data retrieved during the balloon campaigns (in 2002 and in 2003) for testing HASI (Huygens Atmospheric Structure Instrument), launched from the Italian Space Agency Base in Trapani (Sicily), are presented. Both ascending and descending phases are analysed; data reveal interesting features near the tropopause (present in the region between 11km-14km), where temperature cooling can be related to layers with strong winds (2002 flight); in the troposphere a multistratified structure of the temperature field is observed and discussed (particularly in the 2003 flight) Finally, stability and turbulence of the atmosphere are analysed; the buoyancy N2 parameters for both the flights show lowers value respect to standard tropospheric values corresponding to a lower stability of the atmosphere; still there is a higher stability above the tropopause. The energy spectrum of temperature data is consistent with the Kolmogorov theory: the characteristic k(sup -5/3) behaviour is reproduced.

Colombatti, G.↗
NASA NTRS2007

Model Checking a Byzantine-Fault-Tolerant Self-Stabilizing Protocol for Distributed Clock Synchronization Systems

This report presents the mechanical verification of a simplified model of a rapid Byzantine-fault-tolerant self-stabilizing protocol for distributed clock synchronization systems. This protocol does not rely on any assumptions about the initial state of the system. This protocol tolerates bursts of transient failures, and deterministically converges within a time bound that is a linear function of the self-stabilization period. A simplified model of the protocol is verified using the Symbolic Model Verifier (SMV) [SMV]. The system under study consists of 4 nodes, where at most one of the nodes is assumed to be Byzantine faulty. The model checking effort is focused on verifying correctness of the simplified model of the protocol in the presence of a permanent Byzantine fault as well as confirmation of claims of determinism and linear convergence with respect to the self-stabilization period. Although model checking results of the simplified model of the protocol confirm the theoretical predictions, these results do not necessarily confirm that the protocol solves the general case of this problem. Modeling challenges of the protocol and the system are addressed. A number of abstractions are utilized in order to reduce the state space. Also, additional innovative state space reduction techniques are introduced that can be used in future verification efforts applied to this and other protocols.

Malekpour, Mahyar R.↗
NASA NTRS1997

Fiber-optic delay-line stabilization of heterodyne optical signal generator and method using same

The present invention is a laser heterodyne frequency generator system with a stabilizer for use in the microwave and millimeter-wave frequency ranges utilizing a photonic mixer as a photonic phase detector in a stable optical fiber delay-line. Phase and frequency fluctuations of the heterodyne laser signal generators are stabilized at microwave and millimeter wave frequencies by a delay line system operating as a frequency discriminator. The present invention is free from amplifier and mixer 1/.function. noise at microwave and millimeter-wave frequencies that typically limit phase noise performance in electronic cavity stabilized electronic oscillators. Thus, 1/.function. noise due to conventional mixers is eliminated and stable optical heterodyne generation of electrical signals is achieved.

Logan, Ronald T.↗
NASA NTRS2007

Analytical Approach Validation for the Spin-Stabilized Satellite Attitude

An analytical approach for spin-stabilized spacecraft attitude prediction is presented for the influence of the residual magnetic torques and the satellite in an elliptical orbit. Assuming a quadripole model for the Earth s magnetic field, an analytical averaging method is applied to obtain the mean residual torque in every orbital period. The orbit mean anomaly is used to compute the average components of residual torque in the spacecraft body frame reference system. The theory is developed for time variations in the orbital elements, giving rise to many curvature integrals. It is observed that the residual magnetic torque does not have component along the spin axis. The inclusion of this torque on the rotational motion differential equations of a spin stabilized spacecraft yields conditions to derive an analytical solution. The solution shows that the residual torque does not affect the spin velocity magnitude, contributing only for the precession and the drift of the spin axis of the spacecraft. The theory developed has been applied to the Brazilian s spin stabilized satellites, which are quite appropriated for verification and comparison of the theory with the data generated and processed by the Satellite Control Center of Brazil National Research Institute. The results show the period that the analytical solution can be used to the attitude propagation, within the dispersion range of the attitude determination system performance of Satellite Control Center of Brazil National Research Institute.

Zanardi, Maria Cecilia F. P. S.↗
NASA NTRS2008

Verification of a Byzantine-Fault-Tolerant Self-stabilizing Protocol for Clock Synchronization

This paper presents the mechanical verification of a simplified model of a rapid Byzantine-fault-tolerant self-stabilizing protocol for distributed clock synchronization systems. This protocol does not rely on any assumptions about the initial state of the system except for the presence of sufficient good nodes, thus making the weakest possible assumptions and producing the strongest results. This protocol tolerates bursts of transient failures, and deterministically converges within a time bound that is a linear function of the self-stabilization period. A simplified model of the protocol is verified using the Symbolic Model Verifier (SMV). The system under study consists of 4 nodes, where at most one of the nodes is assumed to be Byzantine faulty. The model checking effort is focused on verifying correctness of the simplified model of the protocol in the presence of a permanent Byzantine fault as well as confirmation of claims of determinism and linear convergence with respect to the self-stabilization period. Although model checking results of the simplified model of the protocol confirm the theoretical predictions, these results do not necessarily confirm that the protocol solves the general case of this problem. Modeling challenges of the protocol and the system are addressed. A number of abstractions are utilized in order to reduce the state space.

Malekpour, Mahyar R.↗
NASA NTRS2008

Stability of Formulations Contained in the Pharmaceutical Payload Aboard Space Missions

Efficacious pharmaceuticals with adequate shelf life are essential for successful space medical operations in support of space exploration missions. Physical and environmental factors unique to space missions such as vibration, G forces and ionizing radiation may adversely affect stability of pharmaceuticals intended for standard care of astronauts aboard space missions. Stable pharmaceuticals, therefore, are of paramount importance for assuring health and wellness of astronauts in space. Preliminary examination of stability of formulations from Shuttle and International Space Station (ISS) medical kits revealed that some of these medications showed physical and chemical degradation after flight raising concern of reduced therapeutic effectiveness with these medications in space. A research payload experiment was conducted with a select set of formulations stowed aboard a shuttle flight and on ISS. The payload consisted of four identical pharmaceutical kits containing 31 medications in different dosage forms that were transported to the International Space Station (ISS) aboard the Space Shuttle, STS 121. One of the four kits was stored on the shuttle and the other three were stored on the ISS for return to Earth at six months intervals on a pre-designated Shuttle flight for each kit; the shuttle kit was returned to Earth on the same flight. Standard stability indicating physical and chemical parameters were measured for all pharmaceuticals returned from the shuttle and from the first ISS increment payload along with ground-based matching controls. Results were compared between shuttle, ISS and ground controls. Evaluation of data from the three paradigms indicates that some of the formulations exhibited significant degradation in space compared to respective ground controls; a few formulations were unstable both on the ground and in space. An increase in the number of pharmaceuticals from ISS failing USP standards was noticed compared to those from the shuttle flight. A comprehensive evaluation of results is in progress.

Putcha, Lakshmi↗
NASA NTRS2008

On the Application of a Response Surface Technique to Analyze Roll-over Stability of Capsules with Airbags Using LS-Dyna

As NASA moves towards developing technologies needed to implement its new Exploration program, studies conducted for Apollo in the 1960's to understand the rollover stability of capsules landing are being revisited. Although rigid body kinematics analyses of the roll-over behavior of capsules on impact provided critical insight to the Apollo problem, extensive ground test programs were also used. For the new Orion spacecraft being developed to implement today's Exploration program, new air-bag designs have improved sufficiently for NASA to consider their use to mitigate landing loads to ensure crew safety and to enable re-usability of the capsule. Simple kinematics models provide only limited understanding of the behavior of these air bag systems, and more sophisticated tools must be used. In particular, NASA and its contractors are using the LS-Dyna nonlinear simulation code for impact response predictions of the full Orion vehicle with air bags by leveraging the extensive air bag prediction work previously done by the automotive industry. However, even in today's computational environment, these analyses are still high-dimensional, time consuming, and computationally intensive. To alleviate the computational burden, this paper presents an approach that uses deterministic sampling techniques and an adaptive response surface method to not only use existing LS-Dyna solutions but also to interpolate from LS-Dyna solutions to predict the stability boundaries for a capsule on airbags. Results for the stability boundary in terms of impact velocities, capsule attitude, impact plane orientation, and impact surface friction are discussed.

Horta, Lucas G.↗
NASA NTRS2007

Dispersive Elements for Enhanced Laser Gyroscopy and Cavity Stabilization

We analyze the effect of a highly dispersive element placed inside a modulated optical cavity on the frequency and amplitude of the modulation to determine the conditions for cavity self-stabilization and enhanced gyroscopic sensitivity. We find an enhancement in the sensitivity of a laser gyroscope to rotation for normal dispersion, while anomalous dispersion can be used to self-stabilize an optical cavity. Our results indicate that atomic media, even coherent superpositions in multilevel atoms, are of limited use for these applications, because the amplitude and phase filters work against one another, i.e., decreasing the modulation frequency increases its amplitude and vice-versa. On the other hand, for optical resonators the dispersion reversal associated with critical coupling enables the amplitude and phase filters to work together. We find that for over-coupled resonators, the absorption and normal dispersion on-resonance increase the contrast and frequency of the beat-note, respectively, resulting in a substantial enhancement of the gyroscopic response. Under-coupled resonators can be used to stabilize the frequency of a laser cavity, but result in a concomitant increase in amplitude fluctuations. As a more ideal solution we propose the use of a variety of coupled-resonator-induced transparency that is accompanied by anomalous dispersion.

Smith, David D.↗
NASA NTRS2006

"Far" and "Near" Visual Acuity While Walking and the Collective Contributions of Non-Ocular Mechanisms to Gaze Stabilization

Gaze stabilization was quantified in subjects (n=11) as they walked on a motorized treadmill (1.8 m/s) and viewed visual targets at two viewing distances. A "far" target was positioned at 4 m (FAR) in front of the subject and the "near" target was placed at a distance of 0.5 m (NEAR). A direct measure of visual acuity was used to assess the overall effectiveness of the gaze stabilization system. The contributions of nonocular mechanisms to the gaze goal were also quantified using a measure of the distance between the subject and point in space where fixation of the visual target would require the least eye movement amplitude (i.e. the head fixation distance (HFD)). Kinematic variables mirrored those of previous investigations with the vertical trunk translation and head pitch signals, and the lateral translation and head yaw signals maintaining what appear as antiphase relationships. However, an investigation of the temporal relationships between the maxima and minima of the vertical translation and head pitch signals show that while the maximum in vertical translation occurs at the point of the minimum head pitch signal, the inverse is not true. The maximum in the head pitch signal lags the vertical translation minimum by an average of greater than 12 percent of the step cycle time. Three HFD measures, one each for data in the sagittal and transverse planes, and one that combined the movements from both planes, all revealed changes between the FAR and NEAR target viewing conditions. This reorganization of the nonocular degrees of freedom while walking was consistent with a strategy to reduce the magnitude of the eye movements required when viewing the NEAR target. Despite this reorganization, acuity measures show that image stabilization is not occurring while walking and viewing the NEAR target. Group means indicate that visual acuity is not affected while walking in the FAR condition, but a decrement of 0.15 logMAR (i.e. 1.5 eye chart lines) exists between the standing and walking acuity measures when viewing the NEAR target.

Peters, Brian T.↗
NASA NTRS2008

Laser Frequency Stabilization and Control through Offset Sideband Locking to Optical Cavities

We describe a class of techniques whereby a laser frequency can be stabilized to a fixed optical cavity resonance with an adjustable offset, providing a wide tuning range for the central frequency. These techniques require only minor modifications to the standard Pound-Drever-Hall locking techniques and have the advantage of not altering the intrinsic stability of the frequency reference. In a laboratory investigation the sideband techniques were found to perform equally well as the standard, non-tunable Pound-Drever-Hall technique, each providing more than four decades of frequency noise suppression over the free-running noise. An application of a tunable system as a pre-stabilization stage in a phase-lock loop is also presented with the combined system achieving a frequency noise suppression of nearly twelve orders of magnitude.

Thorpe, James I.↗
NASA NTRS2008

In-Flight Stability Analysis of the X-48B Aircraft

This report presents the system description, methods, and sample results of the in-flight stability analysis for the X-48B, Blended Wing Body Low-Speed Vehicle. The X-48B vehicle is a dynamically scaled, remotely piloted vehicle developed to investigate the low-speed control characteristics of a full-scale blended wing body. Initial envelope clearance was conducted by analyzing the stability margin estimation resulting from the rigid aircraft response during flight and comparing it to simulation data. Short duration multisine signals were commanded onboard to simultaneously excite the primary rigid body axes. In-flight stability analysis has proven to be a critical component of the initial envelope expansion.

Regan, Christopher D.↗
NASA NTRS2007

On the Long-Term Stability of Microwave Radiometers Using Noise Diodes for Calibration

Results are presented from the long-term monitoring and calibration of the National Aeronautics and Space Administration Jason Microwave Radiometer (JMR) on the Jason-1 ocean altimetry satellite and the ground-based Advanced Water Vapor Radiometers (AWVRs) developed for the Cassini Gravity Wave Experiment. Both radiometers retrieve the wet tropospheric path delay (PD) of the atmosphere and use internal noise diodes (NDs) for gain calibration. The JMR is the first radiometer to be flown in space that uses NDs for calibration. External calibration techniques are used to derive a time series of ND brightness for both instruments that is greater than four years. For the JMR, an optimal estimator is used to find the set of calibration coefficients that minimize the root-mean-square difference between the JMR brightness temperatures and the on-Earth hot and cold references. For the AWVR, continuous tip curves are used to derive the ND brightness. For the JMR and AWVR, both of which contain three redundant NDs per channel, it was observed that some NDs were very stable, whereas others experienced jumps and drifts in their effective brightness. Over the four-year time period, the ND stability ranged from 0.2% to 3% among the diodes for both instruments. The presented recalibration methodology demonstrates that long-term calibration stability can be achieved with frequent recalibration of the diodes using external calibration techniques. The JMR PD drift compared to ground truth over the four years since the launch was reduced from 3.9 to - 0.01 mm/year with the recalibrated ND time series. The JMR brightness temperature calibration stability is estimated to be 0.25 K over ten days.

noise diode (ND)↗
NASA NTRS2008

A Theoretical Solid Oxide Fuel Cell Model for Systems Controls and Stability Design

As the aviation industry moves toward higher efficiency electrical power generation, all electric aircraft, or zero emissions and more quiet aircraft, fuel cells are sought as the technology that can deliver on these high expectations. The hybrid solid oxide fuel cell system combines the fuel cell with a micro-turbine to obtain up to 70% cycle efficiency, and then distributes the electrical power to the loads via a power distribution system. The challenge is to understand the dynamics of this complex multidiscipline system and the design distributed controls that take the system through its operating conditions in a stable and safe manner while maintaining the system performance. This particular system is a power generation and a distribution system, and the fuel cell and micro-turbine model fidelity should be compatible with the dynamics of the power distribution system in order to allow proper stability and distributed controls design. The novelty in this paper is that, first, the case is made why a high fidelity fuel cell mode is needed for systems control and stability designs. Second, a novel modeling approach is proposed for the fuel cell that will allow the fuel cell and the power system to be integrated and designed for stability, distributed controls, and other interface specifications. This investigation shows that for the fuel cell, the voltage characteristic should be modeled but in addition, conservation equation dynamics, ion diffusion, charge transfer kinetics, and the electron flow inherent impedance should also be included.

Kopasakis, George↗
NASA NTRS2008

Current Methods for Modeling and Simulating Icing Effects on Aircraft Performance, Stability and Control

Icing alters the shape and surface characteristics of aircraft components, which results in altered aerodynamic forces and moments caused by air flow over those iced components. The typical effects of icing are increased drag, reduced stall angle of attack, and reduced maximum lift. In addition to the performance changes, icing can also affect control surface effectiveness, hinge moments, and damping. These effects result in altered aircraft stability and control and flying qualities. Over the past 80 years, methods have been developed to understand how icing affects performance, stability and control. Emphasis has been on wind tunnel testing of two-dimensional subscale airfoils with various ice shapes to understand their effect on the flow field and ultimately the aerodynamics. This research has led to wind tunnel testing of subscale complete aircraft models to identify the integrated effects of icing on the aircraft system in terms of performance, stability, and control. Data sets of this nature enable pilot in the loop simulations to be performed for pilot training, or engineering evaluation of system failure impacts or control system design.

Ralvasky, Thomas P.↗
NASA NTRS2007

Stability and Control Analysis of the F-15B Quiet Spike Aircraft

The primary objective of the Quiet Spike flight research program was the aerodynamic and structural proof-of-concept of a telescoping, 24 ft, sonic-boom suppressing nose boom on a F-15B aircraft. The program goal was to collect flight data for model validation up to 1.8 Mach. In the area of stability and controls the primary concern was to assess the effect of the spike on the stability, controllability and handling qualities of the aircraft. The primary goal of this test philosophy was maintaining safety of flight. Two main issues are discussed in this paper: the stability and controls approach and analysis in the presence of uncertain spike influenced aerodynamics on the F-15B aircraft flight dynamics; and the analysis of F-15B flight dynamics implications due to spike induced air flow in the vicinity of air data and angle-of-attack sensors. Also addressed are flight test implications based on the analysis

McWherter, Shaun↗