Orion Reentry Guidance with Extended Range Capability Using PredGuid

Inertial Navigation System

Improving the Performance of Plans Executed Under Uncertainty

Microfabrication of Three-Dimensional Engineered Scaffolds

ALHAT System Architecture and Operational Concept

Space Validation of the Inertial Stellar Compass

System Architecture and Operational Concept for an Autonomous Precision Lunar Landing System

Effects of Tooling and Injection Molding Conditions on Nanoscale Replication of Thermoplastic Elastomers

Micro-Injection Molding of High Aspect Ratio Features with Thermoplastic Polyurethanes

Design, Test, and Mathematical Model Validation of a Small Energy-Scavenging Water-Turbine

Risk Assessment Methodology for Lead-Free Solder Assembly

Robust Subspace Learning and Detection in Laplacian Noise and Interference

GN&C Engineering Best Practices for Human-Rated Spacecraft Systems

Fluorescent Ion-Selective Nanosensors for Intracellular Analysis with Improved Lifetime and Size

Ion-Selective Nano-Optodes Incorporating Quantum Dots

Design of a Human-Interactive Autonomous Flight Manager (AFM) for Crewed Lunar Landing

Resolution Limits and Process Latitude of Deep-Ultraviolet Conformable Contact Photolithography

Examination of Planning Under Uncertainty Algorithms for Cooperative Unmanned Aerial Vehicles

Rocket Dispersed Instruments: A Mission Architecture for Exploring Lunar Polar Hydrogen

Optimal Microsatellite Cluster Design for Space-Based Tracking Missions

Automated and Manual Commanding Concepts for Orion Ascent Guidance, Navigation, and Control

Comparison of Accuracy and Computational Efficiency of Three Pseudospectral Methods

MIMO Adaptive Bank-to-Steer Control Algorithms for Guided Reentry Vehicles

Miniature Atomic Clock Preproduction Results

High-Performance MEMS Inertial Instruments Fabricated on LTCC Substrates

Time-Lapse Measurements of Stress Relaxation in MEMS Sensor Die Bonds

Risk Management in the Risk-Aware Mixed-Initiative Dynamic Replanning (RMDR) System for UxVs

Unmanned System Risk Management

Analysis of Biomarker Features from a Differential Mobility Spectrometer for the Detection of Tuberculosis

Optimal Estimation of Dynamic Ionosphere Induced Group Delays of GPS Signals

Operations Simulation Framework to Evaluate Vehicle Designs for Planetary Surface Exploration

Transient, Three-Dimensional, Multiscale Simulations of the Human Aortic Valve

Team Planning for Unmanned Vehicles in the Risk-Aware Mixed-Initiative Dynamic Replanning System

Bairstow, S.H.; Barton, G.H.

Orion Reentry Guidance with Extended Range Capability Using PredGuid

Guidance, Navigation, and Control Conference and Exhibit, Hilton Head, SC, 8/20/2007-8/23/2007. Sponsored by: AIAA (Draper Report no. P-4565)

Abstract: A reentry and precision landing algorithm using bank angle modulation control that enables precision landing for target locations between 2,400 km and 10, 000 km downrange of Entry Interface (EI) was designed for the Orion spacecraft. The algorithm is general enough to be applicable to variations in Orion vehicle design. The algorithm was tested against various reentry scenarios, including perturbations in initial entry conditions, vehicle mass, aerodynamic properties, and atmospheric density. The algorithm was shown to be robust to these uncertainties to allow a delivery error of less than 3.5 km for the entire 2,400 km-10,000 km landing footprint. The guidance algorithm is based on the Apollo entry guidance algorithm and upgraded using PredGuid, a numeric predictor-corrector aerocapture algorithm developed by Draper Laboratory for the Aero-assist Flight Experiment in the late 1980s. The upgrades were sufficient to allow precision landing of skip reentry trajectories for target ranges of up to 10,000 km. In addition, it was shown that skip trajectory shaping can be controlled by modulating the time at which the PredGuid guidance phase takes over.

Subjects: ATMOSPHERIC REENTRY, CREW EXPLORATION VEHICLES (CEV), ALGORITHMS

Barbour, N.M.; Howell, W.E.

Inertial Navigation System

McGraw-Hill Yearbook of Science and Technology, 2007 (Draper Report no. P-4475)

Abstract: A self-contained system that can automatically determine the position, velocity, and attitude of a moving vehicle for the purpose of directing its future course. Based on prior knowledge of time, gravitational field, initial position, initial velocity, and initial orientation relative to a known reference frame (coordinate system), an inertial navigation system is capable of determining its current position, velocity, and orientation without the aid of external information. The generated navigational data are used to determine the future course for a vehicle to follow in order to bring it to its destination. Such systems have found application in the guidance and control of submarines, ships, aircraft, missiles, and spacecraft. The term inertial is derived from the fact that measurements are made based on one of the basic properties of mass - inertia. The sensors making these measurements in the Inertial Navigation System (INS) are gyros and accelerometers. INSs are used in many different types of applications that require vastly different performance from the gyros and accelerometers and are broadly classified by the quality (accuracy limitations) of their gyros and accelerometers: commercial grade (automobiles): >1 deg/s >50 mg; tactical grade (short-range missiles): 1 deg/h 1 mg; navigation grade (aircraft): 0.01 deg/h 25 μg; strategic grade (long-range missiles): 0.001 deg/h 1 μg. In this list, the gyro bias drift rate is given in units of deg/unit time and the accelerometer bias is given in terms of milli-g or μg, where 1 g = 32 ft/s².

Subjects: INERTIAL NAVIGATION, NAVIGATION SYSTEMS

Barnhart, C.; Kolitz, S.E.

Improving the Performance of Plans Executed Under Uncertainty

Infotech at Aerospace Conference 2007, Rohnert Park, CA, 5/7/2007-5/10/2007. Sponsored by: AIAA. (Draper Report number P-4547)

Abstract: We define the concept of robust optimization-based planning under uncertainty as well as associated measures of merit, including those related to the performance of the plans when executed under uncertainty. We discuss the sources of the uncertainty, e.g., in the environment, the system state, and the effects of the activities by the entities. We present an overview of methodologies for developing robust optimization-based plans. We describe a set of problems of interest in a variety of domains, e.g., transportation and logistics, air operations, remote and in-situ sensing, in which there are entities performing activities under uncertainty.

Subjects: ROBUST PLANNING, UNCERTAINTY, MISSION PERFORMANCE

Borenstein, J.T.; Weinberg, E.J.; Orrick, B.; Sundback, C.; Kaazempur-Mofrad, M.R.; Vacanti, J.P.

Microfabrication of Three-Dimensional Engineered Scaffolds

Tissue Engineering, Vol. 13, No. 8, August 2007, pp. 1837-1843 (Draper Report no. P-4434)

Abstract: One of the principal challenges facing the field of tissue engineering over the past 2 decades has been the requirement for large-scale engineered constructs comprising precisely organized cellular microenvironments. For vital organ assist and replacement devices, microfluidic-based systems such as the microcirculation, biliary, or renal filtration and resorption systems and other functional elements containing multiple cell types must be generated to provide for viable engineered tissues and clinical benefit. Over the last several years, microfabrication technology has emerged as a versatile and powerful approach for generating precisely engineered scaffolds for engineered tissues. Fabrication process tools such as photolithography, etching, molding, and lamination have been established for applications involving a range of biocompatible and biodegradable polymeric scaffolding materials. Computational fluid dynamic designs have been used to generate scaffold designs suitable for microvasculature and a number of organ-specific constructs; these designs have been translated into 3-dimensional scaffolding using microfabrication processes. Here, a brief overview of the fundamental microfabrication technologies used for tissue engineering will be presented, along with a summary of progress in a number of applications, including the liver and kidney.

Subjects: TISSUE ENGINEERING, MICROFABRICATION, LIVER, KIDNEY

Borer, N.K.; Mavris, D.N.

Requirements Decomposition for Compact Multidimensional Visualization

45th Aerospace Sciences Meeting and Exhibit, Reno, NV, 1/8/2007-1/11/2007. Sponsored by: AIAA (Draper Report no. P-4448)

Abstract: Most practical system design problems require some form of tradeoff analysis. The use of decision-making techniques helps automate this process, although some additional corrections are likely necessary. The authors have previously devised methods to manipulate the relative importance of decision metrics to account for local changes in utility and interdependence. However, the presence of interdependence among the decision metrics indicates that there is likely an underlying, linearly independent subset of characteristic tradeoffs that can represent the entire decision space. This paper describes a method to determine this independent subset from a system of polynomial response surface equations used to approximate the decision domain. The coefficients for the characteristic tradeoffs follow from a linear decomposition of the coefficients of the original response surfaces representing the requirements. These characteristics are then used for compact multidimensional visualization by viewing the entire decision space though a scatterplot matrix along the most important characteristic dimensions.

Subjects: TRADE OFF ANALYSES, MULTIDIMENSIONAL VISUALIZATION, SYSTEM DESIGN

Brady, T.M.; Schwartz, J.L.

ALHAT System Architecture and Operational Concept

Aerospace Conference 2007, Big Sky, MT, 3/3/2007-3/10/2007. Sponsored by: IEEE (Draper Report number P-4486)

Abstract: An autonomous lunar landing system applicable to a wide variety of crewed and robotic lunar descent vehicles is under development as part of the Autonomous Precision Landing and Hazard Detection and Avoidance Technology (ALHAT) project. This system, referred to as the ALHAT System Module (ASM), is a highly advanced integrated sensor suite that enables landing a lunar descent vehicle within tens of meters of a certified and designated landing location anywhere on the Moon under any lighting condition. This paper describes the basic ASM architecture and its novel concept of operations, and matures this architecture through a description of top-level lunar landing requirements. Working closely with NASA primary stakeholders, a fully developed ASM design will enable global lunar access for the exploration of unique and challenging areas on the lunar surface never before visited.

Subjects: AUTONOMOUS LANDING SYSTEMS, ALHAT SYSTEM MODULE (ASM), AUTONOMOUS PRECISION LANDING AND HAZARD DETECTION AND AVOIDANCE TECHNOLOGY (ALHAT), LUNAR LANDING

Brady, Tye M.; Buckley, Sean; Leammukda, Mitch G.

Space Validation of the Inertial Stellar Compass

Presented at: 21st Small Satellites, Conference, Logan, UT, 8/13-16, 2007. Sponsored by: AIAA/Utah State University (Draper Report number P-4524)

Abstract: Draper's Inertial Stellar Compass (ISC) is a real-time, miniature, low-power stellar inertial attitude determination system, composed of a wide field-of-view active pixel sensor (APS) star camera and a microelectromechanical system (MEMS) gyro assembly with associated processing and power electronics. The integrated APS and MEMS gyro technologies provide a 3-axis attitude determination system with accuracy better than 0.1 deg at very low power and mass. The attitude knowledge provided by the ISC is applicable to a wide range of space missions that may include the use of highly maneuverable, stabilized, or even tumbling spacecraft. Under the guidance of NASA's New Millennium Program's ST-6 project, Draper has developed and now flight validated the ISC. Its completion via flight validation represents a breakthrough in real-time, miniature attitude determination sensors. This paper describes the space validation component and initial on-orbit results of the ISC.

Subjects: INERTIAL STELLAR COMPASS (ISC), STAR CAMERAS, MICROELECTROMECHANICAL SYSTEMS (MEMS)

Brady, T.M.; Schwartz, J.L.; Tillier, C.E.

System Architecture and Operational Concept for an Autonomous Precision Lunar Landing System

30th Guidance and Control Conference, Breckenridge, CO, 2/3/2007-2/7/2007. Sponsored by: AAS (Draper Report no. P-4485)

Abstract: The Precision Landing System (PLS) developed by Draper Laboratory under contract to NASA is an autonomous lunar landing system applicable to a wide variety of crewed and robotic lunar descent vehicles. If developed, this highly advanced integrated sensor suite would be capable of landing a lunar descent vehicle within 10-100 m of a designated landing location anywhere on the Moon under any lighting condition. This paper describes the basic PLS architecture, its novel concept of operations, and a developed set of top-level lunar landing requirements. With NASA as a primary stakeholder, the PLS architectural work has been adopted by the Johnson Space Center-led ALHAT (Autonomous precision Landing and Hazard detection and Avoidance Technology) program as a starting point for a design that will ultimately enable global lunar access for exploration of unique and challenging areas on the lunar surface never before visited.

Subjects: AUTONOMOUS SYSTEMS, PRECISION LANDING SYSTEMS (PLS), LUNAR LANDING

Carter, D.J.; Alabran, M.W.; Mead, J.L.; Barry, C.M.F.; Busnaina, A.A.

Effects of Tooling and Injection Molding Conditions on Nanoscale Replication of Thermoplastic Elastomers

65th Annual Technical Conference, Society of Plastics Engineers, Cincinnati, OH, 5/6/2007-5/11/2007. Sponsored by: Society of Plastics Engineers. (Draper Report number P-4511)

Abstract: The effect of tooling geometry and processing conditions on the ability to injection mold nanoscale features was investigated for thermoplastic polyurethanes (TPUs). While pattern geometry was not as critical as feature size in determining good replication, TPUs exhibited enhanced replication quality when compared to a polycarbonate control. Melt temperature was limited by polymer degradation, but increasing mold temperatures provided better replication. Very high mold temperatures, however, did not improve replication and were detrimental to cycle time.

Subjects: MOLDING MATERIALS, TOOLING, NANOSCALE DEVICES

Carter, D.J., Yoon, S-H., Alabran, M.W., Lee, J.S., Mead, J.L., Barry, C.M.F.

Micro-Injection Molding of High Aspect Ratio Features with Thermoplastic Polyurethanes

65th Annual Technical Conference, Society of Plastics Engineers, Cincinnati, OH, 5/6/2007-5/11/2007. Sponsored by: Society of Plastics Engineers. (Draper Report number P-4512)

Abstract: High aspect ratio (4:1) microscale features were injection moulded using thermoplastic polyurethanes and silicon tooling and measured using atomic force and scanning electron microscopy. Direct filling of the features enhanced replication when compared to indirect filling (i.e., filling during melt pressurization). With direct filling, mould temperature and melt temperature equally impacted replication. For good replication, mould temperatures must selected to balance filling, stretching of moulded features during ejection, and shrinkage of the features.

Subjects: THERMOPLASTIC POLYURETHANES, MOLDING TECHNIQUES

Chhabra, N.K.; Anderson, J.M.; Ogrodnik, T.G.; Sallum, H.M.; Barton, G.H.

Design, Test, and Mathematical Model Validation of a Small Energy-Scavenging Water-Turbine

15th Unmanned Untethered Submersible Technology, Durham, NH, 8/19/2007-8/22/2007. Sponsored by: AUSI (Draper Report no. P-4526)

Abstract: A technique to extend long-term marine missions, whether fixed sensor or mobile platform, is to replenish energy in-situ by scavenging. Moving water (currents in rivers, estuaries, and littoral oceans) is a source of energy for scavenging through an efficient turbine-generator. This project investigates the feasibility of building a scavenging system to generate single watt-scale power for today's low-power environmental sensors at relatively low-water velocities. The same system generates meaningful power (10-30 W) at higher current velocities, making recharge of propulsion batteries feasible for small mobile platforms. Most currently used wind turbines are large, horizontal, must weathervane, and require larger wind speeds for operation. Their heavy generator and gearing is on axis, high above the base. Vertical axis turbines are smaller, omnidirectional, and have slower blade speeds. The generator can be located at ground level, facilitating maintenance. The vertical H-Darrieus (lift-type) configuration was the architecture selected for this study for its simple design (lends itself to unfolding for deployment), better aerodynamic performance, and potential antifouling characteristics. A time-tested approach to designing an efficient prototype system includes analytical models and simulation, physical model testing in a controlled environment, and full-scale field testing. A mathematical model and simulation of water turbines, including relevant blade assembly hydrodynamics and generator (motor) equations, along with various losses, was developed. A compact H-Darrieus turbine with interchangeable blades (number and section) was designed to prove feasibility (1 W at 1 kn with approximately 1 ft^2 projected area) at the relevant scales and Reynolds numbers. Several prototype turbines were built, integrated with instrumentation for measuring performance, and tested in the Tow Tank at the Center for Coastal and Ocean Mapping/Joint Hydrographic Center (CCOM/JHC) at the University of New Hampshire. A Savonius-rotor (drag-type) water turbine was also built and tested with the same instrumentation to serve as a reference. The best turbine blades tested provided peak hydrodynamic (including friction) efficiencies of 18% at 3-kn water speed (low because of low Reynolds number). The efficiency curves extrapolate to higher efficiencies at increased speeds. The reference Savonius-rotor turbine had a peak efficiency of 11% at a 2-kn speed, and its efficiency dropped at 3 kn. At the 3-kn speed, peak hydrodynamic power measured for blades is 33 W and 17 W for a Savonius rotor of same frontal area. At 1 kn, blades produced a power of 0.6 W, and the Savonius rotor turbine of same area produces a power of 0.5 W. The mathematical model predictions for the tested prototypes matched well with measurements.

Subjects: WATER TURBINES, MATHEMATICAL MODELS, ENERGY SCAVENGING, MARINE VEHICLES

Cooper, K.A.; Judge, E.E.; Bjune, C.K.; Marinis, T.F.; Medernach, J.A.; Robert, A.L.; Soucy, J.W.

Risk Assessment Methodology for Lead-Free Solder Assembly

IMAPS National Meeting, San Jose, CA, 11/11/2007-11/15/2007. Sponsored by: International Microelectronics and Packaging Society (IMAPS). (Draper Report number P-4589)

Abstract: Electronics assembly is being disrupted in large industrial concerns as well as engineering prototype laboratories by the rapid transition to lead-free assembly. At the same time, electronics in military systems is becoming more complex, highly miniaturized, and subject to ever harsher treatment. For example, inertial guidance systems are being deployed in many gun-launched projectiles, all types of autonomous vehicles are becoming smaller and more capable, and hand-carried navigation and communications equipment is critical to the effectiveness of deployed soldiers. High reliability is of paramount concern in all these applications. As part of our effort to develop and qualify a lead-free assembly process, we are designing a software tool to estimate the failure rate of component assemblies. Our initial effort is focused on temperature cycle-induced failures, but our intent is to extend the tool capabilities to include shock and vibration stresses as well. We envision two primary applications, the first of which is to estimate the failure rate of individual devices and aggregates of components for designing systems to meet reliability requirements. The second application is to design experiments for demonstrating the reliability of component assemblies or fabrication processes. Our approach to estimating failure rates is to blend accumulated energy density wear out models with Weibull distribution parameters, which have been measured for selected cases. We have adopted an object-oriented programming methodology and are implementing the software in the Java programming language. Measured attributes are assigned to component and circuit board objects. Solder joint properties are determined from a combination of measured attributes, such as initial composition and volume, component and circuit board finishes, and estimates of metallurgical changes due to base metal dissolution and intermetallic growth. These properties are used to calculate coefficients for a fatigue model, which is used to estimate mean cycles to failure. A Weibull distribution is applied to project the time-dependent failure rate.

Subjects: LEAD-FREE SOLDER, TEMPERATURE CYCLING, ACCUMULATED DAMAGE MODEL, RELIABILITY PREDICTION

Desai, M.N.; Mangoubi, R.S.

Robust Subspace Learning and Detection in Laplacian Noise and Interference

IEEE Transactions on Signal Processing, Vol. 55, No. 7, Pt. II, 7/2007, pp. 3585-3595 (Draper Report no. P-4398)

Abstract: We address the problem of maximum likelihood subspace learning and detection in the presence of Laplacian noise and interference whose subspace may be known or unknown. For subspace learning, the Laplacian problem reduces to a maxmin convex mathematical program with polyhedral cost. The minimization involves projection of the measurements onto a subspace orthogonal to the signal and interference spaces and has linear constraints, while the maximization produces the subspace and has polyhedral constraints. The Laplacian noise model for subspace detection and estimation, motivated by applications in functional magnetic resonance imaging and applicable in other areas, yields maximum likelihood detectors and learned subspaces with unique structure. For instance, the optimal learned subspace can consist of vectors whose elements take values of +1 or -1 only. Emergence of such a quantization attests to the robustness property of Laplacian learning, meaning that the solution is insensitive to perturbation in the data set. The resulting detectors are similarly robust to false alarms and have computationally attractive properties.

Subjects: SUBSPACE, LAPLACIAN NOISE, MATCHED FILTERS

Dennehy, C.J.; Lebsock, K.; West, J.J.

GN&C Engineering Best Practices for Human-Rated Spacecraft Systems

Guidance, Navigation, and Control Conference and Exhibit, Hilton Head, SC, 8/20/2007-8/23/2007. Sponsored by: AIAA. (Draper Report no. P-4529)

Abstract: The NASA Engineering and Safety Center (NESC) recently completed an in-depth assessment to identify a comprehensive set of engineering considerations for the Design, Development, Test, and Evaluation (DDT&E) of safe and reliable human-rated spacecraft systems. Reliability subject matter experts, discipline experts, and systems engineering experts were brought together to synthesize the current "best practices" at both the spacecraft system and subsystems levels. The objective of this paper is to summarize, for the larger Community of Practice, the initial set of Guidance, Navigation, and Control (GN&C) engineering Best Practices as identified by this NESC assessment process.

Subjects: GUIDANCE NAVIGATION AND CONTROL (GN&C), BEST PRACTICES

Dubach, J.M.; Harjes, D.I.; Clark, H.A.

Fluorescent Ion-Selective Nanosensors for Intracellular Analysis with Improved Lifetime and Size

Nano Letters, ACS, Vol. 7, No. 6, 6/2007, pp. 1827-1831 (Draper Report number P-4540)

Abstract: We describe the synthesis and characterization of sodium-selective polymeric nanosensors that improves on the lifetime and size of previous fiberless nanosensors. Sonication is used to form the polymer nanospheres that contain all the components needed for ion sensing. Even though the size is small (approximately 120 nm), the lifetime of these sensors in solution is on the order of a week. The surface coating has also been optimized for stability, biocompatibility, and ease of chemical modification.

Subject: NANOSENSORS

Dubach, J.M.; Harjes, D.I.; Clark, H.A.

Ion-Selective Nano-Optodes Incorporating Quantum Dots

Journal of the American Chemical Society, Vol. 129, No. 27, July 11, 2007, pp. 8418-8419. (Draper Report no. P-4541)

Abstract: Ion-selective quantum dots (ISQDs) have been produced that are capable of measuring physiologically relevant ions (such as Na+, K+, Cl-, etc.). ISQDs consist of quantum dots, an ion-selective polymer matrix, and a biocompatible coating. ISQDs work by selective ion extraction by the polymer matrix, which leads to a change in the absorbance intensity of an embedded dye. This attenuates the intensity of the quantum dot by directly absorbing its fluorescence emission. As an example of this technology, a sodium-selective ISQD measures sodium over the range of 1 mM to 1 M with 200-fold selectivity over potassium and a resolution of 80 M at 10 mM.

Subjects: ION SELECTIVE QUANTUM DOTS, BIOCOMPATIBLE MATERIALS

Forest, L. M.; Kahn, A. C.; Thomer, J. L.

The Design and Evaluation of Human-Guided Algorithms for Mission Planning

Human Systems Integration Symposium (HSIS). 2007. Annapolis, MD. 03/19/2007 - 03/21/2007. Sponsored by: American Society of Naval Engineers (Draper Report no. P-4502)

Abstract: Human-guided algorithms can improve the quality of plans and reduce the overall planning time required by mission planners. Mechanisms for the human decision maker to guide the algorithm towards a solution that fits their intent allows the strengths of the human and the algorithm to both be utilized. A framework for designing human-guided algorithms is described and tested through a prototype UAV mission planning system. The results validate that human-guided algorithms successfully assist operators in rapidly reaching the best plan option that meets their objectives.

Subjects: UNMANNED AUTONOMOUS VEHICLES (UAV), HUMAN-GUIDED ALGORITHMS (HGA), HUMAN COMPUTER INTERACTION (HCI), MISSION PLANNING

Forest, L.M.; Kessler, L.J.; Homer, M.L.

Design of a Human-Interactive Autonomous Flight Manager (AFM) for Crewed Lunar Landing

Infotech at Aerospace Conference 2007, Rohnert Park, CA, 5/7/2007-5/10/2007. Sponsored by: AIAA (Draper Report number P-4503)

Abstract: To meet NASA's requirement for more independence from ground control, an Autonomous Flight Manager (AFM) is needed for lunar landings. The AFM will handle the mechanistic tasks such as the vehicle control needed to maneuver and cueing when astronaut input is needed. This technology will allow the astronauts to perform a supervisory role, making higher level knowledge-based decisions. Draper's proven autonomy capability is extended to include mechanisms for a human operator, either onboard or remotely controlling the vehicle, to interrupt and redirect the autonomous system at different levels of autonomous control. A proposed AFM design, including human "reach-in," is described.

Subjects: AUTONOMOUS FLIGHT MANAGER (AFM), LUNAR LANDING, AUTONOMOUS PRECISION LANDING AND HAZARD DETECTION AND AVOIDANCE TECHNOLOGY (ALHAT)

Fucetola, C.P.; Carter, D.J.; Goodberlet, J.G.

Resolution Limits and Process Latitude of Deep-Ultraviolet Conformable Contact Photolithography

51st International Conference on Electron, Ion, and Photon Beam Technology and Nanofabrication, CO, 5/29/2007-6/1/2007. Sponsored by: EIPBN. (Draper Report number P-4557)

Abstract: We present for the first time a study of the exposure latitude of deep-ultraviolet conformable contact photolithography in a nonevanescent regime. Exposures of grating patterns with half-pitches ranging from several hundred nanometers to 100 nm are simulated and experimentally demonstrated using an optimized trilayer resist stack. We show that a mask geometry with the absorber embedded in the glass improves image contrast, and therefore exposure latitude over a conventional chrome-on-glass mask geometry. We show that conformable contact photolithography is suitable for printing 500 nm to100 nm half-pitch features with an exposure latitude of +/-22% for +/-15% linewidth tolerance.

Subject: PHOTOLITHOGRAPHY

Gandhi, R.B.; Yang, L.C.

Examination of Planning Under Uncertainty Algorithms for Cooperative Unmanned Aerial Vehicles

Infotech at Aerospace Conference 2007, Rohnert Park, CA, 5/7/2007-5/10/2007. Sponsored by: AIAA. (Draper Report number P-4538)

Abstract: Cooperation is essential for numerous tasks. Cooperative planning seeks actions to achieve a team's common set of objectives by balancing both the benefits and the costs of execution. Uncertainty in action outcomes and external threats complicates this task. Planning algorithms can be generally classified into two categories: exact and heuristic. In this research, an exact planner, based on Markov decision processes, and a heuristic, receding horizon controller are evaluated in typical planning problems. The exact planner searches for an optimal policy with global contingencies, while the heuristic controIler sequentially approximates the global plans over local horizons. Generally, the two planners trade mission and computational performance. Although the results are limited to specific problem instances, they provide characterizations of the algorithms' capabilities and limitations. The exact planner's policy provides an optimal course of action for all possible conditions over the mission duration; however, the algorithm consumes substantial computational resources. On the other hand, the heuristic approach does not guarantee optimality, but may form worthy plans without evaluating every contingency. On a fully observable battlefield, the planners coordinate a team of unmanned aerial vehicles (UAVs) to obtain a maximum reward by destroying targets. Stochastic components, including UAV capability and attrition, represent uncertainty in the simulated missions. For a majority of the examined scenarios, the exact planner exhibits statistically better mission performance at considerably greater computational cost in comparison to the heuristic controller. Scalability studies show that these trends intensify in larger missions that include increasing numbers of UAVs and targets. Additionally, sensitivity trials are used to capture each algorithm's robustness to real-world planning environments where planners must negotiate incomplete or inaccurate system models. The mission performances of both methods degrade as the quality of their system models worsen.

Subjects: UNCERTAINTY, ALGORITHMS, MISSION PLANNING, UNMANNED AERIAL VEHICLES (UAV)

Garrick-Bethell, I.; West, J.J.

Rocket Dispersed Instruments: A Mission Architecture for Exploring Lunar Polar Hydrogen

38th Enabling Exploration, Lunar Outpost and Beyond, Houston, TX, 10/1/2007-10/5/2007. Sponsored by: Lunar Exploration Analysis Group (LEAG) (Draper Report no. P-4583A)

Abstract: The distribution of lunar hydrogen as mapped by Lunar Prospector is not known at a resolution better than 30-45 km. Even if the neutron spectrometer on the 2008 Lunar Reconnaissance Orbiter (LRO) achieves its maximum potential, the resulting hydrogen abundance map will only have a resolution of 5 km at the poles. Therefore, after LRO, we will not have knowledge of the distribution of hydrogen necessary for planning in-depth surface-based scientific study and human utilization. Without such knowledge, it is possible that the human landing site chosen will be located too far from significant hydrogen deposits. Furthermore, after LRO, we will not know if the hydrogen is actually in the form of water, protons imbedded in the lunar soil, or some other state. Therefore, it will be essential to perform detailed in situ mapping and characterization of polar hydrogen before any human mission that wishes to exploit or study it in detail. Even after an initial site characterization, our proposed architecture can be used indefinitely for followup studies by humans on the surface.

Subjects: ROCKET SYSTEMS, LUNAR LANDING SITES, ROBOTIC SPACE EXPLORATION

Griffith, J.D.; Singh, L.; How, J.

Optimal Microsatellite Cluster Design for Space-Based Tracking Missions

Guidance, Navigation, and Control Conference and Exhibit, Hilton Head, SC, 8/20/2007-8/23/2007. Sponsored by: AIAA. (Draper Report number P-4516)

Abstract: This paper presents an optimization formulation to design a cluster of microsatellites for space-based tracking missions. The first part of this research synthesizes the relative motion of the microsatellites about a formation center in order to minimize the model-based expected tracking position error covariance. Clusters are designed with a variety of constraints on size and number of satellites in the cluster. Primary findings show that cluster size has more influence on tracking performance than the number of satellites in a cluster. In addition, a second optimization approach which also penalizes J2-induced relative drift shows that a cluster can be designed that has a cracking performance that is invariant to relative satellite drift. Results are validated with extensive simulations where clusters are modeled as executing a centralized tracking Kalman filter. In terms of a resource allocation problem, these findings suggest that a clusterized constellation approach for space-based tracking missions may not be the best design approach. A dense, distributed constellation may perform tracking missions with a higher degree of success.

Subjects: MICROSATELLITES, SATELLITE DESIGN, TRACKING SYSTEMS, SPACE MISSIONS

Hart, J.J.; Miotto, P.; Zimpfer, D.J.; Cleary, M.E.; Proud, R.W.; Wells, A.

Automated and Manual Commanding Concepts for Orion Ascent Guidance, Navigation, and Control

Guidance, Navigation, and Control Conference and Exhibit, Hilton Head, SC, 8/20/2007-8/23/2007. Sponsored by: AIAA. (Draper Report number P-4582)

Abstract: The Orion Crew Exploration Vehicle (CEV) program requires automated capability for numerous guidance, navigation, and control (GN&C) functions during the ascent phase of flight, particularly the automated execution of ascent abort scenarios. To satisfy the requirements for automated capability, a GN&C architecture is needed that can sequence through the necessary segments of flight as well as accommodate manual commanding and control. This paper outlines a preliminary architecture for the execution of GN&C for the Orion vehicle. The GN&C segments are described that capture the necessary GN&C functionality used to perform nominal ascent and ascent aborts. This architecture is also used to help determine the division of responsibility between the GN&C executive and the Vehicle Systems Manager, which is responsible for coordination between subsystems at the vehicle level as well as current vehicle phases, segments, modes and the overall mission timeline. As part of this analysis, preliminary manual commanding and control concepts are also captured. These results will be used to derive detailed designs for Orion commanding and sequencing.

Subjects: CREW EXPLORATION VEHICLES (CEV), GUIDANCE NAVIGATION AND CONTROL (GN&C), ASCENT GUIDANCE, VEHICLE SYSTEMS MANAGER (VSM)

Hattis, P. D.; Carter, D. W.; George, S.; McConley, M. W.; Rasmussen, S. A.; Singh, L.; Tavan, S.

Autonomous Large Parafoil Guidance, Navigation and Control System Design Status

Aerodynamic Decelerator Systems Technology Conference. 19th. Williamsburg, VA. 05/21/2007 - 05/24/2007 (Draper Report no. P-4533)

Abstract: Demonstration of autonomous Guidance, Navigation, and Control (GN&C) that can take parafoil airdrop systems from 25,000 feet to accurate landings is a key goal of the Joint Precision Airdrop System. A first instantiation test-flew a 10,000 pound-class parafoil
system and has since been extended to accommodate payloads up to 30,000 pounds and as small as a few hundred pounds. The initial avionics applied by the GN&C software used a two-antenna Global Positioning System (GPS) receiver to obtain position, velocity, and heading data. Upgraded avionics now use a single-antenna GPS receiver providing position and velocity combined with inertial sensors providing three-axis acceleration and angular rate data. The guidance algorithm is partitioned into homing, energy management, and an optimized table-lookup terminal flight phase. The control algorithm is a proportional, integral, derivative design with features to deal with system constraints and with feed forward to improve response time. The GN&C software integration and testing is accomplished using a 6 degree-of-freedom simulation with both software-only and hardware-in-the-loop forms. GN&C with the original avionics enabled the 10,000 poundclass parafoil to achieve an expected delivery accuracy of about 150 meters. The GN&C using the new avionics is generalized for on-going tests with payloads ranging from 300 to 30,000 pounds.

Subjects: JOINT PRECISION AIR DROP SYSTEM (JPADS), GUIDANCE NAVIGATION AND CONTROL (GN&C), GLOBAL POSITIONING SYSTEM (GPS)

Huntington, G.T.; Benson, D.A.; Rao, A.V.

Comparison of Accuracy and Computational Efficiency of Three Pseudospectral Methods

Guidance, Navigation, and Control Conference and Exhibit, Hilton Head, SC, 8/20/2007-8/23/2007. Sponsored by: AIAA. (Draper Report number P-4532)

Abstract: A comparison is made between three pseudospectral methods used to numerically solve optimal control problems. In particular, the accuracy of the state, control, and costate obtained using the Legendre, Radau, and Gauss pseudospectral methods is compared. Three examples with different degrees of complexity are used to identify key differences between the three methods. The results of this study indicate that the Radau and Gauss methods are very similar in accuracy, while both significantly outperform the Legendre method with respect to costate accuracy. Furthermore, it is found that the computational efficiency of the three methods is comparable. Based on these results and a detailed analysis of the mathematics of each method, a rationale is created to determine when each method should be implemented to solve optimal control problems.

Subjects: OPTIMAL CONTROL, PSEUDOSPECTRAL METHOD

Lim, S.; Pileggi, R.A.; Barton, G.H.

MIMO Adaptive Bank-to-Steer Control Algorithms for Guided Reentry Vehicles

Guidance, Navigation, and Control Conference and Exhibit, Hilton Head, SC, 8/20/2007-8/23/2007. Sponsored by: AIAA (Draper Report no. P-4561)

Abstract: This paper proposes new Bank-to-Steer (BTS) control algorithms for controlling the attitude of an Apollo-style capsule during guided reentry phase. The fundamental design challenge is dynamic coupling between roll and yaw axes as a function of trim angle-of-attack (or pitch angle), which varies widely during the guided reentry phase. To solve this problem, two novel approaches are proposed. The trim AOA is estimated in real time using only the polarity of the commanded torque generated by the BTS control algorithms without using air data from direct measurement systems as in the Space Shuttle, or estimation using onboard sensors and stored knowledge about flight mechanics as in Kistler. The coupled roll and yaw axes are controlled by an MIMO gain-scheduled state-feedback control algorithm. This algorithm is based on mature linear parameter varying (LPV) synthesis and proven pulse-width-pulse-frequency (PWPF) modulator. These algorithms have potential advantages over Apollo and Kistler BTS control algorithms: estimation of trim AOA is relatively simple and effective even in the presence of off-nominal flight conditions; the BTS control algorithm does not need the table of optimal gain sets and associated time-consuming procedure of gain design at different trim conditions because it automatically tunes the nominal gains as a function of trim AOA; the BTS control algorithm is so flexible that it can be reused for other phases such as skip reentry phase and attitude-to-velocity phase.

Subjects: SPACECRAFT REENTRY, CONTROL DESIGN

Lutwak, R.; Rashed, A.; Varghese, M.; Tepolt, G.B.; LeBlanc, J.; Mescher, M.J.; Serkland, D.K.; Peake, G.M.

Miniature Atomic Clock Preproduction Results

Frequency Control Symposium, Geneva, Switzerland, 5/29/2007-6/1/2007. Sponsored by: IEEE (Draper Report no. P-4549)

Abstract: The authors have developed a Miniature Atomic Clock (MAC) for applications requiring atomic timing accuracy in portable battery-powered applications. Recently, we have completed a preproduction build of 10 devices in order to evaluate unit-to-unit performance variations and to gain statistical confidence in the performance specifications, environmental sensitivity, and manufacturability.

Subjects: MINIATURE ATOMIC CLOCK (MAC), COMMUNICATION SYSTEMS, NAVIGATION SYSTEM

Madison, R. W.; Andrews, G. L.; DeBitetto, P. A.; Rasmussen, S. A.; Bottkol, M. S.

Vision-Aided Navigation for Small UAVs in GPS-Challenged Environments

Infotech at Aerospace Conference. 2007. Rohnert Park, CA. 05/07/2007 - 05/10/2007. Sponsored by: AIAA (Draper Report no. P-4552)

Abstract: As UAVs become smaller, their flight space will expand to include flying within urban canyons and eventually inside buildings. Flying within these environments is very challenging from a navigation perspective, as GPS is largely denied or degraded by dropouts and multi-path effects. Traditional navigation approaches based on filtering GPS and lowcost inertial sensors produce unacceptably high drift during extended GPS outages. A promising remedy is to augment navigation with an onboard vision sensor that tracks visual landmarks to infer vehicle motion. We propose a vision-aided navigation system that can replace GPS when it is temporarily denied. The system uses a single camera as the vision sensor, because many UAVs already carry a camera as part of their limited payload. The system detects, tracks, and geo-locates 3D landmarks observed in the stream of camera images. We consider several options for initializing the range to landmarks in the navigation filter, including motion stereo. The system geo-locates a set of landmarks while GPS provides accurate navigation. Once GPS is lost, the system combines estimated landmark locations with new observations of these landmarks to both navigate and geolocate new landmarks in a process called boot-strapping. Tests of the system in simulated and on flight data collected with a small UAV show that vision-aided navigation drift is significantly lower than under inertial-only navigation.

Subjects: VISION-AIDED NAVIGATION SYSTEM, UNMANNED AERIAL VEHICLES (UAV), GLOBAL POSITIONING SYSTEM (GPS), VISION SENSORS

Marinis, T.F.; Soucy, J.W.; Johansson, B.D.

High-Performance MEMS Inertial Instruments Fabricated on LTCC Substrates

IMAPS National Meeting, San Jose, CA, 11/11/2007-11/15/2007. Sponsored by: International Microelectronics and Packaging Society (IMAPS). (Draper Report number P-4588)

Abstract: Draper Laboratory's current generation of high-performance, Microelectromechanical System (MEMS) inertial instruments are assembled from a discrete sensor in a ceramic chip carrier, an application-specific integrated circuit (ASIC) control chip in a plastic ball grid array package, one or more op amps, and a dozen or more passive components. The MEMS device in each of these instruments exhibits a minute capacitance shift in response to an acceleration or Coriolis force that changes the gap between its proof mass and sense electrode. Consequently, the physical implementation and mechanical stability of interconnect between components, strongly influences instrument performance. Changes in temperature or humidity may cause the instrument circuit board to expand or contract more than the ceramic sensor package to a degree that the resulting stresses deform the sensor die. This deformation can change the nominal gap distance between sensor proof mass and sense electrode. If the thermal conductivity of the substrate is low and the ambient temperature changes rapidly, the resulting temperature gradients induce thermal mismatch stresses, which also deform the sensor die. Both gyroscope and accelerometer sensors are susceptible to vibration-induced errors, especially at frequencies near their structural resonances. If the instrument circuit board is not sufficiently rigid, then it could induce vibration errors even if the instrument is mounted on a vibration isolation structure. The sensor and control ASIC are mounted to minimize their interface path length and associated parasitic and coupling capacitances. Any change in these capacitance values appears as an inertial input, hence temperature or humidity-induced changes in the thickness or permittivity of the dielectric layers must be minimized. The input/output (I/O) impedance of MEMS sensors is extremely high, so variations in leakage resistance on the instrument circuit board can adversely affect scale factor and isolation of drive and sense signals. This paper will utilize simple electrical and mechanical models to examine the effect of candidate substrate materials on instrument performance. We have elected to build high-performance instruments on low-temperature co-fired ceramic (LTCC) circuit boards. These boards are fabricated in eight layers, with DuPont 951 Green Tapetm and gold-based metallization. They are approximately 25 mm in diameter by 1.25 mm thick, and have 23 braze attached I/O pins, which connect to a copper flex tape interconnect. The instruments are mounted on a system stable member by three 1-mm screws that fit through machined, braze attached eyelets.

Subjects: MICROELECTROMECHANICAL SYSTEMS (MEMS), LOW-TEMPERATURE CO-FIRED CERAMIC (LTCC), INERTIAL SENSORS

Marinis, T.F.; Soucy, J.W.; Johansson, B.D.

High-Performance MEMS Inertial Instruments Fabricated on LTCC Substrates

IMAPS National Meeting, San Jose, CA, 11/11/2007-11/15/2007. Sponsored by: International Microelectronics and Packaging Society (IMAPS). (Draper Report number P-4588)

Abstract: Draper Laboratory's current generation of high-performance, Microelectromechanical System (MEMS) inertial instruments are assembled from a discrete sensor in a ceramic chip carrier, an application-specific integrated circuit (ASIC) control chip in a plastic ball grid array package, one or more op amps, and a dozen or more passive components. The MEMS device in each of these instruments exhibits a minute capacitance shift in response to an acceleration or Coriolis force that changes the gap between its proof mass and sense electrode. Consequently, the physical implementation and mechanical stability of interconnect between components, strongly influences instrument performance. Changes in temperature or humidity may cause the instrument circuit board to expand or contract more than the ceramic sensor package to a degree that the resulting stresses deform the sensor die. This deformation can change the nominal gap distance between sensor proof mass and sense electrode. If the thermal conductivity of the substrate is low and the ambient temperature changes rapidly, the resulting temperature gradients induce thermal mismatch stresses, which also deform the sensor die. Both gyroscope and accelerometer sensors are susceptible to vibration-induced errors, especially at frequencies near their structural resonances. If the instrument circuit board is not sufficiently rigid, then it could induce vibration errors even if the instrument is mounted on a vibration isolation structure. The sensor and control ASIC are mounted to minimize their interface path length and associated parasitic and coupling capacitances. Any change in these capacitance values appears as an inertial input, hence temperature or humidity-induced changes in the thickness or permittivity of the dielectric layers must be minimized. The input/output (I/O) impedance of MEMS sensors is extremely high, so variations in leakage resistance on the instrument circuit board can adversely affect scale factor and isolation of drive and sense signals. This paper will utilize simple electrical and mechanical models to examine the effect of candidate substrate materials on instrument performance. We have elected to build high-performance instruments on low-temperature co-fired ceramic (LTCC) circuit boards. These boards are fabricated in eight layers, with DuPont 951 Green Tapetm and gold-based metallization. They are approximately 25 mm in diameter by 1.25 mm thick, and have 23 braze attached I/O pins, which connect to a copper flex tape interconnect. The instruments are mounted on a system stable member by three 1-mm screws that fit through machined, braze attached eyelets.

Subjects: MICROELECTROMECHANICAL SYSTEMS (MEMS), LOW-TEMPERATURE CO-FIRED CERAMIC (LTCC), INERTIAL SENSORS

Marinis, T.F.; Soucy, J.W.; Marinis, R.T.; Klempner, A.R.; Hefti, P.; Pryputniewicz, R.J.

Time-Lapse Measurements of Stress Relaxation in MEMS Sensor Die Bonds

57th Electronic Components and Technology Conference (ECTC), Reno, NV, 5/29/2007-6/1/2007. Sponsored by: IEEE/CPMT. (Draper Report number P-4528)

Abstract: Thermal compression gold bumps have been used to attach high-precision Microelectromechanical System (MEMS) inertial sensors within hermetic ceramic packages. The bonds can be made at relatively low temperatures, are mechanically robust, and outgas at very low rates in vacuum sealed packages. The thermal expansion coefficients of MEMS die and ceramic packages are not perfectly matched and temperature gradients occur when the assembly is cooled after bonding. As a result, there is considerable residual stress in the bonded assembly, which is accommodated to some extent by distortion of the sensor die. Over time, as these stresses relax, the distortion of the die changes, which causes the spacing between elements of the integral MEMS sensor to change as well. Also, in vibrating instruments, this can change the stress state of the resonant element and cause its operating frequency to shift. An important element of sensor-package design is ensuring that stress relaxation effects do not cause the instrument to drift beyond its performance specification limits over a typical lifetime of 20 years. For high-precision instruments, this type of performance degradation can be reduced greatly by mounting the MEMS sensor on an interposer structure, which isolates it from package displacements. We have used a silicon interposer to closely match the thermal expansion coefficient of a sensor die and to isolate it from the package by compliant beam elements. The sensor die is brazed or gold bump bonded to the interposer, which is attached to a multilayer ceramic package through bump bonded, beam elements. Even though an interposer greatly reduces package-induced strains on the sensor, it does not entirely eliminate them. We have used a phase shifting interferometric system with custom fringe analysis software to measure full-field-of-view with high spatial resolution and nanometer accuracy out of plane, the shape of an interposer-package assembly. The assembly was measured both as-built and over the course of several years of aging. After 6 years, residual stress in the braze material of a chip bonded directly to a ceramic package, relaxes to about half of its initial value. To within the precision that we can measure the residual stress, a similar gold bump bonded assembly fully relaxes within two and a half years. An error analysis of our technique leads us to believe that the measurements are accurate to within a nanometer. In the interposer chip assembly, the observed stress induced deformation of the die is considerably reduced. Over time, as the gold bumps shear, the deflection of the interposer compliant beams diminish, accompanied by some flattening of the die attach area. We have used a combination of analytical and finite-element calculations to model these observed stress relaxation behaviors and to derive a stress relaxation curve for a pattern of gold bump bonds.

Subjects: MICROELECTROMECHANICAL SYSTEMS (MEMS), INERTIAL SENSORS, STRESS RELAXATION

Page, L.A.; DiBiaso, D.M.; Nervegna, M.F.

Risk Management in the Risk-Aware Mixed-Initiative Dynamic Replanning (RMDR) System for UxVs

34th Association for Unmanned Vehicle Systems International Meeting, Washington, DC, 8/6/2007-8/9/2007. Sponsored by: AUVSI (Draper Report no. P-4507)

Abstract: Missions performed by unmanned vehicles involve various risks, including risks of accidental collisions, equipment malfunctions, unfortunate weather perturbations, and sometimes a risk of encountering hostile forces. Some risks jeopardize vehicle safety, some jeopardize mission success, and the consequences of some may far exceed the value of the vehicles themselves. As more is put at stake in the use of unmanned vehicles for commercial, civilian, and military purposes, it is imperative to systematically and rationally address the risks involved in these operations, that is, to manage risk. As stated in Reference [1], "the objective of managing risk is not to remove all risk, but to eliminate unnecessary risk." A significant challenge in managing risks is weighing very disparate factors against each other. Another is that risks are inherently related to uncertainties, which adds complexity to any analysis. Furthermore, the effort expended on managing risk should not overshadow its benefits.

Subjects: UNMANNED VEHICLES (UV), MISSION PLANNING, RISK MANAGEMENT, RISK-AWARE MIXED-INITIATIVE DYNAMIC REPLANNING PROGRAM (RMDR)

Page, L.A.; Nervegna, M.F.; DiBiaso, D.M.

Unmanned System Risk Management

46th Conference on Decision and Control, New Orleans, LA, 12/12/2007-12/14/2007. Sponsored by: IEEE. (Draper Report number P-4522)

Abstract: This paper describes Unmanned System Risk Management, a methodology for managing the risks involved in unmanned vehicle missions. The methodology includes a human/machine collaborative process for risk management that is embedded into a system's broader process for initiating a mission. The methodology also includes an architecture that structures how risk-related information flows throughout the distributed system and how risk information is collected from and presented to the user. It also includes the development and integration of algorithms dedicated to managing specific categories of risk. Each risk category is supported by specific risk analysis and/or mitigation algorithms. The architecture is extendable so that developers can incorporate additional, risk-category-specific algorithms over time without needless complexity. The methodology has been implemented in the Risk-aware Mixed-initiative Dynamic Replanning (RMDR) system, which allows an operator to manage a heterogeneous team of unmanned underwater and air vehicles. RMDR includes autonomy functionality onboard the vehicles as well as on a host platform with an operator in the loop. RMDR currently includes algorithms to analyze and/or mitigate the risks of being detected, of colliding with other vehicles, of running out of energy, and of image collection failure due to environmental conditions. Risk mitigation algorithms are incorporated into both team level and vehicle level plan generation.

Subjects: UNMANNED SYSTEMS, RISK MANAGEMENT, RISK-AWARE MIXED-INITIATIVE DYNAMIC REPLANNING PROGRAM (RMDR)

Robles, A.C.; Rearden, P.R.; Trevejo, J.M.; Gerber, M.L.; Keshava, N.

Analysis of Biomarker Features from a Differential Mobility Spectrometer for the Detection of Tuberculosis

Life Science Systems and Applications Workshop, Bethesda, MD, 11/8/2007-11/9/2007. Sponsored by: IEEE-NIH BISTI. (Draper Report number P-4574)

Abstract: In this article, we present an investigation of an approach to extract discriminating features from differential mobility spectrometer (DMS) signals generated from two sets of in vitro samples of headspace that contain volatile organic compounds. The two classes of signals we analyze are a strain of tuberculosis grown in media and the media alone. Our approach first preprocesses the DMS signals to recover a baselined signal and then applies a wavelet transform to obtain localized measures of chemical activity in the detector output. The approach then ranks the wavelet coefficients using a common measure of class separability to identify distinguishing wavelet coefficients. Our analysis indicates that the subsequent ranking can often identify areas of signal devoid of chemical structures and that when discriminating chemical features are identified, the constraints of the wavelet transform as a decompositional tool can result in mismatches between the main lobe of the wavelet basis function and the chemical peak. Techniques to mitigate these effects are also discussed, and considerations are made for how to track features across multiple experiments.

Subjects: DIFFERENTIAL MOBILITY SPECTROMETRY (DMS), TUBERCULOSIS DETECTION

Soltz, J.A.; Johnson, A.M.

Optimal Estimation of Dynamic Ionosphere Induced Group Delays of GPS Signals

63rd Institute of Navigation Annual Meeting, Cambridge, MA, 4/23/2007-4/25/2007. Sponsored by: ION (Draper Report number P-4536)