Adams, M. et al.

Balboni, E. et al.

Bedrossian, N.S.

Bedrossian, N.

Bernstein, J. et al.

Bibeau, R.T. et al.

Borenstein, J.T. et al.

Chou, P.C. et al.

Chou, P.C. et al.

Connelly, J. et al.

Connelly, J. et al.

Cunningham, B. et al.

DeBitetto, P.A. et al.

Deutsch, O.L.

Draim, J.E. et al.

Edsall, A.C.

Eiceman, G.A. et al.

Girerd, A. et al.

Granholm, G.R.

Requirements for Accurate Near-Real-Time Atmospheric Density Correction

Gustafson, D. et al.

Gustafson, D. et al.

Hattis, P.D. et al.

Hopkins, R. et al.

Jang, J.W. et al.

Kaihara, S. et al.

Laine, J.P. et al.

McCants, E. et al.

McConley, M.W. et al.

McConley, M.W. et al.

Miller, R.A. et al.

Miller, R.A. et al.

Miller, R.A. et al.

Miller, R.A. et al.

Mofrad, M.R.K et al.

Murphy, M. et al.

Ricard, M.J. et al.

Schwartz, G.

Smith, S.R., Jr.

Terai, H. et al.

Tetewsky, A.K.

Tumminelli, R. et al.

Zarchan, P. et al.

Adams, M.; Deutsch, O.; Hall, W.; Hildebrant, R.; Kreamer, W.; McConley, M.; Vuong, H.F.

Closed-Loop Operation of Large-Scale Enterprises: Application of a Decomposition Approach Advances in Enterprise Control

Held in Minneapolis, MN, 07/10/2000 to 07/11/2000. Sponsored by: DARPA. (Draper Report no. P-3827)

Abstract: Real-time, closed-loop optimal control of large-scale dynamic systems (enterprises) remains a challenging problem. We have been developing an approach to problems of this class that employs a distributed, multilevel control architecture wherein planning and execution are decomposed to accommodate the near- and far-term impacts of plant disturbances and modeling uncertainties. The decomposition is based on the theory of multilevel optimization for large-scale systems. The structure of the decomposed solution to the optimization problem obtained from this theory forms a basis for our controller architecture as well. In addition to planning, the controller architecture includes execution management, monitoring, and diagnosis at each level. A previous paper described a decomposed formulation for a large-scale military air operations optimization problem. This paper presents the results of the application of this approach to the control of large-scale military air operations in a simulation-based context. Simulation results indicate that a significant reduction in the time required to achieve specified campaign objectives can be realized by closing the control loop at higher rates facilitated by controller automation. This reduction pertains to the base case and to cases with modeling errors and disturbances and can be quantified as a savings of 0.5 to 2 days for the moderate intensity, 7-day scenario under study.

Subjects: CLOSED-LOOP SYSTEMS (FEEDBACK CONTROL), DYNAMIC SYSTEMS, LARGE-SCALE SYSTEMS, ENTERPRISES, SIMULATION, OPTIMIZATION

Anderson, J.A.; Kerrebrock, P.A.

Biomimetics in Action: Design and Performance of an Autonomous Robotic Fish

Neurotechnology for Biomimetic Robots. Held in Nahant, MA, 05/14/2000 to 05/16/2000. (Draper Report no. P-3851A) Subjects: UNMANNED UNDERSEA VEHICLES (UUV), BIOMIMETICS, FISH, VORTICITY CONTROL UNMANNED UNDERSEA VEHICLE (VCUUV)

Anderson, J.M.; Chhabra, N.K.

Maneuvering and Stability Performance of a Robotic Tuna. Abstract Only

American Zoologist, Vol. 40, No. 6, 12/2000. (Draper Report no. P-3868A-REV-A)

Abstract: The Draper Laboratory Vorticity Control Unmanned Undersea Vehicle (VCUUV) is the first mission-scale, autonomous underwater vehicle that uses vorticity control propulsion and maneuvering. Built as a research platform with which to study the energetics and maneuvering performance of fish-swimming propulsion, the VCUUV is a self-contained free-swimming research vehicle that follows the morphology and kinematics of a yellowfin tuna. The forward half of the vehicle comprises a rigid hull that houses batteries, electronics, ballast, and a hydraulic power unit. The aft section is a freely flooded articulated robot tail that is terminated with a lunate caudal fin. Utilizing optimized body and tail kinematics from the MIT Robotuna experiments, the VCUUV has demonstrated stable steady swimming up to 2.4 kn and aggressive maneuvering trajectories with turning rates up to 75 deg/s. This paper summarizes the vehicle maneuvering and stability performance observed in field trials and compares the results to predicted performance using theoretical and empirical techniques.

Subjects: VORTICITY CONTROL UNMANNED UNDERSEA VEHICLE (VCUUV), ROBOTIC TUNA

Balboni, E.; Ford, J.; Tingley, R.; Toomey, K.; Vytal, J.J.

An Empirical Study of Radio Propagation Aboard Naval Vessels

Antennas and Propagation for Wireless Communications. Held in Waltham, MA, 11/06/2000 to 11/08/2000. pp. 157-160. Sponsored by: IEEE. (Draper Report no. P-3811)

Abstract: Most existing studies of indoor radio wave propagation have addressed operation in common commercial environments such as warehouses, office buildings, and factories. These studies show typical path loss gradients ranging from 3-5, and rms delay spreads ranging from 10-40 ns. This paper reports the results of research conducted to characterize microwave radio propagation aboard navy ships. Because of its principally steel construction, the ship environment displays significantly different characteristics from commercial environments. In particular, rms delay spreads ranging between 70 and 90 ns are common. Likewise, path loss gradients are observed to range from slightly greater than inverse square to smaller than unity. These effects of path loss and delay spread are found to be independent of frequency over the range from 800 MHz to 2.6 GHz.

Subjects: RADIO PROPAGATION, NAVAL VESSELS

Barbour, N.; Schmidt, G.

Inertial Sensor Technology Trends

Date: 11/2000. (Draper Report no. P-3858-REV-A)

Abstract: This paper presents the status of inertial sensor technology in underwater navigation applications, followed by a prediction of where inertial instrument technology is heading and in which applications the future sensor technologies will find a niche. Many kinds of sensors have been developed. The GPS is cheap and ubiquitous, but it is uncertain whether it would be continuously available in military scenarios.

Subjects: INERTIAL SENSORS; GUIDANCE, NAVIGATION, AND CONTROL (GN&C); TECHNOLOGY FORECASTING; TECHNOLOGY DEVELOPMENT; GLOBAL POSITIONING SYSTEM (GPS); INERTIAL NAVIGATION; MOBILE ROBOTS; SENSORS; UNDERWATER VEHICLES; UNDERWATER NAVIGATION; INERTIAL INSTRUMENTS; MILITARY APPLICATIONS

Bedrossian, N.S.

International Space Station Assembly and Operation Control Challenges

Guidance and Control Conference. 23rd. Held in Breckenridge, CO, 02/03/2000 to 02/06/2000, pp. 259-279. Sponsored by: AAS. (Draper Report no. P-3805)

Abstract: For the International Space Station program to be successful, mission requirements must be robustly met in the presence of uncertainties. Changing Station characteristics during assembly, such as variability in structural flexibility and mass properties, pose unique control challenges. Three examples of control challenges are reviewed in this paper, the first two arising out of variability in flex structure and the last one due to mass property variation. Controller/flex structure interaction issues and their origins are reviewed as well as representative examples. Control moment gyroscope (CMG) momentum desaturation issues during robotic operations are addressed and an operational solution is reviewed. Finally, CMG attitude control issues during payload robotic operations are presented as well as an issue resolution technique.

Subjects: INTERNATIONAL SPACE STATION (ISS), CHARACTERISTICS, CONTROL SYSTEMS L VEHICLES (UAV), UNMANNED GROUND VEHICLES (UGV)

Bedrossian, N.

International Space Station CMG Momentum Desaturation Design

Date: Modeling and Simulation Technologies. Held in Denver, CO. 08/14/2000 to 08/17/2000. Sponsored by: AIAA. (Draper Report no. P-3813)

Abstract: The control moment gyroscope (CMG) momentum desaturation method developed by Draper Laboratory for the International Space Station (ISS) for use during robotic payload operations is presented. A frequency optimal feed-forward thruster pulsing strategy that is independent of plant description is developed to minimize structural excitation. It is shown that the appropriate optimization criterion is to minimize the maximum amplitude of the pulsing strategy power spectral density. The flight software implementation details are also presented. Simulation results for ISS CMG desaturation thruster firings are used to demonstrate the effectiveness of the proposed methodology.

Subjects: INTERNATIONAL SPACE STATION (ISS), CONTROL MOMENT GYROSCOPES (CMG), MOMENTUM, PAYLOADS, FLIGHT SOFTWARE

Bernstein, J.J.; Bottari, J.; Houston, K.; Kirkos, G.; Miller, R.; Xu, B.; Ye, Y.; Cross, L.E.

High-Sensitivity MEMS Ultrasound Arrays by Lateral Ferroelectric Polarization

Solid-State Sensors & Actuators Workshop. Held in Hilton Head Island, SC, 06/04/2000 to 06/08/2000. pp. 281-284. (Draper Report no. P-3806)

Abstract: This paper discusses the design of advanced micromachined ferroelectric ultrasound transducers for use at 3 MHz. 16 x 16 arrays of resonant monomorph sensors have been constructed, with sol-gel lead zirconate titanate (PZT) as the active ferroelectric layer deposited on insulating layers of ZrO2 and SiO2. A novel in-plane polarization of the PZT is used to maximize sensitivity, while trading off reduced output capacitance to match the CMOS buffer electronics. This results in about 30-dB improved sensitivity compared with conventional polarizing across the thickness of the PZT layer. Fluid-filled through wafer holes are used as an acoustic matching network to achieve resonance at both 1 and 3 MHz. A lumped element equivalent circuit model is presented, as well as finite-element analysis results. Performance predictions for projector efficiency and receive response are given. Test results are presented, including transmit response, receive sensitivity, and frequency response.

Subjects: MICROELECTROMECHANICAL SYSTEM (MEMS), FERROELECTRIC TRANSDUCERS, ULTRASOUND IMAGES, LEAD ZIRCONATE TITANATE (PZT), FINITE-ELEMENT ANALYSIS

Bernstein, J.; Bottari, J.; Houston, K.; Kirkos, G.; Miller, R.; Xu, B.; Ye, Y.; Cross, L.

In-Plane Polarization for High-Sensitivity Ferroelectric MEMS Ultrasound Transducers

International Symposium on the Application of Ferroelectrics. 12th. Held in Honolulu, HI, 07/30/2000 to 08/02/2000. Sponsored by: IEEE. (Draper Report no. P-3836)

Abstract: This paper discusses the design of advanced micromachined ferroelectric ultrasound transducers for use at 3 MHz. 16 x 16 arrays of resonant monomorph sensors have been constructed, with sol-gel lead zirconate titanate (PZT) as the active ferroelectric layer deposited on insulating layers of ZrO2 and SiO2. A novel in-plane polarization of the PZT is used to maximize sensitivity, while trading off reduced output capacitance to match the CMOS buffer electronics.This results in about 30-dB improved sensitivity compared with conventional polarizing across the thickness of the PZT layer. An equivalent circuit model as well as finite-element results are presented. Test results are reported, including transmit response, receive sensitivity.

Subjects: FERROELECTRIC TRANSDUCERS, ACOUSTIC TRANSDUCERS, LEAD ZIRCONATE TITANATE (PZT), FINITE-ELEMENT ANALYSIS

Bibeau, R.T.; Rubenstein, D.S.

Trajectory Optimization for a Fixed-Trim Reentry Vehicle Using Direct Collocation and Nonlinear Programming

Guidance, Navigation, and Control Conference. Held in Denver, CO, 08/14/2000 to 08/17/2000. Sponsored by: AIAA. (Draper Report no. P-3826)

Abstract: This work examines the feasibility of using a direct solution method to the fixed-trim reentry vehicle optimal control problem as part of a reentry guidance scheme. A procedure was developed to calculate locally optimal trajectories for fixed-trim atmospheric reentry vehicles. A 4-degree-of-freedom vehicle model was introduced, and appropriate environmental models were chosen and implemented. Software was developed to discretize the optimal control problem using a direct collocation method. The resulting parameter optimization probIem was solved using the MINOS nonlinear programming software package. The resulting collocation guidance software was tested using data for the Kistler K-1 vehicle system and an independent vehicle simulation. Mass, wind, density, and entry angle dispersions were considered, as were various strategies for updating the trajectory during flight. The results demonstrated that the collocation method is a viable approach to the reentry vehicIe guidance problem. The collocation method enforced the vehicle equations of motion to a useful degree of accuracy using as few as 10 nodes, and the resulting control histories yielded acceptably small final position errors.

Subjects: TRAJECTORY OPTIMIZATION, REENTRY VEHICLES, NONLINEAR PROGRAMMING, COLLOCATION, OPTIMAL CONTROL, KISTLER K-1 VEHICLE

Borenstein, J.T.; Currie, M.; Gerrish, N.D.; White, R.; Fitzgerald, E.A.

Silicon Germanium Epitaxy: a New Material for MEMS

Date: 2000. (Draper Report no. P-3786-ABSTRACT)

Abstract: A wide array of materials have been investigated as candidate fabrication templates for precision microelectromechanical structures. While ceramics, plastics and polymers have distinct advantages for specific applications, silicon continues to be the mainstay for precision commercial and military applications. Both polycrystalline and highly-boron-doped single crystal silicon are utilized successfully to build gyroscopes, accelerometers, pressure sensors, and other high-volume products. However, each presents its own set of limitations, related to ultimate thickness capability, prospects for integration with electronics, and material quality considerations. Recent emphasis has shifted to Silicon-on-Insulator (SOI) technology, which presents new challenges for plasma etching and other fabrication processes. Here we present the latest fabrication results for epitaxial silicon-germanium alloy layers, a new composition that combines the best features of many of the aforementioned materials. Silicon-germanium alloys are shown to possess excellent crystalline structure, are compatible with non-toxic etchants in bulk micromachining, and are capable of on-chip integration with electronics. Here we describe the performance of this material as applied to the fabrication of a high-precision micromachined structure, the tuning-fork gyroscope. For MEMS applications, silicon-germanium alloy layers are grown using a graded buffer approach, resulting in very high-quality micromachined structures. Very low defect densities are obtained through the use of these relaxed buffers. Figure 1 illustrates the clear delineation between the device layer, which contains very few threading dislocations, and the graded buffer layer, where defects generated by the lattice mismatch between Si and Ge are aggregated. Original etch-stop studies determined that Ge doping provided a very weak selectivity in anisotropic etchants such as potassium hydroxide (KOH) and ethylene-diamene-pyrocatechol (EDP). However, by extending the range of Ge concentration over 20%, we have found extremely high etch selectivities in a variety of etchants. Selectivity is totally independent of background doping concentration, and epilayers with negligible boron concentrations exhibit higher selectivity than do silicon layers doped with the highest achievable concentrations of boron, as seen in Table 1. Unlike boron-doped layers, SiGe exhibits etch stop characteristics in the nontoxic, process-compatible solution TMAH. The combination of independence from boron doping concentration and etchant compatibility makes SiGe a material that is ideal for integration with on-chip electronics. In this work, we present the latest fabrication data on tuning-fork gyroscopes built using SiGe epitaxial layers. Process compatibility issues related to wafer curvature, surface finish and reactive-ion-etching chemistries are addressed. An unexpected result of the fabrication process, curvature of released structures, is resolved by annealing wafers after the SiGe deposition; Figure 2 shows the dependence of part curvature on annealing. Changes in Young's modulus arising from the high atomic fraction of Ge in the device can be determined by simple beam analysis based on observed resonant frequencies. The quality factor of the motor drive resonance is determined by operation of the gyroscopes in vacuum. Overall, build precision for these devices, as seen in Figure 3, is excellent. We conclude by addressing the remaining challenges for wide-scale implementation of silicon-germanium epitaxial MEMS.

Subjects: GERMANIUM, SILICON, EPITAXY, MICROELECTROMECHANICAL SYSTEM (MEMS), SILICON ON INSULATOR (SOI)

Brock, L.D.

Transition to an Open-System Architecture

Digital Avionics Systems Conference (DASC). 19th. Held in Philadelphia, PA, 10/07/2000 to 10/13/2000, Proceedings, Vol. 1, pp. 4.D.5-1-4.D.5-8. Sponsored by: IEEE. (Draper Report no. P-3830)

Abstract: The DoD has directed that an open-system approach be used to the maximum extent practical as one approach to achieving superior war fighting capability with reduced total operating costs. Open systems are expected to reduce development costs and, more importantly, the costs to maintain and upgrade weapons systems over ever increasing lifetimes. The acquisition requirements for open systems, however, are often expressed in broad and general terms that may not be specific enough to achieve the results desired. One problem is the lack of a clear and common understanding between the government and its supplier on just what open systems are and how they will be used. The purpose of this paper is to contribute to a better understanding. In particular, different levels at which open system architectures can be implemented are described, and the alternatives available to system managers are outlined. Finally, the increased advantage of open-system architectures when used in coordinated acquisition of multiple systems is suggested.

Subjects: OPEN SYSTEMS, COST REDUCTIONS

Chou, P.C.; Fini, J,M.; Haus, H.A.

Real-Time Principal State Characterization for Feedback-Free PMD Compensation

Date: 10/2000. (Draper Report no. P-3849)

Abstract: Most polarization mode dispersion (PMD) compensation systems use many feedback parameters that contribute to complexity, instability, and speed limitations. We demonstrate a feedback-free method that quickly and accurately determines the principal states of polarization of a fiber afflicted with PMD.

Subjects: POLARIZATION MODE DISPERSION (PMD), FEEDBACK

Chou, P.C.; Haus, H.A.; Brennan, J.F.

Recofigurable Time-Domain Spectral Shaping of an Optical Pulse Stretched by a Fiber Bragg Grating

Optics Letters, Vol. 25, No. 8, 04/15/2000, pp. 524-526. (Draper Report no. P-3768)

Abstract: We demonstrate a method for spectrally shaping optical pulses that is readily reconfigurable and can produce variable filter functions. This practical technique relies on a compact and robust 3.86-m long linearly-chirped fiber Bragg grating that chromatically disperses the pulse to ~30 ns. We then shape the pulse envelope, and thus the pulse spectrum, with a programmable arbitrary waveform generator and an amplitude modulator to yield several filter functions.

Subjects: BRAGG DIFFRACTION, SPECTRAL SHAPING, OPTICAL PULSES, FILTERING

Chou, P.C.; Lee, H.L.T.; Ram, R.J.; Haus, H.A.; Ippen, E.P.; Brennan, J.F.; Kjebon, O.; Schatz, R.

Stable Picosecond Pulse Generation with a Frequency-Modulated DBR Laser and Chirped Fiber Bragg Grating

Conference on Lasers and Electro-Optics (CLEO). Held in San Francisco, CA, 05/07/0200 to 05/12/2000. Sponsored by: OSA. (Draper Report no. P-3812)

Abstract: We demonstrate a method for generating picosecond pulses at 1553 nm using a passive fiber grating and a semiconductor laser without gain switching, mode locking, nor external modulation. With this technique, we make a stable pulse source with electronically defined repetition rate and potentially low jitter.

Subjects: PULSE GENERATORS, FREQUENCY MODULATION, FIBER BRAGG GRATING (FBG), SEMICONDUCTOR LASERS

Cleary, M.E.

Hierarchical Decomposition of Autonomy Requirements for Naval UCAVs for the Uninhabited Combat Air Vehicle (UCAV) Demonstrations

Date: 07/07/2000. (Draper Report no. CSDL-2000-036)

Subjects: UNINHABITED COMBAT AIR VEHICLES (UCAV), AUTONOMOUS AIRCRAFT, MISSION PLANNING

Cleary, M.E.; Abramson, M.R.

Intelligent Autonomy for Small Throwable Land Robots

Photonics East. Enabling Technologies for Law Enforcement and Security. Held in Boston, MA. 11/05/2000 to 11/08/2000, pp. 421-427. Sponsored by: SPIE. (Draper Report no. P-3824)

Abstract: DARPA's Tactical Mobile Robot (TMR) program includes a Throwable Robot (Throwbot) designed to be thrown into buildings, then teleoperated for surveillance purposes. Use by ground troops imposes significant size and weight limits, as does the requirement that it survive ballistic delivery. The current program stresses the state-of-the-art in robotics and packaging, but further challenges exist. Future Throwbots would benefit from significant increases in autonomy to deal with RF communications difficulties in buildings and to allow simultaneous operation of multiple vehicles by one person. This describes both currently planned and advanced autonomous capabilities. Draper's flexible autonomous systems architecture provides the structure for these current and advanced capabilities. Limited autonomy functions are currently being designed to guard the operator's teleoperation of the vehicle, to quickly hide when danger threatens, to maneuver to improve communications when they are disrupted, and to right itself should it tumble. Advanced capabilities would include autonomous mapping with ranging and imaging sensors, exploration to map communications within the building, and searching for particular targets within the building.

Subjects: TACTICAL MOBILE ROBOT (TMR), THROWABLE ROBOT (THROWBOT), AUTONOMY, INTELLIGENCE, SURVEILLANCE, OBSTACLE AVOIDANCE, EXPLORATION

Cleary, M.E.; Abramson, M.R.; Adams, M.B.; Kolitz, S.

Metrics for Embedded Collaborative Intelligent Systems

Performance Metrics for Intelligent Systems. Held in Gaithersburg, MD, 08/14/2000 to 08/16/2000. Sponsored by: NIST. (Draper Report no. P-3833)

Abstract: The intelligence of a network of agents is reflected in the complexity of missions that can be accomplished, the degree of coordination/cooperation among the agents, and the level of uncertainty the system can tolerate and still accomplish its missions. The networked system must be able to evaluate a situation, devise an appropriate response, and act accordingly. Metrics must be devised to capture the complexity and surprises of the real world, and to capture the system's need to reason about its situation so as to uncover unanticipated problems and opportunities. Inputs for developing autonomous capability specifications (and thus metrics of interest) include: (1) descriptions of expected missions, (2) the space of mission parameters, and (3) the cost/benefit ratio for operational concepts. These inputs come from both current and anticipated missions. Several of our recent projects have sought to quantify operational metrics for autonomous ground, air, and undersea vehicles. This paper presents our approach to high-level design of autonomous vehicles that produces the three inputs for metric development. The approach and parameter spaces are illustrated with examples derived from several vehicle projects.

Subjects: METRICS, INTELLIGENCE, AUTONOMOUS VEHICLES

Connelly, J.; Dennehy, N.; Hattis, P.; Johnson, W.; Socha, M.; Sargent, D.

MEMS-Based GN&C Sensors and Actuators for Micro/Nanosatellites

Guidance and Control Conference. 23rd. Held in Breckenridge, CO, 02/03/2000 to 02/06/2000, pp. 561-576. Sponsored by: AAS. (Draper Report no. P-3796)

Abstract: A new generation of miniature, low/mass/power, high-performance guidance, navigation, and control (GN&C) sensors and actuators will be required for envisioned Microsatellite and Nanosatellite missions. As satellite volume decreases, correspondingly small sensors and actuators are needed to perform satellite operational functions. Therefore, technology that enables very small devices is quite important for miniature satellite development. Draper Laboratory, a world leader in Microelectromechanical System (MEMS) inertial sensing, is currently developing attitude determination and attitude control devices to meet the emerging needs of these new missions. This paper describes designs for both a miniature stellar-inertial attitude sensor package and a MEMS wafer wheel momentum device. The Draper Attitude Sensor Suite (DASS) integrates complementary technologies for electron-bombarded charge-coupled device (EBCCD) stellar cameras and MEMS gyroscopes into one miniature package. Both the EBCCD sensor and MEMS gyro technologies have been continuously matured at Draper over the past several years with all major hardware components having been tested successfully in both laboratory and operational environments. The EBCCD stellar camera provides an order of magnitude improvement in signal-to-noise (S/N) ratio (as compared with standard CCD technology) at high bandwidth allowing detection of faint stars with a relatively small optical aperture. Star detection capability can be further improved by implementing the Draper-developed "drag-back" technique for integrating the star images over periods of several seconds. The back-thinned EBCCD detector is inherently radiation hard. Performance analysis indicates that arcsec accuracy can be accomplished with the DASS. This EBCCD star camera performance is uniquely suited to detect faint stars on highly dynamic Micro/Nano spacecraft or spin-stabilized satellites. Laboratory testing indicates the ability of the unit to detect stars as faint as magnitude 8 while spinning @ 20 rpm. Second-generation MEMS tuning-fork gyros (TFGs) provide low-power/mass/volume, three-axis attitude rate measurements for high-bandwidth updates between stellar fixes. The Draper MEMS Wafer Momentum Device (MWMD) has been designed as a feasible near-term Micro/Nansatellite attitude control actuator. The wafer rotor in this device is planar and is fabricated as a wafer thick (500 microns) silicon part. In the current implementation, spin-axis rotational freedom is furnished by a very small, but standard ball bearing cartridge supplied by a commercial vendor. This MEMS wheel has been designed to operate at high speed of 50,000 rpm, and will provide an angular momentum of about 150 dyne-cm-s. This device can be configured to serve either as a momentum wheel, a reaction wheel, or a control moment gyro. As a long-term alternative to the conventional cartridge bearing, Draper is currently investigating a novel ball bearing in which 11-mil steel balls are captured within raceways fabricated into the silicon rotor. This silicon-steel bearing combination is unique and provides a potentially elegant and compact low-cost design. Limited testing has shown the viability of the silicon-steel approach. This very promising investigation showed that silicon mated to steel was potentially a good bearing combination. Looking even further into the future, another suspension concept has been developed for a wafer control moment gyro device with a hemispherical gas bearing. Here, the gas bearing provides the radial and axial stiffness from the boundary layer dynamic forces.

Subjects: MICROELECTROMECHANICAL SYSTEM (MEMS); GUIDANCE, NAVIGATION, AND CONTROL (GN&C); MICROSATELLITES, NANOSATELLITES; SENSORS; ACTUATORS

Connelly, J.; Kourepenis, A.; Marinis, T.

Micromechanical Sensors in Tactical GN&C Applications

Guidance, Navigation, and Control Conference. Held in Denver, CO, 08/14/2000 to 08/17/2000. Sponsored by: AIAA. (Draper Report no. P-3828)

Abstract: Micromachined silicon inertial sensors offer revolutionary improvements in cost, size, and reliability for guidance, navigation, and control (GN&C). Batch manufacturing techniques produce thousands of virtually identical microelectromechanical system (MEMS) devices, each a few square millimeters in size. Development of inertial MEMS is driven by the high-volume, commercial market that targets modest performance applications at prices below $10 per axis. Draper Laboratory has recently demonstrated higher performance, multi-axis systems using commercial processes for lower-volume tactical applications ranging from guided munitions to microsatellites. More accurate sensors enabled by deep reactive ion etch technology, and new digital electronics are rapidly approaching bias stabilities of 1 deg/h and 100 micro-g over -40°C to +85°C. Future architectures under development reflect a radical departure from early demonstration systems. New sensors with complementary input axes have led to multi-axis sensor arrays, and new wafer-scale processes, integrating sensor arrays, and application-specific integrated circuits (ASICs) are creating complete systems on a chip.

Subjects: INERTIAL SENSORS; GUIDANCE, NAVIGATION, AND CONTROL (GN&C); MICROELECTROMECHANICAL SYSTEM (MEMS)

Cunningham, B.; Kant, R.A.; Daly, C.; Weinberg, M.; Pepper, J.; Clapp, C.; Bousquet, R.; Hugh, B.

Chemical Vapor Detection Using Microfabricated Flexural Plate Silicon Resonator Arrays

Aerospace/Defense Sensing and Controls (AeroSense). Held in Orlando, FL, 04/28/2000 to 04/30/2000. Sponsored by: SPIE. (Draper Report no. P-3767) Chemical and Biological Sensing. Held in Orlando, FL. 04/24/2000 to 04/25/2000, pp. 151-162. Sponsored by: SPIE. (Draper Reports no. P-3797)

Abstract: Draper Laboratory is developing chemical vapor detection and biosensor arrays based on microfabricated silicon resonators coated with thin-film molecular recognition chemistry. The resonators within the micro-Chemical Analysis Array (micro-CANARY) are microelectromechanical flexural plate wave (FPW) sensors that have been miniaturized to allow many independently addressable sensors to be integrated within a single silicon chip. The target analyte of an individual sensor within the chip is selected by placing a microdroplet of the molecular recognition component (or "coating") into a well surrounding the resonating membrane. Detection is performed by monitoring changes in the frequency and damping factor of the resonance as the coating interacts with the environment. In addition to the system capabilities afforded by the ability to monitor many chemical or biochemical interactions simultaneously, the micro-CANARY operates in air or liquid environments, utilizes low-cost, low-power address/excitation/readout circuitry, and has demonstrated high detection sensitivity. This presentation will describe the design, fabrication, and testing of 2-element, 8-element, and 64-element micro-CANARY sensors for vapor and liquid phase detection will be presented. For vapor detection, NRL has applied polymer receptor coatings targeted at the detection of chemical weapon agents, and has performed extensive chemical vapor exposure tests using two chemical weapon simulants and four vapor phase interferents. Data describing temperature dependence, long-term/short-term drift stability, detection limits, detection linearity, and vapor selectivity will be presented. For biodetection, a receptor coating protocol has been developed for the attachment of antibody molecules to the sensor membrane, and preliminary results have been obtained demonstrating the ability of the micro-CANARY to detect dog antigens in aqueous solution with 0.25 ng/ml a detection limit.

Subjects: CHEMICAL VAPOR DEPOSITION (CVD), FLEXURAL PLATES, BIOSENSORS, MICROCHEMICAL ANALYSIS ARRAY (MICRO-CANARY), ACOUSTIC RESONATORS, MICROELECTROMECHANICAL SYSTEM (MEMS)

DeBitetto, P.A.; Rasmussen, S.; Plump, J.; Appleby, B.; Piedmonte, M.; Lorusso, T.

Inexpensive Avionics Designs for Small UAVs

AUVSI 2000. Held in Orlando, FL, 07/10/2000 to 07/13/2000. Sponsored by: AUVSI. (Draper Report no. P-3829)

Abstract: Draper Laboratory has developed both inexpensive commercial-off-the-shelf (COTS)-based avionics systems and advanced microelectromechanical sensor (MEMs) multichip module (MCM) electronics packaging-based systems that have been used to automate small aerial vehicles. The COTS-based designs have had sufficient performance and computational flexibility to support advanced guidance, navigation and control algorithms for relatively small aerial vehicles. The applications have ranged from flight data recording, stability augmentation, controlled hover, waypoint guidance, and autonomous acrobatic maneuvering. The MEMs-based systems have pushed the technology boundaries for extremely small systems. Current prototype MEMs systems are costly, but the fundamental technology will enable the production of extremely small, inexpensive flight avionics system in the near future.

Subjects: UNMANNED AERIAL VEHICLES

Deutsch, O.L.

Guidance Trades for Interceptors Not Constrained by Ground-Based Radar

AIAA/BMDO Technology Conference and Exhibit. 9th. Held in San Diego, CA, 07/17/2000 to 07/20/2000. Sponsored by: AIAA/BMDO. (Draper Report no. P-3782)

Abstract: Virtually all U.S. ballistic missile interceptor designs under development utilize terminal seekers that are cued by high-resolution, surface-based radars. The radar is used for target tracking leading to a fire-control solution, for midcourse target state updates and for end-game target discrimination. New space-based sensor systems such as space-based infrared system (SBIRS)-low are seen as an adjunct that can be used to achieve range extension by cueing of radars and in some concepts, kinematic range extension of interceptors by providing for earlier launch commitments. The availability of global track information from space-based systems, however, coupled with the large design space provided by high throw-weight, retooled submarine-launched ballistic missile (SLBM) launchers enable an entirely new design concept for national missile defense (NMD). The notional system would utilize existing infrastructure, minimally modified SLBM launchers, and exoatmospheric kill vehicles currently under development for global coverage from a few sea-based locations against modest-intensity NMD threats. The post-boost "bus" would dispense multiple kill vehicles and would provide a platform to mount communication, sensors, and possibly special "fly-ahead" packages for mechanizing novel approaches to target discrimination. Assuming that ABM treaty barriers were negotiated successfully, the global coverage of this outermost tier to a layered NMD could simultaneously provide a stabilizing extension of NMD to regional allies.

Subjects: INTERCEPTORS, BALLISTIC MISSILE DEFENSE (BMD), SUBMARINE-LAUNCHED BALLISTIC MISSILES (SLBM)

Draim, J.E.; Cefola, P.J.; Castiel, D.

Elliptical Orbit Constellations - a New Paradigm for Higher Efficiency in Space Systems?

Date: 2000. (Draper Report no. P-3762)

Abstract: Several systems are being developed for satellite cellular telephone use. Examples are Iridium, Globalstar, ICO, and ELLIPSO. Systems designers seem to prefer subsynchronous multisatellite arrays over geostationary satellites as they can more easily communicate with small low-power hand-held cellular telephones, and they also have less signal latency (time delay). The flexibility of the elliptic orbit allows a biasing of earth coverage toward a given latitude. Increased coverage is obtained by placing apogees in a stable orbit over a preferred latitude. If the orbit is both elliptical and sun-synchronous, it can also be biased toward a given (local) time of day. With apogees appearing during daytime, greater capacity is ensured during the peak usage hours for telephone communications. Tailored elliptical-orbit constellations may well become the paradigm for many of these new telecommunications space systems. Lower cost elliptic-orbit constellations with fewer satellites may well prove more profitable than circular arrays for many other space applications as well.

Subjects: ELLIPTICAL ORBITS, SATELLITE CONSTELLATIONS, CELLULAR TELEPHONES, SUN-SYNCHRONOUS ORBITS

Edsall, A.C.

Technology Insertion in Health and Usage Monitoring Systems: An Integrator's Perspective

American Helicopter Society (AHS) Annual Forum. 56th. Held in Virginia Beach, VA, 05/02/2000 to 05/04/2000, pp. 946-955. Sponsored by: AHS. (Draper Report no. P-3793)

Abstract: The Joint Advanced Health and Usage Monitoring System (JAHUMS) is a DoD-sponsored initiative to demonstrate advanced HUMS technologies and an open-systems approach to HUMS deployment. The JAHUMS program is currently developing five technology modules to be integrated into the Navy/BFGoodrich Integrated Mechanical Diagnostics (IMD) HUMS for the SH-60 aircraft. These technology modules from multiple suppliers will provide new functionality and/or new technology to the HUMS. The open-systems technology insertion process involves both business and technical practices. The business issues involve the clear definition of roles, responsibilities, liabilities, and compensation throughout the HUMS life cycle. The technical issues affect the way that systems engineering, component development, and system integration must be performed. Open standards will facilitate the design of system components by multiple sources, but successful integration of the system requires a thorough up-front systems engineering effort, a well-defined integration and verification process, and life-cycle support to ensure that the system is adequately integrated into the end-users' systems and processes. Development of open architectures and standards is itself a significant process that warrants a systematic approach to ensure that the open-system objectives of all stakeholders are satisfied.

Subjects: HEALTH MONITORING SYSTEM (HMS), TECHNOLOGY INSERTION, ROTARY WING AIRCRAFT

Eiceman, G.A.; Nazarov, E.G.; Miller, R.A.

A Micromachined Radio-Frequency Ion Filter for Mass Spectrometry with Atmospheric Pressure Ionization Sources

Date: 2000. (Draper Report no. P-3803)

Abstract: The interface between a mass spectrometer and an ion source at atmospheric pressure is best made when a sample can be introduced to the mass spectrometer under controlled gas environments. This is necessary to avoid interferences from the ambient atmosphere. An inlet attachment for a mass spectrometer should be compact in size and suitable for continuous operation. It should also allow the flexibility to utilize various ion sources and have the facility to handle ions of various kinds and of both positive and negative polarities. Finally, a good inlet should be crafted so that there is high ion transmission to the mass spectrometer. The goal with such an inlet is continuous ion monitoring by APCI-MS with preliminary ion filtering at atmospheric pressure between the ion source and the mass spectrometer. In the approach described here, a small flat micromachined ion filter (total size of 30 x 15 x 2 mm3) was fabricated with two parallel flat electrodes (12 x 5 mm) and two short electrodes (deflector and focusing electrodes). A carrier gas (flow rate 1- 4 liters/min) carries the ions through a gap (0.5 mm) between these electrodes. When an amplitude-asymmetric radio frequency (1-2 MHz) voltage is applied to the electrodes, the ions oscillate perpendicular to the electrodes. The radio frequency (RF) electric field is asymmetric in amplitude, and ion trajectories are proscribed by differences in the high-field dependence of the coefficient of mobility. Only ions whose average velocity in the transverse direction is zero will traverse the drift region. Ions for which this condition is not satisfied can be corrected with an additional DC electric field applied to the electrodes. This DC field can be tuned to select a particular ion species. Consequently, the micromachined IMS can serve as a filter to permit only certain ions to pass into the mass spectrometer (additional electrode is used to record the ion mobility signal.) A focusing electrode with a hole (0.7 mm) at the end of the drift region is located next to the MS orifice; certain potentials on focusing and deflector electrodes make possible the sampling of all ions into MS. Neutrals are swept from the MS using the carrier gas. This filter was added to the flange of a TAGA 6000 MS/MS and the entire analyzer and electronics were floated to 30-100 V above the flange potential. Characterizations using benzene and substituted benzenes demonstrate the operation of the RF ion filter. Low cost and reproducibility are provided through microfabrication.

Subjects: MASS SPECTROSCOPY, RADIO FREQUENCIES, IONIZATION

Eiceman, G.A.; Nazarov, E.G.; Takjikov, B.; Miller, R.A.

Monitoring Volatile Organic Compounds in Ambient Air Inside and Outside Buildings Using a Radio-Frequency-Based Ion Mobility Analyzer with a Micromachined Drift Tube

Field Analytical Chemistry and Technology, Vol. 4, No. 6, 2000, pp. 297-308 (Draper Report no. P-3839)

Abstract: A radio-frequency-based ion mobility analyzer with a micromachined drift tube was operated continuously to monitor volatile organic compounds (VOCs) in ambient air inside a building and in a open space near the union of I-10 and I-25 at Las Cruces, NM. Air was drawn directly without enrichment or preseparation, through the analyzer, which was regulated to 35°C. The ion source was a photodischarge lamp at 10.6 eV providing a preliminary level of selectivity in response toward chemicals with low ionization potentials. The compensation voltage was scanned continuously from- 40 to +20 V at rates of 60-150 V/s providing profiles of ions obtained from VOCs in air. Solvents were detected at 1-ppm levels as fugitive emissions from other experiments underway in the laboratory from 8 am to 6 pm. However, patterns in VOCs levels from 1-5 ppb between 6 pm and 7 am and on weekends was attributed to air exchange between ambient air and the ventilation system of the building. The mobility analyzer results were consistent with VOCs from traffic on major city thoroughfare adjacent to the building. In-field studies near two interstate highways demonstrated that analyzer response could be correlated to traffic patterns and exhibited diurnal trends. These findings demonstrate the concept and practice of micromachined mobility analyzers as continuous monitors for VOCs as airborne vapors in buildings and on-site.

Subjects: ION MOBILITY, RADIO FREQUENCIES, DRIFT TUBES, VOLATILE ORGANIC COMPOUNDS (VOC)

Flueckiger, K.

A High AJ MEMS-Based INS/GPS Navigator

Joint Services Data Exchange (JSDE). 26th. Held in Ventura, CA, 10/22/2000 to 10/26/2000. Sponsored by: GPS/JPO/EGI. (Draper Report no. P-3852)

Subjects: ANTIJAMMING, INERTIAL NAVIGATION SYSTEMS (INS), GLOBAL POSITIONING SYSTEM (GPS), MICROELECTROMECHANICAL SYSTEM (MEMS)

Girerd, A.; Barton, G.

Next-Generation Entry Guidance - Onboard Trajectory Generation for Unpowered Drop Tests

Guidance, Navigation, and Control Conference. Held in Denver, CO, 08/14/2000 to 08/17/2000. Sponsored by: AIAA. (Draper Report no. P-3843)

Abstract: Autonomous algorithms are developed for the real-time onboard design of guidance trajectories for horizontally-landing reusable launch vehicles such as the X-34. Onboard generation obviates the need for Shuttle-era preloaded trajectories, resulting in a host of performance and economic improvements. The general problem is one of energy management of an unpowered low Lift-over-Drag (L/D) vehicle subject to dynamic constraints. The approach takes full advantage of the vehicle's flight capability, generates guidance profiles that are intrinsically flyable and controllable, and allows an inherent abort capability. Automatic trajectories are successfully generated for a variety of flight conditions based on nominal and atypical initializations for subsonic drop tests under 40,000 ft. Furthermore, the guidance output is optimized with respect to robustness. To prove feasibility, the computer-designed trajectories will be flown in a 6-degree-of-freedom X-34 simulator.

Subjects: ALGORITHMS, TRAJECTORIES, X-34, GUIDANCE SYSTEMS, REUSABLE LAUNCH VEHICLES

Granholm, G.R.; Proulx, R.; Cefola, P.; Nazarenko, A.I.; Yurasov, V.

Near-Real-Time Atmospheric Density Correction Using NAVSPASUR Fence Observations

Space Flight Mechanics Meeting. Held in Clearwater, FL, 01/23/2000 to 01/26/2000. Sponsored by: AAS/AIAA. (Draper Report no. P-3794)

Abstract: Mismodeled drag effects are one of the most significant sources of error for low-altitude and highly eccentric orbits. It is currently estimated that predicted densities can differ by as much as 30% from real world conditions, even using the best exosphere/thermosphere models (such as MSISE-90 or Jacchia-Roberts '71) . However, we can use observations from frequently tracked objects in the space catalog to provide an "atmosphere correction service" to users desiring more precise orbit determination for a given target orbit. Observations will be in the form of direction cosines from the NAVSPASUR Fence, a multistatic radar system deployed across the southern United States. Using high-precision special perturbation techniques, orbital elements and ballistic factors will be estimated for 200-300 space objects with perigee heights distributed between 200 and 600 km. The difference between the locally estimated ballistic factor and the time-averaged or "true" ballistic factor can be taken as a measurement of the difference between the modeled and true atmospheric densities. These density variation measurements are used to construct a time and altitude-dependent density correction model. The model coefficients can be treated as samples of a stochastic process and predicted using linear stochastic filtering methods. A thorough mathematical description of density variation estimation, forecasting algorithms, and the NAVSPASUR Fence is presented, along with a detailed outline of operational considerations for an atmosphere correction service.

Subjects: ATMOSPHERIC DENSITY, RADAR SYSTEMS, CORRECTIONS, DRAG MEASUREMENT

Granholm, G.R.; Proulx, R.J.; Cefola, P.J.; Nazarenko, A.I.; Yurasov, V.

Requirements for Accurate Near-Real Time Atmospheric Density Correction

Astrodynamics Specialist Conference. Held in Denver, CO. 08/14/2000 to 08/17/2000. Sponsored by: AIAA/AAS.

Abstract: Several theories have been presented in regard to creating a neutral density model that is corrected or calibrated in near-real time using data from space catalogs. These theories are usually limited to a small number of frequently tracked "calibration satellites" about which information such as mass and cross-sectional area is known very accurately. This work, however, attempts to validate a methodology by which drag information from all available low-altitude space objects is used to update the given density model on a comprehensive basis. The given density model is the model that was used to generate the space catalog. A technique to estimate true ballistic factors is derived in detail. The performance of the method is investigated via an independent simulation capability constructed at Draper Laboratory. The process is initially demonstrated using simulated range, azimuth, and elevation observations so that issues such as required number and types of calibration satellites, density of observations, and susceptibility to disturbed atmospheric conditions can be examined.

Subjects: REAL-TIME OPERATION, ATMOSPHERIC DENSITY, CORRECTIONS, ATMOSPHERIC TURBULENCE, LOW EARTH ORBIT (LEO)

Gustafson, D.; Dowdle, J.; Flueckiger, K.

A Deeply Integrated Adaptive GPS-Based Navigator with Extended-Range Code Tracking

Position Location and Navigation Symposium (PLANS). Held in San Diego, CA, 03/13/2000 to 03/16/2000. Sponsored by: IEEE. (Draper Report no. P-3791)

Abstract: This paper presents a new approach to GPS-based navigation, which offers significant improvement in antijam capability over traditional designs. The algorithms may be implemented at low cost in software in existing and future GPS receivers using, as inputs, post-correlation I and Q data and, optionally, raw data from other sensors. Traditional systems are not optimal at high jammer-to-signal (J/S) ratios as a consequence of modular design, use of traditional fixed-gain or gain-schedule tracking loops, and use of artificial moding logic. The approach described here employs a nonlinear filter that operates efficiently at all J/S levels. Filter gains continuously adapt to changes in the J/S levels. Filter gains continuously adapt to changes in the J/S environment, and the error covariance propagation is driven directly by measurements to enhance robustness under high jamming and dynamics conditions. Extended-range correlation may be included optionally to increase the code tracking loss-of-lock threshold under high jamming scenarios. Computational complexity is comparable to an extended Kalman filter. Results of hardware-in-the-loop simulations are presented that demonstrate improvements of 15 dB or more in antijam capability relative to traditional designs.

Subjects: GLOBAL POSITIONING SYSTEM (GPS), ANTIJAMMING, NAVIGATION SYSTEMS

Gustafson, D.; Dowdle, J.; Flueckiger, K.

A High Antijam GPS-Based Navigator

Institute of Navigation National Technical Meeting. Held in Anaheim, CA, 01/26/2000 to 01/28/2000. Sponsored by: ION. (Draper Report no. P-3776)

Abstract: Current GPS-based navigation system performance is marginal in high-interference environments in both civilian and military applications. This paper presents a new approach to solving these problems using a design that may be implemented at low cost in software in existing and future GPS receivers. The design approach includes GPS-only navigation capability; however, other sensors may be employed, such as inertial instruments (gyros and accelerometers), radars, altimeters, etc. A multidimensional state is estimated recursively in real time using raw measurement data, which includes: (1) in-phase and quadrature data from a bank of correlators, and (2) raw measurements from other sensors. The data are processed in a single processor that produces the desired navigation system outputs (e.g., position, velocity, time, and attitude). In addition, the GPS measurements may be used to calibrate correlated errors in the other sensors. Traditional systems are not optimal at high jammer-to-signal (J/S) ratios as a consequence of modular design, use of traditional fixes-gain or gain-scheduled tracking loops, and use of artificial moding logic. In contrast, the approach described in this paper employs a nonlinear filter that operates efficiently at all J/S levels. The design incorporates traditional code loop functions. Filter gains continuously adapt to changes in the J/S environment, and the error covariance propagation is driven directly by measurements to enhance robustness under high jamming conditions. Extended-range correlation may be optionally included to increase the code tracking loss-of-lock threshold under high jamming scenarios. Computational complexity is comparable to an extended Kalman filter. The system has been tested via simulation and in the laboratory using a Nortel GPS simulator and Plessey receiver. Results indicate a consistent improvement in C/A code tracking of at least 15 dB in wideband antijam capability relative to traditional designs. This improvement can be traced to several factors: (1) elimination of moding logic, resulting in seamless operation at all values of J/S; (2) continuous adaptive estimation of J/S using measurements from the full correlator bank; and (3) effective handling of measurement nonlinearities. This technology is currently being developed for use in next generation deeply integrated INS/GPS navigation systems employing microelectromechanical system (MEMS) sensors with a near-term goal of a single package consuming less than 3 W in a 3-in3 volume.

Subjects: GLOBAL POSITIONING SYSTEM (GPS), ANTIJAMMING, MICROELECTROMECHANICAL SYSTEM (MEMS)

Hattis, P.D.; Fill, T.J.; Rubenstein, D.S.; Wright, R.P.; Benney, R.J.

An Advanced Onboard Airdrop Planner to Facilitate Precision Payload Delivery

Guidance, Navigation, and Control Conference. Held in Denver, CO, 08/14/2000 to 08/17/2000. Sponsored by: AIAA. (Draper Report no. P-3816)

Abstract: Precision airdrop from high altitude is increasingly important for delivery of military and humanitarian supplies. A personal computer (PC)-based, C-language, advanced airdrop planner is being developed as part of the New World Vistas Precision Aerial Delivery program in parallel with an advanced PC-based wind modeling tool. The combined operation of these two new tools onboard airdrop carrier aircraft will enable more accurate delivery of high-altitude airdrop payloads by accounting for actual flight circumstances, by utilizing forecast and in-flight environmental measurements, and by providing timely, high-value airdrop advisory information to the carrier aircraft crew. Embedded in the planner is a 6-degree-of-freedom simulation of ballistic parachutes that has already been developed and tested. The planner software architecture as well as its user and carrier aircraft interfaces have been defined, with implementation planned by 2001. The planner and wind modeling tool will be demonstrated together onboard a C-130 aircraft in 2001. The features and design of the planner are discussed, some example ballistic airdrop simulation results are presented, and the operational procedures for using the planner in combination with the wind modeling tool are reviewed.

Subjects: AIRDROP TECHNOLOGY, PAYLOADS, WIND MODELING

Hopkins, R.; Borenstein, J.; Antkowiak, B.; Ward, P.; Elliott, R.; Weinberg, M.; Depiero, M.; Miola, J.A.

The Silicon Oscillating Accelerometer: a MEMS Inertial Instrument for Strategic Missile Guidance

Missile Sciences Conference. Held in Monterey, CA, 11/07/2000 to 11/09/2000. Sponsored by: AIAA. (Draper Report no. P-3801)

Abstract: The intercontinental ballistic missile (ICBM) and submarine-launched ballistic missiles (SLBM) developed over the past 50 years have employed successive generations of increasingly accurate inertial guidance systems. The comparatively short time of guided flight and high acceleration levels characteristic of the ballistic missile application place a premium on accelerometer performance to achieve desired weapon system accuracy. To date, the accelerometer design of choice for strategic missiles has been the Pendulous Integrating Gyroscopic Acceleometer (PIGA) instrument, an accelerometer whose origins trace back to the German V2 rocket, and has been refined through several generations of development to achieve unsurpassed performance. The specialized technologies of PIGA accelerometers, such as gas bearing wheels, ultrastable ball bearings, precision electromagnetic components, and "designer chemical" flotation fluids require a costly support infrastructure for production and system life-cycle maintenance. The Draper Laboratory is currently in the process of developing the Silicon Oscillating Accelerometer (SOA) a Microelectromechanical System (MEMS)-based sensor that has the potential to achieve the ppm/micro-g performance stability required of the strategic missile application. The MEMS technology is inherently low cost and offers a rapidly expanding commercial business base to leverage and sustain accelerometer production and deployment in next-generation guidance systems. The SOA belongs to the generic category of accelerometers known as Vibrating Beam Accelerometers (VBA), which sense acceleration by measuring the change in the resonant frequency of beam oscillators under the inertial loading of a proof mass. The SOA differs from conventional VBAs in one important respect; namely, the SOA is a silicon MEMS-based device, while VBAs, are typically bulk-fabricated quartz devices. The silicon MEMS process offers several advantages over quartz that enable superior accelerometer design features: (1) semiconductor-grade single-crystal silicon is a perfectly elastic structural material that can be produced with extremely low levels of impurities, (2) the MEMS process enables the fabrication of very small (millimeter scale in the case of the SOA) resonator elements that are well isolated from the influence of parasitic instrument package stresses, and (3) capacitively based, electrostatic resonator actuation and sensing that offers greater design flexibility than the piezoelectric quartz technology. This paper will give an overview of the Draper Lab SOA and current performance data taken to date.

Subjects: TRIDENT - MK6 LIFE EXTENSION - ACCELEROMETER - SILICON OSCILLATING ACCELEROMETERS (SOA), MICROELECTROMECHANICAL SYSTEM (MEMS), TRIDENT - MK6 LIFE EXTENSION - ACCELEROMETER - VBA, PERFORMANCE DATA