Showing papers on "Inertial measurement unit published in 1995"

Inertial navigation systems for mobile robots

Abstract: A low-cost solid-state inertial navigation system (INS) for mobile robotics applications is described. Error models for the inertial sensors are generated and included in an extended Kalman filter (EKF) for estimating the position and orientation of a moving robot vehicle. Two different solid-state gyroscopes have been evaluated for estimating the orientation of the robot. Performance of the gyroscopes with error models is compared to the performance when the error models are excluded from the system. Similar error models have been developed for each axis of a solid-state triaxial accelerometer and for a conducting-bubble tilt sensor which may also be used as a low-cost accelerometer. An integrated inertial platform consisting of three gyroscopes, a triaxial accelerometer and two tilt sensors is described. >

Predictive tracking for augmented reality

Abstract: In Augmented Reality systems, see-through Head-Mounted Displays (HMDs) superimpose virtual three-dimensional objects on the real world. This technology has the potential to enhance a user's perception of and interaction with the real world. However, many Augmented Reality applications will not be accepted unless virtual objects are accurately registered with their real counterparts. Good registration is difficult, because of the high resolution of the human visual system and its sensitivity to small differences. Registration errors fall into two categories: static errors, which occur even when the user remains still, and dynamic errors caused by system delays when the user moves. Dynamic errors are usually the largest errors. This dissertation demonstrates that predicting future head locations is an effective approach for significantly reducing dynamic errors. This demonstration is performed in real time with an operational Augmented Reality system. First, evaluating the effect of prediction requires robust static registration. Therefore, this system uses a custom optoelectronic head-tracking system and three calibration procedures developed to measure the viewing parameters. Second, the system predicts future head positions and orientations with the aid of inertial sensors. Effective use of these sensors requires accurate estimation of the varying prediction intervals, optimization techniques for determining parameters, and a system built to support real-time processes. On average, prediction with inertial sensors is 2 to 3 times more accurate than prediction without inertial sensors and 5 to 10 times more accurate than not doing any prediction at all. Prediction is most effective at short prediction intervals, empirically determined to be about 80 milliseconds or less. An analysis of the predictor in the frequency domain shows the predictor magnifies the signal by roughly the square of the angular frequency and the prediction interval. For specified head-motion sequences and prediction intervals, this analytical framework can also estimate the maximum possible time-domain error and the maximum tolerable system delay given a specified maximum time-domain error. Future steps that may further improve registration are discussed.

Apparatus and method for tracking a vehicle

Abstract: An apparatus and method for tracking a vehicle is provided. The vehicle tracking system may include an inertial measurement unit for providing inertial vehicle state characteristics of the vehicle. The inertial measurement unit may include at least one gyro and at least one accelerometer. The vehicle tracking system additionally includes an inertial converter for generating vehicle state information from the inertial vehicle state characteristics. Clinometers are utilized within the vehicle tracking system to initialize the gyros and may additionally provide acceleration information. The vehicle tracking system may additionally include one or more redundant sensors for providing redundant state information. The redundant sensors can include an odometer/tachometer, Global Positioning System receiver, tag receiver, and a map matching system. A Kalman filter may be utilized to reduce error within the vehicle tracking system and improve the accuracy thereof.

Evaluation of a solid-state gyroscope for robotics applications

Abstract: The evaluation of a low-cost solid-state gyroscope for robotics applications is described. An error model for the sensor is generated and included in a Kalman filter for estimating the orientation of a moving robot vehicle. Orientation estimation with the error model is compared to the performance when the error model is excluded from the system. The results demonstrate that without error compensation, the error in idealization is between 5-15/spl deg//min but can be improved at least by a factor of 5 if an adequate error model is supplied. Like all inertial systems, the platform requires additional information from some absolute position-sensing mechanism to overcome long-term drift. However, the results show that with careful and detailed modeling of error sources, inertial sensors can provide valuable orientation information for mobile robot applications. >

Inertial navigation technology from 1970-1995.

Abstract: The period since 1970 has been characterized by an intense push to develop new inertial navigation technology. Inasmuch as the performance requirements for nearly all of today's missions can be satisfied by instruments that were available 25 years ago, it is reasonable to ask what has driven this creative intensity. The answer to this question also points the way to the probable path of technology development in the next 25 years. The introduction and refinement of dry-tuned two-degree-of-freedom gyroscopes and the emergence of optical gyroscopes, resonator gyros, quartz resonant accelerometers, and micromachined silicon instruments have been driven by the goal of reducing the life-cycle cost of ownership of inertial systems, and by the need for rapid convergence of the navigation system to stable operation after turn-on. Combine these advances with the annual increases in computational power available per unit volume (which supports the compensation of calibratable sensor errors and integration with external sensors, such as GPS), and the trend to smaller, lighter, less-expensive systems is certain to continue well into the next century.

Apparatus and method for determining velocity of a platform

Abstract: An apparatus and method for determining the velocity of a platform includes a GPS receiver and inertial measurement unit (IMU) located at the platform. The GPS receiver provides GPS navigation data using a plurality of GPS satellites while the inertial measurement unit provides inertial navigation data. Acceleration computed from the GPS navigation data is combined with the inertial acceleration generated from the IMU using a Kalman filter to generate a substantially IMU-bias free acceleration of the platform. The resultant acceleration measurement and the GPS navigation data are used to calculate the velocity of the platform in conjunction with a second Kalman filter for removing GPS systematic errors that are normally removed by use of a ground reference station.

Fault tolerant inertial reference system

Abstract: A fault tolerant inertial reference system employs two independent inertial reference units each having its own inertial sensor array with redundant output information. Each inertial reference unit includes an independent source of position and velocity information through employment of a satellite positioning system. In turn, a high-speed error estimator processes inertial sensor output data from a local inertial sensor array with inertial sensor output data from another external inertial sensor array for determining high-level errors, and a low-speed error estimator processes output data from the local inertial sensor array with the velocity and position information separately obtained from the satellite positioning system for determining low-level errors. In turn these high and low-level errors are processed to determine a fault-free inertial sensor configuration for subsequently determining reliable fault tolerant inertial reference data obtainable with a minimum set of inertial sensors.

Design and Evaluation of an Integrated GPS/INS System for Shallow-Water AUV Navigation (SANS).

Abstract: : The major problem addressed by this research is the large and/or expensive equipment required by a conventional navigation system to accurately determine the position of an Autonomous Underwater Vehicle (AUV) during all phases of an underwater search or mapping mission. The approach taken was to prototype an integrated navigation system which combines Global Positioning System (OPS) and Inertial Measurement Unit (IMU), waterspeed and heading information using Kalman filtering techniques. Actual implementation was preceded by a computer simulation to test where the unit would fit into a larger hardware and software hierarchy of an AUV. The system was then evaluated in experiments which began with land based cart tests and progressed to open water trials where the unit was placed in a towed body behind a boat and alternately submerged and surfaced to provide periodic OPS updates to the Inertial Navigation System (INS). Test results and qualitative error estimates indicate that submerged navigation accuracy comparable to that of differential OPS may be attainable for periods of 30 seconds or more with low cost components of a small physical size.

Inertial sensor unit

Abstract: The unit has a number of miniaturised inertial sensors arranged so that they are subjected to the same inertial measurement parameter. The signals from the inertial sensors are fed to the same signal processor for generating an output measurement signal representing the inertial measurement parameter. Each inertial sensor contains a miniaturised resonator, whose resonance characteristic is influenced by the inertial measurement parameter. A number of measurement sensors with different measurement ranges can be used for measurement over an extended measurement range.

Clementine attitude determination and control system

Abstract: The Clementine spacecraft, launched in January 1994, completed a two-month lunar mapping mission, recording high-resolution multispectral images of the lunar surface in unprecedented detail. Mission requirements on the attitude determination and control system included knowledge to within 0.03 deg and control to within 0.05 deg. The typical spacecraft attitude determination system, employing expensive narrow-field-of-view star cameras, highly accurate inertial measurement units, and assorted coarse attitude acquisition sensors, was replaced by an all-new lightweight state-of-the-art sensor suite to meet low-cost, low-weight, and compressed schedule objectives. The sensor suite, which consisted of two wide-field-of-view star cameras and two inertial measurement units incorporating fiber-optic and ring-laser gyroscopes, was delivered in nine months and provided a weight saving of 90% and a cost saving of 75% in comparison with similar systems. A newly developed lightweight reaction wheel, with a weight saving of 50% in comparison with wheels of similar momentum storage capability, was used for fine attitude control. The Clementine mission provided the first space flight for each of these components. Only two anomalies were experienced: a large drift in gyroscope bias along one axis, and a nondestructive single-event latchup in one inertial measurement unit.

Advanced Transfer Alignment for Inertial Navigators (A-Train)

Abstract: Airborne transfer alignment refers to the process of initializing a weapon-grade IMU prior to launch using data provided by the aircraft’s INS. Traditional transfer alignment procedures require the aircraft to execute lengthy horizontal-plane (s-turn) maneuvers lasting several minutes. During the maneuvers, INS and IMU velocity-match data are processed by a Kalman filter algorithm which recursively estimates and corrects IMU attitude and inertial sensor errors. Although capable of attaining milliradian alignment accuracy, lengthy traditional alignment procedures are not generally consistent with the requirements of quick-reaction weapon systems. This paper presents an advanced transfer alignment procedure developed to significantly reduce the alignment maneuver and timeline requirements for an air-launched weapon. An 18-state KaIman filter is designed to recursively process INS and IMU velocity-match and attitude-match data at a 12.5 Hz rate. The aircraft is required only to perform a brief 20-deg wing-rock maneuver during alignment. Laboratory and flight tests on an AH-64A Apache aircraft indicate that the A-TRAIN filter is capable of aligning the IMU to within 1 mrad of truth within 5 sec.

Effects of yaw and pitch motion on model attitude measurements

Abstract: This report presents a theoretical analysis of the dynamic effects of angular motion in yaw and pitch on model attitude measurements in which inertial sensors were used during wind tunnel tests. A technique is developed to reduce the error caused by these effects. The analysis shows that a 20-to-1 reduction in model attitude measurement error caused by angular motion is possible with this technique.

Aerospace robotics laboratory, stanford university, stanford ca 94305 usa.

Abstract: Inertial navigation reference units are often thought of as simply a navigation device which must be augmented by another device to damp the Schuler oscillation and characteristic long-term drift. Emerging applications of Am’s, however, demonstrate a need for increasingly sophisticated inertial sensors. These inertial sensors are used not only for navigation, but as importantly, they provide data for sensor stabilization. Inertial systems have also traditionally represented a significant hotel load, been heavy, bulky, and a source of acoustic and structure-borne noise. This paper presents an overview of two new inertial systems that are now in production at the Guidance and Control Systems Division of Litton Systems, Inc. These units are small, lightweight, require little power, and are silent. Data are presented that show long-term performance as well as shortterm attitude, position, and velocity reference data for the LN-100 system. Attitude, velocity, and body axis rate data are required for stabilization of such devices as laser line scanners and long baseline side-scan sonars. The relationship between the characteristics of these sensors and inertial type errors is explored. This analysis shows that it is not sufficient to specify the inertial system only in terms of its navigation CEP. The specification of the inertial unit must also be based on the needs of the sensor payload and include such considerations as short-term stability, the noise content, phase, and bandwidth of the stabilization reference.

Use of the GPS Aided Inertial Navigation System in the Navy Standard Missile for the BMDO/Navy LEAP Technology Demonstration Program

Abstract: To demonstrate the feasibility of a sea-based theater-wide ballistic missile defense capability, the Navy Program Executive Office Theater Air Defense (PEO TAD), in conjunction with the Ballistic Missile Defense Organization (BMDO), performed two flight tests of a Lightweight Exo-Atmospheric Projectile (LEAP) mounted on a Navy Standard Missile 2 Block III Extended Range Terrier (SM 2 BLK III ER). The SM 2 BLK III ER was augmented with a third stage utilizing an integrated GPS/Inertial Navigation System (INS) allowing increased range, accuracy, and exo-atmospheric control. The SM 2 Flight Test Vehicles (FIV) were fired from the USS Richmond K. Turner (CG-20) located off the coast on the Eastern Test Range, against target vehicles launched from NASA’s Wallops Flight Facility on the Virginia coast. The Navy LEAP mission posed a challenging environment, including high vehicle dynamics, exe atmospheric operation, and short mission duration. An adapted version of the Hughes Aircraft Company’s GPS Aided Inertial Navigation System (GAINS) served as the navigator for the SM 2 third stage. The GAINS unit combines a low cost strapdown Inertial Measurement Unit (IMU) with an embedded GPS receiver module to provide a robust, low cost means of determining position, velocity, attitude, and time. The Navy LEAP Standard Missile flight tests have proven the robustness and reliability of the GAINS unit, successfully achieving the system requirements in the high dynamic and high altitude environment. This paper summarizes the design considerations and flight test results, highlighting the advantages of the low cost, high accuracy GPS aided inertial navigation solution.

Advanced Alignment Concepts for Precision-Guided Weapons

Abstract: The Department of Defense is pursuing several technology programs which specify requirements for advanced air-to-surface weapons. For instance, the JDAM and JSOW programs are investigating the accuracy improvements afforded by standard tactical weapons equipped with GPS-aided IMUs. To exploit the accuracy benefits of such weapons, the weapon IMU must be accurately initialized (i.e. aligned) prior to launch using data transferred from the aircraft INS. Conventional transfer alignment procedures require the aircraft to execute S-turn maneuvers lasting several minutes. Alternatively, advanced abgnment procedures can dramatically reduce this alignment time to just a few seconds, but these procedures do not have sufficient time to calibrate the IMU’s inertial sensors. However, since the weapon is expected to be aided by GPS for at least a portion of the flight, precise IMU sensor calibration may not be required. This paper investigates the timeline/calibration tradeoffs associated with advanced alignment procedures for aircraft employing GPS-aided, IMU-equipped weapons. Results indicate that if GPS aids the IMU over at least a portion of the weapon flight, a 5-set advanced transfer alignment procedure is expected to achieve weapon navigation accuracy comparable to that achieved by a conventional alignment procedure lasting several minutes.

Multi-Sensor Integration for Mobile Robot Navigation

Abstract: Available sensors for robot navigation are unreliable and noisy. Therefore there is a need to employ different types of sensors to acquire the information required for navigation. We discuss the different problems associated with the integration of several sensors in a mobile platform and present the approach we have developed to tackle these problems. We consider the particular problem of a mobile platform navigating in a 2D environment with a priori knowledge of its map. Unknown obstacles are allowed. In this chapter we are concerned with the integration of inertial sensors, odometry, sonars and active vision for navigation in a mobile robot.

GPS/lnertial Mapping (GIM) System for Real Time Mapping of Roadways Using WADGPS

Abstract: Geographic Information Systems (GIS) constitute a multi-billion dollar market for geographic data, and GPS offers a quick and accurate method to meet the demand for this data. A significant problem in the gathering of mapping information using GPS is the gaps in the base map data base caused by satellite shadowing, which may not be discovered until after the survey is complete. Gaps may also exist in the GIS attribute data base because items were missed during the survey. These are costly problems that usually require new surveys to remedy. To address this problem a low-cost, miniaturized GPSnnertial Mapping (GIM) system has been developed that can deliver l-2 meter accuracies in real time even in the event of temporary GPS signal loss. The GIM system combines inertial aided GPS navigation, position synchronized video, and automatic roadway attribute entry, to provide a powerful tool for generating precise, high quality GIS databases. This paper will describe GIS mapping sessions conducted with the GIM system on the roadways of El Paso County, CO. El Paso County offers an ideal geography to test the capabilities of the NAVSYS GIM system because it offers both urban and rural sections where the GPS signals can be blocked by obstructions that vary from buildings to mountain canyons. The paper will include the test data collected during the mapping sessions, and will demonstrate why inertial aiding is an important component for mapping instrumentation. The NAVSYS GIM system incorporates an innovative optimal processing algorithm that enhances the performance of the inertiaYGPS system enabling a low cost Inertial Measurement Unit (IMU) to be employed in combination with a GPS receiver, and the John E. Chance Omnistar wide area accurate, real time position and attitude reference. The overall process is controlled by an intelligent data management system capable of recording feature and attribute information in real time, with associated time tagging for exact location tagging, in both video and electronic formats. The GIM system is packaged into a portable, modular architecture that is suited for various vehicles such as cars, four wheel drives, watercraft, or railroad cars, allowing quick and accurate surveys to be performed in a wide variety of geographies.

A Micromechanical INS/GPS System For Guided Projectiles

Abstract: Recent advances in silicon microfabrication technology have led to the development of low cost, tactical performance grade, micromechanical inertial sensors. The inherent small size, low weight, and low cost of these sensors permit on-board insertion of gyroscopes and accelerometers for inertial instrument applications previously impractical because of size and cost considerations. Among the emerging opportunities for micromechanical inertial sensor insertion is the application to guided projectiles. This application is distinguished by the extremely high acceleration (high g) sensor measurement environment experienced during projectile launch; peak accelerations on the order of 100,000 g are possible during firing. Draper Laboratory has developed a range of l.raccelerometers to measure muzzle velocity and projectile flight acceleration, and a ltgyroscope to measure projectile attitude. Only the high g accelerometer is operational in the barrel; the other sensors operate outside the barrel but must be able to survive the launch environment. The total sensor system furnishes eight orders-of-magnitude acceleration dynamic range capability. A description of the sensors is given. Performance simulations for a high-dynamic range micromechanical inertial navigation system, coupled with a GPS receiver, are provided. GPS supplies position information at low frequencies, and the micromechanical instruments supply high-frequency information. The data are combined with a Kalman filter and navigator to generate high-frequency position, velocity, and attitude information. The high-frequency information is then used in the guidance and control of the projectile. Small micromechanical inertial sensors integrated with miniaturized multi-chip module GPS receivers will soon be available. By incorporating fast acquisition hardware, advanced signal processing techniques and adaptive antenna logic with the GPS receiver, a miniaturized integrated INS/GPS navigation system can be developed that exhibits high anti-jam (A/J) capability for guided projectile scenarios. This is the enabling technology that will lead to the development of GN&C sensors, electronics and pprocessor-based software for precision guided projectiles.

Sensing and control to enhance the safety of heavy vehicles

Abstract: The University of Minnesota and the Minnesota Department of Transportation (MNDOT) are working to improve the safety of heavy trucks on rural highways. The goal is to investigate how reductions in roadway departure accidents can be achieved by integrating emerging sensing and control technologies into a guidance control system that will operate a vehicle in case the driver falls asleep at the wheel. This controller will achieve lateral and longitudinal control of a semi tractor-trailer experimental platform, which is based on a Navistar 9400 series tractor. Vehicle navigation will be based on a differential global positioning system (DGPS) with a bandwidth of 5 Hz and accuracy better than 20 cm CEP. Complementing the DGPS will be an inertial measurement unit and dead reckoning package. The objective is to implement, test, and optimize a Kalman filter based controller, integrating inertial measurements and DGPS data for lateral and longitudinal control of the truck while navigating on the road. The 3.9 km closed course portion of the MNDOT pavement test facility serves as initial proving grounds for the technology. The vehicle control system will be tested and evaluated to ensure that it is robust and reliable under a wide range of operating conditions. The following tasks are currently ongoing: 1) evaluating the DGPS as to its dynamic accuracy, its error covariance, and its bandwidth; and 2) evaluating the truck's dynamic models by performing a series of parameter identification tests on the Navistar truck.

Intersatellite-laser-ranging experiment for global-change sensing and 21st century satellite control

Abstract: The optimal integration of precise multiple-antenna GPS receivers, advanced cryogenic inertial measurement units (IMU's), and ultra-stable frequency laser ranging devices on two low altitude, copolar orbiting spacecraft forms the basis of a multifaceted/interdisciplinary proposal. Scientific objectives are to (1) sense geodynamic gravitation changes and (2) substantially improve a variety of temporal geophysical models. Such models will make the Air Force Satellite Control Network's orbit determination process more accurate and affordable. The use of differential GPS (DGPS) observations, as external updates in an elaborate Kalman filter optimally integrating the three data types, puts a bound on the low frequency IMU and laser error buildups. In the filter the DGPS, IMU, and laser data streams aid each other to obtain the experiment's two navigation goals: determining the satellites' positions and orientations to centimeter and arc second accuracies. If each satellite also possesses stereo optical (3D) and multispectral sensors, global 3D Earth background image files could be built in both the visible and IR regimes.

An Integrated GPS Attitude Determination System For Small Satellites.

Abstract: : This dissertation develops attitude determination methods based on the Global Positioning System (GPS) for small satellites. A GPS attitude receiver is used in combination with other sensors planned for a small, three-axis stabilized satellite called JAWS AT. The other attitude sensors include fiber optic gyros and digital sun sensors. The development of integrated attitude determination systems contributes to critical national technological objectives identified for small spacecraft. A recent study by the National Research Council addresses key technologies for small satellite programs. One of their principal recommendations was that, "GPS in various combinations with other guidance components can determine position and attitude very accurately, probably at significantly reduced weight and cost" (NRC, 1994, p. 4j). The report also identifies specific potential benefits of integrating OPS with other sensors on small spacecraft. "Combining GPS and an inertial measurement unit (with gyroscopes, accelerometers, or trackers) offers major advantages by bounding errors of the inertial set, providing exceptionally good long-term references and thereby ensuring precise, on-board navigation and, with appropriate complimentary techniques, providing a higher level of redundancy and/or accuracy for position, velocity, and attitude" (NRC, 1994, p. 61). This dissertation develops algorithms that result in improved accuracy and redundancy through the development of complimentary techniques for combining GPS measurements with gyroscopes and sun sensors. P. 4-5

Influence of suboptimal navigation filter design on lunar landing navigation accuracy

Abstract: Most onboard guidance, navigation, and control computers will be programmed using suboptimal filter design in an effort to reduce software size and computation speed. Reduction in the order of the gravity-field model of the moon is one method that can be used to reduce the number of calculations the onboard filter must perform, thus increasing the speed of computation. A result of that reduction is an increase in navigation error, which in turn directly influences the accuracy of the guidance commands. This paper investigates two prevalent lunar gravity-field models—the Ferrari 79 and the Sagitov model. A brief history of their origins and a comparison of the models are given. Particular emphasis is placed on studying their effect on guidance and navigation accuracy as the order of the onboard navigation filter model is reduced, resulting in a suboptimal filter design.

Model-based vehicular motion and structure estimation

Abstract: This paper presents a model-based algorithm for estimating vehicle motion and structure from a long sequence of images. In addition to employing a simple kinematic law suitable for modeling the steering control, the unstabilized behavior of a vehicular motion due to the uneven terrain is taken into account. A vehicle model which accounts for bounce, pitch and roll is used. With the aid of inertial sensors such as accelerometers and by tracking a set of points over the image sequence, a feature-based approach is proposed. Simulation results for a particular vehicular motion are presented.

Performance Thresholds for Application of MEMS Inertial Sensors in Space

Abstract: We review types of inertial sensors available and current usage of inertial sensors in space and the performance requirements for these applications. We then assess the performance available from micro-electro-mechanical systems (MEMS) devices, both in the near and far term. Opportunities for the application of these devices are identified. A key point is that although the performance available from MEMS inertial sensors is significantly lower than that achieved by existing macroscopic devices (at least in the near term), the low cost, low size, and power of the MEMS devices opens up a number of applications. In particular, we show that there are substantial benefits to using MEMS devices to provide vibration, and for some missions, attitude sensing. In addition, augmentation for global positioning system (GPS) navigation systems holds much promise.

Next Generation Fiber Optic Gyroscopes for Use with GPS in Vehicle Navigation and Location Systems

Abstract: Fiber-optic gyroscope (FOG) technology has proven to be a suitable candidate for many applications where it is desirable to integrate GPS with a dead reckoning sensor. Open-loop, all-fiber type FOGS have been available commercially for several years for this purpose. Progress in minimizing size and reducing cost for these FOGS has been reported in several conferences previously. As application areas grow and commercial markets materialize, FOG technology is being pushed further to reduce dead reckoning sensor cost and size. In this paper we report the latest progress in the development of a low- cost FOG using an integrated optical circuit. The advantage of this design approach is that several functional devices can be integrated onto one small chip. Hitachi Cable’s approach has been to develop the chip design and the manufacturing technology simultaneously in order to achieve short product development cycle time and low cost in manufacturing. In this paper we will report on several engineering tradeoffs for this new gyro design, with consideration for the perspective of a systems designer who is trying to integrate the FOG with GPS into vehicle navigation and location systems. The FOG design will be reviewed and the development program status will be summarized. We will present FOG data relevant for dead reckoning sensor use in an integrated system. We will discuss existing and potential uses for this new technical approach to low-cost FOG design.

Solving Integrity Insufficiencies of Sat Nav Systems with Complementary Navigation Information

Abstract: In order to comply with the required navigation performance (RNP) parameters and the integrity, a continuous monitoring of the GNSS status is essen- tially needed. The certification process for satellite navigation as “sole means“, primary navigation system is difficult extremely unlikely for high precision / safety critical procedures in aviation applications, due to insufficiencies in the dynamic environment of the vehicle (satellite masking, mul-tipath, cycle slips, etc.). A combination of satellite information with inertial sensors, which have dissimilar characteristics to satellite navigation, is proposed in this paper. The inertial sensors are an ideal complement to GNSS due to their good dynamic properties, although they can be characterized by a longterm drift. A complementary satellite/inertial navigation system enables the estimation and compensation of different sensor errors of the inertial as well as the satellite subsystem within the Airborne Autonomous Integrity Monitoring (AAIM). Some concepts for onboard integrily monitoring, which have shown the potential to compensate the insufficiencies of RAIM, are discussed in this paper.

Automatic data acquisition using a kinematic surveying system

Abstract: New technologies and techniques for data aquisition and processing allow to determine 3D positions of environmental objects, which meet the demands of highest accuracy asked in geodesy and surveying as well as the omnipresent call for low cost systems. This paper presents a new approach to automatic digital information acquisition using the kinematic surveying system for real time data capturing of GPS-, IMU-, and CCD-camera output and post-mission data processing. The absolute position of the moving vehicle within the global corrdinate system (WGS84) is obtained by combining data from a GPS receiver and an inertial measuring unit (strapdown IMU). For compensating the known errors of both sensors, additional sensing devices like odometer and barometer are introduced. Further improvement in position estimation is achieved by stereo photogrammetric measurements of known environmental objects, the so called landmarks. A digital stereo vision-system creates successive series of high resolution grayscale images, while a SVHS video system records a continous image sequence of the traveled road and the nearby surroundings. On its way to complete automatic object positioning, a semi-automatic procedure for image processing has been chosen. The human operator takes care of the image interpretation and the search for wanted objects, while the feature extraction process is completely controlled by software. Depending on the demands of the application, all visible objects can be extracted, classified and photogrammetrically positioned. The parameters and the images of the accumulated objects are indexed to the 3D-trajectory and saved in a GIS-database.

GPS-Based Launch Vehicle Tracking Using a Common Multi-Patch Antenna Configuration

Abstract: A GPS-based launch vehicle tracking architecture is under serious consideration by the Air Force to replace or augment the current radar-based tracking system. Due to the unique launch vehicle configuration, demanding operational environments, and stringent timing and reliability requirements, the application of GPS to launch vehicles presents special implementation and integration challenges different from both earth-surface and satellite navigation. Standardization of GPS antenna configuration and implementation for different launch vehicles is a critical element in AF’s acquisition strategy. Finding such a standardized configuration is the objective of this paper. The paper presents a brief review of the antenna configuration trades including the trade between ring and patch antennas and the trade study on patch size and number. A l/4-wave patch, which is commercially available, has a broad beam width but is more sensitive to edge diffraction effects caused by the neighboring structural elements. Aerospace has developed a prototype l/2-wave patch, which can reduce the edge diffraction effects with a reduced beam width. Results of the trade studies indicate that either three l/4-wave patches or four l/2-wave patches should provide adequate GPS satellites coverage. A four l/2-wave patch configuration, which is less sensitive to peculiar neighboring structural elements of different vehicles, is a better choice for standardization. The first phase of development of a modularized simulation program is completed and has been used to evaluate the system tracking performance. The simulation includes the following key modules: vehicle trajectory and attitude motion, experimentally verified patch antenna models (with user’s choice of patch number, size, location on vehicle, and signal combining scheme), GPS constellation and visibility, antenna switching logic, and an integrated receiver/IMU. Using the actual flight trajectory and geometry of several vehicles, the same four l/2-wave patch antenna configuration was simulated. The results confmed the preliminary finding of the trade studies that the four patch configuration can satisfy the stringent launch vehicle requirements. Therefore, a common patch antenna configuration is feasible for standardized applications.