Showing papers on "Inertial navigation system published in 1992"

Observability analysis of piece-wise constant systems. II. Application to inertial navigation in-flight alignment (military applications)

Abstract: For pt.I see ibid., vol.28, no.4, p.1056-67, Oct. 1992. The method of analyzing the observability of time-varying linear systems as piecewise constant systems (PWCS) is applied to the analysis of in-flight alignment (IFA) of inertial navigation systems (INS) whose estimability is known to be enhanced by maneuvers. The validity of this approach to the analysis of IFA is proven. The analysis lays the theoretical background to, and clearly demonstrates the observability enhancement of, IFA. The analytic conclusions are confirmed by covariance simulations. Although INS IFA was handled to various degrees in the past, a comprehensive control theoretic approach to the problem is introduced. The analysis yields practical conclusions and a procedure previously unknown. >

Unified approach to inertial navigation system error modeling

Abstract: Several inertial navigation system error models have been developed and used in the literature. Most of the models are ad hoc models which were needed to solve certain particular problems and were developed for that purpose only. Consequently, the relationship, correspondence, and equivalence between the various models is not evident. This paper presents a new methodology for developing inertial navigation systems error models which also puts all of the known models in the same framework and shows the equivalence between them. The new methodology is based on several choices the developer has to make which uniquely define the error model. This new approach enables the development of all existing models in a unified way, hence the equivalence and correspondence between them is obvious. Moreover, any new model which is of interest can be developed using the methodology presented in this work. In fact, any new model which will ever be developed for the class of systems considered here will fit into the framework described in this paper.

Error estimation of INS ground alignment through observability analysis

Abstract: A systematic analysis of the observability of an inertial navigation system (INS) in ground alignment with Bar-Itzhack and Berman's error model is presented. It is shown that the unobservable states are separately contained in two decoupled subspaces. The constraints on the selection of unobservable states are discussed. An estimation algorithm which is derived fully from the horizontal velocity outputs for computing the misalignment angles is provided. It reveals that the azimuth error can be entirely estimated from the estimates of leveling error and leveling error rate, without using gyro output signals explicitly. >

The Navstar Global Positioning System

Abstract: 1 The Science of Navigation- What Is Navigation?- A Typical Ground-Based Radionavigation System- The Advantages of Space-based Transmitters- The Transit Navigation Satellites- Gravity Gradient Stabilization- Disturbance Compensation Systems- Compensating for Ionospheric Delays- Compensating for Tropospheric Delays- Navigation Techniques- The Navstar Revolution- Navstar Navigation Techniques- The Navstar Clocks- Practical Benefits for All Mankind- 2 The Navstar GPS- The Space Segment- Signal Structure and Pseudorandom Codes- Navigation Solutions- Correcting for Relativistic Time Delays- Correcting for Ionospheric and Tropospheric Delays- Decoding the 50-Bit-Per-Second Data Stream- The Various Families of Navstar Satellites- The User Segment- A Typical High-Performance 5-Channel Receiver- Operating Procedures- The Control Segment- Inverting the Navigation Solution- The Monitor Stations and The Master Control Station- Field Test Results- 3 Performance Comparisons for Today's Radionavigation Systems- A Sampling of Today's Ground-based Navigation Systems- Loran C/D- Omega- VOR/DME Tacan- The Microwave Landing System- Inertial Navigation- JTIDS Relnav and PLRS- Signpost Navigation Techniques- A Sampling of Today's Space-based Navigation Systems- Transit- The Navstar Global Positioning System- The French Argos- Side-by-side Performance Comparisons- 4 User-Set Architecture- The Major Components of a Typical Navstar Receiver- The Receiver Antenna and Its Associated Electronics- The Tracking Loops- Navigation Processor- Power Supply- Control-Display Unit- Choosing the Proper User-set Architecture- Performance Comparisons- Selecting the Antennas- Selecting the Proper Computer Processing Techniques- Solving for the User's Position- Computing and Interpreting the Geometrical Dilution of Precision- Ranging Error Budgets- Kalman Filtering Techniques- 5 User-set Performance- Accuracy Estimates for Various Methods of Navigation- Performance Criteria to Consider when Purchasing a Navstar Receiver- Receiver Design Choices- Number of Channels and Sequencing Rate- Access to Selective-availability Signals- Available Performance Enhancement Techniques- Computer Processing Capabilities- Receiver Design Smart Card- Today's Available Navstar Receivers- Hand-held Receivers- Commercially Available Navstar Chipsets- 6 Differential Navigation and Pseudo-satellites- Performance Comparisons: Absolute and Differential Navigation- Special Committee 104's Recommended Data-exchange Protocols- The Coast Guard's Differential Navigation System Tests- Motorola's Mini Ranger Test Results- COMSAT's Data Distribution Service for the Gulf of Mexico- Wide-area Differential Navigation Services- Pseudo-satellites- Special Committee 104's Data Exchange Protocols for Pseudo-satellites- Comparisons Between Differential Navigation and Pseudo-satellites- 7 Interferometry Techniques- The Classical Michaelson-Morley Interferometry Experiment- Measuring Attitude Angles with Special Navstar Receivers- Eliminating Solution Ambiguities- Practical Test Results- Using Interferometry to Fix Position- Single, Double, and Triple Differencing Techniques- The POPS Post-Processing Software- Spaceborne Interferometry Receivers- Motorola's Commercially Available Monarch- Tomorrow's Generic Spaceborne Receivers- 8 Integrated Navigation Systems- Integrated Navigation- Inertial Navigation- Error Growth Rates- Reinitialization Techniques- Ring Laser Gyros- Monolithic Ring Laser Gyros- Fiber Optic Gyros- Using the GPS for Testing Inertial Navigation Systems- The Practical Benefits of Integrated Navigation- Chassis-level Integration- 9 Interoperability with Other Navigation Systems- The Soviet Glonass- The Glonass Specification Release at Montreal- The Glonass Constellation- Orbital Maneuvers for the Glonass Satellites- Building Dual-capability GPS/Glonass Receivers- Receiver Design Difficulties- Dual-Capability Receiver Tests at Leeds University- The FAA's Joint Research Efforts with Soviet Scientists- Other Attempts to Build Dual-capability Receivers- Integrity Monitoring Techniques- Interoperability with Other Radionavigation Systems- Eastport International's Integrated System for Underwater Navigation- 10 The Navstar Satellites- The Eight Major Spacecraft Subsystems- The Orbit Injection Subsystem- Tracking, Telemetry and Command- Attitude and Velocity Control- Electrical Power- Navigation Subsystem- Reaction Control- Thermal Control- Structures and Mechanisms- On-orbit Test Results- The Multiyear Spacecraft Procurement- Booster Rockets- Orbital Perturbations- The Spacecraft Ephemeris Constants- Satellite Viewing Angles- Earth-shadowing Intervals- Repeating Ground-trace Geometry- 11 Precise Time Synchronization- John Harrison's Marine Chronometer- Celestial Navigation Techniques- A Short History of Time- The Atomic Clocks Carried Aboard the Navstar Satellites- Cesium Atomic Clocks- Rubidium Atomic Clocks- Developing Atomic Clocks Light Enough to Travel Into Space- The Growing Need for Precise Time Synchronization- Time Sync Methodologies- Fixing Time with the Navstar Signals- Lightweight Hydrogen Masers for Tomorrow's Navstar Satellites- Crosslink Ranging Techniques- 12 Digital Avionics and Air Traffic Control- The Sabreliner's Flight to the Paris Air Show- Four Major Concerns of the Federal Aviation Administration- Selective Availability- User-Set Fees- Integrity-related Failures- Continuous Five-satellite Coverage- Using a Dedicated Constellation for Air Traffic Control- An Alternative Architecture Using the GPS- Comparisons Between Geosynchronous and Semisynchronous Constellations- Piggyback Geosynchronous Payloads- The Autoland System Test Results- 13 Geodetic Surveying and Satellite Positioning- Determining the Shape of Planet Earth- The Theory of Isostasy- The Earth's Contours Under Hydrostatic Equilibrium- GPS Calibrations at the Turtmann Test Range- Static Surveying Techniques- Kinematic and Pseudo-kinematic Surveying- Freeway Surveying During War in the Persian Gulf- Navstar Positioning for Landsat D- The Landsat's Spaceborne Receiver- On-Orbit Navigation Accuracy- Orbit Determination for High-altitude Satellites- Today's Available Spaceborne Receivers- 14 Military Applications- The Military Benefits of the Worldwide Common Grid- Field Test Results- Projected Battlefield Benefits- Test Range Applications- Military Receivers- Carrier-landing Accuracies- Amphibious Warfare Operations- Accuracy-enhancements for Strategic and Cruise Missiles- 15 Civil Applications- Dinosaur Hunting with the GPS- Guiding Archaeological Expeditions- Tracking Hazardous Icebergs- Offshore Oil Exploration- Fixing the Positions of Railroad Trains- Automobile Navigation- Dead Reckoning Systems- Tomorrow's Space-based Vehicle Navigation Techniques- Today's Available Automotive Navigation Systems- Futuristic Applications for Navstar Navigation- Appendix A Additional Sources of lnformation- GPS Information Centers- The US Coast Guard's Information Center- The Computer Bulletin Board at Holloman Air Force Base- Global Satellite Software's Computer Bulletin Board- The Glonass Computer Bulletin Board- Precise GPS Orbit Information- Military GPS Information Directory- GPS Information with a European Flavor- The United Kingdom- The Netherlands- Norway- GPS Clock Behavior- Information for Surveyors- GPS World Magazine- The Federal Radionavigation Plan- Appendix B Today's Global Family of User-set Makers- Domestic User-set Makers- Foreign User-set Makers- Appendix C Navigation-Related Clubs and Organizations- Appendix D Navigation-related Magazines and Periodicals

A sensitive fast-response probe to measure turbulence and heat flux from any airplane

Abstract: The theory, configuration, and accuracy of an inexpensive probe to measure turbulence from a small airplane are presented. The probe employs a nine-hole pressure-sphere design along with inprobe high-frequency pressure, temperature, and acceleration sensors. This sensor suite is specifically designed to extend mass, momentum and energy eddy-flux measurement to the higher frequencies characteristic of marine and nocturnal boundary layers. The probe is part of a mobile flux system, independent of the conveyance, which does not require a separate Inertial Navigation System.

Integrated enroute and approach guidance system for aircraft

Abstract: Data from long range aids such as the global positioning system (GPS) and an inertial navigation system (INS) and short range aids such as a microwave londing system (MLS) are used to smoothly and automatically transition an aircraft from the long range aids to the short range aids. During cruise a Kalman filter (70) combines data from the global positioning system and the inertial navigation system to provide accurate enroute information. When the aircraft arrives in the vicinity of the airport and begins to acquire (70) data from the microwave landing system, the Kalman filter (70) is calibrated with the MLS data to permit precision landing with GPS/INS data alone in case the MLS system subsequently fails. In addition, navigation information begins to be derived from a weighted sum of the GPS/INS and MLS data, the weighting being determined by distance from the airport. In a first region farthest from the airport, the GPS/INS data is given a 1.0 weighting factor; and in a second region nearest the airport, the MLS data is given a 1.0 weighting factor. In a third region intermediate the first and second regions, the GPS/INS data and MLS data are proportionately and complementarily weighted as a function of the distance from the airport. If the MLS system fails, the weighting system (76, 78, 80) is disabled (84) and navigation data is again derived from the GPS/INS combination. In addition, the data from both systems are monitored (74), and a cockpit alarm is sounded if the data diverged beyond a specific amount. The Kalman filter (70) supplies a weighting system comprising two weighting devices (76, 78), one (76) of which weights the MLS data, and the other (78) the GPS/INS combination data. The outputs of these devices (76, 78) are summed (80) and supplied to one terminal of a switch (84) for selecting between the weighting system (76, 78, 80) and the Kalman filter (70).

Calculation of geometric dilution of precision

Abstract: A very simple closed-form formula for the calculation of the geometric dilution of precision (GDOP) in Global Positioning System (GPS) navigation and in Global Navigation Satellite System (GLONASS) navigation is presented, which requires less than 40 multiplications. >

Analysis of image-based navigation system for rotorcraft low-altitude flight

Abstract: Some of the issues in the location of objects using a sequence of images from a passive sensor are examined. Image-object differential equations for a rotorcraft executing an arbitrary maneuver are developed. Assuming an onboard inertial navigation system for rotorcraft and state estimation, this study considers how object location is affected by the choice of Kalman filter estimation technique, the rotorcraft, and the object. Simulation results are presented. >

Fault-tolerant inertial navigation system

Abstract: Disclosed herein is a Fault-Tolerant Inertial Navigation System comprising, in a preferred embodiment, a Redundant Set of at least two Inertial Navigation Systems, from which one may identify and isolate at least one instrument within an Inertial Navigation Unit which shows substantial performance degradation. The two inertial navigation units are fully capable of performing navigational functions. Each of these inertial navigation units has a plurality of navigational instruments, including at least three linear sensors (such as accelerometers) and three angular change sensors (such as gyroscopes or ring laser gyroscopes). No two linear sensors nor any two angular change sensors of either unit are aligned colinearly. Each of the inertial navigation units produces a set of independent navigational solutions at each of their respective outputs. The independent navigational solutions of each of the navigation units are compared and any significantly degraded performance of any one linear sensor or any one angular change sensor is detected.

Instantaneous GPS attitude determination

Abstract: The author describes a procedure for instantaneous GPS (Global Positioning System) attitude determination, i.e., a solution for the GPS integrated carrier Doppler wavelength ambiguities using only measurements at a single epoch. Most previous techniques for solving the phase ambiguity problem have required some form of time history processing relying on GPS satellite and/or user motion to provide enough geometry change to eliminate false solutions. The algorithm described assumes three nonlinear antennas and integrated carrier Doppler measurements from four or more satellites. Double-difference processing provides at least three independent observables for the two antenna separation vectors to compute the three attitude Euler angles. The results obtained also suggest that arbitrarily large separations can be resolved since unambiguous carrier-smoothed pseudorange measurements could provide a coarse measurement with an accuracy falling within the resolution range of the algorithm presented. >

Terrain referenced navigation electromagnetic-gravitational correlation

Abstract: A terrain reference navigation system for an aircraft, surface vessel or subsurface vessel utilizing three sets of geo-physical correlation data. A kalman filter is used to correlate terrain data, electromagnetic data and gravimetric data with the output of a digital map of terrain, electromagnetic field and gravity. An optical disk stores the digitized data for sections of the globe. A Best of 3 selection process decides based on the errors in the kalman filter whether to accept the prediction of the terrain system, electromagnetic system or gravity system. An inertial navigation system uses the results of the Best of 3 selection to update aircraft, surface vessel or sub-surface vessel position and velocity and provide a more accurate positional estimate.

Kalman filter mechanization for INS airstart

Abstract: A strapdown mechanization and associated Kalman filter are developed to provide both ground align and airstart capabilities for inertial navigation systems (INSs) using Doppler velocity and position fixes, while not requiring an initial heading estimate. Position update during coarse mode is possible by defining sine and cosine of wander angle as filter states and modeling the position error in geographic frame while integrating velocity in the wander frame. INS Global Positioning System (GPS) differential position due to GPS antenna moment arm can aid heading convergence during hover turns in helicopter applications. Azimuth error state in the fine mode of the filter is defined as wander angle error to provide continuous estimation of navigational states, as well as inertial/aiding sensor errors, across the coarse-to-fine mode transition. Though motivated by a tactical helicopter application, the design can be applied to other vehicles. Advantages over conventional systems in addition to the airstart capability include robustness and versatility in handling many different operational conditions. >

Acoustic noise reduction in the MK 49 ship's inertial navigation system (SINS)

Abstract: Sperry Marine has devised a passive structure-borne noise isolation system that reduces the noise generated by dithered ring laser gyroscopes to levels below the requirements of MIL-STD-740-2. Descriptions of some of the analytical and experimental processes required to develop this system are presented, together with structure-borne noise test results. Results show that a 47-dB structure-borne noise reduction has been achieved with a noise isolation system that is compatible with the stability and repeatability required by navigation systems. The noise reduction techniques presented have enabled Sperry Marine to develop a dithered ring laser gyroscope navigator feasible for naval applications, the MK 49. >

Requirements for Airborne Vector Gravimetry

Abstract: The objective of airborne vector gravimetry is the determination of the full gravity disturbance vector along the aircraft trajectory. The paper briefly outlines the concept of this method using a combination of inertial and GPS-satellite data. The accuracy requirements for users in geodesy and solid earth geophysics, oceanography and exploration geophysics are then specified. Using these requirements, accuracy specifications for the GPS subsystem and the INS subsystem are developed. The integration of the subsystems and the problems connected with it are briefly discussed and operational methods are indicated that might reduce some of the stringent accuracy requirements.

Receiver autonomous integrity monitoring (RAIM) capability for sole-means GPS navigation in the oceanic phase of flight

Abstract: Receiver autonomous integrity monitoring (RAIM), a GPS integrity monitoring scheme that uses redundant ranging signals to detect a satellite malfunction that results in a large range error, involves two functions: detection of the presence of a malfunctioning satellite and identification of which satellite (or satellites) is malfunctioning. An analysis is presented of GPS RAIM capability for sole-means navigation in the oceanic phase of flight, where the position protection limit requirement for the integrity function is not as stringent as for nonprecision approaches, and yet both detection and identification function may be required if GPS is to be used as a sole-means system. For this purpose, a detection and identification algorithm is developed which takes advantage of the fact that for the oceanic phase of flight, a much larger position error is acceptable than for the nonprecision approach phase of flight. The performance of this algorithm and an algorithm proposed previously by others is estimated via simulation and compared. On the basis of the results, recommendations are made on how RAIM may be used if GPS is to be coupled with an inertial system to provide a sole-means capability in the oceanic phase of flight. >

Self-contained method for correction of an inertial system over a body of water

Abstract: A method and apparatus for performing on-board corrections to the computed navigation variables of an inertial system on an aircraft while flying over a body of water. Onboard instruments, including a barometric altimeter and a radar altimeter, measure the vertical distance of the aircraft above an ellipsoidal model of the earth and above the body of water respectively. An on-board computer calculates the differences between such heights over a plurality of points along the path the aircraft travels over the water as indicated by its inertial navigation system. The differences are compared with a map of the undulation of the geoid encompassing the region to determine the deviation of the navigated course from the true course. Appropriate corrections to the aircraft's inertial system may then be made to reduce error.

Magnetic marker position fixing system for underwater vehicles

Abstract: A magnetic marker position fixing and resetting system for vehicles searching an area on the floor of a body of water. The vehicle has an inertial navigation system for determining its position and angular orientation with respect to a set of cartesian axes fixed in the earth. The vehicle deploys at least one magnetic marker in the search area. The positions of the markers in the earth-based axes and the magnitude of their magnetic moments are determined and are stored in a computer in the vehicle. The vehicle is equipped with a triaxial vector magnetometer in which the magnetic sensors are mutually orthogonal. When the vehicle's navigation system requires a position reset, the triaxial vector magnetometer on the vehicle detects the marker's magnetic induction components along x, y and z cartesian axes fixed in the vehicle. Algorithms are exercised in the vehicle's computer which use the measured x, y and z components of the marker's magnetic induction to provide a precise estimate of the vehicle's position with respect to the fixed magnetic marker in the vehicle-based axes. This relative position is transformed to components along the earth-based axes. The vehicle's position in the earth-based axes is then computed from the measurement of its position relative to the marker in the earth-based axes and the marker's known position in the earth-based axes. Comparing this derived vehicle position with the vehicle's position as determined by its inertial navigation system provides the required position reset.

Inertial navigation sensor integrated motion analysis for autonomous vehicle navigation

Abstract: Recent work on INS integrated motion analysis is described. Results were obtained with a maximally passive system of obstacle detection (OD) for ground-based vehicles and rotorcraft. The OD approach involves motion analysis of imagery acquired by a passive sensor in the course of vehicle travel to generate range measurements to world points within the sensor FOV. INS data and scene analysis results are used to enhance interest point selection, the matching of the interest points, and the subsequent motion-based computations, tracking, and OD. The most important lesson learned from the research described here is that the incorporation of inertial data into the motion analysis program greatly improves the analysis and makes the process more robust.

Architectures and GPS/INS integration: impact on mission accomplishment

Abstract: It is pointed out that the GPS (Global Positioning System) signal contains information which, when properly combined with information from INS (inertial navigation system) and other sensors, provides exceptionally high-accuracy position, velocity, attitude, and time information. These ten elements of information (three each in position, velocity, and attitude, and one in time) are common, in various combinations, to most of the avionics functions. When viewed from a system perspective, this high-precision information can be thought of as the integration basis, or a reference set, which offers opportunities for reconfiguration of the offensive, defensive, communication, navigation, and other sensors. Various integration architectures for fusion of these sensors can inherently enhance, enable, or severely limit these potential mission capabilities. The choice of integration architecture can directly and profoundly affect performance, cost of integration, cost of ownership, and exploitation of much greater mission capability. This is illustrated with the GPS/INS integration example. >

Method of debriefing multi aircraft operations

Abstract: The present invention relates to a method for debriefing aircraft A/C operations. The method comprises forwarding selected flight data obtained, e.g. from a suitable GPS receiver, collected on the aircraft computer to a monitoring device, encoding from said monitoring device the digital data by an Asynchronous protocol, e.g. RS-232 protocol, onto the cassette of the AVTR and thereafter subjecting the cassette on the ground to a data reduction process, thus obtaining a display file. The GPS receiver is, for example, a commercial code receiver which may be connected to one antenna only. The data received from the GPS receiver are being forwarded to the monitoring device, encoded simultaneously with the other flight data and, by the same method, correcting on the ground in the course of the reduction process the Inertial Navigation System (INS) position drifts. Differential GPS technique may be used on the ground. Several individual display files may be syunchronized into a single display file.

Terrain referenced navigation-adaptive filter distribution

Abstract: A terrain referenced navigation system utilizing a five-state kalman filter with a filter distribution based on a fixed grid approach. The five-state kalman filter utilizes an aircraft's altitude, East velocity, East acceleration, a South velocity and South acceleration. The database of the terrain referenced navigation system also utilizes a state variable indicating whether the aircraft is headed over water or land. The accuracy of the terrain referenced navigation system is improved by ignoring filter coefficients over water. The invention provides increased computational efficiency and accuracy by predicting inertial navigation parameters in the line of flight of an aircraft within a circle error of probability at predetermined filter locations within the circle error of probability. The difference between actual and predicted values are then used to compute a new estimate. The method is repeated until the removal of the most divergent filter at each pass results in a single best filter.

Navigation requirements for autonomous underwater vehicles

Abstract: The specification and design of a navigation system for use on an autonomous underwater vehicle (AUV) must be conducted as an integral part of the top-level vehicle design process. This paper addresses the physical characteristics of the navigation system that are likely to have the largest impact on the overall performance of the vehicle. Accuracy requirements are analyzed to match the types and capabilities of equipments that can be included in the navigation subsystem to the desired vehicle task capabilities. Considered among these equipment types are an inertial navigation unit (INU), sonar velocity log (SVL), and acoustic transponder navigation (ATN) system. In general, the outputs of several equipment types need to be combined in order to achieve the desired performance. The expected contributions of the various equipments in an integrated navigation subsystem are identified. In some cases, off-the-shelf equipment is available that will support vehicle requirements. However, most of this equipment was not originally designed for an AUV application. This paper identifies areas where improvements can be made to better support AUV requirements.

Locomotion of an all-terrain mobile robot

Abstract: The authors introduce a framework and prospective solutions for intelligent locomotion, defined as the ability for a mobile robot to cross over obstacles along a path roughly determined either through teleoperation or by a navigation path-finder. Then, they present a simple but efficient control scheme derived from these concepts, taking into account ground clearance, vehicle safety, and possible occlusions in the vision field. This control scheme is applied to Rami, a four-tiltable-track robot equipped with force sensors, an inertial reference system, a laser-stripe range finder, and extensive real-time computing facilities based on a decentralized architecture. >

Differential GPS/inertial navigation approach/landing flight test results

Abstract: In November 1990, a differential GPS/inertial flight test was conducted to acquire a system performance database and demonstrate automatic landing using an integrated differential GPS/INS with barometric and radar altimeters. Flight test results obtained from postflight data analysis are presented. These results include characteristics of DGPS/inertial error, using a laser tracker as a reference. In addition, data are provided on the magnitude of the differential correlations and vertical channel performance with and without radar altimeter augmentation. Flight test results show one sigma DGPS/inertial horizontal errors of 9 ft and one sigma DGPS inertial vertical errors of 15 ft. Without selective availability effects, the differential corrections are less than 10 ft and are dominated by receiver unique errors over the time period of an approach. Therefore, the one sigma performance of the autonomous GPS (8-ft horizontal and 20-ft vertical) is very similar to the DGPS/inertial performance. Postprocessed results also demonstrate significant improvements in vertical channel performance when GPS/inertial is aided with radar altimeter along with a low-resolution terrain map. >

A system for obstacle detection during rotorcraft low-altitude flight

Abstract: Airborne vehicles such as rotorcraft must avoid obstacles such as antennas, towers, poles, fences, tree branches, and wires strung across the flight path. The paper analyzes the requirements of an obstacle detection system for rotorcrafts in low-altitude Nap-of-the-Earth flight based on various rotorcraft motion constraints. It argues that an automated obstacle detection system for the rotorcraft scenario should include both passive and active sensors. Consequently, it introduces a maximally passive system which involves the use of passive sensors (TV, FLIR) as well as the selective use of an active (laser) sensor. The passive component is concerned with estimating range using optical flow-based motion analysis and binocular stereo in conjunction with inertial navigation system information. Experimental results obtained using land vehicle data illustrate the particular approach to motion analysis. >

Autonomous spacecraft docking using a computer vision system

Abstract: An autonomous spacecraft docking scheme is proposed. Emphasis is on the integration of a computer vision system for obtaining position and orientation estimates of the spacecraft with respect to a docking platform and control systems for the rotational and translational motion of the spacecraft. Computer simulations of an integrated spacecraft computer vision and docking control system are described under a specific set of assumptions. The effects of image quantization and sampling and the perturbation effects of orbital motion are included. The simulation results demonstrate the technical feasibility of this proposed approach. This docking control system compares favorably with other methods based on the use of sensors such as laser, infrared, radar, GPS (global positioning system), or INS (inertial navigation system). >

Laser gyro life prediction

Abstract: A laser gyro lifetime prediction method incorporates a memory model that stores a worst case performance parameter for a readout intensity, a laser intensity and a derived quantity known as volts per mode for a laser gyro. A microprocessor based life prediction method utilizes a predetermined failure criteria to judge a estimate of laser gyro life based on historic performance of laser gyro operating parameters. The prediction is based on a linear quadratic or higher order fit of lifetime data for critical temperatures. The performance data is stored in a memory model for each critical temperature and parameter. The laser gyro reports eminent failures to the inertial navigation system or a host controller. Routine scheduled maintenance of the laser gyro is enhanced by knowing its lifetime.

Inertial navigation system including self-contained performance validating arrangement

Abstract: The accuracy of the performance of an inertial navigation system is validated by comparing data measured by a fourth gyro and accelerometer to an analytic equivalent constructed from measurements made by a primary gyro/accelerometer orthogonal triad.

Extracting gravity vectors from the integration of global positioning system and inertial navigation system data

Abstract: Consulting records of a past flight, 1-Hz trajectory, and (roll, pitch, yaw) motion profiles were adopted for a simulated 7.5-hour balloon flight over New Mexico. The assumed pay load of the balloon was an inertial ring laser gyro strap-down system and a three-antenna, minimum 12-channel Global Positioning System (GPS) receiver. The adopted trajectory was assumed to be GPS determined and interferometric in nature reflecting a second, ground-fixed receiver. Owing to the strap-down Inertial Navigation System (INS), a corresponding 1-Hz profile of accelerometer specific force outputs (total (GPS sensitive) inertially referenced accelerations less gravitational accelerations present) was also required to conduct a covariance error analysis. The gravitational accelerations were computed by a spherical harmonic expansion through n = m = 360. A 36-state, 40-noise process, open-loop Kaiman filter integrating GPS and INS data was constructed. A full constellation of 18 GPS satellites was simulated. Related to the two receivers, external GPS updating observation types used were pseudorange differences, single differenced carrier phases, and single differenced phase rates. A fourth type of updating observation used was the error in the INS's estimation of phase differences between GPS antenna pairs (an equilateral triangle balloon-borne configuration was assumed with 1-m baselines). The filter cycle and update frequency were both set at 1 Hz. A postmission covariance analysis based Kaiman filter mechanization was executed, taking into account the major initial INS and GPS error sources. Hybrid alignment errors were reduced to 0.4 arc sec about the north and east axes (leveling errors) and to 0.7 arc sec about the down axis (heading error). Hybrid positioning and velocity errors were held to the 1–2 cm and 1–2 mm\s range, respectively, and were highly correlated to the corresponding position dilution of precision satellite geometry. The benign motions of the balloon allowed for a smooth time behavior of the states. Assuming the accelerometer errors are essentially bias states that can be calibrated in flight based on very accurate GPS observations, the leveling uncertainties are the main error sources in obtaining the three components of the balloon- borne gravity vector. The alignment errors mentioned above contribute a 2.5-mGal error to the computed horizontal components and a 0.05-mGal error to the vertical. Limiting the misalignment contributions to the deflection error budgets to 1 mGal will require leveling errors of 0.2 arc sec. Gravity components obtained from a hybrid system can be compared to upward continued (from extensive ground gravity data) components to validate continuation models and to establish instrumental proof of concept. A successful balloon experiment would be a strong argument for a “high-low” satellite tracking mission involving the GPS constellation and a dedicated, polar orbit, low satellite (altitude e (160 km, 300 km)) possessing the same payload. At such an altitude the leveling concerns are less pronounced. Such a spaceborne mission would allow for a downward continued gravity mapping over all heretofore inaccessible Earth surface regions.