Showing papers on "Inertial navigation system published in 1982"

All-fiber gyroscope with inertial-navigation short-term sensitivity.

Abstract: We report new experimental data for an all-fiber gyroscope with a noise density of 0.004(deg/h)2/Hz. This is compatible with the requirements for inertial navigation. Noise contributions from the coherent Rayleigh backscatter when a phase-modulation bias scheme is used and also from acoustic vibrations are discussed.

Fiber-Optic Rotation Sensors. Tutorial Review

Abstract: The measurement of rotation is of considerable interest in a number of areas. For example, inertial navigation systems as used in aircraft and spacecraft depend critically on accurate inertial rotation sensors. The allowable errors in rotation sensor performance depend on the particular application. Typical requirements for aircraft navigation lie between 0.01 and 0.001 degree/hour. In terms of earth rotation rate Ωe = 15 degrees/hour this becomes 10-3 to 10-4 ΩE. A number of other applications of rotation sensors exist such as surveying where the accurate determination of azimuth and geodetic latitude is important [T]. In this case performance of 10-6 ΩE or better is needed. Geophysics applications include the determination of astronomical latitude, and the monitoring of polar motion caused by wobble, rotation, precession and wandering effects [1]. A highly precise rotation sensor may be used to measure any changes in the length of the day and to detect torsional oscillations in the earth caused by earthquakes. Finally, ultraprecise sensors may find applications in relativity related experiments such as the determination of the preferred frame, dragging of inertial frames, etc. [2].

Attitude sensing system

Abstract: An attitude sensing system which incorporates the precision in attitude sensing of a satellite navigation system with the dynamic tracking capabilities of an inertial measurement unit. Optimally estimated attitude and system error signals are combined with the outputs of an inertial measurement unit to control the phase differences of signals received on an interferometer array from a navigation satellite. The outputs from the inertial measurement unit and the phase differences are processed in an optimal estimator filter to produce periodically updated attitude and system error signals. This permits inertial attitude sensing to benefit from the long term accuracy of attitude estimation based upon signals from the satellite navigation system. During conditions of high dynamic maneuvering in which attitude changes are rapid, the output of the inertial measurement unit continues to provide attitude information and controls the attitude sensing loop to insure that the system is not disoriented by such high dynamic conditions.

Inertial navigation systems aided by G.P.S.

Abstract: : The present work is a Kalman filter study, in indirect feedback configuration, for a proposed integrated inexpensive Inertial Navigation System/Global Positioning System (I.N.S./G.P.S.). A one nautical mile per hour, local-level, two-accelerometer I.N.S. is used where the errors are represented by a 7 state linear model. G.P.S. is assumed to provide four range measurements from an equal number of satellites with the best relative position among those in view. I.N.S. error analysis showed error dependence on Schuler frequency and that it was possible to neglect Foucault modulation for navigation purposes. The present I.N.S./G.P.S. system has been shown to be quite effective since the navigation errors are reduced quickly for both short and long term periods without any divergence. (Author)

Minimal order time sharing filters for INS in-flight alignment

Abstract: Very simple reduced order filters which operate in a time sharing mode are proposed for in-flight and transfer alignment of calibrated inertial navigation systems (INS) such as those in fighter aircraft. The coarsely aligned INS is flown for a short duration in a straight and level flight during which two second-(or third-) order time sharing filters estimate the level misalignment. After removing the estimated level misalignment angles a third(or fourth-) order filter is switched in to estimate the azimuth misalignment as the aircraft starts to maneuver in the lateral plane. A true covariance simulation is carried out, which shows that the proposed filters successfully perform the fine alignment.

AGARD Flight Test Instrumentation Series. Volume 15. Gyroscopic Instruments and Their Application to Flight Testing

Abstract: : This AGARDograph is the 15th of the AGARD Flight Test Instrumentation Series and discusses the use of gyroscopic instruments to support flight testing Gyroscopic instruments are used in flight tests to measure the aircraft angular acelerations and rates, attitude and heading and - in combination with accelerometers - the linear acceleration, the ground velocity and the position This volume describes the measuring principles, the technical lay-out and the error behaviour of the sensors and systems used for these measurements: Gyros, accelerometers, attitude and heading references and inertial navigation systems Attention is also given to integrated and hybrid sensor systems, as they are in the modern instrumentation systems Examples of actual flight instrumentation systems are described and the requirements for the gyroscopic sensors in these systems are discussed for applications in aircraft stability and control flight tests, in performance tests and in airborne and ground systems calibration and testing (Author)

Doppler-Aided Low-Accuracy Strapdown Inertial Navigation System

Abstract: This paper presents a covariance analysis of the performance of a Doppler-aided low-accuracy coarsely aligned strapdown inertial navigation system (INS), whose fine alignment takes place automatically in flight. It is shown that the fine alignment in azimuth, which requires turns, consists of in-flight gyro calibration and inflight gyrocompassing. The spacing of the turns is investigated. The influence of several position fixes is examined, and it is shown that they can replace INS turns. It is also shown that the use of magnetic heading reference reduces system errors but is not necessary for the satisfactory performance of the augmented system. Two suboptimal Kalman filters are designed and evaluated. Their small performance degradation with respect to that exhibited by the optimal filter and their low sensitivity to parameter changes is demonstrated by true covariance simulation runs.

Gravity Model Performance in Inertial Navigation

Abstract: NERTIAL navigation has evolved to the point that the traditional gravity model is a principle error source in advanced, precise systems. Future autonomous strategic systems, such as the cruise missile, will likely require a more accurate gravity model. Mission success depends on navigation system accuracy, not gravity model accuracy per se. So an improved gravity model should be judged by systemlevel performance expressed, for example, as circular-erro rprobable (CEP). Statistical analyses based on Monte Carlo and linear state-space techniques have been used to produce this gravity model performance index. A brief review of these methods will clarify the need for a new analysis approach. The gravity model in an inertial navigation system (INS) is a subsystem or component providing one part of the information required for constructing position, velocity and attitude estimates. The total acceleration is given by

An investigation of quasi-inertial attitude control for a solar power satellite

Abstract: An efficient means, a quasi-inertial attitude mode, is developed for maintaining the normal solar orientation of a space satellite for power collection in a synchronous orbit Formulae are presented which establish the basic parametric properties for ideal quasi-inertial attitude and phasing An active control system is necessary to compensate for the energy loss since energy dissipation in widely oscillating flexible bodies produces an instability of the quasi-inertial attitude in the sense that the spacecraft will tumble at the orbit rate A fixed terminal time and state optimal control problem is formulated and an algorithm for determining the optimal control as a means for the periodical attitude and phase compensation is developed The vehicle orientation affected by internal disturbance (structural flexibility) and external disturbances (eg, drag forces) is maintained by a specialized controller design

The Shuttle inertial system

Abstract: The Space Shuttle inertial system is built around a sensor assembly called the inertial measurement unit (IMU). The system includes a redundant set of three structurally integrated IMU's that operate in conjunction with parallel strung data system computers to provide precise attitude and velocity information to user system functions. The inertial system is actually a separate subsystem function integrated into the overall avionics system. Software resident in the system computers is the final link in the inertial system. The inertial software is comprised of two major sets, including a subsystem operating program (SOP) called the IMU SOP and redundancy management. Attention is given to system applications, systems performance, attitude sensitivities, the IMU platform, IMU thermal management, aspects of IMU calibration, and Shuttle program experience.

Decentralized Relative Navigation and JTIDS/GPS/INS Integrated Navigation Systems

Abstract: : One contribution of this research is a deeper understanding of the stability and performance of community relative navigation, such as is currently implemented in the Joint Tactical Information Distribution System (JTIDS). Relative navigation in the JTIDS system is organized in a decentralized manner with the Kalman filter in each member estimating only the member's own navigation state, but based on measurements that rely in part on the reported positions of other members. Simulations have shown the interacting navigation solutions can be unstable. We have found an analytical proof of the stability of one decentralized organization-the fixed rank hierarchy. Next an alternate approach for the community navigation, based on measurement sharing, is presented. This alternate has no stability difficulties, has superior accuracy, but has some increase in communication and computer requirements. Another contribution of this research is an assessment of the benefits of and approaches to integrating the data from JTIDS, GPS, and inertial systems. Finally, an extensive Fortran simulation of the performance of JTIDS/GPS/INS integrated navigation in a multi member environment has been developed and is used to explore the performance of both JTIDS/INS navigation and JTIDS/GPS/INS navigation.

Simultaneous Calibrations of Voyager Celestial and Inertial Attitude Control Systems in Flight

Abstract: A mathematical description of the data reduction technique used to simultaneously calibrate the Voyager celestial and inertial attitude control subsystems is given. It is shown that knowledge of the spacecraft limit cycle motion, as measured by the celestial and the inertial sensors, is adequate to result in the estimates of a selected number of errors which adversely affect the spacecraft attitude knowledge.

Wellbore inertial navigation system (WINS) software development and test results

Abstract: The structure and operation of the real-time software developed for the Wellbore Inertial Navigation System (WINS) application are described. The procedure and results of a field test held in a 7000-ft well in the Nevada Test Site are discussed. Calibration and instrumentation error compensation are outlined, as are design improvement areas requiring further test and development. Notes on Kalman filtering and complete program listings of the real-time software are included in the Appendices. Reference is made to a companion document which describes the downhole instrumentation package.

Shuttle orbiter stellar-inertial reference system

Abstract: The Space Shuttle stellar-inertial reference system is a velocity and attitude data source during flight operations. An overview of the reference system is presented as well as specifics discussing design concepts, functional operation, and performance capabilities. Techniques for star sighting and inertial measurement unit alignment and calibration are described, and alignment accuracy, star tracker capability, and gyro and accelerometer accuracy are discussed, with emphasis on flight test results. Test programs have confirmed that the system meets performance requirements such as being accurate to within 0.26 degree at the 400,000 foot altitude entry interface in order to execute an accurate touchdown, as well as demonstrating reusability, payload capability, and operational flexibility. Growth possibilities, such as the implementation of rendezvous target tracking, are discussed.

A time-invariant error model for a space-stable inertial navigation system

Abstract: A reduced-order, time-invariant, error model is developed for a class of spacestable systems using electrostatic gyroscopes. Its structure displays more clearly the dynamical characteristics of the system's errors than a commonly used equivalent periodic model. The order reduction results from aggregating gyroscopic errors into observable linear combinations that directly affect platform misalignment. Time-invariance of the model permits a modal analysis of navigation errors which shows the strong interplay between Schuler-loop dynamics, gyroscopic error dynamics, and observability and controllability properties of the system. The results clearly demonstrate the importance of choosing the proper coordinate frame for specifying shaping filters to model instrument error sources.

Shuttle navigation overview

Abstract: Space Shuttle onboard navigation system tasks are related to position and velocity determination, attitude determination, sensor management, sensor Redundancy Management (RM), and navigation-related functions such as transformations, timing system utilization, and user processing for displays, guidance, and flight control. It is pointed out that Shuttle navigation is different in at least two areas from previous manned space flight navigation. The differences are related to the use of multiple units to provide protection from increased risk of failure of off-the-shelf-type equipment used for more than one flight, and the need to land at a runway. Attention is given to the navigation sensor system, the Shuttle Inertial Measurement Units, the Shuttle Star Tracker, the Crew Optical Alinement Sight, the Shuttle Tacan, the Air Data Subsystem, and aspects of navigation system mechanization.

Helical automatic approaches of helicopters with microwave landing systems

Abstract: A program is under way to develop a data base for establishing navigation and guidance concepts for all-weather operation of rotorcraft. One of the objectives is to examine the feasibility of conducting simultaneous rotorcraft and conventional fixed-wing, noninterfering, landing operations in instrument meteorological conditions at airports equipped with microwave landing systems (MLSs) for fixed-wing traffic. An initial test program to investigate the feasibility of conducting automatic helical approaches was completed, using the MLS at Crows Landing near Ames. These tests were flown on board a UH-1H helicopter equipped with a digital automatic landing system. A total of 48 automatic approaches and landings were flown along a two-turn helical descent, tangent to the centerline of the MLS-equipped runway to determine helical light performance and to provide a data base for comparison with future flights for which the helical approach path will be located near the edge of the MLS coverage. In addition, 13 straight-in approaches were conducted. The performance with varying levels of state-estimation system sophistication was evaluated as part of the flight tests. The results indicate that helical approaches to MLS-equipped runways are feasible for rotorcraft and that the best position accuracy was obtained using the Kalman-filter state-estimation with inertial navigation systems sensors.

Evaluation of the Position and Azimuth Determining System's Potential for Higher Accuracy Survey

Abstract: : This paper reports on tests conducted to evaluate the accuracy potential of the U.S. Army Field Artillery's inertial survey system (Position and Azimuth Determining System AN/USQ-70). The tests were conducted by researchers at the U.S. Army Engineer Topographic Laboratories starting in the summer 1981. The test results reported include position, height and gravity anomaly. Also discussed is a post-mission least squares adjustment technique which was applied to the test results and which should have application to other inertial survey system missions. The Position and Azimuth Determining System (PADS) is a self-contained surveying system which provides fourth- and fifth- order control for U.S. Army Artillery surveys. The PADS is essentially a velocity aided inertial navigation system which has been designed to provide positional accuracy to 20 meters circular error probable (CEP) and height accuracy to 10 meters probable error (PE) over a 6-hour mission which starts at a 'known' survey control point.

Inertial navigation system for directional surveying

Abstract: A Wellbore Inertial Navigation System (WINS) was developed and tested. Developed for directional surveying of geothermal, oil, and gas wells, the system uses gyros and accelerometers to obtain survey errors of less than 10 ft (approx. 3 m) in a 10,000-ft (approx. 300-m) well. The tool, which communicates with a computer at the surface, is 4 in. (approx. 10 cm) in diameter and 20 ft (approx. 6.1 m) long. The concept and hardware is based on a system developed by Sandia for flight vehicles.

Aerial profiling of terrain system

Abstract: In 1974 the U.S. Geological Survey entered into an engineering analysis contract with Charles Stark Draper Laboratory to study the concept of executing accurate surveys of the terrain from low-flying aircraft using a laser profiler and inertial guidance technology. This analysis and later studies concluded that the desired accuracy, within 0.5 feet (15 cm) vertically and 2 feet (61 cm) horizontally, could be achieved for extended missions if positional updates are provided at 3-minute time intervals. A laser tracking instrument for ranging and measuring directions to ground reflectors was proposed to provide the update data. The project has progressed through the early experimental phases, system design and component fabrication, and the integration of components into subsystems has begun. Laboratory calibration and testing of the system will be completed in the fall of 1982 and installation in the Twin-Otter aircraft will then begin, and flight testing will follow beginning in early 1983. (Author)

Terrain-aided navigation of an unpowered tactical missile using autopilot-grade sensors

Abstract: This paper assesses the feasibility of applying a terrain-aided navigation concept, using nonlinear Kalman filtering techniques, to an unpowered tactical missile. The brief flight time and predictable missile flight path dynamics lead to the definition of a velocity-based strapdown navigation algorithm which utilizes the existing autopilot-grade sensors. The navigation states are corrected by the error estimates of the Kalman filter which uses frequent radar altimeter measurements and terrain slope information (derived from an onboard digitized map) to provide essentially continuous position updating. Covariance analysis and Monte Carlo simulation techniques are applied to predict system performance. Results are obtained which indicate that the accuracy of this weapon/guidance combination may be sufficient to defeat airfields with area munitions. HIS work was initiated in 1981 to study the application of autonomous terrain-aided navigation to the U.S. Air Force GBU-15 weapon. The purpose was to assess the feasibility of applying the Sandia Inertial Terrain-Aided Navigation (SITAN) guidance concept to the GBU-15 weapon system, as an alternative to the existing guidance concept that employs manual target acquisition and an electro-optic al seeker for terminal guidance. This combination of the GBU- 15 weapon and the SITAN concept was perceived to be a cost- effective solution to the Air Force requirements for an airfield defeat system with all-weather and day/night capabilities. GBU-15 The GBU-15 missile is currently in production for the U.S. Air Force and is an outgrowth of the original "smart bombs" which were first used in the Vietnam conflict. It is an un- powered vehicle that can be launched below 1000 ft at ranges on the order of 5 miles. It was designed as a modular concept and is composed of a 2000 Ib bomb, a control section in the rear, and a television guidance unit on the front end. The control section also includes data link hardware that allows an operator in the launch aircraft to steer the weapon after launch by viewing the video seeker output. Thus it is the role of the "man-in-the-loop" to accomplish the target acquisition function by positioning cross-hairs on the desired target. Tracking can be done either manually by the operator or by switching to the automatic track circuitry in the missile which utilizes an edge (contrast) tracking scheme. The weapon has an analog autopilot and employs either acceleration or at- titude control, depending on the mission epoch. The autopilot sensors include a directional/vertical (D/V) gyro, a roll gyro, and two body-mounted accelerometers. All of these sensors are considered to be "autopilot-grade" devices—that is, their requirements were originally specified without any need to perform a navigation function.

System concept and results of the Canadian Aerial Hydrography Pilot Project

Abstract: The Canadian program for obtaining hydrographic data by aerial methods consists of merging laser bathymeter data with photogrammetric depth data. The main deficiency of the photogrammetric approach for bathymetric measurements is that incomplete stereomodels can occur in areas where little or no land appears. This problem is overcome by using an inertial navigation system (INS) hardmounted to the aerial camera to provide the orientation parameters of position and attitude for each photograph. In order to meet the high accuracy requirement, the INS and other complementary navigation data are processed through a post‐mission track recovery software package. The photogrammetric depths are improved further by merging them with the waterline height information and the laser bathymeter depths using a least‐squares adjustment algorithm. The photogrammetric compilation, depth measurements, shoreline plots, and laser bathymeter integration is done in an analytical stereoplotter. This instrument provides a...

Missile Guidance: Interferometer Homing Using Body-Fixed Antennas

Abstract: : Six chapters comprise this document, which is a discussion of the history and technical development of homing guidance via signals from body-fixed interferometer antennas as it is used in a tactical surface-to-air missile. Chapter 1 provides an introduction and background; Chapter 2 reviews homing guidance, giving brief consideration to the guidance technique and the concept of body-motion decoupling from the interferometer signal, as well as to the attractive features and critical factors that are characteristic of interferometers; Chapter 3 deals with early developments in interfermeter guidance; Chapter 4 presents angle-measurement techniques along with their characteristic ambiguities and the methods for resolving them, describes instrumentation techniques for phase measurement by both scanning and nonscanning systems, and discusses the effects of glint noise and multiple targets; Chapter 5 describes the methods used to decouple body motion from the interferometer signal, the effects of a nonrigid airframe, and the types of measuring instruments and their tolerances; and Chapter 6 considers the use of homing guidance for current and future missiles, its compatibility with other guidance modes for a multimode missile, and its low-frequency capability and suitability for guided projectiles. This last chapter is also directed toward the modern implementation of interferometer homing using strapdown inertial instruments and digital processing.