Showing papers on "Inertial navigation system published in 1984"

The development of radar homing missiles

Abstract: Introduction S World War II, guided missiles have played an increasingly important role in warfare. Earlier papers in this series' reviewed the development of the inertial guidance systems that made possible the accurate delivery of long-range ballistic (and other) missiles for which the target is a known set of Earth coordinates. These systems are not suitable for guidance of missiles against unpredictable targets such as maneuvering aircraft, which requires an ability to sense the target location in real time and respond to rapid changes. To accomplish this, modern air defense missiles use homing guidance, in which an on-board sensor provides the target data on which the guidance is based. Because of the continually improving quality of target information as the missile closes in, homing guidance provides an accuracy that is unmatched by any other form qf missile guidance. This paper is not a comprehensive history of its subject. Rather, it is a summary of the author's first-hand experience, covering the development of continuous wave (CW) radar homing guided missiles, which were pioneered at Raytheon Company. They form an impressive subset of all homing missiles, .with nearly 100,000 airand surface-launched versions produced to date and deployed in some two dozen countries worldwide. Derivatives of these designs form the backbone of the U.S. Navy's ship-based defenses and similar designs are extensively used by the Soviet Union. In reviewing the history, technical descriptions of problems encountered and solutions developed will be given for the three key areas of sensor, navigation, and flight control.

Strapdown System Algorithms

Abstract: : This paper addresses the attitude determination, acceleration transformation, and attitude/heading output computational operations performed in modern-day strapdown inertial navigation systems. Contemporary algorithms are described for implementing these operations in real-time computers. The attitude determination and acceleration transformation algorithm discussions are based on the two-speed approach in which high frequency coning and sculling effects are calculated with simplified high speed algorithms, with results fed into lower speed higher order algorithms.

Method of determining the position and velocity of a vehicle

Abstract: Apparatus for determining the position and velocity of a vehicle over a given area as represented by stored data includes a radar terrain sensor responding to radar pulse returns and generating video signals to a terrain clearance estimator. Also input to the terrain clearance estimator are vehicle vertical position data and vertical speed data which along with the video output of the terrain sensor generates by means of a time of arrival estimator observed clearance signals which are sampled and input to a buffer. Also stored in the buffer are vehicle position and velocity signals from an inertial navigation system with the buffer data accessed by an error correction estimator. The error correction estimator responds to stored data to generate a sequence of position and velocity error correction signals each comprising three components. These error correction estimates of vehicle position and vehicle velocity are input to a data register which is accessed by the inertial navigation system to provide update information on the position and velocity of a vehicle.

Method for determining the magnitude of earth's gravity

Abstract: An improved method that directly and continuously determines the magnitudef the earth's gravity in relation to a user platform at one or more selected points on or above the earth's surface. An improved Global Positioning System (GPS) is used to carry out the method and is made up of a plurality of twenty-four (24) continuously orbiting GPS satellites that are arranged into three groups of eight satellites with each group or constellation being disposed in its respective plane of a series of three longitudinal planes. Each plane is arranged in predetermined angular and spatial relation to the earth's equatorial plane and the other planes of the series. Any GPS satellite continuously transmits a pair of encoded RF signals at predetermined L-band frequencies. By virtue of this global arrangement of the 24 satellites, the antenna field of view of a user platform is capable of receiving at any time the encoded signals of at least six satellites. A geodetic receiver on the platform together with a receiver microprocessor, a navigation microprocessor, and a microcomputer progressively and continuously process signals received from the satellites for the ultimate purpose of comparing GPS dtermined vertical acceleration (that is normal to the earth's modeled ellipsoid) with its platform-measured gravimeter acceleration (that is normal to the earth's geoid) so as to determine, with greater accuracy, the gravity at one or more selected points. By reason of the improved GPS systems carrying out the method of continuously and directly determining gravity with greater accuracy at one or more points, a given area can be readily surveyed in relation to the user platform as well as enabling corrections to inertial navigation equipment and enhancing the guidance of weaponry (missiles, etc.) during firing or launch.

Fiber Optic Gyroscopes

Abstract: Inertial guidance and navigation systems are known to be very useful for aircrafts, missiles, land vehicles, robots… For the moment, they make use of mechanical gyroscopes or gas laser gyroscopes. Now the development of low-loss optical fibers and compact and reliable semi-conductor light sources for the telecommunication industry has made possible a new approach: the fiber-optic gyroscope [l, 2, 3]. This device is only composed of low-mass solid-state components-and does not require any mechanical movement (this is still the case with laser gyros which need dithering to solve their lock-in problem about zero rotation).

Two-axis optical inertial system using a gyro rotor as a stable reference.

Abstract: The present invention provides a two-axis optical inertial reference system wherein the rotor (12) of a gyro (10) is utilized as a stable reference. A surface (19) of the rotor is made reflective. Sighting on the reference is provided through a window (18) in the gyro case, (16) to access rotor reflective surface (19) the gyro case being hard mounted to a moving surface in the coarse gimbal of the system, since the gyro rotor has a finite angle of travel with respect to the case. A stabilized inertial platform (gyro rotor (12)) is achieved without the need of intermediate servoed gimbals. The gyro torquers are used to precess the rotor's spin axis to provide a means for slewing the spin axis and, hence, the optical system's line-of-sight (60) to the desired direction of the optical system. Specific embodiments for obtaining the required reference beam are disclosed.

An algorithm for radiometric and geometric correction of digital SLAR data

Abstract: In The Netherlands an accurate SLAR system with digital data recording is used for measurements within the framework of the national microwave remote sensing research program. However, the images are disturbed by unwanted platform motions due to, e.g., turbulence at the low operating height (300–3000 m) of the SLAR system. An algorithm is developed for the geometric and radiometric correction of the radar data by means of aircraft attitude and position measurements. These measurements can be obtained from an Inertial Navigation System (INS) onboard the plane. Some additional information like the aircraft height and the measurement distance is obtained from the radar signal. The correction model is implemented in a computer program. The results clearly show an improvement of the image quality. Some specific problems that were encountered will be discussed and some results win be shown.

An Autonomous Vehicle Navigation Algorithm

Abstract: We present a simple heuristic-based navigation algorithm for autonomous vehicle con-trol. We assume sensor input in the form of a range scan of distances to closest obstacles at a variety of angles in the vehicle's field of view. The algorithm works within a 2-dimensional model of the world to solve the problem of obstacle avoidance : find a collision-free path from START to GOAL.

An Overview of Passive Optical "Gyros"

Abstract: An Overview of Passive Optical "Gyros"Shaoul EzekielResearch Laboratory of ElectronicsMassachusetts Institute of Technology, Cambridge, MA 02139AbstractA brief and simplified overview of optical gyroscopes is presented with emphasis onrecent developments in passive approaches.Why the Interest in Rotation Sensors?The measurement of rotation is of considerable interest in a number of areas. Forexample, inertial navigation systems as used in aircraft and spacecraft depend criticallyon accurate inertial rotation sensors. The allowable errors in rotation sensor performancedepend on the particular application. Typical requirements for aircraft navigation lie be-tween 0.01 and 0.001 degrees /hour. In terms of earth rotation rate QE = 15 degrees /hourthis becomes 10 -3 to l0 -4 QE. A number of other applications of rotation sensors existsuch as surveying where the accurate determination of azimuth and geodetic latitude isimportant [1]. In this case performance of 10 -6 QE or better is needed. Geophysics appli-cations include the determination of astronomical latitude, and the monitoring of polarmotion caused by wobble, rotation, precession and wandering effects [1]. A highly preciserotation sensor may be used to measure any changes in the length of the day and to detecttorsional oscillations in the earth caused by earthquakes. Finally, ultraprecise sensorsmay find applications in relativity related experiments such as the determination of thepreferred frame, dragging of inertial frames, etc.

State Estimation and Divergence Analysis

Abstract: A growing memory discrete dynamic model for performing temporal extrapolations along a predetermined path in a random field is presented. This dynamic model is used to drive a linear system that is itself driven by discrete white noise. The coupled system is used to derive a state estimation scheme that recursively processes noisy measurements of the system. In addition, using the aforementioned dynamic model as a reference (truth) model, the authors develop a covariance analysis to measure the estimation errors that occur when the dynamics along the path through the field are modeled as a Markov linear model and state estimation is performed using discrete Kalman filtering. The performance evaluation of an inertial navigation system influenced by the Earth's gravity field aboard a maneuvering ship is provided as a specific illustrative example.

Method and device for aligning inertial navigation systems

Abstract: The invention relates to a method and a device for aligning inertial navigation systems in vehicles, especially in aircraft, by means of which their stationary condition is determined by means of a mechanical device or by means of an electronic device, from a bearing detector, and said detector passes on the speed-measurement signal (which originates from the inertia system) to an adder and to a correction unit whose output signal is added to the speed-measurement signal in the adder and is passed from there as a sum signal to an integrator.

A discussion of coning errors exhibited by inertial navigation systems

Abstract: : The mechanisms by which so called 'coning errors' occur in a strapdown inertial navigation system are explained by reference to a single mathematical theorem. Typical values of coning errors are derived and ae shown to be significant for a 1 nm/h inertial navigator. Various methods of evaluating and reducing coning errors are discussed. Originator-supplied keywords include: Dither; Ring laser gyroscope; and Vibration.

Arrangement for determining angular velocity and acceleration

Abstract: The invention relates to an arrangement for determining angular velocity and acceleration by holding an inertial mass suspended in a spatial arrangement by means of position-regulating systems which serve the purposes of measurement and control. This arrangement is particularly applicable for measurements in inertial navigation. It is the object of the invention to configure a three-axis accelerometer in such a way that its operation requires a low outlay on measuring and control systems; this is achieved when the inertial mass is held suspended by six position-regulating systems on the ends of a three-dimensional, symmetrical cross, and the respectively opposite position-regulating systems have the same direction of motion and are arranged perpendicular to the corresponding axis of the three-dimensional cross.

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.

From Autopilot to Strapdown: Electrotechnology in Inertial Guidance and Control

Abstract: Electrotechnology has been a significant factor in the evolution of guidance and control (G & C) over the last half century. Ship stabilizers that used rotating wheels for brute force control were electrically driven. However, the first pilotless aircraft, developed in World War I, was controlled primarily with pneumatic servos. Inertial guidance and electronic control systems surfaced at Peenemunde around World War II. Advances in fire control servos led to development of the floated gyro and ushered in precision inertial navigators. Digital electronics replaced analog designs, so that the level of G & C sophistication increased dramatically. As digital computers became smaller and more powerful their use proliferated. The manned space program in the 60's saw substantial improvements in electronics reliability and performance. The successful first launch of the Space Shuttle, with all its complexity, is a tribute to electronics progress. It is difficult to predict what G & C advances electrotechnology will bring in the next 50 years.

Marine positioning with a GPS-aided inertial navigation system

Abstract: The accuracy requirements for precise horizontal positioning of a moving vessel in the offshore and open ocean are expected to approach the 3m to Sm level within this decade Previous simulation studies and lan d-based tests have shown that such a level of accuracy can be achieved by a combination of inertial navigation and GPS satellite positioning techniques A Kalman filter and an optimal smoother have been developed to integrate an inertial navigation system with a slow switching GPS satellite receiver for marine positioning purposes The Kalman filter and optimal smoother were tested on the Canadian east coast in November 1982 The paper outlines first the operational principle of the GPS aided inertial navigation system and the development of the Kalman filter and smoother It then presents the results and a detailed error analysis of the offshore tests

Autofocus Motion Compensation for Synthetic Aperture Radar and Its Compatibility with Strapdown Inertial Navigation Sensors on Highly Maneuverable Aircraft

Abstract: : This thesis investigated the feasibility of using state-of-the-art strapdown inertial navigation systems to motion compensate synthetic aperture radar aboard highly maneuverable aircraft. The applicable equations were first derived to obtain a comparison between inertial navigation system capabilities and synthetic aperture radar motion compensation requirements. Both turned gyro and laser gyro systems were investigated to determine the applicability for the task. The autofocus motion compensation technique was studied to determine if its range and squint angle boundaries could be improved by the use of highly accurate strap-down inertial navigation system measurements. It was determined that state-of-the-art strapdown inertial systems have the capability to motion compensate synthetic aperture radars in maneuvering aircraft and can improve the range and squint angle boundaries using the autofocus motion compensation technique. The results illustrate the ability of tactical aircraft to obtain high resolution imagery, as well as navigation and target information, while maintaining the low life-cycle cost of strapdown technology.

Self-Contained Real Time Estimation and Compensation of Vertical Deflection in a Precise Marine Inertial Navigator

Abstract: Gravitational vertical deflections have long been a major error source in a precise inertial navigation system (INS). By utilizing the vertical acceleration outputs of a precise INS as a gravimeter the medium and high frequency components of gravity deflections can be estimated as the vehicle maneuvers. By combining these estimates with stored undulation measurements obtained from satellite altimetery data low frequency gravity information can also be estimated. The major portion of position and velocity error in a precise marine INS caused by gravity deflection can thus be compensated for in a self-contained real time manner. This paper presents an algorithm for utilizing the real time spatial measurements of anomaly as obtained from using the vertical channel of a precise marine INS with the spatial undulation measurements that have been previously measured and recorded for estimating gravity deflection. This algorithm provides a marginally optimal method of handling a large array of measurements to utilize the most significant ones. Estimates of gravity deflection are applied in real time to improve navigation velocity and position.

Flight test configuration for verifying inertial sensor redundancy management techniques

Abstract: The Redundant Strapdown Inertial Measurement Unit presently tested in flight configuration consists of a semioctahedral array of four dynamically tuned, two-degree-of-freedom (TDOF) gyros and four TDOF accelerometers which can provide dual, fail-operational performance for integrated avionics systems. Attention is given to the multilevel algorithm used for the detection and isolation of three ranges of sensor failure in an integrated avionics context. A technique for the generation of accelerometer and gyro error thresholds which is sensitive to dynamic sensor errors and separation effects is presented, together with simulation results. Emphasis is placed on the ensuring of highly reliable data for flight control/navigation functions, while minimizing false or missed alarms.

A statistical analysis of gravity-induced errors in airborne inertial navigation

Abstract: This paper describes a simple yet powerful statistical technique for calculating Inertial Navigation System (INS) errors due to errors in the Navigation Gravity Model (NGM). Position and velocity e rror variances are obtained by multiplying the Power Spectral Density (PSD) of horizontal gravity disturbance error by the timedependent frequency response function of the INS and integrating over f requency. Two-dimensional disturbance error spectra a re projected onto the flight path to obtain t he along-track and crosstrack PSDs. These PSDs have dramatically different shapes with t he cross-track component having much greater variance at t he low frequencies (especially when a detailed NGM is used). The response of a lightly damped INS is sharply peaked at the Schuler f requency so that at aircraft speeds nearly a1 1 the error is initially induced in the cross-track channel and only enters the along-track channel through Coriolis coupling. The results obtained f rom this simple analytical method are in excellent agreement with more compl icated error analyses based on

Application of Multifunction Strapdown Inertial System

Abstract: : Reliability, redundancy, and survivability are key issues as integrated requirements for flight control, fire control, propulsion control and navigation are developed. These integrated systems require dependable sources of inertial measurement data. Current inertial systems, however, are expensive to acquire and maintain, dedicated to specific systems, and are not designed to meet integrated reliability, redundancy, and survivability, requirements. The Multifunction Strapdown Inertial System concept uses a minimum number of inertial sensors in a survivable configuration to provide inertial data for flight control, navigation, weapon delivery, cockpit displays, and sensor stabilization. Because of advantages in survivability, life cycle cost, maintainability and performance, the Multifunction Flight Control Reference System (MFCRS) program was initiated to verify, through flight test, on a McDonnel Douglas F-15 Eagle the key issues of redundancy management and flight control. A redundancy management system based on parity equations was designed. The sensors were arranged in two skewed and dispersed clusters. (Author)

Fault-tolerant system considerations for a redundant strapdown inertial measurement unit

Abstract: The development and evaluation of a fault-tolerant system for the Redundant Strapdown Inertial Measurement Unit (RSDIMU) being developed and evaluated by the NASA Langley Research Center was continued. The RSDIMU consists of four two-degree-of-freedom gyros and accelerometers mounted on the faces of a semi-octahedron which can be separated into two halves for damage protection. Compensated and uncompensated fault-tolerant system failure decision algorithms were compared. An algorithm to compensate for sensor noise effects in the fault-tolerant system thresholds was evaluated via simulation. The effects of sensor location and magnitude of the vehicle structural modes on system performance were assessed. A threshold generation algorithm, which incorporates noise compensation and filtered parity equation residuals for structural mode compensation, was evaluated. The effects of the fault-tolerant system on navigational accuracy were also considered. A sensor error parametric study was performed in an attempt to improve the soft failure detection capability without obtaining false alarms. Also examined was an FDI system strategy based on the pairwise comparison of sensor measurements. This strategy has the specific advantage of, in many instances, successfully detecting and isolating up to two simultaneously occurring failures.

The DREO (Defence Research Establishment Ottawa) Inertial Navigation Laboratory: Development and Test Capabilities,

Abstract: : The DREO Inertial Navigation Laboratory was developed between 1977 and 1981 as the only complete gyroscope, accelerometer and inertial system test laboratory for the evaluation of strapdown components and systems in Canada. With the aid of a consultant, the laboratory was designed for maximum flexibility; virtually any type of gyroscope can be excited and tested with existing test equipment. The purpose of such a laboratory is twofold; primarily it provides a test facility for the evaluation of manufacturer's navigation components before procurement of systems but as well it is a flexible, independent facility for experimentation, research and development. More specifically, work within the laboratory has centered upon investigation and characterization of low cost strapdown inertial navigation components ans systems. Strapdown technology holds the promise of low cost, long lifetime and ease of maintenance with the mechanical complexity of the traditional gimballed systems being replaced by software computation. Testing of strapdown gyroscopes is quite different from that of gyroscopes employed on gimballed platforms; a strapdown gyroscope must operate over the entire dynamic range of the vehicle within which it is mounted including not only the possibility of high angular rates but alos severe vibration and shock. This report details the development, equipment types and specifications, data acquisition capabilities and tests that can be performed in the DREO Inertial Navigation Laboratory. Additional keywords: Canada; Specifications.

An Auxiliary Navigation System for an Autonomous Underwater Vehicle

Abstract: It is desirable to have an auxiliary navigation system on-board an autonomous underwater vehicle to increase the reliability of its navigation when it works within an underwater structure. An inertial navigation system has been analyzed for this purpose. It shows an unacceptable positioning error due to the low accuracy of a practical stable platform. A simple gyrocompass with an appropriate algorithm has been proposed as an auxiliary navigation system. A flow chart of the proposed algorithm is given in this paper.

Hybrid navigation apparatus

Abstract: PURPOSE:To combine navigation devices, which can determine a two-dimensional position on a horizontal plane and an inertial navigation device automatically, by measuring a relative range and a bearing with respect to a ground station. CONSTITUTION:A station range and station bearing signal S1 to a station, which is selected by a TACAN device, and an air altitude signal S2 from an air data device 3 are converted into a two-dimensional signal S5 in a horizontal plane by a position computing part 5 based on station position data S4 of a memory 6. A position-error estimating part 7 estimates the position error included in the signal S5, based on the signal S1, i.e., relative positional relationship between the present position of own aircraft and a ground TACAN station, and an estimated position error signal S6 of the TACAN device is outputted. A nearest point detecting part 10 monitors whether the aircraft has passed the nearest point to the ground TACAN station or not based on the signal S5, which represents the present position of the aircraft and the station position data S4 and outputs a combination releasing pulse signal S9 when the aircraft passes the nearest point.