Showing papers on "Inertial navigation system published in 1975"

Detecting Instrument Malfunctions in Control Systems

Abstract: A scheme for automatically detecting incipient failures in the feedback sensors (or instruments) of control systems is described. The feasibility of the scheme is investigated by applying it to a simplified version (fourth order) of the flight control system for a hydrofoil boat. A single set of inertial instruments is used to provide the feedback signals; the redundancy which is normally obtained by multiple instrument sets is obtained here, artificially, by a subsystem of multiple Luenberger observers and logic circuits. Tests indicate that scale factor errors, errors due to threshold effects, and bias errors in the instruments are detected as they occur. The tests also indicate further analytical work which should be done to explore the limitations of the basic scheme.

A Comparison of Two Approaches to Pure-Inertial and Doppler-Inertial Error Analysis

Abstract: Error equations for inertial navigation systems are derived using a perturbation (or true frame) approach and a psi angle (or computer frame) approach in a manner which shows the underlying as sumptions and allows direct comparison of the two methods. The comparison is general since the analysis is not associated with any particular mechanization. Different definitions of velocity errors and misalignment angles result from the two methods of error analysis, and, consequently, have significance in testing and analysis of pure-inertial systems, Doppler-inertial systems, and inertially aided weapon delivery systems. Examples and numerical results are presented for a local-level north-pointing mechanization.

Simplified strapped down inertial navigation utilizing bang-bang gyro torquing

Abstract: A self-contained, strapped down guidance system combining all axes, all attitude navigation having two wide angle, two-degree-of-freedom gyros which provide attitude angle and angular rate signals along three axes. Accelerometer means provide signals representative of the acceleration along three orthogonally displaced independent axes. A first transformation matrix connected to the attitude angle output of the gyros and to the accelerometers transforms the gyro and accelerometer signals from body coordinates to gyro coordinates. A second transformation matrix connected to the output of the gyros, transforms the gyro coordinates into navigation coordinates. In order to perform navigational computations, computing means compute a transformation from gyro momentum vector (referenced to coordinate frame) to a navigational coordinate frame such as a locally vertical frame wherein the Z axis is always along the local vertical direction.

An Experimentally Validated 3-D Inertial Tracking Package for Application in Biodynamic Research

Abstract: A six-accelerometer inertial tracking package currently in intensive use in measuring living human and human surrogate response to impact acceleration is presented and discussed. The discussion includes an enumeration of the various requirements imposed upon the package as well as its design and fabrication. The on-site calibration facility is described, including a discussion of the procedures for routine calibration of the packages. Accounts of the data acquisition link from the packages through the sled borne amplifiers to the hybrid computer are also included. Particular attention is devoted to the theoretical aspects of this system. A statement of errors is developed and compared to the various precision parameters of this system and to a general estimation of the dynamic response envelope demonstrating the overall feasibility of this approach.

Data Compression in Recursive Estimation with Applications to Navigation Systems

Abstract: The goal of data compression or preprocessing is to reduce computational requirements in a Kalman filter while retaining adequate estimation accuracy. A technique which averages batches of data is considered here. Guidelines are given for averaging, such as, how often to sample the data, when to average, and how many data points to average. The averaging technique is applied to aircraft navigation using two DMEs and either air data or inertial data. The results demonstrate that significant computation time reductions are possible with some covariance degradation. VOR/DME flight data of aircraft landing approaches were used to verify the analysis and show agreement with the analytical predictions.

Doppler Radar Error Equations for Damped Inertial Navigation System Analysis

Abstract: The use of Doppler radar measurements to provide velocity damping for an aircraft inertial navigation system is considered. Three different Doppler antenna configurations are examined: two-axis stabilized, azimuth stabilized, and data stabilized antennas. A general reference velocity error equation is presented and appropriately evaluated for each of the Doppler configurations. Specific elements of the error equations are examined and physically interpreted for both local-level and space-stable inertial systems. Detailed examination of the interaction of Doppler radar and inertial navigation velocity error mechanisms is provided.

Apollo experience report guidance and control systems: Lunar module abort guidance system

Abstract: The history of a unique development program that produced an operational fixed guidance system of inertial quality is presented. Each phase of development, beginning with requirement definition and concluding with qualification and testing, is addressed, and developmental problems are emphasized. Software generation and mission operations are described, and specifications for the inertial reference unit are included, as are flight performance results. Significant program observations are noted.

Free-Inertial and Damped-Inertial Navigation Mechanization and Error Equations

Abstract: : The equations that describe both the navigation mechanization and the propagation of errors in an unaided inertial system are detailed. Extensions of these equations which apply to continuous speed and altitude damping are also given. A general vector-matrix notation is employed, thereby eliminating the need to specify a particular navigation mechanization before setting down the error equations. Specific application of the general equations to the local- level, wander-azimuth mechanization is outlined. The detailed form of the error equations is given for both the free-inertial case and various choices of continuous.

Strapdown cost trend study and forecast

Abstract: The potential cost advantages offered by advanced strapdown inertial technology in future commercial short-haul aircraft are summarized. The initial procurement cost and six year cost-of-ownership, which includes spares and direct maintenance cost were calculated for kinematic and inertial navigation systems such that traditional and strapdown mechanization costs could be compared. Cost results for the inertial navigation systems showed that initial costs and the cost of ownership for traditional triple redundant gimbaled inertial navigators are three times the cost of the equivalent skewed redundant strapdown inertial navigator. The net cost advantage for the strapdown kinematic system is directly attributable to the reduction in sensor count for strapdown. The strapdown kinematic system has the added advantage of providing a fail-operational inertial navigation capability for no additional cost due to the use of inertial grade sensors and attitude reference computers.

Inertial navigation performance improvement using gravity gradient matching techniques

Abstract: Theme R there has been considerable interest in the possibility of correcting high performance inertial navigation systems for gravitational anomaly induced errors using gravity gradient measurements aboard the moving vehicle. A combined gravity gradiometer-inertial navigation system integrated for correction of the gravity anomaly will also measure and hence can be used to map the gravitational anomaly field on a real time basis. The primary purpose of this paper is to evaluate the potential of obtaining relative position updates with such a system by cross-correlating the measured to previously mapped gravity gradients over a known location. Both gravity gradient and gravity anomaly map matching have been analyzed to compare their relative merit. To restrict the scope of the problem, the analysis has been conducted with one element of the gravity gradient tensor in a one-dimensional cross correlation process. The accuracy of relative position updates are presented for various vehicle speeds and for a range of geodetic instrumentation performance levels.

Platform Alignment Using a Strapdown Stellar Sensor

Abstract: This paper examines the use of a body-mounted stellar-sighting device to align an aerospace vehicle's gimballed inertial measurement unit. The fundamental observability of not only platform misalignments but also timeinvariant sensor-mounting errors is demonstrated. The performance of an inflight estimation algorithm is shown to be a function of several environmental and navigation hardware parameters as well as the characteristics of the sighting device itself. Parametric case studies are presented for a sample system.

Design of a digital self-alignment controller for a ship's inertial navigation system at sea

Abstract: Mathematical models are developed for the misalignment equations of a ship's inertial navigation system (s.i.n.s.) following restart after a complete shutdown at sea. The ships manoeuvres are modelled as stochastic processes and the misalignment is presented as a linearised stochastic process, which can be controlled by the gyro torqueing currents. The misalignment is observed by accelerometers, assuming base motion isolation, augmented by the `ships log' (a measure of velocity). The alignment is treatedas a discrete stochastic linear regulator problem, using a Kalman-Bucy filter. Simulation results show that good alignment can be achieved in about an hour, but a time-varying estimator must be incorporated.

Recent advances in strapdown inertial navigation

Abstract: The computational requirements and basic features of strapdown gyroscopes for inertial navigation are discussed. Strapdown navigators currently require 20 to 50% of the available time of a minicomputer with a capability of several hundred thousand operations per second; memory requirements are 2000 to 3000 16-bit words. A system in which these computational demands are met by three limited capability microcomputers is described. A technique using dedicated microprocessors in the place of analog electronics in the gyroscope control loops is discussed, and attention is given to applications of microprocessor technology in redundant strapdown navigation systems and associated flight control systems.

Developmental Test of the Honeywell Laser Inertial Navigation System (LINS)

Abstract: : This technical report documents the results of flight test of the Honeywell lLaser Inertial Navigational System (LINS), an engineering model of a ring laser gyro strapdown inertial navigation system The purpose of the testing was to demonstrate strapdown laser inertial navigation system advanced technology and to evaluate the LINS as a potential candidate system to meet future, moderate accuracy, medium cost, inertial navigator needs The testing was considered developmental, rather than verification, within the meaning of applicable DOD/DDR and E directives

Advances in Inertial Navigation: Sensor Technology

Abstract: The purpose of this paper is to look at the nature of the advances being made in inertial navigation and in navigation displays. In avionics as a whole the advance from one generation of equipment to another can take different forms; sometimes, notably in flight control and instrumentation, the potential of new technologies is exploited almost immediately to provide more advanced operational facilities and systems become more complex. Alternatively, as in the application of solid state electronics to produce equipment for general aviation, the technology is exploited to reduce weight, volume and costs. Inertial navigation exhibits both trends but to a comparatively small degree; the basic system requirement is simple to define and has changed very little, one of the reasons being the particularly demanding nature of the technology and the very long development time scales involved.

Use of single star sightings in boost navigation

Abstract: Information obtained from a single inflight star sighting is used to calibrate a boost vehicle's IMU errors. Several error-inducing parameters, including initial alignment, accelerometers, and gyros are included in the estimation state vector. Although the problem studied is shown to be generally unobservable, suitable preflight alignment techniques can be used to induce observability. The resultant induced observability arises from correlations between initial alignment errors and platform gyros or accelerometer s used for initially aligning the platform. When the platform's initial misalignment is directly observable, the presence of correlations between the initial misalignment and formerly unobservable error sources permits estimation of the latter. Additional results and a sample problem demonstrate the effect of variations in initial conditions, dynamic effects, and observation noise as a function of relevant design parameters.

Space Tug laser gyro IMU

Abstract: A redundant inertial measuring unit (IMU) incorporating six strapdown laser gyros and six accelerometers, arranged so that sensitive axes are normal to the faces of a dodecahedron, provides enhanced reliability with reduced hardware weight. Software monitoring of sensor outputs senses failure of sensors and the system is designed for triple redundancy, with built-in test equipment. Attention is centered on redundancy and fail-safe features, and on the closed-path ring laser gyro arrangement.

Alternative Approaches to Integrated Airborne OMEGA/Inertial Navigation

Abstract: Integrated omega/inertial navigation systems appear attractive in airborne applications since the excellent short-term accuracy of an inertial navigator is well-complemented by the intermittent availability of bounded, moderately accurate OMEGA position fixes. There are a number of different approaches which can be taken to accomplish the desired system integration; three such approaches are considered. The first involves a straightforward output reset, the second is essentially a Kalman-based variant of rate-aiding and the third involves conventional optimal integration. These schemes are evaluated using models for various navigation system errors to yield predictions of system position and velocity error behavior. Additionally, the schemes are compared on the basis of operational factors such as ease of implementation and computer utilization.

Inertially-Aided Dynamic Positioning

Abstract: Integration of a commercial inertial navigation unit into a dynamic positioning control loop for offshore drilling rigs will provide improve operation and self-contained backup in the event of signal loss from the primary acoustic or taut wire systems. Tests have demonstrated an average position error buildup of less than two feet per minute for up to one hour of pure inertial operation.

Return-to-launch-site trajectory shaping

Abstract: The results are presented of a study to show the effect on flyback trajectories of constant inertial attitude during the fuel dissipation phase of a return-to-launch-site abort. It is shown that the value of the constant inertial attitude can be chosen to shape the flyback trajectory.

H-modulation for long endurance marine inertial navigation

Abstract: Current versions of sins (Ships Inertial Navigation System) are capable of providing accurate navigational data over periods of several days without the need for intervening position fixes. It is desirable to provide a similar accuracy performance level for periods of several weeks. A primary factor limiting such an extension of present capability is gyro drift, especially nonstationary (ramp-like) random components in the Z (vertical input axis) gyro. Tests have demonstrated that a gyro drift monitoring technique known as H-modulation (or wheel speed modulation) can be used to bound such components of system gyro drift to levels compatible with system accuracy goals. The key to successful H-modulation is to minimize gyro torque disturbance variations that may be induced by the required changes in wheel speed. This paper describes the H-modulation technique, the design of the associated equipment, and some test results and system accuracy simulations. System implementation and data processing configurations are also discussed. Applications of H-modulation other than in SINS are indicated. It is concluded that H-modulation is a cost effective approach for providing significant extensions of SINS performance.

Position accuracy of aircraft area navigation systems and the effect of system parameters

Abstract: The steady-state solution to the stochastic differential equation describing the error covariance matrix for a simplified area navigation system has been obtained. The solution shows that nominal error deviations of less than 1.0 nmi are feasible for a DME system. The manner in which estimates are affected by range, air data system accuracy, measurement time interval, and gust deviations, and their impacts on the area navigation system are discussed.