Showing papers on "Inertial navigation system published in 1981"

Automatic control system for directional control of an aircraft during landing rollout

Abstract: A control system for maintaining an aircraft within the lateral boundaries of a runway during landing rollout under conditions of combined crosswind and low runway friction is disclosed. An automatic mode of operation is provided wherein the system utilizes an input signal representative of the heading of the runway being utilized and signals provided by (or derivable from ) an inertial navigation system to exercise coordinated control of the aircraft rudder, steering and differential braking system. In a semiautomatic mode of operation, signals supplied by the inertial navigation system (or its equipment) are utilized in conjunction with a continuous command signal that is provided by the pilot to indicate the desired aircraft trajectory. An optional provision is included for limiting the aircraft ground velocity slip angle to a range wherein an increase in ground velocity slip angle results in increased lateral corrective force on the aircraft. An additional optional provision modifies operation of the brake-antiskid system employed by the aircraft so as to reduce braking pressure by an amount that substantially optimizes lateral corrective force on the aircraft.

Training evaluation process

Abstract: An air training evaluation process which corrects the position and velocity sensed by an aircraft's inertial navigation system (INS) to obtain more accurate data on the aircraft's position during an engagement. In carrying out the process the aircraft's on-board INS system is employed to obtain pre-flight data on position and velocity, data on position and velocity during the engagement, and post-flight data on position and velocity. The pre-flight data on position and velocity and the post-flight data on position and velocity are compared with independently determined data on the pre-flight position and velocity of the aircraft and with independently determined data on the post-flight position and velocity of the aircraft respectively to obtain pre-flight error functions and post-flight error functions on position and velocity. These functions and the known time variant drift characteristics of position and velocity of the INS are employed to derive position and velocity correction functions during the time of the engagement. The position and velocity correction functions are employed to correct the INS data on position and velocity during the engagement. The corrected data then are employed to display post-flight, a more accurate position of the aircraft during the engagement relative to background portrayals of features or terrain on the earth. During an engagement of two or more aircraft, aircraft-to-aircraft or aircraft-to-ground corrections may be made to the corrected INS data post-flight for further enhancement of accuracy of the INS data.

Origins of inertial navigation

Abstract: Introduction A VIGNETTE* of the stages of development of inertial navigation at the M.I.T. Instrumentation Laboratory has been provided by the author. An earlier work provides a tutorial reference on the basic principles of the instruments and systems that were developed. Because this technology grew largely from classified programs, publication of the description of the technology for specific systems has often lagged by a decade or more, and sometimes has lacked coverage altogether. Also because of the author's responsibility for these classified programs, he was often constrained from publishing until after someone less intimately involved had already disclosed information on the programs of inertial navigation. Even at this late date, a description of the Mark 14 "Draper Sight" has not appeared in the open literature. It is the purpose of this treatise to describe some of the major systems that contributed to the evolution of inertial navigation, and to provide a record of the performance of some of these historically significant programs. An underlying theme is the continuity of gyroscopic sensor technology from the fire control systems of the Mark 14 vintage to the first successful inertial navigators. It is shown how the single degree of freedom gyroscopic element was adapted to perform simultaneously both the sensing and computation requirements for solving the fire control problem associated with close-in attacking aircraft. Refinements made to this gyroscopic element, including precise control of torques applied to the output gimbal, and eventual flotation led to the sensor technology that was eventually adapted to solving the inertial navigation problem.

Superconducting tensor gravity gradiometer for satellite geodesy and inertial navigation

Abstract: A sensitive gravity gradiometer can provide much needed gravity data of the earth and improve the accuracy of inertial navigation. Superconductivity and other properties of materials at low temperatures can be used to obtain a sensitive, low-drift gravity gradiometer; by differencing the outputs of accelerometer pairs using superconducting circuits, it is possible to construct a tensor gravity gradiometer which measures all the in-line and cross components of the tensor simultaneously. Additional superconducting circuits can be provided to determine the linear and angular acceleration vectors. A tensor gravity gradiometer with these features is being developed for satellite geodesy. The device constitutes a complete package of inertial navigation instruments with angular and linear acceleration readouts as well as gravity signals.

Modeling and evaluating an empirical ins difference monitoring procedure used to sequence ssbn navaid fixes

Abstract: In the past, U.S. Polaris (A-3) and Poseidon (C-3) SSBNs (ballistic missile equipped, nuclear powered submarines) took relatively frequent navigation fixes at specified but clsssified periodic rates to compensate for the degradations of gyro drift-rate. However, a randomization of the fix taking was called for to preclude enemy deciphering of the frequency of fix-taking as the enemy attempts to enhance its surveillance of U.S. SSBNs. Since warm-standby navigation configurations (such as two complete Ships Inertial Navigation Systems, SINS) are usually utilized onboard U.S. SSBNs anyway to reap the benefit of high reliability/availability through online modular repair, the so-called Difference Monitoring procedure consisting of a comparison of the outputs of both these available INSs was instituted in 1976 to randomize the fix taking for C-3 SSBNs. One contribution of this paper is to use existing results of Helstrom from level-crossing theory for the output of nonlinear operations (e.g., the RSSing of latitude and longitude error to obtain radial position error) to provide an analytically tractable theoretical model for the previous empirical procedure of Difference Monitoring. Using the parameters of RMS level and correlation-time of the underlying INS, this analytic model can be exploited to set the constant decision threshold to achieve a specified average interval between position fixes. A second contribution of this paper is to present an expression for the related variance. A comparison between actual SSBN patrol statistics and analytically predicted results for alternative threshold settings is included; however, time and navigation accuracy scales are concealed to prevent divulgence of national security information. Measures of SSBN detectability to enemy surveillance should apparently also be updated in a manner herein suggested to no longer assume SSBN fix taking at a periodic rate. Adoption of this suggestion enables use of an absolute evaluation technique (based on Pareto-optimality) already developed and utilized as described herein as a third contribution for gauging the “goodness” of either randomized or deterministic SSBN fix strategies over and specified time epoch. Two Electrostaticially Supported Gyro Navigators (ESGNs) have been postulated as a candidate configuration for D-5 Trident II SSBNs, where Difference Monitoring will again be as appropriate as in C-3 Poseidon SSBNs.

Control, navigation, and guidance

Abstract: Self-contained systems providing control and navigation for vehicles of all kinds use gyroscopic elements to maintain reference directions with respect to inertial space. Sensors for resultant gravity field and inertial reaction forces along input axes determine the vertical and also linear velocities with respect to inertial space. These components divided by an equivalent Earth radius transfer the motion to Earth coordinates in which integration gives location. Corrections for Earth's rotation projected in and perpendicular to the horizontal plane are made as computed cosine and sine projections of Earth's angular velocity. Current systems result with the order of fractional miles per hour performance.

Gravity Induced Position Errors in Airborne Inertial Navigation

Abstract: : The report investigates the feasibility of improving airborne inertial navigation by use of gravity field approximations which are more accurate than the normal model presently applied. The effect of the anomalous gravity field on positioning is investigated by using a simplified dynamical error model and by deriving analytical expressions for the steady state error via the state space approach. In this approach, changes in the anomalous gravity field are cast into the form of first-order differential equations which are related to a position dependent covariance representation of the gravity field by way of the vehicle velocity. Different possibilities for a state space model of the anomalous field are discussed. The procedure chosen combines the consistency of the T.scherning-Rapp model with the advantages of a formulation in terms of Gauss-Markov processes by making use of the essential parameters of a covariance function proposed by Moritz. The expressions for the gravity induced position errors resulting from this approach are easy to compute for a wide variety of cases. The assumptions made to derive them are in general justifiable. Based on the available gravity field information a number of approximation models are proposed and expressed in terms of equivalent spherical harmonic expansions. Results show that the use of presently available global models would reduce the gravity induced position errors from Sigma = 150 m. Improved global models expected in the near future as for instance those from the GRAVSAT mission, would bring errors below Sigma = 50 m.

A mulitplexed analog to digital converter having a feedback stabilised ramp

Abstract: A multiplexed analog-to-digital converter is provided for use in an inertial navigation system comprising a multiplexer, a buffer, a feedback stabilized ramp generator and a comparator controlling a gated counter whose digital output is representative of the analog input signal.

Failure detection and isolation analysis of a redundant strapdown inertial measurement unit

Abstract: The objective of this study was to define and develop techniques for failure detection and isolation (FDI) algorithms for a dual fail/operational redundant strapdown inertial navigation system are defined and developed. The FDI techniques chosen include provisions for hard and soft failure detection in the context of flight control and navigation. Analyses were done to determine error detection and switching levels for the inertial navigation system, which is intended for a conventional takeoff or landing (CTOL) operating environment. In addition, investigations of false alarms and missed alarms were included for the FDI techniques developed, along with the analyses of filters to be used in conjunction with FDI processing. Two specific FDI algorithms were compared: the generalized likelihood test and the edge vector test. A deterministic digital computer simulation was used to compare and evaluate the algorithms and FDI systems.

Superconducting tensor gravity gradiometer

Abstract: A sensitive gravity gradiometer can provide much needed gravity data of the earth and improve the accuracy of inertial navigation. A complete determination of all five independent components of the gravity gradient tensor is possible in principle by rotating a single in-line component gradiometer. In order to avoid dynamically induced noise sources arising from rotation, a hard-mounted assembly of component gradiometers may nevertheless be advantageous in an ultra-sensitive device. Superconductivity and other properties of materials at low temperatures can be used to obtain a sensitive, low-drift, gravity gradiometer. By differencing the outputs of accelerometer pairs using superconducting circuits, it is possible to construct a non-rotating tensor gravity gradiometer. Additional superconducting circuits can be provided to determine the linear and angular acceleration vectors. A three-axis in-line gravity gradiometer (a “vector” gradiometer) is being developed for satellite geodesy. A two-dimensional spring concept for a three-axis cross component gradiometer is discussed. The superconducting tensor gravity gradiometer constitutes a complete package of inertial navigation instruments with angular and linear acceleration readouts as well as gravity signals. Accuracy of inertial navigation could be improved by use of such a gradiometeraided inertial navigator.

Evaluation of the Navigation performance of Shipboa VTOL Landing Guidance Systems

Abstract: The objective of this study was to explore the performance of a VTOL aircraft landing approach navigation system that receives data (1) from either a microwave scanning beam (MSB) or a radar-transponder (R-T) landing guidance system, and (2) information data-linked from an aviation facility ship. State-of-the-art low-cost-aided inertial techniques and variable gain filters were used in the assumed navigation system. Compensation for ship motion was accomplished by a landing pad deviation vector concept that is a measure of the landing pad's deviation from its calm sea location. The results show that the landing guidance concepts were successful in meeting all of the current Navy navigation error specifications, provided that vector magnitude of the allowable error, rather than the error in each axis, is a permissible interpretation of acceptable performance. The success of these concepts, however, is strongly dependent on the distance measuring equipment bias. In addition, the 'best possible' closed-loop tracking performance achievable with the assumed point-mass VTOL aircraft guidance concept is demonstrated.

Sensitive fiber‐optic gyroscopes

Abstract: Special relativity teaches us that no contrivance, mechanical or electromagnetic, confined in a closed vehicle, can detect the uniform rectilinear motion of that vehicle. But anyone who suffers from motion sickness can attest to the fact that nonuniform motion (acceleration or rotation) is a different story. Thus it is possible to direct ships, aircraft or missiles by inertial navigation systems, once an initial direction is established, without reference to magnetic compasses or radio beams.

Gravity Gradiometer Survey and Real Time Techniques for Improving Inertial Navigation System Accuracy

Abstract: : As inertial navigation instrumentation becomes more advanced, erros associated with imprecise knowledge of the true gravity vector become significant. With the development of the moving base gravity gradiometer, a means for detecting the true gravity vector is available. This research explores both real time and a priori schemes for using gradiometer information to reduce the position and velocity error associated with an inertial navigation system. In the real time application, information derived from the gradiometer is filtered to produce estimates of position and velocity error. The problem is to derive accurate filters in the presence of an inherently transcendental gravity field. Conventional Kalman filters are cumbersome to apply in this instance. However, the sensitivity of inertial navigation systems at Schuler frequency makes it possible to neglect errors outside of a narrow band of frequencies centered at Schuler frequency. This approximation leads to low order filters which may be applied with surprising accuracy. For the survey application, the gradiometer is used to establish a reference gravity model to be used in open loop inertial navigation system operation. By determining the root mean squared values of the resulting position and velocity errors. It is possible to evaluate the effectiveness of the survey scheme and to compare the survey application with the real time gradiometer application. Analytic and numeric covariance methods are used again to do these analyses.

GEO-SPIN/IPS-2 Improvements for Precision Gravity Measurement

Abstract: : Improved accuracies must be maintained with the system operated along any trajectory in a ground vehicle or helicopter The most important performance parameter is deflection of the vertical This paper reports the results of the gravity improvement study It addresses hardware, software and operational procedure aspects Supporting data are provided for the assessment of current performance On-line and off-line data reduction and analysis are considered The rather interesting application of both Kalman filtering (using data up to a current point) and Kalman smoothing (total traverse data processing) is covered and its effectiveness evaluated with supporting computer simulations for the gravity measurement problem Use of both ZUPT and control point data is considered in the smoothing process By-products of gravity measurement accuracy improvement are better positioning performance and operational flexibility These topics are also touched upon in this paper Hence, it should be of widespread interest to the surveying and geodesy communities

Advances in Inertial Navigation Systems and Components

Abstract: : Contents: Tuned Gyro Cost Reduction through a Novel Hinge Design; Optical Rotation Rate Sensors; A Nuclear Magnetic Resonance Gyro using Noble Gas Isotopes; Hamilton Standard Superjet TM Solid State Fluidic Rate Sensor; The Cactus Accelerometer; Inertial System Alignment and Calibration on a Moving Base; and Identification and Determination of Strapdown Error-Parameters by Laboratory Testing.

Wheel-speed induced errors in the use of dry tuned gyros

Abstract: It is known that, for a gimbaled inertial measurement unit employing two dry-tuned gyros, a dual gyro wheel supply gives a better performance than a single gyro wheel supply. The effectiveness of the dual gyro wheel supply is explained in this paper by demonstrating the effects of certain vibrations on gyros. It will be shown that a dry-tuned gyro is susceptible to vibrations at frequencies which are either equal to or twice that of the gyro spin frequency. By using two power supplies of slightly different frequencies, external vibrations at these frequencies are avoided. It is recommended that gyro sensitivities with respect to external vibrations at these special frequencies be included in the performance specification of a dry-tuned gyro.

Marine navigation with the LaCoste and Romberg inertial platform

Abstract: The LaCoste and Romberg gravimeter platform constitutes a complete inertial navigation system and can provide navigational information for marine gravity surveys. Potential applications include: (1) Inertial input to an integrated navigation system using Kalman filtering techniques to utilize all available navigation data; (2) provision of a relatively low cost back‐up system to provide navigation continuity in the event of a failure in the primary navigation; and (3) primary navigation in regions not served by long‐range systems such as Loran C and beyond the range of short‐range systems.