Showing papers on "Inertial navigation system published in 1976"

Tetrahedral redundant inertial reference unit

Abstract: A redundant inertial reference system is provided with four gyroscope units, with the spin axes of the gyroscopes in the units being oriented, respectively, perpendicular to the four faces of an equilateral tetrahedron. Incidentally, a tetrahedron is a four sided body, and an equilateral tetrahedron is a four sided body having equilateral triangles for the four sides. With the four gyroscopes mounted perpendicular to the four sides of an equilateral tetrahedron, each of the gyroscopes is located symmetrically with respect to the others, with an angle of approximately 109.4 degrees between the spin axes of the gyroscopes. The system is particularly applicable to strapdown type inertial guidance systems and can provide three dimensional orientation information even if two of the gyros fail. The system uses four gyro units, a minimum number which can accomplish a foregoing function, with the four gyro units arranged substantially symmetrically with respect to one another.

Navigation between the planets

Abstract: Recent advances in spacecraft tracking, chronometry, ephemerides, and orbit and trajectory determinations are reviewed. Improvements in timekeeping are reviewed, as well as precision distance and range measurements; orbit determinations, trajectory-correction maneuvers, flight path optimization, and information provided by rotation of the tracking station with the earth's surface. Doppler and tropospheric wave propagation effects are dealt with. Nongravitational perturbations (solar radiation pressure, release of gases from the spacecraft, stochastic unmodeled accelerations and sequential estimation to cope with them), the effect of the target planet's gravitational field upon close approach, and navigation problems in the outer reaches of the solar system (TV data telemetered back for inertial navigation) are covered. By-products of the research include: refined data on the mass of planets, on planetary mass distributions, planet configurations, on physical properties of the atmospheres and ionospheres of planets, and opportunities for refined tests of gravitation and relativity theories and models.

Error Analysis of Two New Gradiometer-Aided Inertial Navigation Systems

Abstract: Two Kalman filtering integration techniques are presented for using gradiometer measurements to compensate an inertial navigation system for gravity disturbances. Both approaches use knowledge of the reference ellipsoid gravity field in addition to gradiometer data and lead to bounded residual gravity-induced navigation errors. Although the two compensation techniques are similar, one appears to offer significant theoretical and practical advantages. The mechanization and error equations for each technique are outlined and the significance of various terms which appear in these equations is discussed in the context of gradiometer-aided inertial navigation.

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.

Geodetic survey method

Abstract: The present method involves the detection of variations of the direction of gravity from the mathematical model of the earth, which may be caused by the presence of a discontinuity in the earth's surface, with relatively heavy materials in the earth's crust causing a deflection of gravity toward such heavier material. In accordance with the present method an inertial system is mounted in a mobile vehicle and the vehicle is moved along a survey route from a first control point to a second control point, with the locations and the deflection from the vertical being known at the two control points. The vehicle is stopped periodically between the two control points in order to eliminate accumulate errors in the inertial system, and to record the position of intermediate points to the surveyed. At each of the stopping points the indicated position of the stopping points relative to latitude, longitude, and elevation are recorded, and additional inertial system parameters are recorded as required to determine the deflection of the vertical at each of the survey points. To avoid complex intermingling of errors associated with the inertial system with the change in the deflection of the vertical, the inertial platform is not releveled at each of the stopping points. When the vehicle reaches the second control point, the position indicated by the inertial guidance system is compared with the actual position of the second control point as to latitude, longitude, and elevation, and following the determination of errors, the position of the various intermediate stopping points are recalculated taking the overall error and the time at which each point was surveyed into consideration. Similarly, the error in the deflection of the vertical, which is separate from the error in position, is determined, and the deflection from the vertical of each of the intermediate survey points is then determined. The results of the survey may then be plotted on a map.

From Serson to Draper—Two Centuries of Gyroscopic Development

Abstract: In 1752 the first written statement on a gyroscopic device was published. Starting with this apparatus the paper describes the history of the gyroscope within the past two centuries. With the artificial horizon at the beginning, the development continues with the gyrocompass, with stabilizing systems for ships, motor cars and aircrafts, and with rate and course indicators. The development culminates in gyroscopic sensors with an accuracy which makes inertial navigation feasible.

The Effects of Vertical Deflections on Aircraft Inertial Navigation Systems

Abstract: Autocorrelation functions (ACFs) of surface gravity anomalies are used as a method of predicting expected aircraft navigation errors induced by deflection model uncertainties Theoretical methods are developed to propagate ACFs from surface to aircraft altitudes, to determine ACFs of vertical deflection components from ACFs for gravity anomalies, and to predict average position and velocity uncertainties in the aircraft navigation system that arise from uncertainties in modeling vertical deflections Numerical results include a study of navigation error sensitivities to system parameters and estimates of representative navigation errors implied by using several specific deflection models in the United States

Quasi-inertial attitude reference platform

Abstract: An inertial guidance system including a true space stable platform is provided while retaining a simple two-degree-of-freedom gimbal system. An added third degree of freedom is provided by motions of the support itself which maintains desired platform orientation. The output of a third axis instrument is used to maneuver the frame itself about the axis of the frame which most nearly will null any rotation about the platform roll or longitudinal axis. A rotational rate gyroscope is positioned on the space stable platform, and actuates the movement of the frame about the longitudinal or roll axis directly from the reading of the rotational movement along the roll axis of the platform.

Inertial Navigation System Tests having Improved Observability of Error Sources

Abstract: Optimal filtering of simulated inertial navigation system (INS) test data is used to evaluate alternate laboratory and flight test echniques, which are intended to determine the value of each significant source of navigation error. Tests of both gimbaled and strapdown systems are evaluated. The major problem preventing more accurate determination of the dozens of sources of error in an INS is the high correlation between the contributions of many of the sources of error. Laboratory test sequences and flight test trajectories are presented that reduce these correlations and improve the observability of the individual sources of error. Parametric studies include the effects of flight duration and distance, multi directional flights versus straight out-and-out flights, frequency and direction of maneuvers, and supersonic flights vs subsonic flights. The effects of the range instrumentation (reference system) accuracy and measurement frequency are demonstrated.

Apollo experience report guidance and control systems: Primary guidance, navigation, and control system development

Abstract: The primary guidance, navigation, and control systems for both the lunar module and the command module are described. Development of the Apollo primary guidance systems is traced from adaptation of the Polaris Mark II system through evolution from Block I to Block II configurations; the discussion includes design concepts used, test and qualification programs performed, and major problems encountered. The major subsystems (inertial, computer, and optical) are covered. Separate sections on the inertial components (gyroscopes and accelerometers) are presented because these components represent a major contribution to the success of the primary guidance, navigation, and control system.

Multi-star processing and gyro filtering for the video inertial pointing system

Abstract: The video inertial pointing (VIP) system is being developed to satisfy the acquisition and pointing requirements of astronomical telescopes. The VIP system uses a single video sensor to provide star position information that can be used to generate three-axis pointing error signals (multi-star processing) and for input to a cathode ray tube (CRT) display of the star field. The pointing error signals are used to update the telescope's gyro stabilization system (gyro filtering). The CRT display facilitates target acquisition and positioning of the telescope by a remote operator. Linearized small angle equations are used for the multistar processing and a consideration of error performance and singularities lead to star pair location restrictions and equation selection criteria. A discrete steady-state Kalman filter which uses the integration of the gyros is developed and analyzed. The filter includes unit time delays representing asynchronous operations of the VIP microprocessor and video sensor. A digital simulation of a typical gyro stabilized gimbal is developed and used to validate the approach to the gyro filtering.

Failure detection and isolation investigation for strapdown skew redundant tetrad laser gyro inertial sensor arrays

Abstract: The degree to which flight-critical failures in a strapdown laser gyro tetrad sensor assembly can be isolated in short-haul aircraft after a failure occurrence has been detected by the skewed sensor failure-detection voting logic is investigated along with the degree to which a failure in the tetrad computer can be detected and isolated at the computer level, assuming a dual-redundant computer configuration. The tetrad system was mechanized with two two-axis inertial navigation channels (INCs), each containing two gyro/accelerometer axes, computer, control circuitry, and input/output circuitry. Gyro/accelerometer data is crossfed between the two INCs to enable each computer to independently perform the navigation task. Computer calculations are synchronized between the computers so that calculated quantities are identical and may be compared. Fail-safe performance (identification of the first failure) is accomplished with a probability approaching 100 percent of the time, while fail-operational performance (identification and isolation of the first failure) is achieved 93 to 96 percent of the time.

Integrated Inertial Reference - Inertial Navigation System

Abstract: The value of Inertial Navigation Systems (INS) is reduced for long time-duration flights because uncertainties produce increased position errors with time. A reduction in this position error buildup is obtained from a mechanization concept described in this .paper. This mechanization comprises an Electrically Suspended Gyroscope (ESG) mounted on the stabilized platform of a local-level INS. Position is estimated by tracking the local vertical while accounting for the Earth's rotation with an accurate clock. Subsystems are integrated by means of a Kalman-Bucy filter. An accuracy of 0.2 n. mi./hr for 12 hr of flight was obtained in a simulation study using an ESG and a 1 n. mi./hr INS.

Redundant Strapdown Laser Gyro Navigation System

Abstract: For the last several years, NASA has pursued the development of low-cost high-reliability inertial navigation systems that would satisfy a broad spectrum of future space and avionics missions. Two specific programs have culminated in the construction of a Redundant Strapdown Laser Gyro Navigation System. These two programs were for development of a space ultrareliable modular computer (SUMC) and a redundant laser gyro inertial measurement unit (IMU). The SUMC is a digital computer that employs state-of-the-art large-scale integrated circuits configured in a functional modular breakdown. The redundant laser gyro IMU is a six-pack strapdown sensor package in a dodecahedron configuration which uses six laser gyros to provide incremental angular positions and six accelerometers for linear velocity outputs. The sensor arrangement allows automatic accommodation of two failures; a third failure can be tolerated provided it can be determined. The navigation system also includes redundant power supplies, built-in test-equipment (BITE) circuits for failure detection, and software which provides for navigation, redundancy management, and automatic calibration and alignment.

Inertially Derived Flying Qualities and Performance Parameters

Abstract: : A feasibility study was undertaken at the U. S. Naval Test Pilot School (USNTPS) in which an inertial navigation system in an A-7C airplane was successfully used to derive the conventional flying qualities and performance parameters which are used to describe an aircraft's motion. This report presents a discussion on the theoretical and practical aspects of using an inertial navigation system in flying qualities an performance testing. Also presented are some of the data obtained during the feasibility study and a discussion of the numerous advantages of using this concept for flight testing. The data obtained were extremely accurate, and the cost of instrumenting USNTPS A-7C airplanes was reduced significantly (in terms of dollars and aircraft down time) from using the conventional flight test instrumentation method.

Impact of algorithms on low cost NAVSTAR/GPS user terminal design tradeoff studies

Abstract: This paper will describe some of the design tradeoff studies being performed at the Naval Electronics Laboratory Center in support of the development of technologies for a low cost NAVSTAR/GPS user terminal. Particular emphasis is being placed on achieving higher accuracy in position and velocity without the aid of inertial navigation systems. The role of estimation theory in the design and analysis of navigation algorithms is emphasized via the covariance and simulation analyses to support hardware-software tradeoffs.