Showing papers on "Inertial measurement unit published in 1991"

Three-Dimensional Attitude Determination with the Ashtech 3DF 24-Channel GPS Measurement System

Abstract: A method for real-time, 3 dimensional attitude determination (heading, pitch, roll) has been developed using state-of-the-art GPS technology. This method is based on differential carrier phase measurements between four antennas which are connected to one 24-channel receiver. (The 24 channels are divided into four banks of six channels each.) Key advantages of this method over existing methods include the following: the initial phase ambiguity is determined with one epoch of data, the attitude is updated once per epoch, and cycle-slip detection and repair are achieved instantaneously. The differential phase measurements are processed using doublc- differecing techniques, which have already been proven successful in real-time kinematic applications. The attitude angles calculated can be as accurate as one milliradian (3.5 arc-minutes) for antenna spacings on the order of one meter. Since such accurate attitude measurements may be achieved in real time, numerous applications for the Ashtech Three-dimensional Direction Finding (3DF) system will arise. One obvious application is the integration of 3DF with an inertial measurement unit (IMU) for aircraft control and navigation. In this paper, we describe the basic system architecture of the 3DF system, the antenna conligurations, as well as accuracy of attitude as a function of geometry, baseline length, multipath, and number of satellites visible. Also shown are preliminary results from differential kinematic testing.

System for aligning the inertial unit of a carried vehicle on that of a carrier vehicle

Abstract: The system may be used, for example, to initialize the inertial unit of a missile from the inertial unit of a vehicle carrying the missile. According to the invention, a servo-control circuit is provided for slaving data in the missile inertial unit on data from the carrier inertial unit, together with a Kalman filter connected in parallel with said servo-control circuit and designed to identify harmonization errors between the two inertial units.

GPS Inertial Attitude Estimation via Carrier Accumulated-Phase Measurements

Abstract: This paper describes the design and simulation of an integrated GPS/INS that accomplishes space vehicle navigation and attitude estimation. The simulation contains models of an inertial measurement unit (IMU), a GPS receiver processing signals from an array of antennas placed on the spacecraft structure, and an integrated navigation filter. Interferometric equations are employed to process GPS carrier accumulated-phase measurements from precise antenna locations in the user vehicle. Vehicle orientation in inertial space is then obtained by relating baseline-difference phase measurements to orientations of antenna baselines relative to satellite line-of-sight vectors. The method of GPS-aided attitude estimation described herein is distinguished from other methods in that it does not employ search algorithms to resolve the carrier phase cycle ambiguity. Instead, the ambiguity is modeled as a random process and is included as an error state of a statistical filter. As a result, the attitude estimation time history evolves directly for any dynamic environment.

Multiplexed approach for the fiber optic gyro inertial measurement unit

Abstract: A novel approach in fiber-optic gyro (FOG) technology was developed and incorporated into a strapdown inertial measurement unit (IMU). In this approach, optical switches are used to multiplex a single light source, detector, and electronics among three FOG axes. The multiplexed operation of the FOG triad extends the inherent advantages of the single-axis FOG to attain small size, light weight, and low power dissipation and provides a high-performance low-cost IMUs with improved reliability and reduced random drift. A scheme of the triad system is presented.

Development of a GPS-aided motion measurement, pointing, and stabilization system for a Synthetic Aperture Radar. [Global Positioning System (GPS)]

Abstract: An advanced Synthetic Aperture Radar Motion Compensation System has been developed by Sandia National Laboratories (SNL). The system includes a miniaturized high accuracy ring laser gyro inertial measurement unit, a three axis gimbal pointing and stabilization assembly, a differential Global Positioning System (GPS) navigation aiding system, and a pilot guidance system. The system provides several improvements over previous SNL motion compensation systems and is capable of antenna stabilization to less than 0.01 degrees RMS and absolute position measurement to less than 5.0 meters RMS. These accuracies have been demonstrated in recent flight testing aboard a DHC-6-300 Twin Otter'' aircraft.

Integrated System for Automatic Landing Using Differential GPS and Inertial Measurement Unit

Abstract: GPS-receivers have accuracy problems in high precision flight gui­dance applications. In dynamic flight maneuvers they show not only operational problems due to satellite masking but also a reduction in accuracy in accelerated flight and turn flight.

Prelaunch checkout of the inertial upper stage redundant imu in the magellan and galileo missions

Abstract: The Redundant Inertial Measurement Unit (RIMU) is used in the Redundant Inertial Navigation System (RINS) of the Inertial Upper Stage (IUS). Recent IUS missions of critical importance to the space community culminated in successful trajectory insertions of the Magellan and Galileo interplanetary spacecraft. The redundancy features of the strapdown RIMU, combined with a technique for on-pad calibration and sensor consistency checks, provide a comprehensive, self-contained performance-monitoring capability during on-pad, prelaunch checkout. This capability was exploited during launch holds, and recycles of both the Magellan and Galileo missions. The RIMU was maintained in its preliftoff gyrocompass mode of operation with no quiet-time restrictions for extended time periods, thereby allowing a rapid return to launch readiness.

An Introduction to the GPS Guidance Package (GGP)

Abstract: : Under DARPA sponsorship, NOSC has made a dual contract award for advanced development brassboard models of a Global Positioning System Guidance Package (GGP). The approximate $28 million in contracts were awarded to the contractor teams of Texas Instrument & Honeywell and Litton Systems & Rockwell Collins. The existing 48 month (GGP Phase 1) contracts provide for the advanced development of a strapdown inertial guidance package comprised of a navigation grade Interferrometric Fiberoptic Gyro (IFOG) tightly coupled to a miniaturized GPS receiver (MGR). The GGP exploits the synergisms achieved by combining inertially sensed Inertial Measurement Unit (IMU) movement goal is to produce a combined GPS/IMU navigation grade system which will be miniaturized for easy insertion into any host vehicle, and inexpensive for use by expendable vehicles (weapons and platforms). Follow-on Phase 2 contracts will develop preproduction prototype GGP units tailored for specific platforms.

An Observability Analysis of a GPS-Aided Geodetic Inertial Strapdown Measurement Unit

Abstract: A widely used tool to combine data of different measurement devices in real time is the Kalman-Filter-Technique. To guarantee a uniformly asymptotically globally stable filter, the system model upon which the Kalman filter is based has to be both observable and controllable. Thus a first step to design a filter is to check the observability and controllability of the system model. In this paper we restrict ourselves to the observability problem, but because of the Kalman duality theorem the results can easily be extended to the controllability problem. The structure of the system model is not only important in real time filtering, but also for the post-mission adjustment, if, e.g., the state vector is introduced as an unknown quantity in the adjustment.

Testing of the high accuracy inertial navigation system in the Shuttle Avionics Integration Lab

Abstract: The description, results, and interpretation is presented of comparison testing between the High Accuracy Inertial Navigation System (HAINS) and KT-70 Inertial Measurement Unit (IMU). The objective was to show the HAINS can replace the KT-70 IMU in the space shuttle Orbiter, both singularly and totally. This testing was performed in the Guidance, Navigation, and Control Test Station (GTS) of the Shuttle Avionics Integration Lab (SAIL). A variety of differences between the two instruments are explained. Four, 5 day test sessions were conducted varying the number and slot position of the HAINS and KT-70 IMUs. The various steps in the calibration and alignment procedure are explained. Results and their interpretation are presented. The HAINS displayed a high level of performance accuracy previously unseen with the KT-70 IMU. The most significant improvement of the performance came in the Tuned Inertial/Extended Launch Hold tests. The HAINS exceeded the 4 hr specification requirement. The results obtained from the SAIL tests were generally well beyond the requirements of the procurement specification.

Experimental Research on a Strapdown Inertial Navigation Device Working Underwater

Abstract: Exploration as well as exploitation of ocean resources requires accurate underwater navigation for manned as well as remotely controlled vehicles. Thus, more and more attention is given to systems that can be guided to specific locations and can be kept there for any length of time. Such systems have to sense linear and angular velocity to provide position output and guidance. Strapdown inertial navigation systems, because of their small size and high precision, are ideally suited for this purpose. This paper discusses the following implementation problems of such a system: The design characteristics of the IMU (inertial measurement unit) with respect to heat transfer and static and dynamic performance. The design of a horizontal heading reference to attain Euler angles and velocity. A method for decoupling control of the two-degree-of-freedom dynamically tuned gyroscopes in the IMU in order to upgrade its controlability. Algorithm design for data collection, error compensation, real-time computation and communication with other control systems. An analysis of the error detection and separation capability, including a self-test of the redundant Z-axis monitor.

Design for an airborne gps-inertial surveyor

Abstract: The Aerial Profiling of Terrain System (APTS), designed and built at C.S. Draper Laboratory under the sponsorship of the US Geological Survey, achieved accuracies of 60 cm horizontal and 15 cm vertical in terrain profiling. APTS used a high accuracy inertial navigation system periodically updated by measurements from a laser tracker, which used surveyed retroreflectors located on the ground. A laser profiler fixed to the IMU measured distance to the terrain along a known direction. With a full constellation of Global Positioning System (GPS) satellites soon to be available, comparable accuracies could be achieved with a medium-accuracy inertial navigator updated by differential carrier-phase GPS measurements. Additional flexibility could be provided by gimballing the profiler. For appplications in which precise survey of ground points is desired, improvements in the laser tracker would make it possible to acquire retroreflectors that are genuinely unsurveyed. The design provides for the inclusion of additional optional sensors such as imaging devices, and for the use of the surveyor as a test bed for other navigation systems. The design incorporates technology capable of recording data at rates of several megabits per second.

Research on Closed-Loop Kalman Filter Technology of SINS/GPS for Surveying

Abstract: Most INS errors are oscillatory with three harmonic components (Schuler, Earth, and Foucault) and grow with time due to the random noise, such as gyro random walk, coning and sculling motion of the vehicle, and vibration of the IMU base. This is especially true for strapdown INS. Conventional open-loop Kalman filters used in ISS have the same characteristics as closed-loop Kalman filters if no random noise exists in the ISS. In practice, the ZUPT method is used as a standard procedure but it can only be employed if regular vehicle stops are possible.

Mathematical Analysis of the Geodetic Space—Stabilized INS

Abstract: The topic of this paper is the analysis of the space-stabilized geodetic INS Honeywell GEO-SPIN II and its integration with GPS in a Kalman filter. The basic concept of analysis is a rigorous physical description of the inertial sensors and the platform.The analysis results in error models of the ESG gyros, of the platform servo-loops and the fluid-filled pendulous accelerometers. The anomalous gravity field is modeled by a five state shaping-filter based on a 2nd order Gauss-Marcov process for the disturbing potential. In comparison to the existing error rgodel of the GEO-SPIN II a large cross-coupling term and a g2-drift of the gyros are introduced. The platform servo-loop errors consider a mass unbalance of the inner element, friction of the bearings, and the damping of the motors. The error model of the accelerometers is extended by a scalefactor asymmetry, a cubic scalefactor error and a cross-coupling term. After introducing the main system errors, the navigational errors and the GPS-biases a 31 states Kalman filter is derived.