Showing papers on "Inertial reference unit published in 1994"

Gyroscope Free Strapdown Inertial Measurement Unit by Six Linear Accelerometers

Abstract: A six-accelerome ter configuration is presented to compute the rotationa^ and translational acceleration of a rigid body. This theoretical minimum accelerometer configuration has as stable a mechanization equation as that of recent results of nine-accelero meter schemes. Associated equations/that can be used to work with the accelerometer location and orientation errors are also derived. For navigation application, the novel design can be integrated with other sensors of complementary characteristics to enhance the performance.

Gyroscopic system for boresighting equipment by transferring a frame of reference

Abstract: Advanced boresight equipment and methods of using the same to effect a transfer of a two- or three-dimensional frame of reference from an ADL to a device to be boresighted. The equipment includes a stationary inertial sensor that is boresighted with respect to a reference line (such as the aircraft ADL). The stationary inertial sensor includes a first gyroscopic combination for generating a first output indicating a two- or three-dimensional frame of reference based on the ADL, and a docking station. The docking station facilitates alignment of a portable inertial sensor that also has a gyroscopic combination for generating a second output indicating its frame of reference. The portable inertial sensor may be identical to the first inertial sensor, or it may additionally include means for automatic optical operation including a gimbal and a gimbal drive system, an electromagnetic energy beam generator for projecting a beam, a second gyroscopic combination for generating a second output signal indicating a frame of reference, and a collimator for indicating an angle between two beams. The various methods of using both embodiments are also described. The invention provides unique calibration techniques, unique adapter and mirror sets, background electronic calibration, accommodation of personality modules, and a unique common mode stabilization technique to eliminate the effect of motion of the aircraft and the boresight technician, such as ship motion, wind loading, and earth rate. The use of the equipment includes the steps of boresighting the stationary inertial sensor with respect to the ADL reference line, positioning the portable inertial sensor in the docking station of the first inertial sensor for relative alignment relative thereto, processing the first and second outputs from the respective first inertial sensor and second inertial sensor to determine a difference between the respective frames of reference, aligning the portable second inertial sensor with respect to a device to be boresighted, reprocessing the first and second outputs from the respective first inertial sensor and second inertial sensor and determining a third frame of reference of the second portable inertial sensor relative to the first stationary inertial sensor, and translating the first, second and third frames of reference to thereby calculate the difference for alignment of the device with respect to the ADL reference line. The invention minimizes size, weight, and complexity of operation, and it reduces the alignment time associated with prior boresighting systems. There is no compromise of accuracy or of ruggedness for operation in adverse conditions.

A cost-effective inertial motion sensor for short-duration autonomous navigation

Abstract: The need for systems, capable of continuously monitoring the inertial position and orientation of vehicles, has motivated the fields of inertial guidance and autonomous navigation. These systems typically employ suites of sophisticated motion sensors for obtaining measurements of motion occurring in all six axes of the Cartesian coordinate system. Through appropriate arithmetic manipulation of sensor output signals, the position and orientation of aircraft, satellites, submarines, and a host of other vehicles can be derived with respect to inertial space. While a wide variety of inertial sensor technologies have been demonstrated in these applications, there are still advances to be made. For example, gyroscopes are typically used to generate measurements of inertial angular position and inertial angular velocity. Requirements imposed on gyroscope drift rates drive up the cost of these instruments and force them to be fragile and complicated. Although there are applications in which gyroscopes remain the only proven solution, there are a growing number of applications in which conventional gyroscopes do not meet technical or cost requirements. This paper addresses the use of magnetohydrodynamic angular rate sensors (MHD ARS) as an alternative to gyroscopes in applications in which measurements are takers over short time durations. In such applications, drift rates, which exceed those exhibited by typical gyroscopes, can be tolerated in exchange for drastic reductions in sensor costs. The drift performance of the MHD ARS can be predicted based on the spectral description of the noise in the measurements provided by the instrument. A complete discussion of this analysis is presented in this paper. >

Advances in the state of the art for AUV inertial sensors and navigation systems

Abstract: Inertial navigation reference units are often thought of as simply a navigation device which must be augmented by another device to damp the Schuler oscillation and characteristic long-term drift. Emerging applications of AUVs, however, demonstrate a need for increasingly sophisticated inertial sensors. These inertial sensors are used not only for navigation, but as importantly, they provide data for sensor stabilization. Inertial systems have also traditionally represented a significant hotel load, been heavy, bulky and a source of acoustic and structure-borne noise. This paper presents an overview of two new inertial systems that are now in production at the Guidance and Control Systems Division of Litton Systems, Inc. These units are small, lightweight, require little power, and are silent. Data are presented that show long-term performance as well as short-term attitude, attitude rate, position, and velocity reference data for the two systems. Attitude, velocity and body axis rate data are required for stabilization of such devices as laser line scanners and long baseline side-scan sonars. The relationship between the characteristics of these sensors and inertial type errors is explored. This analysis shows that it is not sufficient to specify the inertial system only in terms of its navigation CEP. The specification of the inertial unit must also be based on the needs of the sensor payload and include such considerations as the noise content, phase, and bandwidth of the stabilization reference.

Air-borne gravity and differential gravity surveying system

Abstract: A system for conducting an air-borne gravity survey of earth formations along the flight path of a helicopter or any other aircraft comprises an acceleration/gravity sensor assembly (AGSA) which includes at least one inertial measurement unit (IMU) containing accelerometers and gyroscopes capable of acquiring all three components of total linear as well as angular accelerations and a differential global positioning system (ΔGPS) to provide location of the aircraft for derivation of all three linear motion acceleration components which after subtraction from the total linear inertial acceleration components will yield gravity acceleration components.

Use of the Global Positioning System for evaluating inertial measurement unit errors

Abstract: A trajectory reference system based on the Global Positioning System (GPS) can be used instead of conventional radars during missile flight tests. The high quality of the GPS-based trajectory reference makes it useful for evaluating the performance of the missiles' inertial measurement units. Such a system was installed and flight tested on two recently launched ballistic missiles. The GPS hardware configuration used on these flights is described. A Kalman filter approach is used to estimate individual inertial measurement unit errors based on the GPS range and delta range data. The ability of the GPS-based system to identify inertial measurement unit errors is compared to that of radar; the GPS is found to provide superior estimates.

Assessing the Feasibility of Accelerometer-Only Inertial Measurement Units for Artillery Projectiles

Abstract: : Inertial navigation systems estimate velocity and position information from measurements made with inertial instruments. Most often such systems have included accelerometers and gyroscopes. It has been shown analytically that it is possible to obtain the information necessary to determine both linear accelerations and angular motions using only measurements from linear accelerometers. An accelerometer-only inertial measurement unit would be an attractive candidate for use on artillery projectiles due to the availability of high-g miniature accelerometers. After including coding to compute acceleration forces at arbitrary locations on the projectile, a computerized trajectory model was used to evaluate the abilities of various configurations of linear accelerometers and processing algorithms to accurately estimate the components of the projectiles' linear and angular motion. Projectile guidance, Inertial measurement units, Accelerometers.

Signal processing for fiber optic gyroscope (FOG)

Abstract: A fiber-optic gyroscope (FOG) is expected to be the next generation gyroscope for guidance and control, because of various advantages. We have been developing the FOG-Inertial Navigation and Guidance (ING) for M-V satellite launching rocket of the Institute of Space and Astronautical Science (ISAS) since 1990. The FOG-ING consists of an Inertial Measurement Unit (IMU) and an Central Processing Unit Assembly. At current status, the proto-flight model FOG-IMU is being actively developed. And the flight test of the FOG-ING was performed on February 20, 1993, aboard M-3SII-7 satellite launching rocket at the ISAS test facilities in Uchinoura, Japan. This paper presents the signal processing technologies of our FOG which are used for the above FOG-ING.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Spacecraft attitude determination accuracy from mission experience

Abstract: This paper summarizes a compilation of attitude determination accuracies attained by a number of satellites supported by the Goddard Space Flight Center Flight Dynamics Facility. The compilation is designed to assist future mission planners in choosing and placing attitude hardware and selecting the attitude determination algorithms needed to achieve given accuracy requirements. The major goal of the compilation is to indicate realistic accuracies achievable using a given sensor complement based on mission experience. It is expected that the use of actual spacecraft experience will make the study especially useful for mission design. A general description of factors influencing spacecraft attitude accuracy is presented. These factors include determination algorithms, inertial reference unit characteristics, and error sources that can affect measurement accuracy. Possible techniques for mitigating errors are also included. Brief mission descriptions are presented with the attitude accuracies attained, grouped by the sensor pairs used in attitude determination. The accuracies for inactive missions represent a compendium of missions report results, and those for active missions represent measurements of attitude residuals. Both three-axis and spin stabilized missions are included. Special emphasis is given to high-accuracy sensor pairs, such as two fixed-head star trackers (FHST's) and fine Sun sensor plus FHST. Brief descriptions of sensor design and mode of operation are included. Also included are brief mission descriptions and plots summarizing the attitude accuracy attained using various sensor complements.

In-flight estimation of gyro noise on the Upper Atmosphere Research Satellite (UARS) and Extreme Ultraviolet Explorer (EUVE) missions

Abstract: This paper characterizes the low-frequency noise response of the Teledyne dry rotor inertial reference unit (DRIRU) gyroscopes on the Upper Atmosphere Research Satellite (UARS) and the Extreme Ultraviolet Explorer (EUVE). The accuracy of spacecraft attitude estimation algorithms that use gyro data for propagating the spacecraft attitude is sensitive to gyro noise. EUVE gyro data were processed to validate a single-axis gyro noise model, which is used onboard various spacecraft. The paper addresses the potential impact of temperature effects on the gyro noise model and the overall impact on attitude determination accuracy. The power spectral density (PSD) of the gyro noise is estimated from UARS in-flight data by Fast Fourier Transform (FFT). The role of actuator dynamics on the PSD function is also discussed.

Inertial measurement unit and method for improving its measurement accuracy

Abstract: An inertial measurement unit is provided which includes a core inertial measurement unit (13) having accelerometers (19, 21, 23) and gyroscopes (25, 27, 29) aligned along x, y and z axes to provide signals to an onboard computer (39) to determine position of the vehicle upon which they are mounted while in movement. A fourth accelerometer (35) is pivoted perpendicular to the direction of the gravitational field for measuring the gravitational field about the axis upon which it is mounted to provide a reference set of data to an onboard computer prior to movement of the vehicle upon which the system is mounted.