Showing papers on "Inertial navigation system 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.

Motor vehicle performance monitor and method

Abstract: A system and method are disclosed for monitoring the performance of a motor vehicle. The vehicle's instantaneous accelerations in at least two directions are continually sensed and stored as coded signals in a computer memory. Performance variables of the vehicle are computed from the acceleration signals stored in memory along with associated time and date codes. By means of inertial navigation and/or radio transmissions from global positioning system satellites, the vehicle's global position is also computed and stored. The stored performance variables are analyzed over a period of time in order to evaluate how the vehicle is being driven. When an erratic or otherwise hazardous driving pattern is detected, signals may be generated to warn the driver and/or traffic authorities.

Flight tests of attitude determination using gps compared against an inertial navigation unit.

Abstract: Attitude determination using GPS carrier phase has been applied successfully to aircraft in experiments by a number of researchers. In an effort to formally characterize its accuracy and bandwidth performance, a GPS attitude determination system was flight tested against an inertial navigation unit (INU). Based on completely separate physical principles, this testing provides an independent means of evaluating overall performance. For the flight experiments, a twin-engine turboprop transport aircraft was outfitted with a specially designed attitude determination receiver. A strapdown ring laser gyro INU was operated in the main cabin as the independent reference. For system evaluation, a number of test maneuvers were executed, including pitch angles to ± 30 deg and bank angles to ± 60 deg. Performance in moderate turbulence was measured. The impact of structural flexure during aircraft maneuvering was evaluated.

A Kalman filter model for GPS navigation of land vehicles

Abstract: This paper describes the development of an extended Kalman filter model for autonomous ground vehicle navigation using integrated civilian-band GPS position measurements and inertial navigation information. The Kalman filter model incorporates a detailed statistical model of all major GPS errors including those associated with selective availability (SA) range errors. The resulting model consists of 14 states. Data showing the accuracy of this filter is presented. >

A 15 b electromechanical sigma-delta converter for acceleration measurements

Abstract: Precision accelerometers for applications such as inertial navigation and guidance, tilt measurement and low-level vibration monitoring can be characterized by shown specifications . Drawbacks of classical electromagnetic servo-accelerometers (fabrication cost, power consumption and shock resistance) are overcome by using a bulk micromachined capacitive accelerometer and a CMOS interface circuit. >

Navagation apparatus with improved attitude determination

Abstract: The navigation apparatus with improved attitude determination is intended for use on a mobile platform. It combines data from a platform inertial navigation unit and carrier phase data for a plurality of GPS satellite signals received at a plurality of receiving points on the platform for the purpose of obtaining estimates of the navigation states of the platform. The navigation apparatus comprises a processor which computes estimates of the states from inputs comprising (1) one or more measured phase double-differences calculated from the measured satellite signal carrier phases, (2) the estimated position of the platform, (3) the estimated positions of the receiving points, and (4) the positions of the satellites, a phase double-difference being defined as the difference in phase differences for signals received from two satellites and a phase difference being defined as the difference in carrier phase of a satellite signal received at two receiving points. The navigation and attitude determination solution is obtained by means of a Kalman filter process wherein the observables comprise measured phase double-differences and each predicted phase double-difference is obtained by operating on the Kalman state vector with an observation matrix defined by linearizing the equations relating the phase double-difference to the navigation states.

Method for in-field updating of the gyro thermal calibration of an intertial navigation system

Abstract: An in-field method for correcting the thermal bias error calibration of the gyros of a strapdown inertial navigation system. The method is begun after initial alignment while the aircraft remains parked with the inertial navigation system switched to navigation mode. Measurements are made of navigation system outputs and of gyro temperatures during this data collection period. A Kalman filter processes the navigation system outputs during this time to generate estimates of gyro bias error that are associated with the corresponding gyro temperature measurements. Heading error correcting is performed after the extended alignment data collection period as the aircraft taxis prior to takeoff. The gyro bias error-versus-temperature data acquired, along with the heading error corrections, are employed to recalibrate the existing thermal model of gyro bias error by means of an interpolation process that employs variance estimates as weighting factors.

Internal correction of dead-reckoning errors with the smart encoder trailer

Abstract: This paper presents an innovative method for accurate mobile robot dead-reckoning, called internal position error correction (IPEC). In previous work, the IPEC method was successfully implemented on a specially designed mobile robot with two differential drive axles, called the multi-degree-of-freedom (MDOF) mobile robot. Experimental results with the MDOF robot showed consistently one to two orders of magnitude better dead-reckoning accuracy than systems based on conventional dead-reckoning. Yet, the IPEC system requires neither external references (such as navigation beacons, artificial landmarks, known floorplans, or satellite signals), nor inertial navigation aids (such as accelerometers or gyros). This paper focuses on our current efforts to implement the IPEC method on a device that can be added to any existing mobile robot. This device, called the "Smart Encoder Trailer" (SET), is a small, single-axle trailer with an incremental encoder on each of its two wheels. Although the SET is not functional yet, simulation results combined with experimental results from the (similarly configured) MDOF vehicle strongly suggest the feasibility of the SET implementation. >

GPS and Inertial Integration

Abstract: T HE Global Positioning System (GPS) and inertial navigation systems (INS) have complementary operational characteristics. Even a modest attempt to combine their functionality in an integrated navigation system can produce a system performance superior to either one acting alone. However, because of the costs of such benefits, it is fitting to inquire about trade-offs that would justify the investment. Trade studies typically address the following questions: 1) What benefits of GPS/inertial integration are important in the application being considered? 2) What configuration of data paths (integration architecture) is appropriate for the application? 3) How complex are the integration algorithms required to provide the desired level of performance, with options for growth to meet future requirements? This chapter devotes one section to address each one of these questions. Because of space limitations, the presentation is qualitative, with only limited recourse to the underlying mathematical structures required to understand integration filtering and the performance evaluation of an integrated navigation system. Wherever possible, the reader is directed to other chapters in this text for those details, or to the literature. Furthermore, the properties of GPS user equipment (UE) and inertial navigation systems cited here are generic rather than specific, and they are representative of technology circa 1993.

The CLAPPER: a dual-drive mobile robot with internal correction of dead-reckoning errors

Abstract: Presents a new approach to accurate and reliable dead-reckoning with mobile robots. The approach makes use of special properties of the author's multi-degree-of-freedom (MDOF) mobile platform, in which two differential-drive mobile robots (called "trucks") are physically connected through a compliant linkage. Using one linear and two rotary encoders, the system can measure the relative distance and bearing between the two trucks. During operation, both trucks perform conventional dead-reckoning with their wheel encoders, but, in addition, use information about their relative position to correct dead-reckoning errors. The author's system, called Compliant Linkage Autonomous Platform with Position Error Recovery (CLAPPER), requires neither external references (such as navigation beacons, artificial landmarks, known floorplans, or satellite signals), nor inertial navigation aids (such as accelerometers or gyros). Nonetheless, the experimental results included in this paper show one to two orders of magnitude better positioning accuracy than systems based on conventional dead-reckoning. >

Airborne vector gravimetry using precise, position-aided inertial measurement units

Abstract: Vector gravimetry using a precise inertial navigation system continually updated with external position data, for example using GPS, is studied with respect to two problems. The first concerns the attitude accuracy requirement for horizontal gravity component estimation. With covariance analyses in the space and frequency domains it is argued that with relatively stable uncompensated gyro drift, the short-wavelength gravity vector can be estimated without the aid of external attitude updates. The second problem concerns the state-space estimation of the gravity signal where considerable approximations must be assumed in the gravity model in order to take advantage of the ensemble error estimation afforded by the Kalman filter technique. Gauss-Markov models for the gravity field are specially designed to reflect the attenuation of the signal at a specific altitude and the omission of the long-wavelength components from the estimation. With medium accuracy INS/GPS systems, the horizontal components of gravity with wavelengths shorter than 250 km should be estimable to an accuracy of 4–6 mgal (µg); while high accuracy systems should yield an improvement to 1–2 mgal.

Modern Inertial and Satellite Navigation Systems

Abstract: : Every mobile robot needs to know where it is so everyone who does mobile robotics wants to know how inertial and satellite navigation works. These two technologies are the most sophisticated forms of navigation systems available and they complement each other very well. Applications requiring indications of highly dynamic 3D motion, excellent relative accuracy and high update rates benefit from inertial systems. Applications requiring bounded absolute accuracy for extended excursions or position estimates relative to the earth itself benefit from satellite navigation. This decade has seen the development of inexpensive handheld global positioning systems based on reception of the GPS satellite signals, and advances in optical gyroscopes and integrated circuit accelerometers which promise to put an inertial navigation system in every automobile before the end of the next. This report is a detailed tutorial which explains the principles, practice, and issues of using these new technologies.

Orientation estimate for mobile robots using gyroscopic information

Abstract: An error model for a solid-state gyroscope developed previously by the authors is included in a Kalman filter for improving the orientation estimate of a mobile robot. Orientation measurement with the error model is compared to the performance when no error model is incorporated in the system. The results demonstrate that without error compensation, the error in localization is between 5-15/spl deg//min but can be improved by a factor of 5 to 7 if an adequate error model is supplied. Results from tests of this gyroscope on a large outdoor mobile robot system are described and compared to the results obtained from the robot's own radar-based guidance system. Like all inertial systems, the platform requires additional information from some absolute position sensing mechanism to overcome long-term drift. However, the results show that with careful and detailed modelling of error sources, low cost inertial devices can provide valuable orientation and position information particularly for outdoor mobile robot applications. >

Modified strapdown inertial navigator error models

Abstract: The paper revisits the problem of error modeling for strapdown INS for the purpose of navigation sensor blending with a Kalman filter. This problem has been addressed repeatedly over the last 30 years, and different perspectives on INS error modeling have emerged. The paper reviews these, focussing in particular on the properties and relative advantages and disadvantages of the /spl phi/-angle and /spl psi/-angle error models. The paper then addresses some new concepts for the design of a Kalman filter model for integrated navigation. The sometimes troublesome problem of the explicit occurrence of the specific force in both error models is averted with the modified /spl phi/-angle and /spl psi/-angle error models proposed in the paper, in which the explicit representation of the specific force is canceled via a transformation of the velocity error states. >

System and method for automatic ship steering

Abstract: A real-time ship steering system provides steering of a survey ship along arescribed thumb line track in accordance with a received point location on the thumb line and a received heading of the rhumb line. The system of the present invention requires an integrated navigation system, a track-keeping interface, and a ship autopilot to steer a ship. The computer of the navigation system integrates position data from continuous fixed radio and satellite positioning systems, inertial navigation systems, and dead reckon aids to develop the best present position. At prescribed equally spaced times, the best present position is used to compute the off-track distance of the ship. The off-track distance is used to develop proportional and integral heading corrections, which are applied to the autopilot by way of the track-keeping interface. The autopilot accepts the correction signal as a bias to the desired ground track heading, causing the ship to be steered toward the desired track. Heading corrections are apportioned over a number of increments between computations in order to gradually lock the ship onto the track.

Aided versus embedded-a comparison of two approaches to GPS/INS integration

Abstract: The performance of two major design options for GPS/INS integration are studied in this paper. The first is the embedded approach, in which the receiver card is an integral part of the system and GPS-information at the measurement level is directly integrated into the navigation processor. The second is the aided approach, in which GPS information is processed independently and the resulting position and velocity is used to update the INS after appropriate time intervals. To study the two design options, the same mathematical model is used to operate two different filters. For the embedded approach, a centralized Kalman filter is applied. In this case the INS and GPS error models define the common state vector. INS input is used to define the reference trajectory which is then updated by GPS pseudo-ranges and range rates. For the aided approach, a decentralized filter design is chosen. In this case, the state vectors for INS and GPS are defined and operated independently. At specified time intervals the derived GPS position and velocity is used to update the INS position and velocity. The time intervals are determined from the error spectra of both systems. Results of simulations for a land vehicle application show that for a variety of scenarios the two design approaches give about the same accuracy, i.e. the tighter integration of the embedded approach does not result in superior performance. Reasons for this somewhat surprising result are discussed in the paper. >

SAR/GPS inertial method of range measurement

Abstract: A method that provides precise target location measurement using a synthetic aperture radar (SAR) system jointly with a global positioning inertial navigation system (GPS/INS) located on a moving aircraft. The SAR system provides a precise measurement of the round trip elapsed radar wave propagation time from the aircraft location to a selected pixel in a ground map that includes a portion of the target. The velocity of radar wave propagation is measured at the same time that the range time lapse to the designated SAR map pixel is measured. When combined with position and velocity information derived from the GPS/INS inertial navigation system, the radar wave propagation time is used to calculate the position of the target pixel in GPS/INS coordinates, thereby improving measurement accuracy. The method comprises flying an aircraft containing GPS/INS and SAR systems along a predetermined flight path. The relative position and velocity of the aircraft along the flight path is accurately measured using the the global positioning system. A first SAR map is generated. A target pixel in the first SAR map that corresponds to the target is then designated. A minimum of two additional SAR maps are generated and the target pixel in each of the additional SAR maps is designated. The position of the target pixel relative to GPS/INS coordinates and the velocity of radar wave propagation to the target using aircraft position data derived from the global positioning system are then simultaneously measured. Finally, a more accurate position for the target pixel is calculated using the computed value for the radar wave propagation velocity.

High accuracy navigation and landing system using GPS/IMU system integration

Abstract: In this paper, the accuracy, integrity and continuity of function requirements for automatic landing systems using satellite navigation systems are discussed. Such a landing system is the integrated navigation and landing system (INLS) developed by Deutsche Aerospace (DASA/Ulm, Germany). The system concepts of the INLS are presented. It is shown how an INLS, based on system integration of a satellite navigation system (e.g., GPS) in realtime differential mode with an inertial measurement unit (IMU) in the accuracy class of an attitude and heading reference system (AHRS), can meet the requirements: the results given are mainly devoted to the accuracy issues. Using Kalman filter techniques, an in-flight calibration of the IMU is performed. The advantage of system integration, especially in dynamic flight conditions and during phases of flight with satellite masking, is explained. The accuracy, integrity and continuity of function of the INLS were proven by means of flight tests in a commuter aircraft using a laser tracker as a reference. These flight tests have shown that the short-term accuracy ( >

Motion compensation for airborne SAR based on inertial data, RDM and GPS

Abstract: Two new motion compensation methods for airborne SAR are presented. Both methods are based on the evaluation of acceleration data measured by an Attitude and Heading Reference System (AHRS). The motion compensation algorithms were developed for the Experimental SAR System (E-SAR) of DLR which operates in L/C/X-Band. It is installed in a small Dornier Do-228 turboprop aircraft. Due to atmospheric turbulences and instabilities of the aircraft a highly accurate motion compensation becomes necessary to obtain high quality SAR images. The first method is furthermore based on results obtained by the Reflectivity Displacement Method (RDM). The RDM was developed by DLR and evaluates the radar raw data of the SAR sensor. The RDM provides a very accurate estimate of the forward velocity of the sensor which usually cannot be calculated by an inertial system with the required accuracy. Bias and drift components of the inertial data are eliminated by filtering. Residual systematic position errors are negligible for most applications and a high resolution SAR image can be generated. The advantages of this signal processing method are its robustness and its autonomy. The second method is based on the combination of inertial data and GPS position data. The GPS measurements are used to compensate the bias and drift components of the inertial data. Thus the actual position of the sensor can be estimated very accurately which guarantees a geometrically consistent high resolution SAR image. This signal processing method combines the absolute accuracy of GPS position measurements respectively its long term stability with the high bandwidth and data rate of the inertial measurements. In practice this method also turned out to be very robust. >

Integrated INS/GPS system for high precision navigation applications

Abstract: The paper describes the combination of a Honeywell LASERNAV II ring laser gyro inertial navigation system (INS) and Trimble SSE GPS receivers. A software package for the strapdown system was developed using common terrestrial zero velocity (ZUPT) and coordinate update (CUPT) techniques. An Integrated GPS inertial position and attitude control system (IGIPACS) is built up in different levels. The first level is a separate operation of the GPS receivers and the INS. Here the INS-system is supported by GPS positions with an update rate of at the most 2 Hz. The GPS positions are evaluated by various types of applications (rapid-static, kinematic) with cm-accuracy. The INS is used to interpolate the positions between the update points with a rate of 50 Hz. In the second level the GPS positioning is supported by the INS system during losses of lock using the Kalman filter technique (cascade integration). Within this algorithm differential GPS is applied using double difference code solutions. Numerous tests were made using a station wagon, sometimes with an array of three or four antennas, as well as an aircraft supporting the determination of a digital terrain model with laser scanner and radar altimeter. Problems and differences in terrestrial and airborne applications are outlined. The accuracy of the system, its potential and further steps are discussed. >

A navigation grade micro-machined silicon accelerometer

Abstract: The paper presents the initial results of AlliedSignal Inc. (formerly Sundstrand Data Control) Instrument System's, development of a medium accuracy aircraft inertial navigation grade silicon accelerometer. This effort focused on developing a monolithic bulk-micromachined vibrating beam accelerometer. The accelerometer is designed such that an acceleration along the positive input axis places the vibrating beams in tension. Thus, the resonant frequency of the vibrating beams increase with applied acceleration. An electronic oscillator capacitively couples energy into the vibrating beams to keep them oscillating at their resonant frequency. The acceleration signal is then output from the oscillator as a frequency modulated square wave that can be sent directly to a digital interface. Performance data from the first AlliedSignal silicon vibrating beam accelerometer development program is presented. The data presented includes noise level, short term stability and tumble over temperature tests. This accelerometer is targeted to be incorporated into a system with one nautical-mile-per-hour navigational accuracy. This ambitious goal translates to an accelerometer with 50 /spl mu/g, one sigma bias, and 50 ppm, one sigma long term scale factor accuracy. The data presented demonstrate the feasibility of meeting one-nautical-mile-per-hour accuracy with a vibrating beam micro-accelerometer. The cost savings offered by a micro-machined silicon accelerometer ensure that this technology will be pushed to its limit for application in inertial guidance systems. >

Path tracking, obstacle avoidance and position estimation by an autonomous, wheeled planetary rover

Abstract: This paper presents a set of algorithms for piloting an autonomous planetary rover along a planned path, performing obstacle avoidance, and improving position estimation. Path-tracking is accomplished using feedback-control of position and orientation errors, measured with respect to the planned path trajectory. Obstacle-avoidance is performed through application of an artificial potential field, to data that can be acquired using a scanning rangefinder. Position and velocity estimation is improved by the algorithmic filtering and fusing of odometry and inertial navigation data streams. Results from computer simulation are used to illustrate the path-tracking and obstacle-avoidance capabilities, and experimental data is used to illustrate how sensor fusion mitigates the effects of wheel-slippage and integration-error in position and velocity estimation. >

Cycle-slip detection and repair in integrated navigation systems

Abstract: In order to use pure carrier-phase measurements, the initial ambiguities of the measurements have to be solved. Once obtained, these ambiguity solutions can be lost by shadowing, short-time loss of lock on one or several satellites and other effects, commonly referred to as cycle-slips. Restarting the ambiguity resolution algorithm is a time- and computation-intensive task and should be avoided as long as possible. In order to compensate for such short interruptions, an algorithm would be desirable which detects cycle-slips and is able to correct their magnitude for the individual measurements. In this paper an algorithm is presented which detects, using the redundancy inherent in the GPS-measurements, any cycle-slips. The residuals between the Doppler measurement and a calculated Doppler based on a least-squares solution show significant changes whenever cycle-slips occur. Determining in which channel the cycle slip occurred and calculating its size is possible using external information, for instance an INS-system. Instead of using the least-squares solution, the short-term stability of the INS-system is utilized to generate the calculated Doppler. Results are presented for such an integrated system showing the effectiveness in correcting even multiple simultaneous cycle-slips down to the loss of one cycle. The effects of decreasing satellite redundancy on the effectiveness of the algorithm and the influence of the information supplied by the INS system on the quality of the cycle-slip repair are investigated. Since GPS and INS sensors work in a closed loop for correction of the cycle-slips, error detection at this stage is essential for reliable operation of the integrated navigation system. >

A laboratory in the sky

Abstract: This article describes a research aircraft for airborne measurements and the challenges that were overcome to deploy state-of-the-art measurement technology in an aircraft environment We also focus on the chemical instrumentation and the recent addition of tandem mass spectrometry to the capabilities available for atmospheric characterization The plane that we use to study atmospheric physical and chemical processes is a Grumman Gulfstream 1 (G-1), which is a twin-engine turboprop The G-1 has a visual flight rule range exceeding 1500 nautical mi (endurance of about 6 h) It carries as much as 2800 lb of scientific payload with seats for four scientists and has a sampling speed range of 160-250 knots The data acquisition system on the G-1 contains special interfaces to log data from a Long-Range Navigation system, the Global Positioning System, and an inertial navigation system, as well as particle measurement systems and other scientific probes 3 refs, 7 figs, 2 tabs

Automatic alignment and calibration of an inertial navigation system

Abstract: In this paper we derive a simple six degree of freedom navigator, Earth-surface navigator, for terranean vehicle application, using low grade gyros. The calibration and alignment of the navigator are investigated when the system is at rest. Based on the observability of the error model when the system is at rest, a state transformation is presented. This transformation decouples the observable modes, which are based on physical insight from the unobservable modes. An example is given to illustrate the performance of a Kalman filter for calibration and alignment. >

On the orientation vector differential equation in strapdown inertial systems

Abstract: An alternate derivation of the orientation vector differential equation is given, together with an assessment of the error inherent in the simplified form of this equation commonly utilized in strapdown inertial systems. >

A transfer alignment algorithm study based on actual flight test data from a tactical air-to-ground weapon launch

Abstract: The paper provides results from a joint study of various transfer/alignment (T/A) techniques including velocity matching, integrated velocity matching, and doubly integrated velocity matching approaches. The goal is to determine how the various algorithms perform when driven with actual flight test data. The study addresses key T/A Kalman filter issues such as the effect of wing flexure vibration on instrument error estimation and rapid alignment concepts. A description of how a T/A Kalman filter is implemented and used in inertially guided weapons is included. The data used in the study was acquired from the Air Force Operational Concept Demonstration (OCD) Program. The OCD effort was performed by the Air-To-Surface Weapons System Program Office (SPO) at Eglin AFB in late 1992 and early 1993. The Eglin SPO initiated the flight test program to demonstrate the effectiveness of GPS/INS integration in a tactical weapon. The test was conducted using a Honeywell Integrated Flight Management Unit (IFMU) and an Interstate Electronics 5-channel P-code GPS receiver in a GBU-15 airframe on board a block 40 F-16 aircraft. Telemetry data from this OCD weapon was transmitted continuously from the beginning of weapon alignment to final impact on the ground. The OCD telemetry stream contained INS and GPS data from both the aircraft and weapon during captive carriage T/A maneuvers. After launch, the weapon data alone was transmitted during the free flight to the target. These messages provide the data set used in the T/A study. >

Method for thermal modeling and updating of bias errors in inertial navigation instrument outputs

Abstract: A method for thermal modeling and updating of bias errors in inertial navigation instrument outputs relies upon piecewise cubic spline encoding of data. The temperature range of the thermal model is divided into contiguous intervals of equal length. Instrument bias-versus-temperature data is encoded on an interval-by-interval basis with all intervals normalized so that cubic polynomials of identical form may be fitted between boundary intervals defined by function values and slopes. Instrument bias error at a measured temperature is estimated in the field and an update point (bias, temperature) established. The particular interval is located and the thermal model is re-fit accordingly in the region of the relevant interval. The spline parameters are then adjusted to accommodate the estimated bias error thereby updating the instrument thermal model of bias.

Fault-Tolerant Air Data Inertial Reference System development results

Abstract: A new fault-tolerant inertial system architecture is emerging in commercial transport aircraft. This architecture. through sensor skew redundancy and fault tolerant electronics, provides improvement in the integrity, availability and cost of ownership. The system described is a Fault-Tolerant Air Data Inertial Reference System (FT/ADIRS). The system consists of a Fault-Tolerant Air Data Inertial Reference Unit (FT/ADIRU), a Secondary Air Data Attitude Reference Unit (SAARU) and six Air Data Modules (ADM). The FT/ADIRU is fault-tolerant and the SAARU is 100% monitored. The FT/ADIRU includes one additional level of redundancy above that required to dispatch the aircraft. This feature introduces the concept of deferred maintenance. Deferred maintenance allows airlines to schedule FT/ADIRU maintenance at their convenience and eliminates costs due to flight delays and cancellations caused by inertial system failures. The SAARU includes one level of redundancy above that required to provide the basic function. This feature provides fail-safe performance of the SAARU. >

High accuracy performance capabilities of the military standard ring laser gyro inertial navigation unit

Abstract: The medium accuracy standard ring laser gyro (RLG) inertial navigation unit (INU) exemplified by Litton's LN-93 system has benefited from continual improvements during the production process such that the present navigational accuracy and reliability are better by a factor of two or more over the original requirements as defined by SNU 84-1. Performance enhancements are now available which further improve navigation performance to the high-accuracy category while maintaining the reliability of the production system. Two enhancement mechanizations are described-one that requires software-only changes to improve inertial performance, and one that employs a self-contained (embedded) GPS to augment the inertial performance. These enhancements may be applied in combination to provide uniquely effective immunity to GPS spoofing countermeasures. These enhancements retain the present standard RLG INU form factor, mounting, and electrical interface, and are therefore particularly advantageous for retrofit application. Potential retrofit applications with various aircraft avionics architectures are discussed. >