Showing papers on "Inertial reference unit published in 1982"

Attitude sensing system

Abstract: An attitude sensing system which incorporates the precision in attitude sensing of a satellite navigation system with the dynamic tracking capabilities of an inertial measurement unit. Optimally estimated attitude and system error signals are combined with the outputs of an inertial measurement unit to control the phase differences of signals received on an interferometer array from a navigation satellite. The outputs from the inertial measurement unit and the phase differences are processed in an optimal estimator filter to produce periodically updated attitude and system error signals. This permits inertial attitude sensing to benefit from the long term accuracy of attitude estimation based upon signals from the satellite navigation system. During conditions of high dynamic maneuvering in which attitude changes are rapid, the output of the inertial measurement unit continues to provide attitude information and controls the attitude sensing loop to insure that the system is not disoriented by such high dynamic conditions.

Doppler-Aided Low-Accuracy Strapdown Inertial Navigation System

Abstract: This paper presents a covariance analysis of the performance of a Doppler-aided low-accuracy coarsely aligned strapdown inertial navigation system (INS), whose fine alignment takes place automatically in flight. It is shown that the fine alignment in azimuth, which requires turns, consists of in-flight gyro calibration and inflight gyrocompassing. The spacing of the turns is investigated. The influence of several position fixes is examined, and it is shown that they can replace INS turns. It is also shown that the use of magnetic heading reference reduces system errors but is not necessary for the satisfactory performance of the augmented system. Two suboptimal Kalman filters are designed and evaluated. Their small performance degradation with respect to that exhibited by the optimal filter and their low sensitivity to parameter changes is demonstrated by true covariance simulation runs.

The Shuttle inertial system

Abstract: The Space Shuttle inertial system is built around a sensor assembly called the inertial measurement unit (IMU). The system includes a redundant set of three structurally integrated IMU's that operate in conjunction with parallel strung data system computers to provide precise attitude and velocity information to user system functions. The inertial system is actually a separate subsystem function integrated into the overall avionics system. Software resident in the system computers is the final link in the inertial system. The inertial software is comprised of two major sets, including a subsystem operating program (SOP) called the IMU SOP and redundancy management. Attention is given to system applications, systems performance, attitude sensitivities, the IMU platform, IMU thermal management, aspects of IMU calibration, and Shuttle program experience.

Simultaneous Calibrations of Voyager Celestial and Inertial Attitude Control Systems in Flight

Abstract: A mathematical description of the data reduction technique used to simultaneously calibrate the Voyager celestial and inertial attitude control subsystems is given. It is shown that knowledge of the spacecraft limit cycle motion, as measured by the celestial and the inertial sensors, is adequate to result in the estimates of a selected number of errors which adversely affect the spacecraft attitude knowledge.

DRIRU I/SKIRU - The application of the DTG to spacecraft attitude control

Abstract: The dynamically tuned gyro (DTG) was developed to replace the floated, rate integrating gyro used for space attitude control, as the DTG fulfills cost, performance, and reliability requirements not satisfied by its predecessor. The use of this gyro in the Dry Gyro Inertial Reference Unit I (DRIRU I) marked the first application of a DTG in a spacecraft attitude reference unit. Design and performance characteristics of DTG application in the Singer-Kearfott Inertial Reference Unit (SKIRU) are outlined, for example its minimal weight (7 lb), and operational reliability. The DTG has accomplished 156,000 failure-free hours, and a chart, logging test performance, indicates that this and other requirements were more than sufficiently satisfied. The unit has an unparalleled life span, with several units still operating after 70,000 to 130,000 hours, and a random drift which always remains under 0.0005 deg/h. Potential for improvements, such as drift performance, are considered.