Showing papers on "Inertial reference unit published in 1984"

Adaptation of a strapdown formulation for processing inertial platform data

Abstract: An estimator propagation formulation which ultilizes dynamic data (attitude and sensed acceleration information) from a gimballed inertial platform has been developed to aid in the Shuttle post-flight trajectory reconstruction process and aerodynamic coefficient determination studies. Unlike the classical inertial algorithms, this formulation yields a six degree-of-freedom fully coupled state and attitude estimate. Furthermore, this inertial version is shown to be independent of initial unknown platform misalignments. Results obtained using actual Inertial Measurement Unit (IMU) data and Aerodynamic Coefficient Identification Package (ACIP) strap down data from Shuttle flights are presented.

A discussion of coning errors exhibited by inertial navigation systems

Abstract: : The mechanisms by which so called 'coning errors' occur in a strapdown inertial navigation system are explained by reference to a single mathematical theorem. Typical values of coning errors are derived and ae shown to be significant for a 1 nm/h inertial navigator. Various methods of evaluating and reducing coning errors are discussed. Originator-supplied keywords include: Dither; Ring laser gyroscope; and Vibration.

Marine positioning with a GPS-aided inertial navigation system

Abstract: The accuracy requirements for precise horizontal positioning of a moving vessel in the offshore and open ocean are expected to approach the 3m to Sm level within this decade Previous simulation studies and lan d-based tests have shown that such a level of accuracy can be achieved by a combination of inertial navigation and GPS satellite positioning techniques A Kalman filter and an optimal smoother have been developed to integrate an inertial navigation system with a slow switching GPS satellite receiver for marine positioning purposes The Kalman filter and optimal smoother were tested on the Canadian east coast in November 1982 The paper outlines first the operational principle of the GPS aided inertial navigation system and the development of the Kalman filter and smoother It then presents the results and a detailed error analysis of the offshore tests

Fault-tolerant system considerations for a redundant strapdown inertial measurement unit

Abstract: The development and evaluation of a fault-tolerant system for the Redundant Strapdown Inertial Measurement Unit (RSDIMU) being developed and evaluated by the NASA Langley Research Center was continued. The RSDIMU consists of four two-degree-of-freedom gyros and accelerometers mounted on the faces of a semi-octahedron which can be separated into two halves for damage protection. Compensated and uncompensated fault-tolerant system failure decision algorithms were compared. An algorithm to compensate for sensor noise effects in the fault-tolerant system thresholds was evaluated via simulation. The effects of sensor location and magnitude of the vehicle structural modes on system performance were assessed. A threshold generation algorithm, which incorporates noise compensation and filtered parity equation residuals for structural mode compensation, was evaluated. The effects of the fault-tolerant system on navigational accuracy were also considered. A sensor error parametric study was performed in an attempt to improve the soft failure detection capability without obtaining false alarms. Also examined was an FDI system strategy based on the pairwise comparison of sensor measurements. This strategy has the specific advantage of, in many instances, successfully detecting and isolating up to two simultaneously occurring failures.