Practical Implementation of Multiple Model Adaptive Estimation Using Neyman-Pearson Based Hypothesis Testing and Spectral Estimation Tools

This study investigates and develops various modifications to the Multiple Model Adaptive Estimation (MMAE) algorithm. The standard MMAE uses a bank of Kalman filters, each based on a different model of the system. Each of the filters predict the system response, based on its system model, to a given input and form the residual difference between the prediction and sensor measurements of the system response. Model differences in the input matrix, output matrix, and state transition matrix, which respectively correspond to an actuator failure, sensor failure, and an incorrectly modeled flight condition for a flight control failure application, were investigated in this research. An alternative filter bank structure is developed that uses a linear transform on the residual from a single Kalman filter to produce the equivalent residuals of the other Kalman filters in the standard MMAE. A Neyman Pearson based hypothesis testing algorithm is developed that results in significant improvement in failure detection performance when compared to the standard hypothesis testing algorithm. Hypothesis testing using spectral estimation techniques is also developed which provides superior failure identification performance at extremely small input levels

Real-time flutter identification

The techniques and a FORTRAN 77 MOdal Parameter IDentification (MOPID) computer program developed for identification of the frequencies and damping ratios of multiple flutter modes in real time are documented. Physically meaningful model parameterization was combined with state of the art recursive identification techniques and applied to the problem of real time flutter mode monitoring. The performance of the algorithm in terms of convergence speed and parameter estimation error is demonstrated for several simulated data cases, and the results of actual flight data analysis from two different vehicles are presented. It is indicated that the algorithm is capable of real time monitoring of aircraft flutter characteristics with a high degree of reliability

An Extension to the Kalman Filter for an Improved Detection of Unknown Behavior

The use of Kalman filter (KF) interferes with fault detection algorithms based on the residual between estimated and measured variables, since the measured values are used to update the estimates. This feedback results in the estimates being pulled closer to the measured values, influencing the residuals in the process. Here we present a fault detection scheme for systems that are being tracked by a KF. Our approach combines an open-loop prediction over an adaptive window and an information-based measure of the deviation of the Kalman estimate from the prediction to improve fault detection

Lunar gravitational field estimation and the effects of mismodeling upon lunar satellite orbit prediction

Lunar spherical harmonic gravity coefficients are estimated from simulated observations of a near-circular low altitude polar orbiter disturbed by lunar mascons. Lunar gravity sensing missions using earth-based nearside observations with and without satellite-based far-side observations are simulated and least squares maximum likelihood estimates are developed for spherical harmonic expansion fit models. Simulations and parameter estimations are performed by a modified version of the Smithsonian Astrophysical Observatory's Planetary Ephemeris Program. Two different lunar spacecraft mission phases are simulated to evaluate the estimated fit models. Results for predicting state covariances one orbit ahead are presented along with the state errors resulting from the mismodeled gravity field. The position errors from planning a lunar landing maneuver with a mismodeled gravity field are also presented. These simulations clearly demonstrate the need to include observations of satellite motion over the far side in estimating the lunar gravity field. The simulations also illustrate that the eighth degree and order expansions used in the simulated fits were unable to adequately model lunar mascons

Tightly coupled GPS-gyro integration for spacecraft attitude determination

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1997.Includes bibliographical references (p. 197-199).by Varun Prui.M.S

Enhancement of Trajectory Determination of Orbiter Spacecraft by Using Pairs of Planetary Optical Images

The subject of the present thesis is about the enhancement of orbiter spacecraft navigation capabilities obtained by the standard radiometric link, taking advantage of an imaging payload and making use of a novel definition of optical measurements. An ESA Mission to Mercury called BepiColombo, was selected as a reference case for this study, and in particular its Mercury Planetary Orbiter (MPO), because of the presence of SIMBIO-SYS, an instrument suite part of the MPO payload, capable of acquiring high resolution images of the surface of Mercury. The use of optical measurements for navigation, can provide complementary informations with respect to Doppler, for enhanced performances or a relaxation of the radio tracking requisites in term of ground station schedule. Classical optical techniques based on centroids, limbs or landmarks, were the base to a novel idea for optical navigation, inspired by concepts of stereoscopic vision. In brief, the relation between two overlapped images acquired by a nadir pointed orbiter spacecraft at different times, was defined, and this information was then formulated into an optical measurement, to be processed by a navigation filter. The formulation of this novel optical observable is presented, moreover the analysis of the possible impact on the mission budget and images scheduling is addressed. Simulations are conducted using an orbit determination software already in use for spacecraft navigation in which the proposed optical measurements were implemented and the final results are given

The Pioneer Anomaly

Radio-metric Doppler tracking data received from the Pioneer 10 and 11 spacecraft from heliocentric distances of 20-70 AU has consistently indicated the presence of a small, anomalous, blue-shifted frequency drift uniformly changing with a rate of ~6 x 10^{-9} Hz/s. Ultimately, the drift was interpreted as a constant sunward deceleration of each particular spacecraft at the level of a_P = (8.74 +/- 1.33) x 10^{-10} m/s^2. This apparent violation of the Newton's gravitational inverse-square law has become known as the Pioneer anomaly; the nature of this anomaly remains unexplained. In this review, we summarize the current knowledge of the physical properties of the anomaly and the conditions that led to its detection and characterization. We review various mechanisms proposed to explain the anomaly and discuss the current state of efforts to determine its nature. A comprehensive new investigation of the anomalous behavior of the two Pioneers has begun recently. The new efforts rely on the much-extended set of radio-metric Doppler data for both spacecraft in conjunction with the newly available complete record of their telemetry files and a large archive of original project documentation. As the new study is yet to report its findings, this review provides the necessary background for the new results to appear in the near future. In particular, we provide a significant amount of information on the design, operations and behavior of the two Pioneers during their entire missions, including descriptions of various data formats and techniques used for their navigation and radio-science data analysis. As most of this information was recovered relatively recently, it was not used in the previous studies of the Pioneer anomaly, but it is critical for the new investigation.Comment: 165 pages, 40 figures, 16 tables; accepted for publication in Living Reviews in Relativit

Airborne Vector Gravimetry Using GPS/INS

This report was prepared by Jay Hyoun Kwon, a graduate student, Department of Civil and Environmental Engineering and Geodetic Science, under the supervision of Professor Christopher Jekeli.This research was supported by the National Imagery and Mapping Agency (NIMA); Contract No. NMA202-98-1-1110.It was submitted to the Graduate School of The Ohio State University in the Winter of 2000 in partial fulfillment of the requirements of the Doctor of Philosophy degree.Compared to the conventional ground measurement of gravity, airborne gravimetry is relatively efficient and cost-effective. Especially, the combination of GPS and INS is known to show very good performances in the range of medium frequencies (1-100 km) for recovering the gravity signal. Conventionally, gravity estimation using GPS/INS was analyzed through the estimation of INS system errors using GPS position and velocity updates. In this case, the complex navigation equations must be integrated to obtain the INS position, and the gravity field must be stochastically modeled as a part of the state vector. The vertical component of the gravity vector is not estimable in this case because of the instability of the vertical channel in the solution of the inertial navigation equations. In this study, a new algorithm using acceleration updates instead of position/velocity updates has been developed. Because we are seeking the gravitational field, that is, accelerations, the new approach is conceptually simpler and more straightforward. In addition, it is computationally less expensive since the navigation equations do not have to be integrated. It is more objective, since the gravity disturbance field does not have to be explicitly modeled as state parameters. An application to real test flight data as well as an intensive simulation study has been performed to test the validity of the new algorithm. The results from the real flight data show very good accuracy in determining the down component, with accuracy better than ±5 mGal. Also, a comparable result was obtained for the horizontal components with accuracy of ±6 to ±8 mGal. The resolution of the final result is about 10 km due to the attenuation with altitude. The inclusion of a parametric gravity model into the new algorithm is also investigated for theoretical reasons. The gravity estimates from this filter showed strong dependencies on the model and required extensive computation with no improvement over the approach without parametric gravity model

Orbit Estimation of Geosynchronous Objects Via Ground-Based and Space-Based Optical Tracking

Angles-only orbit estimation of geosynchronous objects is a unique challenge due to the dense population of clustered geosynchronous objects, the singularities of and perturbations to geosynchronous motion, and the error inherent to experimental observations of geosynchronous objects. Passive optical tracking of geosynchronous space objects has traditionally been performed by ground-based sensors, and the capability has advanced significantly through the introduction of space-based angles-only tracking. This research addresses three key facets of geosynchronous orbit estimation accuracy: improvement to the accuracy via appropriate coordinate modeling, empirical characterization of achievable ground-based angles-only estimation accuracy, and analytic modeling of the space-based angles-only estimated uncertainty. This research develops and analyzes improvements to geosynchronous orbit estimation based on high-fidelity dynamic modeling with a specialized set of coordinates designed specifically to address the geosynchronous orbit conditions. The use of an appropriate representation, the GEO elements, enhances the orbit estimation accuracy compared to the more traditional inertial Cartesian state space representation of geosynchronous motion. Simulation and experimental studies demonstrate that GEO element estimation better recovers the in-track motion than inertial position and velocity state estimation. The short-term estimation accuracy given ground-based tracking is characterized empirically using the Wide Area Augmentation System satellite reference ephemerides. The results show that 10 meter accuracy is possible given short sampling intervals (10 to 30 seconds) and long nightly track lengths (3 or more hours). Several tracking scenarios are found to meet accuracy requirements on the order of 100 meters. The observability of relative states using space-based angles-only tracking of geosynchronous objects by a geosynchronous sensor is analyzed, and first-order analytic expressions for the predicted uncertainty of the along-track separation and intersatellite range are developed assuming space-based passive tracking. The uncertainty models are validated via Monte Carlo analysis. The results demonstrate that 1 hour of continuous space-based passive tracking can estimate the range to the order of tens of meters, and 12 hours produces range uncertainty on the order of meters. The outcome of this research is a set of methods to improve the performance of geosynchronous orbit estimation, and an enhanced understanding of the accuracy possibilities of angles-only ground-based and space-based geosynchronous orbit estimation