Analysis of the theta-D filter as applied to hit-to-kill interceptors and satellite orbit determination

When designing feedback control systems, there is often a need for estimation methods that provide system information that is not readily available via sensors placed within the system. In many cases a sensor that measures a particular system state either does not exist or is prohibitively expensive. In addition, all realistic systems contain some degree of nonlinearity. This thesis focuses on two such cases: missile guidance with bearings-only measurements and GPS satellite orbit determination. In each case, a new nonlinear filter, the [theta]-D method, is used and evaluated for its performance in providing the necessary estimation. To aid the filter in the bearings-only application, a guidance law is formulated that assists the filter in estimating the target location despite the lack of range measurement. An implementation procedure, called the Staggered Filter Concept, is also presented for implementing a continuous filter, such as the [theta]-D filter, with measurements taken at discrete intervals. This procedure is used to implement the orbit determination algorithm on the Missouri S&T Satellite Team M-SAT mission --Abstract, page iii

Stationkeeping of an L₂ Libration Point Satellite with θ-D Technique

A new method for L2 libration-point orbit stationkeeping is proposed in this paper using continuous thrust. The circular restricted three-body problem with Sun and Earth as the two primaries is considered. The unstable orbit about the L2 libration-point requires stationkeeping maneuvers to maintain the nominal path. In this study, an approach, called the θ-D technique, based on optimal control theory gives a closed-form suboptimal feedback solution to solve this nonlinear control problem. In this approach the Hamiltonian-Jacobi-Bellman (HJB) equation is solved approximately by adding some perturbations to the cost function. The controller is designed such that the actual trajectory tracks a predetermined reference orbit with good accuracy. Numerical results employing this method demonstrate the potential of this method

A Rice Plastidial Nucleotide Sugar Epimerase Is Involved in Galactolipid Biosynthesis and Improves Photosynthetic Efficiency

Photosynthesis is the final determinator for crop yield. To gain insight into genes controlling photosynthetic capacity, we selected from our large T-DNA mutant population a rice stunted growth mutant with decreased carbon assimilate and yield production named photoassimilate defective1 (phd1). Molecular and biochemical analyses revealed that PHD1 encodes a novel chloroplast-localized UDP-glucose epimerase (UGE), which is conserved in the plant kingdom. The chloroplast localization of PHD1 was confirmed by immunoblots, immunocytochemistry, and UGE activity in isolated chloroplasts, which was approximately 50% lower in the phd1-1 mutant than in the wild type. In addition, the amounts of UDP-glucose and UDP-galactose substrates in chloroplasts were significantly higher and lower, respectively, indicating that PHD1 was responsible for a major part of UGE activity in plastids. The relative amount of monogalactosyldiacylglycerol (MGDG), a major chloroplast membrane galactolipid, was decreased in the mutant, while the digalactosyldiacylglycerol (DGDG) amount was not significantly altered, suggesting that PHD1 participates mainly in UDP-galactose supply for MGDG biosynthesis in chloroplasts. The phd1 mutant showed decreased chlorophyll content, photosynthetic activity, and altered chloroplast ultrastructure, suggesting that a correct amount of galactoglycerolipids and the ratio of glycolipids versus phospholipids are necessary for proper chloroplast function. Downregulated expression of starch biosynthesis genes and upregulated expression of sucrose cleavage genes might be a result of reduced photosynthetic activity and account for the decreased starch and sucrose levels seen in phd1 leaves. PHD1 overexpression increased photosynthetic efficiency, biomass, and grain production, suggesting that PHD1 plays an important role in supplying sufficient galactolipids to thylakoid membranes for proper chloroplast biogenesis and photosynthetic activity. These findings will be useful for improving crop yields and for bioenergy crop engineering

Analysis of 9-D Filter and Observability Enhanced Guidance Law as Applied to Hit-To-Kill Missiles

In this day and age, the need for an ever more reliable missile defense system is becoming increasingly apparent. This need for increased reliability leads to the need for improving existing guidance, control, and estimation architectures. This paper analyzes a new suboptimal filter, 6-D, coupled with a guidance law specifically designed on enhance system observability during hit-to-kill applications. The results presented herein demonstrate the potential effectiveness of the filter/guidance combination against highly maneuvering, evasive targets

Simulation of the Dynamics of a Short Tethered Satellite System

This study investigates the dynamics of a short tethered satellite system composed of two satellites joined by a ten-meter tether. Despite the many studies in the literature regarding tethered satellites and their dynamics, none that specifically concern “short” tethers have been located to date. Equations of motion are derived and numerically integrated to produce the tether tension, system attitude, orbit, and libration characteristics. Techniques have been implemented which add corrections to the integrated states and help reduce longterm simulation errors. Also considered are the effects of perturbations due to the Earth\u27s geopotential, solar and lunar gravity, aerodynamic drag and solar radiation pressure

MR SAT Orbit Determination using the Θ-D Filter

The ME SAT design team at the University of Missouri-Rolla is in the process of developing a pair of microsatellites designed to demonstrate formation flight using low-cost, off-the-shelf technologies. As part of the demonstration, a newly developed nonlinear filter named the θ- D filter, is proposed for purposes of orbit determination. This paper describes the general θ-D filter formulation, the dynamic model used for orbit determination, and a method of implementing a continuous filter in a discrete time sense. The results presented within show the effectiveness of the proposed orbit determination method