A new approach, Multi-Objective Design Exploration (MODE), is presented to address multidisciplinary design optimization (MDO) problems using computational fluid dynamics-computational structural dynamics (CFD-CSD) coupling. MODE reveals the structure of the design space from the trade-off information and visualizes it as a panorama for Decision Maker. The present form of MODE consists of the Kriging Model, adaptive range multi objective genetic algorithms, analysis of variance and a self-organizing map. The main emphasis of this approach is visual data mining. An MDO system using high-fidelity simulation codes, a Navier-Stokes solver and NASTRAN has been developed and applied to a regional-jet wing design. Because the optimization system becomes very expensive computationally, only brief exploration of the design space has been performed. However, visual data mining results demonstrate that design knowledge can produce a good design even after brief design exploration.
This paper presents algorithms for the near-distance rendezvous of on-orbit-servicing spacecraft when approaching, departing and flying around a target vehicle in a circular orbit. These algorithms are based on the closed-form solution of linear Clohessy-Wiltshire equations and adapt the glideslope guidance used in the past for rendezvous and proximity operations of the space shuttle. By using the relationship of either power functions or piece linear functions between distance and speed, the multipulse glideslope approach and departure algorithms of the chaser can be applied at any time and in any direction in space for decelerating when approaching a target or a nearby location and accelerating when departing. The fly-around algorithm enables the chaser to circumnavigate a target in any plane and at any specified time. To save the pulse number for all algorithms, a way to solve the maximum allowable transfer interval between one pulse and the next one is presented, with consideration be given to the constraints about allowable safe velocity and allowable guidance error. Finally, several scenarios are simulated to illustrate these guidance algorithms.
This paper considers the joint detection and filtering problem of discrete-time stochastic systems when the measurements are interrupted in a random fashion. By formulating the measurement interruptions into two-state Markov chains, a sequential multiple model filter is developed from the Bayesian point of view. With a soft switching mechanism, the proposed filter automatically abandons the useless measurements in the interrupted time intervals, and captures the correct measurements for recursive estimation. Compared with the widely used interacting multiple model filter, the new filter has a more simple structure and requires less time for computation. A numerical example shows that the proposed multiple model filter can effectively solve the target tracking problem with interrupted range measurements.
An initial quaternion estimation method for the attitude determination of a spacecraft using an onboard star sensor is presented. In this method, we use a sequence of the number of stars in the field of view (FOV) of the star sensor as the measurement instead of the direction vector pairs of stars. A new statistical observation model is derived and coupled with the kinematics model of attitude to develop a cost function of the estimated initial quaternion. The attitude acquisition method proposed herein exploits generalized simulated annealing to optimize the cost function and find the initial quaternion. In addition, a virtual sub-FOV and its shuffling procedure for a more accurate estimation are presented. The performance of the proposed method is quantified using an extensive simulation.
This paper presents a detailed study of the two-dimensional (2D) differential geometric (DG) guidance problem, as well as its iterative solution and initial conditions. The DG guidance curvature command is transformed from an arc length system to the time domain using the classical DG theory. Subsequently, an algorithm for commanded angle-of-attack is developed to formulate the DG guidance system, whose iterative solution is established based on Newton’s iterative algorithm. Moreover, a flight control system is presented using the classical PID controller so as to form the DG guidance and control system. Finally, a new necessary initial condition is deduced to guarantee the capture of a high-speed target. Simulation results demonstrate that Newton’s iterative algorithm works well and accurately in DG guidance problems and the proposed DG guidance law exhibits similar performance to the proportional navigation guidance (PNG) law in the case of intercepting a non-maneuvering target. However, the proposed method performs better than PNG in the case of intercepting a maneuvering target.
In this paper, a Morphing-based Shape Optimization (MbSO) technique is presented for solving Optimum-Shape Design (OSD) problems in Computational Fluid Dynamics (CFD). The proposed method couples Free-Form Deformation (FFD) and Evolutionary Computation, and, as its name suggests, relies on the morphing of shape and computational domain, rather than direct shape parameterization. Advantages of the FFD approach compared to traditional parameterization are first discussed. Then, examples of shape and grid deformations by FFD are presented. Finally, the MbSO approach is illustrated and applied through an example: the design of an airfoil for a future Mars exploration airplane.
This study investigates a large reconfigurable antenna system consisting of cable networks. The beam shapes of reconfigurable antennas can be modified by changing the shape of the antenna reflectors. Two types of control actuation—one using tie cables and the other using boundary cables—are considered. For each type, two control methods are applied; they are cable tension control and cable initial length control. Numerical simulations are carried out to investigate characteristics such as robustness against disturbances and natural frequencies. The results of these simulations are compared to determine the appropriate control system of the antenna. It is shown that the tie cable control by the initial length control is preferable. In the case where the operation modes are predetermined, the boundary cable controls are also applicable.
A new constraint-handling method based on Pareto-optimality and niching concepts for multi-objective multi-constraint evolutionary optimization is proposed. The proposed method does not require any constants to be tuned for constraint-handling. In addition, the present method does not use the weighted-sum of constraints and thus does not require tuning of weight coefficients and is efficient even when all individuals in the initial population are infeasible or the amount of violation of each constraint is significantly different. The proposed approach is demonstrated to be remarkably more robust than the dynamic penalty approach and other dominance-based approaches through the optimal design of a welded beam and conceptual design optimization of a two-stage-to-orbit spaceplane.
When a satellite separates from the launch vehicle, an initial high angular rate or a tip-off rate is generated. B-dot logic is generally used for controlling the initial tip-off rate. However, it has the disadvantage of taking a relatively long time to control the initial tip-off rate. To solve this problem, this paper suggests a new detumbling control method that can be adapted to micro/nanosatellites using a pitch bias momentum system, and presents simulation results. The proposed detumbling method was able to control the angular rate within 20 min, which is a significant reduction compared to conventional methods. In addition, the momentum wheel initial start-up must be done under stable conditions, and a conventional pitch spin-stabilized initial wheel start-up method is commonly used. Since the conventional wheel start-up method cannot be used if the detumbling controller proposed by this paper is used, a method is also proposed for bringing up the momentum wheel speed to nominal rpm while maintaining stability. The performance of the method is compared and verified through simulation. The overall results show a much faster control time compared to the conventional methods, and achievement of nominal wheel speed and 3-axis stabilization while maintaining stability.
The fundamental characteristics of a laser ablation microthruster were investigated for a 10 kg-class microspacecraft. A single-shot impulse measurement was performed using a thrust stand on which a prototype thruster was installed and the associate ablated mass was estimated from the pressure increase in the space chamber. The best performance of several polymer materials was obtained using polyvinylchloride as the propellant. More heavily carbon doped polyvinylchloride showed higher performance, which means absorption length has a large effect on performance. The intensity of the laser beam on the ablation material was changed using constant laser power, and it was shown that intensity had little effect on the performance. This qualitative behavior agreed with the results of a simple thermal analysis. Mass spectroscopy of the ablation plume showed that the dominant reaction was dehydrochlorination in the range of 470 to 640 K, and the low-temperature reaction resulted in the best performance for polyvinylchloride.