For a reusable space plane, the GPS navigation is essential to perform an accurate onboard navigation. Moreover, if the GPS navigation with the differential GPS technique performs high navigation accuracy and can be applied to the landing phase, the onboard GN&C system of a space plane is simplified and its weight is reduced. The National Space Development Ageacy of Japan (NASDA) and the National Aerospace Laboratory (NAL) have been studying the GPS navigation for an automatic landing. As one of the research items of the Automatic Landing Flight Experiment (ALFLEX), we designed and manufactured the pseudolite DGPS system for ALFLEX and evaluated its function and performance using real flight data. This paper presents mainly the system design results of the Pseudolite DGPS System for ALFLEX. And as the evaluation of these designs, the results of the ground experiment and the flight experiment by airplane are described.
A shock-shock hot interaction problem is studied numerically. A high-order Godunov-type scheme coupled with solution-adaptive unstructured grids has been employed to compute a hypersonic thermochemically nonequilibrium viscous flow; the impinging shock generated by a wedge interacts with the bow shock around a 2-D circular cylinder. The dynamic grid adaptation to solution and the high-resolution methods contribute to a considerable improvement in both accuracy and efficiency. High-temperature real gas effects have been evaluated by a thermal and chemical non-equilibrium model. Type IV interaction of Edney near the transition between Type III and Type IV is obtained. The shock interaction structure is clearly captured with high resolution.
The main feature of one-shot thrusters is discreteness in both time and space domain. We apply discrete-time sliding mode control to the attitude control of a spinning vehicle. And we consider the space discreteness by applying a simple selection algorithm (SSA) to the sdection of the combination of one-shot thrusters prearranged on the vehicle in order to generate the control force. SSA is the new algorithm we proposed, and its calculation load is light in computation load. We adopt a regulator scheme to reject disturbances of precession for a LUNAR-A type penetrator, and conduct numerical simulations of the problem to show the effectiveness of the proposed control algorithm for one-shot thrusters.
Inter-satellite communication instruments require a very-high pointing stability and accuracy, for example, on the order of one micro-radian. This is reachable by means of controlling the employed FPM (Fine Pointing Mechanism) in a wide frequency range. The Japanese Experimental Module (JEM) of the International Space Station will have larger vibrational disturbances than general satellites. When these larger vibrational disturbances occur, it will not be adequate to make a high gain controller suppress these disturbances in a wide frequency range for the precise pointing system. Therefore, we prepose the use of a vibration isolator, which is effective for laser communication instruments, to reduce the transmission of vibration from the spacecraft body such as JEM to the pointing system. The vibration isolator we have developed can attenuate disturbances for six degrees of freedom. This paper describes the mechanism, a hybrid control method that consists of passive and active controls, and experimental resul s. The experimental results for properties of the vibration isolator indicate that under severe vibrational circumstances, the vibration isolator can be effective in reducing the transmission of vibration to sensitive instruments. This work was performed under contract with the Communications Research Laboratory.
The purpose of this study is to design a stabilizing controller of the longitudinal motion of a flying vehicle in ground effect and validate it's properties by experiment. The aerodynamic coefficients are nonlinear to height, which result in a substantial change of the characteristics of motion. Nonlinear simulations and stabilizing experiments in ground effect are carried out. These results demonstrate that H∞ controller based on the normalized coprime factorization is effective to control the vehicle in ground effect.
This paper presents results of an experimental study on the buckling of circular cylindrical shells loaded simultaneously with a bending moment and a compressive force. A high precision loading apparatus was designed, by which both the torque and the axial compression can be applied equally on both ends of the cylinder, so that the state of the bending under axial compression is established in the cylinder. Test specimens were made from polyester films, which had length-to-diameter ratios of 2, 5 and 10 and a diameter-to-thickness ratio of 300. In the experiment, the axial force was applied to induce axial stress varying in the range from 0 to 50% of the classical buckling stress. It has been shown that the buckling occurs when the bending stress added to the compressive stress approaches to the classical buckling stress. The experimental buckling stresses were compared with theoretical ones obtained by solving Budiansky's non-linear shell equations numerically.