Mechanical characteristics of coupled librational and orbital motions of a large-scale spacecraft are investigated. A rigid body of an arbitrary shape is considered as a mathematical model, and a set of nonlinear equations of motion about the librational and orbital motions is formulated. Through Lindstedt’s perturbation method, approximated analytical solutions are obtained. From the analytical solutions, the conditions of instability are clarified, and the characteristics of the orbital motion are shown. The total mechanical energy has the minimum value when the librational and orbital motions coincide with the periodic solution. The formula for the total mechanical energy proves that the periodic solution is the minimum energy solution. From the nonlinear numerical investigations, it is shown that the results stated above are valid even without any approximations. The results of this study provide us the fundamental understandings of the dynamics of large-scale spacecraft in space.
Modularized structures are promising as present and future structures from the viewpoints of their high fault tolerance and easy extensible nature. Averaging interactive cooperation in the decentralized control of modularized structures is studied. The averaging interaction is defined as an interaction, which averages some physical properties of each module such as deformation, shape and stress. The most remarkable point of this study is that analogy of the heat conduction is used to realize the averaging interaction. The interaction based on a heat conduction equation enables us to grasp the physical sense of control parameters intuitively. Furthermore, the stable characteristics of heat conduction imply control stability. As case studies, two subjects are discussed: position control of the end-effector of a variable geometry truss, and deployment control of a modularized structure. Some numerical results are shown to illustrate the capability of the proposed control method.
This paper proposes a method to detect spacecraft attitude rate without rate gyros. In this method, a spatial velocimeter is applied to images acquired by a star tracker (STT), where a spatial velocimeter is normally used to detect object velocities from optical image data. The proposed method requires no priori attitude states or identification of STT acquired images. Therefore, it is directly useful for attitude rate determination right after orbit injection even when the attitude rate is relatively large.
An orbit transfer system that transports a payload from LEO to GEO using multi-stage spinning tethers is studied in this paper. We propose a tether configuration called “Balance Tether.” The variations in the total mass and mission duration of the system are analyzed for different numbers of stages and different lengths of tethers. In addition, the possibility of debris impact damaging each of several tether system configurations is also analyzed. As a result, we obtain the guidelines for a system design that minimizes total system mass while also taking into account the system lifetime as limited by debris impact. In addition, it is shown that the Balance Tether can reduce the total system mass compared to a single-tether system. The results also show the effectiveness of the spinning-tether system as compared to a conventional chemical propulsion system for the same orbit transfer mission.
This paper presents a new laminated plate theory for cylindrical bending of laminated plates. The new theory assumes that inplane displacements vary exponentially through plate thickness. The accuracy of the new theory is examined for symmetric/antisymmetric cross-ply, angle-ply and unsymmetric laminates under cylindrical bending. The numerical results show that the new theory provides displacements and stresses very accurately as compared to three-dimensional elasticity solutions. In particular, transverse shear stresses obtained from constitutive equations are predicted very accurately. The results are compared with those obtained from the first-order shear deformation plate theory and the classical laminated plate theory.
A TVD upwind scheme originally designed for compressible flow is applied to the SMAC finite-difference method for incompressible flow analysis. The receptivity and validity of this application are investigated by an evaluation of the accuracy, stability and convergence rate for the SMAC method combined with the TVD scheme. Using this method, three-dimensional developing entry flows through a square-curved duct are calculated and compared with available experimental data as well as some computational results obtained by QUICKs and third-order upwind schemes. Such comparisons show that the numerical method applying the TVD scheme has the highest computational efficiency without a sharp loss of accuracy, resulting in confidence in the application this scheme to incompressible flow computations.
In this paper, a simple and robust method of unstructured dynamic mesh with surface mesh movement method for unstructured triangle/tetrahedral meshes is proposed. The method is developed to avoid the generation of squashed invalid elements by considering each elemental shape. With several three-dimensional applications, it is demonstrated that the present method significantly improves robustness for problems concerning large body motion without much penalty in CPU time. The use of the present method for mesh movements on curved surfaces is also discussed. Its capability is demonstrated for the surface mesh movement in the tail-fuselage juncture region of an airplane.
Three types of devices were tested for their effects in reducing the strong adverse pressure gradient in a closed-type cavity with a depth of 8 mm and length-to-depth ratio of 15. The first type of control device consisted of embedding arrays of tubes longitudinally along the two sides of the cavity. It sought to move the high-pressure air at the recompression wake to the separation wake by creating a passage. The second type of control device consisted of installing a baffle plate laterally near the shock impingement line or the mid-part of the cavity floor. It aimed at changing the wave structure of the cavity flow through interfering with the reattaching or reattached boundary layer. With the third type of control device, we tried to increase the base pressure by supplementing external fluid with downstream blowing through side-holes along a lateral tube placed at the front corner of the cavity. Of the three types of control devices, the installation of tubes along the two sidewalls of the cavity was found to be the most effective in reducing adverse pressure gradient along the cavity centerline. Of the four combinations of plates installed laterally on the cavity floor, the 4-mm-high plate installed near the middle of the cavity was found to be the most effective. The relative ineffectiveness of downstream blowing near the cavity front corner is believed to be a result of the low blowing rate.
The characteristics of a laser ablation igniter were investigated systematically. This kind of igniter is expected to realize a lightweight rocket engine system that consists of many combustion chambers, such as the Reaction Control System (RCS), without having heavy spark igniters. In this igniter, ignition is accomplished utilizing a high-temperature metal vapor produced by focusing a high-intensity laser pulse transmitted through an optical fiber. The laser ablation igniter was tested in a GH2/GOx thruster (dia. 1 cm). As a result, the minimum ignition energy was found to be lower than 2 mJ, and the required ignition energy decreased with increasing pressure in the combustion chamber.