The rest-to-rest maneuver problem of the flexible space structure is the two point boundary value problem (TPBVP) and is solved by some gradient methods. If TPBVP is strongly restricted by the constraints, TBVP becomes ill-defined problem, and the solution meeting all constraints cannot be obtained. However, reasonable suboptimal solutions are often needed since real plants are necessary to be controlled. In order to obtain such suboptimal solutions, we have developed a modified version of the hierarchy gradient method by installing fuzzy decision logic. Constraints are classified into non-fuzzy constraints and fuzzy constraints according to their priorities. Fuzzy constraints having trade-off relationship with each other are compromised reasonably by fuzzy decision logic. The usefulness of the proposed method is numerically and experimentally demonstrated by applying to the rest-to-rest slew maneuver problem of a flexible space structure, where fuzzy constraints are final time, sensitivity of residual vibration energy with respect to the structure frequency uncertainty, and maximum bending moment at the root of flexible appendage.
The effectiveness of a method to improve the precooler performance under frosting condition was investigated by experiments on a sub-scale heat exchanger model. Addition of a methanol proved to be most effective compared with other possible substances in both cases of low and high cooling wall temperature. Then the effectiveness of the methanol addition was ascertained for the practical condition that means the same tube configuration and flow velocity as the precooler designed for the ATREX engine firing test model. The result showed that the addition of the same quantity as the water vapor could restrain the frost layer from choking the flow in the duration of 300 seconds, which is sufficient time for precooler operation. The required methanol mass along the ATREX engine flight path was estimated to be less than 3% of fuel hydrogen on board. Accordingly, the method came to be promising candidate for practical application.
Thrust performance and internal efficiencies of a Hall thruster using oxygen as the propellant were investigated experimentally. The thrust efficiency reached at 9% with the specific impulse of 1,000s. The relatively poor performance is due to low propellant utilization, which is 45%, in comparison with that in the case of xenon propellant. The propellant utilization increased with mass flow rate and discharge voltage. The optimum channel length for oxygen was found longer than that for xenon, which was 12mm. The use of BN・AlN for the channel wall results in higher propellant utilization than that of BN for channel wall.
This paper discusses on the minimum energy maneuver of a satellite using two reaction wheels. The problem is a rest-to-rest maneuver around the axis, which is perpendicular to each wheel axes. The attitude of satellite is described using the parameters that are presented by Tsiotras et al. The parameters are useful for the description of maneuvers by two wheels. The relation between the optimal maneuver and the moment of inertia is shown analytically and numerically. The results show that the symmetry satellite whose all moments of inertia are same does not have a unique optimal solution. A group of minimum energy trajectories exists. On the other hand, the asymmetry satellite has a unique optimal solution. The numerical solutions show that the wheel on the axis of smaller moment of inertia consumes more energy than the other wheel.
Precise normal acceleration control is essential for missile guidance. Missiles with both front and rear control surfaces have a higher ability to control normal acceleration than missiles with front or rear control surfaces only. From the viewpoint of control, however, the control problem becomes a two-input-one-output problem, where generally control input cannot be determined uniquely. This paper proposes controlling angle of attack as well as normal acceleration, which makes the problem a two-input-two-output one and determines the controls uniquely. Normal acceleration command is given by a guidance system, but angle of attack command must be generated in accordance to the acceleration command without affecting the normal acceleration control. This paper also proposes such a command generator for angle of attack. Computer simulation is conducted using a nonlinear missile model to investigate the effectiveness of the control system along with control systems designed using three other methods.
A cracked plate under tension could manifest a local buckling along the crack due to a compressive stress field in the crack’s vicinity. Crack length and location, loading condition, as well as aspect ratio, thickness, and overall dimensions of the plate are among the contributing parameters to the local buckling characteristics. In this study, the buckling characteristics of a cracked plate on whick the crack’s orientation is not perpendicular to the tensile loading were xs examined. Elastic-plastic buckling analyses of a plate with an oblique crack were conducted by taking into account the effect of the plasticity of the crack tip regions on the local buckling. The elastic-plastic analysis results were compared with experimental results as well as with an elastic buckling analysis. This study reveals that the oblique angle of the crack contributes significantly to the characteristics of the buckling behavior.
An angular momentum control of a tumbling spacecraft by applying repetitive impulses from a space robot arm is discussed. By assuming inputs by the arm, the direction, size and timing of the input forces are relatively free to choose. At each control timing, however, torques parallel to the contact direction cannot be generated. Therefore, the design of controller is not straightforward. To solve this difficulty, the equations of rotational motion are rewritten into simpler forms by applying appropriate coordinates transformation. Then a discrete controller is designed so that the component of the angular momentum parallel to the contact direction is damped out by choosing the directions of input forces properly. The closed loop characteristics considering constant disturbance torques and contact model uncertainty are discussed. Numerical simulations are given to show that the angular momentum is efficiently damped.
The radiative heat transfer is a dominant heat transfer mechanism at high temperature in the insulation materials of the thermal protection system (TPS) of reentry vehicles because of the high porosity of the materials. It has been well known that serious problems come out when a simple heat conductive analysis is conducted with a thermal conductivity measured by a usual static method and that one should take into account the coupling of radiative and conductive heat transfer in the thermal analysis of such insulations. A finite element code for the combined radiation-conduction analysis is developed. A series of experiments with ceramic tile insulator is also conducted to obtain the fundamental radiative heat transfer properties and to examine the validity of the developed FE program.
When a glow discharge is generated across a shock wave in hypersonic flows, the wave is visualized as a nonluminous layer in a uniformly luminous positive column. In this report, a tentative theory that explains why the wave is visualized as stated above is proposed. The idea is as described below. A space charge layer produced due to discontinuity of electron density Ne at the wave lets itself keep off the electrons that is fast thermally enough to excite molecules to radiative states. Consequently the nonluminous layer is observed along the wave surface. To verify the idea, an analysis on two regions upstream and downstream the wave in the positive column is carried out applying Schottky theory. The analysis shows that the electron temperature, the electric field, and the Ne change across the wave discontinuously. The discontinuity of the Ne causes the diffusion of the electrons, and consequently the space charge layer is produced.
Recently, some feasibility studies on a regional positioning system using the quasi-zenith satellites and the geostationary satellites have been conducted in Japan. However, the geometry of this system seems to be unsatisfactory in terms of the positioning accuracy in north-south direction. In this paper, an augmented satellite positioning system by the High Altitude Platform Systems (HAPS) is proposed since the flexibility of the HAPS location is effective to improve the geometry of satellite positioning system. The improved positioning performance of the augmented system is also demonstrated.