Three-dimensional aeroelastic phenomena are numerically simulated for the development of a balloon-based operation vehicle (BOV) proposed by the Japan Aerospace Exploration Agency. The structures of the all-moving tail wing composed of several materials are modeled in detail using a finite element method. The vibration modes obtained from the eigenvalue analysis of the three-dimensional solid model are mapped to two-dimensional iso-parametric shell elements for efficient fluid-structure coupled analysis using unstructured computational fluid dynamics. The methods are validated by the fluttering of the National Aerospace Laboratory wing, which has a similar planform to the BOV tail and is referred to as a standard problem. The shape of the flutter boundary is explained by the characteristic shift of the aerodynamic center. The simulation results show the BOV tail has a sufficient safety margin for flutter along the freefall flight path.
The regression rate enhancement of hydroxyl-terminated-polybutadiene (HTPB) gaseous oxygen (GOX) hybrid rocket motors was investigated experimentally in a ground testing system. The effects of the addition of nano-sized aluminum (Al) or alloyed aluminum-magnesium (Al-Mg) powder to the fuel composition, mass flux of oxygen, and the oxidizer-fuel ratio on the fuel regression rate are presented. The experiments show that multiple-start and shutdown can be realized using gaseous oxygen/RP-1 pre-mixed torch designed in the present study. The fuel surface remained hot enough during the shutdown interval to reestablish combustion if the time of motor shutdown is less than 2 s. The deduced spatially averaged instantaneous regression rate and spatially and time-averaged regression rate fit well in the trend with time. The former way to calculate the regression rate can more precisely describe the fuel combustion process. As the oxidizer-fuel ratio increased during the test, the hybrid rocket motors didn't work at the optimal oxidizer-fuel ratio, which can induce a loss of specific impulse. The addition of alloyed Al-Mg or nano-sized Al to the HTPB fuel can enhance the regression rate. The effect due to the latter is the most significant.
Gas hollow tungsten arc (GHTA) welding experiments on aluminum pipe were performed in a simulated space environment and in a vacuum at 1 G. Square butt welding joints with a non-root gap on aluminum pipes were formed by orbital welding with filler metal using a pulsed DC power supply in a vacuum chamber under 10−2 G and 1 G gravity conditions. The butt welding process during aluminum-pulsed DC GHTA welding with a filler metal was investigated by analyzing images obtained using a high-speed video camera. In addition, the macrostructure and mechanical properties of the butt welding joints were investigated. The results revealed that arc discharge and melting–solidification during pulsed DC GHTA welding were insensitive to the gravity conditions because welding is strongly affected by the impulsive arc pressure generated by the peak current. In addition, GHTA welding experiments performed in a simulated space environment demonstrated that pulsed DC GHTA welding with a filler metal can produce defect-free aluminum butt welding joints with sufficiently high strength.
The frequency of instability waves in a wake flow is uniquely determined by a logarithmic singularity of complex ray trajectories describing the propagation of a two-dimensional wave packet. Conditions for the singularity are given by simultaneous equations indicating that the group velocity and X-derivative of the complex dispersion relation for a given flow field are both equal to zero, where X is the downstream coordinate and the dispersion relation defines the complex frequency as a function of the complex wave number and X. Simple mathematical models are introduced to simulate spatial variations of the wake behind a moderately thin flat plate. Stability calculations of the model flow indicate that the logarithmic singularity is located in the vicinity of the real axis of the complex coordinate X.
A sensitivity analysis was performed using a three-dimensional code to understand the effect of doubly charged ions on the erosion of ion acceleration grids. A preliminary analysis showed that the neutral mass flow rate, estimated by assuming all the ions are singly charged, contained significant error when the doubly charged ion fraction was non-negligible. Calculations were conducted for the μ10 EM1 ion acceleration grid system with different doubly charged ion fractions. For fractions of 0.1 and 0.2, which were similar to the experimental conditions, the simulation results for the acceleration grid current and grid mass loss were in good agreement with the experimental data. Calculations showed that when the doubly charged ion fraction was reduced from 0.1 to 0, the acceleration grid current and grid mass loss changed by -14% and -18%, respectively. Further, when the fraction was increased from 0.1 to 0.2, the acceleration grid current and grid mass loss changed by +9.5% and +32%, respectively. Electron backstreaming was also found to vary with the doubly charged ion fraction: it occurred 14% slower when the fraction was decreased from 0.1 to 0 and 12% faster when the fraction was increased from 0.1 to 0.2. The structural failure of the deceleration grid was less sensitive: the deceleration grid eroded 8.3% slower when the doubly charged ion fraction was reduced from 0.1 to 0 and 8.6% faster when the fraction was increased from 0.1 to 0.2.
Shape memory alloy (SMA) actuators have been widely used for space applications. We used a SMA actuator to implement a fail-safe function on a tilt mirror mechanism for the on-board calibration of a spaceborne imaging sensor. The proposed mechanism prevents the blocking of a main optical path when the tilt mirror is stopped at a certain position during calibration. In the present work, the operation concept of tilt mirror, design, and functional test results of the tilt mirror mechanism have been introduced. The test results demonstrate that the proposed tilt mirror mechanism achieves all of the required deploying and stowing functions for on-board calibration. The use of a shape memory alloy actuator is shown to be effective for application to the fail-safe function of a mechanism driven by a geared stepper motor.
This paper presents a proposal for a split-wing aircraft. The split wing proposed is composed of a number of square plates. The distances between the square plates are varied according to flight conditions. For a flight where high efficiency is required, the distances are 0 and the characteristic of the wing is that of a wing with an aspect ratio equal to the number of square plates. On the other hand, during a flight where wind gusts are experienced, the distance is not 0 and the characteristic of the wing is close to that of a square. The split-wing enhances the flight stability of MAVs. The enhanced stability will increase opportunities where MAVs can be utilized.