The flow field in a micro arcjet thruster using argon as propellant was analyzed numerically using the Direct Simulation Monte Carlo (DSMC) method. Subsonic inlet conditions were imposed to correctly simulate the actual flow inside the thruster. It was assumed that the input power was partitioned to propellant molecules to change their thermal velocities. Wall temperature was determined by the balance of conductive heat flux and radiative heat release. The primary purpose of the present work is to investigate the effects of the nozzle half-cone angle and input power on thruster performance characteristics. The results provide engineering direction to the micro arcjet thruster design.
We examine the stability of three-dimensional supersonic boundary layers over an infinite swept wing made from the semispan model of the NAL supersonic experimental airplane. The original wing was designed so as to suppress both streamwise and crossflow instabilities under cruise conditions. It is confirmed through linear stability analyses of the full boundary layer and the boundary layer without crossflow that the spatial growth of first-mode waves in the full boundary layer is mainly due to streamwise instability and restrained near the design angle of attack.
This paper proposes a new localization method based on the Particle Filter algorithm for intravehicular robots flying inside space vehicles, such as the International Space Station (ISS). Since safety requirements are strict in space vehicles, the development of an accurate and robust localization method is a significant issue. The robot must be capable of actively sensing the environment in order to localize itself, because in general there are no external devices such as beacons that provide positional information. Thus, we have assumed that the robot has only sonar sensors for estimating its position and attitude in three-dimensional space. We developed a simulation environment for evaluation of the proposed method. It should be noted that the proposed method can solve the so-called global localization problem in an environment including some unknown objects.
A generalized scheme based on variable structure output feedback control (VSOFC) and input shaping (IS) technique has been proposed for rotational maneuvers and vibration suppression of an orbiting spacecraft with flexible appendages. The proposed control design process is twofold: design of the attitude controller followed by the design of a flexible vibration attenuator. Based on VSOFC theory, the attitude controller using only the attitude and angular rate measurement consists of linear and discontinuous feedback terms. The linear and discontinuous feedback gains are designed so that the sliding surface exists and is globally reachable. With the presence of this attitude controller, an additional vibration attenuator using input shaping technique is designed to eliminate unwanted flexible modes of vibration while achieving the desired closed-loop motion by producing a command profile that only requires information about the natural frequency and damping of the closed-loop system. The proposed control strategy has been implemented on a flexible spacecraft, which is a hub with a cantilever flexible beam appendage and can undergo a single-axis rotation. The results have proven the potential of this approach to control flexible spacecraft.
Increased space activity has frequently caused satellites to enter the wrong orbits for their missions and become stranded due to rocket failure. Therefore, a rescue system is needed to tow them back to their appropriate orbits. Manipulator capture using visual servoing is one of the most promising ways to capture a stranded satellite with no mechanical interface or visual marker. A study is being conducted to design a manipulator-based capturing system that focuses on the final tracking and capturing of non-cooperative targets and allows for special aspects, such as lighting and available computing power in space. This paper presents the results of our experiments and an explanation of the system.
Thrust performance and operating conditions of a dual-mode engine were calculated with a one-dimensional flow model. Pseudo-shock in the isolator in the ramjet mode was modeled with the momentum balance model. The decelerated air at the end of the pseudo-shock showed the highest pressure in the engine in the ramjet mode. The effects of height of the inflow boundary layer, combustion efficiency, and angle of attack were investigated. Larger thrust was produced with larger angle of attack, while specific impulse was unaffected by the angle of attack but by the contraction ratio of the engine. A small change in the combustion efficiency induced a large change in the position of the pseudo-shock in the isolator. Thrust in the ramjet mode was almost the same as that in the scramjet mode at the same flight Mach number.
Aluminum alloys have been used widely in constructing various space structures including the International Space Station (ISS) and launch vehicles. For space applications, welding experiments on aluminum alloy were performed using the GHTA (Gas Hollow Tungsten Arc) welding process using a filler wire feeder in a vacuum. We investigated the melting phenomenon of the base metal and filler wire, bead formation, and the effects of wire feed speed on melting characteristics. The melting mechanism in the base metal during the bead on a plate with wire feed was similar to that for the melt run without wire feed. We clarified the effects of wire feed speed on bead sizes and configurations. Furthermore, the butt welded joint welded using the optimum wire feed speed, and the joint tensile strengths were evaluated. The tensile strength of the square butt joint welded by the pulsed DC GHTA welding with wire feed in a vacuum is nearly equal to that of the same joint welded by conventional GTA (Gas Tungsten Arc) welding in air.