The concern with a spinning tethered formation flying system has been recently growing because it can keep the formation precisely enough for synthetic aperture radar and interferometry applications. The system also attracts attention because it is expected to be able to deploy and maintain membrane structures to realize a solar sail spacecraft. This paper discusses a control method of formation deployment for a spinning tethered formation flying system. The control method is based on a virtual structure approach, that is one of various strategies and approaches for conventional multi-spacecraft formation control. We consider two types of formation deployment; spin angular velocity is calculated 1) using a tether tension profile, and 2) using an angular momentum profile. We apply the control methods to formation deployment in a circular orbit around the earth, and discuss results of numerical simulations in terms of maximum thrust and tether tension.
This paper describes a new control algorithm for achieving any arbitrary attitude and angular velocity states of a rigid body, even fast and complicated tumbling rotations, under some practical constraints. This technique is expected to be applied for the attitude motion synchronization to capture a non-cooperative, tumbling object in such missions as removal of debris from orbit, servicing broken-down satellites for repairing or inspection, rescue of manned vehicles, etc. For this objective, we have introduced a novel control algorithm called Free Motion Path Method (FMPM) in the previous paper, which was formulated as an open-loop controller. The next step of this consecutive work is to derive a closed-loop FMPM controller, and as the preliminary step toward the objective, this paper attempts to derive a conservative state variables representation of a rigid body dynamics. 6-Dimensional conservative state variables are introduced in place of general angular velocity-attitude angle representation, and how to convert between both representations are shown in this paper.
The low structural mass fraction required for future aerospace vehicles necessitates the development of new materials having improved specific properties at elevated temperatures. Fiber-reinforced titanium matrix composites (TMC) offer significant improvements in strength and stiffness over their monolithic counterparts and are prime candidates for these applications. This study was undertaken to investigate the effects of TMC processing on the axial tensile properties of unidirectional SCS-6/Ti-15V-3Cr-3Sn-3Al (Ti-15-3) titanium matrix composites. The composite was manufactured by using spark plasma sintering (SPS). The Ti-15-3 powder and SCS-6 fiber mats were consolidated by SPS at the temperature of 800, 900 and 1,000ºC, and at pressure of 30 and 60 MPa in vacuum. The tensile specimens of TMC were tested in air at room temperature, 400, 600, and 800ºC, and the resulting properties were compared to those of TMC by hot pressing. The reactions and microstructures were studied in interfaces between SCS-6 and Ti-15-3. TMC consolidated by SPS had tensile strengths of 756 to 1,570MPa from room temperature to 800ºC. The SPS provided superior tensile strengths of TMC, as compared to hot pressing.
Velocity and temperature measurements were conducted for a two-dimensional magnetoplasmadynamic arcjet with hydrogen propellant. To obtain the velocities of both atoms and ions, laser absorption spectroscopy was employed for atom, and time-of-flight technique was used for ions. In a quasi-steady operation at 13kA/0.65g/s, larger ions velocity (33km/s) than that of the atoms (13km/s) was found in the case of flared anode configuration, which implies that large mean free path between the ions and atoms prohibited momentum transfer from the ions to the neutral particles. This velocity difference was not observed in the case of converging-diverging anode, where the high-density plasma inside the discharge chamber enhances momentum transfer from ions to atoms. In addition to the velocity difference, diagnostics by probe methods revealed high ion temperature in comparison with that of electrons at the thruster exit. Using the velocities and temperatures together with the densities of each particle, energy flux of the magnetoplasmadynamic arcjet was discussed. The large energy deposition into thermal and internal energy modes near the thruster exit indicated a large amount of pressure energy that should be converted to velocity energy by an appropriate nozzle design to further improve the thrust performance.
A Whale Ecology Observation Satellite (WEOS) was successfully launched on 14th December 2002. We adopted gravity gradient attitude control technique for the attitude stabilization of the WEOS as the first trial in Japan for pointing the communications antennas toward the earth, and the GPS antenna toward the zenith. The attitude control system of the WEOS consists of a three axis magnetometer, a magnetic torquer coil, and a deployable mast with a mass fixed at the tip, and attitude control software. This system carries out rate damping control of the principal axis of maximum moment of inertia and earth pointing attitude control. Immediately after the separation from the H2A-4 rocket, WEOS tumbled due to the imbalance force of three separation springs. The tumbling was reduced by the closed loop damping control and then the mast was extended. After one week, we confirmed the establishment of the gravity gradient attitude stabilization. This paper describes the attitude control system, operation procedure, and control results.
Fundamental jet performance tests of linear shaped charges (LSC) were conducted to evaluate their jet penetration. The purpose of these tests is to enhance the penetration performance of LSC. The apparatus used for these tests were based on penetration tests for conical shaped charges (CSC). Photos of the aluminum-sheathed LSC jet taken by using flash X-ray confirmed the jet velocities to be about 2,400m/s. The velocity was also verified by the AUTODYN-2D code, and was an unexpected figure as compared to CSC. The penetration velocities of aluminum- and lead-sheathed LSC against steel plates were calculated to be less than 1,000m/s at a maximum region.
The relationship between the momentum-coupling coefficient C and the nozzle cone-angle of laser pulse-jets is investigated using Computational Fluid Dynamics. Temporal variations of thrust and pressure fields inside and outside conical nozzles are obtained, and computed C is compared with measured one. As a result, the computation well reproduces the measured C and its decreasing tendency with the nozzle cone-angle. The reason of this tendency is explained in relation to two-dimensional flow characteristics in its air-refresh process. In addition, it is suggested that the laser pulse width should be short enough that the laser-heated region can be smaller than the optimum nozzle size.