Laser propulsion powered by a CW laser has been studied. Thruster performance and energy balance in the thruster were numerically computed. Laser beam optics, inverse-bremsstrahlung absorption, ionization/recombination reactions, radiation, heat conduction, and convection have been modeled. Computational stiffness resulting from the very small flow speed has been overcome by using a flux vector splitting implicit scheme with a large CFL number. The computed positions of the Laser Sustained Plasma (LSP) in the thruster show good agreement with the measured ones. The estimated energy conversion efficiency was 23%, and the rest of the input power was lost as radiation from the LSP and also carried by the laser beam passing through the LSP.
The aerodynamic heating of a super orbital reentry capsule for MUSES-C is numerically studied by using full viscous-shock-layer (VSL) equations with an 11 air-species model. With a three-temperature model, the thermal nonequilibrium effect is considered. Temperatures, chemical species, and energy exchange rates at three typical altitudes, 74 km, 64 km, and 54 km, are discussed to understand how thermochemical nonequilibrium phenomena change along the reentry trajectory path. The convective and radiative heat fluxes to the wall of the MUSES-C capsule with a 0.2 m nose radius are examined under both noncatalytic wall (NCW) and fully catalytic wall (FCW) conditions. The maximum heat fluxes estimated for FCW and NCW are 8.7 MW/m2 and 6.1 MW/m2 at the altitude of 56 km. The radiative heat flux at the stagnation point of the capsule has also been calculated, and the maximum radiative heat flux of 0.9 MW/m2 has been found at the altitude of 62 km. The intensity of UV and VUV spectra are extremely intense; thus UV and VUV spectra mainly contribute to the radiative heat flux.
The guidance law design problem is formulated as a disturbance attenuation L2 gain control problem where target accelerations are regarded as unpredictable disturbances that are completely unknown, but bounded and guidance parameter errors are viewed as bounded control system parameter uncertainties. By using a Lyapunov-like approach to find the feedback control, a guidance law satisfying the L2 gain performance is derived from a linear time-varying mathematical model that describes the missile-target engagement. During the derivation of the guidance law, its robust stability is proved. Simulation results show that the presented guidance law provides strong robustness properties against heading error, guidance parameter errors, and target maneuvers; thus they obtain excellent miss-distance performance over the conventional realistic true proportional navigation guidance law.
Deployment behavior of modularized space structures is analyzed from the viewpoint of dynamic and simultaneous deployment. Actuators, which are attached to each substructure individually, realize the decentralized and simultaneous deployment. Elastic panels with double-accordion folding pattern are examined as an example of modularized structures. Corresponding analytical model is derived from the hybrid variational principle. At first, the deployment behavior of one module is simulated numerically to analyze the deployment characteristics of the double-accordion folding. The influences of panels’ shape and flexural rigidity on the deployment characteristics are clarified. Furthermore, the deployment behavior of multi modules is simulated numerically to analyze the synchronism of the deployment. It is shown that high flexural rigidity of elastic panels improves the synchronism of the deployment, and the strain energy of each module depends on constraints of the module. The synchronism of the deployment and the distribution of the strain energy are then considered qualitatively for general dynamic and simultaneous deployment.
A theoretical attempt is made to describe local and propagating-wave disturbances with the method of complex characteristics and to examine whether the so-called absolute instability can occur in three-dimensional boundary layers whose basic state and stability properties vary in a specific direction of space. With a complex dispersion relation including one space variable, zeros of the complex group velocity are found not to produce such a drastic phenomenon as the absolute instability predicted in the parallel-flow problems studied so far. This is because the group velocity in the neighborhood of a zero varies in proportion to the square root of the distance from the zero.
Rotating-disk flow is taken as a typical example of three-dimensional boundary layers. Numerical computations of localized disturbances according to the propagation theory given in Part 1 are made with a simplified system of stability equations to show if the conditions of absolute instability can be satisfied in this simple flow. The results indicate no such particular amplification of disturbances near a zero of the complex group velocity. It is also shown how initially localized disturbances propagate and develop into quite a large amplification of some limited wave-number components at a downstream station.
This study proposes an application of the electrodynamic tether to deorbit a spent H-II upper stage to reduce space debris. In such an application, the induced current flows through the tether wire by the tether motion that intersects the geomagnetic field, and the Lorentz force is induced in the opposite direction of tether motion, namely, the direction of the decelerating system, by the interaction between this induced current and the geomagnetic field. The concept is basically the same as that of a ProSEDS space experiment, which is proposed by NASA’s Marshall Space Flight Center. But the main difference is its orbit. The orbit of spent H-II upper stage is ellipse, although the orbit of ProSEDS is circular. So the operation and dynamics are different compared with those of ProSEDS. In this study, the performance of an H-II upper stage deorbit system by electrodynamic tether is analyzed by the mission analysis model, and the presumable dynamics of this system is also shown. The results show that this system can deorbit an H-II upper stage in a few months, but there is a possibility that the performance of deorbit will degrade if a rotation of the tether system is occurred.
It is well known as the coning effect that even the motion around an axis with no angular rate results in the residual rotation when it resumes the original orientation. However, there has been little investigation concerning the residual rotation when the motion is not closed and does not resume the original orientation. A definition of rotation angle is newly proposed in this paper, and the calculation method of the rotation angle is shown. The new attitude reference system with a one-degree-of-freedom platform was developed using the rotation angle defined in this paper and two parameters showing the rotational axis orientation. The attitude reference system was actually onboard the M-rocket, and it worked well.
The fuzzy control law to improve dutch roll characteristics of aircraft was designed and its control performance was evaluated. First, the control law was designed for a small-high speed aircraft at low altitude and low-speed flight conditions. The control law was then applied to flight conditions from minimum speed to supersonic speed and from sea level to high altitude. The control performance for these conditions was evaluated. Furthermore, this control law was adapted to a large transport aircraft with no parameter changes. The evaluation showed good control performance to improve the dutch roll characteristics under all flight conditions for both small high-speed aircraft and large transport aircraft without the parameter changes. This means that the fuzzy control proved to provide effective flexible application to aircraft stability augmentation. If an aircraft in actual flight is in strong air turbulence, inputs to the fuzzy controller may exceed the limit of its effective range. To cope with this problem, the countermeasures were introduced, their methods tested, and their effectiveness proved.