An impulsive glow discharge technique is proposed to visualize shock waves around models in short duration hypersonic facilities. To clarify the characteristics of the discharge generated across a shock wave in hypersonic flows, gap voltage and current measurements are carried out. It shows a constant voltage characteristic of a typical normal glow discharge, that is, when the gap current increases, the gap voltage is kept constant. A shock wave is visualized as a nonluminous layer in its uniform positive column region. The shock wave inclination angle generated around a flat plate agreed well with that predicted by oblique shock wave theory, namely, the glow discharge did not distort the shock shape. The ratio of the electric energy discharged into the flow to the total enthalpy is found to be at most 0.1.
Gravity gradient stabilization is applied to from small satellites to large space structures because energy is not necessary for attitude control and actuator is not either. The stability and accuracy of attitude depend on the mass property of satellite. Large moment of inertia is selected for suppression of the attitude error due to external disturbance torque. ‘Gravity gradient boom’ is often attached on the main body of satellite for this purpose. This paper discusses on the relation between mass property of gravity gradient boom and attitude accuracy using transfer functions from the disturbance forces to the attitude angles. The results show that gravity gradient boom does not always improve the attitude accuracy. For satellites with a long or heavy gravity gradient boom, the second orbital mode of roll and yaw angles are excited by solar radiation pressure torque when the orbit of satellite goes through the shadow of the earth.
This paper presents a method of designing and keeping three-dimensional flyaround trajectory for a space robot (chaser) flying periodically around a malfunctioning satellite (target) on a circular orbit around the earth. The trajectory is designed by considering orbital dynamics of the chaser represented by the Hill’s equation. An optimal feedback control scheme for the thrust is proposed to maintain the designed trajectory in the presence of disturbances. The extended Kalman filter is employed to estimate state and control variables which are not available for measurement. Simulation results that verify the trajectory keeping capability of the proposed thrust control are also presented.
The Structures and Materials Research Center of the National Aerospace Laboratory of Japan (NAL) and Kawasaki Heavy Industries, Ltd. (KHI) conducted the 2nd vertical drop test of a fuselage section cut from a NAMC YS-11 transport airplane in July 2002. The main objective of this test program was to obtain background data for aircraft cabin safety by drop test of a full-scale fuselage section and to develop computational tool for crash simulation of aircraft fuselage structure. The test article including seats and anthropomorphic test dummies was dropped to a rigid impact surface by free-fall method at a velocity of 7.6m/s (25ft/s). The impact environment and the resultant response of the fuselage structure and the passenger dummies were considered to be severe but potentially survivable. A description of the results of the 1st drop test and the 2nd drop test is presented in this paper.
A new calculation method of supersonic/hypersonic flows based on the finite element method (FEM) has been developed. In this study, the pressure term of Navier-Stokes equations was included in the flux vector Gi expressing by the stress tensor. By doing this scheme, the pressure term could be expressed as a non-differential form. This treatment made it possible to calculate supersonic/hypersonic flowfields with high speed, little discrepancies, and good stability, compared with previous simulations by the FEM. The correctness of the calculated results was confirmed by comparing shock shapes obtained by the schlieren system and by comparing streamlines obtained by the electric discharge method. As a demonstration of the new calculation method, a stabilization time of wake behind a hypersonic MESUR capsule model was investigated.
We examined hyper-velocity impact tests for CFRP (Carbon Fiber Reinforced Plastics) laminates using laser accelerated multi-layered flyers. The multi-layered flyer consists of three layers; aluminum (Al), polyethylene (CH) and Al. The third layer of the flyer can be accelerated to hyper-velocity by irradiation of a high-power pulsed laser. The thickness of each layer was designed on the basis of the results of numerical analyses. The velocity of the flyers measured in experiments was more than 23km/s using a 30J laser beam. The damages and fracture, such as crater, delamination, spallation and fiber breakage, were observed in the CFRP target after the experiments. It is considered that, in the three-layered flyer impact tests, hyper-velocity damage and fracture occurred according to a series of fracture processes; (1) spallation, (2) crack propagation by shear, (3) fiber kinking and breakage. These processes are similar to those of the Al mono-layered flyer impact tests.
Impulse generation experiments of a liquid propellant laser thruster were conducted using glycerin propellants in the energy range of 60mJ–60J. Momentum coupling coefficients and specific impulses were obtained from impulse and propellant mass measurements. The maximum specific impulse was 18s at the laser beam energy of 55J. Experimental data were scaled in terms of energy and the radius of the glycerin droplet to extrapolate laser thruster performance. The results indicate that the radius of the glycerin droplet must be less than 0.24 mm in these experiments to achieve specific impulse more than 1,000s that will be required to compete with other space propulsion systems.