Daisuke Abe
(Aoyama Gakuin University, Japan)

A low-ballistic-coefficient atmospheric-entry system using a flexible aeroshell has an attractive attention as an innovative space transportation system because it can reduce the aerodynamic heating. While this system requires large and light weight, it has to withstand the aerodynamic force during atmospheric-entry. An inflatable structure is considered as one of solutions that meet the contradictory requirements. Because the characteristics of the inflatable structure in hypersonic flow are less obvious, the hypersonic wind tunnel test was carried out using 10cm-dimameter spherical inflatable models made by Silicon film and ZYLON textile. In this experiment, the model surface temperature was measured by the infrared thermography and the inner pressure was monitored to confirm the health of inflatable structure. The spherical inflatable model was stable in hypersonic flow. Though the surface temperature reached almost 500 degrees Celsius by being exposed to hypersonic flow in 30 seconds, the airtight of model could maintain. The surface temperature history was measured by changing the combination of the layers of the inflatable structure and the uniform flow condition. The date will be compared with the numerical analysis considering the heat conduction of inside of inflatable structure in order to predict the aerodynamic heating environment of inflatable structure.

Kensaku Tanaka
(The University of Tokyo, Japan)

A laser driven plasma wind tunnel is one of promising ground test facilities for developments of thermal protecting systems. It has several advantages including higher total pressure than atmosphere, availability of active gases and low contamination of flows over conventional plasma wind tunnels. In our previous study, 2 kW class CO2 laser was used to generate laser sustained plasma (LSP) and high enthalpy flows were successfully produced. Although the CO2 laser is currently lowest in cost per unit power, toward the development of a future plasma wind tunnel, it has some problems such as an upper power limit, an apparatus size and difficulty of maintenance due to special infrared optics. Then, we focus on a high power diode laser as an alternative. Its advantages are compactness, high power efficiency, a prospect for higher power in future, and flexibility of optical systems. Because of its wavelength in the visible region, however, the energy conversion efficiency through inverse bremsstrahlung might be lower than that of CO2 laser, resulting in more severe generating conditions of a LSP. In this study, we experimentally examined LSP generating conditions using the 250 W class diode laser, parametrically varying pressure, mass flow rate and gas species.

Kenta Gibo
(University of the Ryukyus, Japan)

Re-entry capsule has a heat shield system to protect inner equipments against severe heating environments during re-entry. Charring ablator is usually used for the heat shield system. In order to design the ablator, it is necessary to predict the thermal behavior during re-entry of the capsule by ablation analysis. The computer code for charring ablation and thermal response analysis is developed for simulation of one-dimensional transient thermal behavior of charring ablation materials. This paper describes the mathematical model for the charring ablation code including basic equation and computational method of ablation analysis. Analytical solutions of several thermal response problems are compared with numerical results. The agreement is found to be very well. A new ultra light weight phenolic carbon ablator called LATS (Lightweight Ablator series for Transfer vehicle) is recently developed. Arc-heated tests of the ultra light weight ablator are carried out and measured results of the temperature response, surface recession and mass loss data are compared with the simulation results of the ablation analysis, using the mathematical model. The validity of the mathematical model is discussed based on the evaluation of the comparison between the results of arc-heated test and simulation.

Satoshi Nomura
(The University of Tokyo, Japan)

At the ground testing of the thermal protection system of reentry vehicles, the arc heated wind tunnel is used and it is important to put the material at the uniform region of the plasma flow. Thus the radial distribution of the flow parameters such as temperature, number density and velocity should be investigated in detail. Spatially resolved and non-intrusive measurement has been achieved by the Abel inversion with the laser absorption spectroscopy. But the Abel inversion is sometimes sensitive to the noise and it is difficult to estimate the error at the measurement. In this work a new spatially resolved technique is achieved by using the saturation absorption spectroscopy. The schematic of this technique is shown in Fig. 1. At the point where two laser beams crosses the saturation occurs. By comparing the result of non-saturation absorption spectroscopy and saturation absorption spectroscopy, the spatially resolved absorption profile can be obtained. In this work this measurement is applied to the arc heated wind tunnel and the distribution of temperature is obtained then compared with the result obtained by the Abel inversion.

Daisuke Harada
(Ryukoku University, Japan)

The toroidal ballute is an inflatable large aerodynamic decelerating device that can enhance the drag force. Figure shows the schematic view of reentry vehicle system with the toroidal ballute. The reentry vehicle is consisted of the reentry capsule, the cable and the toroidal ballute. The device can be deployed when it is necessary. The ballistic coefficient of the toroidal ballute is much smaller than that of typical reentry vehicles because the device is very large and light. Thus, both reentry heating and reentry deceleration can be reduced effectively by using the toroidal ballute. In this study, we performed the wind tunnel testings in the University of Tokyo. We evaluated the appearance of the shock wave and the aerodynamic characteristics of the test model. The experimental results showed that the L/D increases when the toroidal ballute was tilted and the maximum value of L/D was 0.23 at the tilt angle of 30 degree. Additionally, the pitching motion of the reentry vehicle with the tilted toroidal ballute was measured. The results showed that even with the tilted ballute the pitching motion of the vehicle was found to be stable.

Fumiaki Niwa
(Teikyo University, Japan)

It is necessary to reduce both of aerodynamic drag and heating in the ascent flight for accomplishment of the future space-plane. However, especially the reduction of aerodynamic drag is focused in this study. For the purpose of such requirement, the concept of Directed Energy Air Spike (DEAS), which makes a virtual spike by applying a heat source forward of the vehicle with use of high power laser, is applied. Experiment using a hypersonic wind tunnel of Mach 7 is conducted to study the effect of reduction of aerodynamic drag by DEAS. The experiment aimed to compare the results of effects by DEAS with actual aero-spike. Obvious favorite results have not been obtained because the period of presence of laser plasma was too short to acquire a reliable measurement. But it succeeded in taking a picture of the shock wave by laser breakdown when the wind tunnel does not run with the high-speed camera using the Schlieren system. While the wind tunnel is running, the laser plasma could not be established, because the pressure inside the test section is very low as 200[Pa]. If those issues described above are solved, the expected outcome of reduced drag is considered to be achievable.