A thermodynamic assessment on space transportation systems and propulsion is proposed. Propulsion system is formulated as thermodynamic cycle independent of specific engine configurations. A thermodynamic cycle that enables space transportation systems to gain orbital energy indicates guidelines for flight path, vehicle shape, propulsion system and it provides references to compare among different type space transportation systems. This assessment is useful in a conceptual design to evaluate effectiveness of various space transportation systems. The example suggests that design flexibility of space transportation system with air-breathing propulsion is limited in spite of its high specific impulse.
For laser propulsion system, it is very important to research the most effective way to utilize the optical energy. We have simulated the propagation condition of Laser-Supported Detonation Wave (LSD) because it can cause enough high pressure and high temperature to be used by laser propulsion. In this temperature level, the main absorption mechanism is Inverse Bremsstrahlung: The laser energy is transformed into the kinetic energy of free electrons by photon absorption during electron-ion/neutral collision, which is re-distributed among heavy particles through collisions. In this paper, we numerically simulate a room-temperature Argon gas which absorbs CO2 gasdynamic laser, using a 2-temperature model. As a numerical method, we have used Harten-Yee non-MUSCL modified-flux-type TVD scheme in which real gas effects are considered.
For semiactive vibration suppression of truss structures with variable dampers, on-off control laws are newly derived suggested by the sliding-mode control theory. The control laws are shown to be in the same form as previously proposed control laws which are derived suggested by LQR control theory. The vibration suppression performances of the new control laws are investigated and compared with those of the previously proposed control laws by using numerical simulations. The results of the simulation show that the vibration suppression by the new control laws is effective and that performances of them are approximately the same as the previous laws although they result in different values of control law constants.
Spacecraft surfaces are exposed to energetic and/or reactive particles during space missions. In this study, the influences of ion bombardment on chemical structures and optical properties of spacecraft surface materials were examined. Spacecraft polymer films of polyimide BPDA-PDA (UPILEX-S (UBE)) and Teflon FEP (DAIKIN) were exposed to oxygen and nitrogen ion beams with 0.5 and 1.0keV under a dose of 8.2×1016ions/cm2. The in-situ X-ray photoelectron spectroscopy and quadrupole mass spectrometer analyses showed that an addition reaction and a desorption of structural components occurred by ion bombardment and that the spectral transmittances of the films were decreased. They are expected to cause the decrease in the performance of spacecraft thermal control.
Damping property of composite laminates with very flexible interlayer of very high damping coefficients under longitudinal excitation is studied analytically. Insertion of interlaminar damping sheet (s) inside beams and plates is said to little improve the damping performance for longitudinally excited members such as truss elements, though it dramatically increases their damping performance for bending vibration. However, the composite laminates with interlaminar damping sheets may have high damping capability owing to its inhomogeneity even under longitudinal excitation. Present paper shows the possibility of the improvement of damping property due to the interlaminar damping sheet (s) under longitudinal excitation through a derivation of an approximate expression of the damping property of angle-ply laminates based on a quasi-static assumption. A governing factor of the damping performance of the laminates is obtained and geometrical and material properties necessary to get sufficient improvement is explicitly given. The approximate solution shows a good agreement with the results of a finite element analysis.
The interaction between combustion and flowfield in a rectangular scramjet combustor is investigated experimentally and numerically. The combustion mode is categorized into two modes; one is intensive combustion (IC) mode and the other is weak combustion (WC) mode. In IC mode, large separation region is generated by the precombustion shock wave, and fuel is rolled up and transported toward the core of the main airflow. The combustion is controlled by the rate of mixing, and both the mixing efficiency and the combustion efficiency are high. On the other hand, in WC mode, the fuel reacts gradually in the shear layer at the downstream of the step and the rate of heat release is low. The combustion is controlled by the rate of chemical reaction of the mixture generated in the shear layer, and the mixing efficiency and the combustion efficiency remain low.
An igniter tube is newly installed into a rectangular cross-sectional ram accelerator working in Hiroshima University to accelerate successfully a two-dimensional sharp-wedged supersonic projectile under the thermally choked propulsive cycle. This new ignition mechanism is designed to initiate combustion and to prevent the transition from combustion to detonation in the ram acceleration tube. An over 10.000G acceleration has been achieved in a 2m long tube filled with CH4+2O2+5.5CO2 mixture at 0.45MPa when the projectile weighing 6g has been launched into the ram acceleration tube with entrance velocity around 1km/s. The flowfield and the combustion zone around and behind a projectile have also been measured at several measurement stations by a pressure transducer, a luminosity detector and a magnetic detector which were placed at each station.
Contamination produced in a discharge chamber of an ion thruster was experimentally investigated using carbon-carbon composite grids. The contamination was caused by the grid material that was damaged and eroded by the ion sputtering. The contaminant has the possibility to cause the electrical short between the electrodes, resulting in a total loss of the ion thruster system. For avoidance of such an accident, the statistical features of the carbon contaminant were evaluated.