The laser-driven in-tube accelerator in which the propellant is supplied from laser-ablated gas from the tube wall was
developed. Proof-of concept demonstrations of vertical launch were successfully done. The device had a 25mm X 25mm
square cross-section; two opposing walls were made of polyacetal and acted as the propellant, the other two acrylic
window with guide grooves to the projectile. The upper end of the launch tube was connected to a vacuum chamber of
an inner volume of 0.8 m2, in which the initial pressure was set to lower than 20 Pa. With plugging the bottom end of
the launch tube, a momentum coupling coefficient exceeding 2.5 mN/W was obtained. Even with the bottom end
connected to the same vacuum chamber through a different duct, the projectile was vertical launched successfully,
obtaining 0.14 mN/W.
The aim of the present study is to clarify the time-dependent characteristics of the impulsive force generated by
irradiating a laser pulse onto metallic and polymer materials. A Velocity Interferometer System for Any Reflector
(VISAR) is employed to measure the acceleration driven by the laser ablation. The VISAR has two delay-lines that
enable the velocity measurement in the range from 10 m/s to 100 m/s. The ablation impulse is inferred from the
measured acceleration history. The influence of the ambient air on the ablation pressure is investigated for aluminum
using a Nd:YAG laser (wavelength: 1064 nm, pulse energy < 1 J, pulse duration ~ 10 ns) and for a polymer material
using a CO2 laser (wavelength: 1.06 μm, pulse energy < 10 J, pulse duration ~ 2 μs). The results of the preliminary
experiments revealed the promising potential of the VISAR measurement.
Impulse generation using laser energy has advantages for aerospace propulsion; energy can be supplied from a remote device, thereby reducing a necessary mass on board and accompanied cost; the specific input energy is not limited by inherent energy of working fluid. After Kantrowitz proposed the concept of laser propulsion in 1972, impulse generation and launch performance either with single or multiple laser pulses has been experimentally studied. Possible application of this technique ranges even to space debris de-orbiting. As the example which actually launched a projectile, Yabe conducted an experiment that 0.1-gram paper airplane with an acryl overlay was launched at about 1.4 m/s using 0.6-J-class Nd:YAG laser. In Tanaka et al.'s experiment, 7 -microgram multi-layered flyer was accelerated to about 13 km/s using 20-J-class Nd:glass laser. Myrabo, using a 10-kW-class repetitive-pulse carbon dioxide laser, successfully launched a 51-gram 'lightcraft' at about 15 m/s up to altitude of 71 m. In these experiments, the values of impulse (i.e., momentum) and momentum coupling coefficient were estimated about 0.14 x 10-3 kg-m/s, 91x10-3 kg-m/s and 765x10-3 kg-m/s and about 240 N/MW, 4 N/MW and 50 N/MW, respectively. The objective of this study is to enhance a laser-driven impulse using a 300-J-class single pulsed laser owing to fluid-dynamic process. In this paper, we discuss a high-speed launch performance of a 1-gram projectile by enhanced impulse and achieved momentum coupling coefficient which are significantly improved using fluid-dynamic effect.
The laser-driven in-tube accelerator (LITA) is a unique concept of laser propulsion. It is characterized by accelerating an object in a tube. Owing to a confinement effect, the thrust performance can be improved. This device has other advantages over the existing technology on the simplicity and suitability to environment. Experiments on the thrust performance of LITA were conducted. The thrust was determined from the object hovering condition. The measured dimensionless momentum coupling coefficient agrees between xenon and argon as the working gas. This implies that in order to obtain a high impulse chemical species with a low speed of sound is useful.
Time-resolved spectroscopy using a combination of a monochromator, streak camera, image intensifier and CCD camera is conducted to investigate the radiative flow field generated in the in-tube laser propulsion configuration. A 5-J CO2 TEA laser beam is focused through a specially-designed, double- reflection optical system in atmospheric air. Radiation emission in the wavelength range of 320 to 850 nm is observed during a typical period of 10 microseconds.
In the Shock Wave Research Center, Institute of Fluid Science, Tohoku University, a streak camera system has been used to study high-speed phenomena associated with hypervelocity flow conditions. In the different facilities available, including the expansion tube, different test conditions can be produced for the study of the shock layer around bodies. In certain extreme conditions, the flow is in non-equilibrium and the radiation inside the shock layer is strong enough to be measured by existing spectroscopic techniques. Analysis of the spectra can provide information on the properties of the gas and can be used to validate numerical models. In the present study, time-resolved spectroscopy has been carried out in order to investigate the useful test time of the expansion tube, a very important parameter in the process of calibration of this facility. A spectroscopic system consisting of an Action Research spectrograph of 500 mm focal length, a streak unit (Hamamatsu Photonics) and a CCD camera has been used to measure time-resolved spectra down to microsecond time scales. The system is also equipped with a lens-coupled intensifier of high dynamic range.
When a high speed train enters a long tunnel, compression waves which were generated in front of the high speed train, coalesce into a weak shock wave and the shock wave eventually is emitted from the tunnel exit as a sonic boom. In order to investigate the tunnel sonic boom a 1/300 scaled tunnel simulator was constructed in which a plastic cylinder slides down along a 8 degree(s) inclined long tube with a speed of 60 to 110 m/s. The high speed cylinder and the steel tube represent the train and the tunnel, respectively. Double exposure holographic interferometric flow visualization was used for clarifying the formation and propagation of weak shock waves in the scale tunnel simulator. For interpretation of behaviors of weak shock waves, a shock tube experiment was also carried out again by using holographic interferometry.