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a0: speed of sound in ambient air Cd: drag coefficient Cm 1⁄4 I=E: momentum coupling coefficient D: quasi-steady-state drag d: diameter of flyer disk E: laser pulse energy effectively incident on flyer disk I: impulse m: mass of flyer disk t: time elapsed after U attains U0 U: flyer disk speed U0: peak value in U UTOF: flyer disk speed determined by time-of-flight method m: mass reduction of flyer disk (or separate ablator) after laser pulse irradiation x: distance from initial location : constant, Eq. (4) 0: density of ambient air Subscripts 1: sensor 1 for time-of-flight method 2: sensor 2 for time-of-flight method Impulse generation using laser energy from a remote device has several advantages in aerospace propulsion, such as remote manipulation ability and vastly reduced onboard mass (along with accompanying cost). Moreover, the specific input energy is not limited by the inherent energy of the working fluid. After Kantrowitz proposed the concept of laser propulsion in 1972, impulse generation using laser pulse irradiation has been examined experimentally using various configurations, such as ballistic pendulum tests, flyer (including micro-airplane) launches, and vertical launches with repetitive laser pulses. This technology even holds promise for removal of space debris. Since laser impulse generation has nonlinear characteristics, laser pulse energy is an important parameter to specify. For example, in order to obtain an impulse on the order of 0.1Ns, which corresponds to a speed increment of 100 m/s for a 1-g mass, a laser pulse with an energy on the order of 100 J or more is required. To our knowledge, laser impulse generation under such conditions is not reported extensively in the open literature. The objective of this study is to obtain a large impulse using a 300-J class single-laser pulse and to examine the fluid dynamic confinement effects. All experimental data are obtained in air at atmospheric pressure.

Impulse Generation Using 300-J Class Laser with Confinement Geometries in Air