The impulse generated by ablating aluminum targets was investigated in this study using the micro-impulse measurement method with a torsion pendulum, and the plasma plume characteristics were researched using fast photography and optical emission spectroscopy. The experiment was carried out with a pulsed laser with a wavelength of 1064 nm and a pulse duration of 8.7 ns. The fluence varied from 5.69 J/cm ² to 33.67 J/cm ² . The impulse coupling coefficients were obtained from the impulse measurements and the images of the plasma plume were recorded with a gate width of 500 ns. The results indicated that the variation of the impulse coupling coefficient was affected by the change of the laser fluence and the decline of the coefficient at high fluence was because of the plasma shielding effect. The intense radiation region located above the target surface in the corresponding plume was evident. Additionally, the differential coupling coefficient was presented and compared with the impulse coupling coefficient. The plasma temperature and the electron number density were estimated with the Boltzmann plot method and the Stark broadening method, respectively, using optical emission spectroscopy. Furthermore, the relative energy coupling efficiency was deduced from the plume front positions to determine the influence of the plume expansion dynamics on the impulse coupling. The obtained results showed that the variation trend of efficiency versus the laser fluence was similar to that of the impulse coupling coefficient.

The ejection of the plasma plume produced by laser ablation is an important process for inducing mechanical effects. Therefore, in this paper, the characteristics of the plasma plume are investigated in order to analyze the impulse coupling mechanism with two laser spot diameters, 300 μm and 1100 μm, respectively. The impulse generated by laser irradiating the copper target was measured by the torsion pendulum, and the plasma plume was investigated using fast photography and optical emission spectroscopy. The experimental results show that the optimal laser intensity is independent of the beam spot size. However, when the laser intensity is greater than 2.8 × 10⁹ W/cm², the impulse coupling coefficient with the small beam spot starts to gradually decrease, while that with the large beam spot tends to saturate. Additionally, the stream-like structure and the semi-ellipsoid structure of the plasma plume were observed, respectively. Furthermore, the electron number density was estimated using the Stark broadening method, and the effect of the plasma plume on the impulse coupling coefficient was discussed. The results provide a technical reference for several applications including orbital debris removal with lasers, laser thrusters, and laser despinning.

Laser micro-thrust technology is a type of propulsion that uses a laser beam to ablate a propellant such as a metal or plastic. The ablated material is expelled out the back of the spacecraft, generating thrust. The technology has the advantages of high control precision, high thrust–power ratios, and excellent performances, and it has played an important role in the field of micro-propulsion. In this study, a solid propellant laser micro-thruster was developed and then applied for the attitude control of satellites during on-orbit tests. The micro-thruster had a volume of 0.5 U, a weight of 440 g, and a thrust range of 10 μN–0.6 mN. The propellant, 87% glycidyl azide polymer (GAP) + 10% ammonium perchlorate (AP) + 3% carbon nano-powder, was supplied via a double-layer belt, and the average power was less than 10 W. We present the development of the laser micro-thruster, as well as the results regarding the thruster propulsion performance. The thruster was launched into orbit on 27 February 2022 with the Chuangxin Leishen Satellite developed by Spacety. The on-orbit test of the thruster for satellite attitude control was carried out. The thruster was successfully fired in space and played an obvious role in the attitude control of the satellite. The experimental results show that the thrust is about 315 μN.

In this article, experiments on a coil-magnet assembly were conducted to discuss the influences of the relative positions between a coil and a magnet on the electromagnetic calibration force. The experimental methods and steps were discussed. The input-output relationship of some coil-magnet assembly and the working ranges of the relative positions between the coil and the magnet were obtained. The error of the output electromagnetic force did not exceed 3% when the relative positions between the coil and the magnet were in the proposed working ranges. Based on the input-output relationship and the working ranges, the error of the electromagnetic force from the deviation error (3%) and the data fitting was obtained. The error of the data fitting can be ignored so that the electromagnetic force error of the coil-magnet assembly would not exceed 3%. When the error of the electromagnetic force was assessed accurately, the working ranges can be used to guide the design of the thrust pendulum, and the calibration error and the performance of the thrust pendulum can be evaluated accurately.

The ablation impulse of typical asteroid simulants irradiated by a nanosecond pulsed laser has been investigated in a vacuum environment. A torsional pendulum measurement system was constructed to calculate the impulse of laser ablation. A 10 ns pulsed laser was used, with a 1064 nm wavelength, a 900 mJ maximum pulse energy, and a millimeter-scale ablation spot diameter. Impulsive coupling characteristics of six typical targets that imitate the substance of asteroids with various laser fluences were analyzed. Furthermore, the impulse coupling coefficient curves of different materials were fitted. The results reveal that the minimum laser fluence corresponding to a measurable ablation impulse is approximately 2.5 J/cm², and the optimum laser fluence corresponding to the maximum impulse coupling coefficient is approximately 14.0 J/cm². The trends of the laser ablation impulse coupling curves are roughly consistent for the six materials. Impulse coupling characteristics of the six typical materials can be represented by the same polynomial within a 95% confidence interval, so a unified rule has been given. In actual deflection tasks of asteroids, the unified impulse coupling characteristic can be used to implement laser deflection techniques, especially when the material of the asteroid cannot be accurately judged in time.

The micro-impulse generated by ablating an aluminum target in double-pulse laser bursts with different interpulse delays was investigated using a torsion pendulum. The plasma plume was simultaneously visualized using high-speed photography to analyze the coupling mechanism of the ablation impulse. The experiment was carried out using a pulsed laser with a pulse width of 8 ns and a wavelength of 1064 nm. The experimental results show that an impulse with an interpulse delay of 60 ns is roughly 60% higher than that with no delay between the two pulses, when the energy of both laser pulses is 50 mJ. Therefore, double-pulse schemes could enhance the ablation impulse under certain conditions. This is because the ablation of the first laser pulse changes the optical properties of the aluminum target surface, increasing the absorptivity. However, the ablation impulse is reduced with a time delay of 20 ns when the energy of both laser pulses is 100 mJ or 150 mJ. It can be concluded that the plasma produced by ablating the aluminum with the first pulse shields the second laser pulse. To summarize, the experimental results show that different delay times in a double-pulse scheme have a significant effect on the ablation impulse. The study provides a reference for the optimization of the parameters when laser ablation propulsion with a double-pulse scheme is applied in the fields of space debris removal, laser ablation thrusters, and so on.