Down-the-hole hammer (DTH) drilling is an air hammer drilling technique designed for drilling through bedrock and features a typical drill string length of 200 m or shorter due to its technical specifications. During DTH drilling of granite-like hard rocks, the impacts of the piston-bit-rock system cause the drill string to generate severe vibration and noise pollution. In addition, the rapid wear of the button bit and drill string significantly decreases the drilling efficiency. Based on a distributed parameter drill string model of a DTH, this paper studies the phenomenon of the drill string’s axial forced vibration with a periodic impacting force under DTH drilling in an innovative manner. With the focus of study on the DTH button bit, the transient impact force on the button bit during the drilling of the piston-bit-rock system is determined, and the impact force is converted to a periodic excitation force function using polynomial fitting. Then, the periodic impulse is transformed into a harmonic series using Fourier transforms, and finally, the drill string vibration response under the harmonic excitation force series is determined. The results reveal that a periodic impulse can mainly be determined by the nature of the DTH drill string and rock and the impact frequency during drilling. Further evidence demonstrates that at least one frequency component of the impulse harmonic series will be equal to the modal frequencies of the drill string insofar as the condition $2\mathrm{nf}0l=i\sqrt{E/\rho }$ is met; the coupling of the short drill string with the DTH may cause resonance at a specific hole depth, whose resonance regions are adjacent to but not continuous with the extension of the drill string. This work should serve as an important theoretical guide for designers in the dynamic design, modification, and use of a DTH drilling system.

The multiple working modes, complex working conditions, frequent changes in external heat flux, and high power consumption of communication satellites all pose great difficulties to their thermal design. This paper mainly describes the design of a thermal control system for high-power communication satellites. Firstly, new efficient heat transfer technologies and thermal control materials for spacecraft are introduced. Secondly, the structure and internal heat source of the satellite are introduced. Thirdly, the external heat fluxes are analyzed, and the position of the heat dissipation surface and extreme conditions are confirmed. Then, a thermal control system is designed around the difficulties of thermal control. With heat pipes, the temperature uniformity of +Y deck, −Y deck, and +Z deck increased by 8 °C, 9.9 °C, and 34.2 °C, respectively. Furthermore, the maximum temperature of the power controller, secondary power supply, bidirectional frequency converter, and solid discharge decreased by 32.5 °C, 22.0 °C, 14.0 °C, and 164 °C, respectively. Finally, a thermal balance test is performed. The test results show that the temperatures of the solid-state power amplifier, on-board computer, power controller, secondary power supply, and bidirectional frequency converter meet the requirements of the thermal control indices. In addition, the temperature of thermal-sensitive components such as batteries and the storage tank also meets the requirements. The thermal design scheme is reasonable and feasible, and the thermal balance test verifies the correctness of the thermal design.

The multiple working modes, complex working conditions, frequent changes in external heat flux, and high-power consumption of satellites all pose great difficulties to their thermal design. In this paper, the material MB15 magnesium alloy was used, which has not been performed for the main structure of satellites. This material not only reduces the weight of the structure and the launch cost, but also its good thermal conductivity is very helpful for the thermal control design of the satellite. This paper mainly describes the design of a thermal control system for lightweight microsatellites. Firstly, the satellite structure, thermal control indices of the main equipment, and the power consumption of the equipment in different working modes are introduced. Then, the external heat fluxes are analyzed, the position of the heat dissipation surface and extreme conditions are confirmed, and detailed thermal designs of each part of the satellite are determined via the combination of active and passive thermal control. Finally, the thermal balance test is carried out for the whole satellite. It is found that the deviation between the temperature of the thermistor and thermocouple at the same moment in the thermal analysis simulation data and thermal balance test is generally within 0.5 °C, and the maximum difference is not more than 1.7 °C, which indicates that the simulation model is well established and that the thermal analysis is reliable.

The undisturbed sampling of the overburden soil is attracting increased attention due to the rapid increases in the construction of large-scale domestic foundations and environmental protection engineering. To date, systematic theoretical research on sonic drilling technology has rarely been published. In the present paper, the vibration response induced by sonic harmonic excitation is studied by modeling the flexible drill string of a sonic drill; its dynamic theory and design methodology have been developed, which reveal effects of the excitation frequency, the structural parameters on vibration response of the drill string. The study of sonic drill string vibration is beneficial for improving the drilling efficiency and reducing the damage.

The sonic drill mainly utilizes a sonic vibrator to initiate standing wave resonance of the drill string to achieve high-speed drilling. However, the explicit function relation between the lumped mass and modal frequency could not be revealed. Precisely controlling the sonic vibrator frequency to maintain the standing wave resonance of the drill string is difficult. In this study, the one-dimensional wave theory is employed to establish the longitudinal vibration differential equations of the sonic drill string with vibrator mass. The modal frequency equation of the sonic drill string with an inertial boundary is obtained via the method of separation of variables. The explicit expression of the modal frequency with respect to the vibrator mass and system structure parameters is calculated by mathematical analysis. Moreover, the influence of the large vibrator mass on the dynamic characteristics of the drill string is revealed during drilling of a shallow hole. This can precisely track the vibration control frequency of the sonic drill during shallow hole drilling, while maintaining the standing wave resonance of the drill string coupled with the sonic vibrator. Thus the efficiency of sonic drilling is improved.