Solid propulsion is one of the most studied rocket technologies from an environmental perspective. Despite being widely documented since the early flights of NASA’s Space Shuttle (STS), its effective impact on the global and local environment remains unclear. Studies in this field have always blamed solid rockets for emitting hydrogen chloride and solid aluminum oxide particles, contributing to the global ozone depletion. However, the rate of launches and the quantity of propellant consumed do not support this kind of urgent concern. New models and experimental evidence have emerged over the last 20 years regarding the potential effects of exhaust gases, but knowledge gaps still exist. This document presents an overview of the subject, focusing on chlorine-based combustion products. The paper concludes that solid propulsion does not pose a global environmental problem due to its HCl emissions, being effects on the atmosphere rather confined in space and time. However, questions remain regarding other types of emissions, such as aluminum oxide and soot.

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This study aims to clarify the influence of gas generation on ignition delay during laser ignition of Boron/Potassium Nitrate (B/KNO₃) mixture. Ignition experiments under both vertical and horizontal laser irradiation were conducted with a diode laser to irradiate a B/KNO₃ sample, and ignition delay was measured. It was revealed from high-speed imaging that gas generation occurs prior to ignition and interferes with laser. The ignition delay with horizontal irradiation is smaller than vertical irradiation because the generated gas might attenuate the laser intensity. The numerical calculation was performed by solving transient thermal conduction with laser transmittance of 80-100% and showed agreement in the range with the transmittance.

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Equation of state (EOS) for unreacted high explosives, PETN and HMX has been formulated thermodynamically aiming at using it in numerical code of shock to detonation transition processes. In this paper, a generalized procedure of providing the Rice-Walsh type EOS, i.e., pressure-volume-enthalpy EOS is proposed based on the available static isothermal compression curve. The present method can be used to describe the EOS for unreacted high explosives by using the specific heat at constant pressure as a function of entropy, C_p(S), and the pressure-dependent Wu-Jing parameter with the material parameter β introduced previously by the author.
Birch-Murnaghan functional form is adopted as an isothermal compression curve. Specific heat function C_p(S) was derived from the measured temperature dependence of specific heat at atmospheric pressure. In order to estimate the parameter β in the Wu-Jing parameter, shock Hugoniot curve for PETN and HMX were calculated by varying the value, β as a parameter. Values of β for both PETN and HMX were determined to reproduce the available shock Hugoniot data for TMD and porous samples of these two explosives and were found to be very similar for both explosives and were very small compared with those estimated previously for various metals.
By using the established EOS for high explosives, shock Hugoniot U_s-U_p for both TMD and porous samples were calculated and shown. Calculated shock Hugoniot curves are in good agreement with the available dynamic data.

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Laser ignition is insensitive to electrical disturbances and is expected to improve the safety of ignition systems by replacing classical electric ignition systems. To evaluate ignition reliability and design a laser ignition system for extraterrestrial missions, it is essential to clarify the ignition threshold in a deep space environment, where the temperature of a spacecraft could be low. The purpose of this study is to clarify the ignition threshold by obtaining the boundary of ignition/no-ignition and to construct a numerical model that simulates the ignition of the ignition charge under low-temperature conditions. The ignition threshold was obtained through laser ignition experiments conducted at -50 to -55°C. The experimental results indicate that the laser power required for ignition is higher at low temperature than at room temperature, with the power ratio ranging from approximately 1.1 to 1.25. The numerical calculations showed agreement with experimental results within 10% for standard temperatures and within 20% for low temperatures. The numerical model was confirmed to be effective for predicting ignition thresholds.

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Ammonium perchlorate (AP) is one of the most commonly used energetic oxidizers in solid propellants, providing strength and playing a crucial role in customizing propellant formulations. Preparing ultrafine AP with controllable particle size and crystal shape is essential for improving propellant formulations, especially for adjusting the burning rate. Traditional preparation methods face complicated steps, high energy consumption, and limited ability to control the quality. Therefore, this study developed an ultrasound-assisted antisolvent crystallization process as an alternative for producing ultrafine AP particles. The solubilities of AP in various organic solvents were determined, and the effect of solvent/antisolvent combination and solvent-to-antisolvent ratio was first screened to meet the goal of acceptable crystallization recovery. Then, several ultrasound-assisted antisolvent crystallization experiments were performed with the screened combination and ratio. By selecting the appropriate solvent/antisolvent system and applying sonication during the crystallization step, ultrafine AP particles with a mean size of 3.8 μm, a recovery of 83%, and a quasi-spherical crystal shape were successfully produced. In addition, the crystal structure, spectrometric properties, thermal properties, and decomposition behavior of the ultrasound-assisted recrystallized AP were compared with those of the unprocessed and the recrystallized AP without sonication. These results indicate that ultrasound-assisted antisolvent crystallization offers an efficient approach to designing ultrafine AP particles and has the potential for preparing other energetic materials.

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