Formulation of minimum signature solid rocket propellant based on ammonium perchlorate and sorbitol with magnesium as a metal additive

Minimum-signature smoke solid propellants were developed using ammonium perchlorate (AP) and sorbitol, integrated with metal additives such as magnesium (Mg). Different fuel compositions were also blended with metal catalysts, notably ferric oxide (Fe₂O₃). Minimum smoke solid propellants are already widely available in the solid rocket propulsion field. Minimum-smoke solid propellants are widely available but remain complex and costly to produce, with much related research kept confidential in developed countries. An optimized AP/sorbitol-based formulation containing 77 wt% AP and 5 wt% Mg exhibited the highest burning rate (0.126 cm/s) at ambient conditions. The heat of combustion increased with oxidizer content up to zero oxygen balance, and the addition of metal additives enhanced the heat of combustion 4142.57 kJ/mol and specific impulse 183.56 s. Mechanical properties were evaluated using tensile and Shore A hardness tests. The results showed that incorporating 5 wt% magnesium and 1 wt% ferric oxide significantly improved mechanical durability. In particular, the combined addition of Mg and ferric oxide in formulation SP8 produced the highest tensile stress at 1.116 N/mm² along with increased hardness, indicating enhanced structural integrity. AP/sorbitol based solid propellant formulations were synthesized and characterized using FTIR, XRD, and CHNO-S analyses. The incorporation of magnesium significantly enhanced thermal stability, increasing the decomposition and ignition temperature to 243.59 °C. In contrast, 0.05 wt% ferric oxide acted primarily as a catalyst and did not directly contribute to energy release. Kinetic analysis using the Kissinger–Akahira–Sunose methods showed activation energies ranging from 75 to 161 kJ/mol, with formulation SP6 exhibiting the highest values, attributed to its energy-dense combustion pathway. The static firing tests demonstrate that the incorporation of magnesium significantly enhances propellant performance, producing a peak thrust of 4.40 N and a specific impulse of 29.60 s. Formulations employing a weaker oxidizer generated a lower thrust of 2.61 N compared to 3.00 N for formulations with a stronger oxidizer, despite using the same fuel composition. Among all samples, SP4 and SP5 exhibited the highest light transmittance and lowest particle mass, qualifying under Advisory Group for Aerospace Research and Development (AGARD). In contrast, SP6 to SP8, which included metal additives, showed increased smoke opacity and particle mass, falling under AGARD Class BA or BB. The findings in this research of AP/sorbitol-based propellants, enhanced with optimized metal additives, as promising low-signature alternatives for regional space and defence applications.