Measurements of Burning Rates of BKNO₃ Pellets with a Diameter of 3.2 mm under Vacuum Conditions in a Temperature Range between −40 and 60°C for Micro-thruster Applications

Abstract

The burning rate of boron potassium nitrate (BKNO₃) pellets with a diameter of 3.2 mm under vacuum in the temperature range between −40 and 60°C for micro-thrusters and pyrotechnics for small spacecraft was measured. The effects of the boundaries of the pellets –such as joints and bases when stacking and bonding the pellets– on the burning rate were also investigated. The measurements showed that the burning rate of BKNO₃ pellets with a diameter of 3.2 mm increased with increasing initial pellet temperature, and the burning rate at 60°C was approximately twice that at −40°C. The increase in the burning rate was small in the temperature range of −40 to 0°C, ranging from 3.8 ± 0.3 mm/s to 3.9 ± 0.2 mm/s. The rate of increase rose significantly above 0°C, and the burning rate was 5.3 ± 0.5 mm/s at 40°C and 7.9 ± 0.6 mm/s at 60°C. In contrast, the burning rate of infinitely stacked BKNO₃ pellets with a diameter of 3.2 mm and a length of 2.0 mm decreased by approximately 20% due to the presence of joints. The decrease in the burning rate due to the presence of bases is relatively greater when the pellet length is shorter and the temperature is higher.