Heat Sterilizable Propellants for Planetary Missions

Abstract

Dry-heat sterilization, a requirement of all planetary lander missions, places severe requirements on solid rocket propellants that will be used on them. In an ongoing program, which has a goal of producing heat Sterilizable motors with 130 kg of propellant, numerous insights into the problems associated with developing dry-heat Sterilizable propellants have been gained. The one most significant means of increasing propellant stability at sterilization temperature (125°C) is to decrease the ammonium perchlorate (AP) particle size. One possible explanation is that some of the AP crystals larger than 250 n in diameter are unstable at sterilization temperature. Another important findings is the effect grain diameter has on survivability at sterilization temperature. As the grain diameter increases, the time to failure decreases. This is probably due to the increased stress that results from the thermal gradients, which occur during grain heat up or cool down. In this work, 7cm-diam grains have been made that survived 70 sterilization cycles (the requirement is eight); however, 71-cmdiam grains from the same propellant batch have survived only seven cycles.