Optimal Topological Design of a Thermal Isolator for a Monopropellant Space Thruster

Abstract

This work is focused on the study of the thermal-structural behavior of a thermal isolator device employed in a monopropellant thruster for space applications. Engines of this kind are widely used to perform attitude corrections in artificial satellites. Their operating principle is based on the catalytic decomposition of the fuel (hydrazine), producing gasification with a consequent heat generation. These gases are properly conducted to a nozzle to produce thrust. A couple of redundant solenoid on-off electro-valves, in a serial configuration, are used to control the fuel supply system. To avoid leak risk in this system, soft seals are also used. Duration and performance of this kind of engine rely on two main aspects. The first one is the number of cold ignitions. When the engine starts at low temperature conditions, the catalytic bed is subjected to a thermal transient (high gradient—hundreds of∘ C/s) which generates a breakage of grains, causing low size particles to fill the inter-granular spaces, clogging the downstream gas flow. The second aspect to consider in the reduction of the life span is the loss of reliability in the soft seals used in the fuel supply system due to high temperature degradation. Such degradation can drive the module out of service, generate a catastrophic failure in the reactor, or lead to mission stoppage. A thermal isolator is used to protect the seals from a premature degradation due to thermal effects. Its structural design is optimized by using a novelty structural optimization methodology based on topological sensitivity analysis in this work. This analysis allows achieving the best structural configuration that minimizes the temperature field around the seals and also the isolator weight. Finally, a thermal and structural evaluation of the monopropellant thruster is presented in order to validate the structural strength and integrity. Inertial forces due to high G’s are considered in this analysis.