Design of a Thermal Protection System for a Mars Entry Vehicle with Ceramic Matrix Composites

Abstract

Advancements in the space sector have driven the democratization of planetary exploration. As a longstanding target of scientific interest, Mars will consequently witness an increasing demand for surface missions of various sizes. Its thin atmosphere, however, is a challenging environment for entry, descent, and landing (EDL). An incoming spacecraft will encounter extreme heating while experiencing low levels of atmospheric deceleration. This atmospheric constraint places limitations on payload mass. Lightweight approaches to entry vehicle design beyond current technologies are critical to allow safe and precise landings for a variety of Mars missions. Thermal protection systems (TPS) constructed from low-density structural materials with high-temperature capabilities are a promising solution for rigid aeroshells. This is because the need for a separate load-bearing carrier structure can be reduced, thus conserving vehicle mass and internal volume. Among the materials currently available, ceramic matrix composites (CMC) such as C/C and C/SiC are essential to the realization of thermally-resistant lightweight structures. They have attracted international interest for Mars entry applications and offer potential versatility for components within various EDL architectures. Novel ultra-high temperature ceramic matrix composites (UHTCMCs) also emerge as good candidates as their capabilities extend beyond the operational temperature limits of traditional ceramic matrix composites.

This thesis explores the use of (UHT)CMCs in the design of a demonstrator heat shield for a low-mass Mars mission delivering a wind-driven spherical rover. Five CMC-based TPS concepts were proposed. Based on a high-level trade-off, a hot structure solution with internal lightweight insulation was selected due to its mission suitability and potential for minimal weight. A ballistic entry trajectory model was used to define the thermomechanical loads. These loads were used as inputs for thermal and structural simulations using the FEA package Ansys Workbench. The TPS layers were sized for minimum mass and appropriate temperature limits, and thermomechanical stress responses were analyzed.

Based on mass and stress margins of safety, a comparison between sized heat shields utilizing a baseline CMC and a UHTCMC was made across two aeroshells with different size configurations. It was found that a traditional CMC provides a heat shield that does not only save mass, but shows a noticeably higher thermostructural performance compared to a UHTCMC; it is better suited for Mars entry unless a degree of reusability and longer entry times are involved. Within a limitation of vehicle mass and base diameter, heat shields with higher vertex angles are noticeably lighter. This work aims to provide a first step towards the exploration of novel structures for Mars entry, enabling a range of robotic and human missions to the red planet.