Mars Exploration Rover TIRS Cover Thermal Protection System Design Verification

Abstract

This paper summarizes the arc jet test results of the Mars Exploration Rover (MER) Silicone Impregnated Reusable Ceramic Ablator (SIRCA) Transverse Impulse Rocket System (TIRS) Cover test series in the Panel Test Facility (PTF) at NASA Ames Research Center (ARC). NASA ARC performed aerothermal environment analyses, Thermal Protection System (TPS) sizing and thermal response analyses, and arc jet testing to evaluate the MER SIRCA TIRS Cover design and interface to the aeroshell structure. The primary objective of this arc jet test series was to evaluate specific design details of the SIRCA TIRS Cover interface to the MER aeroshell under simulated atmospheric entry heating conditions. Four test articles were tested in an arc jet environment with three different seal configurations. The test condition was designed to match the predicted peak flight heat load at the gap region between the SIRCA and the backshell TPS material, SLA-561S, and resulted in an over-test (with respect to heat flux and heat load) for the apex region of the SIRCA TIRS Cover. The resulting pressure differential was as much as twenty times that predicted for the flight case, depending on the location. There was no post-test visual evidence of over-heating or damage to any interfaces to the backshell structure. Repeatable thermocouple data were obtained and compared to SIRCA thermal response analyses. The one-dimensional thermal response prediction compared well with the thermocouple data for the location at the backshell TPS interface. For the apex region of the SIRCA TIRS Cover, a one-dimensional thermal response analysis resulted in an over-prediction, as there were strong multi-dimensional conduction effects due to the TIRS Cover geometry. In general, the test results provide strong experimental evidence that supports the adequacy of the baseline seal design. Introduction This report details the results of a test series in a simulated entry environment for a new design on the Mars Exploration Rover (MER) spacecraft. The MER mission is slated to land two large scientific rovers on the surface of Mars. The launch window for MER-A is May 30 to June 19, 2003, and it will land on Mars on January 4, 2004. The launch window for MER-B is June 25 to July 15, 2003 and it will land on January 25, 2004. The goal of the identical rovers is to learn about ancient water and climate on Mars. The entry, descent, and landing of the rovers will duplicate the Mars Pathfinder (MPF) mission. The Thermal Protection Systems (TPS) on the two spacecraft, shown in Figure 1, will use identical materials to those used on MPF. MPF used the NASA Ames Research Center (ARC)invented TPS material, Silicone Impregnated Reusable Ceramic Ablator (SIRCA-15F) on the Backshell Interface Plate (BIP) due to the material’s excellent ablative and insulative properties. In addition, SIRCA offered ease of machinability to any shape, and versatility in integrating numerous penetration hardware required on the BIP, since the BIP is the interface to the cruise stage. The nomenclature of SIRCA-15F refers to SIRCA manufactured from 0.19 g/cc (12 lb/ft) bulk density Fibrous Refractory Ceramic Insulation (FRCI-12), with a final SIRCA bulk density of 0.264 g/cc± 0.024 g/cc (16.5 lb/ft ± 1.5 lb/ft). For the MER spacecraft, NASA ARC manufactured the SIRCA material for use on the BIP, just as was done for MPF. In addition, NASA ARC manufactured SIRCA material for thermal protection of the Transverse Impulse Rocket System (TIRS) Covers. The TIRS is a new feature that was not required for MPF. Its purpose is to minimize the total self-induced horizontal velocity at impact such that it meets the airbag system impact velocity requirements. Three TIRS rocket nozzles are *Research Scientist †Research Scientist, Associate Fellow AIAA 1