Shingle presumed to be flown on the Mercury-Atlas 8 Sigma 7 spacecraft that carried astronaut Wally Schirra around the Earth six times on October 3, 1962. The shingle measures 12″ x 11.5″, and is marked on the back in black paint: "-7, Cap 16, Shop," attributing it to the Sigma 7 spacecraft (Mercury capsule #16). Also attached to the reverse is a segment of the thermocouple probe. The panel has several cuts along the top and bottom edges, where material was removed for analysis.
In order to understand the effects of reentry on the materials used for the shell of the Mercury capsule, NASA transferred this panel to Dr. John F. Radavich of Purdue University. Dr. Radavich's obituary makes note of his distinguished career as a researcher: 'His principal contribution to high temperature material technology had been his pioneering work in the transition of analytical procedures from optical to electron microscopy. In so doing, he developed preparation procedures that opened the doors to all future metallographic studies of superalloys. The current state-of-the-art practices for phase extraction and identification are dependent upon the fundamental knowledge that he developed.'
The shingles of the Mercury capsules were composed of a nickel-based high temperature alloy called René 41, used due to its ability to retain high strength at extreme temperatures. Based on his expertise in this specific field, it is evident why Dr. Radavich would have been chosen to receive these shingles for study. In August 1962, he published a paper entitled 'Microstructural Changes Produced in Orbited Rene' 41 Heat Shingles,' in which he noted that the panel surfaces displayed no obvious meteorite impacts; that the outer oxide layer undergoes an enrichment of chromium oxide relative to preflight material; and that the amount of M6C carbide phase in flown material decreases relative to the TiC phase, among other observations.
On December 9, 1962, the Terre Haute Tribune featured an image of Dr. Radavich posing with the painted Sigma 7 shingle, but noted that he received two, offering contemporary confirmation that this shingle was likely flown on MA-8: 'Sigma 7 Shingle Studied by Scientist—One of two high-temperature alloy shingles from U.S. astronaut Walter Schirra's Sigma 7 space capsule being studied to determine structural changes during orbit and re-entry is displayed by Dr. John F. Radavich, Purdue University materials researcher, in LaFayette, Ind.'
Terms and abbreviations used in our descriptions.