THE SERGEANT TEST VEHICLE

While these developments were occurring at Thiokol, JPL worked with a test vehicle named the Sergeant, not to be confused with the later missile of that name. Army Ordnance had authorized the de­velopment of this test vehicle, a sounding rocket with a diameter of 15 inches, which was quite large for the day (although only an inch larger than an aircraft rocket developed at the Naval Ordnance Test Station, Inyokern, California, in 1945 and called the “Big Richard"). Designed with an extremely thin steel case of 0.065 inch and a star­shaped perforation, the Sergeant test vehicle was expected to attain an altitude of up to 700,000 feet while carrying a 50-pound payload. Static tests with a thicker case in February 1949 showed that a poly­sulfide grain of that diameter could function without deformation.

But when the JPL researchers (including Bartley, Shafer, and Thackwell) shifted to the thinner case, the result was 12 succes­sive explosions through April 27, 1950. At this point, JPL director Louis G. Dunn canceled the project for the sounding rocket and re­duced all solid-propellant work at the laboratory to basic research. The researchers soon determined that the causes of the explosions included a chamber pressure that was too high for the thin case and points on the star configuration that were too sharp, causing cracks as pressure built up. An easy solution would have been a thicker case and rounded points on the star. When Dunn canceled the proj­ect, Thackwell took his knowledge of solid-propellant rocketry to Thiokol’s Redstone Division in Huntsville.15