PROTECTING THE ASTRONAUTS
After much deliberation and testing, a decision had been reached on the style and composition of the capsule’s heat shield. For the initial suborbital flights, it had been decided to adopt a proven system known as a ‘heat sink,’ which had been developed for the ballistic missile program. Previous testing had revealed that although the intense shock wave generated by a missile cone’s trajectory through the atmosphere managed to keep the massively high temperatures away from the forward-facing blunt end of the cone, enough heat – estimated at a temperature of around 3,000°F – could potentially soak through to melt or even vaporize in an explosive release of gases any normal metal, greatly endangering the life of an astronaut. However, beryllium, with its unusual ability to absorb extremely large quantities of heat, was the obvious candidate to test as the heat sink for a manned capsule.
On Monday, 8 June 1959, after details had been kept secret to that time, it was announced that the Brush Beryllium Company, which operated a plant near Elmore, Ohio, had been assigned the task of producing six gently curved heat shields to protect astronauts from the tremendous frictional heat encountered when their spacecraft reentered the atmosphere.
Beryllium is a hard, light metal that has a high melting point and it was used due to its ability to absorb heat as well as its high conductivity, preventing disastrous buildups of concentrated surface temperatures. Specifications called for the heat shield to be constructed of “hot-pressed” beryllium, with a diameter of 80 inches and a radius of curvature of 120 inches. It would prove to be the largest single piece of beryllium ever forged to that time.17
In July 1959 Brush Beryllium and the Aluminum Company of America announced the successful production of the first giant, dish-shaped beryllium piece, forged by Alcoa from a record-size billet supplied by Brush.
To produce the heat-sink shield, Brush first hot-pressed a beryllium billet 62 inches in diameter, one of the largest ever made to that time using powder-metallurgy techniques. This was achieved using the company’s patented QMV (quantum mechanical vacuum) process, involving simultaneous applications of vacuum, heat and pressure to beryllium powder. Following preliminary machining by Brush, the billet was encased in steel for the high-temperature forging operation. It was then delivered to the Alcoa factory in Cleveland, where it was heated to approximately 2000°F in a specially designed furnace. A huge manipulator then removed the glowing,
steel-jacketed beryllium piece and placed it onto a pre-heated die. The mighty force of a 50,000-ton press, operated by Alcoa under the U. S. Air Force’s Heavy Press Program, squeezed the beryllium billet into a saucer-shaped disc 80 inches across and three inches thick.
Under the contract, Brush Beryllium then forged the final dimensions in their precision machine shop in Cleveland. The last operation in the manufacturing process – ultrasonic inspection – was carried out by Alcoa. Following this, the McDonnell Aircraft Corporation received the finished piece, 72 inches in diameter, ready to be installed as a heat sink of one of the Mercury spacecraft.18
While a beryllium heat shield would be used on capsules in the early booster test flights and the two suborbital missions of Shepard and Grissom, for orbital missions a new, ablative heat shield weighing far less was developed for the Mercury-Atlas flights that would follow.