Tag Archives: Rocketdyne XLR-89-1

11 June 1957

Convair XSM-65A Atlas 4A launch, 11 June 1957. (U.S. Air Force)

11 June 1957, 4:37 p.m., EST, (20:47 UTC): The Convair XSM-65A Atlas, number 4A, lifted off from Launch Complex 14 at the Cape Canaveral Auxiliary Air Force Station in Florida. This was the first launch of a prototype Atlas intercontinental ballistic missile.

At T+26 seconds, the number two engine lost thrust. The rocket began to tumble and at T+50 seconds, the destruct signal was sent by the range safety officer. The Atlas had reached a peak altitude of approximately 9,800 feet (2,987 meters).

Convair Atlas 4A is launched from the Cape Canaveral Auxiliary Air Force Station 11 June 1957. (San Diego Air & Space Museum Archives, Catalog #:14_015602)

Despite the missile’s destruction, the first flight test of the XSM-65A (also known as Atlas A) was actually considered to be a success. The engines had started normally, the launch pad release mechanism functioned as intended, and perhaps most importantly, the lightweight structure of the missile body withstood the forces experienced during the launch.

Following data analysis of the short flight, engineers determined that engine exhaust had circulated back into the engine’s thrust section, causing it to overheat. The propellant ducts were not sufficiently shielded from the heat and began to collapse. This reduced the flow of the liquid oxygen to the engine, effectively throttling it back.

Atlas 4A had been previously tested at Convair’s static test facility in Sycamore Canyon, east of MCAS Miramar, in the Scripps Ranch area of San Diego, California. It is possible that Atlas 4A had suffered internal damage during test firing.

Static test stands for Atlas rockets at Convair’s Sycamore Canyon Test Facility, near San Diego, California. (siloworld.net)

The Atlas A was a prototype for an intercontinental ballistic missile, designed to test the structure, engines and launch system. Unlike the production Atlas, Atlas A used only two engines. The missile was designed and built by the Convair Astronautics Division of General Dynamics at San Diego, California.

Atlas A 4A

Atlas A was 76 feet, 11 inches (23.444 meters) long and 11 feet (3.353 meters) in diameter. At liftoff the missile weighed 180,666 pounds (81,949 kilograms), and at burnout 17,721 pounds (kilograms).

The Atlas is primarily constructed of very thin stainless steel sheet. Rather than using a supporting internal structure, the rocket used “balloon tanks” so that it could be built with minimal weight. The fuel and oxidizer tanks supported the outer skin, but could only do so when pressurized. When the rocket was not fueled, these tanks were pressurized with nitrogen at 5 pounds per square inch (34 kilopascals). If left unpressurized, the rocket would collapse under its own weight.

Atlas A 4A before erection at Launch Complex 14 (Drew Ex Machina)

Atlas 4A was powered by two Rocketdyne XLR-89-1 engines, which produced 271,432 pounds of thrust (1,207 kilonewtons) at takeoff, burning RP-1, a highly refined kerosene, with liquid oxygen. The two engines shared a single turbopump to provide the fuel. Early versions of this engine had a conical exhaust nozzle, while improved models used a bell-shaped nozzle. Production Atlas missiles added a Rocketdyne LR105-NA sustainer engine which continued to accelerate the missile after the LR-89 booster engines were jettisoned. Because of this configuration, the Atlas was known as a “1½-stage rocket.” The LR105 produced 60,473 pounds of thrust (269 kilonewtons) at Sea Level.

Yaw, pitch and roll control of the Atlas after the booster section was jettisoned was provided by two smaller Rocketdyne LR101 vernier thrusters, producing 1,060 pounds of thrust (4.7 kilonewtons) at Sea Level.

Convair XSM-65A Atlas 4A at Launch Complex 14, 11 June 1957. (NASA 19570611-004A-0408)
Atlas A 4A, Launch Complex 14, Cape Canaveral Air Force Station, Florida. (U.S. Air Force)
Three-view diagram of Convair Atlas A. (Drew Ex Machina)
Atlas A MA-1 with two Rocketdyne LR-89-1 engines. (Rocketdyne)

The SM-65A Atlas ICBM became operational 31 October 1959. The rockets were housed in underground “silos,” or hardened above ground shelters located throughout the continental United States. These missiles carried a single W-49 thermonuclear warhead with a yield of 1.44 megatons. The W-49 was designed by the Los Alamos Scientific Laboratory (LASL) and is believed to be a development of the earlier B-28 two-stage radiation-implosion bomb. It incorporated a 10-kiloton W-34 warhead as a gas-boosted fission primary, and had a one-point-safe safety system. The warhead had a diameter of 1 foot, 8 inches (0.508 meters) and length of 4 feet, 6.3 inches (1.379 meters). It weighed 1,665 pounds (755 kilograms).

An unexpected side effect of the Atlas missile programs was the development by the Rocket Chemical Company of its Water-Displacing Formula 40, popularly known by its trade name of WD-40. This universal lubricant was used on the stainless steel surfaces of the Atlas to prevent rust and corrosion.

© 2023, Bryan R. Swopes