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"On This Day" In Engineering History

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July 17, 1956 – The X-17 Research Rocket

Posted July 17, 2008 2:21 PM by Steve Melito

On this day in engineering history, the U.S. Air Force launched the first operational X-17, an all-solid-fuel, three-stage, re-entry rocket built by Lockheed. Data from this and other X-17 research flights was used in the design of nose cones for intercontinental ballistic missiles (ICBMs). During the 1950s, the United States and Soviet Union raced to be the first to develop these long-range rockets, which could deliver nuclear payloads. Although the Soviets trumped the West with the success of their R-7 rocket in August 1957, the U.S. would launch its first Atlas ICBM several months later.

Lockheed Engineers Get the Job Done

A research rocket, the Lockheed X-17 enabled the U.S. Air Force to determine how an ICBM's nose cone would react during high-speed re-entry through Earth's atmosphere. By studying flight data, American rocket scientists determined the best size, shape and aerodynamic characteristics for re-entry vehicles with nuclear payloads. In January 1955, the Air Force awarded Lockheed a contract for the design and construction of the X-17. Using existing rocket motors and a simple control system, Lockheed engineers were able to provide a quarter-scale proof-of-concept vehicle in May 1955. The full-scale version of the X-17 that was launched on July 17, 1956 was 40-ft. long and weighed 12,000 lbs.

Powered by Thiokol

The Lockheed X-17 featured three solid-propellant rocket stages. Powered by a Thiokol XM20 motor, the first stage featured four stabilizing fins and two externally-mounted, spin-stabilization motors. Measuring 31 inches in diameter, the first stage was a modified Sergeant missile that produced 48,000 lbs. of thrust for 28 seconds. After reaching an apogee of approximately 500,000 ft, the X-17 pitched over for a nose-down re-entry and achieved first-stage separation between 70,000 and 90,000 feet. Measuring 17 inches in diameter, the X-17's second stage then engaged its three Thiokol XM19 Recruits for 1.53 seconds. Each of these Thiokol motors provided 33,900 lbs. of thrust.

Blunt is Best

The third and final stage of the X-17 measured 9.72 inches in diameter and was powered by a single, solid-fueled, XM19E1 Thiokol Recruit. Depending on the re-entry angle, the X-17 achieved a speed between Mach 11 and 14.5. To test different nose cone designs, these missiles used hemisphere, cubic paraboloid and blunt shapes. Ultimately, Lockheed and the U.S. Air Force determined that blunt nose cones provided the best shape for the Atlas ICBM.

Resources:

http://www.astronautix.com/lvs/x17.htm

http://www.spaceline.org/rocketsum/x-17.html

http://en.wikipedia.org/wiki/ICBM

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