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
| 
