'Chicken gun' helps shuttle return to flight

Airman, Nov, 2004 by Tina Barton

ARNOLD AIR FORCE BASE, Tenn.--Experts are launching rectangular pieces of foam, traveling up to 1,500 mph, at the space shuttle's solid rocket booster to help National Aeronautics and Space Administration officials ensure the vehicle is ready to return to flight.

Arnold Engineering Development Center engineers and test operators in the ballistic impact range, affectionately known as the chicken gun, are launching hundreds of block-shaped projectiles. These will simulate pieces of external tank foam breaking away during flight and striking various parts of the space shuttle, such as the solid rocket booster.

The range got its nickname because, in normal use, technicians fire chicken carcasses at a test target at varying speeds to simulate a direct bird-strike during flight.

In the NASA tests, operators launch the blocks at various velocities and angles to simulate the different ways foam might strike the solid rocket booster. These tests will help determine the effects of foam strikes, provide information on the booster hardware's ability to withstand them and help fill a database for future reference, officials said.

Before each shot, employees cut the projectiles to specified lengths, widths and weights.

"If the foam projectile is too loose in the barrel, it can cause the velocity to be lower than desired," said Lanny Bell, a project engineer. "If the projectile is too tight, it could break in the barrel during launch."

Jeff Venable, procurement quality assurance representative for United Space Alliance, works with center employees to make sure each projectile and target meets test specifications.

"The [center's] folks are fantastic," Mr. Venable said. "You can tell they are completely dedicated and professional. Everybody is working toward the same goal of getting the shuttle back to flight."

During each shot, employees use high-pressure helium gas to launch the projectiles at speeds between 102 and 1,537 mph down an 86-foot-long rectangular barrel, Mr. Bell said. The targets include the struts connecting the solid rocket booster and external fuel tank, core panels representing the thermal protection system materials and cover material for the range safety system antennas that would be used to abort a mission if the shuttle was damaged.

High-speed video cameras operating up to 20,000 frames per second document the events and provide test experts a way to measure the projectiles' velocity. Strain gauges and accelerometers on the target's panels acquire data at a sample rate of 50,000 samples per second to provide information on the stresses the target sustains during the event, Mr. Bell said.

"As we carry out the [Columbia Accident Investigation Board] recommendations for safe return to flight, it's imperative that we determine the tolerance of the space shuttle elements, including the solid rocket booster, to withstand debris strikes and understand the effects," said Jack Hengel, NASA shuttle solid rocket boosters project manager. "These tests will identify [strikes] that result in component failures that may lead to loss of vehicle and crew. In these cases, changes will be required to either control the debris source, strengthen the component design or both."

--Tina Barton Arnold Engineering Development Center Public Affairs