Five-segment shuttle solid rocket booster test fired
Posted: October 24, 2003

The most powerful Space Shuttle Reusable Solid Rocket Motor ever tested pushed beyond typical launch performance boundaries at a Utah test facility Thursday, Oct. 23.

The most powerful shuttle solid rocket booster is test fired Thursday. Credit: Thiokol
The five-segment test motor, which ran for 128 seconds and generated more than 3.6 million pounds of thrust, appeared to perform flawlessly, in line with preliminary data, according to Jody Singer, manager of the Space Shuttle Reusable Solid Rocket Motor Project Office at NASA's Marshall Space Flight Center in Huntsville, Ala. Final results from the test are not immediately available.

"It was a great success. We are believers in the 'test before you fly -- fly it on the ground first' program," said Singer. "We look forward to getting the data because we want to make sure we understand all aspects of the safety and reliability of the Shuttle's motor."

The full-scale static -- or stationary -- test was performed at ATK Thiokol Propulsion Division, an Alliant Techsystems Inc., company in Promontory, Utah, north of Salt Lake City. ATK Thiokol manufactures the Shuttle's Solid Rocket Motor.

An engineering test motor is used to simulate the conditions experienced in flight. It offers engineers an opportunity to better assess the strength of the motor's current design, to spot any flaws in the new designs, to verify new materials and to certify manufacturing processes. Engineers placed more than 630 data-gathering instruments at strategic points on the test motor -- about one-third more collection points than on a four segment motor.

This test motor -- the third in a series of four to be tested -- ran five seconds longer than the motors fire when launching the Space Shuttle, produced 300,000 pounds of thrust over the motor's maximum limit of 3.3 million pounds, and included an additional fifth motor segment adding 25 percent more propellant. Of the test motor's total weight of 1.56 million pounds, propellant accounts for 1.37 million pounds.

Credit: Thiokol
The test demonstrates additional performance capabilities, or risk margins, on the Reusable Solid Rocket Motor, according to Singer. "This was a true margin test for the solid rocket motor," said Singer. "Demonstrating capabilities, or margins, above the existing flight design limitations, allows us to learn more about how our current design performs.

This particular test motor, with five segments, was designed to expand the performance envelope above the four-segment Reusable Solid Rocket Motor that is currently used to launch the Space Shuttle. The five-segment solid rocket motor was originally proposed as a performance enhancement to reduce or eliminate potential abort scenarios; however, it was determined to provide benefits by expanding our knowledge of our operating environment and performance capabilities, as well as enhancing our critical skills. The design of Engineering Test Motor-3 provided a much needed opportunity for government and contractor engineers, both veteran and new, to work through design process to develop a new solid rocket motor variant. There are currently no plans to introduce the five-segment solid rocket motor into the Space Shuttle fleeting in the foreseeable future.

"Adding 300,000 pounds of thrust can make a big difference in how the motor's nozzle and thrust vector control system -- used to guide the Shuttle -- works," she said. "This test increases our understanding of motor component design capabilities and the processes and materials used to build those elements by extending our operational envelop."

The test also provides an opportunity for the project to determine if its computer analytical models are effective, said Singer. Analytical models generate solutions that predict how a system will perform based on a given set of circumstances or conditions. These models are used to test and certify new designs, to forecast difficulties with existing motors, and to gather information to predict any problems that might occur before or during a Space Shuttle launch.

Credit: Thiokol
Another test benefit is training for new engineers, said Singer. "By adding a fifth segment, it makes this a different motor than the one we fly -- adding 8.7 inches to the aft, or bottom, exit cone of the nozzle and widening the nozzle throat 2.25 inches makes it a new configuration," Singer said. "The new data could influence future design hardware and the experience gained through the design process by engineers, both veteran and fresh is invaluable."

There were 67 test objectives, including testing the aft motor insulation and nozzle liners, gathering information on the pressure in the field joints, and improving the capability to better predict the rate at which the propellant burns.

Following the test, the data will be analyzed and the results for each objective provided in a final report.

At 126 feet (38.4 meters) long and 12 feet (3.6 meters) in diameter, the Shuttle's Reusable Solid Rocket Motor is the largest solid rocket motor ever flown, and the first designed for reuse. During it's approximately 123 seconds burn at liftoff, each motor generates an average thrust of 2.6 million pounds (1.2 million kilograms). The five-segment motor tested is 27.5 feet longer than a four-segment motor.

The Marshall Center requires full-scale tests such as this before new materials or processes are included in motors flown on the Space Shuttle.

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