Minuteman III upper stage rocket motors test fired in J-6
By Philip Lorenz III
/ Published May 07, 2007
ARNOLD AIR FORCE BASE, TENN --
Arnold Engineering Development Center (AEDC) recently conducted the successful test firing of a Minuteman III Intercontinental Ballistic Missile (ICBM) Stage 2 Production Quality Assurance (PQA) rocket motor in the Large Rocket Test Facility J-6. This test was followed by a successful test firing of a Stage 3 rocket motor.
The purpose of these tests is to check the quality of a representative sample taken from a production lot of rocket motors manufactured by ATK Thiokol, which took over production of the ICBM's Stage 2 and Stage 3 rocket motors in 1997.
The Stage 2 rocket motor, which was tested at a simulated altitude of approximately 85,000 feet, comes from a production lot comprised of 33 motors. Each test helps to determine the quality and performance consistency of a lot's rocket motor, including the nozzle and propellant.
"ATK has production ongoing for both stages," said James Brooks, Aerospace Testing Alliance (ATA) project engineer at J-6. "One motor from each lot will be randomly selected and designated for PQA testing. They usually select a Stage 2 and Stage 3 motor pretty close together, but not out of the same batch of propellant. They cast four motors at a time -- two Stage 2 and two Stage 3 motors. They want the motors to represent two different batches of propellant."
This is done to ensure the motor's performance is consistent, regardless of which batch of propellant was used throughout the production process.
"We measured thrust, chamber pressure, strain, temperature (from different places on the case and nozzle) and acceleration during this test," Brooks said. "The challenge is to get
everything right. You only get one chance to test a rocket motor. You can't go back up and repeat the data point."
The Minuteman ICBM program began in the late 1960s. The Air Force initiated a thorough long-term maintenance program to ensure that the ICBM force remained a strong and viable deterrent for years.
"It was originally supposed to be replaced by the Peacekeeper ICBM, but with all the different treaties and the disarmament agreements, the Peacekeeper program was eventually discontinued," Brooks said. "Since the Minuteman motors were aging out, they're taking the old motors out of the silo and replacing them with these newly remanufactured ones."
The PRP requirement is to extend the service life of the current Minuteman III rocket motors through 2020. The Stage 2 motor has been successfully fired with new insulation materials, including environmentally friendly propellant manufacturing processes.
"Testing this fiscal year at AEDC will consist of four PQA motors -- two Stage 2 and two Stage 3 motors," he said. "In addition, we'll be testing a fifth Stage 3 motor this year as a nozzle qualification motor. Up until now the Stage 3 program has used existing refurbished nozzles. They're running out of those, so they'll have to make a certain number of new ones. The Stage 3 test in April will be the first of three tests to qualify ATK to make these new nozzles. The second and third test will be early next fiscal year ."