A full-scale space shuttle Reusable Solid Rocket Motor is scheduled to test fire for 123.2 seconds Thursday at a Utah test facility.

The test, in Promontory, Utah, at Thiokol Propulsion, an Alliant Techsystems, Inc., company, will be used to qualify a new insulation design on the motor's nozzle to case joint that will improve flight safety and help reduce costs on the motor.

A solid rocket booster undergoes testing in Utah after the Challenger accident. Photo: NASA

The Reusable Solid Rocket Motor Project Office at NASA's Marshall Space Flight Center in Huntsville, Ala., tests Flight Support Motors annually to qualify any proposed upgrades or changes to the motor. The static - or stationary -- test is part of Shuttle's ongoing verification of components, materials and manufacturing processes required by the Marshall Center, which oversees the Reusable Solid Rocket Motor project.

Support motors are used to evaluate, validate and qualify changes proposed for the Shuttle's Reusable Solid Rocket Motor. On this motor, there are 93 objectives and a total of 576 instrumentation channels being tested. The two-minute test duration is the same length of time that the motors perform during Shuttle flights.

"Full-scale static testing is a key element in our program, providing valuable information on design, process and material changes," said Mike Rudolphi, manager of the Reusable Solid Rocket Motor Project Office. "The rule is: Everything we fly, we static test first."

There are four major certification objectives for the test of Flight Support Motor-9. One of the more important tests is a change in insulation design on the nozzle-to-case joint J-leg. The proposed design change improves the thermal barrier protecting the O-rings on the motor by eliminating polysulfide, a putty-like material applied to the joint surface as the motor is assembled.

During assembly, polysulfide can trap air which may work its way through the putty-like material exposing the thermal barrier to motor combustion gases. The new design incorporates a J-joint - a joint shaped like a J - made of rubber for a better seal and a carbon fiber braided rope. Essentially, it is designed so that as the motor pressure increases, the seal tightens; a proven design used in the case field joints.

The rope, which is downstream of the J-joint, is another safety addition because it absorbs heat should gas seep past the joint. Basically, the new design enhances the primary thermal barrier and adds another thermal barrier with the rope.

Artist's concept of SRBs separating in flight. Photo: Thiokol

The J-joint design should be easier to install and inspect during assembly, require less technical maintenance, and therefore cost less. The upgrade is slated to fly in late 2004.

The firing also will retest a new adhesive that bonds metal parts to phenolic parts in the nozzle; new environmentally-friendly solvents; and demonstrate a new nozzle ablative insulation for the motor.

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 its two-minute burn at liftoff, each motor generates an average thrust of 2.6 million pounds (1.2 million kilograms).

The test will be conducted in the T-97 bay of the Thiokol test facility, located north of Salt Lake City. Following the test, the data will be analyzed and the results for each objective provided in a final report. The metal case segments and nozzle components will be refurbished for reuse.

The Marshall Center is NASA's lead center for development of space transportation and propulsion systems and advanced large optics manufacturing technology, as well as microgravity research -- scientific research in the unique low-gravity environment inside the International Space Station and other spacecraft.