In the final test of its kind before Artemis-1, a full-scale motor analog for one of the five-segment Solid Rocket Boosters (SRBs) that will provide over three-quarters of the liftoff muscle for the first Space Launch System (SLS) was put through its paces earlier today (Wednesday, 2 September). With a roaring torrent of continuous solid fire and an estimated 3.6 million pounds (1.6 million kg) of staccato thrust, the Flight Support Booster (FSB)-1 undertook a full-flight-duration test-firing, lasting a little more than two minutes at Northrop Grumman Corp.’s facility in Promontory, Utah.
The FSB-1 test—the last firing of an SRB before Artemis-1 flies late next year—served to evaluate motor performance and the manufacturing quality of new booster materials and processes.
As outlined in yesterday’s AmericaSpace article, the 154-foot-long (47-meter) FSB-1 motor — a component of the full 177-foot-long (53.9-meter) booster, minus the avionics in its forward assembly and Thrust Vector Control (TVC) in its aft skirt—was transported from its storage facility at Promontory to the T-97 test stand over a three-month period between mid-April and mid-July of this year. Preparation for the test got underway in March.
According to Northrop Grumman, the five case segments of the FSB-1 motor—known as Forward, Center-Forward, Center-Center, Center-Aft and Aft—have a lengthy heritage. They previously helped to launch 43 shuttle missions between STS-51F in July 1985 and STS-134 in May 2011, together with nine static-fire tests.
“The cases composing FSB-1 had flown or been tested,” Northrop Grumman’s Kay Anderson told AmericaSpace. “It’s not really considered a “new case”; rather a new motor, composed of five cases that have components that were used in varying flights and tests.”
At 1 p.m. MDT (3 p.m. EDT), five minutes preceding the start of the test, T-97 was confirmed “Clear for Static Test”. Low-speed data recorders were activated at T-3 minutes, with high-speed recorders coming online at T-60 seconds. At this point, the motor was committed and warning sirens sounded across the test area. The siren fell silent at T-20 seconds.
During today’s test, which began with a thunderous roar at 1:05 p.m. MDT (3:05 p.m. EDT), the performance of the 1.6-million-pound (725,000 kg) FSB-1 motor was monitored by over 302 data channels as Northrop Grumman and NASA engineers worked methodically through a series of primary and secondary test objectives.
Key focuses included the validation of all ballistic parameters, the ignition sequence interval, pressure and thrust build-up rates and performance tolerances and limits. Additionally, FSB-1 facilitated an all-up demonstration of the Solid Rocket Motor (SRM) nozzle forward exit cone housing and measured its load response to the sound suppression water deluge system during the ignition sequence.
But a core aim was to evaluate new solid fuel ingredients, which, like the shuttle-era SRBs, consist of powdery Ammonium Perchlorate Composite Propellant (APCP).
“The aluminum powder manufacturer moved its facility, bringing the need to obtain from a new supplier, which was the initial purpose of FSB-1,” Ms. Anderson explained. “Once the test was established, more objectives were added. FSB-1 will qualify various propellant ingredients for both supplier obsolescence issues and to have multiple qualified resources. Propellant ingredients are the same as shuttle and were modified slightly to meet the performance requirements for the longer rocket motor and new vehicle.”
Following the completion of Artemis-1 late next year, the next SRB motor ground test at Promontory—known as FSB-2—is presently targeted for 2022, ahead of the launch of Artemis-2, currently slated to be the first mission with humans to voyage beyond low-Earth orbit since Apollo 17. As for the FSB-1 casing, its future remains unclear at present. “It will be disassembled and analyzed for data post-test,” Ms. Anderson told us. “The cases may or may not be used again, depending on what is needed. It will likely not be “recreated” as a motor or booster with the same exact cases.”
Five-segment SRBs with modified nozzles were considered during the shuttle program, as a means of improving safety, payload-to-orbit performance and reducing system costs. In particular, it was expected to eliminate the shuttle’s hairy Return to Launch Site (RTLS) and Transoceanic Abort Landing (TAL) abort modes and provide greater capacity for an Abort Once Around (AOA) in the event of a Space Shuttle Main Engine (SSME) failure shortly after liftoff.
And it would boost the shuttle’s payload-to-orbit capacity by almost 20,000 pounds (9,000 kg) to 60,000 pounds (27,200 kg). Shelved after the February 2003 loss of Columbia, the five-segment SRB was later revived (for a time) in support of NASA’s Constellation Program and Ares V super-heavylift rocket.
With the cancelation of Constellation and Ares V by the Obama Administration in 2010, new life was breathed into the five-segment SRB when NASA unveiled the SLS concept in September 2011. A two-minute Qualification Motor (QM)-1 test firing took place in March 2015 to evaluate booster performance at peak operating temperatures of 32 degrees Celsius (90 degrees Fahrenheit), the expected “high-end” of its accepted propellant temperature range.
This was followed by QM-2 in June 2016, which repeated the exercise at 4.5 degrees Celsius (40 degrees Fahrenheit), the “low-end” of the temperature range.
Earlier this summer, the ten SRB segments for Artemis-1—the first uncrewed test flight of the combined SLS/Orion vehicle—were delivered by rail from Promontory, Utah, to the Kennedy Space Center (KSC) in Florida for processing.